GB1586671A

GB1586671A - Manufacture of esters

Info

Publication number: GB1586671A
Application number: GB15744/77A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1977-04-15
Filing date: 1977-04-15
Publication date: 1981-03-25
Also published as: BE865821A; AU519306B2; IT1095480B; IT7821367A0; JPS53130627A; FR2387211B1; NZ186666A; DE2812365A1; AU3394078A; ZA781292B; NL7803569A; FR2387211A1

Description

(54) MANUFACTURE OF ESTERS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Milibank, London SW1P 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an improved pro cess for the manufacture of esters of mphenoxybenzyl alcohol.

A number of esters of m-phenoxybenzyl alcohol are of insecticidal value, for example, those with certain substituted 2,2-dimethyl cyclopropane carboxylic acids. These esters may be prepared from the corresponding acids by converting the latter into the acid chloride which may then be reacted with m-phenoxy benzyl alcohol. The cyclopropanecarboxylic acids are conveniently isolated in the form of their methyl and ethyl esters, and the latter provide an altemative route to the correspond ing m-phenoxybenzyl esters, which can con veniently be obtained from the methyl or ethyl esters by an ester interchange reaction with m-phenoxybenzyl alcohol or certain derivatives thereof, in the presence of an ester interchange catalyst.

Our copending United Kingdom Patent Application No. 15582/76 (Serial No.

1,571,388) discloses the use of tetramethyl- or tetraethyl titanate as a transesterification catalyst in the conversion of the methyl or ethyl esters of carboxylic acids into their esters with m-phenoxybenzyl alcohol or its ,orcyano or e ethinyl derivative. These tetra-alkyl titanates are also effective transesterification catalysts and do not affect the cis/trans isomer ratio of pyrethin-type esters of cyclopropane carboxylic acids. However, the tetra-alkyl titanates are very reactive towards water, and because of this their quality is variable according to whether or not they have been freshly prepared and to the extent to which they have been excluded from contact with moisture. Poor quality catalyst may adversely affect the ester interchange reaction, leading to the formation of by-products, with consequent reduction in the purity and yield of thc desired esters.

According to the present invention there is provided a process for the preparation of esters of m-phenoxybenzyl alcohol and its loxcyano and a-ethinyl derivatives with carboxylic acids which comprise mixing a methyl or ethyl ester of the carboxylic acid, m-phenoxybenzyl alcohol or its,Oe-cyano orla-ethinyl derivative and an ester interchange catalyst which is a diol or polyol titanate or a chelate compound of titanium with a diketone or a ,,B-ketoester, any residual valencies on the titanium atom being satisfied by a diol, a polyol, OH or OR in which R is a lower alkyl group, and heating the mixture at a temperature such that the methanol or ethanol are removed by distillation as they are formed.

Diol titanates are obtained by reaction of tetra-alkyltitanate Ti(OR)4 in which R is a lower alkyl group, with one or two moles of a diol, for example, to give a compound of the formula Ti(diol)(OR)2 or Ti(diol)2. Compounds Ti(diol) (OR)2 may be further reacted with water to give Ti(diol)(OH)2 or compounds with the condensed structures [Ti(diol)O] wherein n is an integer, which are also catalysts within the scope of the present invention.

The reaction of a tetra-alkyltitanate with a polyol, for example gives a polyol titanate of indeterminate, possibly polymeric, structure which is, however, an effective catalyst within the scope of the present invention.

The chelate compounds of titanium which may be used as catalysts are obtained by re action of a tetra-alkyltitanate Ti(OR)4 in which R is a lower alkyl group with a diketone, for example, acetylacetone, or with a ,ss-ketoester, for example ethyl acetoacetate, to give compounds having the formula Ti(chelate)2(OR)2.

These latter may be further reacted with a diol to give Ti(chelate)2(diol) or with water to give Ti(chelate)2(OH)2 or compounds with the condensed structure [Ti(chelate)2O] wherein n is an integer, which are also catalysts within the scope of the present invention.

Examples of the diols and polyols which may be used in preparing the titanium-based catalysts for use in the process of the present invention are ethylene glycol, propan-1,2-diol, propan-1,3-diol, butan- 1,2-diol, butan-1,3-diol, butan-2, 3-diol, butan- 1,4-diol, 2-ethylhexan 1,3-diol, neopentyl glycol, hexan-1,6diol, pinacol, glycerol, pentaerythritol and secondary cellulose acetate.

Particularly preferred catalysts are those of the formula Ti(diol)(OH)2 in which the diol is an loyw unbranched diol, because these catalysts are generally insoluble in the reaction mixture and consequently can easily be removed and recycled.

The term "lower alkyl" in this specification means an alkyl group containing from 1 to 4 carbon atoms.

The ingredients of the process may be mixed in any order and the mixture, preferably stirred or otherwise agitated, raised to reaction temperature. The preferred reaction temperatures are between 80" and 200"C. Temperatures outside this range may be used but lower temperatures may necessitate prolonged reaction times and higher temperatures involve a risk of decomposition of the product.

If desired a solvent may also be used, especially one which gives a reaction mix boiling at the desired reaction temperature so that the methanol or ethanol formed during the process is distilled off with a part of the solvent.

Suitable solvents are for example hydrocarbons such as toluene or methylcyclohexane, halogenated hydrocarbons wherein the halogen atom is inert under the reaction conditions, e.g. chlorinated aromatic hydrocarbons such as chlorobenzene, and ethers such as dioxan.

Lower boiling solvents such as cyclohexane may be used but need a longer reaction period at atmospheric pressure.

Many of the catalysts the use of which is within the scope of the present invention are not sensitive to moisture, and consequently it is not necessary in such cases for any of the reactants, or solvents if used, to be especially dry. This applies to catalysts which are free from OR groups, and is one advantage of the use of this particular group of catalysts.

The amount of catalyst used is at least 0.0005 Mol., and preferably from 0.001-0.2 Mol per mol., of carboxylic ester.

The preferred proportions of m-12hu0xy- benzyl alcohol or its ,a-cyano or lorethinyl derivative and methyl or ethyl ester of carboxylic acid are equimolar. Excess of either reactant may be used if desired and may generally be recovered unreacted at the end of the process, for example by distillation under reduced pressure.

The ester produced by the process of the invention may be isolated by any convenient procedure, for example by removing the solvent, if any, and any unchanged reactant, by distillation to leave the crude ester which could be purified by conventional means suitable for the ester concerned.

The dimethyl or ethyl ester of a carboxylic acid which may be used in the process of the invention is any of such esters which has a boiling point significantly higher than the reaction temperature. Such esters may be derived from aliphatic aromatic, cycloaliphatic or heterocyclic carboxylic acids but the process of the invention is of particular value for the manufacture of m-phenoxybenzyl, a-cyano and la-ethinyl-m-phenoxybenzyl esters of insecticidal activity, for example from 4 methyl,ahisopropylphenylacetic acid or more especially of pyrethrin-type esters of 2,2-dimethylcyclopropanecarboxylic acids.

Examples of these are particularly esters of 2,2-dimethylcyclopropanecarboxylic acids containing in the 3- position substituted vinyl groups such as 2',2'-dimethylvinyl, 2',2'-dichlorovinyl, 2'-ethylvinyl and 2',2'-dibromovinyl. These acids are normally obtained as mixtures of cis and trans forms, which in the case of the desired m-phenoxybenzyl esters have different insecticidal potency. The process of the invention is particularly valuable in that it brings about a minimum of interconversion of the cis into the less potent trans forms and also lower formation of byproducts.

The process also has the advantage that in general it gives a greater conversion of the methyl or ethyl esters into pyrethrin-type esters of cyclopropane carboxylic acids compared with the comparable processes in which the catalyst is tetramethyl- or tetraethyl-titanate, sodium methoxide or sodium ethoxide.

The preparation of typical catalysts for use in the process of the present invention is described in the following: Catalyst Preparation A A solution of 28.4 parts of isopropyl titanate in 50 parts of petroleum ether boiling point 100-1200C was treated with 7.6 parts of propan-1,3-diol. The reaction was mildly exothermic and the temperature was held at 40"C by external cooling. After stirring the mixture for 2 hours the solvent was removed by vacuum evaporation, leaving 24 parts of a yellow oil.

Catalyst Preparation B A solution of 28.4 parts of isopropyl titanate in 50 parts of petroleum ether boiling point 100120UC C was treated with 7.6 parts of propan-1,3-diol. The reaction was mildly exothermic and the temperature was held at 40"C by external cooling. After stirring the mixture for 2 hours, 80 parts of water were added with rapid stirring. A precipitate was formed, the mixture was stirred for a further hour and then filtered to obtain the product, which after washing with petroleum ether and drying consisted of 14.7 parts of a white powder.

Catalyst Preparation C The preparation described in Preparation B was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 9 parts of butan-2,3-diol. 15.0 parts of product were obtained.

Catalyst Preparation D The preparation described in Preparation B was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 7.6 parts of propan-1,2-diol. 12.1 parts of product were obtained.

Catalyst Preparation E The preparation described in Preparation B was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 6.2 parts of ethylene glycol. 13.3 parts of product were obtained.

Catalyst Preparation F The preparation described in Preparation B was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 9.0 parts of butan-1,4-diol. 11.6 parts of product were obtained.

Catalyst Preparation G The preparation described in Preparation B was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 11.8 parts of pinacol. 14.6 parts of product were obtained.

Catalyst Preparation H The preparation described in Preparation B was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 11.8 parts of hexan-1,6-diol. 13.4 parts of product were obtained.

Catalyst Preparation I The preparation described in Preparation B was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 10.4 parts of neopentyl glycol. 15 parts of product were obtained.

Catalyst Preparation J A solution of 34.1 parts of isopropyl titanate in 50 parts of petroleum ether boiling point 100-1200C was treated with 17.5 parts of 2-ethylhexan-1,3-diol in 50 parts of petrol eum ether. The temperature of the exothermie reaction was held at 40"C by external cooling.

The mixture was stirred for a further 2 hours and then 100 parts of water were added with rapid stirring. After stirring the mixture for 30 minutes and then allowing it to settle, the petroleum ether layer was separated, then dried and evaporated to yield 19.6 parts of white solid product.

Catalyst Preparation K To a solution of 28.4 parts of isopropyl titanate -is 40 parts of petroleum ether boiling point 100--120"C was added a solution of 10.4 parts of neopentyl glycol in 40 parts of 1,4-dioxan. The mixture was maintained at 40"C for one. hour, treated with 30 parts of water at 35"C, stirred and refluxed for one hour, and then filtered to obtain 16 parts of white granular product.

Catalyst Preparation L A solution of 42.6 parts of isopropyl titanate in 50 parts of dry 1,4-dioxan was treated with a solution of 9.2 parts of glycerol in 20 parts of dry 1,4-dioxan. The . mixture was stirred for 4 hours, treated with 25 parts of water, stirred for a further hour and filtered. The residue was washed with water and dried to yield 19.7 parts of pale yellow solid.

Catalyst Preparation M A solution of 56.8 parts of isopropyl titanate in 50 parts of dry 1,4-dioxan was treated with a solution of 12.6 parts of pentaerythritol in 20 parts of dry 1,4-dioxan. The mixture was stirred for 4 hours, treated with 25 parts of water, stirred for a further hour and filtered.

The residue was washed with water and dried to yield 18.4 parts of a pale yellow product.

Catalyst Preparation N A solution of 10.0 parts of isopropyltitanate in 50 parts of dry 1,4-dioxan was treated with a solution of 10.0 parts of cellulose acetate in 20 parts of dry 1,4-dioxan. The mixture was stirred for 4 hours, treated with 25 parts of water, stirred for a further hour and filtered.

The residue was washed with water and dried to yield 12.7 parts of a yellow product.

Catalyst Preparation O A solution of 28.4 parts of isopropyl titanate in 50 parts of petroleum ether boiling point 100--120"C was treated with 20 parts of acetylacetone in 50 parts of petroleum ether.

The mixture, which changed in colour from colourless to red during the addition of acetyl acetone, was stirred for 2 hours, then evapo rated under vacuum to leave 32.0 parts of a deep red oil.

Catalyst Preparation P The preparation described in Preparation O was repeated except that the 20 parts of acetylacetone were replaced by 36.6 parts of ethylacetoacetate. 40.1 parts of an orange oil were obtained.

Catalyst Preparation Q A solution of 28.4 parts of isopropyltitanate in 50 parts of petroleum ether boiling point 100--120"C was treated with 26 parts of ethyl acetoacetate in 50 parts of petroleum ether.

After being stirred for 2 hours the mixture was treated with 80 parts of water, stirred for one hour, then filtered to collect the product, which was washed with water and dried to yield 12.5 parts of a pale yellow solid.

Catalyst Preparation R The preparation described in Preparation Q was repeated except that the 26 parts of ethyl acetoacetate were replaced by 20 parts of acetylacetone. 10.2 parts of a pale yellow solid were obtained.

Catalyst Preparation S A solution of 28.4 parts of isopropyl titanate in 50 parts of petroleum ether boiling point 100-1200C was treated with 20 parts of acetylacetone in 50 parts petroleum ether and the mixture was stirred for 2 hours. 7.6 parts of propan-1,3-diol were added dropwise and the mixture was boiled under reflux for one hour. The solvent was then evaporated under vacuum to leave 32.1 parts of a red oil.

Catalyst Preparation T The preparation described in Preparation S was repeated except that the 20 parts of acetylacetone were replaced by 26 parts of ethylacetoacetate. 37.4 parts of an orange oil were obtained.

Catalyst Preparation U The preparation described in Preparation S was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 6.2 parts of ethylene glycol. 21 parts of a fine, off white powder were obtained.

Catalyst Preparation V The preparation described in Preparation S was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 11.6 parts of cyclohexane-1,4-diol. 35 parts of a deep red solid were obtained.

Catalyst Preparation W The preparation described in Preparation S was repeated except that the 7.6 parts of propan-1,3-diol were replaced by 14.6 parts of 2-ethylhexan-1,3-diol. 36 parts of a red oil were obtained.

Catalyst Preparation X A solution of 28.4 parts of isopropyl titanate in 50 parts of petroleum ether boiling point 100--120"C was treated with 15.2 parts of propan-1,3-diol. The stirred mixture was then boiled under reflux for one hour, cooled, and the suspended solid product was filtered off, washed with petroleum ether and dried to yield 16.3 parts of a white powder.

The invention is illustrated but not limited by the following Examples in which parts and percentages are by weight.

Example 1.

The mixture of 42.1 parts of m-phenoxy benzyl alcohol (95 /O strength), 49.9 parts of ethyl 2,2- dimethyl - 3 - (2',2' - dichlorovinyl) cyclopropane carboxylate (cis: trans ratio 40:60, strength 95%) and 2.5 parts of the propanediol titanate catalyst Preparation B was stirred at 170CC under a gentle stream of nitrogen in order to entrain the ethanol which is evolved during the reaction. After 10 hours at 1700C the mixture was cooled and filtered to remove the catalyst. The product was dis tilled under vacuum to remove low boiling material and the 71.3 parts of residue remain ing was shown on analysis to contain 89.7% of m - phenoxy - benzyl 2,2 - dimethyl - 3 (2',2' - dichlorovinyl) - cyclopropane carboxy late having a cis-trans ratio of 37:63.

Example 2.

The catalyst residue from Example 1 was washed with toluene and dried at 60"C in vacuo. A preparation as described in Example 1 was carried out using the recovered catalyst and yielded 72.6 parts of product containing 88.3% of m - phenoxybenzyl 2,2 - dimethyl 3 - (2',2' - dichlorovinyl)cyclopropane carboxylate having a cis : trans ratio of 38:62.

Example 3.

The catalyst recovered from the preparation described in Example 2 was again recycled and employed in a transesterification reaction as described in Example 2. The preparation yielded 73.5 parts of product containing 90.4% of m - phenoxybenzyl 2,2 - dimethyl - 3 (2',2' - dichlorovinyl)cyclopropane carboxylate having a cis : trans ratio of 37:63.

Example 4.

The preparation described in Example 1 was repeated using 2.5 parts of catalyst Preparation T. After the 10 hours reaction period at 1700C the mixture was cooled, treated with 80 parts of toluene and 10 parts of 2N hydrochloric acid, heated at reflux temperature for 30 minutes, cooled and filtered followed by removal of the toluene from the filtrate by vacuum evaporation. The product was distilled to remove 8.5 parts of unreacted ethyl 2,2 - dimethyl - 3 - (2',2' - dichloro vinyl) cyclopropane carboxylate and the 72 parts of residue contained 85% of m - phen oxybenzyl 2,2 - dimethyl - 3 - (2',2' - di chlorovinyl)cyclopropane carboxylate having a cis-trans ratio of 40:60.

Example 5.

A transesterification reaction was carried out as described in Example 1, using as catalyst 2.5 parts of the product from Preparation H. At the end of the 10 hour reaction period at 1700C the reaction mixture was filtered to remove the catalyst but was not distilled under vacuum to recover unreacted ethyl ester. The product on analysis was found to contain 74.0% of m - phenoxybenzyl 2,2 - dimethyl - 3 (2',2' - dichlorovinyl)cyclopropane carboxylate having a cis-trans ratio of 37.4:62.6, and 1.7% of m - phenoxybenzyl alcohol. The product was subjected to superheated steam distillation using steam at 160-1800C for 100 minutes. After working up and drying the residue from the steam distillation, analysis showed it to contain 90.2% of m - phenoxybenzyl 2,2 - dimethyl - 3 - (2',2' - dichlorovinyl)cyclopropane carboxylate having a cistrans ratio of 37.4:62.6, and 0.4% of mphenoxybenzyl alcohol.

Example 6.

A mixture of 201.8 parts of m - phenoxybenzyl alcohol (99.1% strength) 240.6 parts of ethyl 2,2 - dimethyl - 3- - (2',2' - dichlorovinyl)cyclopropane carboxylate (98.5% strength, cis-trans ratio 38:62), 2.5 parts of catalyst Preparation J and 400 parts of a dichlorobenzene was stirred and heated until the mixture started to distil. The distillation was carried on for 6 hours and fresh o - dichlorobenzene was added to the reaction mixture periodically to replace the volume lost by distillation. A temperature of 1700C was required in the mixture at the beginning of the distillation and this was gradually increased so that by the end of the reaction period a temperature of 1800C was attained.

At the end of the reaction period the mixture was cooled to 90"C and 9 parts of 12% hydrochloric acid were added and stirred with the mixture at 90"C for 20 minutes. The pre- cipitated catalyst residue was then filtered off and the filtrate was distilled to remove the o - dichlorobenzene. The residue (381 parts) was found to contain 89.2% of m - phenoxy wbenzyl 2,2 - dimethyl - 3 - (2,2' - dichlorovinyl)cyclopropane carboxylate having a cis: trans ratio of 37:63.

Example 7.

The preparation described in Example 6 was repeated except that the 2.5 parts of catalyst Preparation J were replaced by 2.5 parts of catalyst Preparation R. 388 parts of product were obtained containing 87.2% of mphenoxybenzyl 2,2 - dimethyl - 3 - (2',2' - dichlorovinyl)cyclopropane carboxylate having a cis:trans ratio of 38:62.

Example 8.

The preparation described in Example 6 was repeated except that the 2.5 parts of catalyst Preparation J were replaced by 2.5 parts catalyst Preparation S. 382 parts of product were obtained containing 91.1 % of mphenoxybenzyl 2,2 - dimethyl - 3 - (2',2'dichlorovinyl)cyclopropane carboxylate having a cis: trans ratio of 38 : 62.

Example 9.

The preparation described in Example 6 was repeated except that the 2.5 parts of catalyst Preparation J were replaced by 2.5 parts of catalyst Preparation K. 384 parts of product were obtained containing 91.7% of mphenoxybenzyl 2,2 - dimethyl - 3 - (2',2'dichlorovinyl(cyclopropane carboxylate having a cis : trans ratio of 40:60. (The ethyl ester used in this Example had a cis : trans ratio of 42:58).

WHAT WE CLAIM IS: 1. A process for the preparation of esters of m-phenoxybenzyl alcohol and its a-cyano and evethinyl derivatives with carboxylic acids which comprises mixing a methyl or ethyl ester of the carboxylic acid, m?henoxybenzyl alcohol or its la-cyano or ,ovethinyl derivative and an ester interchange catalyst which is a diol or polyol titanate or a chelate compound of titanium with a diketone or a -ketoester, any residual valencies on the titanium atom being satisfied by a diol, a polyol, OH or OR in which R is a lower alkyl group, and heating the mixture at a temperature such that the methanol or ethanol are removed by distillation as they are formed.

2. A process as claimed in claim 1 wherein the catalyst has the formula Ti(diol)(OH)2 in which the diol is an $ (o-unbranched diol.

3. A process as claimed in claim 1 or claim 2 wherein the reaction temperature is between 80 and 200 C.

4. A process as claimed in any one of claims 1 to 3 wherein the reaction is carried out in a solvent.

5. A process as claimed in claim 4 wherein the solvent is such that the reaction mixture boils at the desired reaction temperature so that the methanol or ethanol formed during the process is distilled off with a part of the solvent.

6. A process as claimed in any one of claims 1 to 5 wherein the amount of catalyst used is at least 0.0005 mol per mol of the methyl or ethyl ester of the carboxylic acid.

7. A process as claimed in claim 6 wherein the amount of catalyst is from 0.001 to 0.2 mol per mol of the methyl or ethyl ester of the carboxylic acid.

8. A process as claimed in any one of claims 1 to 7 wherein the m-phenoxybenzyl alcohol or its 1orcyano or a-ethinyl derivative and the methyl or ethyl ester of the carboxylic acid are employed in equimolecular proportions.

9. A process as claimed in any one of claims 1 to 8 wherein the carboxylic acid is a 2,2

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 5. A transesterification reaction was carried out as described in Example 1, using as catalyst 2.5 parts of the product from Preparation H. At the end of the 10 hour reaction period at 1700C the reaction mixture was filtered to remove the catalyst but was not distilled under vacuum to recover unreacted ethyl ester. The product on analysis was found to contain 74.0% of m - phenoxybenzyl 2,2 - dimethyl - 3 (2',2' - dichlorovinyl)cyclopropane carboxylate having a cis-trans ratio of 37.4:62.6, and 1.7% of m - phenoxybenzyl alcohol. The product was subjected to superheated steam distillation using steam at 160-1800C for 100 minutes. After working up and drying the residue from the steam distillation, analysis showed it to contain 90.2% of m - phenoxybenzyl 2,2 - dimethyl - 3 - (2',2' - dichlorovinyl)cyclopropane carboxylate having a cistrans ratio of 37.4:62.6, and 0.4% of mphenoxybenzyl alcohol. Example 6. A mixture of 201.8 parts of m - phenoxybenzyl alcohol (99.1% strength) 240.6 parts of ethyl 2,2 - dimethyl - 3- - (2',2' - dichlorovinyl)cyclopropane carboxylate (98.5% strength, cis-trans ratio 38:62), 2.5 parts of catalyst Preparation J and 400 parts of a dichlorobenzene was stirred and heated until the mixture started to distil. The distillation was carried on for 6 hours and fresh o - dichlorobenzene was added to the reaction mixture periodically to replace the volume lost by distillation. A temperature of 1700C was required in the mixture at the beginning of the distillation and this was gradually increased so that by the end of the reaction period a temperature of 1800C was attained. At the end of the reaction period the mixture was cooled to 90"C and 9 parts of 12% hydrochloric acid were added and stirred with the mixture at 90"C for 20 minutes. The pre- cipitated catalyst residue was then filtered off and the filtrate was distilled to remove the o - dichlorobenzene. The residue (381 parts) was found to contain 89.2% of m - phenoxy wbenzyl 2,2 - dimethyl - 3 - (2,2' - dichlorovinyl)cyclopropane carboxylate having a cis: trans ratio of 37:63. Example 7. The preparation described in Example 6 was repeated except that the 2.5 parts of catalyst Preparation J were replaced by 2.5 parts of catalyst Preparation R. 388 parts of product were obtained containing 87.2% of mphenoxybenzyl 2,2 - dimethyl - 3 - (2',2' - dichlorovinyl)cyclopropane carboxylate having a cis:trans ratio of 38:62. Example 8. The preparation described in Example 6 was repeated except that the 2.5 parts of catalyst Preparation J were replaced by 2.5 parts catalyst Preparation S. 382 parts of product were obtained containing 91.1 % of mphenoxybenzyl 2,2 - dimethyl - 3 - (2',2'dichlorovinyl)cyclopropane carboxylate having a cis: trans ratio of 38 : 62. Example 9. The preparation described in Example 6 was repeated except that the 2.5 parts of catalyst Preparation J were replaced by 2.5 parts of catalyst Preparation K. 384 parts of product were obtained containing 91.7% of mphenoxybenzyl 2,2 - dimethyl - 3 - (2',2'dichlorovinyl(cyclopropane carboxylate having a cis : trans ratio of 40:60. (The ethyl ester used in this Example had a cis : trans ratio of 42:58). WHAT WE CLAIM IS:

1. A process for the preparation of esters of m-phenoxybenzyl alcohol and its a-cyano and evethinyl derivatives with carboxylic acids which comprises mixing a methyl or ethyl ester of the carboxylic acid, m?henoxybenzyl alcohol or its la-cyano or ,ovethinyl derivative and an ester interchange catalyst which is a diol or polyol titanate or a chelate compound of titanium with a diketone or a -ketoester, any residual valencies on the titanium atom being satisfied by a diol, a polyol, OH or OR in which R is a lower alkyl group, and heating the mixture at a temperature such that the methanol or ethanol are removed by distillation as they are formed.

dimethylcyclopropane-1-carboxylic acid which gives esters having insecticidal activity with m-phenoxybenzyl alcohol or its 1orcyano or rethinyl derivative.

10. A process as claimed in claim 9 wherein the 2,2 - dimethylcyclopropane - 1 - carboxylic acid contains a 2',2' - dimethylvinyl 2',2'dichlorovinyl, 2' - ethylvinyl or 2',2' - dibromovinyl group in the 3-position.

11. A process for the preparation of esters of m-phenoxybenzyl alcohol and its α-cyano andlor-ethinyl derivatives with carboxylic acids substantially as hereinbefore described in any one of the foregoing Examples 1 to 9.

12. Esters of m-phenoxybenzyl alcohol and its loxcyano and a-ethinyl derivatives with carboxylic acids whenever obtained by a process as claimed in any one of claims 1 to 11.