Fe(OH)_3催化苯酚羟基化反应

Hydroxylation of Phenol with Hydrogen Peroxide Catalyzed by Fe(OH)_3

以Fe(OH)3为催化剂催化苯酚进行羟基化反应,讨论了催化剂用量、反应温度、n(H2O2):n(苯酚)、反应时间等因素对苯酚羟基化反应的影响,并对反应诱导期和反应机理进行了初步的探讨。实验结果表明,苯酚羟基化反应经历诱导期和快速反应期两个阶段,诱导期后反应在很短的时间(小于3min)内完成,这种反应动力学特征可能是由于反应过程中的催化活性物种在诱导期为Fe(Ⅲ)/Fe(Ⅱ)redoxpair(自由基机理)、而在快速反应期为Fe(Ⅲ)与苯二酚的络合物(亲电取代机理)所致。在水20.0mL、苯酚1.880g、反应温度40～90℃、催化剂用量(占苯酚的质量分数)0.5%～4.0%、n(H2O2):n(苯酚)=0.80的条件下,苯酚的转化率达40.0%以上,苯二酚的选择性在88.0%左右。

Hydroxylation of phenol with H2O2 catalyzed by Fe （OH）3 was studied. Effects of catalyst dosage, reaction temperature, reaction time and mole ratio of H2O2 to phenol on the hydroxylation were investigated. The reaction induction period and reaction mechanism were discussed preliminarily. The hydroxylation reaction includes an induction period and a rapid reaction stage before completion. To rationalize the reaction kinetics a mechanism was suggested that a Fe （Ⅱ）/Fe （ Ⅲ） redox pair acts as active species（ involving a free radical mechanism） in the reaction induction period, and a complex consisted of ferric ion and diphenol acts as active species （involving an electrophilic substitution mechanism） in the rapid reaction stage. Under the condition： water as solvent 20.0 mL, phenol 1. 880 g, reaction temperature 40 - 90 ℃, dosage of Fe （OH） 3 as catalyst （ based on phenol mass） 0.5% - 4.0%, n （ H2O2 ） ; n （phenol） 0. 80, conversion of phenol is above 40.0% and selectivity to diphenol is about 88.0%.