Hanusek Jirí, Hejtmánková Ludmila, Sterba Vojeslav, Sedlák Milos
Department of Organic Chemistry, Faculty of Chemical Technology, University of Pardubice, 532 10 Czech Republic.
Org Biomol Chem. 2004 Jun 21;2(12):1756-63. doi: 10.1039/b401866d. Epub 2004 May 13.
Twelve new substituted S-(1-phenylpyrrolidin-2-on-3-yl)isothiuronium bromides and twelve corresponding 2-imino-5-(2-phenylaminoethyl)thiazolidin-4-ones have been prepared and characterised. Kinetics and mechanism of transformation reaction of S-[1-(4-methoxyphenyl)pyrrolidin-2-on-3-yl]isothiuronium bromide and its N,N-dimethyl derivative 5a into corresponding substituted thiazolidin-4-ones 2a and 6a have been studied in aqueous solutions of amine buffers (pH 8.1-11.5) and sodium hydroxide solutions (0.005-0.5 mol l(-1)) at 25 degrees C and at I= 1 mol l(-1) under pseudo-first-order reaction conditions. The kinetics observed show that the transformation reaction is subject to general acid-base, and hydroxide ion catalyses. Acid catalysis does not operate in the transformation of 1a; the rate-limiting step of the base-catalysed transformation is the decomposition of bicyclic tetrahedral intermediate In(+/-) and the Brønsted dependence is non-linear (pK(a) approximately 9.8). In the case of derivative 5a both base and acid catalyses make themselves felt. In the base catalysis, the rate-limiting step consists of the decomposition of bicyclic intermediate In, and the Brønsted dependence is linear (beta = 0.9; pK(a) > 11.5). The acid-catalysed transformation of 5a also proceeds via the intermediate In, and the reaction is controlled by diffusion (alpha approximately equal to 0). With compound 5a in triethylamine and butylamine buffers, the general base catalysis changes into specific base catalysis. The effect of substitution in aromatic moiety of compounds 1a-h and 3a-h on the course of the transformation reaction has been studied in solutions of sodium hydroxide (0.005-0.5 mol l(-1)) at 25 degrees C by the stopped-flow method. The electron-acceptor substituents 4-NO(2) and 4-CN do not obey the Hammett correlation, which is due to a suppression of cross-conjugation in the ring-closure step of the transformation reaction.
已制备并表征了12种新的取代S-(1-苯基吡咯烷-2-酮-3-基)异硫脲溴化物和12种相应的2-亚氨基-5-(2-苯基氨基乙基)噻唑烷-4-酮。研究了S-[1-(4-甲氧基苯基)吡咯烷-2-酮-3-基]异硫脲溴化物及其N,N-二甲基衍生物5a在25℃、I = 1 mol·L⁻¹的胺缓冲水溶液(pH 8.1 - 11.5)和氢氧化钠溶液(0.005 - 0.5 mol·L⁻¹)中在准一级反应条件下转化为相应取代噻唑烷-4-酮2a和6a的动力学及反应机理。观察到的动力学表明，转化反应受广义酸碱催化，氢氧根离子也有催化作用。酸催化在1a的转化中不起作用；碱催化转化的限速步骤是双环四面体中间体In(⁺/⁻)的分解，且布仑斯惕相关性是非线性的(pKₐ约为9.8)。对于衍生物5a，酸碱催化都有体现。在碱催化中，限速步骤是双环中间体In的分解，布仑斯惕相关性是线性 的(β = 0.9；pKₐ > 11.5)。5a的酸催化转化也通过中间体In进行，且反应受扩散控制(α约等于0)。在三乙胺和丁胺缓冲液中，化合物5a的广义碱催化转变为特定碱催化。通过停流法研究了化合物1a - h和3a - h的芳环部分取代基对25℃下氢氧化钠溶液(0.005 - 0.5 mol·L⁻¹)中转化反应进程的影响。吸电子取代基4 - NO₂和4 - CN不遵循哈米特相关性，这是由于在转化反应的闭环步骤中交叉共轭受到抑制。
