Abstract:
Hydrogen bond assisted alkylation of phenols is compared
with the classical base assisted reactions. The influence of solvents on
the fluoride assisted reactions is discussed,· with emphasis on the
localization of hydrogen bond charge density. Polar aprotic solvents
such as DMF favour a-alkylation, and nonpolar aprotic solvents such as
toluene favourC-alkylation of phenol. For more reactive and soluble
fluorides, such as tetrabu~ylammoniumfluoride, the polar aprotic solvent
favours a-alkylation and nonpolar aprotic solvent favours fluorination.
Freeze-dried potassium fluoride is a better catalytic agent in hydrogen
bond assisted alkylation reactions of phenol than the oven-dried fluoride.
The presence of water in the alkylation reactions reduces the expected
yield drastically. The tolerance of the reaction to water has also been
studied. The use ofa phase transfer catalyst such as tetrabutylammonium
bromide in the alkylation reactions of phenol in the presence of potassium
fluoride is very effective under anhydrous conditions. Sterically
hindered phenols such as 2,6-ditertiarybutyl-4-methyl phenol could not be
alkylated even by using the more reactive fluorides, such as tetrabutylammonium
fluoride in either polar or nonpolar aprotic solvents. Attempts
were also made to alkylate phenols in the presence of triphenylphosphine
oxide.
