CHROMIUM HALOCARBOXYLATE CATALYSTS FOR ESTER SYNTHESIS

Abstract: This invention relates to a method of producing esters of alpha, beta-unsaturated carboxylic acids using a chromium halo-carboxylate as the esterification catalyst. The process is particularly suited to producing hydroxy alkyl(meth)acrylates and the catalyst is preferably a trihalocarboxylate of chromium. The process reduces the formation of unwanted diesters and improves the yield of the desired monoesters.

Description: CHROMIUM HALOCARBOXYLATE CATALYSTS FOR ESTER SYNTHESIS The present invention relates to a method of producing esters of alpha, betaunsaturated carboxylic acids using a chromium halo-carboxylate as an esterification catalyst. Esters of alpha, betaunsaturated carboxylic acids are generally produced by reacting the unsaturated acid with an olefin oxide in the presence of a catalyst. The catalyst used is generally a compound of cadmium, manganese, nickel, iron or chromium, compounds of chromium being preferred. For instance, GB 1195485 (BP Chemicals) claims and describes a method of producing such esters using a chromium carboxylate as catalyst. Specifically, the use of chromium-acrylate and -methacrylate as catalysts is disclosed. It has now been found that the catalyst performance and efficiency of the esterification reaction can be improed by using a halocarboxylate of chromium as the catalyst. Accordingly, the present invention is a method of producing esters by reacting an alpha, beta-unsaturated carboxylic acid with an epoxide in the presence of a chromium carboxylate as catalyst characterised in that the catalyst is a halocarboxylate of chromium. The invention is particularly applicable to alpha, beta-unsaturated carboxylic acids, which contain from 3 to 24 carbon atoms. For example, unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid and linseed fatty acids may be used as starting material. Alternatively, unsaturated polycarboxylic acids such as fumaric acid, maleic acid, itaconic acid and citraconic acid, or the half esters of these polycarboxylic acids may be used. The epoxide may be an alkylene oxide derived from a straight chain, branched chain or cyclic olefin, such as, for example, ethylene, propylene, n-butylene, isobutylene, heptylene, cyclohexene or styrene. Epichlorohydrin or glycidyl ethers of monohydric alcohols may also be used. It is preferred to use a slight molar excess of the epoxide in the reaction mixture. For example, the mole ratio of the epoxide to the alpha, betaunsaturated carboxylic acid is suitably greater than 1:1. It is preferable to use 1.05 to 1.2 moles of the epoxide per mole of the unsaturated acid. The halocarboxylates of chromium used as catalyst may be derived from acids which may be saturated monocarboxylic or dicarboxylic acids. The carboxylic acids may be aliphatic, alicyclic or aromatic carboxylic acids. The halocarboxylates suitably contain from 1-10 carbon atoms, preferably from 1 to 4 carbon atoms. Haloacetates are most preferred. The halogen atom in the halocarboxylate may be fluorine, chlorine, bromine or iodine, but is preferably chlorine. The halocarboxylate may contain one, two or three halogen atoms which may be the same or different. Trihalocarboxylates, especially trichlorocarboxylates, are preferred. The chromium compound used in deriving the halocarboxylate may be a trivalent or a hexavalent chromium compound. The amount of chromium halocarboxylate used is suitably less than 1 mole per cent based on the unsaturated carboxylic acid reactant, preferably less than 0.1 mole X, more preferably from 0.02 to 0.1 mole Z. When necessary, a polymerisation inhibitor may be employed in the reaction which is any of the polymerisation inhibitors well known in the art. Examples of such inhibitors are hydroquinone, para-methyoxyphenol, nitric oxide and methylene blue. The concentration of inhibitor may be up to 1% by weight. When using nitric oxide as inhibitor, the reaction may be carried out in an atmosphere of nitric oxide. The reaction of the present invention may take place at an eleated temperature, for example 40 to 1200C, preferably from 70-90"C. Temperatures above 1200C may result in excessive polymer formation. Temperatures below 40"C may be employed but at such temperatures the reaction time may be undesirably long. The reaction may be carried out at a pressure above atmospheric, eg about 40 psig. The process may be operated batchwise or continuously, and in the homogeneous or th < eterogeneous phase. The course of the reaction may be followed by measuring the acidity of the reaction mixture from time to time and hence determining the content of the unreacted unsaturated acid. A preferred process when using acrylic or methacrylic acid and an epoxide is as follows: an autoclave is charged with the unsaturated acid (containing an inhibitor and catalyst). The autoclave is evacuated and the vacuum broken with nitrogen; the mixture is then heated to a temperature in the range 40 to 1200C. The epoxide is then slowly pumped into the vessel, to give a steady reaction pressure of say 20 to 60 psig. The reaction thus commenced is continued at a temperature within the range 40 to 1200C until the acid number of the mixture, determined by titration of selected portions of the mixture, is at the desired value. Immediately the desired acid number is reached the reaction mixture is crash cooled by indirect heat exchange, for example by contact with water cooled coils. Vacuum is then applied to the autoclave to remove excess epoxide. The 2-hydroxyalkyl acrylate or methacrylate may be removed from the catalyst by distillation. The process of the present invention is further illustrated by the following Examples. EXAMPLES In the Examples below the following abbreviations have been used. HEA - Hydroxyethyl acrylate HPA - Hydroxypropylacrylate DPGMA - Dipropylene glycol monoacrylate HPMA - Hydroxypropyl methacrylate DPGMMA - Dipropylene glycol monomethacrylate HEMA - Hydroxyethylmethacrylate DEGMMA - Diethylene glycol monomethacrylate 1. HPA Production using Chromium Halocarboxylates Acrylic acid (8 moles) inhibited with p-methoxy phenol (700 ppm) and 0.08 mole X of the appropriate chromium carboxylate or halocarboxylate were heated to 80"C. Propylene oxide (8.8 moles) was added over 150 mins., with appropriate cooling to maintain the reaction temperature at 80"C. After completion of oxide addition, the reaction temperature was maintained at 800C until the concentration of acrylic acid became less than 0.1X wt/wt. The product compositions determined by GC analysis for various chromium (halo)carboxylate catalysts are given in Table 1. Table 1 EMI4.1 <tb> Examples <SEP> Composition <SEP> of <SEP> Product <tb> Test <SEP> No. <SEP> Catalyst <tb> <SEP> HPA <SEP> DPGMA <tb> <SEP> C <SEP> Chromium <SEP> III <SEP> Acrylate <SEP> 88.0 <SEP> 8.2 <tb> <SEP> 1 <SEP> Chromium <SEP> III <SEP> Trifluoroacetate <SEP> 90.3 <SEP> 6.4 <tb> <SEP> 2 <SEP> 1 <SEP> Chromium <SEP> III <SEP> Trichloroacetate <SEP> 93.3 <SEP> 3.4 <tb> <SEP> 3 <SEP> ! <SEP> Chromium <SEP> III <SEP> Tribromoacetate <SEP> 90.2 <SEP> 6.4 <tb> C - Comparative Test 2. HPMA Production using Chromium Halocarboxylates Methacrylic acid (8 moles) inhibited with p-methoxy phenol (700 ppm) and 0.08 mole Z of the appropriate chromium carboxylate or chromium halo-carboxylate were heated to 800C. Propylene oxide (8.8 moles) was added over 150 mins, with appropriate cooling to maintain the reaction temperature at 800C. After the completion of oxide addition the reaction temperature was maintained at 800C until the concentration of methacrylic acid was less than 0.1X wt/wt. The product composition, as determined by GC analysis, is given in Table 2. Table 2 EMI4.2 <tb> <SEP> Composition <SEP> of <SEP> Product <tb> Example <SEP> Catalyst <tb> <SEP> No <SEP> HPMA <SEP> DPGMMA <tb> <SEP> 4 <SEP> Chromium <SEP> III <SEP> Trichloroacetate <SEP> 97.5 <SEP> 2.2 <tb> <SEP> C <SEP> " <SEP> <SEP> " <SEP> <SEP> Methacrylate <SEP> 94.0 <SEP> 2.5 <tb> C - Comparative Test 3. HEMA Production using Chromium Ralocarboxylates Methacrylic acid (8 moles) inhibited with p-methoxy phenol (700 ppm) and 0.08 mole x of the appropriate chromium carboxylate or chromium halocarboxylate were charged to an autoclave and heated to 8000. Ethylene oxide (8.8 moles) was injected over 150 mins. with appropriate cooling to maintain the reaction temperature at 80"C. After the completion of oxide addition, the reaction temperature was maintained at 80"C until the concentration of methacrylic acid was less than 0.1% wt/wt. The product composition, as determined by GC analysis, is given in Table 3. Table 3 EMI5.1 <tb> <SEP> Composition <SEP> of <SEP> Product <tb> Example <SEP> Catalyst <tb> <SEP> No <SEP> HEMA <SEP> DEGMMA <tb> <SEP> 5 <SEP> Chromium <SEP> III <SEP> Trichloroacetate <SEP> 96.2 <SEP> 3.1 <tb> <SEP> C <SEP> - <SEP> <SEP> - <SEP> <SEP> Methacrylate <SEP> 94.6 <SEP> 4.7 <tb> C - Comparative Test The above results show that there is a reduction in the amount of dialkylene glycol mono(meth)acrylate formed during production of HPA, HPMA and HEMA compared with normal, unsubstituted chromium carboxylates such as chromium acetate. 4. HEA Production using Chromium Halocarboxylates Acrylic acid (8 moles) inhibited with p-methoxy phenol (1200 ppm) and 0.08 mole X of the appropriate chromium carboxylate or halocarboxylate were heated to 80"C. Ethylene oxide (8.8 moles) was added over 150 mins with appropriate cooling to maintain the reaction temperature at 800C. After completion of oxide addition, the reaction temperature was maintained at 800C until the concentration of acrylic acid became less than 0.1% wt/wt. The product composition as determined by GC analysis is given in Stable 4. Table 4 EMI5.2 <tb> Catalyst <SEP> Composition <SEP> of <SEP> Product <tb> <SEP> UKA <SEP> DECKA <SEP> <tb> Cr <SEP> III <SEP> acrylate <SEP> 86.0 <SEP> 10.0 <tb> Cr <SEP> III <SEP> trichioroacetate <SEP> 90.0 <SEP> 7.5 <tb> C - Comparative Test

Claims: Claims: 1. A method of producing esters by reacting an alpha, beta-unsaturated carboxylic acid with an epoxide in the presence of a chromium carboxylate as catalyst characterised in that the catalyst is a halocarboxylate of chromium. 2. A method according to claim 1 wherein alpha, beta-unsaturated carboxylic acids contains from 3 to 24 carbon atoms. 3. A method according to any one of the preceding claims wherein the alpha, beta-unsaturated carboxylic acid is a monocarboxylic acid selected from acrylic acid, methacrylic acid, crotonic acid and linseed fatty acids, or a polycarboxylic acid selected from fumaric acid, maleic acid, itaconic acid and citraconic acid, or the half esters of these polycarboxylic acids. 4. A method according to any one of the preceding claims wherein the epoxide is epichlorohydrin, a glycidyl ether of a monohydric alcohol or an alkylene oxide derived from a straight chain, branched chain or cyclic olefin. 5. A method according to any one of the preceding claims wherein the mole ratio of the epoxide to the alpha, beta-unsaturated carboxylic acid in the reaction mixture is greater than 1:1. 6. A method according to any one of the preceding claims wherein the halocarboxylates of chromium used as catalyst are derived from halogenated acids selected from a saturated monocarboxylic acid, a saturated dicarboxylic acid and an aromatic carboxylic acid. 7. A method according to claim 6 wherein a halogenated acid is derived from containing from 1-10 carbon atoms. 8. A method- according to any one of the preceding claims wherein the chromium halocarboxylate used is a trihalocarboxylate. 9. A method according to any one of the preceding claims wherein the amount of chromium halocarboxylate used is less than 1 mole per cent based on the unsaturated carboxylic acid reactant. 10. A method according to any one of the preceding claims wherein the reaction is carried out at a temperature from 40 to 1200C.

Inventors: BIGGIN, IAN STUART, DAWES, STEPHEN JOHN
Applicants: BP CHEMICALS LIMITED
Application year: 1984
Main classification: C07C69
IPC codes: C07C69, C07B61, B01J31, C07C67