Why are some organic compounds with benzene entirely safe to eat?

Answer 1

Some aromatic compounds are safe to eat because either they are not particularly well metabolised by the

liver

, and are not polar/reactive enough themselves to induce any particular damage - passing right through the body. Whilst in some cases they are metabolised by the liver to form more polar compounds, but these compounds themselves are not particularly toxic. Then you get to the aromatics that can be oxidised, forming compounds such as epoxides (three-membered ethers) and epoxy-diols. For example, the

polycyclic aromatic hydrocarbons

(PAHs) such as benzo[a]pyrene, a constituent in burnt toast, are metabolized in the liver by cytochrome P450-enzymes which convert them into epoxydiol derivatives. These derivatives are more polar and reactive, and can induce DNA damage through e.g. intercalation. It basically comes down to whether they are themselves reactive molecules, whether they can/cannot be oxidized by enzymes in the liver, and if they can, whether not they are formed in sufficiently large quantities that they pose a biological threat. You may have heard the term "pro-carcinogen". The PAHs are examples of these. In their unaltered states, they are not particularly harmful. It is only upon being converted by

cytochrome P450 enzymes

that they gain this carcinogenic character. Another interesting thing is considering benzene and toluene. Toluene is not a particularly noted carcinogen. It seems that the amount of active carcinogen that might be formed upon its oxidation is rather minimal.