Benz But Doesn’t Break. Part III

The thiamine catalyzed coupling reaction of 4-methylbenzaldehyde created an off-white solid product. Upon analysis the product contained one to three different peaks in the GC-FID that corresponded to the coupled products. After the oxidation step was completed, one of the three peaks remained. It is reasonable to conclude that the peak after oxidation was 4,4’-dimethylbenzil. It is also reasonable that one of the three peaks is 4,4’-dimethylbenzoin. The GC-MS confirmed this assumption. One peak was a C16H16O2 (240 m/z) and another at C16H14O2 (238 m/z). The third peak was at 224 m/z which could correspond to C16H16O. With proton NMR mixed samples had a peak at 4.236 ppm which was easily distinguished from the sp3 methine of 4,4’-dimethylbenzoin which shows up at 5.924 ppm. Carbon NMR of mixed samples had a C/CH2 peak at 45 ppm which was easily distinguished from the sp3 methine of 4,4’-dimethylbenzoin which shows up at 75.8 ppm. The only reasonable explanation for the third peak was 4-4’-dimethyl deoxybenzoin [1,2-di(4-methylphenyl)ethanone].

DMbenzoin_GC-FID01

DMbenzoin_NMR01

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