Preparation method of phthalide

The invention belongs to the technical field of chemistry and chemical engineering, and particularly relates to a preparation method of phthalide. The preparation method comprises the following steps: dissolving o-toluic acid in absolute ethyl alcohol, adding sulfuryl chloride, carrying out substitution reaction by taking azodiisobutyronitrile as a catalyst, and removing ethyl alcohol after the reaction is completed, so as to obtain o-methylchlorobenzoic acid; taking methylbenzene as a solvent, and carrying out cyclization reaction on the o-methylchlorobenzoic acid and caustic soda liquid to obtain phthalide. The raw materials are low in price and easy to obtain in the market, o-toluic acid does not belong to dangerous chemicals and is high in safety, the preparation method is simple in process and high in yield which reaches 93%, and the purity of the prepared phthalide is high and reaches 99%. 本发明属于化学化工技术领域，具体涉及一种苯酞的制备方法。所述制备方法包括以下步骤：将邻甲基苯甲酸溶于无水乙醇，加入硫酰氯以偶氮二异丁腈为催化剂，进行取代反应，反应完成后脱去乙醇，获得邻甲基氯苯甲酸；以甲苯为溶剂，所述邻甲基氯苯甲酸