PROCESS FOR THE PREPARATION OF UNSATURATED CARBOXYLATE ESTERS

Abstract: Process for the preparation of carboxylate esters of alpha-ethylenically unsaturated alcohols by reacting an ethylenically unsaturated compound with carbon monoxide and an enolizable ketone in the presence of a catalytic system formed by combining a palladium catalyst, a triarylphosphine and a protonic acid having a pK a below 1.5, except hydrohalogenic acids and carboxylic acids.

Description: The invention relates to a process for the preparation of carboxylate esters of alpha-ethylenically unsaturated alcohols. Carboxylate esters of alpha-ethylenically unsaturated alcohols can be polymerized to yield polyvinyl-type polymers. It has now surprisingly been found that such carboxylate esters can be prepared with high selectivity and acceptable yield using relatively simple starting compounds. The invention, therefore, provides a process for the preparation of carboxylate esters of alpha-ethylenically unsaturated alcohols, which process comprises causing an ethylenically unsaturated compound to react with carbon monoxide and an enolizable ketone in the presence of a catalytic system formed by combining:- (a) a palladium catalyst, (b) a phosphine having the general formula (I) in which R¹, R² and R³ each individually represent an optionally substituted aryl group, and (c) a protonic acid having a pK a below 1.5 as a promoter (measured at 18 °C in aqueous solution), except hydrohalogenic acids and carboxylic acids. The reaction may schematically be represented by means of the following equation: in which the hydroxy compound represents the enolized form of a ketone having the structure: The two carbon atoms marked with an asterisk are the same carbon atoms. The ethylenically unsaturated compound may be an optionally substituted alkene or an optionally substituted cycloalkene, preferably having in the range of from 2 to 30, in particular 2 to 20 and, more particularly, 2 to 10 carbon atoms per molecule, and preferably 1 to 3 carbon-carbon double bonds per molecule. Very good results have been obtained with ethylene. The alkene or cycloalkene may be substituted, for instance with one or more halogen atoms, or cyano, ester, alkoxy or aryl groups. Examples of suitable ethylenically unsaturated compounds are propene, 1-butene, 2-butene, isobutene, the isomeric pentenes, hexenes, heptenes, octenes and dodecenes, 1,5-cyclooctadiene, cyclododecene, 1,5,9-cyclododecatriene, methyl acrylate, ethyl acrylate, methyl methacrylate, acrylonitrile, acrylamide, N,N-dimethylacrylamide, vinyl chloride, allyl chloride, methyl allyl ether and styrene. The enolizable ketone should have a hydrogen atom bound to a carbon atom adjacent to the carbonyl group. A wide variety of enolizable ketones may be used. The enolizable ketone may have optionally substituted alkyl, optionally substituted cycloalkyl or optionally substituted aryl groups bound to the carbonyl group. Preference is given to alkanones, two optionally substituted alkyl groups being bound to the carbonyl group; the optionally substituted alkanones suitably have in the range of from 3 to 30 carbon atoms per molecule. Particularly preferred are methyl alkyl ketones having in the range of from 3 to 30 carbon atoms per molecule; among the latter ketones those having 3 or 4 carbon atoms per molecule are preferred. Enolizable alkyl phenyl ketones are also very suitable, particularly those in which the alkyl group has in the range of from 1 to 10 carbon atoms. Very good results have been obtained with acetophenone. Other examples of suitable enolizable ketones are methyl butyl ketone, methyl isobutyl ketone, diheptyl ketone, dioctyl ketone, 3-butylheptyl ethyl ketone, methyl cyclohexyl ketone and ethyl phenyl ketone. Enolizable ketones which are symmetric with respect to the carbonyl group yield one carboxylate ester. Enolizable ketones which are not symmetric with respect to the carbonyl group and in which ketones the two carbon atoms bound to the carbonyl group each carry a hydrogen atom yield two different carboxylate esters of the same carboxylic acid, two different enolized forms being possible. Both homogeneous and heterogeneous palladium catalysts may be used in the process according to the invention. Homogeneous catalysts are preferred. The palladium catalyst preferably contains a compound of divalent palladium. Suitable homogeneous catalysts are the salts of palladium with, for example, nitric acid, sulphuric acid or, particularly, alkanoic acids; among the alkanoic acids those having not more than 12 carbon atoms per molecule are preferred. Very good results have been obtained with palladium acetate. Moreover, palladium complexes may be used, for instance palladium acetylacetonate, tetrakistriphenylphosphinepalladium, bis-tri-o-tolylphosphinepalladium acetate or bis-triphenylphos­ phinepalladium sulphate. Palladium on charcoal and palladium bonded to an ion exchanger - for instance an ion exchanger comprising sulphonic acid groups - are examples of suitable heterogeneous catalysts. It was found that when at least 5 mol of the phosphine having the general formula (I) are used per gram atom of palladium, a considerable increase in the reaction rate is obtained. Preferably at least 20 mol of the phosphine having the general formula (I) are used per gram atom of palladium. In general, more than 500 mol phosphine per gram atom of palladium need not be used. Usually, in the range of from 10 to 150 mol phosphine per gram atom of palladium are used. If the palladium catalyst already contains phosphine, this should be taken into account when calculating the amount of phosphine to be used. The protonic acid having a pK a below 1.5 preferably has a non-coordinating anion, by which is meant that little or no covalent interaction takes place between the palladium and the anion (cf. British patent application No. 2,058,074). Typical examples of such anions are PF₆ - , SbF₆ - , BF₄ - and ClO₄ - . Preferred acids are sulphonic acids and acids that can be formed, possibly in situ, by interacting a Lewis acid such as, for example BF₃, AsF₅, SbF₅, PF₅, TaF₅ or NbF₅ with a Broensted acid such as, for example, a hydrogen halide, in particular HF, or fluorosulphonic acid, orthophosphoric acid or sulphuric acid. Specific examples of acids of the latter type are fluorosilicic acid, HBF₄, HPF₆ and HSbF₆. Examples of usable sulphonic acids are fluorosulphonic acid and chlorosulphonic acid and the hereinafter specified sulphonic acids. A preferred group of non-carboxylic protonic acids having a pK a below 1.5 are those having the general formula (II): wherein Z represents sulphur or chlorine and, if Z is chlorine, R⁴ represents oxygen and, if Z is sulphur, R⁴ represents an OH group or an optionally substituted hydrocarbon group. When the hereinbefore-stated acids of the general formula (II) are used in the process according to the invention, the anions thereof can be considered to be non-coordinating. The optionally substituted hydrocarbon group represented by R⁴ is preferably an alkyl, aryl, aralkyl or alkaryl group having 1 to 30, in particular 1 to 14, carbon atoms. The hydrocarbon group may be substituted for example with halogen atoms, in particular fluorine atoms. Examples of suitable acids of the general formula (II) are perchloric acid, sulphuric acid, 2-hydroxypropane-2-sulphonic acid, benzenesulphonic acid, 1-naphthalenesulphonic acid, 2-naphthalenesulphonic acid, p-toluenesulphonic acid and trifluoromethanesulphonic acid, p-toluenesulphonic acid being the most preferred. The optionally substituted aryl groups R¹, R² and R³ in the general formula (I) preferably contain not more than 18, and in particular in the range of from 6 to 14 carbon atoms. Examples of suitable aryl groups are naphthyl groups and, in particular, phenyl groups. Suitable substituents on the aryl groups are halogen atoms and alkyl, aryl, alkoxy, trihalomethyl, cyano, dialkylamino and alkanoyloxy groups. Examples of suitable phosphines are tri(p-tolyl)phosphine, tri(p-methoxyphenyl)phosphine and, in particular, triphenylphosphine. The number of equivalents of the phosphine having the general formula (I) which is used per equivalent of non-carboxylic protonic acid having a pK a below 1.5 is not critical and may vary within wide limits. This number is suitably in the range of from 0.5 to 50. The quantity of palladium catalyst is not critical and may vary within wide limits. Preference is given to the use of quantities in the range between 10⁻⁵ and 10⁻¹ gram atom palladium per mol of ethylenically unsaturated compound. A separate solvent is not essential in the process according to the invention, and often a large excess of one of the reactants, usually the enolizable ketone, may form a convenient liquid phase. However, it may in some cases be desirable to use a separate solvent and any inert solvent may be used. A suitable solvent may for example, be selected from aromatic hydrocarbons, for example benzene, toluene, ethylbenzene and the three xylenes; sulphoxides, for example dimethyl sulphoxide and diethyl sulphoxide; sulphones, for example diisopropyl sulphone and tetrahydrothiophene 1,1-dioxide( also referred to as "sulfolane") and ethers, for example anisole, 2,5,8-trioxanonane (also referred to as "diglyme"), diphenyl ether and diisopropyl ether. In the process according to the invention the carbon monoxide may be used pure or diluted with an inert gas, such as nitrogen, noble gases or carbon dioxide. Generally, the presence of more than 10% by volume of hydrogen is undesirable, since under the reaction conditions it may cause hydrogenation of carbon-carbon double bonds. Preference is given to the use of pure carbon monoxide or a carbon monoxide-containing gas which contains less than 5% by volume of hydrogen. The process according to the invention permits the use of very mild reaction conditions. Temperatures in the range of from 50 °C to 200 °C, especially 100 °C to 150 °C, are generally suitable. The pressure may vary over a wide range. Generally, a pressure in the range of from 1 to 100 bar is suitable, with pressures of from 5 to 50 bar being preferred. Pressures higher than 100 bar may be used, but are usually economically unattractive. The molar ratio of the ethylenically unsaturated compound to the enolizable ketone is not critical and may vary within wide limits. The molar ratio carbon-carbon double bonds to enolizable ketone may lie, for instance, between 0.1:1 and 10:1. The process according to the invention may be carried out batchwise, continuously or semi-continuously. The following examples further illustrate the invention. The selectivity to a certain compound, expressed in a percentage, is defined as 100 a/b, in which "a" is the amount of ketone that has been converted into that certain compound and "b" is the total amount of ketone that has been converted. Example 1 A 250-ml magnetically stirred Hastelloy C autoclave ("Hastelloy" is a trade name) was charged with o-xylene (50 ml), methyl ethyl ketone (20 ml), palladium acetate (0.2 mmol), tri­ phenylphosphine (10 mmol) and p-toluenesulphonic acid (2 mmol). The autoclave was flushed with carbon monoxide, filled with carbon monoxide and ethylene until partial pressures thereof of 20 bar each were obtained and heated to a temperature of 110 °C. After a reaction time of 5 h at this temperature the contents of the autoclave were analysed by means of gas-liquid chromatography. The conversion of methyl ethyl ketone was 30 %, with a total selectivity to 1-ethylvinyl propionate and 1-methylallyl propionate of 95 %; the former and the latter propionate were obtained in a molar ratio of 2.3. Example 2 The experiment of Example 1 was repeated with the difference that 20 ml of methyl ethyl ketone were replaced with 20 ml of acetone. The conversion of acetone was 26%, with a selectivity to isopropyl propionate of 95%. Example 3 The experiment of Example 1 was repeated with the difference that 20 ml of methyl ethyl ketone were replaced with 20 ml of acetophenone. The conversion of acetophenone was 15 %, with a selectivity to 1-phenylvinyl propionate of 95%. Example 4 An experiment was carried out in the manner of Example 1, using o-xylene(50 ml), acetophenone (20 ml), palladium acetate (0.2 mmol), triphenylphosphine (20 mmol) and p-toluenesulphonic acid (5 mmol). After a reaction time of 2.5 h at 100 °C the conversion of acetophenone was 15%, with a selectivity to 1-phenylvinyl propionate of 95%. Example 5 The experiment of Example 4 was repeated with the difference that 10 mmol instead of 5 mmol of p-toluenesulphonic acid were used and that the reaction was carried out for 3.5 h at 115 °C. The conversion of acetophenone was 23%, with a selectivity to 1-phenylvinyl propionate of 95%. Example 6 An experiment was carried out in the manner of Example 1, using o-xylene (50 ml), acetophenone (20 ml), palladium acetate (0.2 mmol), triphenylphosphine (30 mmol) and p-toluenesulphonic acid (10 mmol). The partial pressures of ethylene and carbon monoxide were 30 bar each. After a reaction time of 5 h at 125 °C the conversion of acetophenone was 30%, with a selectivity to 1-phenylvinyl propionate of 95%. Example 7 An experiment was carried out in the manner of Example 1, using o-xylene (50 ml), acetophenone (20 ml), palladium acetate (0.1 mmol), triphenylphosphine (50 mmol) and p-toluenesulphonic acid (15 mmol). The partial pressures of ethylene and carbon monoxide were 30 bar each. After a reaction time of 5 h at 125 °C the conversion of acetophenone was 33%, with a selectivity to 1-phenylvinyl propionate of 95%. Example 8 An experiment was carried out in the manner of Example 1, using o-xylene (50 ml), acetophenone (20 ml), palladium acetate (0.1 mmol), triphenylphosphine (30 mmol), p-toluenesulphonic acid (10 mmol) and propionic acid (2 ml). The partial pressures of ethylene and carbon monoxide were 30 bar each. After a reaction time of 5 h at 125 °C the conversion of acetophenone was 25%, with a selectivity to 1-phenylvinyl propionate of 95%. Propionic acid was converted into propionic anhydride with a yield of 90%. Example 9 An experiment was carried out in the manner of Example 1, using o-xylene (50 ml), acetophenone (20 ml), palladium acetate (0.1 mmol), triphenylphosphine (50 mmol) and methanesulphonic acid (15 mmol). The partial pressures of ethylene and carbon monoxide were 30 bar each. After a reaction time of 5 h at 125 °C the conversion of acetophenone was 22%, with a selectivity to 1-phenyl­ vinyl propionate of 95%. Example 10 The experiment of Example 9 was repeated with the difference that 15 mmol of methanesulphonic acid were replaced with 15 mmol of mesitylenesulphonic acid. The conversion of acetophenone was 14%, with a selectivity to 1-phenylvinyl propionate of 95%. Example 11 An experiment was carried out in the manner of Example 1, using diglyme (50 ml), acetophenone (20 ml), palladium acetate (0.1 mmol), triphenylphosphine (50 mmol) and p-toluenesulphonic acid (15 mmol). The partial pressures of ethylene and carbon monoxide were 30 bar each. After a reaction time of 5 h at 125 °C the conversion of acetophenone was 30%, with a selectivity to 1-phenylvinyl propionate of more than 95%. Example 12 An experiment was carried out in the manner of Example 1, using diglyme (50 ml), acetophenone (20 ml), palladium acetate (0.1 mmol), tri(m-chlorophenyl)phosphine (20 mmol) and p-toluene­ sulphonic acid (5 mmol). The partial pressures of ethylene and carbon monoxide were 30 bar each. After a reaction time of 3 h at 125 °C the conversion of acetophenone was 8%, with a selectivity to 1-phenylvinyl propionate of more than 95%. Example 13 The experiment of Example 11 was repeated with the difference that the partial pressures of ethylene and carbon monoxide were 20 and 40 bar, respectively. The conversion of acetophenone was 25%, with a selectivity to 1-phenylvinyl propionate of 95%. Example 14 The experiment of Example 11 was repeated with the difference that the partial pressures of ethylene and carbon monoxide were 40 and 20 bar, respectively. The conversion of acetophenone was 25%, with a selectivity to 1-phenylvinyl propionate of 95%. Example 15 The experiment of Example 11 was repeated with the difference that 50 ml instead of 20 ml of acetophenone were used and that no diglyme was present. The conversion of acetophenone was 18%, with a selectivity to 1-phenylvinyl propionate of 95%. Comparative Experiment A The experiment described in Example 1 was repeated with the difference that p-toluenesulphonic acid (2 mmol) was replaced with benzenephosphonic acid (pK a = 1.5, 2 mmol). The conversion of the ketone was below 5% and propionate could not be detected in the reaction mixture. Comparative Experiment B The experiment described in Example 1 was repeated with the difference that p-toluenesulphonic acid (2 mmol) was replaced with 2,6-dichlorobenzoic acid (pK a = 1.5, 2 mmol). The conversion of ketone was below 5% and propionate could not be detected in the reaction mixture.

Claims: 1. A process for the preparation of carboxylate esters of alpha-­ ethylenically unsaturated alcohols, which process comprises causing an ethylenically unsaturated compound to react with carbon monoxide and an enolizable ketone in the presence of a catalytic system formed by combining:- (a) a palladium catalyst, (b) a phosphine having the general formula (I) in which R¹, R² and R³ each individually represent an optionally substituted aryl group, and (c) a protonic acid having a pKa below 1.5 as a promoter (measured at 18 °C in aqueous solution), except hydrohalogenic acids and carboxylic acids. 2. A process as claimed in claim 1, in which the ethylenically unsaturated compound is an optionally substituted alkene having in the range of from 2 to 30 carbon atoms per molecule. 3. A process as claimed in claim 2, in which the optionally substituted alkene has in the range of from 2 to 10 carbon atoms per molecule. 4. A process as claimed in claim 3, in which the alkene is ethylene. 5. A process as claimed in any one of the preceding claims, in which an optionally substituted alkanone having in the range of from 3 to 30 carbon atoms per molecule is used as enolizable ketone. 6. A process as claimed in claim 5, in which the alkanone is a methyl alkyl ketone. 7. A process as claimed in claim 6, in which the alkanone has 3 or 4 carbon atoms per molecule. 8. A process as claimed in any one of claims 1 to 4, in which an enolizable alkyl phenyl ketone is used. 9. A process as claimed in claim 8, in which the enolizable ketone is acetophenone. 10. A process as claimed in any one of the preceding claims, in which the palladium catalyst contains a compound of divalent palladium. 11. A process as claimed in claim 10, in which the compound of divalent palladium is a palladium alkanoate. 12. A process as claimed in claim 11, in which the palladium alkanoate is palladium acetate. 13. A process as claimed in any one of the preceding claims, in which at least 5 mol of the phosphine having the general formula (I) are used per gram atom of palladium. 14. A process as claimed in any one of the preceding claims, in which an acid with a non-coordinating anion is used as promoter. 15. A process as claimed in any one of the preceding claims, in which a sulphonic acid or an acid that can be formed by interaction of a Lewis acid with a Broensted acid is used as promoter. 16. A process as claimed in any one of claims 1 to 14, in which an acid having the general formula (II) in which Z represents a sulphur or a chlorine atom, and, if Z represents a chlorine atom, R⁴ represents an oxygen atom, and, if Z represents a sulphur atom, R⁴ represents an OH group or an optionally substituted hydrocarbyl group, is used as a promoter. 17. A process as claimed in claim 16, in which the hydrocarbyl group represented by R⁴ is an alkyl, aryl, aralkyl or alkaryl group having not more than 30 carbon atoms. 18. A process as claimed in claim 17, in which the acid is p-toluenesulphonic acid. 19. A process as claimed in any one of the preceding claims, in which the aryl groups represented by the groups R¹, R² and R³ in formula (I) have in the range of from 6 to 14 carbon atoms. 20. A process as claimed in any one of the preceding claims, in which the aryl groups represented by the groups R¹, R² and R³ are phenyl groups. 21. A process as claimed in any one of the preceding claims, which is carried out at a temperature in the range of from 50 °C to 200 °C.

Inventors: DRENT, EIT
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1986
Main classification: C07C67
IPC codes: B01J31, C07C67, C07B61, C07C69