论文部分内容阅读
对羟基苯甲酸酯又名尼泊金酯,对霉菌、酵母菌有较强的抗菌作用,本身具有毒性较低、无刺激性、不受酸碱影响、化学性质稳定等特点,已广泛应用于食品、化妆品、日用化工品、饲料和药物等领域中,是安全有效的防腐剂[1～2]。目前许多生产对羟基苯甲酸酯的企业仍采用传统的浓硫酸催化酯化法合成,其优点在于硫酸可溶于反应体系,使酯化反应在均相中进行,反应条件缓和。李玲珍[3～4]等用浓硫酸在最佳工艺条件下合成对羟基苯甲酸乙酯、丁酯的最高产率分别达到95%和97.6%。但浓硫酸催化酯化缺点也非常明显:反应时间长,醇、浓硫酸用量大;产品色泽变深;醚化、氧化、磺化等副反应多;对设备腐蚀性强;催化剂不能回收重复利用,废液污染环境。因此近十年来越来越多的研究者寻找可代替浓硫酸的环境友好催化剂,诸如固体超强酸、杂多酸、固载杂多酸、对甲基苯磺酸以及简单无机盐等。作者调研了近十年来的国内文献发现,固载杂多酸和简单无机盐具有更多的优点和良好的催化性能,前者催化酯化反应时间短、催化剂用量少,后者简单易得价廉[5]。本课题组选择硫酸氢钾为催化剂合成了各种对羟基苯甲酸脂肪酯,同时研究了硫酸氢钾的重复使用性能。
Parabens, also known as parabens, have a strong antibacterial effect on molds and yeasts. They are inherently less toxic, non-irritating, free from acid and alkali, and chemically stable. They are widely used It is a safe and effective preservative in the fields of food, cosmetics, household chemicals, feed and medicine [1 ~ 2]. At present, many companies producing p-hydroxybenzoates still use the traditional esterification of concentrated sulfuric acid for esterification. The advantage is that sulfuric acid is soluble in the reaction system and the esterification reaction proceeds in a homogeneous phase, and the reaction conditions are mild. Li Lingzhen [3 ~ 4] and other concentrated sulfuric acid synthesis of p-hydroxybenzoate under the best process conditions, the highest yield of butyl 95% and 97.6%. But the esterification of concentrated sulfuric acid catalytic shortcomings are also very obvious: long reaction time, alcohol, concentrated sulfuric acid dosage; product color darker; etherification, oxidation, sulfonation and other side effects; corrosion of the equipment; catalyst can not be recycled and reused Waste water pollutes the environment. Therefore, more and more researchers in recent ten years have been looking for environment-friendly catalysts that can replace concentrated sulfuric acid, such as solid superacid, heteropolyacid, heteropolyacid, p-toluenesulfonic acid and simple inorganic salts. The authors investigated the domestic literature over the past decade and found that the supported heteropoly acids and simple inorganic salts have more advantages and better catalytic properties. The former catalyzes the esterification reaction time is short, the catalyst dosage is small, the latter is easy to get the price Lian [5]. The group selected potassium hydrogen sulfate as a catalyst for the synthesis of a variety of fatty acid esters of p-hydroxybenzoate, while the reuse of potassium bisulfate performance.