Benzene used to be a common solvent in organic chemistry, but is no longer used because it is a suspected carcinogen. Benzene undergoes metabolic oxidation by cytochrome P450 enzymes to form an electrophilic epoxide which can alkylate proteins and DNA. Toluene is also oxidized by cytochrome P450 enzymes, but the metabolite is less toxic and is rapidly excreted. Suggest what the metabolite might be and why the metabolism of toluene is different from that of benzene
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Toluene is less toxic than benzene because the methyl group of toluene is easily oxidised to non-carcinogenic benzoyl alcohol (95 – 96%) in presence of enzyme cytochrome P450, and only 4 – 5 % is converted to carcinogenic epoxide. Hence it is less toxic. The benzoyl alcohol is further oxidised to benzoic acid and hippuric acid that are excreted in urine.
However benzene on oxidation in presence of cytochrome P450 enzymes is completely converted to carcinogenic epoxide ion. The epoxide ion further undergoes reaction to form different carcinogens. Hence benzene is more carcinogenic than toluene