The benzoin condensation is a synthesis of benzoin from benzaldehyde, catalyzed by cyanide.  For years, cyanide was the only catalyst used for the reaction. More recently, it was found that thiamine a much safer alternative, could be used as well. The newer synthesis is a common experiment in organic chemistry laboratory courses. The aim of our project is to add variety to the synthesis and extend the characterization of the benzoin condensation currently in use in organic chemistry courses. Our work investigates synthesis of additional benzoin analogs from substituted benzaldehydes using thiamine catalysis. The benzoins formed were evaluated using standard analytical techniques (mp, IR, NMR). In addition, a qualitative and colorful redox analysis is performed. The redox analysis is based on the blue bottle experiment, where redox indicators catalyze the autoxidation of benzoin. The reactions involve reversible color changes in solution when the redox dyes are oxidized or reduced. For example, when benzoin analogs are tested with indigo carmine, a reversible cycle of color changes begins: the green solution turns red and then to yellow within 1-2 minutes. Shaking the solution induces the reverse process. Incorporating autoxidation into analysis provides an entertaining educational experience of organic redox chemistry.

Green synthesis of substituted benzoin analogs and qualitative analysis with redox indicators for organic chemistry laboratory

253rd National Meeting (2017)

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