Introduction to Deamination Mechanisms

In an earlier review (Zollinger, 1994, Chapt. 8) we explained that the dediazoniation of aromatic diazonium ions to aryl cations and dinitrogen, or to aryl radicals and dinitrogen in the presence of suitable electron donors, is based primarily on the high stability of N2. Analogous aliphatic diazonium ions show similar behavior, but the existence of diazenides (R —Nf) and diazoalkanes also opens the possibility of generating carbanions, e.g., in the Wolff-Kishner reduction and related reactions (see the classic book of Cram, 1965, and the monographs of Staley, 1985, and Buncel and Durst, 1980-1987), and carbenes (see Chapt. 8 of this book). 

The primary products of dediazoniations of all types (except AnDn) are extremely reactive and undergo secondary reactions with relatively low activation barriers. Accordingly, the selectivity of these transient intermediates in consecutive steps is also low. A multitude of final products is formed in most cases. 

The immediate molecular neighborhood of these species is much more productdetermining than in intermediates with lower reactivity. For example, counterions have a greater influence in consecutive steps than similar ions in the bulk solution. It was shown by isotope labeling that the transient intermediates react preferentially with the water molecules formed during deamination steps rather than with molecules in the bulk water. 

Diazo Chemistry II Aliphatic, Inorganic and Organometallic Compounds. By Heinrich ZoUinger Copyright 1995 VCH Verlagsgesellschaft mbH ISBN 3-527-29222-5 

As mentioned in Section 1.1, the first diazotization of amines, followed by dediazoniation, was carried out by Piria in 1848, well before Griess discovered and isolated aromatic diazo compounds (1858). Piria added an impure HNO3 —HCl solution to a mixture of asparagine and aspartic acid in water and obtained malic acid (7-1). It was not possible for Piria, however, to realize that the primary reaction products were diazonium ions. Yet, Piria s process was one of the few types of reaction via aliphatic diazonium ions that became important for synthetic purposes, after Ingold s group (Brewster et al., 1950) discovered that a-amino acids undergo clean retentive deamination (see Sect. 7.7). 

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