Influence of hydroxyl group configuration on pyrolytic formation of 1,6-anhydrohexopyranoses from various hexoses: An experimental and theoretical study

详细信息    查看全文

• 作者：Seiji Matsuoka ; Haruo Kawamoto ; Shiro Saka
• 关键词：Pyrolysis ; 1 ; 6-Anhydrohexopyranose ; Hydroxyl group configuration ; Density functional theory ; Heterolysis
• 刊名：Journal of Analytical and Applied Pyrolysis
• 出版年：2013
• 出版时间：September, 2013
• 年：2013
• 卷：103
• 期：Complete
• 页码：300-306
• 全文大小：1248 K

文摘

1,6-Anhydrohexopyranose, which is a major pyrolysis product of cellulose and other carbohydrates, has a unique ¹C₄ chair conformer. Thus, during pyrolysis, the molecule must undergo a conformational transformation from the ⁴C₁ to the ¹C₄ geometry, and this interconversion is expected to be influenced by the sugar's hydroxyl group configuration. In this article, the influences of the C2-, C3-, and C4-OH configuration on the 1,6-anhydrohexopyranose yield were evaluated under vacuum pyrolysis conditions for five hexoses (glucose, mannose, allose, galactose, and gulose). Furthermore, the results are discussed within the context of theoretical results that indicate the relative stability of two types of the conformers of glycopyranosyl oxocarbenium ions with C6-pseudo-equatorial and C6-pseudo-axial orientations, which were calculated with density functional theory (DFT). The latter conformation would lead to the formation of the 1,6-anhydrohexopyranose with a ¹C₄ conformation. The theoretical results were in good agreement with the experimental yields; C2-OH (both axial and equatorial) and C3-OH (equatorial) enhance 1,6-anhydrohexopyranose formation, while C4-OH (axial) inhibits the formation (axial/equatorial: in ⁴C₁ form). These results also support the heterolysis mechanism for this transformation, and such conformational change was suggested to be more effective in the evaporation process from liquid to gaseous substance.