苯酚羟基化合成苯二酚反应过程中酚焦油的生成机理

对铁基复合氧化物催化苯酚羟基化合成苯二酚反应过程中酚焦油的生成机理进行了研究。苯酚羟基化反应是典型连串反应,模拟研究表明,苯二酚比苯酚更容易氧化,且邻苯二酚比对苯二酚更易缩合生成酚焦油。对苯二酚进一步氧化生成对苯醌和4,4′-二羟基二苯醚,后者为氧化缩合产物。对苯醌能够氧化邻苯二酚生成邻苯醌,自身被还原为对苯二酚,邻苯醌不稳定在热水中很快降解。反应液中残留催化剂对苯二酚氧化缩合生成酚焦油具有促进作用。对废催化剂沉积酚焦油、蒸馏所得酚焦油进行了分析,结果表明,废催化剂上所含酚焦油热失重峰在320℃左右,含有C=O 结构物质,与从邻苯二酚水溶液中回收所得废催化剂沉积焦油相似。蒸馏所得酚焦油含有条状结晶物和非晶物质,前者为多元酚类物质,后者是不溶于热水和丙酮的醌类或醚类缩合物。最后,推测了苯二酚进一步氧化缩合生成酚焦油的途径和酚焦油的生成机理。

MECHANISM FOR THE FORMATION OF HPENOLIC TARS IN PREPARATION OF DIPHENOLS BY THE HYDROXYLATION OF PHENOL

The mechanism for the formation of phenolic tars in the process for the preparation of diphe- nols by the hydroxylation of phenol using iron-based composite oxides as catalyst was studied.It was found that catechol bacome phenolic tars more easlily than hydroquinone in water solution.After the hydroxylation reaction,the waste catalyst should be extracted from the reaction products completely as soon as possible since the remnant catalyst could accelerate the formation of phenolic tars.Diphe- nols are more easily further oxidized than phenol.The products of further oxidation of hydroquinone are benzoquinone and 4,4'-dihydroxy-dibenzoaesters which originate from the oxidative condensation of hydroquinone by hydyogen peroxides and were detected by GC/MS.Para-benzoquinone can oxidize catechol into ortho-benzoquinone.Ortho-benzoquinone is unstable and easily disappear or form phe- nolic tars.And then the characteristics of phenolic tars including those deposited in waste catalyst and distillation residue were analyzed.It was found that phenolic tars deposited in waste catalyst are simi- lar to those formed in the hydroxylation and these recycled from catechol solution,which show peak of loss weight at 320 ℃ and C=O bond,acquired by TG/DrTG and IR analyses,respectively.The crystals in the phenolic tars,which are soluble in hot water or acetone(C/O atomic ratio:6/3),might be multi phenols.The remains,which are insoluble and incrystallizable(C/O atomic ratio:6/1.43), might be the quinone-like compounds or the condensation or dehydration products of phenolic com- pounds in the phenol hydroxylation or in the extraction of reaction products.In comparison,the C/O atomic ratio of the phenolic tars deposited in waste catalyst was 6/4.Finally,the formation mecha- nism of the phenolic tars was discussed.