Electrochemical preparation of branched unsaturated dinitriles

The preparation of branched unsaturated dinitriles as the major products (along the branched saturated dinitriles as the by-products) is achieved by electrolytic coupling of unsaturated mono nitriles in acetonitrile. All dinitrile products have an odd number of carbons between the two nitrile groups. The starting aliphatic unsaturated nitriles include 2-pentenenitrile, 3-pentenenitrile, 2-butenenitrile and 3-methyl-2-butenenitrile.

BRIEF DESCRIPTION 
This invention relates to the preparation of branched unsaturated 
dinitriles having an odd number of carbon atoms between the cyano-groups 
having the formula 
##STR1## 
by the electrolytic coupling of aliphatic unsaturated nitriles having 4 or 
5 carbon atoms. The product of this process may be hydrogenated by known 
methods to produce unsaturated branched diamines that are useful in the 
preparation of barrier resins. 
As a by-product of the process a dinitrile of the formula: NCCH.sub.2 
CH(R)CH(R')CN is produced, where R is C.sub.2 H.sub.5 and R' is hydrogen, 
and when R is CH.sub.3, then R' is either hydrogen or CH.sub.3. 
BACKGROUND OF THE INVENTION 
The electrolytic coupling of nitriles to produce dinitriles is known. See 
for example Sloan U.S. Pat. Nos. 3,488,267, and also 3,193,480 to Baizer. 
The chemical formation of unsaturated dinitriles using precious metal 
catalysts is disclosed in U.S. Pat. Nos. 4,211,725 and 4,211,725 to Kluger 
et al. 
SUMMARY OF THE INVENTION 
The present invention is a process for the non-symmetric dimerization of an 
aliphatic unsaturated nitrile having 4 or 5 carbon atoms by passing a 
direct electric current between electrodes located in a non-aqueous 
reaction mixture containing the aliphatic unsaturated nitrile, and 
recovering an aliphatic unsaturated dinitrile in which there is an odd 
number of carbon atoms between the cyano-groups. 
Among the suitable starting aliphatic unsaturated nitriles are 
2-pentenenitrile, 3-pentenenitrile, 2-butenenitrile, and 
3-methyl-2-butenenitrile. 
The reaction mixture must contain a conductive compound (electrolyte).

DETAILED DESCRIPTION 
In a preferred embodiment the reaction mixture is a non-aqueous mixture of 
the aliphatic unsaturated nitrile having 4 or 5 carbon atoms, acetonitrile 
and an electron conducting compound (electrolyte) selected from the class 
consisting of tetrabutylammonium fluoroborate, LiClO.sub.4, CF.sub.3 
COONa, Ph.sub.4 BNa, and [(CH.sub.3).sub.2 N].sub.3 SBF.sub.4. The 
concentration of the electron conducting compound in the acetonitrile 
should be at least about 0.1 molar. The concentration of the aliphatic 
unsaturated nitrile having 4 or 5 carbon atoms in the reaction mixture can 
vary widely, but is usually present in the amount of about 1 to 10% by 
volume based on the total volume of the liquids in the reaction mixture. 
The desired reaction occurs at the cathode, and if desired an electrolytic 
cell having separated cathode and anode compartments may be employed. In 
the case of a separated cell the electrolyte in the anode compartment need 
not contain any of the aliphatic unsaturated nitrile. A suitable means for 
separation of the compartments is a glass frit diaphragm. 
The electrodes in the electrolytic cell may both be graphite, or the 
electrode that is connected as cathode may be platinum. 
The voltage in the cell should be in the range of 10 to 100 volts, and the 
amperage should be in the range of about 15 to about 70 milliamps. 
The reaction may be initiated at room temperature and at atmospheric 
pressure. 
The reaction is apparently initiated electrolytically, but is continued 
spontaneously, because the current efficiency is greater than 100%. 
The following example illustrates the invention. 
EXAMPLE 
Both compartments of a two-compartmented cell in which the compartments 
were separated by a medium glass frit diaphragm were filled with about 150 
ml of the following mixture 270 ml of acetonitrile, 30 ml 3-pentene 
nitrile, 9.5 gr tetrabutylammonium fluoroborate. Both electrodes were 
graphite rods (3/8 inch in diameter) and were immersed 3 inches in the 
solution. The two electrodes were connected to 30 volt direct current 
power supply. Initially the observed current was 28 milliamps. The current 
then increased to a maximum of 44 milliamps after one hour and dropped to 
36 milliamps, when the current was turned off after 145 minutes. 330 
coulombs passed through the reaction mixture. The catholyte solution was 
concentrated by vacuum distillation to remove most of the solvent, 
acetonitrile. Then a 50 ml of 10% solution of sodium bicarbonate was added 
to basicify acidic species and to allow a better two-phase separation. The 
solution was then extracted twice with diethylether. The etheral phase was 
washed twice with water and dried over magnesium sulfate, then filtered 
and concentrated by evaporation. The oily residue (10.8 grams) was 
distilled to afford 2.1 grams of product mixture which contained 3 main 
components, cis and trans-1,3-dicyano-2-ethyl-3-hexene, and 
1,3-dicyano-2-ethyl propane, in the percentages shown below. The current 
efficiency in this reaction is greater than 800%. 
##STR2## 
Similar results were obtained when a 1% solution of 2-pentene nitrile (3 ml 
in 297 ml of acetonitrile) was used and the electricity consumed was 33 
coulombs.