水溶液中催化剂量无机碱和有机碱催化葡萄糖异构制果糖(英文)

Isomerization of Glucose to Fructose in Aqueous Solution With a Catalytic Amount of Inorganic or Organic Base

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 isomerization of glucose to fructose was examined in aqueous solution with a catalytic amount of inorganic or organic base, NaOH or tetramethylguanidine （TMG）, as catalyst. The effects of several parameters on the isomerization were investigated in detail, including molar ratio of base to glucose（n（Base）/n（Glucose））, reaction time, reaction temperature, solvent and alcohol additives. The results showed that 33%-37% yield of fructose could be obtained at 100℃ with n（Base）/n（Glucose） range of 0. 06-0. 25. Due to the instabilities of sugars under basic condition, the selectivity of fructose and the overall yield of glucose and fructose decreased with the increase of the base amount. Elevating temperature could effectively accelerate the isomerization reaction. Moreover, the isomerization reaction was reversible and fructose could undergo the isomerization to produce glucose as well. The catalytic activity of TMG for the isomerization of glucose in water was higher than those in organic solvents, possibly because TMG could react with water to releaseOH- , which worked as the actual catalyst for the isomerization. The negligible effect of additive alcohol compounds on the base-catalyzed isomerization of glucose implied that the isomerization occurred involving the carbonyl group and proceeded through a 1, 2-enediol intermediate mechanism, while the -OH groups being not adjacent to the carbonyl group did not play a key role in the isomerization.