Benz But Doesn’t Break. Part I

I wanted to do a variation of the Benzaldehyde to Benzilic Acid synthesis as our final project. The premise was simple: We would use derivatives of benzaldehyde for the reaction. This is a common way to explore synthetic reactions. Many articles that feature synthetic reaction have dozens of experiments done by varying the structural characteristics of the reactants while retaining the same reactive functional group. I found that 4-methoxybenzaldehyde (p-anisaldehyde) and 4-methylbenzaldehyde (p-tolualdehyde) were inexpensive benzaldehyde derivatives. Coupling these reactants was not totally unknown in the literature but data was a little scarce. The self-coupling product of 4-methoxybenzaldehyde was called anisoin or 4,4′-dimethoxybenzoin.  The self-coupling product of 4-methylbenzaldehyde was called toluoin or 4,4′-dimethylbenzoin. James and Ippolito in an article entitled “Rearrangement of p, p’-Disubstituted Benzils” refer to two articles written in the German in 1881 and 1889 for their synthesis of 4,4′-dimethoxybenzoin and 4,4′-dimethylbenzoin respectively. Shacklett and Smith in “The Preparation of Substituted Benzilic Acids” refer to the literature synthesis of both of these compounds as well. Apparently, the 4,4′-dimethylbenzoin synthesis was done with the potassium cyanide catalyzed benzoin condensation methodology. Sumrell, Stevens, and Goheen in “Benzoin Condensation of Anisaldehyde” use potassium and sodium cyanide as a catalyst. Xu et al. in “Efficient and mild benzoin condensation reaction catalyzed by simple 1-N-alkyl-3-methylimidazolium salts” report on the synthesis of 4,4′-dimethylbenzoin.



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