Tosh B, Saikia C N, Dass N N
Regional Research Laboratory, Jorhat, Assam, India.
Carbohydr Res. 2000 Jul 24;327(3):345-52. doi: 10.1016/s0008-6215(00)00033-1.
Commercial rayon grade cellulose was dissolved in the lithium chloride-N,N-dimethylacetamide (LiCl-DMAc) solvent system and esterified with acetic anhydride using p-toluenesulfonyl chloride (p-TsCl) and pyridine as catalysts. The reaction temperature was varied from 28 to 70 degrees C and the time of reaction from 2 to 24 h. Full substitution took place at 60 and 70 degrees C at respective reaction times of 10 and 8 h for p-TsCl, and 10 and 6 h for pyridine. Esterification of cellulose followed a second-order reaction path. The rate constants at different reaction temperatures and the activation energy for the reaction are reported. Mechanisms for these reactions using the two catalysts are also suggested. The degrees of substitution (DS) of the esters prepared using both catalysts show that pyridine is a better catalyst than p-TsCl. Molecular weights of the esters, determined viscosimetrically, show that some degradation in the cellulose chain occurred at a reaction temperature of 70 degrees C. Hence, the optimum temperature for esterification appears to be 50-60 degrees C at 10 h reaction time to obtain full degree of acetyl substitution.
将商业人造丝级纤维素溶解于氯化锂 - N，N - 二甲基乙酰胺（LiCl - DMAc）溶剂体系中，并使用对甲苯磺酰氯（p - TsCl）和吡啶作为催化剂，用乙酸酐进行酯化反应。反应温度在28至70摄氏度之间变化，反应时间为2至24小时。对于p - TsCl，在60和70摄氏度下，分别在10小时和8小时的反应时间实现完全取代；对于吡啶，在60和70摄氏度下，分别在10小时和6小时的反应时间实现完全取代。纤维素的酯化反应遵循二级反应路径。报告了不同反应温度下的速率常数以及该反应的活化能。还提出了使用这两种催化剂的反应机理。使用两种催化剂制备的酯的取代度（DS）表明，吡啶是比p - TsCl更好的催化剂。通过粘度法测定的酯的分子量表明，在70摄氏度的反应温度下纤维素链发生了一些降解。因此，为获得完全乙酰取代度，酯化反应的最佳温度似乎是在50 - 60摄氏度下反应10小时。
