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Der zweistufige Carbanion‐Mechanismus der Fragmentierung von 3‐Aminopropylbenzoaten. Fragmentierungs‐Reaktionen. 25. Mitteilung
Author(s) -
Grob C. A.,
Unger F. M.,
Weiler E. D.,
Weiss A.
Publication year - 1972
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19720550221
Subject(s) - chemistry , carbanion , medicinal chemistry , benzoates , protonation , fragmentation (computing) , dimethylamine , organic chemistry , ion , computer science , operating system
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.