Analysis of cinnamyl alcohol- and cinnamyl aldehyde end groups in lignin by trimethylsilylation/pyrolysis-gas chromatography

Abstract

Pyrolysis-gas chromatography in the presence of N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA), BSTFA/Py-GC, was developed for analyzing the end groups of cinnamyl alcohols and cinnamyl aldehydes in lignin simultaneously, using a dry-iced cooled sample-introduction apparatus for a Curie-point pyrolyzer suitable for the analysis of thermal labile samples. BSTFA/PyGC of a dehydrogenative polymer (M-DHP), enzymatically prepared from a mixture of coniferyl alcohol and coniferyl aldehyde (1:1 mol/mol), and a Japanese cedar (Cryptomeria japonica D. Don) wood, were performed at 590°C for 4 s. BSTFA/Py-GC of M-DHP provided trimethylsilyl (TMS) ethers of coniferyl alcohol and coniferyl aldehyde as the main products, along with vanillin TMS ether. The cedar wood provided a large level of coniferyl alcohol diTMS ether and a trace level of coniferyl aldehyde TMS ether, suggesting that the cedar native lignin contains a very small abundance of the pyrolytic sources, producing coniferyl aldehyde. A comparison of the pyrolytic efficiencies producing coniferyl alcohols and aldehydes among different pyrolysis methods showed the high sensitivity of BSTFA/Py. Unlike BSTFA/Py-GC, capable of analyzing both end groups, the pyrolysis of M-DHP in the presence of tetramethylammonium hydroxide provided coniferyl alcohol dimethyl ether and no coniferyl aldehyde methyl ether, suggesting that this method provides useful information on cinnamyl alcohol end groups, but no information on cinnamyl aldehyde end groups.