Choice of suitable micellar catalyst for 2,2′-bipyridine-promoted chromic acid oxidation of glycerol to glyceraldehyde in aqueous media at room temperature
作者:Aniruddha Ghosh、Rumpa Saha、Kakali Mukherjee、Sumanta K. Ghosh、Pintu Sar、Susanta Malik、Bidyut Saha
DOI:10.1007/s11164-013-1415-6
日期:2015.5
The micellar catalyzed 2,2′-bipyridine (bipy)-promoted oxidation of glycerol to glyceraldehyde by chromic acid is investigated under the criteria [glycerol]T ≫ [Cr(VI)]T at 30 °C. The critical micellar concentrations values of the three representative surfactants, N-cetylpyridinium chloride (CPC), sodium dodecyl sulphate (SDS), and TX-100, are determined by conductometric and spectrophotometric methods. The oxidized product glyceraldehyde is identified by 2,4-DNP test and FTIR spectral measurement. The pseudo-first-order rate constants (k obs, s−1) are calculated from the slope of plots of ln(A 450) versus time (t) which are linear. From these plots, the kinetic parameter k eff values are calculated and the k eff value of SDS-catalyzed bipy-promoted reaction path was found to be highest among all the combinations. In the bipy-promoted oxidation path, Cr(VI)–bipy complex is the main active oxidant which undergoes attack by the substrate to form the product. The active oxidant Cr(VI)–bipy complex reacts with glycerol to form a ternary complex which undergoes redox decomposition in a rate-limiting step. Here, the anionic surfactant SDS and the neutral surfactant TX-100 both catalyze the reaction in the presence of bipy, whereas the cationic surfactant CPC and neutral surfactant TX-100 inhibit the reaction in the absence of bipy. SDS is found to be the most suitable micellar catalyst for the bipy-promoted chromic acid oxidation of glycerol.
在[甘油]T ≫ [Cr(VI)]T 条件下,研究了在 30 ℃ 下铬酸催化 2,2′-联吡啶(bipy)将甘油氧化成甘油醛的胶束催化过程。通过电导和分光光度法测定了三种代表性表面活性剂 N-十六烷基氯化吡啶(CPC)、十二烷基硫酸钠(SDS)和 TX-100 的临界胶束浓度值。氧化产物甘油醛通过 2,4-DNP 测试和傅立叶变换红外光谱测量进行鉴定。伪一阶速率常数(k obs,s-1)是根据 ln(A 450)与时间(t)的线性斜率图计算得出的。根据这些曲线图计算出动力学参数 k eff 值,发现在所有组合中,SDS 催化的双促进反应路径的 k eff 值最高。在双促进氧化路径中,Cr(VI)-bipy 复合物是主要的活性氧化剂,它在底物的攻击下生成产物。活性氧化剂 Cr(VI)-bipy 复合物与甘油反应形成三元复合物,在限速步骤中发生氧化还原分解。在这里,阴离子表面活性剂 SDS 和中性表面活性剂 TX-100 都能在双酚存在的情况下催化反应,而阳离子表面活性剂 CPC 和中性表面活性剂 TX-100 则能在双酚不存在的情况下抑制反应。研究发现,SDS 是最适合用于联吡促进的甘油铬酸氧化反应的胶束催化剂。