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The Carbocation: A Forgotten Lewis Acid Catalyst
Author(s) -
Naidu Veluru Ramesh,
Ni Shengjun,
Franzén Johan
Publication year - 2015
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201500225
Subject(s) - carbocation , lewis acids and bases , catalysis , chemistry , lewis acid catalysis , acid catalysis , selectivity , reactivity (psychology) , photochemistry , organic chemistry , medicinal chemistry , medicine , alternative medicine , pathology
Abstract A Lewis acid that has received negligible attention as a catalyst is the carbocation. The carbocation is isoelectronic to boron and owes its Lewis acidity to a low‐lying empty p C orbital. In terms of reactivity and stability carbocations are very versatile Lewis acids, from the extremely unstable methylium cation to the water‐stable tris( N , N ‐dimethylaniline) methylium ion (crystal violet). Although the Lewis acid properties of carbocations have been extensively studied since the discovery of the tropolium ion more than 130 years ago there is only a handful examples on the application of carbocations as Lewis acid catalysts. Herein, the research on triarylmethylium (trityl)‐cation catalysis is summarized. In light of the reports the trityl ion emerges as a highly efficient and highly versatile Lewis acid catalyst capable of catalyzing different classes of reactions often with high selectivity and low catalyst loadings (for some reactions down to ppm levels).