Method for preparing organic sulfate salts of amino acid esters

Abstract

The present invention relates to a method for synthesizing organic sulfate salts of amino acid esters, comprising the steps of reacting at least one lactam having at least three carbon atoms in the lactam ring with sulfuric acid in an aqueous solution; followed by esterifying the reaction product of the previous step with at least 200 mol-% of at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxy group, branched alkyl alcohols containing one hydroxy group, linear alkyl ether alcohols containing one hydroxy group, branched alkyl ether alcohols containing one hydroxy group, phenoxyalkanols containing one hydroxy group, and mixtures thereof; followed, optionally, by removing water and / or excess alcohol.

Description

[Technical field]

[0001] The present invention relates to a method for preparing organosulfate salts of amino acid esters. [Background technology]

[0002] Organic sulfates, such as alkyl sulfates and alkyl ether sulfates, are known to be water-soluble salts used as detergents or wetting agents.

[0003] Amino acid esters from amino acids having three or more carbon atoms can be synthesized from the corresponding lactams, which synthesis involves, as a first step, ring-opening of the lactam in the presence of an acid to give the amino acid, and, as a second step, an esterification reaction with an alcohol.

[0004] FR2977585B1 discloses a process for the preparation of a cyclohexyl ether derivative ... 7 - to C 36 This application discloses a method for synthesizing α-amino acid esters of α-alcohols from amino acids or their salts.

[0005] WO2015172158 discloses salts of ethanesulfonic acid alpha and higher amino acid esters.

[0006] WO2011002746 discloses the preparation of amino acid esters using sulfuric acid.

[0007] TRIVEDI, TJ et al., ChemSusChem 2011, No. 4, pp. 604-608, 2011, alpha-C 3 ~C 4 describes a synthetic route to salts from amino acid esters and lauryl sulfate, which involves the formation of the amino acid ester as the hydrochloride salt, followed by ion exchange with sodium lauryl sulfate.

[0008] SU1276661 discloses salts from protonated amino acid esters and anionic alkyl sulfates, which are obtained from amino acids using 2 moles of hexadecanol in dioxane and an excess of sulfuric acid.

[0009] JP49076822 and JP51036735 disclose a method for preparing amino acid ester salts using alkyl sulfates by heating 1 mole of amino acid with at least 3 moles of lauryl alcohol in the presence of sulfuric acid. The synthesis is carried out in toluene as a solvent.

[0010] Currently available methods for the synthesis of organosulfates of amino acid esters, which apply amino acids as starting materials, are carried out in organic solvents and often involve an anion exchange, after synthesis of the amino acid ester, to replace the anion present in the esterification reaction with an organosulfate.

[0011] There is a continuing need for improved methods of preparing organosulfates of amino acid esters in high yields with fast reaction times without handling organic solvents and without handling corrosive gaseous acids. There is also a need for methods of preparing organosulfates and amino acid esters in high yields in a single reaction with reduced reaction times and synthetic complexity. There is also a need for methods of quantitatively reacting amino acids and amino acid precursors, such as lactams, with alcohols that have low water solubility and therefore can only be dispersed in water to obtain organosulfates of amino acid esters.

[0012] There is a continuing need for amino acid ester salts that are active in detergent formulations and combine organic sulfate detergents for incorporation into improved detergent formulations for fabric and home care applications, such as hard surface cleaning. Summary of the Invention [Problem to be solved by the invention]

[0013] It was an object of the present invention to provide a method which meets the above identified objectives and needs. [Means for solving the problem]

[0014] This object has been achieved by the present invention as described hereinafter and reflected in the claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Throughout this specification and the claims which follow, unless the context requires otherwise, the words "comprise" and variations such as "comprises" and "comprising" are understood to imply the inclusion of a stated integer or step or group of integers or steps, but not the exclusion of any other integers or steps or group of integers or steps. The term "comprising" as used herein may be replaced with the terms "containing" or "including," or, as used herein, may sometimes be replaced with the term "having."

[0016] "Consisting of," as used herein, excludes any element, step, or ingredient not specified in the claim element. "Consisting essentially of," as used herein, does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim.

[0017] In each instance herein, any of the terms "comprising," "consisting essentially of," and "consisting of" may be replaced with either of the other two terms.

[0018] In general, the term "obtainable by" as used herein means that the corresponding product does not necessarily have to be produced (i.e. obtained) by the corresponding method or process described in each specific context, but also includes a product that exhibits all the characteristics of a product produced (obtained) by said corresponding method or process, said product not actually produced (obtained) by such a method or process. However, the term "obtainable by" also includes the more restrictive term "obtained by", i.e. a product actually produced (obtained) by the method or process described in each specific context.

[0019] Certain definitions that require a compound or a substituent of a compound to consist of "at least some carbon atoms," as used herein, refer to the total number of carbon atoms in said compound or the substituent of a compound. For example, in a substituent disclosed as an "alkyl ether having at least 8 carbon atoms containing an alkylene oxide group," the total number of at least 8 carbon atoms must be the sum of the number of carbon atoms in the alkyl portion and the number of carbon atoms in the alkylene oxide portion.

[0020] The term "containing one hydroxy group" means that only one -OH group is present. Any functionalized group derived from the hydroxy group, such as an ether group, is not considered an -OH group.

[0021] The present invention provides a method for synthesizing an organosulfate salt of an amino acid ester, comprising the steps of: (i) reacting at least one lactam having at least three carbon atoms in the lactam ring with sulfuric acid in an aqueous solution; (ii) esterifying the reaction product of step (i) with at least 200 mol-% of at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxy group, branched alkyl alcohols containing one hydroxy group, linear alkyl ether alcohols containing one hydroxy group, branched alkyl ether alcohols containing one hydroxy group, phenoxyalkanols containing one hydroxy group, and mixtures thereof; and (iii) Optionally, removing the water and / or the excess alcohol of step (ii). The present invention relates to a method comprising the steps of:

[0022] Organic sulfates are esters derived from alcohols and sulfuric acid. Organic sulfates R-SO 4 - SO 4 It comprises a nucleus and an R group which may be selected from the group consisting of straight chain alkyl, branched alkyl, straight chain alkyl ether, branched alkyl ether and phenoxyalkyl.

[0023] Lactams are cyclic amides starting with α-lactams (3 ring atoms), followed by β-lactams (4 ring atoms), γ-lactams (5 ring atoms), etc. When hydrolyzed, the lactams form the corresponding α-, β-, γ-amino acids. All lactams having at least 3 carbon atoms in the lactam ring can be used in the method for synthesizing organosulfates of amino acids. In one embodiment of the invention, lactams having 4 to 12 carbon atoms in the lactam ring are used. In another embodiment of the invention, lactams having 5 to 7 carbon atoms in the lactam ring are used. In a further embodiment, lactams having 6 carbon atoms in the lactam ring, ε-lactams, are used.

[0024] The reaction of the lactam ring is carried out by reacting at least one lactam with sulfuric acid. The reaction of the lactam ring with sulfuric acid is carried out in an aqueous solution. In one embodiment of the present application, the reaction of the lactam ring is carried out by reacting at least one lactam with sulfuric acid in an aqueous solution containing only water.

[0025] The term "water-free" refers to a composition that contains 5 wt.-% or less water based on the total amount of solvent, in another embodiment 1 wt.-% or less water based on the total amount of solvent, and in a further embodiment the solvent does not contain any water.

[0026] The term "aqueous solution" means that the solvent contains more than 50 wt.-% water, based on the total amount of the solvent. In a further embodiment, the term means that the solvent contains more than 80 wt.-% water, based on the total amount of the solvent. In another embodiment, the term means that the solvent contains more than 95 wt.-% water, based on the total amount of the solvent. In a further embodiment, the term means that the solvent contains more than 99 wt.-% water, based on the total amount of the solvent. In yet a further embodiment, the term means that the solvent contains only water.

[0027] In one embodiment of the invention, no additional solvent other than water is present in step (i) of the process.

[0028] In one embodiment of the invention, the lactam is selected from the group consisting of lactams having 5 carbon atoms in the lactam ring and lactams having 6 carbon atoms in the lactam ring, and the reaction with sulfuric acid is carried out in an aqueous solution.In another embodiment of the invention, the lactam has 5 carbon atoms in the lactam ring and the reaction with sulfuric acid is carried out in an aqueous solution.

[0029] In one embodiment, the lactam is either dissolved in water or dispersed in the aqueous phase.Typical lactam concentrations in water range from 50% to 99% by weight based on the total weight of lactam and water.In one embodiment of the invention, lactam concentrations in water range from 55 to 90% by weight based on the total weight of lactam and water.In a further embodiment, lactam concentrations in water range from 65 to 80% by weight based on the total weight of lactam and water.

[0030] In one embodiment, the sulfuric acid is used as concentrated sulfuric acid. In another embodiment, the sulfuric acid is used as a 96 to 98 wt.-% sulfuric acid solution in water. In a further embodiment, the sulfuric acid is used as an 80 wt.-% sulfuric acid solution in water.

[0031] In one embodiment of the present invention, the total amount of sulfuric acid is added at the beginning of the reaction to the at least one lactam. In another embodiment, the sulfuric acid is added dropwise to the at least one lactam over a period of 0.1 to 10 h.

[0032] The molar ratio of sulfuric acid to lactam ranges from 90 to 200 mol-%. In one embodiment of the invention, the molar ratio of sulfuric acid to lactam ranges from 90 to 150 mol-%. In another embodiment, the molar ratio of sulfuric acid to lactam ranges from 95 to 125 mol-%. In a further embodiment, the molar ratio of sulfuric acid to lactam is 100 mol-%.

[0033] The reaction of the at least one lactam with sulfuric acid is carried out at a temperature of 50 to 150° C. In one embodiment of the invention, the reaction is carried out at a temperature of 80 to 140° C. In another embodiment, the reaction is carried out at a temperature of 90 to 130° C. In one embodiment of the invention, the temperature is kept constant for the duration of the reaction. In another embodiment, the temperature varies within a temperature range for the duration of the reaction. The reaction of the at least one lactam with sulfuric acid is carried out for a period of 0.1 to 15 hours. In another embodiment of the invention, the period is 1 to 10 hours. In another embodiment, the period is 2 to 5 hours. In one embodiment of the invention, the reaction of the at least one lactam with sulfuric acid is carried out under atmospheric pressure. In another embodiment, the reaction of the at least one lactam with sulfuric acid is carried out in a closed vessel under a pressure of 1 to 10 bar. In a further embodiment, the reaction of the at least one lactam with sulfuric acid is carried out in a closed vessel under a pressure of 1 to 5 bar. In another embodiment, the reaction of the at least one lactam with sulfuric acid is carried out in a closed vessel under a pressure of 1 to 4 bar. In one embodiment, a protective atmosphere, for example nitrogen or argon gas, is used to carry out the reaction. In another embodiment, the reaction of at least one lactam with sulfuric acid is carried out at atmospheric pressure at a temperature of 50 to 150° C. for a period of 0.1 to 10 h. In a further embodiment of the invention, the reaction of at least one lactam with sulfuric acid is carried out at atmospheric pressure at a temperature of 90 to 130° C. for 3 hours. In another embodiment of the invention, the reaction of at least one lactam with sulfuric acid is carried out in a closed vessel at a pressure of 1.0 to 10 bar at a temperature of 50 to 150° C. for a period of 0.1 to 10 h.

[0034] In step (ii), two parallel esterification reactions are carried out. One esterification reaction is the formation of an ester of the carboxylic acid group formed by ring opening of the lactam with sulfuric acid and at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxyl group, branched alkyl alcohols containing one hydroxyl group, linear alkyl ether alcohols containing one hydroxyl group, branched alkyl ether alcohols containing one hydroxyl group, phenoxyalkanols containing one hydroxyl group, and mixtures thereof. The other esterification reaction is the formation of an ester of sulfuric acid and at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxyl group, branched alkyl alcohols containing one hydroxyl group, linear alkyl ether alcohols containing one hydroxyl group, branched alkyl ether alcohols containing one hydroxyl group, and mixtures thereof.

[0035] In one embodiment of the present invention, the reaction of at least one lactam with sulfuric acid is carried out as a separate step (i) of the method. In another embodiment, the reaction of at least one lactam with sulfuric acid and at least one alcohol is carried out in a single step, i.e. step (i) is carried out in combination with step (ii), an esterification reaction with at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxyl group, branched alkyl alcohols containing one hydroxyl group, linear alkyl ether alcohols containing one hydroxyl group, branched alkyl ether alcohols containing one hydroxyl group, phenoxyalkanols containing one hydroxyl group, and mixtures thereof. In a further embodiment, the reaction of at least one lactam with sulfuric acid and the reaction with at least one alcohol are carried out in a single step in an aqueous solution containing only water, i.e. step (i) is carried out in combination with step (ii), an esterification reaction with at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxyl group, branched alkyl alcohols containing one hydroxyl group, linear alkyl ether alcohols containing one hydroxyl group, branched alkyl ether alcohols containing one hydroxyl group, and mixtures thereof.

[0036] When step (ii) is carried out as a separate step subsequent to step (i) of the process, the reaction of step (i) is carried out until hydrolysis of the lactam ring is complete, where complete is understood to mean that no further hydrolysis can take place, either because the lactam ring has been fully hydrolyzed or because no further hydrolysis is possible given the chemical nature and amounts of the reaction partners.

[0037] The alcohol in step (ii) is added either as a material without additional solvent or as a material dissolved in water. In one embodiment of the present invention, the at least one alcohol is selected from the group consisting of linear alkyl alcohols containing one hydroxy group, branched alkyl alcohols containing one hydroxy group, linear alkyl ether alcohols containing one hydroxy group, branched alkyl ether alcohols containing one hydroxy group, phenoxyalkanols containing one hydroxy group, and mixtures thereof.

[0038] In one embodiment of the present invention, at least one linear or branched C 2 - to C 36 In another embodiment, at least one C 1 -alcohol containing one hydroxy group is used. 8 - to C 22 In another embodiment, C -aliphatic alcohols each containing one hydroxy group are used. 16 - and C 18 In another embodiment, a mixture of C -aliphatic alcohols, each of which contains one hydroxy group, is used. 18 - and C 22 In one embodiment, a mixture of at least one branched C 9 - to C 17 In a further embodiment, a linear or branched C alcohol containing one hydroxy group is used. 8 - to C 10 In a further embodiment, a mono-alcohol is used. In a further embodiment, 2-propylheptanol or 2-ethylhexanol is used. In yet a further embodiment, 2-ethylhexanol is used.

[0039] In another embodiment, an alkyl ether alcohol is used. The alkyl ether alcohol is, for example, an alkyl alcohol alkoxylated with ethylene oxide and / or propylene oxide and / or butylene oxide. In one embodiment of the present invention, at least one linear or branched C alkoxylated with ethylene oxide and / or propylene oxide and / or butylene oxide containing one hydroxyl group is used. 2 - to C 36 In another embodiment, at least one C alkoxylated with ethylene oxide and / or propylene oxide and / or butylene oxide containing one hydroxy group is used. 8 - to C 22 -alcohols are used. The alkoxylation of the alcohols is carried out either with only one alkylene oxide or with more than one alkylene oxide. When more than one alkylene oxide is used, the resulting alkyl ether alcohols contain either randomly distributed alkylene oxide units or a block of one alkylene oxide followed by a block of another alkylene oxide. In one embodiment of the present invention, alkyl alcohols alkoxylated with only a single alkylene oxide are used. In a further embodiment, alkyl alcohols alkoxylated with a first alkylene oxide followed by a second alkylene oxide are used, thereby forming a block structure of different alkylene oxide blocks. In yet another embodiment, alkoxylated 2-propylheptanol is used.

[0040] In a further embodiment of the invention, at least one phenoxyalkanol is used. In another embodiment, phenoxyethanol is used.

[0041] In one embodiment of the present invention, the molar ratio of the alcohol containing one hydroxyl group to the lactam having at least three carbon atoms is in the range of 200 to 400 mol-%. In another embodiment, the molar ratio of the alcohol containing one hydroxyl group to the lactam having at least three carbon atoms is in the range of 200 to 300 mol-%. In another embodiment, the molar ratio of the alcohol containing one hydroxyl group to the lactam having at least three carbon atoms is in the range of 200 to 250 mol-%.

[0042] In another embodiment of the present invention, the molar ratio of the alcohol containing one hydroxyl group to sulfuric acid ranges from 200 mol-% to 400 mol-%. In a further embodiment, the molar ratio of the alcohol containing one hydroxyl group to sulfuric acid ranges from 200 mol-% to 300 mol-%. In another embodiment, the molar ratio of the alcohol containing one hydroxyl group to sulfuric acid ranges from 200 mol-% to 250 mol-%.

[0043] The esterification reaction of step (ii) is carried out at a temperature in the range of 80 to 200° C. In another embodiment of the invention, the esterification reaction is carried out at a temperature in the range of 120 to 140° C. In one embodiment of the invention, the temperature is kept constant for the duration of the reaction. In another embodiment, the temperature varies within a temperature range for the duration of the reaction. The duration of the esterification reaction of step (ii) is 1 to 30 h. In another embodiment of the invention, the duration of the esterification reaction is 2 to 5 h. In a further embodiment, the esterification is carried out in a closed vessel under a pressure of 1 to 10 bar. In a further embodiment, the esterification is carried out in a closed vessel under a pressure of 1 to 5 bar. In another embodiment, the esterification is carried out in a closed vessel under a pressure of 1 to 4 bar. In one embodiment, a protective atmosphere, for example nitrogen gas or argon gas, is used to carry out the reaction. In another embodiment, the esterification is carried out at atmospheric pressure at a temperature of 80 to 200° C. for a period of 0.1 to 10 h. In a further embodiment of the invention, the esterification is carried out at atmospheric pressure at a temperature of 90 to 130° C. for 3 hours. In another embodiment of the invention, the esterification reaction is carried out in a closed vessel at a pressure of 1.0 to 10 bar at a temperature of 80 to 200° C. for a period of 0.1 to 30 h.

[0044] In one embodiment of the present invention, the combining steps (i) and (ii) is carried out by mixing at least one lactam having at least 3 carbon atoms in an aqueous solution and at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxy group, branched alkyl alcohols containing one hydroxy group, linear alkyl ether alcohols containing one hydroxy group, branched alkyl ether alcohols containing one hydroxy group, phenoxyalkanols containing one hydroxy group, and mixtures thereof, adding sulfuric acid, followed by sealing the vessel and reacting the mixture at a temperature of 80 to 200° C. for 1 to 30 h. In a further embodiment of the invention, the combining steps (i) and (ii) are carried out by mixing at least one lactam having at least 3 carbon atoms and at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxy group, branched alkyl alcohols containing one hydroxy group, linear alkyl ether alcohols containing one hydroxy group, branched alkyl ether alcohols containing one hydroxy group, phenoxyalkanols containing one hydroxy group and mixtures thereof, adding sulfuric acid, followed by sealing the vessel and reacting the mixture at a temperature of 80 to 200° C. for 1 to 30 h under a pressure of 1.0 to 10 bar.

[0045] After step (ii), or after steps (i) and (ii) combined, water and / or excess alcohol may be removed. Removal of water and alcohol may be carried out by any technique known in the art, for example by application of a vacuum. In one embodiment of the invention, step (iii) optional removal of water and / or excess alcohol is carried out by applying a vacuum in the range of 0.1 mbar to 800 mbar. In another embodiment, a vacuum in the range of 1 mbar to 500 mbar is applied. In a further embodiment, a vacuum in the range of 10 mbar to 100 mbar is applied.

[0046] [Example] method 1H NMR was measured in MeOD on a Bruker Avance 400 MHz spectrometer.

[0047] The hydroxy value is determined according to DIN 53240-1, 2016.

[0048] [Example 1] 6-Amino-hexanoic acid-diethylene glycol-C12 / C14-alkyl esters as diethylene glycol-C12 / C14-alkyl sulfates In a four-necked vessel equipped with a thermometer, reflux condenser, nitrogen inlet, dropping funnel and stirrer, 28.3 g of caprolactam (80 wt.-% aqueous solution) and 11.5 g of water are placed and 20.8 g of concentrated sulfuric acid are added within 5 minutes. The temperature is increased from room temperature to 60° C. during the addition. The mixture is heated to reflux and stirred for 4 hours. 130.7 g of C12 / C14 aliphatic alcohol ethoxylated with 2 moles of ethylene oxide (hydroxy value 185 mg KOH / g) are placed and heated to 115° C. Water is distilled off from the reaction mixture. The reaction mixture is stirred under these conditions for 4 hours. 155.0 g of off-white soft wax are obtained. 1H-NMR in MeOD shows complete conversion to 6-amino-hexanoic acid-diethylene glycol-C12 / C14-alkyl ester as diethylene glycol-C12 / C14-alkyl sulfate.

[0049] [Example 2] 6-Amino-hexanoic acid-2-ethyl-hexyl ester as 2-ethyl-hexyl sulfate In a four-necked vessel equipped with a thermometer, reflux condenser, nitrogen inlet, dropping funnel and stirrer, 99.0 g of caprolactam (80 wt.-% aqueous solution), 40.3 g of water and 227.9 g of 2-ethylhexanol are placed. 72.9 g of concentrated sulfuric acid are added within 15 min. The temperature is increased from room temperature to 50 ° C during the addition. The mixture is heated to reflux and stirred under reflux for 3 h. The reflux condenser is replaced by a distillation head and water is distilled off from the reaction mixture at 107-130 ° C. The reaction mixture is stirred under these conditions for 4 h. 310.0 g of a pale yellow oil is obtained. 1H-NMR in MeOD shows a 92% conversion to 6-amino-hexanoic acid-2-ethyl-hexyl ester as ethyl-hexyl sulfate.

[0050] [Example 3] 6-Amino-hexanoic acid-2-ethyl-hexyl ester as 2-ethyl-hexyl sulfate (under pressure) In a 50 ml round-bottom glass pressure vessel, stable to 10 bar, equipped with a magnetic stirrer, 6.3 g of caprolactam (90 wt.-% aqueous solution) and 16.3 g of 2-ethylhexanol are placed. 5.2 g of concentrated sulfuric acid are added within 15 min. The temperature is allowed to rise during the addition from room temperature to 50° C. The vessel is sealed and placed in an oil bath. The oil bath is heated to 135° C. and the mixture is stirred under these conditions in a sealed vessel for 3 h. The mixture is transferred to a three-neck vessel equipped with a stirrer, thermometer and nitrogen inlet. Under a constant nitrogen flow into the liquid, the reaction mixture is stirred at an oil bath temperature of 135° C. for 6.5 h. 21.0 g of a yellow oil are obtained. 1H-NMR in MeOD indicates a 98% conversion to 6-amino-hexanoic acid-2-ethyl-hexyl ester as ethyl-hexyl sulfate.

Claims

1. 1. A method for synthesizing an organosulfate salt of an amino acid ester, comprising the steps of: (i) reacting at least one lactam having at least three carbon atoms in the lactam ring with sulfuric acid in an aqueous solution; (ii) esterifying the reaction product of step (i) with at least one alcohol selected from the group consisting of linear alkyl alcohols containing one hydroxy group, branched alkyl alcohols containing one hydroxy group, linear alkyl ether alcohols containing one hydroxy group, branched alkyl ether alcohols containing one hydroxy group, phenoxyalkanols containing one hydroxy group, and mixtures thereof, wherein the molar ratio of the alcohol containing one hydroxy group to the lactam having at least 3 carbon atoms is at least 200 mol-%; and (iii) Optionally, removing the water and / or the excess alcohol of step (ii). Including, The process, wherein the molar ratio of the alcohol containing one hydroxy group to the sulfuric acid is in the range of 200 mol-% to 400 mol-%.

2. The method of claim 1 , wherein steps (i) and (ii) are carried out in a single step.

3. 3. The process according to claim 1 or 2, wherein the molar ratio of sulfuric acid to lactam is in the range of 90 to 200 mol-%.

4. 4. The process according to claim 1, wherein the molar ratio of the alcohol containing one hydroxy group to the lactam having at least 3 carbon atoms is in the range of 200 mol-% to 400 mol-%.

5. 3. The method of claim 2, wherein the combined steps (i) and (ii) comprise reacting a mixture of sulfuric acid, at least one lactam and at least one alcohol at a temperature of from 80 to 200° C. for from 1 to 30 h.

6. 6. The method of claim 2 or 5, wherein the combined steps (i) and (ii) comprise reacting a mixture of sulfuric acid, at least one lactam and at least one alcohol, which steps are carried out in a closed vessel under a pressure of 1.0 to 10.0 bar.

7. 7. The process according to any one of claims 1 to 6, wherein the lactam used in step (i) is an ε-lactam.