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高二化学课本第146页说:“用铁屑作催化剂,苯也能跟其它卤素起取代反应”,还说:把苯和少量溴放在烧瓶里,同时加入少量铁屑作催化剂……很快就会看到……白雾……褐色不溶于水的液体”(见实验4—14)。 实验证明是看不到这些明显反应现象的。原因是这个反应起催化作用的并不是铁而是三溴化铁。我们可以从实验和理论分析两方面证明和阐述这一点。 若将课本实验4—14作如下改动:先在烧瓶里加入少量铁屑,再加入少量溴,最后加入苯。摇动烧瓶使其混和均匀,不久反应很激烈。这说明先加入的Fe和Br_2作用生成了FeBr_3,它作为催化剂加快了苯环上的氢原子与溴原子的取代
On page 146 of the Chemistry Bulletin, page 146, “Using iron as a catalyst, benzene can also react with other halides,” adding that benzene and a small amount of bromine were placed in flasks while adding a small amount of iron as a catalyst ... very quickly You will see ... white mist ... brown, water-insoluble liquid "(see Experiments 4-14) .Experiments show that these obvious reactions can not be seen because the reaction is not catalyzed but iron Ferric Ferric Bromide This can be demonstrated both experimentally and theoretically in the following aspects: Experiment 4-14 is modified as follows: add a small amount of iron filings to the flask, add a small amount of bromine, and finally add benzene. The flask was mixed uniformly, and the reaction was very fierce, indicating that the addition of Fe and Br2 first formed FeBr3, which acts as a catalyst to accelerate the substitution of the hydrogen atom and the bromine atom on the benzene ring