Accelerated decomposition of benzoyl peroxide in the presence of sulfides and disulfides
Accelerated decomposition of benzoyl peroxide in the presence of sulfides and disulfides
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硫化物和二硫化物存在下过氧化苯甲酰的加速分解
DOI：
10.1021/jo00983a020
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发表时间：
1972
影响因子：
3.6
通讯作者：
H. Bickley
中科院分区：
文献类型：
--
作者：
W. Pryor;H. Bickley
过氧化苯甲酰（BPO）在脂肪族硫化物或二硫化物存在下分解速度加快。对甲基硫化物的影响最为显著：在四氯化碳中0.5 M的甲基硫化物使BPO的消失速率常数比纯CC14提高了约104，并且BPO在纯甲基硫化物中以爆炸速度分解。通过使用自由基清除剂、氧、可聚合烯烃和不可聚合烯烃进行的一系列实验表明，这些反应是离子过程。硫化物和二硫化物分别被氧化为亚砜或亚硫酸硫。在一个或多个这样的反应中分离出的其他产物包括苯甲酸、苯甲酸酐、烯烃、苯甲酰氧基硫化物和多硫化物。这些反应在二硫或硫化物中是一级反应，在过氧化物中是一级反应。我们提出了所有这些反应的机制，其中BPO的0-0键受到硫化合物的亲核攻击，产生存在于两个共振结构2和3中的中间体1。我们在中间体的描述中包含了非离子结构3，因为从CCh到甲醇作为溶剂的变化只产生了11倍的速率提高，比完全离子反应的预期效果要小。中间的1可以分解成若干条路径。例如，苯甲酸盐离子对羰基碳的攻击产生苯甲酸酐和亚砜，对a氢的攻击产生乙烷和苯甲酸。该系统与文献中类似的工作进行了比较和对比。在使用小浓度的相当无效的硫化合物的情况下，一些BPO经历正常的均解，与离子分解不竞争。因此，探究这种均裂是否会由于含硫化合物的存在而加速发生是很有趣的。文献中的一些研究表明，这种辅助均解可能是预期的。然而，关于苯乙烯在BPO和二硫化物存在下聚合速率的数据表明，该体系中的所有自由基都是由BPO的正常单分子分解产生的，没有发生辅助均解。并给出了硫化物对过苯甲酸叔丁酯、过丙酰、过月桂酰、过氧叔丁酯和硝基苯基偶氮三苯甲烷分解速率的影响。过氧化苯甲酰（BPO）在脂肪族硫化物或二硫化物存在下分解速度加快。对甲基硫的影响最为显著：CC14中0.5 M的甲基硫使BPO的分解速率比纯CC14提高了104，并且BPO在纯甲基硫中以爆炸性的速度分解。我们研究的含硫化合物（表1）包括RSR和RSSR类型的化合物，其中R=
Benzoyl peroxide (BPO) decomposes at an accelerated rate in the presence of aliphatic sulfides or disulfides. The effect is most dramatic for methyl sulfide: 0.5 M methyl sulfide in carbon tetrachloride increases the rate con-stant for BPO disappearance by about 104 over that forpure CC14, and BPO decomposes with explosive speed in neat methyl sulfide. These reactions have been shown to be ionic processes by a series of experiments using free-radical scavengers, oxygen, and polymerizable and nonpolymerizable olefins. The sulfides and disulfides are oxi-dized to the sulfoxide or thiolsulfinate, respectively. Other products that have been isolatedin one or more of these reactions include benzoic acid, benzoic anhydride, olefin, an-benzoyloxy sulfide, and polysulfides. The reactions are first order in disulfide or sulfide, and first order in peroxide. We suggest a mechanism for all of these reactions in which the 0-0 bond of BPO undergoes nucleophilic attackby the sulfur compound to produce an intermediate 1 which exists in two resonance structures, 2 and 3. We have included the nonionic structure 3 in the description of the intermediate since the change from CCh to methanol as solvent produces a rate enhancement of only a factor of 11, a smaller effect than would be expected for a totally ionic reaction. The intermediate 1 can decompose by a number of paths. For example, attack by the benzoate ion on the carbonyl carbon produces benzoic anhydride and the sulfoxide, and attack on the a hydrogen produces an ylide and benzoic acid. This system is compared and contrasted with similar work in the literature. In cases where a small concentration of a rather ineffective sulfur compound is used, some of the BPO undergoes normal homolysis incompetition with the ionic decomposition. It is interesting, therefore, to inquire whether this homolysis might occur at an accelerated rate due to the presence of thesulfur compound. Several studies in the literature suggest that such an assisted homolysis might be expected. 8-6 Data on the rate of polymerization of styrene in the presence of BPO and di-sulfides, however, show that all of the radicalsin this system are produced by the normal, unimolecular decompo-sition of BPO, and no assisted homolysis occurs. Some data on the effectof sulfur compounds on the rate of de-composition of terf-butyl perbenzoate, propionyl peroxide, lauroyl peroxide, fert-butyl peroxylate, and-n-nitrophenylazotriphenylmethane also are given.Benzoyl peroxide (BPO) decomposes at an accel-erated rate in the presence of aliphatic sulfides or di-sulfides. The effect is mostdramatic for methyl sul-fide: 0.5 M methyl sulfide in CC14 increases the rate of BPO decomposition by 104 over that for pure CC14, and BPO decomposes at an explosive rate in pure methyl sulfide. The sulfur compounds which we have studied (Table I) include compounds of the type RSR and RSSR where R=