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在合成三聚甲醛的过程中,硫酸在反应过程的始终都应当严格控制。由于甲醛水溶液中含有甲醇和少量甲酸,还有微量的铁锈等杂质,而且硫酸在催化反应中,自身的氧化性使部分甲醛被氧化成甲酸,因此总酸的测定不能反映合成三聚甲醛过程中的真实情况。我们为了分别测定甲酸和硫酸的含量,将纯硫酸分子与联苯胺结合生成沉淀物,而单独测定硫酸,反应中已变成硫酸盐的那部分不计算在硫酸含量中,且可以测定出有机酸的含量。
In the process of synthesis of paraformaldehyde, sulfuric acid in the reaction process should always be strictly controlled. Due to the formaldehyde aqueous solution containing methanol and a small amount of formic acid, as well as traces of rust and other impurities, and sulfuric acid in the catalytic reaction, its own oxidation of part of the formaldehyde is oxidized to formic acid, the total acid determination does not reflect the synthesis of paraformaldehyde The real situation. In order to separately determine formic acid and sulfuric acid content, a pure sulfuric acid molecule is combined with benzidine to form a precipitate, whereas in the case of sulfuric acid alone, the portion of the reaction that has become sulfated is not counted in the sulfuric acid content, and the organic acid Content.