Effects of aromatic ring type on reactions subsequent to the β-O-4 bond cleavage of non-phenolic lignin model compounds under alkaline pulping conditions

The reaction products of an alkaline treatment of non-phenolic β-O-4-type lignin model compounds (C6–C2-type) consisting of p-hydroxyphenyl (H), guaiacyl (G), and/or syringyl (S) nuclei were identified and quantified. This was performed to examine how the type of H, G, or S nucleus affect the reaction product profiles. The major identified and quantified reaction products were phenol derivatives that were liberated from the aryl sides of the β-O-4 ether bonds of the lignin model compounds. Other products included derivatives of phenylethane-1,2-diol (glycol-type), benzaldehyde, and acetophenone, which originated from the alkyl sides of the β-O-4 ether bonds of the lignin model compounds. Although the type of aromatic nucleus of the aryl side of the β-O-4 ether bond of the lignin model compounds did not significantly affect the profile of the reaction products, the type of the alkyl side nucleus was influential. The glycol-type compound was the exclusive major reaction product when the S nucleus was on the alkyl side of the β-O-4 ether bond. On the other hand, when the H or G nucleus was present, a benzaldehyde derivative was the other major reaction product.