CAJ | 학술논문

为了解木质素三聚体的热解机理，采用密度泛函理论方法，对同时含有β-O-4和α-O-4连接的木质素三聚体模型化合物（4-(1,2-二苯氧基)-丙基苯酚）的热解过程进行了理论计算研究，分析了三聚体中α-O-4和β-O-4醚键断裂的相互影响，以及三聚体的整体热解反应机理和产物形成途径。计算结果表明，Cα-O均裂是三聚体初步热解的最主要反应， Cβ-O和Cα-Cβ均裂则是竞争反应。三聚体的α-O-4和β-O-4醚键在初步热解过程中的相互影响作用很小；但是在后续热解过程中，α-O-4(β-O-4)醚键断裂产物继续发生β-O-4(α-O-4)醚键断裂的解离能却显著降低。基于 Cα-O 均裂反应的热解产物主要有苯酚、4-丙烯基苯酚、4-烯丙基苯酚和含双键的二聚体（大分子产物的前驱物）等；基于Cβ-O均裂反应的热解产物主要有苯酚、4-丙烯基苯酚和4-丙基苯酚等；基于Cα-Cβ均裂反应的热解产物主要有苯乙醚、4-羟基苯甲醛、苯、4-甲基苯酚和苯酚等。该文的研究结果将为深入了解木质素的热解机理提供理论依据。
위료해목질소삼취체적열해궤리，채용밀도범함이론방법，대동시함유β-O-4화α-O-4련접적목질소삼취체모형화합물（4-(1,2-이분양기)-병기분분）적열해과정진행료이론계산연구，분석료삼취체중α-O-4화β-O-4미건단렬적상호영향，이급삼취체적정체열해반응궤리화산물형성도경。계산결과표명，Cα-O균렬시삼취체초보열해적최주요반응， Cβ-O화Cα-Cβ균렬칙시경쟁반응。삼취체적α-O-4화β-O-4미건재초보열해과정중적상호영향작용흔소；단시재후속열해과정중，α-O-4(β-O-4)미건단렬산물계속발생β-O-4(α-O-4)미건단렬적해리능각현저강저。기우 Cα-O 균렬반응적열해산물주요유분분、4-병희기분분、4-희병기분분화함쌍건적이취체（대분자산물적전구물）등；기우Cβ-O균렬반응적열해산물주요유분분、4-병희기분분화4-병기분분등；기우Cα-Cβ균렬반응적열해산물주요유분을미、4-간기분갑철、분、4-갑기분분화분분등。해문적연구결과장위심입료해목질소적열해궤리제공이론의거。
In order to understand the pyrolysis mechanism of lignin trimer, 4-(1,2-diphenoxy)-propylphenol was selected as lignin trimer model compound containing both β-O-4 and α-O-4 linkages, and its pyrolysis processes were theoretically investigated by employing density functional theory method at M06-2X level with 6-31++G(d,p) basis set. The equilibrium geometries of the reactant, intermediates, transition states and products in the pyrolysis processes were fully optimized. The activation energy in each pyrolysis pathway was calculated. Analyses were performed to reveal the interaction of theβ-O-4 andα-O-4 linkages in their cleavages, as well as the overall pyrolytic mechanisms and the pathways of product formation. The calculation results indicated for the 6 primary homolytic ways of the lignin trimer model compound, and the bond dissociation energies were in the order of Cα-O<Cβ-O<Cα-Cβ<Cα-C4<C4″-O<C4′-O, with the lowest energy of Cα-O (250.6 kJ/mol) and the second lowest energy of Cβ-O (286.9 kJ/mol), followed by that of Cα-Cβ(300.5 kJ/mol). Hence, the homolytic cleavage of Cα-O bond should be the major reaction of primary pyrolysis for the trimer model compound, while the homolytic cleavages of Cβ-O and Cα-Cβbonds were competitive pyrolysis reactions. Theβ-O-4 andα-O-4 linkages had little interaction effects in their primary cleavage reactions, because the bond dissociation energies of Cα-O and Cβ-O in the lignin trimer model compound were similar to those of the corresponding lignin dimer model compounds. However, after the initial cleavage of theα-O-4 (β-O-4) linkage, the formed intermediate had significantly reduced bond dissociation energy for the further cleavage of theβ-O-4 (α-O-4) linkage. Based on the energy barrier of each reaction pathway for the primary homolytic cleavage of Cα-O bond, the major pyrolytic products of the model compound included phenol, 4-propenylphenol, 4-allyphenol, and dimer compound with double bonds (the precursor of large molecular products). Based on the primary homolysis of Cβ-O bond, the major pyrolytic products included phenol, 4-propenylphenol and 4-propylphenol. From the primary homolysis of Cα-Cβbond, the major pyrolytic products included phenetole, 4-hydroxy benzaldehyde, benzene, p-cresol and phenol. In conclusion, based on the 3 homolytic mechanisms, the pyrolysis of the lignin trimer model compound will produce phenol, 4-propenylphenol, 4-allyphenol, and dimer compound with double bonds as the major products, as well as 4-propylphenol, phenetole, 4-hydroxy benzaldehyde, benzene and p-cresol as the competitive products. The research results will provide theoretical basis for the deep understanding of the pyrolysis mechanism of lignin.