摘要
乳酸是制备可降解聚合物聚乳酸的主要单体。利用秸秆等原生生物质为原料经过化学催化转化制备乳酸对于碳减排具有重要意义。本工作利用同位素核磁和质谱详细探究了不同Lewis酸(Y^(3+),Sc^(3+),Al^(3+))催化纤维素制乳酸的反应选择性和机理。发现葡萄糖异构化为果糖的过程是决定纤维素制乳酸多步串联反应最终选择性的关键步骤,并明确了1,3-二羟基丙酮生成乳酸经历了烯醇互变异构过程而非经典的1,2-shift机理。
Because fossil fuels are continuously depleted,valorization of biomass into valuable liquid products and chemicals is of great significance yet it remains challenging.Among many biomass-derived products,lactic acid is one of the most important renewable monomers for preparing the degradable polymer polylactic acid.The use of raw biomass to produce lactic acid through catalytic conversion is an attractive approach.In this work,the catalytic reaction performance and mechanism of different Lewis acids(Y^(3+),Sc^(3+),and Al^(3+))for the production of lactic acid from cellulose were investigated in detail by isotopic nuclear magnetic resonance(NMR)and mass spectrometry.The production of lactic acid from cellulose includes tandem and competing reactions.The order of catalytic activity for the one-pot conversion of cellulose into lactic acid is as follows:Y^(3+)>Al^(3+)>Sc^(3+).The main tandem reactions involve the hydrolysis of cellulose into glucose,the isomerization of glucose into fructose(the order of catalytic activity,the same below:Y^(3+)>Al^(3+),Y^(3+)>Sc^(3+)),the cleavage of fructose via a retro-aldol reaction to glyceraldehyde(GLY)and 1,3-dihydroxyacetone(DHA)(Sc^(3+)>Y^(3+)>Al^(3+)),and the conversion of DHA or GLY to the final product lactic acid(Al^(3+)>Y^(3+)>Sc^(3+)).It was found that the process of glucose isomerization to fructose was the key step to the final selectivity of the tandem reaction of cellulose conversion to lactic acid,and it was clarified that the production of lactic acid from DHA underwent a keto-enol(K-E)tautomerization process rather than a classical 1,2-shift process.First,DHA was transformed into GLY via the isomerization process,then the adjacent hydroxyl group of GLY was removed in the form of water to produce anα,β-unsaturated species.After that,theα,β-unsaturated species underwent KE tautomerization to generate unsaturated aldehyde-ketone intermediates.Meanwhile,a molecule of water was added to aldehyde-ketone intermediates to obtain a diol product,the hydrogen atom at the
作者
郝睿
关伟翔
刘菲
张磊磊
王爱琴
Rui Hao;Weixiang Guan;Fei Liu;Leilei Zhang;Aiqin Wang(CAS Key Laboratory of Science and Technology on Applied Catalysis,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,Liaoning Province,China;State Key Laboratory of Catalysis,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,Liaoning Province,China.)
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2022年第10期57-64,共8页
Acta Physico-Chimica Sinica
基金
国家重点研发计划(2018YFB1501602)
国家自然科学基金(22132006)
中国博士后科学基金(2021M690149)资助。
关键词
纤维素
葡萄糖
果糖
乳酸
LEWIS酸
烯醇互变
Cellulose
Glucose
Fructose
Lactic acid
Lewis acid
Keto-enol tautomerization
