Hillier, Kenneth (1972)
Chemical reactivity and hydrogen bonding in relation to hydroxyl group acylation in carbon tetrachloride.
Full text access: Open
A kinetic study was made of the reaction between phenols and carboxylic acid anhydrides in the presence of pyridine bases in carbon tetrachloride. Linear free energy relationships were applied and results are consistent with a general base catalysis, i.e. reaction via a pyridine/phenol hydro gen-bonded complex. Values were found for the Hammett reaction constant, the Bronoted reaction constant and the Taft (storic effects) reaction constant. The energy of activation was found for the reaction between p-chloro phenol and acetic anhydride with pyridine. The catalytic ability of bases, other than pyridine bases, was deteimined. The mechanism of the pyridine catalysis is discussed and a transition state proposed. Phenols do not react with carboxylic acid anhydrides in carbon tetrachloride in the absence of a base. Although 2-picoline and 2,6-lutidine have high pKa values, they do not catalyse this reaction because of steric effects and for this reason also, 2,6-lutidine inhibits aeylation in the presence of a catalytic pyridine base.At higher base concentrations, a fast reaction was observed between phenols and anhydrides in the presence of 2,6-lutidine, but this did not go to completion. At the low base concentrations used in the work above, this fast acylation accounts for only a small percentage of the reaction and no further esterification occurs. Results are consistent with a highly reactive phenol/2,6-lutidine dimer hydrogen-bonded complex or ion pair. Acetic acid inhibits this initial rapid reaction and the solvent does not significantly affect results. Acetylation of alcohols by acetic anhydride was studied in carbon tetrachloride. Alcohols containing intramolecular hydrogen bonds reacted slower than non-chelated alcohols.Reasons for this reduced reactivity are proposed.Preliminary experiments are reported for an esterification at a water-carbon tetrachloride boundazy.
This is a Accepted version
This version's date is:
is not peer reviewed
Deposited by () on
in Royal Holloway Research Online.Last modified on 01-Feb-2017
Digitised in partnership with ProQuest, 2015-2016.
Institution: University of London, Royal Holloway College (United Kingdom).