GB2240545A - Preparation of eaters of alpha-ethylenically unsaturated alcohols - Google Patents

Abstract

A process for the preparation of an ester of an alpha-ethylenically unsaturated alcohol, comprises reacting an olefinically unsaturated compound or an acetylenically unsaturated compound with carbon monoxide and an enolizable ketone in the presence of a catalyst system comprising:- (a) a source of a Group VIII metal. (b) a phosphine having an aromatic substituent which contains an imino nitrogen atom, and (c) a protonic acid. an

Description

PREPARATION OF ESTERS OF ALPHA-ETHYLENICALLY UNSATURATED ALCOHOLS The present invention relates to a process for the preparation of esters of alpha-ethylenically unsaturated alcohols.

Esters of alpha-ethylenically unsaturated alcohols are of interest as starting materials for the preparation of polymers.

Processes for their preparation are disclosed in European patent applications publication Nos. EP-A1-0218282 and EP-A1-0218283.

European patent application publication No. EP-Al-0218282 discloses 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 ec in aqueous solution), except hydrohalogenic acids and carboxylic acids.

European patent application publication No. EP-A1-0218283 discloses a process for the preparation of esters of alpha-ethylenically unsaturated alcohols and alpha-ethylenically unsaturated carboxylic acids, which process comprises causing an acetylenically 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 (II)

in which R1, R2 and R3 each individually represent a phenyl group carrying an electron-withdrawing substituent, and (c) a non-carboxylic protonic acid having a pK not greater than 1.5 (measured at 18 "C in aqueous solution).

European patent application publication No. EP-A1-0271144 discloses a process for the carbonylation of an acetylenically unsaturated compound with a hydroxyl-containing compound in which a catalyst system comprising a palladium compound, a heterocyclic nitrogen-containing phosphine such as a pyridylphosphine, and a protonic acid is used. At page 6, line 27 to page 7, line 3, a description of solvents said to be inert and suitable for use in the process is given. According to the description, the solvent may be a ketone such as acetone or methyl isobutyl ketone.

European patent application publication No. EP-A1-0282142 discloses a process for the carbonylation of an olefinically unsaturated compound with water, an alcohol or a carboxylic acid, in which a catalyst system comprising a palladium compound, a heterocyclic nitrogen-containing phosphine such as a pyridylphosphine and a protonic acid is used. The paragraph bridging columns 5 and 6 provides a description of solvents said to be inert and suitable for use in the process. This description includes ketones such as acetone or methyl isobutyl ketone.

Surprisingly, it has now been found that esters of alpha-ethylenically unsaturated alcohols may be prepared at a remarkably high rate by reacting an olefinically unsaturated compound with carbon monoxide and an enolizable ketone in the presence of a carbonylation catalyst comprising a pyridylphosphine.

Accordingly, the present invention provides a process for the preparation of an ester of an alpha-ethylenically unsaturated alcohol, which comprises reacting an olefinically unsaturated compound or an acetylenically unsaturated compound with carbon monoxide and an enolizable ketone in the presence of a catalyst system comprising: (a) a source of a Group VIII metal, (b) a phosphine having an aromatic substituent which contains an imino nitrogen atom, and (c) a protonic acid.

The process according to the invention has been found to afford esters of alpha-ethylenically unsaturated alcohols at a higher rate than those employing a triphenylphosphine, as disclosed in EP-A1-0218282.

It is surprising that phosphines having an aromatic substituent which contains an imino nitrogen atom are active as catalyst components in the preparation of alpha-ethylenically unsaturated compounds. This is because phosphines possessing an aromatic substituent containing an imino nitrogen atom have different chemical properties from phosphines possessing only simple aromatic substituents such as phenyl. It is especially surprising that phosphines containing an imino nitrogen atom have been found to be more active than simple triarylphosphines such as triphenylphosphine.

The olefinically unsaturated compound is preferably 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. The alkene or cycloalkene may be substituted, for instance with one or more halogen atoms, or cyano, ester, alkoxy or aryl groups. Examples of olefinically unsaturated compounds are ethene, propene, l-butene, 2-butene, isobutene, the isomeric pentenes, hexenes, heptenes, octenes and dodecenes, 1,5-cyclo- octadiene, 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 acetylenically unsaturated compound is preferably an optionally substituted alkyne having in the range of from 2 to 30 carbon atoms and in particular 2 to 10 carbon atoms per molecule, and preferably 1 to 3 carbon-carbon triple bonds per molecule. The acetylenically unsaturated compound may be substituted, for instance with one or more halogen atoms, or cyano, ester, alkoxy or aryl groups. Examples of suitable acetylenically unsaturated compounds are ethyne, l-butyne, 2-butyne, l-pentyne, l-hexyne, l-heptyne, l-octyne, l-nonyne, l-decyne, benzylethyne and cyclohexylethyne.

Preferably an olefinically unsaturated compound is used.

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 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 to 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. Examples of enolizable ketones are acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diheptyl ketone, dioctyl ketone, 3-butylheptyl ethyl ketone, methyl cyclohexyl ketone, acetophenone 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.

The catalyst system used in the process according to the invention comprises a source of a Group VIII metal. The source of a Group VIII metal may be the metallic element or, preferably, a Group VIII metal compound.

Examples of Group VIII metals are iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium and platinum.

The catalyst system employed in the process according to the invention preferably comprises a palladium compound.

Examples of compounds of Group VIII metals include salts, for example salts of nitric acid; sulphuric acid; sulphonic acids phosphonic acids, perhalic acids, carboxylic acids such as alkane carboxylic acids having not more than 12 carbon atoms, e.g. acetic acid; and hydrohalic acids. Since halide ions can be corrosive, salts of hydrohalic acids are not preferred. Other examples of compounds of Group VIII metals include complexes, such as complexes with acetylacetonate, phosphines and/or carbon monoxide.For example the compound of a Group VIII metal may be palladium acetylacetonate, tetrakis - triphenylphosphinepalladium, bis-tri-o-tolylphosphinepalladium acetate, bis-diphenyl-2-pyridylphosphinepalladium acetate, tetrakis-diphenyl-2-pyridylphosphinepalladium, bis-di-o-tolylpyridylphosphinepalladium acetate, or bis-diphenylpyridylphosphinepalladium sulphate.

The catalyst system used in the process according to the invention further comprises a phosphine having an aromatic substituent which contains an imino nitrogen atom.

As used herein, the term "imino nitrogen atom" means a nitrogen atom which may be represented in the structural formula of the aromatic substituent containing it by the formula

For example, if the aromatic substituent is a pyridyl group, the structural formula of the aromatic substituent is

The phosphine preferably comprises one or two phosphorus atoms. Each phosphorus atom has three substituents. At least one of these substituents is an aromatic substituent which contains an imino nitrogen atom. The remaining substituents are preferably selected from optionally substituted aliphatic and aromatic hydrocarbyl groups.When the phosphine comprises more than one phosphorus atom, it is possible for one substituent to be shared by more than one phosphorus atom, as for example in

The aromatic substituent which contains an imino nitrogen is preferably a 6-membered ring containing one, two or three nitrogen atoms. The aromatic substituent may itself be optionally substituted.

When a substituent is said to be optionally substituted in this specification, unless otherwise stated, the substituent may be unsubstituted or substituted by one or more substituents. Examples of suitable substituents include halogen atoms; alkyl groups; alkoxy groups; haloalkyl groups; haloalkoxy groups; acyl groups; acyloxy groups; tertiary amino groups, hydroxyl groups; nitrile groups; acylamino groups; and aromatic hydrocarbyl groups.

An aliphatic hydrocarbyl group is preferably an alkyl group or a cycloalkyl group.

An alkyl group, as such or in an alkoxy group, is preferably a C1-10 alkyl group, more preferably a C16 alkyl group. Examples of alkyl groups are methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl and tert-butyl.

A cycloalkyl group is preferably a C36 cycloalkyl group, for example cyclopentyl or cyclohexyl.

An aromatic hydrocarbyl group is preferably a phenyl group.

A halogen atom, as such or in a haloalkyl group, is preferably a fluorine, chlorine or bromine atom.

An acyl group in an acyl, acyloxy or acylamino group is preferably a 02.5 alkanoyl group such as acetyl.

A tertiary amino group is preferably a dialkylamino group.

Examples of aromatic substituents containing an imino nitrogen atom are pyridyl, pyrazinyl, quinolyl, isoquinolyl, pyrimidinyl, pyridazinyl, cinnolinyl, triazinyl, quinoxalinyl, and quinazolinyl.

Preferred substituents are pyridyl and pyrimidyl.

An imino group in an aromatic substituent containing an imino nitrogen atom is preferably connected to a phosphorus atom through a single bridging carbon atom. For example, if the aromatic substituent is a pyridyl group, it is preferably connected through the carbon atom at the 2-position in the pyridyl group.

Accordingly, examples of preferred aromatic substituents containing an imino nitrogen atom are 2-pyridyl; 2-pyrazinyl; 2-quinolyl; l-isoquinolyl; 3-isoquinolyl; 2-pyrimidinyl; 3-pyridazinyl; 3-cinnolinyl; 2-triazinyl; 2-quinoxalinyl; and 2-quinazolinyl.

2-Pyridyl and 2-pyrimidyl are particularly preferred.

When the phosphine contains one phosphorus atom, it may conveniently be represented by the general formula

in which Rl represents an aromatic substituent containing an imino nitrogen atom, and R2 and R3, which may be the same or different, represent a group R1 or an optionally substituted aliphatic or aromatic hydrocarbyl group.

Particularly preferred phosphines are: bisphenyl-(2-pyridyl)phosphine, bis(2-pyridyl)phenylphosphine, and tris(2-pyridyl)phosphine.

The catalyst system used in the process according to the invention further comprises a protonic acid. The function of the protonic acid is to provide a source of protons. Accordingly, the protonic acid may be generated in situ.

Preferably the pro tonic acid is selected from acids having a non-coordinating anion. Examples of such acids include sulphuric acid; a sulphonic acid, e.g. an optionally substituted hydrocarbylsulphonic acid such as benzenesulphonic acid, p-toluenesulphonic acid, naphthalenesulphonic acid, an alkyl sulphuric acid such as methanesulphonic acid or tertiary butyl sulphuric acid, 2-hydroxypropanesulphonic acid, trifluoromethanesulphonic acid, chlorosulphonic acid or fluorosulphonic acid; a phosphonic acid, e.g. orthophosphonic acid, pyrophosphonic acid or benzenephosphonic acid; a carboxylic acid, e.g.

chloroacetic acid, dichloroacetic acid, trichloroacetic acid, trifluoroacetic acid, oxalic acid or terephthalic acid; or a perhalic acid such as perchloric acid. The protonic acid may also be an acidic ion exchange resin, for example a sulphonated ion exchange resin.

Our copending British patent application No.9 O..G I............, filed on even date (our ref. T 1452 GBR) discloses and claims: a carbonylation catalyst system, which comprises: a) a source of a Group VIII metal, b) a source of a phosphine having an aromatic substituent containing an imino nitrogen atom, c) a source of protonic acid, d) a source of an alkylsulphonate anion, and the use of such a catalyst system in the carbonylation of olefinically and acetylenically unsaturated compounds.

Our co-pending British patent application number

filed on even date (our ref. T 1304 GBR II) discloses and claims: a catalyst system which comprises: a) a Group VIII metal compound, and b) a phosphine of formula

R1 2 wherein R represents an aliphatic hydrocarbyl group, R represents an optionally substituted aromatic heterocyclic group having 5 or 6 ring atoms of which at least one is nitrogen, which may form part of an optionally substituted, larger condensed ring structure, and R3 independently has the R1 2 weaning of R or R or represents an optionally substituted aryl group or an acid addition salt thereof, and its use in the carbonylation of unsaturated compounds.

Our co-pending British patent application number

filed on even date (our ref. T 1357 GBR II) discloses and claims: a catalyst system, which comprises a) a source of a Group VIII metal, and b) a phosphine of general formula:

R1 R2 and R3 in which R1, R2 and R3 are independently selected from an optionally substituted aryl group and a group of general formula::

wherein each of A, X, Y and Z is independently selected from a nitrogen atom, a CH group and a group of formula CR wherein R represents a hydroxyl group, an amino group, an amido group, a cyano group, an acyl group, an acyloxy group, a halogen atom, an optionally substituted hydrocarbyl group or an optionally substituted hydrocarbyloxy group, it also being possible for two adjacent CR groups to form a ring, provided that at least one of RI R2 and R3 R1 R2 and R3 represents a group of formula (II) in which at least one of A and Z represents a group of formula CR; or an acid addition salt thereof, and its use in the carbonylation of acetylenically and olefinically unsaturated hydrocarbons.

The catalyst system used in the process according to the invention may be homogeneous or heterogeneous. Preferably it is homogeneous.

The ratio of the number of moles of phosphine per gram atom of Group VIII metal is not critical. Preferably it is in the range of from 1 to 1000, more preferably from 2 to 500, especially from 10 to 100.

The ratio of the number of moles of phosphine per mole of protonic acid is not critical. Preferably it is in the range of from 0.1 to 50, more preferably from 0.5 to 25, especially from 1 to 10.

The process according to the invention is conveniently effected in the liquid phase. A separate solvent is not essential.

Solvents suitable for use in the process according to the invention include for example, sulphoxides and sulphones, for example dimethylsulphoxide, diisopropylsulphone or tetrahydrothiophene-2,2-dioxide (also referred to as sulfolane), 2-methylsulfolane, 3-methylsulfolane, 2-methyl-4-butylsulfolane; aromatic hydrocarbons such as benzene, toluene, xylenes; esters such as methylacetate and butyrolactone; and ethers such as anisole, 2,5,8-trioxanone (also referred to as diglyme), diphenyl ether and diisopropyl ether.

The process according to the present invention is conveniently effected at a temperature in the range of from 10 to 200 "C, preferably from 20 "C to 130 C.

The process according to the invention is preferably effected at a pressure of from 1 to 100 bar. Pressures higher than 100 bar may be used, but are generally economically unattractive on account of special apparatus requirements.

The molar ratio of the olefinically or acetylenically unsaturated compound to the enolizable ketone may vary between wide limits and generally lies within the range of 0.01 to 100:1.

The quantity of the Group VIII metal is not critical.

-7 -l Preferably, quantities are used within the range of 10 to 10 gram atom Group VIII metal per mol of unsaturated compound.

The carbon monoxide required for the process according to the present invention may be used in a practically pure form or diluted with an inert gas, for example nitrogen. The presence of more than small quantities of hydrogen in the gas stream is undesirable on account of the hydrogenation of the unsaturated hydrocarbon which may occur under the reaction conditions. In general, it is preferred that the quantity of hydrogen in the gas stream supplied is less than 5 vol%.

The process according to the invention may be carried out continuously or batchwise.

The catalyst systems used in the process according to the invention may be prepared by any convenient method. Thus they may be prepared by combining a separate Group VIII metal compound, the phosphine (III) and the protonic acid. Alternatively, they may be prepared by combining a Group VIII metal compound and an acid addition salt of the phosphine. Alternatively, they may be prepared from a Group VIII metal compound which is a complex of a Group VIII metal with the phosphine, and the protonic acid.

Phosphines having an aromatic substituent which contains an imino nitrogen atom are known in the art. They are conveniently prepared by reacting a phosphorus halide or alkali metal phosphide with a appropiate alkali metal or halide derivative of a heterocyclic compound containing an imino nitrogen atom.

The invention will now be illustrated by the following Examples.

In the Examples, the selectivity to a certain compound, expressed as a percentage, is defined as 100 a/b, in which "a" is the amount of acetylenically or olefinically unsaturated compound that has been converted into a certain compound and "b" is the total amount of that unsaturated compound that has been converted.

Preparation 1 Preparation of diphenyl-(6-methyl-2-pyridyl)-phosphine All manipulations were carried out in an inert atmosphere (nitrogen or argon). Solvents were dried and distilled prior to use. 36 ml of a 1.6M n-butyllithium solution in hexane was added to 40 ml diethyl ether, and the mixture was cooled to -40 "C. To the stirred mixture was added in the course of 20 minutes a solution of 10 g 2-bromo-6-methylpyridine in 15 ml diethyl ether; during this addition, the temperature was kept at -40 "C. After the addition, the temperature was raised to -5 "C, kept there for 5 minutes, and then lowered again to -40 "C. A solution of 12.8 g chlorodiphenylphosphine in 15 ml diethyl ether was added in the course of 15 minutes to the stirred mixture.After the addition, the mixture was warmed to room temperature, the solvents were removed in vacuo, and 50 ml water and 50 ml dichloromethane were added. After 5 minutes of vigorous stirring, the dichloromethane layer was separated. The water layer was extracted with two 50 ml portions of dichloromethane, the organic reactions were combined, and the solvent removed in vacuo. The residue was crystallized from toluene/hexane to afford 12 g (75%) of diphenyl-(6-methyl-2-pyridyl)-phosphine as 31 off-white crystals. The product was characterized by P NMR: S - p -5.6 ppm.

Preparation 2 Preparation of diphenyl-(3-methyl-2-pyridyl)-phosphine This compound was prepared as described in Preparation 1, but using 10.0 g 2-bromo-3-methylpyridine instead of the 2-bromo-6 31 methylpyridine. It was characterized by P NMR: 5p = -8.1 ppm.

Preparation 3 Preparation of phenyl-bis(6-methyl-2-pyridyl)-phosphine This compound was prepared as described in Preparation 1, but using 5.2 g phenyldichlorophosphine instead of the chlorodiphenyl 31 phosphine. It was characterized by 31p NMR: S - -5.1 ppm.

p Preparation 4 Preparation of tris(6-methyl-2-pyridyl)-phosphine This compound was prepared as described in Preparation 1, but using 2.7 g phosphorus trichloride instead of the chlorodiphenylphosphine. It was characterized by 31p NMR: & - -3.8 ppm.

p Preparation 5 Preparation of diphenyl- (4, 6-dimethvl-2-pyridvl) -phosphine This compound was prepared as described in Preparation 1, but using 10.8 g 2-bromo-4,6-dimethylpyridine instead of the 2-bromo-6 31 methylpyridine. It was characterized by 3 P NMR: 5 - -5.6 ppm.

p Preparation 6 Preparation of diphenyl- C6-methoxy- 2-pyridyl) -phosphine 2.7 g Sodium was added to 100 ml liquid ammonia at -80 "C, and then 15.2 g triphenylphosphine was added in 6 portions with stirring. The solution was slowly warmed to -40 ec, kept at that temperature for 30 min, and then cooled again to -80 "C. Then, 3.1 g ammonium chloride was added to the stirred solution, followed by 10.9 g 2-bromo-6-methoxypyridine in three portions. The cooling bath was removed and the ammonia was allowed to evaporate. The residue was worked up with water/dichloromethane as described in Preparation 1.Crystallization from hexane afforded 7 g of a somewhat impure product (characterized by 31p NMR: s - -4.4 ppm) p Preparation 7 Preparation of di(n-butyl)-2-pyridyl phosphine To a magnetically stirred solution of 2.5 g phenyl (2-pyridyl)2P in 20 mol tetrahydrofuran, cooled to -80 OC, was added in the course of 10 min 5.9 ml of a 1.6 M solution of n-butylLi in hexane. The resulting deep-red solution was allowed to 31 NMR warm to room temperature, and analysis of the solution by 3 P NMR showed it to contain the phosphide (n-butyl)(2-pyridyl)PLi as the only phosphorus-containing compound CS " -16.3 ppm).

p The solution was cooled to -40 "C and a solution of 1.3 g l-bromobutane in 10 ml tetrahydrofuran was added. The mixture was again warmed to room temperature, the solvents were removed in vacuo, and 25 ml of diethylether and 10 ml of water were added.

After 10 min of stirring, the organic layer was separated and the water layer was extracted with 10 ml of ether. The organic layers were combined and the solvent was removed in vacuo (66 Pa). The 1 13 31 resulting light-yellow liquid was analyzed by H, C and P NMR and shown to consist of a 1:1 (molar ratio) mixture of 2-phenylpyridine and (n-butyl)2(2-pyridyl)P CS - -19.5 ppm).

p Preparation 8 Preparation of dimethyl 2-pyridyl phosphine and methylphenyl-2-pvridyl phosphine The method of Preparation 7 was repeated, except that a 1.6 M solution of methylLi in diethylether was used instead of the n-butylLi solution, and 1.3 g iodomethane instead of the bromobutane. The reaction product was a mixture of (methyl)2 C2-pyridyl)P, methyl phenyl 2-pyridylP and 2-phenyl pyridine in the approximate ratio 70:30:60, from which the (methyl)2(2-pyridyl)P was isolated by distillation.

The physical characteristics of the products were S - -41.2 p ppm (dimethyl-2-pyridylphosphine) and 5p - -24.1 ppm (methylphenyl 2 -pyridylphosphine).

Preparation 9 Preparation of n-butyl tert-butyl 2-pyridyl phosphine The method of Preparation 7 was repeated, except that 5.6 ml of a 1.7 M solution of t-butylLi in pentane was used instead of the n-butylLi solution. The final product was identified as n-butyl t-butyl 2-pyridylP by NMR analysis CS - 7.4 ppm).

p Preparation 10 Preparation of dimethyl 2-pyridylphosphine The method of Preparation 8 was repeated, except that 1.91 g methyl(2-pyridyl)2P and only 0.7 g iodomethane were used. Workup as described in Example 1 afforded dimethyl 2-pyridyl phosphine, which was further purified by distillation (65% yield). CS - -41.2 ppm).

p Preparation 11 Preparation of n-butvl (4-metho:--yphenyl) (2-pyridyl)phosphine All manipulations were carried out in an inert atmosphere nitrogen or argon). Solvents were dried and distilled prior to use. 18 ml of a 1.6M n-butyllithium solution in hexane was added to 30 ml diethyl ether, and the mixture was cooled to -40 "C.To the stirred mixture was added in the course of 20 minutes a solution of 4.6 g 2-bromopyridine in 15 ml diethyl ether; during this addition, the temperature was kept at -40 "C. After the addition, the temperature was raised to -5 "C, kept there for 5 minutes, and then lowered again to -40 "C. The resulting solution was added to a cooled (-40 C) solution of 7.6 g 4-methoxyphenyl-bis(2-pyridyl)phosphine in 30 ml THF. The mixture was warmed to room temperature.

After stirring for 10 minutes, the solvents were removed in vacuo.

Water (25 ml) and dichloromethane (25 ml) were added. After 5 minutes of vigorous stirring, the dichloromethane layer was separated. The water layer was extracted with two 25-ml portions of dichloromethane, the organic fractions were combined, and the solvent removed in vacuo. The residue was distilled, giving 4.7 g (60%) of (n-butyl)(4-methoxyphenyl)(2-pyridyl)phosphine as a 31 yellowish liquid. The product was characterized by 31p NMR: S - -14.9 ppm.

p In this experiment, n-butyllithium is believed to react with 2-bromopyridine to afford a mixture of n-butylbromide and 2-pyridyllithium. Then the 2-pyridyllithium reacts with 4-methoxybis(2-pyridyl)phosphine to afford 4-methoxyphenyl(2-pyridyl)lithium phosphide (and 2,2'-bipyridine). The lithium phosphide then reacts with n-butylbromide to afford (n-butyl)(4-methoxyphenyl) (2-pyridyl)phosphine.

Preparation 12 Preparation of methyl di(2-pyridyl)phosphine All manipulations were carried out in an inert atmosphere nitrogen or argon). Solvents were dried and distilled prior to use. 36 ml of a 1.6M n-butyllithium solution in hexane was added to 40 ml diethyl ether, and the mixture was cooled to -40 "C. To the stirred mixture was added in the course of 20 minutes a solution of 9.2 g 2-bromopyridine in 15 ml diethyl ether; during this addition, the temperature was kept at -40 C. After the addition, the temperature was raised to -5 "C, kept there for 5 minutes, and then lowered again to -40 "C. A solution of 3.4 g methyldichlorophosphine in 15 ml diethyl ether was added to the stirred mixture.

After the addition, the mixture was warmed to room temperature, the solvents were removed in vacuo, and 50 ml water and 50 ml dichloromethane were added. After 5 minutes of vigorous stirring, the dichloromethane layer was separated. The water layer was extracted with two 50-ml portions of dichloromethane, the organic fractions were combined, and the solvent removed in vacuo. The residue was distilled, giving 4.0 g (68%) of methyl-bisC2-pyridyl)- phosphine as a yellowish liquid. The product was characterized by 31p NMR = -20.5 ppm.

EXAMPLE 1 w A 250 ml magnetically stirred stainless steel autoclave was filled with palladium acetate (0.1 mmol), bisphenyl(2-pyridyl)- phosphine (5 mmol), para-toluenesulphonic acid (4 mmol), and acetone (50 ml). The autoclave was then flushed with carbon monoxide, and then charged with carbon monoxide (30 bar) and ethene (20 bar). The autoclave was then sealed and heated to a temperature of 90 "C.

After a reaction time of 3 hours, the contents of the autoclave were analyzed by gas-liquid chromatography. The selectivity to isopropenylpropionate was found to be > 95%, and the mean reaction rate was calculated to be 500 mol ethene/g.atom Pd/hour.

COMPARATIVE EXAMPLE A The method of Example 1 was repeated, but using triphenylphosphine (5 mmol) instead of bisphenyl(2-pyridyl)- phosphine (5 mmol), and allowing the reaction to proceed for 5 hours before analyzing the contents of the autoclave. The selectivity was found to be > 95%, and the mean reaction rate was calculated to be 250 mol ethene/g.atom Pd/hour.

EXAMPLE 2 The method of Example 1 was repeated, but using acetophenone (50 ml) instead of acetone (50 ml). The selectivity to l-phenylvinylpropionate was found to be > 95%; the conversion of acetophenone was calculated to be 30% and the mean reaction rate was calculated to be 300 mol ethene/g.atom Pd/hour.

COMPARATIVE EXAMPLE B The method of Example 2 was repeated, but using triphenylphosphine (5 mmol) instead of bisphenyl(2-pyridyl)phosphine (5 mmol), and allowing the reaction to proceed for 5 hours before analyzing the contents of the autoclave. The selectivity was found to be about 95%, the conversion was calculated to be about 15%, and the mean reaction rate was calculated to be 100 mol ethene/g.atom Pd/hour.

EXAMPLE 3 The method of Example 1 was repeated, but using methyl ethyl ketone (50 ml) instead of acetone (50 ml), and allowing the reaction to proceed for 5 hours before analyzing the contents of the autoclave.

Analysis of the contents of the autoclave revealed the presence of l-ethylvinyl propionate, l-methylallyl propionate and 3-methyl-3-propenyl propionate. The mean reaction rate was calculated to be 500 mol ethene/g.atom Pd/hour.

Claims (11)

1. A process for the preparation of an ester of an alpha-ethylenically unsaturated alcohol, which comprises reacting an olefinically unsaturated compound or an acetylenically unsaturated compound with carbon monoxide and an enolizable ketone in the presence of a catalyst system comprising: (a) a source of a Group VIII metal, (b) a phosphine having an aromatic substituent which contains an imino nitrogen atom, and (c) a protonic acid.

2. A process as claimed in claim 1, in which an olefinically unsatured compound is used which is an optionally substituted alkene having from 2 to 10 carbon atoms.

3. A process as claimed in claim 1, in which an acetylenically unsaturated compound is used which is an optionally substituted alkyne having from 2 to 10 carbon atoms.

4. A process as claimed in any one of claims 1 to 3, in which the enolizable ketone is an optionally substituted alkanone or alkylphenyl ketone.

5. A process as claimed in any one of claims 1 to 4, in which the source of a Group VIII metal is a palladium compound.

6. A process as claimed in any one of claims 1 to 5, in which an imino nitrogen atom is connected to a phosphorus atom through a single bridging carbon atom.

7. A process as claimed in claim 6, in which the phosphine is a 2-pyridyl phosphine or a 2-pyrimidinylphosphine.

8. A process as claimed in any one of claims 1 to 7, in which the protonic acid is a sulphonic acid, a phosphonic acid, a carboxylic acid or a perhalic acid.

9. A process as claimed in any one of claims 1 to 8, in which the ratio of the number of moles of phosphine per gram atom of Group VIII metal is in the range of from 2 to 500, and the ratio of the number of moles of phosphine per mole of pro tonic acid is in the range of from 0.5 to 25.

10. A process as claimed in any one of claims 1 to 9, in which the temperature is in the range of from 20 to 30 0C, and the pressure is in the range of from 1 to 100 bar.

11. A process for the preparation of an ester of an ethylenically unsaturated alcohol, substantially as described in any one of Examples 1 to 3 herein.