...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Crystal growth & design >Polymorphism and Crystallization of p-Aminobenzoic Acid
【24h】

Polymorphism and Crystallization of p-Aminobenzoic Acid

机译：对氨基苯甲酸的多态性和结晶

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

p-Aminobenzoic acid (PABA) crystallizes in two different polymorphic forms:the alpha-polymorph,which is the commercially available form and appears as long,fibrous needles,and the beta-polymorph,which appears in the form of prisms.The thermodynamic stability and crystallization from different solvents have been studied experimentally.The system is found to be enantiotropic with a transition temperature of 25degC,below which the beta-form is the stable polymorph.The compound has been crystallized from 13 different solvents,either by slow cooling after which the product is allowed to mature in suspension,or by rapid cooling followed by immediate isolation.Needles were obtained from all solvents by both methods.In water and in ethyl acetate,at slow cooling below 20degC,the prismatic beta-form is obtained,however,often together with the needles.The beta-form crystals usually needed hours or days to grow at the very slow cooling used,while needles usually appeared in seconds.By careful control of supersaturation and temperature,cooling crystallization can be performed to produce the pure beta-form in water and in ethyl acetate.The influence of the solvent is explained by analysis of the crystal structures versus the possible interaction of the solvent molecules with the solute in solution.The alpha-form structure is governed by carboxylic acid dimers and is kinetically favored since it is believed that the corresponding dimers easily form in the solution,especially in less polar solvents.
机译：对氨基苯甲酸（PABA）结晶为两种不同的多晶型物：α-多晶型物（可商购并以长纤维针状出现）和β-多晶型物以棱柱形出现。热力学稳定性实验发现，该体系是对映体，其转变温度为25℃，在该温度以下，β型为稳定的多晶型物。该化合物已从13种不同的溶剂中结晶，然后通过缓慢冷却两种方法均可从所有溶剂中获得针。在水和乙酸乙酯中，于20℃以下缓慢冷却，可得到棱柱形β-型，但是，在使用非常缓慢的冷却后，β型晶体通常需要数小时或数天才能生长，而针状晶体通常在几秒钟内出现。过饱和度和温度的反应，可以进行冷却结晶，从而在水和乙酸乙酯中生成纯的β-型。通过分析晶体结构以及溶剂分子与溶质中可能的相互作用来解释溶剂的影响。 α-型结构由羧酸二聚体控制，在动力学上是有利的，因为据信相应的二聚体容易在溶液中形成，尤其是在极性较小的溶剂中。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号