Benzyl bromide ions, decomposition

Quaternary ammonium salts are generally stable under neutral or acidic conditions up to 150°C, but decomposition can occur with the quaternary ammonium ion acting as an alkylating agent in its reaction with anions (Scheme 1.1). Soft nucleophiles, such as RS, are more reactive with tetra-n-butylammonium bromide and benzyltriethylammonium chloride, although the latter salt also C-benzylates phenyl-acetonitrile under basic conditions [46], These side reactions are considerably slower than the main catalysed reactions with, for example, a haloalkane and the amount of unwanted impurity in the final alkylated product is never greater than the amount of catalyst used (i.e. generally > 2%). Harder anions, e.g. R2N and RO, rarely react with the ammonium salts. 

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