Processes for preparing pesticidal intermediates

Details Processes for preparing pesticidal intermediates Processes for preparing pesticidal intermediates

1998-12-01

2000-10-17

McKane, Joseph

Organic compounds -- part of the class 532-570 series

Organic compounds

Azo

5483641, 5483717, 558332, 5462754, 534770, 534771, 534581, C09B 7900, C09B 2942, C07D23102, C07D23104, C07C25300

Patent

active

061334324

DESCRIPTION:

BRIEF SUMMARY
The instant Application is A 371 of PCT/EP97/01036 filed on Mar. 3, 1997.
This invention relates to a process for preparing certain cyanomethylpropane derivatives and the use of these compounds in the synthesis of pesticides and pesticide intermediates.
Ethyl 2,3-dicyanopropionate was first prepared and characterised by Higson and Thorpe (J.Chem.Soc. 89, 1460 (1906)) who obtained the material in good yield (70-81%) by reaction of formaldehyde cyanohydrin with the sodium salt of ethyl cyanoacetate. Dickinson {J. Am. Chem. Soc. 82, 6132 (1960)} repeated this work. This method of preparing the dicyanopropionate suffers from a significant drawback in that it is first necessary to isolate the intermediate formaldehyde cyanohydrin. This highly water soluble cyanohydrin is obtained by lengthy continuous extraction and has a limited stability, often decomposing violently upon attempted distillation. Furthermore, this reaction requires care given the risk of formation of dimeric side-products. The preparation of dicyanopropionates has also been described by Whiteley and Marianelli (Synthesis (1978), 392) with the process leading to 2,3-disubstituted succinodinitriles from the cyanoacetate, an aldehyde (a 1 to 3 carbon alkylaldehyde or benzaldehyde) and potassium cyanide via 3-substituted-2,3- dicyanopropionates (which were not isolated). However, the yield decreases dramatically from isobutyraldehyde to acetaldehyde. In the same manner Smith and Horwitz (J. Am. Chem. Soc. 1949, 71, 3418) described the same reaction with a ketone with a yield of 70%. This prior art therefore teaches that yields improve with increasing size of group adjacent to the carbonyl group.
In one aspect the present invention seeks to provide a process for preparing cyanomethyl propane derivatives satisfying one or more of the following criteria:
Therefore the present invention provides a process for preparing a compound of formula (I): ##STR2## wherein R represents straight- or branched- chain alkyl having up to 18 carbon atoms; or a salt thereof; source thereof.
Preferably R represents straight- or branched-chain alkyl having from 1 to 6 carbon atoms and most preferably R represents ethyl.
Suitable salts of cyanide include metal salts and organic salts (e.g. tetra-alkylammonium cyanides such as tetrabutylammonium cyanide). Preferably the cyanoacetate of formula (II) reacts with an alkali or alkaline earth metal cyanide salt, with alkali metal cyanide salts being especially suitable for use in the present invention, particularly potassium cyanide or sodium cyanide. The product may conveniently be isolated as the alkaline earth metal or alkali metal salt. Alternatively, the reaction mixture is acidified, for example with a mineral acid such as sulphuric acid or hydrochloric acid, to give the compound of formula (I). Where a compound of formula (I) above is desired (rather than a salt thereof) high yields are generally obtained when the reaction mixture is acidified without the addition of water. Whilst formaldehyde itself can be used in the reaction it is more convenient to use the polymerised form known as paraformaldehyde [(HCOH).sub.n ], available for example from Aldrich Chemical Company.
The reaction is generally performed using about 1 molar equivalent of a compound of formula (II); about 0.95 to 1.0 molar equivalents of cyanide salt, and about 1 molar equivalent of formaldehyde compound (based on the formaldehyde content).
The reaction may be carried out in the presence of a solvent. Preferably, the reaction is performed in a solvent medium which is usually an alcoholic medium or dimethyl formamide (DMF), N-methyl pyrrolidone (NMP), dioxan, tetrahydrofuran (THF) or dimethoxyethane. Especially preferred solvents are C.sub.1 -C.sub.6 alcohols such as methanol or, most preferably, anhydrous ethanol. Although the temperature of the reaction is not critical the reaction will normally be performed from about 0 to about 120.degree. C. or at the reflux temperature of the solvent. Generally best results are obtained by introducing the formaldehy

REFERENCES:
patent: 5232940 (1993-08-01), Hatton et al.
patent: 5451598 (1995-09-01), Salmon et al.
Smith et al, J. Am. Chem. Soc., 71, pp. 3418-3419 (1949).
Whiteley et al, Synthesis, pp. 392-394 (1978).
Higson et al, J. Chem. Soc. 89, pp. 1455-1472 (1906).
Dickinson et al, J. Am. Chem. Soc. 82, pp. 6132-6136 (1960).

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