Diazo Preparation via Dehydrogenation of Hydrazones with “Activated” DMSO.

Abstract

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Optimization of continuous-flow diphenyldiazomethane synthesis: an integrated undergraduate chemistry experiment

“…The small amount of product was obtained as a crystalline solid and the NMR spectra did not show any starting material or major impurities. The NMR and IR spectra (available as Supporting Information) corresponded to literature [3,40]. We conclude that the purified product should in principle be clean enough for further use in synthetic applications.…”

“…Although assessing the yield and purity of diazo compounds is notoriously difficult [3,39], we attempted to purify an amount of continuous-flow product for further characterization by NMR and IR spectroscopy. The small amount of product was obtained as a crystalline solid and the NMR spectra did not show any starting material or major impurities.…”

“…As such, in the context of chemical education, it can even be used to teach undergraduate students how to observe properly, how to take notes of observations in their laboratory notebook and to think about the meaning of observations and scientific evidence in general. & Have students synthesize their own hydrazone, either benzophenone or an alternative, such as the ones mentioned by Javed and Brewer [3,4] according to procedures such as described in [41,42]. In our lab, one couple of students have successfully synthesized acetophenone hydrazone and subsequently observed at least partial successful conversion into the corresponding methylphenyldiazomethane ((1-diazoethyl)benzene).…”

“…Apart from losses due to purification itself, the pure compounds are unstable and may present safety problems. Determining the yield in another manner is not trivial [3,39]; standard options are measuring the nitrogen evolution upon the addition of acid or quantifying a derivative such as an ester that can be formed upon the addition of a Fig. 5 Two depictions of the response surface of the corrected absorbance as a measure for relative conversion of 1 into 2.…”

“…In 2013, we realized that this same reaction could also be used to convert benzophenone hydrazone (1, Fig. 1) to diphenyldiazomethane (2) [3,4], This reaction is more appealing from a didactic viewpoint, for several reasons: & the product is a relatively stable diazo compound: a chemically interesting type of compound [5,6], attractive to students, but not frequently encountered in undergraduate education; & the mechanism of the formation of the product (Fig. 2B) differs sufficiently from that of the commonly encountered aldehyde or ketone analogues (Fig.…”