PROCESS FOR THE PREPARATION OF DIHALOVINYL COMPOUNDS

Abstract: Dihalovinyl compounds, many of which are useful in the preparation of pyrethroid insecticide, and having the general formula: wherein R¹ represents an optionally-substituted cyclopropyl or an optionally-substituted alkyl group, R² a methyl group or a hydrogen atom or R¹ and R², together with the carbon atom to which they are attached jointly form a cycloalkylidene group, and each Hal stands for a chlorine or bromine atom, are prepared by a process wherein a dihalophosphite of the general formula: wherein R¹, R² and Hal have the same meaning as in formula I and Q represents a halogen atom, and is contacted with zinc in the absence of an alkanoic acid with fewer than 5 carbon atoms per molecule.

Description: PROCESS FOR THE PREPARATION OF DIHALOVINYL COMPOUNDS This invention relates to a process for the production of dihalovinyl compounds. Some of these compounds may be employed as intermediates in the manufacture of pyrethroids which is an important group of new pesticides having outstanding insecticide properties coupled with a low mammalian toxicity. Many pyrethroids contain a dihalovinyl group and thus the present invention is of considerable use in the manufacture of such pyrethroids. According to Coll. Czech. Chem. Comm. 24 (1959) 2230-2236 3-methyl-i -trichloromethyl-2-butenyl acetate and 3-methyl-I -tri- chloromethyl-3-butenyl acetate can be converted with zinc and acetic acid into 1 , 1-dichloro--methyl-1 , 3-pentadiene and 1,1-dichloro-4- methyl-1,4-pentadiene, respectively. Surprisingly it has nowbeen found that certain esters afford dihalovinyl compounds by reaction with zinc in the absence of an alkanoic acid. Accordingly, the invention provides a process for the preparation of a dihalovinyl compound of the general formula: EMI1.1 wherein R1 represents an optionally-substituted cyclopropyl or an optionally-substituted alkyl group, R2 a methyl group or a hydrogen atom or RÚ and Rê, together with the carbon atom to which they are attached jointly form a cycloalkylidene group, and each Hal stands for a chlorine or bromine atom, characterized in that a dihalophosphite of the general formula: EMI1.2 wherein RÚ, Rê and Hal have the same meaning as in formula I and Q represents a halogen atom, and is contacted with zinc in the absence of an alkanoic acid with fewer than 5 carbon atoms per molecule. The zinc is suitably employed as powdered zinc, for example zinc dust. The molar ratio of zinc to the dihalophosphite of formula II is not critical and may vary within a wide range, suitably between 1:1 and 10:1 and preferably between 1:1 and 5:1. The process is suitably carried out at a temperature in the range -200C to 100 C, for example 0 to 500C. Temperatures in the range 0 to 3500, are usually very suitable. Preferred dihalophosphites of formula II are those in which R1 represents an optionally-substituted cyclopropyl group, particularly an optionally 3-substituted 2,2-dimethylcyclopropyl group and R2 represents a hydrogen atom, because many of such compounds are intermediates in the preparation of pyrethroid insecticides. Among these compounds those in which P represents a 2-alkoxycarbonyl-3,3 -dimethylcyclopropyl group, in--which the alkoxy group has fewer than five carbon atoms, are preferred. This alkoxy group is preferably a methoxy or an ethoxy group; methoxy groups are most preferred. Other preferred dihalophosphites of formula II are those in which R1 represents a 2-( 2, 2-dimethoxyethyl )-3 , 3-dimetbylcyclopropyl group. Good results have also been obtained with dihalophosphites of formula II in which R represents an optionally-substituted alkyl group, particularly with fewer than ten carbon atoms. Examples of such alkyl groups are isopropyl, ethyl and methyl groups. Very suitable are dihalophosphites of formula II in which R represents a cyclopropyl-substituted methyl group, particularly a 2,2-dimethyl3-(2-oxypropyl)cyclopropylmethyl group. Q -in the group -PQ2 of formula II preferably represents a chlorine or bromine atom. Preferred dihalophosphites of formula II are 2,2 ,2-tribromo-1-( 2-ethoxycarbonyl-3 ,3-dimethylcyclopropyl)ethyl dichlorophosphite (compound 1) and 2,2,2-tribromo-1-(2-ethoxycarbonyl-3,3-dimethylcyclopropyl)ethyl dichlorophosphite (compound 2), as shown below. EMI2.1 The dihalophosphites of formula II can be obtained by reacting an alcohol of the general formula: EMI3.1 wherein R , R2 and Hal have the same meaning as in formula II, with a phosphorous trihalide. Alternatively they may be prepared by reacting a carbonate of the general formula: EMI3.2 wherein R , R2 and Hal have the same meaning as in formula I and M -represents an alkali metal atom, with a phosphorus trihalide to give a compound of formula II. The carbonates of formula II can be prepared by reacting a carbonyl compound of the general formula: EMI3.3 wherein RÚ and Rê have the same meaning as in formula III, with a trihaloacetate of the general formula: EMI3.4 wherein M and Hal have the same meaning as in formula III, under substantially anhydrous conditions and in the presence of a highly polar, aprotic, inert solvent. Suitable highly polar, aprotic, inert solvents include N,Ndimethylformamide, N,N-dimethylacetamide, dimethyl sulphoxide, hexamethylphosphorictriamide -/(CH3)2N/3PO-, tetrahydrothiophene 1,1 - 3 dioxide (also named "sulpholane"), 3-methyltetrahydrothiophene 1,1dioxide, N-methyl-2-pyrolidone and acetonitrile. The carbonates of formula III and the dihalophosphites of formula II and the dihalovinyl compounds of formula I are preferably prepared in the same reaction vessel or pot or sequence of reaction vessels or pots. Many common organic solvents possess some degree of polarity arising from asymmetry in their molecules, but an essential feature of the latter process is that the solvent should be "highly polar", a term used herein to denote the presence of a dielectric constant, measured at 250C, of at least 25. The term "aprotic" as used herein denotes a solvent which is free from hydrogen atoms that are able to form hydrogen bonds with anions. These definitions are in accordance with "Physical Chemistry of Organic Solvent Systems", edited by A.K. Corrington and T. Dickinson, Plenum Press (1973), pages 332 and 333. Thus, alcohols and glycols do not come within this definition since the hydrogen atom of the hydroxyl group(s) form a hydrogen bond with the negative oxygen atom of the starting aldehyde. Benzene, carbon tetrachloride, 1,2-dimethoxyethane and pyridine also do not come within the definition since they are not highly polar. Nitromethane is highly polar and aprotic but not inert. According to an aspect of the present invention, the dihalophosphite starting material of general formula II can be prepared by a process which comprises the reaction of a carbonyl compound of the general formula: EMI4.1 wherein R1 and R2 have the same meaning as in formula I with a trihaloacetate of the general formula: EMI4.2 wherein Hal has the same meaning as in formula I and M represents an alkali metal atom, under substantially anhydrous conditions and in the presence of a highly polar, aprotic, inert solvent, with formation of a carbonate of the general formula: : EMI4.3 wherein RÚ, R2 and Hal have the same meaning as in formula I and M has the same meaning as in formula V, followed by reaction of the carbonate of formula III with a phosphorus trihalide to give a compound of formula II. As mentioned above the route to the dihalovinyl compounds starting from the carbonyl compound of general formula IV has the advantage that it can be carried out in one reaction zone, under substantially similar reaction conditions, and without separating the intermediates of general formulaeIIand III. The following examples further illustrate the invention. Yields and purities were determined by nuclear magnetic resonance (NMR) spectroscopy. EXAMPLE I - Preparation of 1,1-dichloro-3-metbyl-1-butene An NMR tube was charged with isobutyraldehyde (0.59 mmol) and a solution of sodium trichloroacetate (o.6h mmol) in N,N-dimethylformamide (0.4 ml). After standing for 30 min. at 20 C - the solution then contained sodium 1,1,1-trichloro-3-methyl-2-butyl car bonate-phosphoroustrichloride (o.64 mmol) was added which caused an exothermic reaction with formation of 1,1,1-trichloro-3-methyl2-butyl dichlorophosphite. Then, zinc powder (0.96 mmol) was added and the mixture in the tube was shaken at 200C for 3 min. The title compound was obtained in a yield of 60%. EXAMPLE II - Preparation of ethyl trans 2-(2,2-dibromo vinyl)-3,3-dimethylcyclopropanecarboxylate A 25-ml flask provided with a magnetic stirrer and calcium chloride tube and placed in an ice bath was charged with a solution of ethyl trans 2-( 2,2, 2-tribromo-1-hydroxyethyl )-3 , 3-dimethylcyclo- propanecarboxylate (1.18 mmol) in N,N-dimethylformamide (5 ml) and then with phosphorus trichloride (1.30 mmol). After stirring for one hour - the solution then contained trans 2,2,2-tribromo-1-(2 ethoxycarbonyl-3 ,3-dimethylcyclopropyl) ethyl dichlorophosphite zinc powder (2.60 mmol) was added at OOC over a period of 40 min. Then, the reaction mixture was poured out in water (50 ml) and the mixture obtained was three times extracted with n-pentane (10 ml portions). The combined extract phases were twice washed with water (5 ml portions), the washed liquid was dried over anhydrous magnesium sulphate and the solvent was evaporated from the dried liquid at sub-atmospheric pressure, leaving a colourless oil of which the content of the title compound was more than 90%. The conversion of the starting ethyl ester was more than 95% with a selectivity to the title compound of more than 65%. The NMR spectrum of trans 2,2,2-tribromo-1-(2-ethoxycarbonyl 3,3-dimethylcyclopropyl)ethyl dichlorophosphite was recorded at 90 MHz and showed the following absorptions relative to a tetramethylsilane standard. #=1.24 ppm, singlet, CH3-C-CH3 6=1.38 ppm, singlet, CH3-C-CH3 6=1.24 ppm, triplet, 6=1.93 ppm, double doublet, C(O)O-CH2-CH3 CBr3-C-CH - J=5Hz (with the ring proton) and J=9Hz (with the side chain proton) 6=2.08 ppm, doublet, O=C-CH 6=4.50 ppm,- double doublet, CBr3-CH ; JpH = 11 Hz 6=4,14 ppm, multiplet, CH3-CH2

Claims: CLAIMS 1. Process for the preparation of a dihalovinyl compound of the general formula: EMI7.1 wherein R represents an optionally-substituted cyclopropyl or an optionally-substituted alkyl group, Rê a methyl group or a hydrogen 1 2 atom or R and R , together with the carbon atom to which they are attached jointly form a cycloalkylidenegroup, and each Hal stands for a chlorine or bromine atom, characterized in that a dihalophosphite of the general formula: EMI7.2 wherein R1 R and Hal have the same meaning as in formula I and Q represents a halogen atom, and is contacted with zinc in the absence of an alkanoic acid with fewer than 5 carbon atoms per molecule. R1 2. A process according to claim 1, characterized in that R re- presents an optionally-substituted cyclopropyl group and Rê is a hydrogen atom. 3. A process according to claim 2, characterized in that R represents a 2-alkoxycarbonyl-3,3-dimethylcyclopropyl group in which the alkoxy group has fewer than five carbon atoms. 4. A process as claimed in claim 2 or 3, characterized in that R represents a 2-( 2,2-dimethoxyethyl)-3 ,3-dimethylcyclopropyl group. 5. A process according to claim 1, characterized in that R represents an optionally-substituted alkyl group with fewer than ten carbon atoms. 6. A process according to any one of the preceding claims, characterized in that each of the two Q atoms in the group -PQ2 is a chlorine or bromine atom. 7. A process according to any one of the preceding claims, characterized in that the zinc is powdered zinc. 8. A process according to any one of the preceding claims, characterized in that the molar ratio of zinc to dihalophosphite of formula II is in the range 1:1 to 5:1. 9. A process according to any one of the preceding claims, characterized in that it is carried out at a temperature in the range of from -200C to 1000C. 10. A process according to any one of the preceding claims, characterized in that the starting dihalophosphite of the general formula II is prepared by reaction of a carbonyl compound of the general formula: EMI8.1 wherein R1 and R2 have the same meaning as in formula I with a trihaloacetate of the general formula: EMI8.2 wherein Hal has the same meaning as in formula I and M represents an alkali metal atom, under substantially anhydrous conditions and in the presence of a highly polar, aprotic, inert solvent, with formation of a carbonate of the general formula: EMI8.3 wherein RÚ, Rê and Hal have the same meaning as in formula I and M has the same meaning as in formula V, followed by reaction of the carbonate of formula III with a phosphorus trihalide to give a compound of formula II.

Inventors: KRAMER, PETRUS ANTHONIUS, VERBRUGGE, PIETER ADRIAAN
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1980
Main classification: C07C69
IPC codes: C07C21, C07B61, C07C67, C07C17, C07C41, A01N53, C07C43, C07C69