University of Coimbra, CIEPQPF, Department of Chemical Engineering, Rua Sílvio Lima, Pólo II - Pinhal de Marrocos, 3030-790 Coimbra, Portugal.
University of Coimbra, CQC, Department of Chemistry, Rua Larga, 3004-535 Coimbra, Portugal.
Int J Biol Macromol. 2021 Jul 1;182:1681-1689. doi: 10.1016/j.ijbiomac.2021.05.175. Epub 2021 May 28.
Transesterification of starch with methyl betainate was studied for the first time, both in aprotic media and in solid state, and both under alkaline and acidic conditions. Betaine hydrochloride was first esterified in methanol, attaining a conversion of 86%. Starch was then converted into starch betainate in either N,N-dimethylformamide or dimethyl sulfoxide, and using sulfuric acid as catalyst or pre-activating the polymer in NaOH/ethanol. Furthermore, solid-state transesterification was carried out in a ball mill, for which sulfuric acid was replaced with the less corrosive sulfamic acid. Cationic starch esters were characterised by H and C NMR spectroscopy, infrared spectroscopy, thermogravimetric analysis, viscometry, optical microscopy (in water) and scanning electron microscopy (dry). In solution, the process attained degrees of substitution up to 0.4. No by-products, dehydration, oxidation or colouring were detected, but starch underwent severe depolymerization in wet media. In solid state, whilst the resulting degree of substitution was lower, degradation was minimal. In any case, transesterification, with its variety of possibilities, yields cationic starches that offer a promising alternative to conventional ethers.
首次在非质子介质和固态条件下，分别在碱性和酸性条件下研究了甜菜碱甲酯与淀粉的酯交换反应。首先将盐酸甜菜碱在甲醇中酯化，转化率达到 86%。然后，在 N,N-二甲基甲酰胺或二甲基亚砜中使用硫酸作为催化剂或在 NaOH/乙醇中预先激活聚合物将淀粉转化为淀粉甜菜碱。此外，在球磨机中进行了固态酯交换反应，其中硫酸被腐蚀性较小的氨基磺酸所取代。通过 H 和 C NMR 光谱、红外光谱、热重分析、粘度、光学显微镜（在水中）和扫描电子显微镜（干燥）对阳离子淀粉酯进行了表征。在溶液中，该过程的取代度可达 0.4。未检测到副产物、脱水、氧化或着色，但淀粉在湿介质中会发生严重的降解。在固态下，尽管取代度较低，但降解最小。在任何情况下，酯交换反应都能产生阳离子淀粉，为传统醚类提供了有前景的替代品。
