Reduction of aromaticompound with hydrazine hydrate in the presence of iron oxide hydroxide catalyst.docx

Reduction of aromaticompound with hydrazine hydrate in the presence of iron oxide hydroxide catalyst.docx

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Reductionofaromaticompoundwithhydrazinehydrateinthepresenceofironoxidehydroxidecatalyst

Reductionofaromaticnitrocompoundswithhydrazinehydrateinthepresenceofanironoxidehydroxidecatalyst.I.Thereductionofmonosubstitutednitrobenzeneswithhydrazinehydrateinthepresenceofferrihydrite

MaxLauwiner,PaulRys*,JoÈrgWissmann

ChemicalEngineeringandIndustrialChemistryLaboratory,SwissFederalInstituteofTechnology,ETHZentrum,CH-8092Zurich,Switzerland

Received30December1997;receivedinrevisedform26March1998;accepted27March1998

Abstract

Agreatvarietyofmonosubstitutednitrobenzenederivativeshasbeenreducedingoodyieldtothecorrespondinganilineswithhydrazinehydrateinthepresenceofanironoxidehydroxidecatalystpreparedbyprecipitationfromanaqueousiron（III）solutionwithsodiumhydroxide.Thedependenceoftherateofreductiononthenatureandthepositionofadditionalsubstituentsotherthanthenitrogroupwasdeterminedbymeasuringthereactionkinetics.Therateisenhancedbyelectron-attractingsubstituentsanddecreasedbyelectron-donatinggroups,whichresultsinapositiveslopeofσ=0.546fortheHammettplot.Competitivereductionexperimentswithmixturesoftwodifferentlysubstitutednitrobenzenederivativesrevealedthatthenitrocompoundwiththemoreelectron-attractingsubstituentisreducedfirst.#1998ElsevierScienceB.V.Allrightsreserved.

Keywords:

Reduction;nitroarenes;Hydrazinehydrate;Ironoxideferrihydrite;H-transfercatalysis

1.Introduction

Aromaticaminesareimportantstartingmaterialsandintermediatesforthemanufactureofagreatvarietyofchemicals,suchasdyestuffs,pharmaceu-ticalproducts,agriculturalchemicals,photographicchemicals,additives,surfactants,textileauxiliaries,chelatingagentsandpolymers.Theyaregenerallysynthesizedbythereductionofnitroarenes.

Aromaticaminescanbepreparedbyagreatvarietyofreductionmethods.Probablytheoldestindustriallyappliedmethodisthereductionofnitrobenzeneswithmetal（usuallyiron,butalsotin,zincandaluminiumcanbeemployed）andwaterinthepresenceofsmallamountsofacid,firstdescribedbyBechampin1854[1].Itwouldcertainlyhavebeenreplacedmuchearlierbyanalternativereductionmethod,ifithadnotbeenpossibletoobtainironoxidepigmentsasaby-productofthereductionstep.Thereactionswithmetalsandacidarethemostvigorousreductionmethodsprodu-cingmerelytheaminoproducts.Therefore,ifthearomaticmoietycontainsadditionalsubstituentspronetobeingreduced（ase.g.cyano,azoorfurthernitrogroups）,thisdrasticreductionmethodwillpro-duceasignificantamountofby-products.Inthosecases,thereductioncanbecarriedoutselectivelybyemployingsulphides（Zinin-reduction[2]）.Thisselec-tivesulphidereductionismoreexpensivethanthereductionbyironandacid,butisneverthelesswidelyappliedfortheselectivereductionofnitrofunctionsinazoandanthraquinonedyes.TheZinin-method[2]hasaseveredrawback,however,becauseinindustryitisaccompaniedbytheproduc-tionofalargeamountofwasteproductsthathavetobedisposedinanecologicallyunfavourableway.More-over,atlowpHvalues,theevolvingofH2Sgasmightendangertheoperatingpersonnel.Theseproblemswithprocesssecurityandmorerigorousenvironmen-tallegislationinthehandlingofuselesswasteproductsrequiredthedevelopmentofasafe,econom-icallyandecologicallybeneficialalternativetothesenon-catalyticreductionmethodsstillemployedinindustry.

Nowadays,mostlarge-scalearomaticaminesarebeingproducedbycatalytichydrogenationofthecorrespondingnitroarenes.Withalargevarietyofcatalysts（e.g.Ni,Cu,Co,Cr,Fe,Sn,Ag,Pt,Pd,Zn,Ti,Mo,metaloxidesandsulphides）,inmostcasesthecorrespondingamineisobtainedquantitativelywith-outtheproductionofwasteproducts.Becauseoftheexothermicnatureofthereactionandtheneedforaclosedhigh-pressuresystem,numeroussafetyprecau-tionshavetobetaken.

Thereductionofaromaticnitrocompoundswithhydrazineorhydrazinehydraterepresentsaspecialvariationofthecatalyticreduction,wherehydrazineisthesourceofthehydrogen.ThehydrogencanbegeneratedbyavarietyofH-transfercatalysts[3±5].Especiallywiththeuseofnoblemetalcatalysts,suchasPd,PtorRu,butalsowiththeapplicationofNiorCu,thecatalytichydrazinereductiongiveshighyieldscomparabletoorbetterthanthecatalytichydrogena-tion.Inthepast,therelativelyhighcostsforhydrazinehydrateandforthenoblemetalcatalystsprevented

thisreductionmethodfrombeingappliedatanindus-trialscale.However,therearetwomainreasonswhicharecurrentlyenhancingtheattractivityofthiscatalyticH-transferreduction:

（a）Ithasbeenobservedrepeat-edlythatseveralcheapiron（III）compounds,espe-ciallyaseriesofironoxideorhydroxidemodifications,exhibitanappreciableactivitywithregardtocatalyticH-transfer[6±8],thebestresultsbeingobtainedwithβ-FeO（OH）[7,9]inmethanolorethanol[8];（b）Incaseswherethecatalytichydro-genationisnotthemethodofchoice,thismethodoffersasafeaswellasanecologicallyandeconomic-allybeneficialalternative,aboveallforsmallproductvolumesinfinechemicalmanufacture,wherethereactioncanbecarriedoutinmulti-usebatchesundernormalpressure.

Fig.1.Reductionofnitroareneswithhydrazinehydrateandanironoxidehydroxidecatalyst.

ThispromptedustoinvestigatetheH-transferactivityofthesecheapandeasilysynthesizableironoxidehydroxidecatalysts[10]byexaminingtheinfiuenceofadditionalsubstituentsontherateofthereduction[11]anddeterminingtheselectivity[12]ofthecatalyticreductionforaselectionofmonosubstitutednitrobenzenes（Fig.1）.

Thecatalystwaspreparedbyprecipitationofanironoxidehydroxidefromanaqueousiron（III）chlor-idesolutionwithsodiumhydroxide.Itshowedamuchhigheractivitythanthe_-FeO（OH）usedbyMiyataetal.[7]andAyyangaretal.[8].Thismostactiveironoxidehydroxidemodificationwasfound[10]tobetheferrihydriteFe5HO8Á4H2O[9].

2.Experimental

2.1.Preparation,characterizationandhandlingofthecatalyst

Theironoxidehydroxidemodificationwaspreci-pitatedfromanaqueoussolutionof32giron（III）chloridedissolvedin4lofdistilledwater.300mlof2MsodiumhydroxidewereaddeddropwisetoadjustthepHto7±8.Thetemperatureofthereddish-brownmixturewasraisedslowlyto608Cin2handkeptatthislevelfor12handapHvalueoflessthan8.

Aftercentrifugationanddryingthecatalystwasredis-persedandmilledtoafinepowder.TheironoxidehydroxidecatalystwascharacterizedbyBenzandPrins.Theyalsoexaminedthein¯uenceofitssurfacestructureontheH-transferactivity[10].

Halfanhourbeforethereactionusedtobestarted,thecatalystwasactivatedbyaddingsomedropsofdistilledwatertodevelopitsfullcatalyticactivityinorganicsolvents.Afterthereactionthecatalystcanbefilteredoff,andiswashedandreusedforfurtherreductions.Attemperaturesabove708Cthecatalystchangesitscolourfromreddish-browntoblack.Thiscolourchangeisaccompaniedbyalmostacompletelossofactivity.Thechangesinsurfacestructureandthelossofactivityathighertemperatureswereinves-tigatedbyMoÈssbauerspectroscopy[10].Obviously

thecatalyticallyactiveferrihydriteistransformedintoathermodynamicallymorestablemodi®cationwithalowersurfaceandaweakerH-transferactivity.

2.2.Generalprocedureforthereductionsatpreparativescale

Asolutionof10mmolofthenitrocompoundin100mlethanolorwaterisheatedtoreactiontempera-ture.Duringthisheatingthereactionsolutionispurgedwithanitrogenstream.ThecatalystisweighedandactivatedasdescribedinSection2.1.andaddedtothereactionmixture.Thereactionisstartedbyaddingastoichiometricamount（15mmol）ofhydrazinehydrateandmonitoredbythinlayerchromatographyandGC-MS.Afterallstartingmaterialhasdis-appeared,thecatalystisfilteredoff.Theamineisisolatedbyevaporatingthesolvent,purifiedby

recrys-tallization,destillationorsublimationandcharacter-izedbyGC-MS,NMR（1H,13Cand19F）andelementarymicroanalyses.

2.3.Kineticmeasurements

Allexperimentswerecarriedoutina100mlther-mostattedglassvesselwithacoolingjacket.Thereactionsolutionwasstirredvigorouslywithamag-neticstirrerat1000rpm.ThekineticmeasurementsforthedeterminationofHammett's'&-relationshipwereruninethanolat558Candwithatenfoldexcessofhydrazinehydrate.Theconcentrationswere0.1Mofsubstitutednitrobenzeneswith0.1gcatalystper100mlethanol.Underthesereactionconditionsnodiffusioneffectscouldbeobserved[11].

Afteradditionofthecatalysttothereactionsolu-tion,thereactionswerestartedbyaddinghydrazinehydrate.Fortheevaluationofthereductionkineticssamplesfromthereactionmixtureweredrawnatdifferenttimes.After®lteringoffthecatalystbyamicro®lterwithaporediameterof0.2mm,thecom-positionofthereactionmixtureswasmonitoredbyUV-VISspectroscopyorgaschromatography.Theconcentrationsofthenitrobenzenesandthecorre-spondinganilinesweredeterminedbymeasuringtheabsorbanceofthe®ltratebetween270and350nm.Themolarextinctioncoef®cientsofthenitroandaminocompoundsweredeterminedwithpurereferencecompounds.

Thekineticmeasurementsforthecompetitiveexperimentswerecarriedoutunderthesamereactionconditionsexceptthattheconcentrationsofthenitro-benzeneswere0.05Mforeachsubstitutednitro-benzene.Onlyforthe