Studies on the mechanism of toxicity of acetaminophen. Synthesis and reactions of N-acetyl-2,6-dimethyl- and N-acetyl-3,5-dimethyl-p-benzoquinone imines.

N-Acetyl-2,6-dimethyl-p-benzoquinone imine and N-acetyl-3,5-dimethyl-p-benzoquinone imine were prepared from 2,6-dimethylacetaminophen and 3,5-dimethylacetaminophen by oxidation with lead tetraacetate. Reaction of N-acetyl-2,6-dimethyl-p-benzoquinone imine with hydrochloric acid gave 3'-chloro-2',6'-dimethyl-4'-hydroxyacetanilide, whereas ethanethiol, aniline, and ethanol gave tetrahedral adducts resulting from addition to the imine carbon. Water gave 2,6-dimethyl-p-benzoquinone. With N-acetyl-3,5-dimethyl-p-benzoquinone imine, water and aniline gave substitution on the imine carbon, yielding 2,6-dimethyl-p-benzoquinone and 3,5-dimethyl-N-phenyl-p-benzoquinone imine, respectively. Ethanethiol gave 3'.5'-dimethyl-2'-(ethylthio)-4'-hydroxyacetanilide. The toxicity of 2,6-dimethylacetaminophen and 3,5-dimethylacetaminophen was examined histologically in mice and rats. 3,5-Dimethylacetaminophen was slightly more nephrotoxic but showed a similar hepatotoxicity to acetaminophen. 2,6-Dimethylacetaminophen, like N-methylacetaminophen, showed very little tissue damage.