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以无机碱氢氧化钠(NaOH)和有机碱四甲基胍(TMG)为催化剂研究了葡萄糖异构化制果糖的反应。考察了碱与葡萄糖的摩尔比(n(Base)/n(Glucose))、反应时间、温度、溶剂以及醇类添加物对反应的影响,并考察了果糖在碱性条件下的稳定性。结果表明,100℃下,n(Base)/n(Glucose)在0.06～0.25范围时,葡萄糖异构化反应制果糖的收率为33%～37%。随着碱量的增加,果糖选择性以及果糖和葡萄糖的总收率下降,这是由果糖和葡萄糖在碱性溶液中的不稳定性导致的。提高反应温度可以有效加快反应的进行。该异构化反应在碱性体系下具有可逆性,果糖也会发生异构化反应生成葡萄糖。TMG在水溶液中的催化活性高于其在有机溶剂中的,这可能是由于在水溶液中TMG可以与水反应生成OH-,而OH-作为催化剂进一步催化该反应。一系列醇类添加物对反应的微小影响表明,葡萄糖中的醛基基团在异构化反应中起重要作用,而葡萄糖分子中不与醛基相邻的羟基在反应中不起明显的作用,反应可能遵循1,2-烯醇中间体的机理。
The reaction of glucose isomerization of fructose with inorganic base sodium hydroxide (NaOH) and organic base tetramethylguanidine (TMG) as catalyst was studied. The effects of the molar ratio of base to glucose (n / Glucose), reaction time, temperature, solvents and alcohol additives on the reaction were investigated. The stability of fructose under alkaline conditions was also investigated. The results showed that the fructose yield of glucose isomerization was 33% -37% at 100 ℃ under n (Base) / n (Glucose) range of 0.06 ~ 0.25. As the amount of base increases, the fructose selectivity and the overall yield of fructose and glucose decrease, resulting from the instability of fructose and glucose in alkaline solutions. Increase the reaction temperature can effectively speed up the reaction. The isomerization reaction is reversible in a basic system, and fructose also undergoes isomerization reaction to produce glucose. The catalytic activity of TMG in aqueous solution is higher than that in organic solvent, probably because TMG can react with water to form OH- in aqueous solution, while OH- acts as catalyst to further catalyze the reaction. The slight influence of a series of alcoholic additions on the reaction indicates that the aldehyde group in glucose plays an important role in the isomerization reaction while the hydroxyl groups in the glucose molecule that are not adjacent to the aldehyde group do not play a significant role in the reaction , The reaction may follow the mechanism of the 1,2-enol intermediate.