IL35709A

IL35709A - Process for the production of loweralkyl esters of dichlorobenzylic acid

Info

Publication number: IL35709A
Application number: IL35709A
Authority: IL
Original assignee: Yeda Res & Dev
Priority date: 1970-11-23
Filing date: 1970-11-23
Publication date: 1973-04-30
Also published as: IL35709A0

Description

PROCESS FOR THE PRODUCTION OF LOWER-ALKYL ESTERS OF DICHLOROBENZYLIC ACID The present invention relates to a novel process for the production of chlorobenzilate (the ethyl ester of dichlorobenzilic acid). More particularly ,~ it relates to a novel and advantageous process for the oxidation of [~ di-(p-chlorophenyl) - ethyl acetate J , which is also known as ethyl-DDA, to chlorobenzilate.

Esters of dichlorobenzilic acid, and in particular the ethyl ester, are highly effective and selective acaricides. These, and especially chlorobenzilate, are produced by a number of conventional processes, which have a number of drawbacks.

The conventional oxidation of ethyl-DDA to chlorobenzilate is effected \ either by air or oxygen in dimethyl formamide (DMF) as solvent, in the presence ■ \ . — of a quarternary ammonium base as catalyst. A\ catalyst used in the conventional process is that known by the trade designation Triton B (trimethyl-benzyl ammonium hydroxide, 40% aqueous solution). The conventional process, in DMF as reaction medium, does not give high yields and this is generally attributed, to water formed by. the oxidation, which accumulates in the reaction medium An initial quantity of water is introduced: with the catalyst, . as >. Trito B cannot be obtained in'the anhydrous state. As Triton B is insoluble in most conventional solvents, DMF must be used as reaction medium, and apart from the* low yields, the recovery of the DMF is quite cumbersome, as , it is obtained together with the water and quite substantial .quantities iare lost; ; in the recovery step, making the process quite uneconomic.

.The process according to the present invention comprises oxidizing ethyl-DDA to chlorobenzilate by means of air' or by means of oxygen in the presence of a strong alkali metal base as catalyst.. The reaction is ■ advantageously effected in a simple non-polar volatile solvent such as benzene, toluene, or an aliphatic hydrocarbon in combination with a low boiling aliphatic alcohol, DMF or DMSO (dimethylsulf oxide).. Especially suitable solvent systems for the process according to the invention are combinations of benzene and DMF or of ligroin and DMSO and t-butanol .

Suitable bases are potassiun odium alcoholates, such as potassium t-butoxide or even potassium hydroxide as such.

According to a preferred embodiment -of the invention, the process is carried out in the presence of a drying agent, such as calcium sulfate hemihydrate, calcium oxide, active magnesium oxide or the like. When such drying agent is added to the reaction system, there are obtained substantially quantitative yields.

^After the completion of the reaction the product may be isolated by first filtering off the drying agent and then stripping the solvents preferably in a vacuum. The product is then obtained in substantially pure form as an involatile residue. ] ■ Alternatively water may be added after the reaction, the aqueous phase -separated, and the organic phase is stripped of -the solvent leaving the product as an involatile residue. The evaporated solvents are recovered and may be used as recovered for a subsequent batch.j The compound ethyl-DDA used as starting material in the process according to the present invention is advantageously obtained by the hydrolysis of DDT.

The invention is illustrated in the following with reference to a number of examples, which are to be construed in a non- limitative manner.

EXAMPLE 1 : A quantity of 100 g ethyl-DDA, 100 g benzene and 300 g_t-butanol was introduced into a 1-liter vessel. The reaction mixture was cooled to 0°C and 1 stirred at 500 r.p. m. under an oxygen atmosphere. 5 g of Potassium t-butoxide were added during the reaction. The temperature was maintained throughout the reaction at between 0°C and +5°C . After 1 hour the stoichiometric quantity of oxygen had been absorbed. 100 ml water were added, forming an aqueous and an organic phase. The aqueous phase was removed. From the organic phase, the solvent was removed by evaporation and there remained a quantity of 95 g of chlorobenzilate (ethyl ester of dichlorobenzilic acid). The purity of the product, as obtained, was better than 95% based on g. I. e. analysis. ! j EXAMPLE 2 : ' . j The oxidation of 100 g ethyl-DDA was effected with -300 g DMF and 1 g KOH as initiator, as set out in Example 1. After 3 hours the stoichiometric The oxidation of ethyl-DDA was effected as in Example 1, with 100 g ethyl-DDA, 100 g DMF, 100 g benzene, 50 g CaO and 1 g KOH. The reaction was effected between -5°C and +5°C. .

;. : : After 1 hour the stoichiometric quantity of oxygen had;been absorbed.. The ·· solvents were stripped in vacuum. ■ 98 g chlorobenzilate was obtained, same purity as in Example 1. · '. j | E A PLE 4 ; ·· ' ! · - ; ■ ■ '■; An oxidation was effected as in Example 1, and the. reaction mixture comprised 100 g butyl-DDA, 100 g benzene, 200 g DMF, 50 g MgO and 1 g KOH.

The reaction was complete after 1 hourj the separation was effected as: in Example 38 and there was obtained 90 g of the butyl ester of dichloro- .J benzilic acid, purity as in Example 1.

EXAMPLE 5 : An oxidation was effected as in Example 1, the reaction mixture comprising 100 g ethyl-DDA, 100 g toluene, 100 g DMSO, 50 g CaS04 and 1 g sodium t-butoxide.

After 3 hours the stoichiometric quantity of oxygen had been absorbed. The reaction was effected at between 0°C and +10°C. The reaction mixture was worked up as in Example 1, and there~was obtained 87 g chlorobenzilate, -purity better than 96%. j .

EXAMPLE 6 : A quantity of 100 g ethyl-DDA, 100 g DMF, 100 g petrol ether, 50 g CaO and 1 g KOH were introduced into a 1 - liter vessel. Air was bubbled through the reaction vessel at a rate of 250 ml/minute at a temperature of 15°C. After an hour and a half the stoichiometric quantity of, air had been absorbed, the reaction mixture was worked up as in Example 3 and there was obtained 86 g of chlorobenzilate, purity : better than 95%. ' In a similar manner there were prepared other lower - alkyl esters of di-chlorobenzilic and dibromobenzilic acid. ' '

Claims

C L A I M S :

1. A process for the production of lower-alky I esters of 4,4'-dlchlorobenzl I lc acid, which comprises oxidizing lower-alkyl esters of dlchlorodlphenyl acetic acid in a suitable reaction medium, as hereinbefore defined, with air or oxygen In the presence of an alkali metal base as catalyst,

2. A process as claimed In claim I, wherein the reaction Is effected In the range of temperatures between -30 and +30°C, and preferably between -10 and +I0°C.

3. A process as claimed In claim I or 2, wherein the reaction medium Is an aromatic or aliphatic hydrocarbon In combination with an aliphatic alcohol, dimethyl formamlde or dimethyl sulfoxide.

4. A process as claimed In any of claims I to 3, wherein the catalyst Is an alkali-metal hydroxide or an alkali metal alcohol ate.

5. A process as claimed in claim.4, wherein the catalyst Is KOH, NaOH, potassium t-butoxlde, sodium t-butoxlde.

6. A process as claimed In any of claims I to 5, whenever effected In the presence of a drying agent,

7. A process as claimed In any of claims I to 6, wherein the starting compound ts ethyl -dlchlorodl henyl acetic acid and the product Is 4, 4' -dichlorobenzl lie acid ethyl ester.

8. Process for the production of lower-alkyl esters of dichlorobenzl I Ic acid, substantially as hereinbefore described and with reference to any of the Exam les.

9. Lower-alkyl esters of dichlorobenzl lie acid, whenever obtained by a process as claimed in any of claims I to 8.