酸度对林丹水解的影响

Influence of acidity on lindane hydrolysis

为了更好地理解林丹的环境行为,采用安瓿瓶-震荡器研究水体系,对不同酸度条件下林丹水解反应进行实验.结果表明,酸度是影响林丹转化速率的重要因素.以pH值～7.4为界分为两部分,pH值＜～7.4为酸性和中性催化,反应周期长(半衰期＞1000d),检测到的产物少(只有五氯环己烯),是与酸度无关的零级反应;pH值＞～7.4为碱性催化,随着pH值的升高,水解速率从pH8.30的0.0057d-1增加到pH12.02的46.58d-1, 是OH-的一级反应.在碱性条件下,产物的分布也与酸度相关,1,2,4-三氯苯和1,2,3-三氯苯是中间产物五氯环己烯和OH-的二级反应产物, 1,3,5-三氯苯的形成受pH值影响最大,从pH8.30的次要产物(1%)成为pH12.02的主要水解产物之一(18%).

Ampoule-shaker research system was employed to test the influence of acidity on lindane hydrolysis for better understanding its environmental behavior under the condition of different acidity. The results show that acidity is an important influence factor for the transformation rate of lindane, and divided into two parts with pH value ~7.4 as boundary. It is acidic and neutral catalysis when pH<~7.4 with long period (half-life>1000d) and only one product (pentachlorocyclohexene) is determined in test; and it is a zero-order-rate reaction not related with acidity. When pH>~7.4, it is a basic catalysis, the hydrolysis rate constant increases with rising of pH from 0.0057d-1 at pH 8.3 to 46.58d-1 at pH 12.02, and it is first-order-rate grade reaction of OH-; under basic condition the distribution of product is related with acidity. 1,2,4-trichlorobenzenne(TCB) and 1,2,3-TCB are the products of second-order-rate reaction between OH- and the medium product pentachlorocyclohexene. The formation of 1,3,5-TCB is influenced the most by pH value, and it is a minor product (1%) at pH 8.30 while a dominant one (18%) of hydrolysis at pH 12.02.