Forming aromatic compounds electrolytically

Abstract

Abstract Acyloxy derivatives of polynuclear aromatic compounds are made by electrolysing an anhydrous mixture of the aromatic compound e.g. naphthalene or methyl naphthalene, an alkanoic acid, the sodium salt of the acid, and preferably also the anhydride of the acid, which also acts as solvent. Where alkanoic acids of higher molecular weight are used, formamide, or acetonitrile may be added as solvent. Polynuclear aromatic compounds include naphthalene, and alkyl naphthalenes, phenanthrene, pyrene; indene; quinoline, dibenzopyridine, phenazine, and like 5 plus 6 ring compounds e.g. including coumarone and thi<\>aa naphthene. Suitable alkanoic acids are acetic, propionic, hexanoic acid and branched chain acids e.g. trimethyl acetic acid. The anode used is lead dioxide which suppresses side reactions, and is made by plating a carbon rod using a bath containing lead nitrate and a little copper nitrate, and neutralizing acidity by adding PbO to the bath at intervals. The number of acyloxy groups introduced into the aromatic nucleus is controlled either by duration of electrolytic treatment i.e. quantity of power applied, or by adjusting the concentration of the alkali salt. When 1/4 of the aromatic compound is consumed the product consists of the mono-derivative; at 1/2 consumption both mono- and diforms are present, and by continuing electrolysis (or increasing C.D.) the higher products are made. A graph of this relationship is given. Alternatively, with a concentration of the sodium salt at 5-20 g.p.l., the dicompound is suppressed, but at double this concentration the dicompound is pre-dominant. In examples, a mixture of 8 g. sodium acetate, 25.6 g. naphthalene, 60 c.c. of glacial acetic acid and 60 c.c. of acetic anhydride are electrolysed using the PbO2 anode and a graphite or metal cathode, in an inert atmosphere. The anode may be rotated or submitted to ultrasonic vibration. A current of 1.5A at 47V is applied for 160 minutes. The product is 56% naphthalene, 29% naphthyl acetate, 8% naphthalene diolacetate, and the balance higher acetates. By increasing the sodium acetate content to 16.4 g., the product contains 5% of the mono-derivative and 23% of the di-derivative. Naphthalene is removed by sublimation, and the residue extracted and fractionated. Other examples describe tri- and tetraforms.

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