Der zweistufige Carbanion-Mechanismus der Fragmentierung von 3-Aminopropylbenzoaten. Fragmentierungs-Reaktionen. 25. Mitteilung

✍ Scribed by C. A. Grob; F. M. Unger; E. D. Weiler; A. Weiss

• Publisher: John Wiley and Sons
• Year: 1972
• Tongue: German
• Weight: 631 KB
• Volume: 55
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19720550221

✦ Synopsis

Abstract

The unsubstituted and p‐substituted benzoates 2b–2e of 3‐dimethylamino‐2,2bis(p‐nitrophenyl)‐propanol (2a) undergo quantitative fragmentation in 80% ethanol yielding 1,1‐bis(p‐nitrophenyl)‐ethylene (5) besides formaldehyde and dimethylamine, the hydrolysis products of the imonium ion 3. The corresponding alcohol 2a, however, yields 2,2‐bis(p‐nitrophenyl)‐ethanol (9) in addition to fragmentation products. Conversely, no fragmentation is observed with the benzoates 6b–6e of 3‐dimethylamino‐2,2‐diphenylpropanol (6a) which lack electronwithdrawing substituents in the β‐phenyl groups.

These results are in agreement with a two‐step carbanion mechanism (Scheme 2) involving the ionization of the aminoalkohol 2a and its esters 2b–2e to the imonium ion 3 and the carbanions 4a–4e. The latter undergo competitive cleavage, recombination and protonation to 5, 2 and 9, respectively, depending on the nucleofugal activity of –X.

These conclusions are supported by the first‐order rate constants for the benzoates 2b–2e which differ merely by a factor of three. Since the p‐substituents in the benzoate groups have only a minor effect on the reaction rate the bonds to the nucleofugal groups are not appreciably broken in the rate determining step.