Correa N Mariano, Zorzan Daniel H, D'Anteo Loredana, Lasta Ermanno, Chiarini Marco, Cerichelli Giorgio
Dipartimento di Chimica Ingegneria Chimica e Materiali. Facoltà di Scienze MM FF NN, Università degli Studi dell'Aquila, L'Aquila 67100, Italy.
J Org Chem. 2004 Nov 26;69(24):8231-8. doi: 10.1021/jo049172v.
Kinetics of the reduction of 3-chloroacetophenone (CAF) with sodium borohydride (NaBH(4)) were followed by UV-vis spectroscopy at 27.0 degrees C in different reverse micellar media, toluene/BHDC/water and toluene/AOT/water, and compared with results in an isooctane/AOT/water reverse micellar system. AOT is sodium 1,4-bis-2-ethylhexylsulfosuccinate, and BHDC is benzyl-n-hexadecyl dimethylammonium chloride. The kinetic profiles were investigated as a function of variables such as surfactant and NaBH(4) concentration and the amount of water dispersed in the reverse micelles, W(0) = [H(2)O]/[surfactant]. In all cases, the first-order rate constant, k(obs), increases with the concentration of surfactant as a consequence of incorporating the substrate into the interface of the reverse micelles where the reaction takes place. The reaction is faster at the cationic interface than at the anionic one probably because the negative ion BH(4)(-) is part of the cationic interface. The effect of the external solvent on the reaction shows that reduction is favored in the isooctane/AOT/water reverse micellar system than that with an aromatic solvent. This is probably due to BH(4)(-) being more in the water pool of the toluene/AOT/water reverse micellar system. The kinetic profile upon water addition depends largely on the type of interface. In the BHDC system, k(obs) increases with W(0) in the whole range studied while in AOT the kinetic profile has a maximum at W(0) approximately 5, probably reflecting the fact that BH(4)(-) is part of the cationic interface while, in the anionic one, there is a strong interaction between water and the polar headgroup of AOT below W(0) = 5 and, above that, BH(4)(-) is repelled from the interface once the water pool has formed. Application of a kinetic model based on the pseudophase formalism, which considers the distribution of the ketone between the continuous medium and the interface and assumes that reaction takes place only at the interface, has enabled us to estimate rate constants at the interface of the reverse micellar systems. At W(0) < 10, it was considered that NaBH(4) is wholly at the interface and, at W(0) >/= 10, where there are free water molecules, also the partitioning between the interface and the water pool was taken into account. The results were used to evaluate CAF and NaBH(4) distribution constants between the different pseudophases as well as the second-order reaction rate constant of the reduction reaction in the micellar interface.
在27.0℃下，采用紫外可见光谱法跟踪了硼氢化钠（NaBH₄）还原3-氯苯乙酮（CAF）的动力学过程，该反应在不同的反胶束介质甲苯/BHDC/水和甲苯/AOT/水中进行，并与异辛烷/AOT/水反胶束体系中的结果进行了比较。AOT是1,4-双（2-乙基己基）磺基琥珀酸钠，BHDC是苄基正十六烷基二甲基氯化铵。研究了动力学曲线随表面活性剂浓度、NaBH₄浓度以及反胶束中分散水的量W(0)=[H₂O]/[表面活性剂]等变量的变化情况。在所有情况下，由于底物被纳入反应发生的反胶束界面，一级速率常数k(obs)随表面活性剂浓度的增加而增大。该反应在阳离子界面比在阴离子界面更快，这可能是因为负离子BH₄⁻是阳离子界面的一部分。外部溶剂对反应的影响表明，与芳香溶剂体系相比，异辛烷/AOT/水反胶束体系更有利于还原反应。这可能是由于BH₄⁻在甲苯/AOT/水反胶束体系的水池中含量更多。加水后的动力学曲线很大程度上取决于界面类型。在BHDC体系中，在所研究的整个范围内k(obs)随W(())的增加而增大，而在AOT体系中，动力学曲线在W(0)约为5时出现最大值。这可能反映了这样一个事实，即BH₄⁻是阳离子界面的一部分，而在阴离子界面中，在W(0)=5以下，水与AOT的极性头基之间存在强烈相互作用，而在W(0)>5时，一旦形成水池，BH₄⁻就会被排斥在界面之外。应用基于假相形式的动力学模型，该模型考虑了酮在连续介质和界面之间的分布，并假设反应仅在界面发生，这使我们能够估计反胶束体系界面处的速率常数。在W(0)<10时，认为NaBH₄完全处于界面，而在W(0)≥10时，存在自由水分子，同时也考虑了界面与水池之间的分配情况。这些结果用于评估CAF和NaBH₄在不同假相之间的分配常数以及胶束界面还原反应的二级反应速率常数。
