The initial step in the metabolic transformation of toluene to
benzoic acid, after oral administration, appears to be
hydroxylation of toluene to benzyl alcohol (Fig. 1) by the
microsomal mixed-function oxidase system. In rats, rabbits, and
man, approximately 20% of the dose is excreted unchanged via the
lungs, while approximately 80% is converted to benzoic acid and
excreted in the urine unchanged or as its glycine conjugate,
hippuric acid. Furthermore, it has been found that toluene is
excreted as benzylmercapturic acid in smaller quantities in rats.
Small amounts of benzoic acid may be conjugated with glucuronic