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Concerning the weakness of intramolecular general acid catalysis in the hydrolysis of vinyl ethers. o ‐carboxy‐α‐methoxy‐β,β‐dimethylstyrene
Author(s) -
Kresge A. J.,
Yin Y.
Publication year - 1988
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610010502
Subject(s) - chemistry , intramolecular force , vinyl ether , hydrolysis , ether , catalysis , acid catalysis , intramolecular reaction , medicinal chemistry , organic chemistry , carboxylic acid , ketone , polymer chemistry , copolymer , polymer
The rate of hydrolysis of the aromatic vinyl ether o‐carboxy‐α‐methoxy‐β,β‐dimethylstyrene was found to be accelerated 25‐fold by ionization of its carboxylic acid group, but the effective molarity which may be calculated if all of this rate acceleration is ascribed to intramolecular general acid catalysis is only EM = 1 · 1 m. This is similar to the small effective molarities found before for intramolecular catalysis by carboxylic acid groups of aliphatic vinyl ethers, which shows that, unlike the situation in other intramolecular reactions, e.g. ketone enolization, the extra rigidity of aromatic over aliphatic systems does not improve the efficiency of intramolecular catalysis in vinyl ether hydrolysis. It is suggested that this behaviour is the result of reduced conjugation between the vinyl ether group and the aromatic ring in the transition state of the vinyl ether hydrolysis reaction, which retards the rate and offsets any improvement effected by increased rigidity of the aromatic system.