Acceptor properties of metal halides. Part VI. Metal halides as catalysts for the acylation of β-naphthol by acetyl chloride in diethyl ether

Abstract

The acylation of β-naphthol by acetyl chloride catalysed by gallium chloride, aluminium chloride, stannic chloride, trichlorophenyltin, and antimony trichloride has been studied kinetically, in diethyl ether solutions, at 25 °C. For all the catalysts the reaction is of the first order in β-naphthol and in acetyl chloride. The reaction order in catalyst depends upon the system: with gallium and stannic chlorides it is first, with aluminium chloride a mixture of first and second, with trichlorophenyltin second, and with antimony trichloride third. The reaction mechanism is discussed, and the high orders interpreted as representing stabilisation of the acylating species by polar catalyst–ether adducts.

The stannic chloride-catalysed reaction has also been studied in the presence of hydrogen chloride, of acetic acid, and of water. Hydrogen chloride leads to some increase in reaction rate, probably owing to solvation of the acylating species by hydrogen chloride–ether adducts. Addition of water, however, decreases the reaction rate; the reduction corresponds to the formation of 1SnCl₄:2H₂O adducts. Addition of acetic acid does not affect the reaction rate.

Molecular weight determinations show that stannic chloride and antimony trichloride are monomeric in ether.