Structural features of lignite humic acid in light of NMR

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1、JournalofMolecularStructure826(2007)131–142www.elsevier.com/locate/molstrucStructuralfeaturesoflignitehumicacidinlightofNMRandthermaldegradationexperimentsa,*bbcaJ.Peuravuori,A.J.Simpson,B.Lam,P.Zˇba´nkova´,K.PihlajaaDepartmentofChemistry,UniversityofTurku,FIN-20014Tur

2、ku,FinlandbDepartmentofPhysicalandEnvironmentalSciences,TheUniversityofToronto,ScarboroughCollege,1265MilitaryTrail,Scarborough,Ont.,CanadaM1C1A4cDepartmentofPhysicalandAppliedChemistry,BrnoUniversityofTechnology,Purkynˇova118,61200Brno,CzechRepublicReceived17March2006

3、;accepted25April2006Availableonline5June2006Abstract131Structuralcompositionofalignitehumicacid(HA)fractionwasstudiedbymeansofsolid-stateCNMR,differentsolution-stateHNMRpulsetechniquesandthermallyassistedhydrolysis–methylationwithTMAHandTMAAcfollowed-upwithpyrolysis–GC–

4、MSexperiments.TheresultsverifiedthatcertainaliphaticcompoundshavetheirspecialtasksinthecomplicatedstructuralnetworkofligniteHAmaterial,andaproticsolventswithstrongelectron-donorpowersareneededtoreleasethetightlyboundcertainaliphaticsfromthemacromolecularnetworkforobtain

5、ingafullydissolvedHAsolution.Theoccurrenceoftherelativelylargecontentofdifferentcarbox-1ylicacidsastheirfree-acidformswassurprising.ThestructuralinterpretationsperformedbyspecialHNMRpulsetechniquesverifiedthecomplexityofaliphaticmoieties,thepresenceofhydroaromaticcarbons

6、,residualligninderivatives,theabundanceofaliphaticandaromaticcarboxylicacids,andtheabilityofaliphaticstoformintermolecularbridgesbetweenaromaticbuildingblocks.Ó2006ElsevierB.V.Allrightsreserved.113Keywords:Lignite;Humicacids;Freefattyacids;Structuralcomposition;HNMR;CN

7、MR;Pyrolysis1.IntroductionorganicfractionbuttheHAcontentisusuallymostabun-dantinligniteandespeciallyinnaturallyoxidizedligniteThealkali-solublefractionofso-calledhumicsubstancesderivatives(e.g.,leonardite)beingseveraltensofpercent-isextremelyimportantandinterestingpart

8、ofthenaturalages.TheligniteHAhascontinuallybeenofspecialinter-organicmatterindependentofitssource.Thealkali-solublees