Patent ID: 7491834

Claim:
A process for the preparation of 3-isochromanone which comprises the steps of: a) partially chlorinating o-tolylacetic acid with sulphuryl chloride or chlorine gas in an inert organic solvent in the presence of a free radical initiator to form a reaction mixture containing 2-chloromethylphenylacetic acid and unreacted o-tolylacetic acid; b) (i) treating the reaction mixture from step (a) with an aqueous salt-forming base to convert the 2-chloromethylphenylacetuic acid to 3-isochromanone and to form a salt of the unreacted o-tolylacetic acid; or (ii) extracting the 2-chloromethylphenylacetic acid and o-tolylacetic acid from the reaction mixture from step (a) at high pH with a strong aqueous base to give an aqueous solution of an o-tolylacetic acid salt and a 2-hydroxylmethylphenylacetic acid salt, acidifying the aqueous extract to convert the 2-hydroxymethylphenylacetic acid salt to 3-isochromanone and the o-tolylacetic acid salt to o-tolylacetic acid, and, in the presence of an added water-immiscible organic solvent, adjusting the pH with a salt-forming base to reconvert the o-tolylacetic acid to an o-tolylacetic acid salt; c) separating the 3-isochromanone from the salt of o-tolylacetic acid obtained in step (b) by a phase separation technique, the 3-isochromanone being dissolved in a water-immiscible organic solvent and the o-tolylacetic acid salt being dissolved in an aqueous solution; and d) converting the separated o-tolylacetic acid salt to o-tolylacetic acid by controlled acidification of the aqueous solution separated in step (c) to a pH of 4 or below, extracting the o-tolylacetic acid so formed into a solvent suitable for use in step (a) and recycling the solvent extract in a subsequent operation of step (a).