The adductive crystallization is an effective method of purifying aromatic dicarboxylic acids. In this paper crystallizations of three phthalic acids (tere;ortho-,iso-) in six organic solvents were investigated by spectrophotometries, TGA and XRD, respectively. The results show that, for terephthalic acid (TA), three of its crystallization products in six solvents are normal TA crystals, while the other three are the adducts that containing both TA and solvent in crystals, and among them only TA-dimethyl acetylamide (DMAC) and TA-N-methyl pyrrolidone (NMP) adducts exhibit a high selectivity to TA. XRD shows that, in the adduct crystals, each TA molecule connects two solvent molecules tied by O-H...O hydrogen-bonding. Crystallizations of tere-,ortho-,iso-phthalic acids in DMAC demonstrate different behaviors, that both TA and IPA can form adducts with DMAC, while OPA could not. The reason can be explained by the different roles of hydrogen-bonds, that the joint force between TA/IPA and solvents is the inter-molecule hydrogen-bonding which is stronger than the joint force between OPA and DMAC because OPA has an intra-molecule hydrogen-bond which results in weakening the joint force with solvents and therefore could not form a steady adduct with solvents.%加合结晶是一种新型的结晶分离方法.对三种芳香羧酸(对、邻、间苯二甲酸,TA、OPA、IPA)在6种溶剂中的结晶物质进行了分光光度法测定、热重分析和XRD表征,发现TA在6种溶剂中的结晶3种是普通结晶,3种是溶剂与溶质-同析出的加合结晶,其中又只有TA-二甲基乙酰胺(DMAC)、TA-N-甲基吡咯烷酮(NMP)两种加合结晶对溶质具有高度的选择性.XRD表明加合物晶体是一个TA分子与两个溶剂分子通过O-H…O的氢键作用形成的结晶体.3种芳香羧酸在溶剂DMAC中的结晶状态有很大差别:TA、IPA都能与DMAC形成加合物晶体,OPA与DMAC难以形成加合物.其原因是:TA/IPA与溶剂分子之间的结合属分子间氢键,作用较强;OPA带有分子内氢键,与溶剂的作用弱,不能形成稳定的加合物晶体.
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