One-pot synthesis of cyclic carbonates from aromatic alcohols

Abstract

The present invention relates to a method for preparing cyclic carbonates comprising the steps of a) mixing an aromatic alcohol and a base with glycidol, wherein previously said aromatic alcohol is optionally dissolved in a solvent, and wherein the mixture of an aromatic alcohol and a base is heated before adding the glycidol; and b) adding dimethyl carbonate (DMC) to the mixture obtained in step a) to obtain a reaction product; wherein the method is carried out in a one-pot process.

Description

[0001] ONE-POT SYNTHESIS OF CYCLIC CARBONATES FROM AROMATIC ALCOHOLS

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method of preparing cyclic carbonates. The process of the present invention comprises a one-pot direct reaction that is based on reacting an aromatic alcohol and a base with glycidol followed by the reaction of the product obtained with dimethyl carbonate. The present invention also relates to the cyclic carbonates obtainable by the said method.

[0004] STATE OF THE ART

[0005] Cyclic carbonates are characterized by presenting a carbonyl group flanked by two oxygen atoms. Cyclic carbonates are a class of compounds that is receiving growing interest both at academic and industrial level because their preparation and applications present several attractive features in the context of green chemistry and sustainability.

[0006] In fact, cyclic carbonates are widely used in a huge range of industrial applications: as polar solvents, additives, antifoam agents for anti-freeze, plasticisers, precursors for polycarbonate materials, electrolytes in lithium batteries, in the production of pharmaceuticals and as raw material in various chemical reactions. Among the cyclic carbonates, five and six-membered cyclic carbonates show promise in a number of different applications. For instance, five-membered ring cyclic carbonates are useful alkylating agents for aromatic amines, phenols and thiols, though high temperatures are required.

[0007] Cyclic carbonates can be obtained from different routes, including via phosgene, dimethyl carbonate, urea, carbon monoxide, halohydrins, alkenes or propargyl alcohols. Notwithstanding, one of the most common and effective routes to prepare cyclic carbonates, also at industrial level, is the cycloaddition of CO2 to epoxides. The reaction starts with epoxide ring opening induced by the catalyst, followed by CO2 activation by a metal-alkoxide intermediate and finally a cyclization step in which the cyclic carbonate product is released while regenerating the catalyst for subsequent turnover. This later route is a reaction thermodynamically favoured due to the release of the ring-strain energy contained in the epoxide substrate. In turn, these epoxides must be synthesized, and the most straightforward method is the epoxidation of double bonds. However, there are only a few bio-based molecules with defined amount of unsaturations per molecule (some vegetable oils have instaurations but are composed by triglycerides with different combinations of unsaturated fatty acids). In practice, the only naturally available molecules with double bonds are terpenes. The double bonds in these compounds can be converted catalytically into epoxide groups and subsequently the cycloaddition of CO2 to the epoxide groups can take place, but it is rather challenging due to steric hindrance of these compounds.

[0008] Thus, the synthesis of biobased cyclic carbonates usually requires the introduction of an epoxide, and then the reaction with CO2 to form the carbonate.

[0009] One of the widely studied route of synthesis of cyclic carbonates is by using epichlorohydrin as epoxide, which can be in turn prepared from a renewable resource as glycerol. For instance, US 6,924,379 B2 relates to a process for the preparation of cyclic carbonates by cycloaddition of CO2 to an epoxide such as epichlorohydrin using catalytic system consisting of Zinc-substituted-polyoxometalate catalyst and a Lewis base with very high turnover number. However, despite most bio-based (macro)molecules such as (poly)alcohols are reacted with epichlorohydrin, the safety of the synthesis of cyclic carbonates by using epichlorohydrin is compromised because epichlorohydrin is a toxic reagent. Besides, a stoichiometric amount of salt is formed in the reaction. Consequently, finding safer and more sustainable alternatives routes of formation of cyclic carbonates has been the subject of intense studies over the last years.

[0010] Glycerol carbonate is a more relevant cyclic carbonate typically used in the preparation of cyclic carbonates. Five and six-membered cyclic carbonates can be obtained through the combination of CO2 with diols and epoxides or by conversion of glycerol into glycerol carbonate and derivatives. For instance, Kuhnel, I. et al. (Macromol. Chem. Phys., 2018, 219, 1700613) and Sternberg, J. et al. (Green Chem., 2020, 22, 6922) succeeded in preparing cyclic carbonates to a renewable lignin-based building block equipped with cyclic carbonate functionalities. Specifically, cyclic carbonates were prepared by reaction of lignin with glycerol carbonate (GO) followed by reaction with dimethyl carbonate (DMC). This process consisted of two steps, the oxyalkylation and the cyclocarbonation. The first step involved the reaction of lignin with 10 equivalents of glycerol carbonate (respective of lignin OH groups) and reacting it at 150-170 °C for 1.5- 3 hours using 0.1 equivalents of a base that acted as a catalyst. Then the oxyalkylated lignin was precipitated in acidified water, washed, filtered and dried under vacuum. In the second step, the oxyalkylated lignin was dissolved in DMSO and 0.4 equivalents of base (K2CO3) and 5 equiv. of dimethylcarbonate (DMC) were added, keeping the reaction at 75 °C during 4 hours. Then the cyclocarbonated lignin was precipitated in acidified water, washed, filtered and dried under vacuum. However, this process presents important drawbacks such as: 1) the need for two steps; 2) the harsh conditions of the first step results in the degradation of lignin; 3) glycerol carbonate is expensive, and prevents an industrialized process, especially since excess (10 equivalents) is used; and 4) the large amount of base used (0.1 equivalent of first step plus 0.4 equivalents of the second step).

[0011] Therefore, there is a need for developing new methods of synthesis of cyclic carbonates that avoid the above-mentioned problems of currently known methods.

[0012] The present invention overcomes the drawbacks mentioned above by providing a direct method of synthesis of cyclic carbonates that uses environmentally friendly reagents through one-pot reaction process, not requiring the purification of the intermediate.

[0013] BRIEF DESCRIPTION OF THE INVENTION

[0014] The authors of the present invention have developed an improved method of preparing cyclic carbonates, which is carried out by using suitable environmentally friendly reagents at mild conditions since it may be carried out at lower temperatures and shorter reaction times compared to currently known methods.

[0015] Therefore, a first aspect of the present invention is directed to a method for preparing cyclic carbonates comprising the following steps: a) mixing an aromatic alcohol and a base with glycidol, wherein previously said aromatic alcohol is optionally dissolved in a solvent, and wherein the mixture of an aromatic alcohol and a base is heated before adding the glycidol; and b) adding dimethyl carbonate (DMC) to the mixture obtained in step a) to obtain a reaction product; wherein the method is carried out in a one-pot process.

[0016] Thus, the method of preparation of cyclic carbonates described herein allows obtaining cyclic carbonates, more specifically five and six-membered cyclic carbonates, through two-steps and one-pot reaction of aromatic alcohol and a base with glycidol, followed by reaction of the mixture obtained therein with dimethyl carbonate (DMC), without the need of purifying intermediate compounds such as it happens in most of conventional methods of synthesis of cyclic carbonates which are carried out by the cycloaddition of CO2 to the epoxide groups.

[0017] Additional advantages and features of the invention will become apparent from the detailed description that follows and will be particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] To complete the description and provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the invention, which should not be interpreted as restricting the scope of the invention, but just as examples of how the invention can be carried out. The drawings comprise the following figures:

[0019] Figure 1 shows the31P-NMR spectra of the glycidylation of lignin (step a) of the method described herein, and the subsequent cyclocarbonation reaction (step b) of the method described herein. Top: starting lignin. Middle: glycidylated lignin after 2 hours. Bottom: Cyclocarbonated lignin.

[0020] Figure 2 shows the FTIR spectra of lignin, glycidylated lignin (step a) of the method described herein, and cyclocarbonated lignin (step b) of the method described herein.

[0021] Figure 3 shows the13C-NMR spectra of the obtained cyclic carbonates with lignin according to the method of the present invention.

[0022] Figure 4 shows the 1 H-NMR spectra of the obtained cyclic carbonate with phenol in DMF according to the method of the present invention.

[0023] Figure 5 shows the FTIR spectra of the obtained cyclic carbonate with phenol in DMF according to the method of the present invention.

[0024] Figure 6 shows the 1 H-NMR spectra of the obtained cyclic carbonate with 4- methoxyphenol in DMF according to the method of the present invention.

[0025] Figure 7 shows the FTIR spectra of the obtained cyclic carbonate with 4- methoxyphenol in DMF according to the method of the present invention.

[0026] Figure 8 shows the FTIR spectra of the obtained cyclic carbonate with hydroquinone in MEK according to the method of the present invention.

[0027] DESCRIPTION OF THE INVENTION

[0028] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs.

[0029] The method of the present invention present invention intends to solve the shortcomings of prior-art methods of preparing cyclic carbonates, which is carried out by using suitable environmentally friendly reagents at mild conditions since it may be carried out at lower temperatures and shorter reaction times.

[0030] It is an object of the present invention to provide a method for preparing cyclic carbonates.

[0031] In particular, the method of the present invention comprises the steps of: a) mixing an aromatic alcohol and a base with glycidol, wherein previously said aromatic alcohol is optionally dissolved in a solvent, and wherein the mixture of an aromatic alcohol and a base is heated before adding the glycidol; and b) adding dimethyl carbonate (DMC) to the mixture obtained in step a) to obtain a reaction product; wherein the method is carried out in a one-pot process.

[0032] In the context of the present invention, the term “one-pot process” is used to refer to a strategy to improve the efficiency of a chemical process whereby all the reactants of said chemical process are subjected to successive chemical reactions in a single reactor, avoiding a lengthy and costly separation and purification process.

[0033] In the context of the present invention, the term “cyclic carbonates” is used to refer to 5 or 6 member rings having a carbonyl group flanked by two oxygen atoms.

[0034] As previously mentioned, the method of the present invention comprises a step (a), which may be referred herein as glycidylation, that comprises mixing an aromatic alcohol and a base with glycidol, wherein previously said aromatic alcohol is optionally dissolved in a solvent, and wherein the mixture of an aromatic alcohol and a base is heated before adding the glycidol.

[0035] In the context of the present invention the term “aromatic alcohol” or “aryl-alcohol” is used to refer to a class of chemical compounds containing a hydroxyl group (-OH) bonded directly to an aromatic hydrocarbon group.

[0036] The aromatic alcohol according to the present invention may be in any physical state. In particular embodiments, the aromatic alcohol according to the present invention may be in liquid or solid state. For alcohol in solid state, i.e., having a melting point higher than room temperature, they may be heated to liquid state before mixing them with the base and the glycidol.

[0037] In more particular embodiments, the aromatic alcohol is miscible with glycidol and do not need a previous step of dissolving them in a suitable solvent. Non-limiting examples of suitable aromatic alcohols which are soluble in glycidol are phenol, 4- methoxyphenol, benzyl alchohol, orto-, meta- and para-cresols, xylenols, 4- chlorophenol, benzenediols such as hydroquinone, and benzenetriols.

[0038] In a particular embodiment, the aromatic alcohol is selected from phenol, 4- methoxyphenol, benzyl alchohol, orto-, meta- and para-cresols, xylenols, 4- chlorophenol, benzenediols such as hydroquinone, and benzenetriols.

[0039] In more particular embodiments, the aromatic alcohol is not miscible with glycidol and the method described herein may further comprise, previous to step (a), a step of dissolving the aromatic alcohol in a suitable solvent. In preferred embodiments, it may be needed to heat the solvent to favor its deprotonation. Non-limiting examples of suitable aromatic alcohols which are not miscible with glycidol are bio-based macromolecules such as lignin, tannins and derivatives of them.

[0040] In the context of the present invention, the term “bio-based” refers to products derived from plants and other renewable materials. As an example, lignin is present in wood and bark, and tannins (or tannoids) are found in wood, seeds, bark, leaves and fruit skins.

[0041] Non-limiting examples of lignin derivatives are sulfonate, phenolic, organosolv, kraft and sodium sulfonate lignin.

[0042] Non-limiting examples of tannins derivatives are complex tannins, condensed tannins, and hydrolysable tannins.

[0043] In a particular embodiment, the aromatic alcohol is a bio-based macromolecule, more preferably lignin, tannins or derivatives thereof, even more preferably lignin or derivatives thereof.

[0044] Non-limiting examples of suitable solvents to be used with those aromatic alcohols which are not miscible with glycidol are polar aprotic solvents such as dimethylformamide (DMF), tetra hydrofuran (THF), acetonitrile (ACN), dichloromethane (CH2CI2), chloroform (CHCI3), butanone or methyl ethyl ketone (MEK), toluene, diethyl ether, dimethyl sulfoxide (DMSO) and ethyl acetate (AcOEt); and polar protic solvents having a pKa higher than the pKa of the based used. Non-limiting examples of said polar aprotic solvents that can be used are methanol, ethanol, propanol, isopropanol, tertbutanol and butanol.

[0045] In more particular embodiments, the aromatic alcohol non-miscible with glycidol is dissolved in a solvent according to the present invention which has been previously heated at a temperature between about 25 °C and 150 °C, preferably about 40 °C to about 120 °C, more preferably between about 75 °C to about 90 °C, even more preferably at about 90 °C. In yet more particular embodiments, the aromatic alcohol non-miscible with glycidol is dissolved in a solvent according to the invention in a weight ratio aromatic alcohol :solvent of 1 :100, preferably in a weight ratio of 1 :10; more preferably in a weight ratio of 1 :5.

[0046] In the context of the present invention, the term “equivalents” refers, based on a stoichiometric relationship, to the number of moles of one reagent that reacts with one mole of another reagent. Particularly, the expression “based on one equivalent of aromatic alcohol” refers to one mole of hydroxyl groups taking part in the reaction that reacts with one mole of another reagent (for example, glycidol). Therefore, for example, one equivalent of benzenediol would have two equivalents of reactive groups (two hydroxyl groups) and thus would react with 2 moles of another compound if the relationship is stoichiometric.

[0047] In some preferred embodiments, the glycidol is added in step a) of the method according to the present invention in an amount from about 1 to about 3 equivalents, based on one equivalent of aromatic alcohol. Indeed, it has been surprisingly found that, contrary to other conventional methods of synthesis of cyclic carbonates such as those that occur via epoxidation with epichlorohydrin or with glycerol carbonate which typically require 10 equivalents of the reagent epoxide, the method according to the present invention only utilizes glycidol in slight excess. That is, it has been shown that in the method according to the present invention an amount from about 1 to about 1.2 equivalents of glycidol is sufficient to obtain yields of cyclic carbonates comparable to those obtained by conventional methods of epoxidation with epichlorohydrin or glycerol carbonate.

[0048] In some preferred embodiments, the base is also added in step a) of the method according to the invention in a relative lower amount. In a particular example, the base in step a) may be added in an amount from about 0.05 to about 1.2 equivalent, based on one equivalent of aromatic alcohol, more preferably from about 0.2 to 0.4 equivalents, based on one equivalent of aromatic alcohol.

[0049] In the method according to the present invention, the base acts as catalyst that provides the mixture obtained in step a) and starts the reaction between the glycidol and the aromatic alcohol to obtain an intermediate diol. This intermediate, that is not isolated, reacts with dimethyl carbonate (DMC) in the second step (step b)) to form cyclic carbonates. The reaction of step b) is also catalyzed by the same base as in step a).

[0050] Non-limiting examples of suitable bases to be used in the method described herein may be organic or inorganic bases. For instance, non-limiting examples of suitable organic bases that may be used according to the invention are pyridines, alkylamines (such as methylamine, trimethylamine, triethylenediamine and quinuclidine), imidazoles, guanidines (such as 1 ,5,7-triazabicyclo[4.4.0]dec-5-ene (also known as triazabicyclodecene or TBD)), phosphazenes, sodium methoxide, sodium ethoxide, potassium tert-butoxide, amidines (such as 1 ,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)) and combinations thereof.

[0051] Non-limiting examples of suitable inorganic bases to be used in the method according to the present invention may be selected from the group consisting of potassium carbonate (K2CO3), sodium bicarbonate (Na2COs), sodium hydroxide (NaOH), potassium hydroxide (KOH) and combinations thereof.

[0052] In step a) of the method of preparation of cyclic carbonates as described herein, the mixture of an aromatic alcohol and a base is heated before adding the glycidol.

[0053] In a particular embodiment, in step a) of the method of preparation of cyclic carbonates as described herein, the mixture of an aromatic alcohol and a base is heated before adding the glycidol at temperatures between about 25 °C and 170 °C, preferably at temperatures between about 50 °C and 120 °C, more preferably at temperatures between 60 °C and 90°C.

[0054] In another particular embodiment, the mixture of an aromatic alcohol and a base with glycidol obtained in step a) of the method of preparation of cyclic carbonates as described herein is maintained at temperatures between about 25 °C and 170 °C, preferably at temperatures between about 50 °C and 120 °C, more preferably at temperatures between 60 °C and 90 °C.

[0055] It has been surprisingly found that a method according to the invention is faster, safer and produces less waste, being more environmentally friendly and economically more competitive in comparison with conventional two-steps methods of synthesis of cyclic carbonates such as the cycloaddition of CO2 to the epoxide groups. Indeed, the inventors surprisingly found that the method according to the invention is able to achieve yields comparable to those conventional methods even when performed at mild reaction conditions (at temperatures lower than about 100 °C) for relatively short reaction times (about 3 hours) and without the need of applying pressure at any of the steps of the method.

[0056] In a more particularly preferred embodiment, the reaction mixture obtained from an aromatic alcohol and a base with glycidol in step a) of the method of preparation of cyclic carbonates as described herein is maintained at temperatures between 50 °C and 120 °C for about 5 min to about 24 hours. As the skilled person would understand, the exact time may depend on the exact conditions used. Indeed, the higher the temperature at which the mixture of step a) is maintained, the shorter the duration of the said reaction step a).

[0057] In preferred embodiments, the reaction mixture of an aromatic alcohol and a base with glycidol obtained in step a) of the method according to the invention may be maintained at temperatures between about 25 °C to about 170 °C, more preferably at temperatures between about 50 °C and about 120 °C, even more preferably between about 60 °C and 90 °C; during a period of time between about 5 minutes and about 6 hours, preferably between about 90 minutes and about 3 hours, and more preferably about 2 hours.

[0058] In step a) the mixture of an aromatic alcohol and a base with glycidol, if needed, previously dissolved in a solvent, at the range of temperatures as described above, may be done by using methods known in the art. Mixing and dissolving is typically performed until a homogeneous phase of the glycidol and the aromatic alcohol, which may have been previously dissolved into a solvent, is obtained. Moreover, the mixture obtained in step a) may be further kept under stirring during the reaction time to facilitate the reaction process.

[0059] In some preferred embodiments, the glycidol is added in a dropwise manner, i.e. , one drop at a time, to the mixture of the aromatic alcohol and the base, which may have been optionally previously dissolved in a solvent. By mixing the glycidol with the aromatic alcohol (solution) in a dropwise manner the formation of a homogeneous mixture in step a) is facilitated and consequently the reaction step a) of the method according to the present invention.

[0060] As previously mentioned, the method of the present invention further comprises a step b) of adding dimethyl carbonate (DMC) to the mixture obtained in step a) to obtain a reaction product.

[0061] In some preferred embodiments, the dimethyl carbonate (DMC) may be added in step b) of the method described herein in an amount from about 1 to about 10 equivalents based on one equivalent of aromatic alcohol, preferably about 2 to about 7 equivalents based on one equivalent of aromatic alcohol, more preferably about 3 to 5 equivalents based on one equivalent of aromatic alcohol.

[0062] In some preferred embodiments, the reaction mixture of step b) of the method of preparation of cyclic carbonates as described herein is kept at temperatures between about 25°C and about 150°C, preferably about 90°C.

[0063] In more yet preferred embodiments, the reaction mixture of step b) of the method of preparation of cyclic carbonates as described herein is maintained at temperatures between about 60°C and about 120 °C, preferably about 90°C, for about 5 min to about 5 hours, more preferably for about 1 hour.

[0064] In particular, in the method of preparation of cyclic carbonates as described herein the yield of the reaction between the aromatic alcohol and the glycidol may be varied from 0 to 100, in particular, the yield may be from 50 to 99, more particularly from 75 to 95. The yield of the reaction between the aromatic alcohol and the glycidol can be determined by techniques known by the skilled person. For example, the yield of reaction can be determined by quantifying the number of moles of product generated and comparing it with the amount of moles of the starting material. Another option is to determine the residual amounts of starting materials (i.e. , aromatic alcohol).

[0065] The method of preparation of cyclic carbonates as described herein may further comprises a step c) of precipitating the reaction product obtained in step b) (corresponding to the cyclic carbonates) by using a diluted acid thereby obtaining a precipitate. After that, the precipitate may be washed with acidified water, filtrated, and dried. This applies to the case of large molecules such as lignin. For small molecules such as phenol, a liquid-liquid extraction using first diluted acid and the brine, followed by evaporation of the organic phase under reduced pressure yields the product.

[0066] Non-limiting examples of suitable diluted acids to be used in the method according to the present invention are inorganic acids such as chlorohydric acid, sulfuric acid and phosphoric acid; and organic acids such as lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, malic acid and tartaric acid. In addition, carbon dioxide in gas form can be also used to acidify the mixture, in combination with an organic or an inorganic acid.

[0067] Step c) may be performed by means known in the art. For instance, filtrating may be carried out, for example, by centrifugation, vacuum filtration or pressure filtration. Drying the precipitate may be performed by using for example, by using a rotary evaporator.

[0068] In the method of preparation of cyclic carbonates as described herein the formation of the intermediate compounds obtained in the first step a) and the cyclic carbonates obtained in step b) can be monitored by techniques such as Fourier transform infrared (FTIR), gas chromatography-mass spectrometry (GC-MS), gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). FTIR technique gives information about the increase in -OH groups in step a) and the formation of the cyclic carbonate in step b). GC-MS can quantitatively indicate the yield of each step, for small molecules. GPC can be used to follow the reaction of biomacromolecules, such as lignin, whose molecular weight changes during the reaction. Finally, NMR, similar to GC-MS can confirm the structure and the purity of the final product.

[0069] A further aspect of the present invention is providing a cyclic carbonate obtainable by the method of the invention.

[0070] In summary, the method as defined above allows obtaining cyclic carbonates, particularly five and / or six membered cyclic carbonates.

[0071] As an example, between 94 and 95 % of 5-member cyclic carbonates based on the total of cyclic carbonates can be obtained by the method of the present invention, whereas between 5 and 6 % of 6-member cyclic carbonates based on the total of cyclic carbonates can be obtained by the method of the present invention.

[0072] The inventors have surprisingly found that the method of the present invention as defined above allows obtaining higher carbonate concentration than those obtained by other methods. Furthermore, by using milder reaction conditions, when the aromatic alcohol is a bio-based macromolecule, such as lignin, it is less altered by the process (less depolymerizated and repolymerizated) and thus the yield of the method is higher.

[0073] The term “about” when used in the context of the present invention preceding a number and referring to it, is to be understood as designating any value lying within the range defined by the number ±5 %, more preferably a range defined by the number ±2 %. For example, the expression “about 10” should be construed as “within the range of 9.5 to 10.5”, preferably “within the range of 9.8 to 10.2”.

[0074] Through the description and the claims, the word “comprises” and variations thereof are not intended to exclude other technical features, ingredients or steps. Additional advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention without undue burden.

[0075] EXAMPLES

[0076] In the following, the present invention will be further illustrated by means of Examples. The Examples should in no case be interpreted as limiting the scope of the present invention, but only as an illustration of the same. REAGENTS

[0077] Reagents used in the examples included below are the following:

[0078] Dimethylformamide (DMF) had a purity equal to 99.98 % and was provided by Scharlab. Methyl ethyl ketone (MEK) had a purity equal to 99.7 % and was provided by Acros Organics. Potassium carbonate (K2CO3) had a purity equal to or higher than 99.5 to 100.5 % and was provided by Scharlab. 1 ,8-diazabicyclo[5.4.0]undec-7-ene (DBU) had a purity higher than 98 % and was provided by Acros Oganics. 2, 3-Epoxy-1 -propanol or glycidol had a purity equal to 99.9 % and was provided by Sigma Aldrich. Phenol had a purity of 90% and was provided by Fluka.4-methoxyphenol had a purity of 99% and was provided by Fluka. Hydroquinone had a purity of 99% and was provided by Sigma Aldrich. Lignin had an average Mwstarting of 8509 Da.

[0079] Example 1 : Synthesis of cyclic carbonates

[0080] 1.1. Study of the reaction conditions of the glycidylation step.

[0081] 1 g of lignin of Mw of 8509 Da was dissolved in 5 ml of DMF as solvent and warmed up to 90 °C. Then, an amount of 1 .2 equivalents of glycidol (based on 1 mole of hydroxyl group of lignin) was dropwise added, together with K2CO3 as inorganic base. The resulting mixture was kept stirring and the reaction time was monitored for 2 up to 24 hours (see Table 1). Different concentrations of K2CO3 as inorganic base were assayed, in particular, from 0.2 to 1.2 equivalents of K2CO3 based on 1 mole of phenolic hydroxyl groups in lignin (see Table 1 below). Additionally, 1.2 equivalents of DBU were also assayed as organic base.

[0082] The reactions were followed by FTIR. The products were thus analysed by both FTIR and Gel Permeation Chromatography (GPC).

[0083] Table 1. Results of the reaction of lignin with glycidol using different equivalents of the base, reaction time and temperature for the glycidylation step (“PD” refers to polydispersity).

[0084] The FTIR and GPC results showed that the best conditions were achieved when running the glycidation reaction for 2 hours at 90 °C, wherein 0.2 equivalents of the inorganic base K2CO3 were sufficient to catalyze the glycidylation reaction. These conditions generated the product without excessive increase in the molecular weight (Mw), in particular the obtained product had a Mw of 13961 (see the eight column of Table 1).

[0085] It was seen that, after two hours, the glycidylation reaction did not proceed further since the intensity of the OH band did not increase after 2 hours, which indicates that no more OH groups were formed (Figure 2, OH vibration stretch in FTIR). On the contrary, it showed a decrease in the OH intensity, likely due to self-condensation, as evidence by the increase in the molecular weight as the reaction time increases (Table 1).

[0086] Moreover, it was seen that the glycidylation was not complete if the reaction time with glycidol was shortener than 2 hours (see Table 2). Table 2 shows the results of the reaction of lignin with glycidol for 2 hours. It is noted that time 0 corresponds to the starting lignin. As can be seen in Table 2, it was shown that by reacting lignin with glycidol for 2 hours most aromatic OH groups were converted into aliphatic groups. This can be seen as the change in the OH groups of lignin after glycidylation and cyclocarbonation.

[0087] Table 2. Results of the reaction of lignin with glycidol at different reaction times.

[0088] In Table 2, mmol / g of hydroxyl groups and carboxyl groups were determined by31P-NMR and quantified according to the protocol developed by Xianzhi Meng et al. in Nature Protocols, vol. 14, pages 2627-2647 (2019).

[0089] 1.2. Study of the reaction conditions of the cyclocarbonation step. The conversion of the aliphatic OH groups formed in the glycidylation (or step a) of the method according to the invention performed for 2 hours at 90 °C and using 0.2 equivalents of K2CO3 as base, followed by the cyclocarbonation (or step b)) of the method according to the present invention) can be appreciated in Table 3.

[0090] It was seen that the addition of 5 equivalents (based on 1 mole of hydroxyl group of lignin) of DMC to the glycidylated lignin and running the reaction product for 1 hour were sufficient to complete the formation of cyclocarbonated lignin.

[0091] Indeed, Table 3 shows that there was a reduction of aliphatic OH from 5.31 mmol / g to 1.26 mmol / g. The reduction can be also appreciated in Figure 1 that shows the change in the OH groups of lignin after glycidylation and cyclocarbonation.

[0092] FTIR (Figure 2) also shows that the OH band from the glycidylated lignin is reduced and a new band at 1800 cm-1appears. The band at 1800 cm-1is broad and a shoulder can be seen at 1750 cm-1. This is likely to correspond to the linear carbonates that are formed.

[0093] Table 3. One-pot cyclocarbonation of lignin.

[0094] In Table 3, mmol / g of hydroxyl groups and carboxyl groups were determined by31P-NMR and quantified according to the protocol developed by Xianzhi Meng et al. in Nature Protocols, vol. 14, pages 2627-2647 (2019).

[0095] Thus, it was concluded that by keeping the reaction at 90 °C, at both steps (glycidylation and cyclocarbonation), the whole reaction of lignin as aromatic alcohol with glycidol and the subsequent reaction of the glycidylated lignin mixture with DMC was complete in 3 hours.

[0096] Example 2: Characterization of the obtained cyclic carbonate with lignin in dimethyl formamide (DMF) and 1.1. equivalents of glycidol.

[0097] 1 gr of lignin of Mw of 8509 Da was dissolved in 5 ml the solvent DMF. Then, 0.2 equivalents of K2CC>3 were added and the mixture was warmed up to 90°C. Then, 1.1 equivalent of glycidol (corresponding to one mol of OH group in the lignin) were dropwise added. The resulting mixture was kept stirring for 2 hours at 90 °C. Then, 5 equivalents of DMC were added to the glycidylated lignin mixture obtained. After 1 hour of reaction, the product was precipitated in diluted HCI solution. The product was washed with acidified water, filtered and dried under vacuum.

[0098] The product resulting from each step was analyzed by FTIR and GPC.

[0099] The amount of cyclic carbonate groups was determined by13C-NMR spectroscopy. Based on literature data (Spectral Database for Organic Compounds, SDBS, of National Institute of Advanced Industrial Science and Technology (AIST), Japan), it is known that the carbonyl carbon of dimethylcarbonate (DMC) appears at 156.65 ppm whereas linear carbonates appear downfield (ethylene carbonate at 155.92 ppm, propylene carbonate 155.05 ppm,). 5 and 6- member cyclic carbonates have the carbonyl carbon even more downfield (1 ,3-dioxan-2-one appear at 148.5 ppm as shown in Christopher J. Whiteoak et al. Adv. Synth. Catal. 2012, 354, 469-476).

[0100] Thus, the observed peak in the product obtained by this method at 155 ppm could be attributed to linear carbonate, the peak at 151-153 ppm to the 5-member cyclic carbonate and the small peak at 149 to the 6-member cyclic carbonate ppm (Figure 3).

[0101] As a skilled person would understand, by using DMF as internal standard, the quantitative analysis of the concentrations of cyclic carbonates can be determined. In particular, as the amount of DMF used is known, the concentration of DMF in the sample is known, and the area of the peak corresponding to it in the NMR spectra can be compared against the area of the other peaks and correlate the area of those other peaks with the concentrations of those signals (the cyclic carbonates). From the concentration in the sample, it can be inferred the mmols per gram of product. The amounts of the obtained cyclic carbonates were collected in Table 4 below.

[0102] The linear carbonate results from the reaction of one hydroxyl group of the diol formed after the reaction of the aromatic hydroxyl group with glycidol. The linear carbonate can lead to cyclic carbonate if the other hydroxyl group from the diol attacks the linear carbonate. If that does not happen, it will remain linear, this is with the following structure: -O(C=O)OCH3.

[0103] Table 4. Quantitative concentrations of cyclic carbonates obtained by13C-NMR.

[0104] Example 3: Characterization of the obtained cyclic carbonate with phenol in DMF and 1 equivalent of glycidol.

[0105] 2 g of phenol (0.021 mol) and 0,588g of K2CO3 (0.0043 mmol, 0.2 equiv.) were dissolved in 10 mL of DFM and were heated in a glass reactor equipped with cooler to 90°C. A solution of glycidol (1.42 mL, 0.021 mol, 1 equiv. respect to OH groups in phenol) in 5 mL of DMF was added dropwise to the other solution and left stirring for 3h. Afterwards, 5.37 mL of DMC (0.064 mol, 3 equiv.) in 5mL of DMF were added dropwise, letting it react for 3h. Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HCI 1% solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid.

[0106] The cyclic carbonate product obtained by following this protocol was also analyzed by1H-NMR and FTIR and it showed analogous spectra as in Figures 4 and F i g u re 5. Example 4: Characterization of the obtained cyclic carbonate with phenol in methyl ethyl ketone (MEK) and 1 equivalent of glycidol.

[0107] 2 g of phenol (0.021 mol) and 0,588g of K2CO3 (0.0043 mmol, 0.2 equiv.) were dissolved in 10 mL of MEK and were heated in a glass reactor equipped with cooler to 78°C. A solution of glycidol (1.42 mL, 0.021 mol, 1 equiv. respect to OH groups in phenol) in 5 mL of MEK was added dropwise to the other solution and left stirring for 3h. Afterwards, 5.37 mL of DMC (0.064 mol, 3 equiv.) in 5mL of MEK were added dropwise, letting it react for 3h Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HCI 1% solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid.

[0108] The cyclic carbonate product obtained by following this protocol was also analyzed by1H-NMR and FTIR and it showed analogous spectra as in Figure 4 and Figure 5. Example 5: Characterization of the obtained cyclic carbonate with phenol in methyl ethyl ketone (MEK) and 1.2 equivalents of glycidol.

[0109] 2 g of phenol (0.021 mol) and 0,588g of K2CO3 (0.0043 mmol, 0.2 equiv.) were dissolved in 10 mL of MEK and were heated in a glass reactor equipped with cooler to 78°C. A solution of glycidol (1.7 mL, 0.026 mol, 1.2 equiv. respect to OH groups in phenol) in 5 mL of MEK was added dropwise to the other solution and left stirring for 3h. Afterwards, 5.37 mL of DMC (0.064 mol, 3 equiv.) in 5mL of MEK were added dropwise, letting it react for 3h. Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HCI 1% solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid.

[0110] The cyclic carbonate product obtained by following this protocol was analyzed by1H-NMR (Figure 4) and FTIR (Figure 5).

[0111] Example 6: Characterization of the obtained cyclic carbonate with phenol, without solvent and with 1.2 equivalents of glycidol.

[0112] 5 g of phenol (0.053 mol) and 1.469g of K2CO3 (0.0106 mmol, 0.2 equiv.) were dissolved and heated in a glass reactor equipped with cooler to 50°C. Glycidol (4.25 mL, 0.064 mol, 1.2 equiv. respect to OH groups in phenol) was added dropwise to the other solution and left stirring for 3h. Afterwards, 13.42 mL of DMC (0.159 mol, 3 equiv.) were added dropwise, letting it react for 3h. Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HCI 1% solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid.

[0113] The cyclic carbonate product obtained by following this protocol was also analyzed by1H-NMR and FTIR and it showed analogous spectra as in Figure 4 and Figure 5.

[0114] Example 7: Characterization of the obtained cyclic carbonate with 4- methoxyphenol in DMF.

[0115] 2 g of phenol (0.016 mol) and 0,445g of K2CO3 (0.0032 mmol, 0.2 equiv.) were dissolved in 10 mL of DFM and were heated in a glass reactor equipped with cooler to 90°C. A solution of glycidol (1.08 mL, 0.016 mol, 1 equiv. respect to OH groups in 4- methoxyphenol) in 5 mL of DMF was added dropwise to the other solution and left stirring for 3h. Afterwards, 4.07 mL of DMC (0.0483 mol, 3 equiv.) in 5mL of DMF were added dropwise, letting it react for 3h. Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HC1 1 % solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid.

[0116] The cyclic carbonate product obtained by following this protocol was also analyzed by1H-NMR and FTIR and it showed analogous spectra as in Figure 6 and Figure 7.

[0117] Example 8: Characterization of the obtained cyclic carbonate with 4- methoxyphenol in MEK.

[0118] 2 g of 4-methoxyphenol (0.016 mol) and 0,445g of K2CO3 (0.0032 mmol, 0.2 equiv.) were dissolved in 10 mL of MEK and were heated in a glass reactor equipped with cooler to 78°C. A solution of glycidol (1.08 mL, 0.016 mol, 1 equiv. respect to OH groups in 4-methoxyphenol) in 5 mL of MEK was added dropwise to the other solution and left stirring for 3h. Afterwards, 4.07 mL of DMC (0.0483 mol, 3 equiv.) in 5mL of MEK were added dropwise, letting it react for 3h. Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HC1 1 % solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid.

[0119] The cyclic carbonate product obtained by following this protocol was also analyzed by1H-NMR and FTIR and it showed analogous spectra as in Figure 6 and Figure 7.

[0120] Example 9: Characterization of the obtained cyclic carbonate with 4- methoxyphenol in MEK and 1.2 equivalents of glycidol.

[0121] 2 g of 4-methoxyphenol (0.016 mol) and 0,445g of K2CO3 (0.0032 mmol, 0.2 equiv.) were dissolved in 10 mL of MEK and were heated in a glass reactor equipped with cooler to 78°C. A solution of glycidol (1.29 mL, 0.019 mol, 1.2 equiv. respect to OH groups in 4-methoxyphenol) in 5 mL of MEK was added dropwise to the other solution and left stirring for 3h. Afterwards, 4.07 mL of DMC (0.0483 mol, 3 equiv.) in 5mL of MEK were added dropwise, letting it react for 3h. Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HC1 1 % solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid.

[0122] The cyclic carbonate product obtained by following this protocol was analyzed by1H-NMR (Figure 6) and FTIR (Figure 7).

[0123] Example 10: Characterization of the obtained cyclic carbonate with 4-

[0124] 5 g of 4-methoxyphenol (0.040 mol) and 1 ,469g of K2CO3 (0.0081 mmol, 0.2 equiv.) were dissolved were heated in a glass reactor equipped with cooler to 78°C. Glycidol (3.23mL, 0.0483 mol, 1.2 equiv. respect to OH groups in 4-methoxyphenol) was added dropwise to the other solution and left stirring for 3h. Afterwards, 13.57 mL of DMC (0.0483 mol, 3 equiv.) were added dropwise, letting it react for 3h. Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HC1 1% solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid.

[0125] The cyclic carbonate product obtained by following this protocol was also analyzed by1H-NMR and FTIR and it showed analogous spectra as in Figure 6 and Figure 7.

[0126] Example 11 : Characterization of the obtained cyclic carbonates with luinone in MEK and 3 equivalents of glycidol.

[0127] 2 g of hydroquinone (0.018 mol) and 1 g of K2CO3 (0.007 mmol, 0.4 equiv.) were dissolved in 10 mL of MEK and were heated in a glass reactor equipped with cooler to 78°C. A solution of glycidol (7.25 mL, 0.109 mol, 3 equiv. respect to OH groups in hydroquinone) in 5 mL of MEK was added dropwise to the other solution and left stirring for 3h. Afterwards, 9.17 mL of DMC (0.109 mol, 6 equiv.) in 5mL of MEK were added dropwise, letting it react for 3h. Then it was let to cool down to room temperature and 20 mL of AcOEt was added to the reaction media and liquid-liquid extractions were carried out with 20 mL HC1 1 % solution and then with brine. The organic phase was evaporated under reduced pressure to obtain a white solid

[0128] The reaction product was characterized by FTIR, since it did not dissolve to make GC-MS or1H-NMR analysis (Figure 8).

Claims

CLAIMS1. A method for preparing five and / or six-membered cyclic carbonates comprising the following steps: a) mixing an aromatic alcohol and a base with glycidol, wherein previously said aromatic alcohol is optionally dissolved in a solvent, and wherein the mixture of an aromatic alcohol and a base is heated before adding the glycidol; and b) adding dimethyl carbonate (DMC) to the mixture obtained in step a) to obtain a reaction product; wherein the base in step a) is selected from the group consisting of pyridines, alkylamines, imidazoles, guanidines, phosphazenes, sodium methoxide, sodium ethoxide, potassium tert-butoxide, amidines, potassium carbonate (K2CO3), sodium bicarbonate (Na2COs), sodium hydroxide (NaOH), potassium hydroxide (KOH) and combinations thereof, wherein the base in step a) is mixed in an amount from about 0.05 to about 1.2 equivalent, based on one equivalent of aromatic alcohol, wherein the glycidol in step a) is mixed in an amount from about 1 to about 3 equivalents, based on one equivalent of aromatic alcohol, wherein the reaction mixture obtained in step a) is maintained at a temperature between about 25 °C and 170 °C, wherein the DMC in step b) is added in an amount from about 1 to about 10 equivalents based on one equivalent of aromatic alcohol, wherein the reaction mixture of step b) is maintained at a temperature between about 25 °C and about 150 °C, and wherein the method is carried out in a one-pot process.

2. The method according to claim 1, wherein the solvent is selected from the group consisting of dimethylformamide (DMF), butanone or methyl ethyl ketone (MEK), tetra hydrofuran (THF), acetonitrile (ACN), dichloromethane (CH2CI2), chloroform (CHCI3), toluene, diethyl ether, dimethyl sulfoxide (DMSO), ethyl acetate (AcOEt), methanol, ethanol, propanol, isopropanol, tert-butanol and butanol.

3. The method according to claim 1 or 2, wherein the solvent in step a) is previously heated at a temperature between about 25 °C to about 150 °C.

4. The method according to claims 1 to 3, wherein the aromatic alcohol in step a) is selected from phenol, 4-methoxyphenol, benzyl alchohol, orto-, meta- and para-cresols, xylenols, 4-chlorophenol, benzenediols such as hydroquinone and benzenetriols.

5. The method according to claims 1 to 3, wherein the aromatic alcohol in step a) is a bio-based macromolecule, preferably lignin, tannins or derivatives thereof.

6. The method according to claims 1 to 5, wherein in step a) the glycidol is mixed in an amount from about 1 to about 1.2 equivalents, based on one equivalent of aromatic alcohol.

7. The method according to any of claims 1 to 6, wherein in step a) the base is mixed in an amount from about 0.2 to about 0.4 equivalent, based on one equivalent of aromatic alcohol.

8. The method according to any of claims 1 to 7, wherein the reaction mixture obtained in step a) is maintained at a temperature between about 50 °C and 120 °C.

9. The method according to any of claims 1 to 8, wherein the reaction mixture of step b) is maintained at a temperature about 60 °C and about 120 °C.

10. The method according to any of the preceding claims, wherein in step b) the DMC is added in an amount from about 1 to about 10 equivalents based on one equivalent of aromatic alcohol.

11. The method according to any of the preceding claims, wherein the method further comprises a step c) of precipitating the cyclic carbonate obtained in step b) by using a diluted acid or a liquid-liquid extraction.

12. The method according to claim 11 , wherein the diluted acid is selected from the group consisting of chlorohydric acid, sulfuric acid, phosphoric acid, lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid, malic acid, tartaric acid, combinations thereof, and carbon dioxide gas in combination with the previously mentioned acids.

Images