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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >S-Oxygenation of Thiocarbamides I:Oxidation of Phenylthiourea by Chlorite in Acidic Media
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S-Oxygenation of Thiocarbamides I:Oxidation of Phenylthiourea by Chlorite in Acidic Media

机译：硫脲的S氧化I：酸性介质中亚氯酸盐对苯硫脲的氧化

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The oxidation of l-phenyl-2-thiourea (PTU) by chlorite was studied in aqueous acidic media.The reaction is extremely complex with reaction dynamics strongly influenced by the pH of reaction medium.In excess chlorite concentrations the reaction stoichiometry involves the complete desulfurization of PTU to yield a urea residue and sulfate:2C1O_2~-+PhN(H)CSNH_2+H_2O - SO_4~(2-)+PhN(H)CONH_2+2C1~-+2H~+.In excess PTU,mixtures of sulfinic and sulfonic acids are formed.The reaction was followed spectrophoto-metrically by observing the formation of chlorine dioxide which is formed from the reaction of the reactive intermediate HOC1 and chlorite:2C1O_2~-+HOC1+H~+ ->2ClO_2(aq)+Cl~-+H_2O.The complexity of the C1O_2~- - PTU reaction arises from the fact that the reaction of C1O_2 with PTU is slow enough to allow the accumulation of C1O_2 in the presence of PTU.Hence the formation of C1O_2 was observed to be oligooscillatory with transient formation of C1O_2 even in conditions of excess oxidant.The reaction showed complex acid dependence with acid catalysis in pH conditions higher than pK_a of HC1O_2 and acid retardation in pH conditions of less than 2.0.The rate of oxidation of PTU was given by -d[PTU]/dt = k_1[ClO_2~-][PTU]+k_2[HC1O_2]-[PTU] with the rate law:-d[PTU]/dt = [Cl(III)]_T[PTU]_0/K_(a1)+[H~+ ] [k_1K_a+k_2[H ~+]];where [C1(III)]_T is the sum of chlorite and chlorous acid and K_(a1) is the acid dissociation constant for chlorous acid.The following bimolecular rate constants were evaluated;k = 31.5+-2.3 M~(-1) s~(-1) and k_2 = 114+-7 M~(-1) s~(-1).The direct reaction of C1O_2 with PTU was autocatalytic in low acid concentrations with a stoichiometric ratio of 8:5;8C1O_2+5PhN(H)CSNH_2+9H_2O -> 5SO_4~(2-)+5PhN(H)CONH_2+8Cl~-+18H~+.The proposed mechanism implicates HOC1 as a major intermediate whose autocatalytic production determined the observed global dynamics of the reaction.A comprehensive 29-reaction scheme is evoked to describe the complex reaction dynamics.
机译：研究了在酸性介质中亚氯酸盐对l-苯基-2-硫脲（PTU）的氧化作用，该反应极其复杂，反应动力学受反应介质pH值的影响很大;亚氯酸盐浓度过高时，反应化学计量会完全脱硫PTU产生尿素残基和硫酸盐：2C1O_2〜-+ PhN（H）CSNH_2 + H_2O-SO_4〜（2-）+ PhN（H）CONH_2 + 2C1〜-+ 2H〜+ .PTU过量时，亚硫酸的混合物分光光度法通过观察反应性中间体HOC1和亚氯酸盐：2C1O_2〜-+ HOC1 + H〜+-> 2ClO_2（aq）+的反应形成二氧化氯的形成来进行反应。 Cl〜-H_2O.C1O_2〜--PTU反应的复杂性是由于C1O_2与PTU的反应足够缓慢以至于在PTU存在下C1O_2的积累，因此观察到C1O_2的形成即使在氧化剂过量的情况下，也会发生短暂的C1O_2振荡。反应在高于HC1O_2的pK_a的pH条件下表现出复杂的酸依赖性和酸催化作用，而在低于2.0的pH条件下酸阻滞。PTU的氧化速率为-d [PTU] / dt = k_1 [ClO_2〜-] [PTU] + k_2 [HC1O_2]-[PTU]的变化率定律为：-d [PTU] / dt = [Cl（III）] _ T [PTU] _0 / K_（a1）+ [H〜+] [k_1K_a + k_2 [H〜+]];其中[C1（III）] _ T为亚氯酸盐和亚氯酸之和，K_（a1）为亚氯酸的酸离解常数。评估以下双分子速率常数; k = 31.5 + -2.3 M〜（-1）s〜（-1）和k_2 = 114 + -7 M〜（-1）s〜（-1）.C1O_2与PTU的直接反应是在低酸浓度下自动催化的。化学计量比为8：5; 8C1O_2 + 5PhN（H）CSNH_2 + 9H_2O-> 5SO_4〜（2-）+ 5PhN（H）CONH_2 + 8Cl〜-+ 18H〜+。生产确定了观察到的反应的整体动力学。提出了一个综合的29反应方案来描述复杂的反应动力学。

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