Caffeic acid subjected to mild pyrolysis (225−226 °C) under vacuum
resulted in rapid decarboxylation
and the formation of simple catechol monomers as well as more complex
cyclocondensed dimers
and polymers. This reaction yielded the same spectrum of products
as did acid-catalyzed cyclization
of caffeic acid. The major pyrolysis products were identified by
reversed-phase HPLC and LC−tandem mass spectrometry. Two novel compounds, identified by MS,
1H NMR, and 13C NMR as
1,3-cis- and 1,3-trans-tetraoxygenated
phenylindans, were present as major products in both the
caffeic acid pyrolysate and the acid-treated sample. The stability
and reactivity of the pyrolysis
products in weakly buffered aqueous solutions were determined
concomitantly by measuring
hydrogen peroxide generation and by monitoring the concentration of the
individual components
by reversed-phase HPLC. Such model studies may provide information
pertaining to reaction
mechanisms and the nature of the compounds involved in hydrogen
peroxide formation in coffee.
Keywords: Pyrolysis; caffeic acid; hydrogen peroxide; phenylindan isomers;
model system studies