Kinetics and mechanism of methanolysis and cyclization of 1-acyl-3-(2-halo-5-nitrophenyl)thioureas
Kinetics and mechanism of methanolysis and cyclization of 1-acyl-3-(2-halo-5-nitrophenyl)thioureas
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DOI：
10.1002/poc.351
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发表时间：
2001-03-01
影响因子：
1.8
通讯作者：
Sterba, V
中科院分区：
文献类型：
--
作者：
Sedlák, M;Hanusek, J;Sterba, V
研究了甲氧基离子催化1-酰基-3-（2-卤-5-硝基苯基）硫脲在25℃甲醇溶液中的溶解动力学和氟衍生物的环化动力学。环化反应是用硫脲的硫阴离子取代氟，分两步进行。对于乙酰基衍生物，第一步是甲醇分解，第二步是慢得多的2-氟-5-硝基苯基硫脲阴离子的环化，形成2-氨基-5-硝基-1,3-苯并噻唑。对于苯甲酰衍生物，第一步是将苯甲酰基平行甲醇分解并环化成2-苯甲酰氨基-5-硝基-1,3-苯并噻唑。当甲醇钠浓度高于0.01 mol l（-1）时，所有酰基卤代硫脲的溶解率均降低；当甲醇钠浓度高于0.4 mol l（-1）时，除环化产物外，其他产物的生成增加。18-冠-6加入后，不形成副产物，氟衍生物的环化反应明显加快。溶解反应的减慢和环化反应的加速很可能是由于离子的形成。版权所有John Wiley & Sons， Ltd。
The kinetics of methoxide ion-catalysed solvolysis of 1-acyl-3-(2-halo-5-nitrophenyl)thioureas and cyclization of fluoro derivatives were studied in methanol at 25 degreesC. The cyclization involved the substitution of fluorine by sulphur anion of thiourea and proceeded in two steps. With the acetyl derivative, the first step is methanolysis and the second step is much slower cyclization of the 2-fluoro-5-nitrophenylthiourea anion formed to give 2-amino-5-nitro-1,3-benzothiazole. With the benzoyl derivative, the first step involves parallel methanolysis of the benzoyl group and cyclization to 2-benzoylamino-5-nitro-1,3-benzothiazole. At concentrations of sodium methoxide higher than ca 0.01 mol l(-1) the rates of solvolyses of all the acyl halothioureas decreased and at concentrations higher than ca 0.4 mol l(-1) there was an increase in the formation of other product(s) than the product of cyclization. After the addition of 18-crown-6, the side products were not formed and the cyclizations of fluoro derivatives were considerably accelerated. The slowing of the solvolytic reaction and acceleration of the cyclization reaction are most probably due to the formation of dianions. Copyright (C) 2001 John Wiley & Sons, Ltd.