Thiosemicarbazones (TSCs) are traditionally synthesized using an alcoholic solvent and refluxed for as long as four hours.1 Our group previously developed a greener synthesis for 20 TSCs but several of the TSCs did not result in pure products. Our improved greener synthesis still uses a lactic acid and water solvent system, but now includes a brief heating period on a water bath at 85OC and agitation of the mixture using a spatula. After heating for up to 20 minutes, the reaction mixture is allowed to cool in an ice bath, filtered, and then allowed to dry overnight. This procedure was optimized for eight TSCs, and consistently results in 80-90 % yield. For example, we previously attained yields of 58 % for salicylaldehyde TSC and 27 % for p-chloroacetophenone TSC, two previously problematic TSCs. Quantitative 1H NMR determined water to be the chief impurity, typically present between 10-15 %. We are now able to consistently yield over 85 %, with an 11 percent impurity of water for salicylaldehyde TSC, and 83 % for p-chloroacetophenone TSC with a 11 % water impurity. Note: the NMR solvent used was DMSO-d6 and some (perhaps all) of this water comes from the solvent itself, as our melting points are very sharp for these compounds. We are currently working on a method to remove water from DMSO-d6 that would be practical for use in organic chemistry student laboratories. Analysis using 1H NMR and qualitative NMR (qNMR) revealed that our syntheses consistently produced high yields, &gt;85 %, and purities, up to 90 %, for all other TSCs.

Improved greener synthesis of thiosemicarbazones

253rd National Meeting (2017)

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