Significant lability of guaiacylglycerol beta-phenacyl ether under alkaline conditions.
It was observed that the beta-O-4 bond cleavage of a dimeric phenolic lignin model compound with an alpha-carbonyl group at the B-ring, 2-(2-ethoxy-4-formylphenoxy)-1-(4-hydroxy-3-methoxyphenyl)propane-1,3-diol (I), is extremely fast in a mild anaerobic alkaline treatment (0.45 mol/L NaOH, 95 degrees C, 0.8 MPa of N2). This phenomenon significantly contrasts with the case of a common dimeric phenolic lignin model compound without any specific functional group, 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol (II). The most plausible mechanism is the migration of the B-ring from the beta- to the alpha-position following the SNAr mechanism. Because this migration affords the alkaline labile phenolic alpha-O-4-type compound (XI), the formation of the quinone methide as well as the cleavage of the originally alkaline very stable alkyl-aryl ether bond is promoted. This promotion of the quinone methide formation explains why a relatively large amount of 4-hydroxy-3-methoxybenzaldehyde (IV) is produced from I in an oxygen-alkali treatment.
Imai
Aiko
A
Laboratory of Wood Chemistry, Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Yokoyama
Tomoya
T
Matsumoto
Yuji
Y
Meshitsuka
Gyosuke
G
D001547:Benzaldehydes / Q000737:chemistry*; D005990:Glycerol / Q000031:analogs & derivatives* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D045563:Indolequinones / Q000737:chemistry; D008031:Lignin / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry
C525180:2-(2-ethoxy-4-formylphenoxy)-1-(4-hydroxy-3-methoxyphenyl)propane-1,3-diol; D001547:Benzaldehydes; D045563:Indolequinones; C068040:quinone methide; D008031:Lignin; D005990:Glycerol; D010100:Oxygen