Potassium cyanide, reaction with benzyl halides

The data for the reactions of potassium cyanide with benzyl halides at 85 C and 25 C are summarized in Tables I-III and graphical representations of these data are shown in Figures 1-3. The reactions carried out at 85 C were followed to 70% completion, while those at 25 C were followed to 50% completion. In general, excellent first-order kinetic plots were obtained. Each point on the graphs represents an average of at least three kinetic determinations. It is interesting to note that in the absence of added water (solid-liquid phase transfer catalysis), the rates of benzyl halide disappearance were more accurately described by zero-order kinetics. 

Potassium tellurocyanate, prepared from potassium cyanide and tellurium in DMSO, reacts with benzyl halides to produce benzyl tellurium cyanides in good yields. Because of the sensitivity of potassium tellurocyanate to oxygen and of some of the benzyl tellurium cyanides to light, the reactions must be carried out in an inert atmosphere (nitrogen or argon) under red light. 

Alkylation of Alkali Metal Cyanides by Alkyl Halides Activated in the a-Posi-tion by a Double Bond. When a mixture consisting of 4 to 8 moles of an alkyl halide activated in the apposition by a double bond is heated with 1 mole of alkali metal ferrocyanide, several alkylation products of the ferrocyanide anion can be isolated from the reaction mixture (12). The relative proportions of the tetra-, penta-, and hexaalkylated complexes can be varied by varying the alkyl halide to ferrocyanide ratio and the time of reaction. When potassium ferrocyanide is alkylated with benzyl bromide at a ratio of 4 alkyl halides to ferrocyanide anion, short reaction times favor the tetraalkylated complex an 8 to 1 ratio and long reaction times favor the hexaalkylated complex of the alkylating agents tested benzyl bromide provided the fastest alkylation ... 

The transformation of alkyl halides with cyanides (equation 1) represents not only the classical route to nitriles, but, if modified properly, is still of very great practical importance even today. A whole series of review articles stress the scope and value of this reaction. Although the substituent R may be varied to a large extent, the primary as well as the benzylic halides generally give higher yields than secondary and tertiary ones, as, with the latter, the formation of alkenes gains in importance. This side reaction as well as the undesired formation of alcohols and ethers, which sometimes takes place in aqueous media or with alcohols as solvent, is of course due to the basicity of the cyanide ion. Under deleterious conditions one may even observe carboxylic acids, which result fi-om the hydrolysis of the nitriles. - Some of these undesired side reactions may be avoided by the use of CuCN instead of sodium or potassium cyanide. ... 

Halides can be converted into cyanides. Thus, the reaction of benzyl bromide in toluene with potassium cyanide, catalysed by alumina, on sonication gives the substitution product, viz. benzyl cyanide in 76% yield. In the absence of ultrasound alkylation is the preferred pathway (Scheme 4). The difference is because ultrasound forces cyanide into the surface of alumina, enhancing cyanide nucleophilicity and reducing the lewis acid character. 

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