第三节木素的化学构造

第三节木素的化学构造Chapter3Chemicalstructureoflignin木素的功能基木素的结构单元木素结构单元间的联接光谱的基本概念及其在木素结构研究上的应用木素模型构造图木素-碳水化合物复合体（LCC）2一、木素的功能基主要包括甲氧基（-OCH3）、羟基（-OH）和羰基（-CO）。（一）元素组成及甲氧基（methoxylgroup）木素元素分析值/%示性式CHOOCH3云杉MWL64.776.3928.5816.13C9H8.83O2.37(OCH3)0.96山毛榉MWL60.586.2333.1921.46C9H8.49O2.86(OCH3)1.43云杉和山毛榉MWL的元素分析值与甲氧基含量C/H比例比较高，显示芳香族特性。3甲氧基是木素最重要的特征基团，其含量为：针叶木木素：14％－16％阔叶木木素：19％－22％草本类木素：14％－15％阔叶木木素中甲氧基含量比针叶木高,why?木素中的甲氧基是联接在芳香环上的，而不是联接在脂肪族侧链上。4甲氧基位置的确定甲氧基所处的位置不同，裂开速度不同。是连接在苯环上还是连接在脂肪族侧链上？5HowtoanalyzetheMethoxylGroups?Themethoxylcontentisawidelyusedforcharacterizationoflignins.Itgivesameasureoftheirpurityandoftheirplantorigin.Themethodmostwidelyusedisbasedontheformationofmethyliodidewhenthesampleistreatedwithhydriodicacidatrefluxtemperature.6酚羟基（phenolichydroxylgroup）：存在于苯环上；脂肪族羟基（aliphatichydroxylgroup）：存在于木素结构单元侧链上。1.酚羟基多数醚化，少数游离。（二）羟基（hydroxylgroup）72.脂肪族羟基8使羟基甲基化的试剂97.6830.960.300.85CH(OCH)(PhOH)(AlOH)97.6830.961.15CH(OCH)(OH)硫酸二甲酯重氮甲烷几乎全部游离羟基甲基化游离的酸性酚羟基甲基化可以测得游离羟基的含量97.6830.960.300.85CH(OCH)(PhOH)(AlOH)9-碳原子上的－OH处于侧链上最活泼的部位，制浆化学反应中成为木素和制浆药液的反应点H10Howtoanalyzethephenolichydroxylgroups?Commoninstrumentalmethodsfortheestimationofphenolicgroupsinligninarepotentiometricandconductormerictitration,ionizationdifferenceUVspectroscopy,andNMRspectroscopyChemicalmethodsincludedeterminationoftheincreaseinmethoxylcontentafterreactionwithdiazomethane,selectivedeacetylationofacetylatedligninwithaminolysis（氨基水解）,anddeterminationoftheamountofmethanolformedafteroxidationwithsodiumperiodate11Howtoanalyzethephenolichydroxylgroups?（continued）AmoreindirectmethodisbasedonpermangnateoxidationafteralkylationofthephenolicgroupsTheperiodatemethodisbasedontheguaiacylandsyringylstructureswithaqueoussodiumperiodatetoo-quinonestructureswiththereleaseof1Mmethanolfromeachphenolicunit(Fig.4.27)12Fig.4.2713Howtoanalyzethephenolichydroxylgroups(continued)?Theaminolysisisbasedonthefindingthatphenolicacetatesarecleavedwithpyrrolidine(吡咯烷）muchfasterthanaliphaticacetates.ThepyrrolidineacetatesformedinthereactionofanacetylatedligninisdeterminedbyGC(gaschromatography)(Fig.4.28)14Fig.4.2815Howtoanalyzethealiphatichydroxylgroups?Thetotalamountofhydroxylgroupsinaligninpreparationcanbedeterminedbyacetylationwithaceticanhydrideandpyridinefollowedbyhydrolysisoftheacetateandtitrationoftheliberatedaceticacidwithastandardsodiumhydroxidesolution.Thealiphatichydroxylcontentisdeterminedbysubtractionofthephenolichydroxylcontentfromthetotalhydroxylcontentofthelignin.16（三）羰基（carbonylgroup）存在于木素单元的侧链上，分为共轭羰基和非共轭羰基。1.共轭羰基2.非共轭羰基17羰基的测定全羰基可以通过硼氢化钠还原来测定。共轭羰基可以通过还原示差紫外吸收光谱法定量。18Howtoanalyzethecarbonylgroups?Anearlymethodforthedeterminationofthecarbonylcontentofligninpreparationsisbasedontheuseofhydroxylamine.Thecarbonylgroupreactswithhydroxylaminehydrochlorideforminganoximeandreleasing1Mhydrochloricacid.ThetotalcarbonylcontentofaligninpreparationcanbedeterminedbytitrationoftheHClacid.19Alternatively,thecarbonylcontentmaybedeterminedbyreductionwithsodiumorpotassiumborohydride（硼氢化钠）.Afterthereaction,excessofsodiumorpotassiumborohydrideisdecomposedbyadditionofdilutesulfuricacid,andthevolumeofhydrogenthusliberatedidmeasuredvolumetrically.Thecarboxylcontentisconsumedborohydride.20Howtoanalyzetheunitscontainingdoublebonds?Twomethodshavebeenusedwithsomesuccess.OneisbasedonthecatalytichydrogenationofthedoublebondsincinnamaldehydeandcinnamylalcoholstructuresandmeasurementoftheUVdifferencespectrum.TheotherusesthedifferenceinUVadsorptioninneutralandalkalinesolutiontomeasuretheamountofphenolicstilbenestructures.21HowtoanalyzethoseCarboxylicandSulfonicAcidGroups?Boththeresiduallignininkraftpulpsandthesolublelignininkraftblackliquorscontaincarboxylgroups.Spectroscopicmethodshavebeenusedforthedeterminationofcarboxylicacidgroupsinisolatedligninsamples.22Theresiduallignininsulfitepulpscontainssulfonicacidgroupsthatcanbedeterminedselectivelyinthepresenceofcarboxylgroups.Asforthesolublelignosulfonatesamplesisolatedfromsulfitespentliquors,perhapsthemostreliablemethodsfortheirdeterminationarethosebasedonconductometrictitration.23针、阔叶材木质素主要官能团的比较24二、木素的结构单元木素的基本结构单元为苯丙烷（phenylpropaneunit），可用C9表示。如何证实木素是C9单元?通过化学降解的方法，如氢解、酸解、乙醇解、硫代醋酸解、硝基苯氧化、高锰酸钾氧化等证实木质素的C9单元。25（一）氧化分解法高锰酸钾氧化-P87OHOCH3COHHHCCH2OH67HHCCHOOCHCHOH2CH3C8OHCCHCH2OHCH2OHOOCH3C910OH3C12HOCH2OHH3C13OCOCHOCHOH3CHCH3CHOHOCHH3CCHH2COH1516CarbohydrateCH2OHOHOCH3HC14OCHOCHCH2OCOCH3O1.KMnO42.H2O2OxidationOxidationAlklylation3.4.MethylationOCH2CH3OCH3CO2CH3OCH2CH3OCH3CO2CH3CH3O2COCH2CH3OCH3CO2CH3H3COCH3CH2OCH3O2C26硝基苯氧化分解（nitrobenzeneoxidation）-P88分解产物中含有大量的香草醛，体现了木素的芳香性。产物中还含有紫丁香醛（酸）、5-甲酰基香草醛（酸）以及对羟基苯甲醛，证明了木素是由愈疮木基、紫丁香基和对羟基苯基三种结构单元构成。不同原料的木素其硝基苯氧化产物不同，每种氧化产物的含量也不一样。27云杉、枫、玉米秆硝基苯氧化产物结构树种氧化产物云杉枫玉米秆香草醛27.510.55.3紫丁香醛0.06034.33.2对羟苯甲醛0.251.85-甲酰基香草醛0.23脱氢二香草醛0.80香草酸4.8紫丁香酸0.025-甲酰基香草酸0.105-羧基香草醛1.2脱氢二香草酸0.03乙酰愈疮木酚0.05针：香草醛少量对羟基苯甲醛阔：香草醛紫丁香醛少量苯甲醛禾：香草醛紫丁香醛对羟基苯甲醛可证明：针、阔、禾三中原料的木素结构是不同的28（二）乙醇解（ethanolysis）木素乙醇解的产物为一系列的希伯特酮的多种酮类化合物。针叶材主要产物有五种，都有愈疮木基，说明针叶材木素的单体是愈疮木基丙烷单元。阔叶材木素乙醇解产物有十种，比针叶材增加五种紫丁香基型产物，说明阔叶材木素是由愈疮木基丙烷和紫丁香基丙烷单元