The condensation of 3-hydroxy-4-methylbenzoic acid with aqueous formaldehyde and hydrochloric acid yields the lactone of 6-hydroxymethyl-1,3-benzodioxane-8-methyl-5-carboxylic acid. This dioxanylphthalide has also been produced in a similar type of condensation from 5-hydroxy-4-methylphthalide which can be obtained by demethylation with aluminum chloride of 5-methoxy-4-methylphthalide.Proof of the presence of the m-dioxane and phthalide rings in the condensation product has been obtained by opening these rings in succession. The action of alkaline permanganate opens the phthalide ring to yield a substituted phthalic acid. Acid hydrolysis then opens the m-dioxane ring with loss of formaldehyde and the formation of a new phthalide ring. Successive steps of decarboxylation, methylation, and oxidation of the new phthalide yield the known 3-methyl-4-methylphthalic acid.
3-羟基-4-甲基苯甲酸与水甲醛和盐酸的缩合反应产生6-羟甲基-1,3-苯并二噁烷-8-甲基-5-羧酸内酯。这种二噁烷酞环内酯也可以通过类似的缩合反应从5-羟基-4-甲基酞环内酯中制得,后者可以通过氯化铝去甲基化得到。通过逐步打开这些环来证明缩合产物中存在m-二噁烷和酞环。碱性高锰酸盐的作用打开酞环,产生取代酞酸。酸水解然后打开m-二噁烷环,失去甲醛并形成一个新的酞环。对新酞环的脱羧、甲基化和氧化的连续步骤产生已知的3-甲基-4-甲基酞酸。