Mascavage Article Explains Hoffmann-Schiff Dichotomy on Nitrogen Basicity

By Purnell T. Cropper | September 21, 2010

Dr. Linda M. Mascavage, Associate Professor of Chemistry, co-authored an article on “The Hoffmann-Schiff Dichotomy: on the Reaction Between Chloral and Amines” in ARKIVOC—Free Journal of Organic Chemistry (ARKIVOC Journal 2010 (viii) 278-284), with John Tierney of Pennsylvania State University and Philip E. Sonnet and David R. Dalton of Temple University.

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In their abstract, the authors write, “In the nearly two centuries since the discovery of chloral (2,2,2-trichloroacetaldehyde), numerous nitrogenous reactants have been used to generate products resulting from attack at the carbonyl group by nitrogen. The resulting tetrahedral species, a carbinolamine, is often unstable and has been reported to lose water to produce an imine as well as to lose chloroform to produce an amide. We find that the path, and hence the product, is a function of the electron density at the nitrogen of the reacting amine. The weaker arylamines produce imine whilst the more strongly basic alkylamines produce amide.”

They conclude, “The long-standing Hoffmann-Schiff dichotomy is explained on the basis of nitrogen basicity. Thus, for the reaction of chloral with weak bases such as arylamines, the weakly held proton on nitrogen is lost along with the carbinol OH forming water and yielding imines. Additionally, the aryl group permits delocalization of electron density as the imine forms. Stronger bases, such as alkylamines, bind the proton on nitrogen more strongly and so lose chloroform to yield formamides. The delocalization of nitrogen lone pair electron density helps stabilize the forming Nalkylamide.” Read the entire article.