Study of a novel reaction between p-benzoquinone and resorcinol in aqueous solution
作者:Asok K. Mukherjee、Kalikinkar Datta
DOI:10.1039/ft9928800563
日期:——
The kinetics of the simultaneous formation and decay of the charge-transfer (CT) complex between p-benzoquinone (A) as acceptor and resorcinol (B) as donor have been studied in aqueous solution. At 550 nm, the wavelength of absorption of the complex alone, the variation of the absorbance of the system with time suggests the following reaction path: A + B [graphic omitted] AB [graphic omitted] product(s). The rate constants k1, k–1 and k2 have been found from an analysis of the absorbance data at different instants of time to be 0.25 min–1, 0.05 × 10–1 min–1 and 2.48 × 10–2 min–1, respectively, and the molar absorption coefficient of AB was found to be 543 ± 9.5 at the experimental temperature, 25 °C. The stability constant of the intermediate CT complex, AB, was found to be k1/k–1= 50, a value somewhat greater than that found in methanol where AB does not decay into other product(s). It has been shown that, according to the above reaction scheme, tmax, the time required to reach the maximum absorbance, should be independent of the initial concentration [A]0 of A with a fixed initial concentration [B]0 of B and that Amax, the absorbance of the intermediate CT complex at t=tmax should be directly proportional to [A]0 with a fixed [B]0. These theoretical predictions of the kinetics of the above reaction scheme have been verified experimentally with [A]0 and [B]0 of ca. 10–3 and 10–1 mol dm–3, respectively.Using aqueous solutions of A and B at concentrations of 10–2 and 10–1 mol dm–3 respectively, the product(s) could be isolated in solid form. The solid, however, could not be precipitated from mixtures of non-aqueous solutions of A and B at similar concentrations, where the coloured CT complex is formed instantaneously, and is stable, not showing a gradual disappearance of colour. The solid (P) obtained from the aqueous mixture was found by NMR studies in [2H6] dimethyl sulfoxide ([2H6] DMSO) to be a 1 : 1 resorcinol–p-benzoquinone molecular complex. This was further confirmed by some chemical tests in solutions of P in organic solvent and by conductometric titration of the solution of P in water–dioxan mixtures with Na2S2O3. Elemental (C, H) analysis of P also confirmed the 1 : 1 stoichiometry. The IR spectrum of the solid in the form of a KBr pellet showed that it is either an H-bonded adduct of one molecule of A and one molecule of B or an H-bonded polymeric chain A⋯B⋯A⋯B⋯.
研究了对苯醌(A)作为受体和间苯二酚(B)作为供体在水溶液中同时形成和衰减电荷转移(CT)复合物的动力学。在 550 纳米波长处,即复合物单独吸收的波长处,系统吸光度随时间的变化提示了以下反应路径:A + B [图略] AB [图略] 产物。通过分析不同时刻的吸光度数据,发现速率常数 k1、k-1 和 k2 分别为 0.25 min-1、0.05 × 10-1 min-1 和 2.48 × 10-2 min-1,并发现 AB 的摩尔吸收系数在实验温度 25 °C 时为 543 ± 9.5。发现 CT 中间复合物 AB 的稳定常数为 k1/k-1=50,该值略大于 AB 在甲醇中不会衰变为其他产物的稳定常数。研究表明,根据上述反应方案,在 B 的初始浓度[B]0 固定的情况下,达到最大吸光度所需的时间 tmax 应与 A 的初始浓度[A]0 无关,而在 t=tmax 时,中间 CT 复合物的吸光度 Amax 应与[B]0 固定的情况下的[A]0 成正比。实验验证了上述反应方案动力学的这些理论预测,[A]0 和 [B]0 的浓度分别约为 10-3 和 10-1 mol dm-3。然而,从浓度相似的 A 和 B 的非水溶液的混合物中却无法析出这种固体,在这种混合物中,彩色 CT 复合物是瞬间形成的,而且很稳定,不会出现颜色逐渐消失的现象。在 [2H6] 二甲基亚砜([2H6] DMSO)中进行的核磁共振研究发现,从水混合物中得到的固体(P)是 1 : 1 的间苯二酚-对-苯醌分子络合物。在有机溶剂中的 P 溶液中进行的一些化学测试以及用 Na2S2O3 对水-二恶烷混合物中的 P 溶液进行的电导滴定进一步证实了这一点。P 的元素(C、H)分析也证实了 1 : 1 的化学计量。KBr 粒状固体的红外光谱显示,它要么是一分子 A 和一分子 B 的 H 键加合物,要么是 H 键聚合链 A⋯B⋯A⋯B⋯。