Paradigms and Paradoxes: Diazomethane and Ethyl Diazoacetate: The Role of Substituent Effects on Stability

Abstract

Diazomethane and ethyl diazoacetate are highly reactive and highly versatile synthetic reagents that undergo numerous related reactions. However, while the former is highly dangerous because of its toxicity and explosive behavior; the latter is much more benign. This is usually ascribed to resonance stabilization in ethyl diazoacetate involving an extra carbonyl group that is absent in diazomethane, cf.

$$\begin{gathered} {\text{EtOOC}}---{\text{CH}} = {\rm N}^ + = {\rm N}^ - \leftrightarrow {\rm E}{\text{tOOC}}---{\text{CH}}^ - ---{\text{N}}^{\text{ + }} \equiv {\text{N}} \leftrightarrow {\text{EtOC(O}}^ - {\text{)}} = {\text{CH}}---{\text{N}}^{\text{ + }} \equiv {\rm N} \hfill \\ {\text{CH}}_{\text{2}} = {\rm N}^ + = {\rm N}^ - \leftrightarrow {\text{CH}}_{\text{2}}^ - ---{\text{N}}^{\text{ + }} \equiv {\rm N} \hfill \\ \end{gathered}$$

The additional resonance stabilization is derived using a recent literature measurement of the enthalpy of an ethyl diazoacetate/aldehyde reaction, key enthalpies of formation, also from the literature, and some simplifying assumptions. The resonance stabilization is deduced to be but 16 kJ/mol, merely 4 kcal/mol. But, oh how grateful we are for this!