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探究了碱性条件下聚6-羟基己酸水解反应的机理和最优化工艺条件。实验过程中选用碱度较大的氢氧化钠及碱度较小的碳酸氢钠作为反应试剂。研究表明:碱度不同,其反应机理,反应工艺条件亦不同。碱度越大,OH~-浓度越大,亲核基团[OH~-]直接进攻聚6-羟基己酸的酯基结构,使酯基键发生断裂反应,生成小分子的6-羟基己酸;反应工艺条件缓和,在100℃的集热式恒温加热磁力搅拌器中既可完全解聚。碱度大的氢氧化钠参与反应的最优化工艺条件:氢氧化钠/聚6-羟基己酸摩尔比为4.4,乙二醇/聚6-羟基己酸摩尔比为6.5,水用量100g,催化剂0.1g,反应时间2h,反应温度100℃条件下,6-羟基己酸产率达到84.07%;碱度小的碳酸氢钠钠参与反应的最优化工艺条件:碱度越小,OH~-浓度越小,在反应初期亲核基团[-OCH_2CH_2OH]占主导地位,发生醇解反应的概率大,整个反应体系为醇解反应与水解反应相互促进进行;反应工艺条件苛刻,须在180℃密闭高压釜中完全解聚。碳酸氢钠/聚6-羟基己酸摩尔比为1.1,乙二醇/聚6-羟基己酸摩尔比为3,水用量100g,催化剂0.1g,反应时间1h,反应温度180℃~190℃条件下,6-羟基己酸产率达到90.38%。在整个反应系统中,乙二醇作为溶剂来使用。
The mechanism of hydrolysis of poly-6-hydroxycaproic acid under alkaline conditions and the optimum process conditions were explored. In the course of experiment, sodium hydroxide with a greater alkalinity and sodium bicarbonate with a lower alkalinity were selected as reaction reagents. Studies have shown that: different alkalinity, the reaction mechanism, the reaction process conditions are also different. The larger the alkalinity is, the larger the concentration of OH ~ - is. The nucleophilic group [OH ~ -] directly attacks the ester structure of poly 6-hydroxycaproic acid and cleaves the ester bond to form a small molecule 6-hydroxyhexyl Acid; reaction conditions to ease, at 100 ℃ heat collector heated magnetic stirrer can be completely depolymerization. Alkalinity of sodium hydroxide to participate in the reaction of the optimum conditions: sodium hydroxide / poly-6-hydroxycaproic acid molar ratio of 4.4, ethylene glycol / poly 6-hydroxy caproic acid molar ratio of 6.5, the amount of water 100g, the catalyst 0.1g, reaction time 2h and reaction temperature 100 ℃, the yield of 6-hydroxycaproic acid reached 84.07%. The optimum technological conditions of sodium bicarbonate with low alkalinity were as follows: the smaller the alkalinity, the lower the concentration of OH ~ - The smaller the number of nucleophilic groups [-OCH 2 CH 2 OH] is, the higher the probability of alcoholysis reaction occurs. The reaction system promotes the progress of alcoholysis and hydrolysis reaction. The reaction conditions are harsh and must be sealed at 180 ℃ Complete depolymerization in the autoclave. Hydroxybutyrate molar ratio of 1.1, ethylene glycol / poly 6-hydroxycaproic acid molar ratio of 3, the amount of water 100g, the catalyst 0.1g, the reaction time was 1h, the reaction temperature 180 ℃ ~ 190 ℃ conditions , The yield of 6-hydroxycaproic acid reached 90.38%. Ethylene glycol is used as a solvent throughout the reaction system.