Process for the production of benzoyl cyanide (II)

Benzoyl cyanide is made by reacting benzoic anhydride with an alkali cyanide in an inert organic solvent.

BACKGROUND OF THE INVENTION 
The invention is directed to a process for the production of benzoyl 
cyanide by reaction of benzoic anhydride with an alkali metal cyanide. 
Benzoyl cyanide is an important intermediate product for the production of 
herbicides. 
It is known to produce benzoyl cyanide by the action of more than 
stoichiometrical amounts of copper (I) cyanide on benzoyl chloride. The 
reaction is carried out at temperatures up to 80.degree. C. in 
acetonitrile or benzonitrile or in ether with the addition of more than 
stoichiometrical amounts of lithium chloride or lithium iodide (Normant et 
al, Bull. Soc. Chim. France (1972) pages 2402-2403) or at temperatures of 
220.degree. to 230.degree. C. in the absence of a solvent (Org. Synth. 
Coll. 3, 112-114). At best these processes give a yield of 65%. 
It is also known to convert benzoyl chloride to benzoyl cyanide by means of 
an alkali cyanide in a two phase system consisting of water and a solvent 
which is immiscible with water in the presence of a quaternary alkyl 
ammonium salt (Koenig, Tetrahedron Letters No. 26 (1974), pages 2275 to 
2278). In this process the yield only amounts to 60%. 
Furthermore, it is known to produce benzoyl cyanide from benzoyl chloride 
by reaction with water free hydrogen cyanide and an at least equimolar 
amount of pyridine (Z. Phys. Chem. 192 (1943), 200-201). This process 
gives yields of 78%. 
A disadvantage of these known processes is that there are formed byproducts 
to a considerable extent, particularly the dimer of benzoyl cyanide (the 
benzoyloxy-phenyl malonitrile). Consequently, not only is the yield 
unsatisfactory but also its purity. Benzoyl cyanide can be separated from 
its dimer only with considerable difficulty and even then only 
incompletely. 
Finally, it is known to produce benzoyl cyanide by reaction of a mixture of 
benzoic anhydride and potassium cyanide at a temperature of 190.degree. C. 
(Erlenmeyer, Liebigs Ann. Chem. 287 (1895) 302 et seq., particularly pages 
305 to 307). This process merely results in a yield of 10%. 
SUMMARY OF THE INVENTION 
There has now been found a process for the production of benzoyl cyanide 
from benzoic anhydride and alkali metal cyanide characterized by carrying 
out the reaction in an inert organic solvent. According to this process it 
is possible to recover a pure benzoyl cyanide in a yield of at least 95%. 
To carry out the process of the invention, benzoic anhydride is reacted 
with alkali cyanide, preferably sodium cyanide or potassium cyanide, but 
there also can be used lithium cyanide. Generally it is suitable to use at 
least stoichiometrical amount of cyanide. Advantageously there is used 
about 1.05 to 2.0 equivalents of cyanide, especially 1.05 to 1.5 
equivalents of cyanide, per mole of benzoic anhydride. 
The reaction of the invention is carried out in an organic solvent which is 
inert to the reactants. As the solvent there can be used for example 
ethers, e.g., dioxane, dibutyl ether, dioxolane, ethylene glycol diethyl 
ether, ethylene glycol dibutyl ether, ethylene glycol dimethyl ether or 
esters, e.g., alkyl alkanoates such as butyl acetate, propyl acetate, amyl 
acetate, isobutyl acetate, octyl acetate, ethyl propionate, methyl 
butyrate, ethyl butyrate or methyl valerate. Especially suitable are 
hydrocarbons, e.g., aromatic hydrocarbons, such as ethyl benzene, 
mesitylene, cumene, p-cymene, t-butyl benzene or 1,3,5-triethyl benzene 
and especially benzene, toluene and xylene or aliphatic hydrocarbons such 
as ligroin with a boiling range of 90.degree. to 140.degree. C., octane or 
decane, or cyclic hydrocarbons such as cyclohexane, decalin and tetralin, 
or halogenated hydrocarbons, particularly chlorinated aromatic or 
aliphatic hydrocarbons such as chlorobenzene, dichlorobenzene, symmetrical 
tetrachloroethane, carbon tetrachloride, trichloroethylene, trimethylene 
bromide, ethylene dibromide. There can also be used mixtures of these 
solvents. 
The amount of solvent to be used depends to a certain extent on the type of 
solvent. Generally it is suitable to add at least about 100 ml of solvent 
per mole of benzoic anhydride. Advantageously there is used about 200 to 
5000 ml, particularly 300 to 1000 ml, of solvent per mole of benzoic 
anhydride. 
The reaction temperature in a given case depends on the type of solvent. 
Generally there are used temperatures of about 80.degree. to 200.degree. 
C., especially 100.degree. to 140.degree. C. 
Although the pressure can be selected essentially at random (i.e., it is 
not critical) in order to use a simple apparatus it is advantageous to use 
a pressure which does not vary substantially from normal pressure, e.g., 
to use atmospheric pressure. In many cases because of the presence of 
volatile substances it can be suitable to use an elevated pressure 
corresponding to the temperature. 
Unless otherwise indicated all parts and percentages are by weight. 
The materials employed can comprise, consist essentially of or consist of 
those set forth.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
EXAMPLE 1 
A mixture of 45.2 grams (0.2 mole) of benzoic anhydride, 12.3 grams (0.25 
mole) of sodium cyanide and 150 ml of chlorobenzene were held under reflux 
at the boiling point (about 135.degree. C.) for 4 hours. The mixture was 
then cooled and filtered off under suction. The residue, which essentially 
consisted of sodium benzoate was washed with chlorobenzene. The filtrate 
was brought to dryness at 16 mbar and a temperature up to 90.degree. C. 
There remained a yellow product which according to the infrared spectral 
analysis was pure benzoyl cyanide. The yield amounted to 25 grams, 
corresponding to 96% based on the benzoic anhydride employed. 
EXAMPLE 2 
The procedure was the same as in Example 1 but instead of chlorobenzene 
there were added 200 ml of xylene and the reaction was carried out at 
125.degree. C. The yield amounted to 25 grams, corresponding to 96%, based 
on the benzoic anhydride employed.