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Title Pulse radiolysis and laser flash photolysis studies of the lignin model{alpha}-(p-methoxyphenoxy)-p-methoxyacetophenone and related compounds
Creator/Author Scaiano, J.C. ; Whittlesey, M.K. ; Berinstain, A.B. [Univ. of Ottawa (Canada)][and others]
Publication Date1994 Jun 01
OSTI IdentifierOSTI ID: 369927
Other Number(s)CMATEX; ISSN 0897-4756
Resource TypeJournal Article
Resource RelationChemistry of Materials ; VOL. 6 ; ISSUE: 6 ; PBD: Jun 1994
Subject40 CHEMISTRY ; LIGNIN; DECOMPOSITION; ACETOPHENONE; PHOTOLYSIS; RADIOLYSIS; REACTION INTERMEDIATES; EXCITATION; RADICALS; COLOR
Description/Abstract The reactivity of reaction intermediates derived from{alpha}-(p-anisyl)-p-methoxyacetophenone (IIa) and related compounds has been studied in solution and in the solid state, by a combination of laser photolysis techniques, pulse radiolysis, X-ray crystallography, solid-state NMR, emission spectroscopy, molecular modeling, and product studies. In solution the photolysis of IIa proceeds predominantly through the nonfluorescent singlet state that fragments to yield p-CH{sub 3}OC{sub 6}H{sub 4}O{center_dot} (VI) and p-CH{sub 3}OC{sub 6}H{sub 4}COCH{sub 2}{center_dot} (VII) radicals. The latter shows an absorption band at 540 nm. Molecular modeling calculations support the presence of this band and provide a rationalization for this absorption. In the solid state IIa is essentially photostable. The long-lived triplet state decays exclusively by second-order kinetics (triplet-triplet anihilation). In solution the ketyl radical derived from IIa fragments rapidly to yield VI and CH{sub 3}OC{sub 6}H{sub 4}C(OH)=CH{sub 2} with a lifetime of<20 ns. In the context of the lignin photodegradation processes responsible for the yellowing of lignin-rich papers, these results imply that the fragmentation of both the triplet state of IIa and ketyl radicals derived from alcohol groups in lignin will be very difficult to inhibit. Prevention of discoloration is more likely to succeed if the radicals produced from the fragmentations mentioned above are targeted for scavenging before they undergo the oxidative processes that promote yellowing. 41 refs., 8 figs., 1 tab.
Country of PublicationUnited States
LanguageEnglish
Formatpp. 836-843 ; PL:
System Entry Date2001 May 05

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