METHOD FOR MANUFACTURING DIESTERS AND DIESTERS THEREFORE OBTAINED

Abstract

The invention relates to a process for preparing at least one diester, said process comprising: a) a reaction transforming the acid function of at least one hydroxycarboxylic acid, or the ester function of at least one ester of hydroxycarboxylic acid and alcohol, into an alcohol function to obtain at least one diol, said hydroxycarboxylic acid having from 11 to 25 carbon atoms; b) an esterification reaction of the diol with at least one saturated or unsaturated acid having from 2 to 24 carbon atoms to form at least one diester. The invention also relates to the use of diesters as a base oil in a lubricating composition or as an emollient in a cosmetic or pharmaceutical composition.

Description

Title of the invention: METHOD FOR MANUFACTURING DIESTERS AND DIESTERS THUS OBTAINED TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a process for preparing diesters by a simple process to be implemented from widely accessible raw materials.

[0002] The invention also relates to diesters that can be obtained by the process of the invention and their use as a base oil in a lubricating composition. The diester composition according to the invention can also be used in cosmetic or pharmaceutical compositions. STATE OF THE ART

[0003] Lubricating compositions, also called lubricants, are widely used to reduce friction between the surfaces of moving parts and thus reduce wear and prevent surface damage to these parts. Lubricants typically comprise a base oil and one or more functional additives.

[0004] When the lubricating composition is subjected to high stresses (i.e. high pressures) during its use, lubricating compositions whose base oil consists of hydrocarbons tend to degrade and the parts are then damaged.

[0005] Lubricant manufacturers must constantly improve their formulations to meet increasing fuel economy requirements while maintaining engine cleanliness and reducing emissions. These requirements compel manufacturers to examine their formulation capabilities and / or search for new base oils that can meet performance requirements.

[0006] To manufacture lubricants, such as engine oils, transmission fluids, gear oils, industrial lubricating oils, metalworking oils, etc., one typically begins with a petroleum-based, lubricant-grade oil from a refinery, or a suitable polymerized petrochemical fluid. Additives are then mixed into this base oil to improve its properties and performance, such as increasing lubricating power, anti-wear and anti-corrosion properties, and the lubricant's resistance to heat and / or oxidation. Thus, various additives, such as antioxidants, corrosion inhibitors, dispersants, antifoaming agents, metal deactivators, and other additives that can be used in lubricant formulations, can be added in typical effective quantities.

[0007] Environmental concerns and restrictions are leading manufacturers to seek alternatives to petroleum (fossil) sources. Vegetable and animal oils have therefore proven to be interesting sources of base oils. In particular, these vegetable and animal oils can be transformed into acids or esters using conventional processes.

[0008] In the API classification of base oils, esters are referenced as Group V base oils. Synthetic esters can be used both as base oils and as additives in lubricants. Compared to cheaper, but less environmentally friendly, mineral oils, synthetic esters were primarily used as base oils in applications where strict viscosity / temperature behavior was required. The growing importance of environmental acceptance and biodegradability has led to a desire to find alternatives to mineral oil as a raw material in lubrication applications.

[0009] The cosmetics, dermatology, and pharmaceutical markets are increasingly demanding ingredients of organic origin for their product formulations. While bio-based active ingredients, emulsifiers, and vegetable oils have been significantly developed in recent years and are now widely available on the market, 100% organic emollients remain rare.

[0010] Emollients currently used in cosmetics are either petrochemical-derived isoparaffins (mainly isododecane and isohexadecane), white oils, silicone oils, or ester-based oils (synthetic or natural). Isoparaffins, white oils, and silicone oils are widely used because they are very stable and odorless, but they are not derived from renewable resources. Although volatile silicones such as cyclomethicone were long considered harmless emollients and solvents for the skin (International Journal of Toxicology, Vol. 10, No. 1, pp. 9-19, 1991), concerns have been raised in recent years regarding their potential harmful effects on the environment and even on human health (particularly with regard to octamethylcyclotetrasiloxane).

[0011] Environmental concerns and restrictions are leading manufacturers to seek alternatives to petroleum (fossil) sources. Vegetable and animal oils have thus proven to be valuable sources of base oils or emollients. In particular, these vegetable and animal oils can be converted into acids or esters using conventional processes. These acids can then be transformed into unsaturated alcohols, for example, from triglyceride oils, through one or more steps of fatty acid hydrogenation or methyl esters.

[0012] US patent 2010 / 120642 discloses lubricant compositions based on Diesters obtained via an epoxy intermediate. US patent 5,008,126 discloses diol diesters in which the ester groups are separated by one or two methylene groups. These diol diesters are used as fat substitutes in food.

[0013] The invention thus aims to provide a composition of diesters with high selectivity towards a specifically targeted diester, and with high conversion. This composition of diesters can also be obtained from raw materials of vegetable or animal origin. Summary of the invention

[0014] The invention relates to a method for preparing at least one diester, said method comprising:

[0015] a) a reaction transforming the acid function of at least one hydroxycarboxylic acid, or the ester function of at least one ester of hydroxycarboxylic acid and alcohol, into an alcohol function in order to obtain at least one diol, said hydroxycarboxylic acid comprising from 11 to 25 carbon atoms,

[0016] b) an esterification reaction of the diol using at least one saturated or unsaturated acid comprising 2 to 24 carbon atoms in order to form at least one diester.

[0017] According to one embodiment, the process according to the invention further comprises, after step a) and before step b), a step a-bis) of purification of the diol composition from step a) in order to increase the diol content of the diol composition from step a), said purification step a-bis) preferably comprising at least one diol crystallization step.

[0018] According to one embodiment, the process according to the invention further comprises, prior to step a), a preliminary step of purifying the hydroxycarboxylic acid or hydroxycarboxylic acid ester composition in order to increase the hydroxycarboxylic acid or hydroxycarboxylic acid ester content of the hydroxycarboxylic acid or hydroxycarboxylic acid ester composition implemented in the subsequent step a), said preliminary purification step preferably comprising at least one step of crystallizing the hydroxycarboxylic acid or hydroxycarboxylic acid ester.

[0019] Preferably, the hydroxycarboxylic acid corresponds to formula (1) and / or the saturated or unsaturated acid corresponds to formula (2):

[0020] [Chem.l] OH O r*' "n:"''on

[0021] [Chem.2] Q

[0022] in which:

[0023] R1 represents an alkyl or alkenyl radical, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 3 to 18 carbon atoms, more preferably from 5 to 12 carbon atoms,

[0024] R2 represents a linear or branched alkyl or alkenyl divalent radical comprising from 1 to 22 carbon atoms, preferably from 4 to 22 carbon atoms, more preferably from 8 to 18 carbon atoms,

[0025] it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 23, preferably from 9 to 20 carbon atoms, and even more preferably from 10 to 18 carbon atoms,

[0026] R3 represents a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, preferably a linear or branched alkyl comprising from 2 to 17 carbon atoms, advantageously a linear alkyl comprising from 4 to 12 carbon atoms.

[0027] Preferably, the diol corresponds to formula (3) and the diester to formula (4):

[0028] [Chem.3] OH ""OH

[0029] [Chem.4]

[0030] in which

[0031] R1 represents a linear or branched alkyl radical comprising from 1 to 22 carbon atoms or a linear or branched alkenyl radical comprising from 2 to 22 carbon atoms, preferably an alkyl or alkenyl radical comprising from 3 to 18 carbon atoms, preferably still from 5 to 12 carbon atoms,

[0032] R2 represents a linear or branched alkyl divalent radical comprising from 1 to 22 carbon atoms or a linear or branched alkenyl radical comprising from 2 to 22 carbon atoms, preferably an alkyl or alkenyl radical comprising from 4 to 22 carbon atoms, preferably still from 8 to 18 carbon atoms,

[0033] it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 23, of preferably 9 to 20 carbon atoms, preferably 10 to 18 carbon atoms,

[0034] R3 and R4 represent, independently of each other, a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, or a monovalent alkenyl radical, linear or branched comprising from 1 to 18 carbon atoms, preferably a linear or branched alkyl or alkenyl comprising from 2 to 17 carbon atoms, advantageously a linear alkyl or alkenyl comprising from 2 to 12 carbon atoms.

[0035] The invention also relates to a composition of diester(s) comprising at least one diester of formula (4):

[0036] [Chem.4] G O R1 '"R?' ''vox ^R^

[0037] in which

[0038] R1 represents a linear or branched alkyl radical comprising from 1 to 22 carbon atoms or a linear or branched alkenyl radical comprising from 2 to 22 carbon atoms, preferably an alkyl or alkenyl radical comprising from 3 to 18 carbon atoms, preferably still from 5 to 12 carbon atoms,

[0039] R2 represents a linear or branched alkyl divalent radical comprising from 1 to 22 carbon atoms or a linear or branched alkenyl radical comprising from 2 to 22 carbon atoms, preferably an alkyl or alkenyl radical comprising from 4 to 22 carbon atoms, preferably still from 8 to 18 carbon atoms,

[0040] it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 23, preferably from 9 to 20 carbon atoms, and even more preferably from 10 to 18 carbon atoms,

[0041] R3 and R4 represent, independently of each other, a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, or a monovalent alkenyl radical, linear or branched comprising from 1 to 18 carbon atoms, preferably a linear or branched alkyl or alkenyl comprising from 2 to 17 carbon atoms, advantageously a linear alkyl or alkenyl comprising from 2 to 12 carbon atoms,

[0042] said composition of diester(s) comprising, in relation to the total weight of the composition of diester(s), at least 70% by weight of diesters of formula (4) which are distinguished from each other only by the groups R3 and R4.

[0043] According to one embodiment, the composition of diester(s) according to the invention can be obtained by the process according to the invention.

[0044] Preferably, the composition of diester(s) according to the invention comprises, in relation to to the total weight of the composition, at least 70% by weight of a single diester meeting formula (4), preferably at least 80% by weight of a single diester meeting formula (4), preferably at least 90% by weight of a single diester meeting formula (4).

[0045] The invention also relates to the use of the diester(s) composition according to the invention, as a base oil in a lubricating composition or as an emollient in a cosmetic or pharmaceutical composition.

[0046] Finally, the invention relates to a lubricating composition comprising the composition of diester(s) according to the invention and:

[0047] (i) at least one base oil other than the diesters, and / or

[0048] (ii) at least one additive other than the diesters

[0049] The process of the invention makes it possible to obtain good selectivity towards the formation of a specific diester, without formation of positional isomer(s).

[0050] The process is simple to implement, using readily available raw materials. DETAILED DESCRIPTION OF THE INVENTION

[0051] The invention relates to a method for preparing a composition of diesters, said method comprising:

[0052] a) a reaction transforming the acid function of at least one hydroxycarboxylic acid, or the ester function of at least one ester of hydroxycarboxylic acid and alcohol, into an alcohol function in order to obtain at least one diol, said hydroxycarboxylic acid comprising from 11 to 25 carbon atoms,

[0053] b) an esterification reaction of the diol using at least one acid comprising 2 to 24 carbon atoms in order to form at least one diester.

[0054] According to one embodiment, the process according to the invention comprises, prior to step a), a preliminary step of purifying a hydroxycarboxylic acid or hydroxycarboxylic acid ester composition in order to increase the hydroxycarboxylic acid or hydroxycarboxylic acid ester content of the hydroxycarboxylic acid or hydroxycarboxylic acid ester composition. A purified hydroxycarboxylic acid or hydroxycarboxylic acid ester composition is then obtained. According to this embodiment, step a) of the process according to the invention (reduction reaction) will be carried out using the hydroxycarboxylic acid or hydroxycarboxylic acid ester composition purified in the preliminary step.

[0055] Preferably, this preliminary purification step is carried out by crystallization.

[0056] Indeed, a composition of hydroxycarboxylic acid or hydroxycarboxylic acid ester may include impurities, such as saturated or unsaturated acids (without a hydroxyl group) or saturated or unsaturated esters (without a hydroxyl group). hydroxyl). Preliminary purification will remove these impurities in order to increase the content of hydroxycarboxylic acid or hydroxycarboxylic acid ester.

[0057] Preferably, the purified composition of hydroxycarboxylic acid or hydroxycarboxylic acid ester comprises at least 90% by weight of hydroxycarboxylic acid or hydroxycarboxylic acid ester, preferably at least 95% by weight of hydroxycarboxylic acid or hydroxycarboxylic acid ester, preferably even at least 98% by weight of hydroxycarboxylic acid or hydroxycarboxylic acid ester, relative to the total weight of the purified hydroxycarboxylic acid or hydroxycarboxylic acid ester composition.

[0058] Typically, the purified composition of hydroxycarboxylic acid or hydroxycarboxylic acid ester comprises at most 10% by weight of impurities, preferably at most 5% by weight of impurities, relative to the total weight of the composition of hydroxycarboxylic acid or hydroxycarboxylic acid ester, said impurities comprising, for example, saturated or unsaturated acids (without hydroxyl function) and / or saturated or unsaturated esters (without hydroxyl function).

[0059] According to one embodiment, the process according to the invention comprises, after step a) and before step b), a step a-bis) of purification of the diol composition from step a) in order to increase the diol content of the diol composition from step a). If it is to be carried out, this step a-bis) will preferably be carried out when the process does not include a preliminary purification step.

[0060] Indeed, a hydroxycarboxylic acid or hydroxycarboxylic acid ester composition may include impurities, such as saturated or unsaturated acids (without a hydroxyl group) or saturated or unsaturated esters (without a hydroxyl group). The reduction step a) of the process according to the invention may form monoalcohols from these impurities. This intermediate purification will eliminate the initial impurities as well as the reaction by-products of these impurities (for example, the monoalcohols).

[0061] According to a preferred embodiment, this purification step a-bis) is carried out by crystallization.

[0062] Preferably, the purified diol composition comprises at least 90% by weight of diols, preferably at least 95% by weight of diols, preferably still at least 98% by weight of diols, relative to the total weight of the purified diol composition.

[0063] According to one embodiment, when a purification step is implemented, the process of the invention comprises one or more treatment steps, in particular to remove the crystallization solvent if the purification step is a crystallization step. The treatment step may, for example, be a filtration step and a drying step.

[0064] The process of the invention may optionally include additional washing and / or purification steps. It should be noted that the process of the invention may include one or more operations for separating the acid and / or hydroxycarboxylic acid, the starting reagents of the process of the invention. These operations may be, for example, stripping steps or distillation operations.

[0065] The process according to the invention may also include one or more washing operations to separate the homogeneous catalyst from the product obtained from the process of the invention or one or more filtration steps to separate the heterogeneous catalyst from the product obtained from the process of the invention.

[0066] As a preliminary matter, it should be noted that, in the following description and claims, the expression "between" should be understood as including the stated limits. Composition Cl of hydroxycarboxylic acids

[0067] The process of the invention uses, as a reagent, at least one hydroxycarboxylic acid or at least one ester of hydroxycarboxylic acid and alcohol.

[0068] For the purposes of the present invention, the hydroxycarboxylic acid comprises at least one carboxylic acid group (-COOH) and at least one hydroxyl group (-OH). Preferably, the hydroxycarboxylic acid comprises a single carboxylic acid group and a single hydroxyl group.

[0069] Hydroxycarboxylic acid can be saturated or unsaturated. Preferably, hydroxycarboxylic acid is a saturated acid that typically does not include any functional group other than the carboxylic acid group and the hydroxyl group.

[0070] If it is unsaturated, the hydroxycarboxylic acid is preferably monounsaturated.

[0071] According to a preferred embodiment, the hydroxycarboxylic acid comprises a linear or branched alkyl chain, preferably linear.

[0072] The hydroxycarboxylic acid that can be used in the invention comprises 11 to 25 carbon atoms, preferably 12 to 24 carbon atoms, more preferably 14 to 20 carbon atoms.

[0073] According to a preferred embodiment, the hydroxycarboxylic acid used in the invention comprises at least one hydroxyl function carried by a secondary carbon atom (a compound known as a secondary alcohol type compound).

[0074] According to one embodiment, the hydroxycarboxylic acid used in the invention comprises at least one carboxylic acid function carried by a primary carbon atom.

[0075] Preferably, the hydroxycarboxylic acid corresponds to formula (1):

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087] [Chem.l] OH p ' R2 ûH in which: R1 represents an alkyl or alkenyl radical, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 3 to 18 carbon atoms, and more preferably from 5 to 12 carbon atoms, R2 represents a divalent alkyl or alkenyl radical, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 4 to 22 carbon atoms, and more preferably from 8 to 18 carbon atoms, it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 23, preferably from 9 to 20 carbon atoms, preferably still from 10 to 18 carbon atoms. Preferably, in formula (1), if the hydroxycarboxylic acid is unsaturated, then only one of the radicals among R1 and R2 is monounsaturated, the other radical being saturated. Preferably, in formula (1): - R1 represents an alkyl radical, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 3 to 18 carbon atoms, and even more preferably from 5 to 12 carbon atoms, - R2 represents a divalent alkyl radical, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 4 to 22 carbon atoms, and even more preferably from 8 to 18 carbon atoms, it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 20 carbon atoms, preferably from 10 to 18 carbon atoms. Preferably, in formula (1): - R1 represents a linear alkyl radical comprising 3 to 18 carbon atoms, preferably 5 to 12 carbon atoms, - R2 represents a linear alkylene divalent radical comprising 4 to 22 carbon atoms, preferably 8 to 18 carbon atoms, it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 20 carbon atoms, preferably from 10 to 18 carbon atoms. According to one embodiment, the transformation reaction to obtain at least one diol is carried out using, as reactants, an ester of a hydroxycarboxylic acid (as defined in the invention) and an alcohol. The reduction will allow, in a single step, the reduction of the ester function to an alcohol function. For the purposes of this invention, the expression "hydroxycarboxylic acid ester" or the expression "hydroxycarboxylic acid ester" or the expression "Hydroxycarboxylic acid and alcohol ester" refers to an ester obtained by the reaction of a hydroxycarboxylic acid and an alcohol.

[0088] The hydroxycarboxylic acid at the base of the hydroxycarboxylic acid and alcohol ester preferably has one or more of the characteristics or preferences described above.

[0089] The alcohol at the base of the hydroxycarboxylic acid ester is preferably a saturated monoalcohol comprising preferably from 1 to 18 carbon atoms, preferably from 1 to 16 carbon atoms, preferably from 1 to 12 carbon atoms.

[0090] Preferably, the hydroxycarboxylic acid used in the invention is 12-hydroxystearic acid. If the ester form is used in the process of the invention, the ester could, according to a particular embodiment, be the methyl or ethyl ester of 12-hydroxystearic acid.

[0091] According to one embodiment, the hydroxycarboxylic acid is unsaturated and is ricinoleic acid.

[0092] According to one embodiment, prior to the reduction step a), the process further comprises a preliminary purification step of the composition Cl of hydroxycarboxylic acid(s) or ester(s) thereof. Said preliminary purification step preferably comprises crystallization of the diol.

[0093] The crystallization step can be carried out using a solvent or a mixture of solvents in one or more crystallization steps. The solvent(s) can be chosen from heptane, toluene, acetone, methanol, ethanol, ethyl acetate, or a mixture thereof. The ratio between the volume of crystallization solvent (in mL) and the mass of diol (in g) is preferably from 1 to 50, and preferably from 2 to 30.

[0094] The process according to the invention may include, before step a) and before the possible preliminary purification step, a step of supplying a composition Cl of hydroxycarboxylic acid(s) or ester(s) thereof.

[0095] Typically, the reduction reaction according to the invention (transformation of an acid or ester function into an alcohol function) is carried out in the presence of a composition Cl comprising at least 50% by weight of hydroxycarboxylic acid(s) or ester(s) thereof, preferably at least 70% by weight, more preferably at least 75% by weight, or even at least 80% by weight of hydroxycarboxylic acid(s) or ester(s) thereof, relative to the total weight of the composition Cl

[0096] According to one embodiment, the composition Cl implemented in the invention comprises at least 50% by weight of 12-hydroxystearic acid or methyl or ethyl ester of 12-hydroxystearic acid, preferably at least 70% by weight, and even more preferably at least 80% by weight of 12-hydroxystearic acid or methyl or ethyl ester of 12-hydroxystearic acid, relative to the total weight of the composition CL

[0097] Preferably, the composition Cl implemented in the invention comprises at least 50% by weight of 12-hydroxystearic acid, preferably at least 70% by weight, and even more preferably at least 80% by weight of 12-hydroxystearic acid, relative to the total weight of the composition Cl.

[0098] If the process includes a preliminary step of purifying the composition Cl, then the reduction step a) of the process will preferably be carried out in the presence of a composition Cl' comprising at least 90% by weight of hydroxycarboxylic acid or hydroxycarboxylic acid ester, preferably at least 95% by weight of hydroxycarboxylic acid or hydroxycarboxylic acid ester, preferably still at least 98% by weight of hydroxycarboxylic acid or hydroxycarboxylic acid ester, relative to the total weight of the purified composition Cl' of hydroxycarboxylic acid or hydroxycarboxylic acid ester.

[0099] Preferably, the composition Cl' that can be implemented in the invention comprises at least 90% by weight of 12-hydroxystearic acid, preferably at least 95% by weight, preferably even at least 98% by weight of 12-hydroxystearic acid, relative to the total weight of the composition Cl'.

[0100] Composition Cl or Cl' may be commercially available. Composition C2 of saturated or unsaturated acids

[0101] The process of the invention uses for step b) of esterification at least one acid comprising from 2 to 20 carbon atoms, preferably an acid comprising from 2 to 18 carbon atoms, as a reagent in order to react on the alcohol functions of the diol.

[0102] Preferably, said at least one acid is a monoacid. The acid may be a linear or branched acid, saturated or unsaturated.

[0103] According to one embodiment, said at least one saturated acid corresponds to formula (2):

[0104] [Chem.2] O H OH

[0105] wherein R3 represents a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, or a monovalent alkenyl radical, linear or branched comprising from 1 to 18 carbon atoms, preferably a linear or branched alkyl or alkenyl comprising from 2 to 17 carbon atoms, advantageously a linear alkyl or alkenyl comprising from 2 to 12 carbon atoms.

[0106] Preferably, if R3 is an alkenyl, said alkenyl is monounsaturated.

[0107] According to one embodiment, the acid is a saturated fatty acid and comprises 2 to 12 carbon atoms. This chain length allows for further optimization of the cold properties of the diester composition resulting from the process, which is particularly preferred in lubricating applications.

[0108] According to another embodiment, the acid is an unsaturated acid and comprises 8 to 18 carbon atoms. Unsaturated acids may be particularly preferred in biodiesels intended for cosmetic applications.

[0109] According to one embodiment, the acid used in the invention is chosen from one or more acids among: acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, lauric acid and their mixture, these acids may be linear or branched.

[0110] During esterification, the process according to the invention may use a single acid or a mixture of several acids. Preferably, the process according to the invention uses a single acid.

[0111] Typically, the process according to the invention will implement for the esterification step either only saturated acids (i.e. from a composition of saturated acids with at least 90% by weight of saturated acids), or only unsaturated acids (i.e. from a composition of unsaturated acids with at least 85% by weight of unsaturated acids).

[0112] During esterification, a mixture of at least two different acids can also be used. The proportions can be adjusted according to the desired properties of the diester composition.

[0113] The two esterification reactions (on the two alcohol groups of the diol) can be carried out simultaneously or sequentially. When at least two different acids are used, it is possible to adjust the operating conditions to select the saturated or unsaturated acid that will react first with the most reactive alcohol group of the diol. Thus, the saturated or unsaturated acids can be introduced simultaneously or sequentially, depending on the desired diester.

[0114] The process according to the invention is selective since it allows obtaining precisely chosen diesters with a specific structure.

[0115] According to one embodiment, the esterification reaction is carried out using a composition C2 of saturated acid(s) typically comprising at least 90% by weight of saturated acid(s), preferably at least 95% by weight, or even at least 98% by weight of saturated acid(s), relative to the total weight of composition C2.

[0116] According to another embodiment, the esterification reaction is carried out using a C2 composition of unsaturated acid(s) typically comprising at least 85% by weight of unsaturated acid(s), preferably at least 90% by weight, or even at least 95% by weight of unsaturated acid(s), relative to the total weight of the C2 composition.

[0117] Composition C2 may be commercially available and may be of origin natural or synthetic, preferably of natural origin. Implementation of the process of the invention

[0118] The process of the invention involves two chemical reactions: - reduction reaction of the acid or ester function to the alcohol function, and - esterification reaction.

[0119] The two chemical reactions implemented in the process of the invention are typically carried out in the presence of one or more catalysts. However, it is possible to carry out step b) of esterification of the diols in the absence of a catalyst. Reduction reaction

[0120] Typically, the acid function of a hydroxycarboxylic acid or the ester function of a hydroxycarboxylic acid ester is converted to an alcohol function by a reduction reaction. The reduction reaction can be carried out by a hydrogenation step or by contacting the hydroxycarboxylic acid or its ester with a reducing agent. Those skilled in the art are familiar with the methods for reducing an acid or ester function to an alcohol function.

[0121] The reducing agent may be chosen from metal hydrides, preferably from lithium hydrides and sodium hydrides. By way of example, the reducing agent is chosen from lithium aluminohydride and sodium borohydride.

[0122] Typically, when the hydroxycarboxylic acid or its ester is brought into contact with the reducing agent, the temperature of the mixture ranges from -10°C to +15°C, preferably from -5°C to +10°C.

[0123] The step of reducing the acid function of the hydroxycarboxylic acid or the ester function of the ester derived from the hydroxycarboxylic acid can be carried out under conditions known to the person skilled in the art.

[0124] The hydrogenation step can be carried out under the following conditions: - a temperature ranging from 100 to 450°C, preferably from 200 to 400°C, preferably still from 250 to 380°C, and / or - a pressure ranging from 30 to 300 bars, preferably from 50 to 250 bars, preferably still from 150 to 230 bars.

[0125] A non-limiting example of a hydrogenation catalyst enabling the reduction of acid or ester functions to alcohol is copper chromite.

[0126] According to a non-limiting embodiment, hydrogenation is carried out at a temperature of 350°C and a pressure of 200 bars in the presence of hydrogen and copper chromite.

[0127] According to one embodiment, the diol formed at the end of the reduction step corresponds to formula (3):

[0128] [Chem.3] OH 7 / X"R2X'XOH

[0129] in which:

[0130] R1 represents a linear or branched alkyl radical comprising from 1 to 22 carbon atoms or a linear or branched alkenyl radical comprising from 2 to 22 carbon atoms, preferably an alkyl or alkenyl radical comprising from 3 to 18 carbon atoms, preferably further from 5 to 12 carbon atoms,

[0131] R2 represents a linear or branched alkyl divalent radical comprising from 1 to 22 carbon atoms or a linear or branched alkenyl radical comprising from 2 to 22 carbon atoms, preferably an alkyl or alkenyl radical comprising from 4 to 22 carbon atoms, preferably still from 8 to 18 carbon atoms,

[0132] it being understood that the total number of carbon atoms of R1 and R2 ranges from 9 to 23, preferably from 9 to 20 carbon atoms, preferably still from 10 to 18 carbon atoms.

[0133] If the hydroxycarboxylic acid or its ester is unsaturated, then it is possible to choose reaction conditions such that step a) of reduction does not reduce the carbon-carbon double bond(s) of the hydroxycarboxylic acid or its ester. Copper chromite is an example.

[0134] According to one embodiment, the reduction reaction uses a hydroxycarboxylic acid of formula (1) to obtain a diol of formula (3), according to the following scheme:

[0135] [Chem.5]

[0136] in which R1 and R2 are such as defined in formulas (1) and (3) respectively.

[0137] During the hydroxycarboxylic acid reduction step, by-products may be formed. Among these by-products are monoalcohols obtained by reduction of the acidic functional group of acidic impurities that may be present in the hydroxycarboxylic acid composition. For example, the composition of 12-hydroxystearic acid may include, in addition to 12-hydroxystearic acid, palmitic acid and / or stearic acid.

[0138] According to one embodiment, after the reduction step a) and before the esterification step b), the process further comprises a step a-bis) of purification of the diol composition(s) obtained after step a). Said purification step a-bis) preferably comprises a crystallization of the diol.

[0139] The crystallization step can be carried out using a solvent or a mixture of solvents in one or more crystallization steps. The solvent(s) can be chosen from heptane, toluene, acetone, methanol, ethanol, ethyl acetate, or a mixture thereof. The ratio between the volume of crystallization solvent (in mL) and the mass of diol (in g) is preferably from 1 to 50, and preferably from 2 to 30.

[0140] After crystallization, if present, the process may further include a step a-ter) of washing the diol, using for example a solvent, for example heptane.

[0141] The washing step helps to reduce the residual content of monoalcohols. Esterification reaction

[0142] The esterification reaction can be carried out using homogeneous catalysis, heterogeneous catalysis, and / or enzymatic catalysis. It is also possible to carry out the esterification reaction in the absence of a catalyst. The catalyst can, for example, be a supported enzymatic catalyst.

[0143] The esterification reaction can be carried out according to any process well known to those skilled in the art for the esterification of alcohols.

[0144] The catalyst for esterification can be chosen from Lewis acid-based catalysts, for example tin-based, titanate-based or boron trifluoride type.

[0145] By way of example, the catalyst may be para-toluenesulfonic acid (p-TSA), methanesulfonic acid (AMS), sulfuric acid, boron trifluoride etherate (BF3.EtO), tin tetrachloride (FASCAT 4400), tin dichloride (FASCAT 2004), tin dibutyl dichloride (FASCAT 4210), monobutyl tin oxide (FASCAT 4100, TIB KAT 256), dibutyl tin oxide (FASCAT 4201, TIB KAT 248), dioctyl tin oxide (FASCAT 8201, TIB KAT 232), monobutyl tin tris(2-ethylhexanoate) (FASCAT 4102), or tin oxalate (FASCAT 2001, TIB KAT 160), tin dibutyl diacetate (FASCAT 4200, TIB KAT 233), tin dioctyl diacetate (TIB KAT 223) and tin dioctyl dicarboxylate (TIB KAT 318).

[0146] According to one embodiment, step b) of esterification of the process of the invention is carried out at a temperature ranging from 50 to 200°C.

[0147] According to one embodiment, the esterification reaction uses a diol of formula (3) and one or more saturated acid(s) of formula (2), according to the following scheme:

[0148] [Chem.6]

[0149] in which R1, R2 and R3 have the same definition as in formulas (1) and (2) respectively, it being understood that the R3 groups may be identical or different in the diester formed.

[0150] In particular, if two different saturated acids are used, the R3 groups may be identical or different in the diester formed.

[0151] According to one embodiment, the reaction of the diol with the saturated acid in the presence of the catalyst is carried out according to one or more of the following conditions: - the molar ratio of diol to saturated acid goes from 1 / 2 to 1 / 10, preferably from 1 / 2 to 1 / 8, preferably again from 1 / 2 to 1 / 6; - the catalyst for the esterification reaction with the fatty acid(s) is implemented in a proportion ranging from 0.01 to 3.0% by weight, preferably from 0.02 to 2.5% by weight, relative to the total weight of the reaction medium.

[0152] Unlike estolide or diester manufacturing processes involving unsaturated compounds, as described in US patent 2015 / 0094246, the process according to the invention will not lead to a mixture of positional isomers depending on the position of the saturated fatty acid addition to the carbon-carbon double bond of the unsaturated compound. Indeed, in the prior art, the saturated fatty acid can react with either carbon atom of the carbon-carbon double bond of the unsaturated compound, thus leading to two positional isomers. Furthermore, some of the unsaturated compounds can be isomerized under the conditions of the acid addition reaction, so that the carbon-carbon double bond can change position for some of the unsaturated compounds.Furthermore, under the reaction conditions, this double bond can migrate along the alkyl chain, leading to a large number of isomers differentiated by the position of the functionalization and to the possible formation of lactones.

[0153] Unlike these prior art processes, the process according to the invention leads to a composition of diesters free from positional isomers, insofar as the addition reaction of the saturated fatty acid takes place selectively only in the position fixed by the hydroxyl function of the hydroxycarboxylic acid.

[0154] The diesters that can be obtained at the end of the process can be represented by formula (4):

[0155] [Chem.4] G O .1 ..... It . R1 R" "O'" ''R"

[0157] R1 represents an alkyl or alkenyl radical, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 3 to 18 carbon atoms, more preferably from 5 to 12 carbon atoms,

[0158] R2 represents a linear or branched alkyl or alkenyl divalent radical comprising from 1 to 22 carbon atoms, preferably from 4 to 22 carbon atoms, more preferably from 8 to 18 carbon atoms,

[0159] it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 23, preferably from 9 to 20 carbon atoms, and more preferably from 10 to 18 carbon atoms,

[0160] R3 and R4 represent, independently of each other, a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, or a monovalent alkenyl radical, linear or branched comprising from 1 to 18 carbon atoms, preferably a linear or branched alkyl or alkenyl comprising from 2 to 17 carbon atoms, advantageously a linear alkyl or alkenyl comprising from 2 to 12 carbon atoms.

[0161] The term "process composition" refers to the reactants, products, and by-products of the reaction. The catalyst is not included when referring to the process composition. Therefore, it will generally be necessary to separate the catalyst from the reaction mixture to obtain the process composition of the biodiesels.

[0162] The process can be implemented continuously, semi-continuously, or in batches.

[0163]

[0164] The progress of the reaction can be monitored by gas chromatography coupled with a flame ionization detector (GC-FID), by high-performance liquid chromatography (HPLC) or by infrared, according to methods known to those skilled in the art.

[0165] The diester composition obtained at the end of the process advantageously has a kinematic viscosity at 100°C ranging from 1 to 50 mm2 / s, preferably from 2 to 25 mm2 / s, advantageously from 3 to 10 mm2 / s, measured according to ASTM D445.

[0166] It should be noted that the composition of diesters may optionally include from 0.1 to 30% by weight of unreacted reagents or intermediates (monoesters of the diol or monoalcohols) possibly formed in situ, relative to the total weight of the composition of diesters, preferably from 0.2 to 10% by weight, preferably still from 0.5 to 5% by weight.

[0167] The process according to the invention may optionally include, after the diester formation reaction, a separation step in which unreacted reagents of the saturated fatty acid, hydroxycarboxylic acid, and / or hydroxycarboxylic acid ester type are removed from the diester composition. For the purposes of the present invention, the diesters are not reagents.

[0168] According to one embodiment, the process for preparing at least one diester consists of the following steps:

[0169] a) a reaction transforming the acid function of at least one hydroxycarboxylic acid, or the ester function of at least one ester of hydroxycarboxylic acid and alcohol, into an alcohol function in order to obtain at least one diol, said hydroxycarboxylic acid comprising from 11 to 25 carbon atoms,

[0170] b) an esterification reaction of the diol using at least one saturated or unsaturated acid comprising 2 to 24 carbon atoms in order to form at least one diester.

[0171] According to one embodiment, the process for preparing at least one diester consists of the following steps:

[0172] a) a reaction transforming the acid function of at least one hydroxycarboxylic acid, or the ester function of at least one ester of hydroxycarboxylic acid and alcohol, into an alcohol function in order to obtain at least one diol, said hydroxycarboxylic acid comprising from 11 to 25 carbon atoms,

[0173] a-bis) a purification step of the diol composition from step a) in order to increase the diol content of the diol composition from step a), said purification step a-bis) preferably comprising at least one diol crystallization step and preferably being followed by one or more washing steps,

[0174] b) an esterification reaction of the diol using at least one saturated or unsaturated acid comprising 2 to 24 carbon atoms in order to form at least one diester.

[0175] According to one embodiment, the process for preparing at least one diester consists of the following steps:

[0176] 0) a preliminary step of purifying a hydroxycitric acid composition boxyl or hydroxycarboxylic acid ester in order to increase the hydroxycarboxylic acid or hydroxycarboxylic acid ester content of the hydroxycarboxylic acid or hydroxycarboxylic acid ester composition, said preliminary purification step preferably comprising at least one crystallization step of the hydroxycarboxylic acid or its ester and preferably being followed by one or more washing steps

[0177] a) a reaction transforming the acid function of at least one hydroxycarboxylic acid, or the ester function of at least one ester of hydroxycarboxylic acid and alcohol of the composition purified in step 0), into an alcohol function in order to obtain at least one diol, said hydroxycarboxylic acid comprising from 11 to 25 carbon atoms,

[0178] b) an esterification reaction of the diol using at least one saturated or unsaturated acid comprising 2 to 24 carbon atoms in order to form at least one diester. Diesters

[0179] The present invention also relates to a composition of diester(s) of formula (4) as such and a composition of diester(s) capable of being obtained by the process of the invention.

[0180] The composition of diester(s) according to the invention comprises at least one diester corresponding to formula (4):

[0181] [Chem.4] O ■ he R" OQ i ..... 11. R1 'FL 'O' ''R"

[0182] in which

[0183] R1 represents an alkyl or alkenyl radical, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 3 to 18 carbon atoms, more preferably from 5 to 12 carbon atoms,

[0184] R2 represents a linear or branched alkyl or alkenyl divalent radical comprising from 1 to 22 carbon atoms, preferably from 4 to 22 carbon atoms, more preferably from 8 to 18 carbon atoms,

[0185] it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 23, preferably from 9 to 20 carbon atoms, and more preferably from 10 to 18 carbon atoms,

[0186] R3 and R4 represent, independently of each other, a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, or a monovalent alkenyl radical, linear or branched comprising from 1 to 18 carbon atoms, preferably a linear or branched alkyl or alkenyl comprising from 2 to 17 carbon atoms, advantageously a linear alkyl or alkenyl comprising from 2 to 12 carbon atoms.

[0187] The expression "said diester composition(s) comprising, relative to the total weight of the diester composition(s), at least 70% by weight of diesters of formula (4) which are distinguished from one another only by the R3 and R4 groups" is synonymous with the expression "said diester composition(s) comprising, relative to the total weight of the diester composition(s), at least 70% by weight of diesters of formula (4) in which the R1 groups are identical and in which the R2 groups are identical, it being understood that R1 may be different from R2." These two expressions mean that at least 70% by weight of the diester(s) conform to the same formula (4) in which only the R3 and R4 groups may vary, the R1 and R2 groups remaining constant (for at least 70% by weight of the diesters).

[0188] In other words, the composition of diester(s) according to the invention does not comprise, or substantially does not comprise, positional isomers where the R3COO- (or R4COO-) branch at the level of the R'CHR2- chain could be located at different locations lizations of said chain (as is the case with acid addition reactions on a carbon-carbon double bond).

[0189] According to one embodiment of the composition of diesters of formula (4), if the diesters are unsaturated, then the diesters can be monounsaturated or polyunsaturated, the unsaturation(s) being in one or more of the groups RI, R2, R3 and R4.

[0190] Preferably, if they are unsaturated, the radicals R3 and R4 are monounsaturated.

[0191] Preferably, in formula (4), only one of the radicals among R1 and R2 is mono- unsaturated, the other radical being saturated.

[0192] According to a preferred embodiment, the composition of diester(s) according to the invention comprises at least 75% by weight, preferably at least 80% by weight, preferably again at least 85% by weight, of diesters of formula (4) in which the R1 groups are identical and in which the R2 groups are identical, it being understood that R1 may be different from R2.

[0193] According to a preferred embodiment: - R1 is a linear alkyl group with 5 to 8 carbon atoms, preferably a linear alkyl group with 6 carbon atoms, and / or - R2 is a linear alkyl containing 8 to 12 carbon atoms, preferably is a linear alkyl of 10 carbon atoms.

[0194] The composition of diesters according to the invention advantageously has a kinematic viscosity at 100°C ranging from 1 to 50 mm2 / s, preferably from 2 to 25 mm2 / s, advantageously from 3 to 10 mm2 / s, measured according to ASTM D445.

[0195] According to one embodiment, the composition of diester(s) comprises from 70 to 99.8% by weight, preferably from 75 to 99% by weight, preferably still from 80 to 98% by weight, of diester(s) of formula (4), relative to the total weight of the composition of diester(s).

[0196] According to a particular embodiment, the diester(s) composition according to the invention comprises from 70 to 99.8% by weight, preferably from 75 to 99% by weight, preferably still from 80 to 98% by weight, of diester(s) of formula (7), relative to the total weight of the diester(s) composition, the diesters conforming to formula (7) being:

[0197] [Chem.7] "" '-yx,. / - a 4 1 v. . 0 U

[0198] in which:

[0199] R3 and R4 represent, independently of each other, a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, or a monovalent alkenyl radical, linear or branched comprising from 1 to 18 carbon atoms, preferably a linear or branched alkyl comprising from 2 to 17 carbon atoms, advantageously a linear or branched alkyl comprising from 2 to 12 carbon atoms.

[0200] The diester composition(s) according to the invention is preferably obtained according to the process of the invention. In particular, the diester composition(s) according to the invention will typically not include positional isomers, since it does not involve unsaturated compounds, such as unsaturated alcohols undergoing an addition reaction of a saturated acid onto the carbon-carbon double bond. Uses

[0201] The process according to the invention makes it possible to obtain a diester composition exhibiting high selectivity in favor of a single diester. The diester composition(s) according to the invention can thus be used as a base oil in a lubricating composition.

[0202] The diester composition can be used in a lubricating composition as the sole base oil, but advantageously in combination with another base oil. By "another base oil" is to be understood a base oil other than the diesters.

[0203] The lubricating composition comprising the diester composition according to the invention can be used to lubricate the various parts of a vehicle, in particular the various parts of a vehicle engine or transmission or the various parts of a marine engine or an industrial machine engine, for example, public works machinery.

[0204] The diester composition that can be obtained can also be used as an emollient in a cosmetic or pharmaceutical composition, alone or in combination with another fat. "Another fat" should be understood to mean a fat other than the diesters according to the invention.

[0205] The cosmetic or pharmaceutical composition comprising the diester composition according to the invention can be used for topical application, typically on the skin, nails, lips, hair and scalp.

[0206] The invention also relates to the cosmetic or pharmaceutical use of the composition of diesters according to the invention as a skin care product (serums, creams, balms, etc.) as a hygiene product, as a sun / after-sun product, as a makeup product, as a makeup remover, as a perfumed product, as an antiperspirant product.

[0207] The invention also relates to a cosmetic or pharmaceutical process for treating the skin, nails, lips, hair or scalp, comprising at least one application step on the skin, nails, lips, hair or scalp, of a composition of diesters according to the invention.

[0208] Finally, the invention also covers a cosmetic treatment method comprising at least one application step, preferably by spreading, on the skin, nails, lips, hair or scalp of the diester composition according to the invention. Lubricating composition

[0209] The invention also relates to a lubricating composition comprising the composition of ester diesters according to the invention and at least one additive and / or at least one other base oil.

[0210] Preferably, the diester composition used in the lubricating composition has one or more of the characteristics defined above within the framework of the diester composition. According to a particular embodiment, the diester composition according to the invention used in the lubricating composition comprises at least one saturated diester.

[0211] These other base oils may be chosen from among the base oils conventionally used in the field of lubricating oils, such as mineral, synthetic or natural, animal or vegetable oils or mixtures thereof.

[0212] The other base oils of the lubricating compositions according to the invention may in particular be oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) and presented in Table 1 below or their mixtures.

[0213] [Tables 1] Saturates (by weight) Sulfur content (by weight) Viscosity index (VI) Group I Mineral oils <90% > 0.03% 80 < VI < 120 Group II Hydrocracked oils >90% < 0.03% 80 < VI < 120 Group III Hydrocracked or hydroisomerized oils >90% < 0.03% > 120 Group IV Polyalphaolefins (PAO) Group V Esters and other bases not included in Groups I to IV

[0214] Other mineral base oils include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, desalpha removal, solvent dewaxing, hy hydrotreatment, hydrocracking, hydroisomerization and hydrofinishing.

[0215] Mixtures of synthetic and mineral oils, which may be bio-based, may also be used.

[0216] Other base oils for the lubricating compositions according to the invention can also be chosen from synthetic oils, such as certain esters of carboxylic acids and alcohols, polyalphaolefins (PAO), and polyalkylene glycol (PAG) obtained by polymerization or copolymerization of alkylene oxides comprising 2 to 8 carbon atoms, in particular 2 to 4 carbon atoms.

[0217] PAOs used as other base oils are, for example, obtained from monomers comprising 4 to 32 carbon atoms, for example from octene or decene. The weight-average molecular weight of the PAO can vary quite widely. Preferably, the weight-average molecular weight of the PAO is less than 600 Da. The weight-average molecular weight of the PAO can also range from 100 to 600 Da, from 150 to 600 Da, or even from 200 to 600 Da. Advantageously, when low-viscosity applications are targeted, PAO 2 and / or PAO 4 are typically chosen.

[0218] Advantageously, the other base oil(s) of the lubricating composition according to the invention are chosen from polyalphaolefins (PAO), polyalkylene glycol (PAG) and esters of carboxylic acids and alcohols.

[0219] According to an alternative embodiment, the other base oil(s) of the lubricating composition according to the invention can be chosen from base oils of group II or III.

[0220] It is for a person skilled in the art to adjust the base oil content to be used in a lubricating composition.

[0221] According to one embodiment, the lubricating composition according to the invention comprises: - from 5 to 95% by weight, preferably from 10 to 70% by weight, advantageously from 15 to 50% by weight, of the diester composition according to the invention, and - 5 to 95% by weight, preferably 30 to 90% by weight, advantageously 50 to 85% by weight, of one or more other base oils,

[0222] relative to the total weight of the lubricating composition according to the invention.

[0223] According to one embodiment, the additive(s) in the lubricating composition are selected from friction modifiers, detergents, anti-wear additives, extreme-pressure additives, dispersants, antioxidants, pour point depressants, anti-foaming agents, metal passivators, and mixtures thereof. These additives are well known to those skilled in the art in the field of mechanical lubrication.

[0224] These additives can be introduced individually and / or in the form of a mixture similar to those already available for sale for lubricant formulations commercial for vehicle engines, of performance level as defined by ACEA (European Automobile Manufacturers' Association) and / or API (American Petroleum Institute), well known to those skilled in the art.

[0225] A lubricating composition according to the invention may include at least one friction-modifying additive. The friction-modifying additive may be selected from a compound containing metallic elements and an ash-free compound. Among the compounds containing metallic elements, transition metal complexes such as Mo, Sb, Sn, Fe, Cu, and Zn may be used, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur, or phosphorus atoms. The ash-free friction-modifying additives are generally of organic origin and may be selected from fatty acid and polyol monoesters, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides, fatty amines, or fatty acid glycerol esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising 10 to 24 carbon atoms.

[0226] A lubricating composition according to the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or from 0.1 to 2% by weight of friction modifier additive, relative to the total weight of the lubricating composition.

[0227] A lubricating composition implemented according to the invention may include at least one antioxidant additive.

[0228] The antioxidant additive generally helps to delay the degradation of the composition in service. This degradation can notably result in the formation of deposits, the presence of sludge, or an increase in the viscosity of the composition.

[0229] Antioxidant additives act, in particular, as radical inhibitors or hydroperoxide scavengers. Commonly used antioxidant additives include phenolic antioxidants, amine antioxidants, and phosphosulfur antioxidants. Some of these antioxidant additives, for example, phosphosulfur antioxidants, may generate ash. Phenolic antioxidant additives may be ash-free or in the form of neutral or basic metal salts. Antioxidant additives may be selected, in particular, from sterically hindered phenols, sterically hindered phenol esters, and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted with at least one C1-C12 alkyl group, N,N'-dialkylaryl diamines, and mixtures thereof.

[0230] Preferably according to the invention, the sterically hindered phenols are selected from compounds comprising a phenol group of which at least one carbon vicinal of the carbon bearing the alcohol function is substituted by at least one alkyl group in Cl- CIO, preferably an alkyl group in C1-C6, preferably an alkyl group in C4, preferably by the tert-butyl group.

[0231] Amino compounds are another class of antioxidant additives that can be used, possibly in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of formula NQ1Q2Q3 in which Q1 represents an aliphatic or aromatic group, possibly substituted, Q2 represents an aromatic group, possibly substituted, Q3 represents a hydrogen atom, an alkyl group, an aryl group or a group of formula Q4S(O)ZQ5 in which Q4 represents an alkylene or alkenylene group, Q5 represents an alkyl, alkenyl or aryl group and z represents 0, 1 or 2.

[0232] Sulfurized alkyl phenols or their alkali and alkaline earth metal salts may also be used as antioxidant additives.

[0233] Another class of antioxidant additives is that of copper compounds, for example copper thio- or dithio-phosphates, copper salts of carboxylic acids, dithiocarbamates, sulfonates, phenates, copper acetylacetonates. Copper I and II salts, succinic acid or succinic anhydride salts can also be used.

[0234] A lubricating composition according to the invention may contain all types of antioxidant additives known to those skilled in the art.

[0235] Advantageously, a lubricating composition according to the invention comprises at least one ash-free antioxidant additive.

[0236] A lubricating composition according to the invention may comprise from 0.5 to 2% by weight of at least one antioxidant additive, relative to the total weight of the composition.

[0237] A lubricating composition according to the invention may also include at least one detergent additive.

[0238] Detergent additives generally make it possible to reduce the formation of deposits on the surface of metal parts by dissolving secondary oxidation and combustion products.

[0239] Detergent additives usable in a lubricating composition according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head group. The associated cation may be a metallic cation of an alkali or alkaline earth metal.

[0240] Detergent additives are preferably selected from alkali metal or alkaline earth metal salts of carboxylic acids, sulfonates, sa- Licylates, naphthenates, and phenate salts. The alkali and alkaline earth metals are preferentially calcium, magnesium, sodium, or barium.

[0241] These metallic salts generally comprise the metal in stoichiometric quantities or in excess, i.e., in a quantity greater than the stoichiometric quantity. These are then referred to as over-basic detergent additives; the excess metal giving the detergent additive its over-basic character is then generally in the form of a metallic salt insoluble in oil, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate.

[0242] A lubricating composition according to the invention may, for example, comprise 2 to 4% by weight of detergent additive, relative to the total weight of the composition.

[0243] Also, a lubricating composition according to the invention may include at least one dispersing agent, distinct from succinimide-type compounds defined according to the invention.

[0244] The dispersing agent can be chosen from Mannich bases, succinimides, for example of the polyisobutylene succinimide type.

[0245] A lubricating composition implemented according to the invention may, for example, comprise from 0.2 to 10% by weight of dispersing agent(s) distinct from succinimide-type compounds defined according to the invention, relative to the total weight of the composition.

[0246] A lubricating composition according to the invention may further comprise at least one anti-wear and / or extreme-pressure agent.

[0247] There is a wide variety of anti-wear additives. Preferably, for the lubricating composition according to the invention, the anti-wear additives are chosen from organophosphates. They have the advantage of not forming ash and being thermally stable. Examples include phospho-sulfur additives such as metallic alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTP. Preferred compounds have the formula Zn((SP(S)(OQ6)(OQ7))2, in which Q6 and Q7, identical or different, independently represent an alkyl group, preferably an alkyl group comprising from 1 to 18 carbon atoms.

[0248] Amine phosphates are also anti-wear and extreme pressure additives that can be used in a composition according to the invention. However, the phosphorus supplied by these additives can act as a poison for the catalytic converters of automobiles because these additives generate ash. These effects can be minimized by partially substituting the amine phosphates with additives that do not supply phosphorus, such as, for example, polysulfides, in particular sulfur olefins.

[0249] A lubricating composition according to the invention may comprise from 0.01 to 15% in weight, preferably 0.1 to 10% by weight, preferably 1 to 5% by weight of anti-wear agent(s), relative to the total weight of the composition.

[0250] A lubricating composition according to the invention may further comprise at least one antifoaming agent.

[0251] The antifoaming agent may be selected from polyacrylates, polysiloxanes or their hybrids.

[0252] A lubricating composition according to the invention may comprise from 0.01 to 2% by mass or from 0.01 to 5% by mass, preferably from 0.1 to 1.5% by mass or from 0.1 to 2% by mass of antifoaming agent, relative to the total weight of the composition.

[0253] A lubricating composition suitable for the invention may also include at least one pour point depressant additive, (also called "PPD" agents for "Pour Point Depressant" in English).

[0254] By slowing down the formation of paraffin crystals, pour point lowering additives generally improve the cold behavior of the composition. Examples of pour point lowering additives include alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, and alkylated polystyrenes.

[0255] The lubricating composition according to the invention may comprise: - from 5 to 94.9% by weight, preferably from 10 to 70% by weight, advantageously from 15 to 50% by weight, of the composition of diesters according to the invention, and - from 5 to 94.9% by weight, preferably from 30 to 90% by weight, advantageously from 50 to 85% by weight, of one or more other base oils, - from 0.1 to 15% by weight, preferably from 0.5 to 10% by weight, advantageously from 1 to 5% by weight of one or more additives selected from friction modifiers, viscosity index modifiers, detergents, dispersants, anti-wear and / or extreme-pressure additives, antioxidants, pour point depressants, anti-foaming agents and mixtures thereof,

[0256] relative to the total weight of the lubricating composition according to the invention.

[0257] The lubricating composition according to the invention can be obtained by mixing the constituents of the lubricating composition. The present invention also relates to a method for preparing a lubricating composition comprising the steps: - preparation of a diester composition according to the method described above, and - mixing of at least one other base oil and / or at least one additive with the diester composition.

[0258] Preferably, the process for preparing a lubricating composition according to the invention does not include an intermediate step of separating the products formed during the preparation step of the diester composition, prior to the mixing step. Preferably, the process for preparing a lubricating composition according to The invention does not include a hydrogenation step, in particular hydrogenation of the diester composition obtained at the end of the diester composition preparation step.

[0259] The other base oil(s) and the additive(s) used in the process of preparing the lubricating composition may have one or more of the characteristics described above in the context of the lubricating composition of the invention.

[0260] The lubricating composition obtained by this preparation process may have one or more of the characteristics described above in the context of the lubricating composition according to the invention. Cosmetic or pharmaceutical composition

[0261] The invention also relates to a cosmetic or pharmaceutical composition comprising (i) the composition of diesters according to the invention and (ii) at least one fatty substance and / or (iii) at least one cosmetic additive.

[0262] Preferably, the diester composition used in the cosmetic or pharmaceutical composition has one or more of the characteristics defined above within the diester composition. According to a particular embodiment, the diester composition according to the invention used in the cosmetic or pharmaceutical composition comprises at least one unsaturated diester.

[0263] The fatty substance can be chosen from among hydrocarbon oils of biological or petrochemical origin, vegetable oils, vegetable butters, fatty ethers and alcohols, oily esters (different from the diesters of the invention), alkanes and silicone oils.

[0264] Hydrocarbon oils are fatty substances derived from petrochemical processes. Examples include mineral oils, isoparaffins, waxes, paraffins, polyisobutenes, and polydecenes.

[0265] Examples of vegetable oils include wheat germ, sunflower, grapeseed, sesame, corn, apricot, castor, shea, avocado, olive, soybean, sweet almond, palm, rapeseed, cottonseed, hazelnut, macadamia, jojoba, alfalfa, poppy, pumpkin, sesame, squash, rapeseed, blackcurrant, evening primrose, millet, barley, quinoa, rye, safflower, candlenut, passionflower, rosehip, and camellia oils. Vegetable butters are fats that have the same properties as vegetable oils. The difference between the two is that butters are solid at room temperature. Also, unlike vegetable oils, the raw material from which butter is extracted (pulp, seeds or almonds) is heated after being crushed to extract the fat.Like vegetable oils, butters can be refined to ensure better preservation, neutralize the . They improve odors, color, and consistency. Rich in antioxidants and nourishing properties, plant-based butters enhance skin elasticity, protect against external aggressors by leaving a protective film on the epidermis and thus reducing dehydration, and repair and soothe by regenerating the skin's natural hydrolipidic film. Examples of plant-based butters include shea butter, cocoa butter, mango butter, shorea butter, and olive butter.

[0266] Fatty ethers and alcohols are long-chain, waxy, fatty substances with remarkable properties, including film-forming, emollient, moisturizing, softening, and protective effects. They act as moisturizing oils and emulsifiers. Examples of fatty alcohols or ethers include: cetyl alcohol, stearyl alcohol, myristyl alcohol, auryl alcohol, behenyl alcohol, cetearyl alcohol, dicaprylyl ethers, stearyl ethers, and octyldodecanol (identified by their INCI names).

[0267] Oily esters or esterified oils (distinct from the diesters of the invention) are the product of a reaction between fatty acids (longer-chain acids, such as stearic acid, oleic acid, palmitic acid) and alcohols (fatty alcohols or polyols such as glycerol). These oils may contain substances derived from petrochemicals, as is the case for isopropyl palmitate. Examples of oily esters include caprylic / capric triglyceride, coco-caprylate / caprate, oleyl erucate, oleyl linoleate, decyl oleate, and PPG-3 benzyl ether myristate (identified by their INCI names).

[0268] Silicone oils or polysiloxanes are defined as an oil comprising at least one silicon atom, and in particular at least one Si-O group. Examples of silicone oils include phenylpropyldimethylsiloxysilicate, dimethicones, and cyclopentasiloxane (identified by their INCI name).

[0269] The additive, distinct from the fatty substance and the composition of biodiesels, may be chosen from any adjuvant or additive commonly used in the fields concerned, and in particular in the cosmetic, dermatological, or pharmaceutical fields. Of course, a person skilled in the art will ensure that the possible additive(s) to the composition according to the invention are chosen in such a way that the advantageous properties intrinsic to the emollient composition according to the invention are not, or are not substantially, altered by the envisaged addition.Among the classic adjuvants that may be contained (depending on whether these adjuvants are water-soluble or fat-soluble), we can mention in particular anionic foaming surfactants (such as sodium lauryl ether sulfate, sodium alkyl phosphate, sodium trideceth sulfate), amphoteric surfactants (such as alkyl betaine, disodium cocoamphodiacetate) or non-ionic surfactants with an HLB greater than 10 (such as POE / PPG / POE, Alkylpolyglucoside, polyglyceryl-3-hydroxylauryl ether); preservatives; sequestrants (EDTA); antioxidants; . Perfumes; coloring agents such as soluble dyes, pigments, and pearlescent pigments; mattifying, tightening, whitening, or exfoliating agents; cosmetic actives that improve the skin's cosmetic properties, whether hydrophilic or lipophilic; electrolytes; hydrophilic or lipophilic polymers, anionic, nonionic, cationic, or amphoteric, thickening, gelling, or dispersing agents; slimming agents such as caffeine; optical brighteners; antiseborrheic agents; and mixtures thereof. The quantities of these various cosmetic additives are those typically used in the relevant field, and, for example, the cosmetic composition includes an overall content ranging from 0.01 to 20% by weight of additives relative to the total weight of the composition.

[0270] In the case where the cosmetic, dermatological, or pharmaceutical composition of the invention is a dermatological or pharmaceutical composition, said composition may comprise one or more therapeutic active ingredients. Examples of active ingredients usable in the dermatological or pharmaceutical composition of the invention include, for example, sunscreens; water-soluble or fat-soluble vitamins such as vitamin A (retinol), vitamin E (tocopherol), vitamin C (ascorbic acid), vitamin B5 (panthenol), vitamin B3 (niacinamide), derivatives of these vitamins (in particular esters) and mixtures thereof; antiseptics; antibacterial agents such as 2,4,4'-trichloro-2'-hydroxydiphenyl ether (or triclosan), 3,4,4'-trichlorocarbanilide (or triclocarban); antimicrobials such as benzoyl peroxide, niacin (vitamin PP); and mixtures thereof.

[0271] This cosmetic or pharmaceutical composition comprises a physiologically acceptable medium, that is to say, one which does not present any deleterious side effects and in particular which does not produce redness, heating, pulling or tingling unacceptable to a user.

[0272] According to one embodiment, the cosmetic, dermatological or pharmaceutical composition has a composition content of diesters according to the invention ranging from 0.5 to 80%, preferably from 1 to 50% and advantageously from 5 to 30% by weight relative to the total weight of the cosmetic or pharmaceutical composition.

[0273] According to one embodiment of the invention, the cosmetic or pharmaceutical composition comprises, relative to the total weight of the cosmetic or pharmaceutical: - from 0.5 to 80% by weight, preferably from 1 to 50% by weight and advantageously from 5 to 30% by weight, of the composition of diesters according to the invention, - from 0 to 90% by weight, preferably from 5 to 80% by weight and advantageously from 10 to 70% by weight, preferably from 20 to 60% by weight, and advantageously from 30 to 50% by weight, of fatty substances, - from 0 to 20% by weight of additives, - from 0 to 20% by weight of therapeutic active ingredients,

[0274]

[0275]

[0276]

[0277]

[0278] provided that the composition includes at least one additive or at least one fat. According to one embodiment of the invention, the cosmetic or pharmaceutical composition comprises, relative to the total weight of the cosmetic or pharmaceutical product: - from 0.5 to 80% by weight, preferably from 1 to 50% by weight and advantageously from 5 to 30% by weight, of the composition of diesters according to the invention, - from 0 to 90% by weight, preferably from 5 to 80% by weight and advantageously from 10 to 70% by weight, preferably from 20 to 60% by weight, and advantageously from 30 to 50% by weight, of fatty substances selected from hydrocarbon oils of biological or petrochemical origin, vegetable oils, vegetable butters, fatty ethers and alcohols, oily esters (other than diesters), alkanes and silicone oils, - 0 to 20% by weight of additives chosen from anionic, amphoteric or non-ionic foaming surfactants with an HLB greater than 10; preservatives; sequestrants; antioxidants; perfumes; coloring agents; mattifying, tightening, whitening or exfoliating fillers; cosmetic actives that improve the cosmetic properties of the skin, hydrophilic or lipophilic; electrolytes; hydrophilic or lipophilic polymers, anionic, non-ionic, cationic or amphoteric, thickening, gelling or dispersing; slimming agents; optical brighteners; antiseborrheic agents; and mixtures thereof, - possibly from 0 to 20% by weight of therapeutic active ingredients, it being understood that the composition includes at least one additive or at least one substance fat. The cosmetic or pharmaceutical composition according to the invention can thus be an anhydrous composition, an emulsion such as a water-in-oil (W / O) emulsion, an oil-in-water (O / W) emulsion or a multiple emulsion (in particular O / O / W or O / O / O), a nano-emulsion, or even a dispersion. The cosmetic or pharmaceutical composition according to the invention is in the form of a more or less flexible cream or a sprayable emulsion; it may constitute, for example, a makeup removal or skin cleansing composition, a lip cleansing composition, an after-sun composition, a composition for skin massage, a shower balm composition, an anti-perspirant composition, a mask composition, a repairing balm composition, a scrub and / or exfoliating composition for both face and hands (when it contains exfoliating particles), a makeup composition, a shaving composition, an after-shave balm composition, a perfumed composition, a composition for wipes, or a sprayable composition.

[0279] The cosmetic or pharmaceutical composition according to the invention may also constitute a sun composition when it includes at least one sun filter.

[0280] The cosmetic or pharmaceutical composition according to the invention is a cosmetic composition when it provides only a cosmetic effect. Typically, the cosmetic composition according to the invention is free of therapeutic active ingredients.

[0281] On the contrary, the cosmetic or pharmaceutical composition according to the invention is a dermatological or pharmaceutical composition when it provides a therapeutic effect. Typically, the dermatological or pharmaceutical composition according to the invention comprises at least one therapeutic active ingredient, for example selected from sunscreens; antiseptics; antibacterial active ingredients such as 2,4,4'-trichloro-2'-hydroxy diphenyl ether (or triclosan), 3,4,4'-trichlorocarbanilide (or triclocarban); antimicrobials such as benzoyl peroxide, niacin (vit. PP); and mixtures thereof. EXAMPLES

[0282] In the remainder of this description, examples are given by way of illustration of the present invention and are not intended in any way to limit its scope.

[0283] Example 1: Process for preparing a diester

[0284] Step a): reduction of 12-hydroxystearic acid (12-HSA) into 1,12-octadecanediol

[0285] A solution of 60 g of 12-HSA is prepared in V2 = 250 mL of dry THF.

[0286] The commercial lithium aluminohydride (LAH) solution is loaded into the three-necked tube then Vj = 250 mL of dry THF.

[0287] The mixture is cooled to -5°C.

[0288] The 12-HSA solution is added over 30 minutes via the dropping funnel without exceeding +10°C.

[0289] The reaction mixture is brought to a solid consistency. 200 mL of THF is added. Stirring is carried out overnight at room temperature until complete conversion of the starting material.

[0290] A TLC control (SiO2 / aluminium; heptane 70 / AcOEt 30 / PMA) indicates the end of the reaction.

[0291] Treatment: The medium is cooled to +10°C. Hydrolysis is carried out by the dropwise addition of 250 mL (3.3 vol.) of potable water. The mixture is acidified to pH 2 by the addition of 180 mL (3 vol.) of 30% sulfuric acid. After settling and separation of the two phases, the aqueous phase is extracted with 3 x 150 mL of MTBE. The combined organic phases are washed with 250 mL of potable water, 250 mL of saturated NaHCO3 solution, and 250 mL of brine. The organic phase is concentrated to dryness using a rotary evaporator at 45°C.

[0292] 1,12-Octadecanediol is obtained as a white solid.

[0293] Step a-bis): Crystallization of 1,12-octadecanediol

[0294] Crude 1,12-Octadecanediol was recrystallized by refluxing 5 to 20 g of diol suspended in 30 to 200 mL of heptane. The mixture remained cloudy, and heptane was gradually added in 10 mL portions, with 10 min reflux between each addition. The mixture was left under slow stirring at room temperature for 2 hours. The diol began to crystallize at approximately 50-55°C.

[0295] The precipitate is isolated by filtration on sintered plate no. 4.

[0296] A white solid is obtained dried for 2 h by nitrogen percolation.

[0297] Crystallization makes it possible to obtain a 1,12-octadecanediol purity of at least 80% or even at least 90%.

[0298] Step a-ter): washing

[0299] The solid obtained at the end of step a-bis), composed mainly of 1,12-octadecanediol, is filtered on a thermostatically controlled filter and then the cake is washed once with 6 volumes of cold heptane.

[0300] This protocol makes it possible to obtain a residual content of fatty alcohols of less than 0.1% by weight.

[0301] Step b): esterification of 1,12-octadecanediol into diester

[0302] The 1,12-octadecanediol diol, optionally purified as described in step a-bis), is esterified with butyric acid in the presence of a catalyst (APTS) in toluene with a diol / saturated acid mass ratio of 1 / 4.

[0303] Example 2: Properties of the diester

[0304] The diester obtained, either without purification or with purification (crystallization in step a-bis) followed by washing in step a-ter), is tested for its physicochemical properties. The results are shown in Table 2 and demonstrate that the diesters obtained by the process of the invention have properties that make them suitable for lubricating applications.

[0305] [Tables2] Purification Diester Purity (% GC) Minimum Pour Point ASTM D7346 KV100 (cSt) ASTM D7042 Viscosity Index ASTM D2270 Noack per TGA (%) ASTM D6375 None 83.2 -6 3.424 150 12.7 Crystallization 98 -24 3.586 150 10.1

Claims

Demands

1. A process for preparing at least one diester, said process comprising: a) a reaction transforming the acid function of at least one hydroxycarboxylic acid, or the ester function of at least one ester of hydroxycarboxylic acid and alcohol, into an alcohol function in order to obtain at least one diol, said hydroxycarboxylic acid comprising from 11 to 25 carbon atoms, b) an esterification reaction of the diol using at least one saturated or unsaturated acid comprising from 2 to 24 carbon atoms in order to form at least one diester, the diester corresponding to formula (4): [Chem. 4] R4'" "'-Ç 0. r1 ' xr4'" in which R1 represents a linear or branched alkyl radical containing from 1 to 22 carbon atoms or a linear or branched alkenyl radical containing from 2 to 22 carbon atoms, R2 represents a linear or branched alkyl or alkenyl divalent radical comprising from 4 to 22 carbon atoms, it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 23, R3 and R4 represent, independently of each other, a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, or a monovalent alkenyl radical, linear or branched, comprising from 1 to 18 carbon atoms.

2. A method according to claim 1, further comprising after step a) and before step b), a step a-bis) of purification of the diol composition from step a) in order to increase the diol content of the diol composition from step a), said purification step a-bis) preferably comprising at least one diol crystallization step.

3. A method according to claim 1 or 2, further comprising, before step a), a preliminary step of purifying the hydroxycarboxylic acid or hydroxycarboxylic acid ester composition in order to to increase the hydroxycarboxylic acid or hydroxycarboxylic acid ester content of the hydroxycarboxylic acid or hydroxycarboxylic acid ester composition implemented in subsequent step a), said preliminary purification step preferably comprising at least one crystallization step of the hydroxycarboxylic acid or hydroxycarboxylic acid ester.

4. A process according to any one of claims 1 to 3, wherein the hydroxycarboxylic acid corresponds to formula (1) and / or the saturated or unsaturated acid corresponds to formula (2): [Chem.l] OH O .1 J R' R" "OH [Chem. 2] R'' ''OH in which: R1 represents an alkyl or alkenyl radical, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 3 to 18 carbon atoms, preferably still from 5 to 12 carbon atoms; R2 represents a divalent alkyl or alkenyl radical, linear or branched, comprising from 4 to 22 carbon atoms, preferably still from 8 to 18 carbon atoms, it being understood that the total number of carbon atoms of R1 and R2 is from 9 to 23, preferably from 9 to 20 carbon atoms, preferably still from 10 to 18 carbon atoms. R3 represents a monovalent alkyl radical, linear or branched, comprising from 1 to 19 carbon atoms, preferably a linear or branched alkyl comprising from 2 to 17 carbon atoms, advantageously a linear alkyl comprising from 4 to 12 carbon atoms.

5. A process according to any one of claims 1 to 4, wherein the diol corresponds to formula (3) and the diester corresponds to formula (4): [Chem. 3] OH [Chem. 4] O R4' ""O O. RR 0' R in which R1 represents an alkyl or alkenyl radical comprising 3 to 18 carbon atoms, preferably 5 to 12 carbon atoms; R2 represents a divalent alkyl or alkenyl radical comprising 8 to 18 carbon atoms. it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 20 carbon atoms, preferably from 10 to 18 carbon atoms, R3 and R4 represent, independently of each other, a monovalent linear or branched alkyl or alkenyl radical comprising 2 to 17 carbon atoms, advantageously a linear alkyl or alkenyl comprising 2 to 12 carbon atoms.

6. Composition of diester(s) comprising at least one diester of formula (4): [Chem. 4] O O ,1.X , R "R" O" "R' in which R1 represents a linear or branched alkyl radical comprising from 1 to 22 carbon atoms or a linear or branched alkenyl radical comprising from 2 to 22 carbon atoms, preferably an alkyl or alkenyl radical comprising from 3 to 18 carbon atoms, preferably still from 5 to 12 carbon atoms, R2 represents a linear or branched alkyl or alkenyl divalent radical comprising 4 to 22 carbon atoms, preferably 8 to 18 carbon atoms, it being understood that the total number of carbon atoms in R1 and R2 ranges from 9 to 23, preferably from 9 to 20 carbon atoms, and even more preferably from 10 to 18 carbon atoms, R3 and R4 represent, independently of each other, a radical mo- novalent alkyl, linear or branched, comprising from 1 to 19 carbon atoms, preferably a linear or branched alkyl comprising from 2 to 17 carbon atoms, advantageously a linear alkyl comprising from 2 to 12 carbon atoms, said diester composition(s) comprising, in relation to the total weight of the diester composition(s), at least 70% by weight of diesters of formula (4) which are distinguished from each other only by the R3 and R4 groups.

7. Composition of diester(s) according to claim 6, obtained by the process according to any one of claims 1 to 5.

8. Composition according to claim 6 or 7, comprising, in relation to the total weight of the composition, at least 70% by weight of a single diester corresponding to formula (4), preferably at least 80% by weight of a single diester corresponding to formula (4), preferably at least 90% by weight of a single diester corresponding to formula (4).

9. Use of the diester composition(s) according to any one of claims 6 to 8, as a base oil in a lubricating composition or as an emollient in a cosmetic or pharmaceutical composition.

10. Lubricating composition comprising the composition of diester(s) according to any one of claims 6 to 8 and: (i) at least one base oil different from the diesters, and / or (ii) at least one additive different from the diesters.