One-pot conversion of cyclohexanol to ?-caprolactam using a multifunctional Na2WO4-acidic ionic liquid catalytic system

Article abstract of DOI:10.1016/S1872-2067(16)62563-9

Na₂WO₄-acidic ionic liquid was used as a simple, ecofriendly, recyclable and efficient catalytic system for the one-pot conversion of cyclohexanol to ?-caprolactam. The effect of the structure of the ionic liquid on the catalytic activity of this system was investigated, and the results revealed that sulfonic acid-functionalized ionic liquids with HSO₄^?as an anion gave the best results. The highly efficient performance of this catalyst system was attributed to the phase-transfer behavior of the cation of the ionic liquid, the improved coordination of the substrate to bisperoxotungstate during the oxidation reaction, and the stabilization of the intermediate formed during the Beckmann rearrangement.

Full text of DOI:10.1016/S1872-2067(16)62563-9

ChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ58–64
ꢀ
ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
ꢀ
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
ꢀ
ꢀ
Article
One‐potꢀconversionꢀofꢀcyclohexanolꢀtoꢀε‐caprolactamꢀusingꢀaꢀ ꢀ
multifunctionalꢀNa WO ‐acidicꢀionicꢀliquidꢀcatalyticꢀsystemꢀ
2
4
HefangꢀWang,ꢀLiyuanꢀJia,ꢀRongbinꢀHu,ꢀMeidanꢀGao,ꢀYanjiꢀWangꢀ*
ꢀ
SchoolꢀofꢀChemicalꢀEngineeringꢀandꢀTechnology,ꢀHebeiꢀUniversityꢀofꢀTechnology,ꢀTianjinꢀ300130,ꢀChinaꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Na WO ‐acidicꢀionicꢀliquidꢀwasꢀusedꢀasꢀaꢀsimple,ꢀecofriendly,ꢀrecyclableꢀandꢀefficientꢀcatalyticꢀsys‐
Articleꢀhistory:ꢀ
2
4
Receivedꢀ30ꢀSeptemberꢀ2016ꢀ
Acceptedꢀ24ꢀOctoberꢀ2016ꢀ
Publishedꢀ5ꢀJanuaryꢀ2017ꢀ
temꢀforꢀtheꢀone‐potꢀconversionꢀofꢀcyclohexanolꢀtoꢀε‐caprolactam.ꢀTheꢀeffectꢀofꢀtheꢀstructureꢀofꢀtheꢀ
ionicꢀliquidꢀonꢀtheꢀcatalyticꢀactivityꢀofꢀthisꢀsystemꢀwasꢀinvestigated,ꢀandꢀtheꢀresultsꢀrevealedꢀthatꢀ

sulfonicꢀacid‐functionalizedꢀionicꢀliquidsꢀwithꢀHSO
4
ꢀasꢀanꢀanionꢀgaveꢀtheꢀbestꢀresults.ꢀTheꢀhighlyꢀ
efficientꢀperformanceꢀofꢀthisꢀcatalystꢀsystemꢀwasꢀattributedꢀtoꢀtheꢀphase‐transferꢀbehaviorꢀofꢀtheꢀ
cationꢀofꢀtheꢀionicꢀliquid,ꢀtheꢀimprovedꢀcoordinationꢀofꢀtheꢀsubstrateꢀtoꢀbisperoxotungstateꢀduringꢀ
theꢀoxidationꢀreaction,ꢀandꢀtheꢀstabilizationꢀofꢀtheꢀintermediateꢀformedꢀduringꢀtheꢀBeckmannꢀrear‐
rangement.ꢀ
Keywords:ꢀ
Cyclohexanolꢀ
ε‐Caprolactamꢀ
One‐potꢀsynthesisꢀ
Acidicꢀionicꢀliquidꢀ
Cyclohexanoneꢀoxime
©ꢀ2016,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
beꢀobtainedꢀbyꢀtheꢀhydrogenationꢀofꢀphenolꢀ[2],ꢀtheꢀpreferredꢀ
routeꢀ forꢀ theꢀ industrialꢀ manufactureꢀ ofꢀ thisꢀ materialꢀ involvesꢀ
theꢀdirectꢀoxidationꢀofꢀcyclohexane.ꢀHowever,ꢀtheꢀaerobicꢀoxi‐
dationꢀofꢀcyclohexaneꢀtoꢀcyclohexanoneꢀhasꢀlimitedꢀtheꢀoverallꢀ
efficiencyꢀofꢀthisꢀthree‐stepꢀprocessꢀbecauseꢀofꢀtheꢀlowꢀyieldsꢀ
achievedꢀ withꢀ eachꢀ pass,ꢀ whichꢀ areꢀ usuallyꢀ inꢀ theꢀ rangeꢀ ofꢀ
3%–8%ꢀ withꢀ aꢀ selectivityꢀ ofꢀ aroundꢀ 80%ꢀ forꢀ cyclohexanoneꢀ
overꢀ cyclohexanolꢀ [3].ꢀ Basedꢀ onꢀ theꢀ increasingꢀ demandꢀ forꢀ
environmentallyꢀ friendlyꢀ processes,ꢀ theꢀ developmentꢀ ofꢀ anꢀ
ecofriendlyꢀandꢀeconomicallyꢀviableꢀprocedureꢀforꢀtheꢀone‐potꢀ
synthesisꢀofꢀCLꢀisꢀhighlyꢀdesirable.ꢀSeveralꢀgroupsꢀhaveꢀinves‐
tigatedꢀtheꢀdirectꢀsynthesisꢀofꢀCLꢀfromꢀcyclohexaneꢀusingꢀvari‐
ousꢀ strategies,ꢀ includingꢀ conductingꢀ theꢀ reactionꢀ inꢀ theꢀ pres‐
enceꢀofꢀnitrosylꢀsulfuricꢀacidꢀ[4–9]ꢀorꢀusingꢀnitrocyclohexaneꢀasꢀ
aꢀsubstrateꢀ[10].ꢀOneꢀgroupꢀevenꢀinvestigatedꢀtheꢀpossibilityꢀofꢀ
usingꢀcyclohexanoneꢀinꢀcombinationꢀ withꢀ ammoximationꢀ andꢀ
BeckmannꢀrearrangementꢀreactionsꢀoverꢀNb‐MCM‐41ꢀcatalystsꢀ
ε‐Caprolactamꢀ (CL)ꢀ isꢀ anꢀ importantꢀ precursorꢀ ofꢀ nylon‐6ꢀ
andꢀseveralꢀotherꢀplastics,ꢀandꢀtheꢀglobalꢀmarketꢀforꢀthisꢀmate‐
rialꢀreachedꢀ5ꢀmillionꢀmetricꢀtonsꢀperꢀannumꢀinꢀ2015ꢀ[1].ꢀCLꢀisꢀ
currentlyꢀ manufacturedꢀ fromꢀ cyclohexanone,ꢀ whichꢀ isꢀ con‐
vertedꢀ toꢀ cyclohexanoneꢀ oximeꢀ (CHO)ꢀ beforeꢀ undergoingꢀ aꢀ
rearrangementꢀprocessꢀtoꢀgiveꢀCLꢀviaꢀaꢀthreeꢀstepꢀprocess.ꢀTheꢀ
yieldꢀ forꢀ theꢀ Beckmannꢀ rearrangementꢀ ofꢀ CHOꢀ toꢀ CLꢀ isꢀ highꢀ
whenꢀ fumingꢀ sulfuricꢀ acidꢀ isꢀ usedꢀ asꢀ catalystꢀ andꢀ solvent.ꢀ
However,ꢀthereꢀareꢀseveralꢀdisadvantagesꢀassociatedꢀwithꢀthisꢀ
process,ꢀincludingꢀ(1)ꢀtheꢀformationꢀofꢀaꢀlargeꢀamountꢀofꢀam‐
moniumꢀsulfate,ꢀwhichꢀisꢀgeneratedꢀasꢀaꢀby‐productꢀduringꢀtheꢀ
neutralizationꢀ ofꢀ theꢀ hazardousꢀ sulfuricꢀ acidꢀ wasteꢀ withꢀ am‐
monia,ꢀ(2)ꢀtheꢀcorrosionꢀofꢀtheꢀreactorsꢀbecauseꢀofꢀtheꢀstronglyꢀ
acidicꢀconditions,ꢀandꢀ(3)ꢀtheꢀenvironmentalꢀpollutionꢀcausedꢀ
byꢀtheꢀuseꢀofꢀfumingꢀsulfuricꢀacid.ꢀAlthoughꢀcyclohexanoneꢀcanꢀ
*ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+86‐22‐60202419;ꢀFax:ꢀ+86‐22‐60204697;ꢀE‐mail:ꢀyjwang@hebut.edu.cnꢀ ꢀ
ThisꢀworkꢀwasꢀsupportedꢀbyꢀtheꢀNationalꢀNaturalꢀScienceꢀFoundationꢀofꢀChinaꢀ(20636030,ꢀ2090618,ꢀ21236001)ꢀandꢀtheꢀNaturalꢀScienceꢀFoundationꢀ
ofꢀHebeiꢀProvinceꢀ(B2017202226).ꢀ ꢀ
DOI:ꢀ10.1016/S1872‐2067(16)62563‐9ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ38,ꢀNo.ꢀ1,ꢀJanuaryꢀ2017ꢀ ꢀ ꢀ

ꢀ
HefangꢀWangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ58–64ꢀ
59ꢀ
[
[
11],ꢀwhichꢀresultedꢀinꢀaꢀCLꢀyieldꢀofꢀaboutꢀ10%.ꢀIshii’sꢀgroupꢀ
12]ꢀreportedꢀtheꢀsynthesisꢀofꢀCLꢀfromꢀcyclohexaneꢀandꢀt‐butylꢀ
nitrite,ꢀusingꢀN‐hydroxyphthalimideꢀ(NHPI)ꢀasꢀaꢀcatalyst,ꢀwhichꢀ
gaveꢀaꢀCLꢀyieldꢀofꢀ43%.ꢀHowever,ꢀtheꢀconditionsꢀusedꢀinꢀthisꢀ
reactionꢀresultedꢀinꢀtheꢀdecompositionꢀofꢀNHPIꢀtoꢀgiveꢀphthalicꢀ
acidꢀandꢀseveralꢀotherꢀrelatedꢀimpurities,ꢀtherebyꢀlimitingꢀtheꢀ
utilityꢀofꢀthisꢀ approach.ꢀRajaꢀetꢀal.ꢀ[13]ꢀdevelopedꢀaꢀone‐stepꢀ
processꢀforꢀtheꢀconversionꢀofꢀcyclohexanoneꢀtoꢀCLꢀusingꢀbime‐
tallicꢀMn(III)Mg(II)AlPO‐5ꢀasꢀaꢀbifunctionalꢀcatalyst.ꢀTheꢀmax‐
imumꢀconversionꢀofꢀcyclohexanoneꢀachievedꢀunderꢀtheseꢀcon‐
ditionsꢀwasꢀ68.3%,ꢀwithꢀselectivityꢀofꢀ5.7%ꢀandꢀ77.9%ꢀforꢀCHOꢀ
andꢀCL,ꢀrespectively.ꢀMoreꢀrecently,ꢀShinꢀetꢀal.ꢀ[14]ꢀreportedꢀaꢀ
multifunctionalꢀ Pd/Sc(OTf)
/ionicꢀ liquidꢀ catalystꢀ forꢀ theꢀ tan‐
3
demꢀone‐potꢀconversionꢀofꢀphenolꢀtoꢀCLꢀinꢀ67%ꢀyieldꢀusingꢀaꢀ
largeꢀ excessꢀ (300ꢀ mol%)ꢀ ofꢀ 1‐butyl‐methylimidazoliumꢀ hex‐
Fig.ꢀ1.ꢀStructuresꢀofꢀnineꢀacidicꢀionicꢀliquids.ꢀ
afluorophosphateꢀ ([bmim]PF )ꢀ asꢀ anꢀ additive.ꢀ Althoughꢀ thisꢀ
6
products,ꢀ includingꢀ cyclohexanoneꢀ andꢀ CHO.ꢀ Theꢀ resultsꢀ ulti‐
matelyꢀrevealedꢀthatꢀNa WO ‐sulfonicꢀacid‐functionalizedꢀionicꢀ
liquidsꢀ couldꢀ beꢀusedꢀasꢀ catalystꢀ forꢀtheꢀ synthesisꢀofꢀ CL.ꢀFur‐
thermore,ꢀtheꢀfinalꢀproductsꢀwereꢀ readilyꢀ separatedꢀfromꢀtheꢀ
catalystꢀsystemꢀbyꢀaꢀsimpleꢀextraction.ꢀ
reactionꢀgaveꢀaꢀhighꢀphenolꢀconversionꢀandꢀgoodꢀselectivityꢀforꢀ
CL,ꢀitꢀwasꢀdifficultꢀtoꢀseparateꢀtheꢀILꢀfromꢀtheꢀreactionꢀmixture,ꢀ
therebyꢀlimitingꢀtheꢀeffectivenessꢀofꢀthisꢀapproach.ꢀ
Weꢀenvisagedꢀthatꢀitꢀwouldꢀbeꢀpossibleꢀtoꢀovercomeꢀtheꢀis‐
suesꢀ describedꢀ aboveꢀ byꢀ directlyꢀ synthesizingꢀ CLꢀ fromꢀ cyclo‐
hexanol,ꢀwhichꢀisꢀanꢀunavoidableꢀby‐productꢀofꢀtheꢀoxidationꢀofꢀ
cyclohexane.ꢀThus,ꢀtheꢀoxidationꢀofꢀcyclohexanolꢀinꢀtheꢀliquidꢀ
2
4
2.ꢀ ꢀ Experimentalꢀ ꢀ
phaseꢀusingꢀH
2
O ,ꢀfollowedꢀbyꢀsequentialꢀoximationꢀandꢀBeck‐
2
2.1.ꢀ ꢀ Preparationꢀofꢀionicꢀliquidsꢀ ꢀ
mannꢀrearrangementꢀreactionꢀinꢀaꢀsingleꢀpotꢀwouldꢀrepresentꢀ
anꢀ attractiveꢀ alternativeꢀ forꢀ theꢀ synthesisꢀ ofꢀ CLꢀ (Schemeꢀ 1).ꢀ
Thisꢀrouteꢀwouldꢀbeꢀparticularlyꢀinterestingꢀfromꢀanꢀindustrialꢀ
perspective,ꢀbecauseꢀallꢀthreeꢀsteps,ꢀincludingꢀ(1)ꢀtheꢀoxidationꢀ
ofꢀ cyclohexanolꢀ toꢀ cyclohexanone,ꢀ (2)ꢀ theꢀ oximationꢀ ofꢀ cyclo‐
hexanoneꢀ toꢀ CHO,ꢀ andꢀ (3)ꢀ theꢀ rearrangementꢀ ofꢀ CHOꢀ toꢀ CLꢀ
couldꢀbeꢀperformedꢀasꢀaꢀone‐potꢀprocedureꢀinꢀtheꢀpresenceꢀofꢀaꢀ
multifunctionalꢀcatalysts.ꢀ ꢀ
Allꢀ ofꢀ theꢀ chemicalsꢀ usedꢀ inꢀ theꢀ currentꢀ studyꢀ wereꢀ pur‐
chasedꢀ asꢀ theꢀ ARꢀ gradeꢀ fromꢀ Theꢀ Tianjinꢀ Fuꢀ Chenꢀ Chemicalꢀ
ReagentꢀFactoryꢀ(Tianjin,ꢀChina).ꢀ
[
Hnmp]HSO
BSMin]HSO ,ꢀ[BSTea]HSO
BSTma]p‐TAꢀ wereꢀ preparedꢀ usingꢀ previouslyꢀ reportedꢀ pro‐
4
,ꢀ [Hmin]HSO
4
,ꢀ [Tma]HSO
4
,ꢀ [Tea]HSO
4
,ꢀ
[
[
4
4
,ꢀ[BSTma]HSO
4
,ꢀ[BSTma]H
2
PO ꢀandꢀ
4
1
ceduresꢀ[18–24].ꢀTheꢀresultingꢀILsꢀwereꢀidentifiedꢀbyꢀ HꢀNMRꢀ
andꢀIRꢀanalyses.ꢀ
Theꢀ“green”ꢀoxidationꢀofꢀalcoholsꢀusingꢀtungstenꢀperoxideꢀasꢀ
anꢀoxidant,ꢀwhichꢀmayꢀbeꢀpreparedꢀbyꢀtheꢀreactionꢀofꢀH
2
O ꢀwithꢀ
2
aꢀcatalyticꢀamountꢀofꢀsodiumꢀtungstateꢀ(Na WO ),ꢀhasꢀattractedꢀ
2
4
2.2.ꢀ ꢀ Catalyticꢀtestingꢀ ꢀ
considerableꢀattentionꢀ[15].ꢀHowever,ꢀitꢀisꢀonlyꢀpossibleꢀtoꢀob‐
tainꢀhighꢀyieldsꢀofꢀtheꢀalcoholꢀproductsꢀinꢀthisꢀwayꢀunderꢀacidicꢀ
conditionsꢀwithꢀaꢀphaseꢀtransferꢀcatalystꢀ[15,16].ꢀWeꢀrecentlyꢀ
investigatedꢀtheꢀdirectꢀsynthesisꢀofꢀε‐caprolactamꢀfromꢀcyclo‐
Inꢀ aꢀ typicalꢀ procedure,ꢀ Na WO4ꢀ (2.75ꢀ mmol)ꢀ andꢀ anꢀ ionicꢀ
2
liquidꢀ wereꢀmixedꢀ withꢀcyclohexanolꢀ(50ꢀmmol)ꢀinꢀ aꢀ100‐mLꢀ
three‐neckedꢀflaskꢀequippedꢀwithꢀaꢀrefluxꢀcondenser,ꢀmagneticꢀ
stirrerꢀ andꢀ aꢀ thermometer.ꢀ Theꢀ resultingꢀ mixtureꢀ wasꢀ thenꢀ
heatedꢀ toꢀ theꢀ requiredꢀ temperature,ꢀ andꢀ treatedꢀ withꢀ 30%ꢀ
hexanolꢀusingꢀ[n‐C16
H
33N(CH
3
)
3
]H PW12O40ꢀasꢀaꢀcatalystꢀ[17].ꢀ
2
Inꢀthisꢀstudy,ꢀweꢀsynthesizedꢀnineꢀBrønstedꢀacidicꢀILsꢀ(Fig.ꢀ
)ꢀandꢀinvestigatedꢀtheirꢀuseꢀasꢀcatalystsꢀforꢀtheꢀone‐potꢀsyn‐
1
H
2
O ꢀ(75ꢀmmol),ꢀwhichꢀwasꢀaddedꢀinꢀaꢀdropwiseꢀmannerꢀtoꢀtheꢀ
2
thesisꢀofꢀCLꢀfromꢀcyclohexanolꢀusingꢀH
2
O ꢀandꢀhydroxylamine.ꢀ
2
reactionꢀ mixtureꢀ withꢀ vigorousꢀ stirringꢀ overꢀ 5ꢀ h.ꢀ Hydroxyla‐
mineꢀsulfateꢀ(25ꢀmmol)ꢀwasꢀthenꢀaddedꢀtoꢀtheꢀflaskꢀwithꢀvig‐
orousꢀstirringꢀoverꢀaꢀcertainꢀperiodꢀofꢀtime.ꢀUponꢀcompletionꢀofꢀ
theꢀ reaction,ꢀ theꢀ mixtureꢀ wasꢀ allowedꢀ toꢀ settleꢀ toꢀ giveꢀ twoꢀ
phases.ꢀ Theꢀ aqueousꢀ phaseꢀ wasꢀ collectedꢀ andꢀ extractedꢀ withꢀ
dichloromethane,ꢀ andꢀ theꢀ extractedꢀ productsꢀ wereꢀ identifiedꢀ
byꢀ gasꢀ chromatography‐massꢀ spectrometryꢀ usingꢀ aꢀ Thermoꢀ
Traceꢀ DSQꢀ gasꢀ chromatograph‐massꢀ spectrometerꢀ (Thermoꢀ
Electron,ꢀMassachusetts,ꢀAmerica).ꢀTheꢀproductsꢀwereꢀanalyzedꢀ
onꢀanꢀSP‐3420AꢀgasꢀchromatographꢀequippedꢀwithꢀaꢀKB‐Waxꢀ
columnꢀ(30ꢀmꢀ×ꢀ0.32ꢀmmꢀ×ꢀ0.25ꢀμm).ꢀ
Inꢀ additionꢀ toꢀ CL,ꢀ weꢀ alsoꢀ obtainedꢀ severalꢀ otherꢀ valuableꢀ
Theꢀcyclohexanolꢀconversionꢀ(XANOL),ꢀproductꢀselectivityꢀ(S
andꢀcarbonꢀbalanceꢀwereꢀcalculatedꢀasꢀfollows:ꢀ
ANOLꢀ=ꢀ(Molesꢀofꢀcyclohexanolꢀaddedꢀ–ꢀmolesꢀofꢀunconvert‐
edꢀcyclohexanol)/molesꢀofꢀcyclohexanolꢀaddedꢀ×ꢀ100%.ꢀ
i
)ꢀ
X
Schemeꢀ1.ꢀOne‐potꢀconversionꢀofꢀcyclohexanolꢀtoꢀCL.ꢀ

60ꢀ
HefangꢀWangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ58–64ꢀ
S ꢀ =ꢀ Molesꢀ ofꢀ productꢀ i/(molesꢀ ofꢀ cyclohexanolꢀ addedꢀ –ꢀ
i
molesꢀofꢀunconvertedꢀcyclohexanol)ꢀ×ꢀ100%.ꢀ
Carbonꢀ balanceꢀ =ꢀ (Molesꢀ ofꢀ unconvertedꢀ cyclohexanolꢀ +ꢀ
molesꢀofꢀcarbonꢀinꢀcyclohexanoneꢀ+ꢀmolesꢀofꢀcarbonꢀinꢀCHOꢀ+ꢀ
molesꢀ ofꢀ carbonꢀ inꢀ CL)/molesꢀ ofꢀ carbonꢀ inꢀ cyclohexanolꢀ ×ꢀ
1
00%.ꢀ
.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
.1.ꢀ ꢀ Effectꢀofꢀionicꢀliquidꢀstructureꢀonꢀselectiveꢀoxidationꢀofꢀ ꢀ
Fig.ꢀ2. Bisperoxotungstateꢀcompoundsꢀinvolvedꢀinꢀtheꢀoxidationꢀpro‐
cess.ꢀ
3
3
compoundꢀ wasꢀ readilyꢀ transferredꢀ toꢀ theꢀ organicꢀ phaseꢀ byꢀ aꢀ
cyclohexanolꢀtoꢀcyclohexanoneꢀ
+
+
Na –Q ꢀ ionꢀ exchangeꢀ mechanism.ꢀ Theꢀ catalyticꢀ activityꢀ ob‐
servedꢀduringꢀtheꢀoxidationꢀprocessꢀwouldꢀthereforeꢀbeꢀhighlyꢀ
dependentꢀonꢀtheꢀacidityꢀofꢀtheꢀreactionꢀmedium,ꢀwhereasꢀtheꢀ
efficiencyꢀofꢀtheꢀaqueous–organicꢀphaseꢀtransferꢀwouldꢀbeꢀde‐
TheꢀdirectꢀsynthesisꢀofꢀCLꢀfromꢀcyclohexanolꢀwouldꢀrequireꢀ
threeꢀsteps.ꢀTheꢀfirstꢀstepꢀwouldꢀinvolveꢀtheꢀselectiveꢀoxidationꢀ
ofꢀcyclohexanolꢀtoꢀcyclohexanone.ꢀTheꢀproductꢀcyclohexanoneꢀ
wouldꢀ thenꢀ reactꢀ withꢀ hydroxylamineꢀ toꢀ formꢀ CHO,ꢀ whichꢀ
wouldꢀundergoꢀaꢀrearrangementꢀreactionꢀtoꢀgiveꢀCL.ꢀToꢀidentifyꢀ
aꢀsuitableꢀcatalyticꢀsystemꢀforꢀtheꢀoxidationꢀofꢀcyclohexanolꢀtoꢀ
+
pendentꢀonꢀtheꢀactiveꢀspeciesꢀaidedꢀbyꢀQ ꢀ(Qꢀrefersꢀtoꢀtheꢀcati‐
onꢀofꢀtheꢀILs)ꢀ[25].ꢀTheꢀhighꢀcatalyticꢀperformanceꢀofꢀsulfonicꢀ
acid‐functionalizedꢀionicꢀliquidsꢀcanꢀthereforeꢀbeꢀattributedꢀtoꢀ
theꢀ improvedꢀ hydrophobicityꢀ ofꢀ theirꢀ cation,ꢀ whilstꢀ theirꢀ im‐
provedꢀ acidityꢀ canꢀ beꢀ attributedꢀ toꢀ theꢀ introductionꢀ ofꢀ al‐
kanesulfonicꢀacidꢀgroups.ꢀAꢀsimilarꢀeffectꢀwasꢀalsoꢀobservedꢀforꢀ
changesꢀinꢀtheꢀalkylꢀchainꢀlengthꢀduringꢀaꢀstudyꢀofꢀtheꢀselectiveꢀ
oxidationꢀofꢀcyclohexanolꢀtoꢀcyclohexanoneꢀ[26,27].ꢀ
cyclohexanoneꢀusingꢀNa
2
WO ,ꢀweꢀscreenedꢀaꢀvarietyꢀofꢀdiffer‐
4
entꢀ ionicꢀ liquidsꢀ (Tableꢀ 1).ꢀ Inꢀ theꢀ absenceꢀ ofꢀ theꢀ catalyst,ꢀ theꢀ
yieldꢀ ofꢀ cyclohexanoneꢀ wasꢀ onlyꢀ 1.08%ꢀ (Tableꢀ 1,ꢀ entryꢀ 1).ꢀ
Amongꢀ theꢀ fourꢀ non‐sulfonicꢀ acid‐functionalizedꢀ ILsꢀ testedꢀ inꢀ
theꢀ currentꢀ studyꢀ (Tableꢀ 1,ꢀ entriesꢀ 2–5),ꢀ [Tma]HSO ꢀ showedꢀ
4
Asꢀ shownꢀ inꢀ Tableꢀ 1,ꢀ theꢀ catalyticꢀ activitiesꢀ ofꢀ
theꢀhighestꢀcatalyticꢀactivity.ꢀTheꢀcatalyticꢀactivitiesꢀofꢀILsꢀfea‐
turingꢀalkanesulfonicꢀacidꢀgroupsꢀ(Tableꢀ1,ꢀentriesꢀ6–10)ꢀwereꢀ
muchꢀ higherꢀ thanꢀ thoseꢀ ofꢀ theꢀ ILsꢀ withoutꢀ anꢀ alkanesulfonicꢀ
[
BSTma]H
2
PO ꢀandꢀ[BSTma]p‐TAꢀwereꢀpoor.ꢀTheꢀacidityꢀofꢀanꢀ
4
ILꢀ isꢀ dependentꢀ onꢀ theꢀ natureꢀ ofꢀ itsꢀ cationsꢀ andꢀ anions.ꢀ Theꢀ
aciditiesꢀofꢀILsꢀbearingꢀtheꢀsameꢀcationsꢀareꢀdependentꢀonꢀtheꢀ
acidꢀgroupꢀ(Tableꢀ1,ꢀentriesꢀ2–4).ꢀInꢀparticular,ꢀ[BSTma]HSO
4
‐
ꢀ
differenceꢀinꢀtheirꢀanions.ꢀILsꢀfeaturingꢀ[H
baseꢀ areꢀ muchꢀ lessꢀ acidicꢀ thanꢀ thoseꢀ featuringꢀ [HSO
2
PO
4
]–ꢀasꢀaꢀconjugateꢀ
]–ꢀ asꢀ aꢀ
Na WO ꢀgaveꢀanꢀexcellentꢀcatalyticꢀperformanceꢀwithꢀaꢀcyclo‐
2
4
4
hexanolꢀ conversionꢀ ofꢀ 97.7%ꢀ andꢀ aꢀ selectivityꢀ forꢀ cyclohexa‐
noneꢀofꢀ96.2%.ꢀ
Theꢀ oxidationꢀ reactionꢀ proceededꢀ smoothlyꢀ inꢀ anꢀ organ‐
ic‐aqueousꢀbiphasicꢀsystem.ꢀInꢀtheꢀaqueousꢀphase,ꢀtheꢀcatalystꢀ
conjugateꢀ base,ꢀ accordingꢀ toꢀ H
0
ꢀ [27].ꢀ Theꢀ catalyticꢀ activityꢀ ofꢀ

[BSTma]p‐TAꢀwasꢀpoor,ꢀmostꢀlikelyꢀbecauseꢀitsꢀp‐CH
C H SO
3 6 4 3
ꢀ
anionꢀcannotꢀprovideꢀprotons,ꢀresultingꢀinꢀtheꢀlowꢀacidityꢀofꢀtheꢀ
IL.ꢀBasedꢀonꢀtheseꢀresults,ꢀweꢀconcludedꢀthatꢀtheꢀhydrophobicꢀ
cation,ꢀhydrophilicꢀanionꢀandꢀacidityꢀcharacteristicsꢀofꢀtheꢀILsꢀ
wereꢀresponsibleꢀforꢀtheꢀoxidationꢀofꢀcyclohexanolꢀ[28].ꢀ
2 4
precursorꢀ Na WO ꢀ wasꢀ rapidlyꢀ oxidizedꢀ byꢀ H
2
O ,ꢀ asꢀ follows:ꢀ
2
Na WO ꢀ+ꢀ2H
2
4
2
O
2
ꢀ=ꢀNa
2
[WO(O (OH) ]ꢀ+ꢀ2H Oꢀ[25].ꢀAccordingꢀ
2
)
2
2
2
toꢀNoyori’sꢀreportꢀ[25],ꢀtheꢀresultingꢀbisperoxotungstateꢀcom‐
poundꢀAꢀwouldꢀexistꢀinꢀequilibriumꢀwithꢀcompoundsꢀBꢀandꢀCꢀ
duringꢀ theꢀ oxidationꢀ processꢀ (Fig.ꢀ 2).ꢀ Noyoriꢀ etꢀ al.ꢀ [25]ꢀ alsoꢀ
indicatedꢀthatꢀtheꢀdianionꢀinꢀAꢀexhibitedꢀveryꢀlittleꢀactivityꢀto‐
wardꢀalcohols,ꢀwhereasꢀtheꢀmono‐ꢀandꢀdi‐protonatedꢀformsꢀinꢀ
Bꢀ andꢀ Cꢀ wereꢀ sufficientlyꢀ reactive.ꢀ Theꢀ bisperoxotungstateꢀ
3.2.ꢀ ꢀ One‐potꢀconversionꢀofꢀcyclohexanoneꢀtoꢀCLꢀ
Itꢀseemsꢀalmostꢀcontradictoryꢀtoꢀsuggestꢀthatꢀaꢀstrongꢀacidꢀ
andꢀdehydratingꢀmediaꢀareꢀrequiredꢀtoꢀensureꢀtheꢀprotonationꢀ
ofꢀ theꢀ oximeꢀ intermediateꢀ duringꢀ theꢀ rearrangementꢀ step,ꢀ
whenꢀwaterꢀfromꢀtheꢀH
2
O ꢀcouldꢀleadꢀtoꢀtheꢀhydrolysisꢀofꢀtheꢀ
2
Tableꢀ1ꢀ
oximeꢀorꢀtheꢀformationꢀofꢀundesirableꢀby‐productsꢀunderꢀtheꢀ
stronglyꢀacidicꢀconditionsꢀ[29,30].ꢀWithꢀthisꢀinꢀmind,ꢀweꢀinves‐
tigatedꢀ theꢀ effectꢀ ofꢀ theꢀ molarꢀ ratioꢀ ofꢀ cyclohexanoneꢀ toꢀ
Effectꢀofꢀtheꢀstructureꢀofꢀtheꢀionicꢀliquidꢀonꢀtheꢀoxidationꢀofꢀcyclohexa‐
nol.ꢀ
ANOLꢀ(%)ꢀ YANONꢀaꢀ(%)ꢀ Carbonꢀbalanceꢀ(%)
X
Entryꢀ
Ionicꢀliquidꢀ
Noneꢀ
4
[BSTma]HSO ꢀ onꢀ theꢀ outcomeꢀ ofꢀ theꢀ one‐potꢀ conversionꢀ ofꢀ
1
ꢀ
1.08ꢀ
92.2ꢀ
91.6ꢀ
92.5ꢀ
91.7ꢀ
96.2ꢀ
97.1ꢀ
97.7ꢀ
26.8ꢀ
10.6ꢀ
1.06ꢀ
91.2ꢀ
90.4ꢀ
92.0ꢀ
90.5ꢀ
95.2ꢀ
93.2ꢀ
96.2ꢀ
26.3ꢀ
10.0ꢀ
99.5ꢀ
98.7ꢀ
2ꢀ
[Hnmp]HSO
[Hmin]HSO
[Tma]HSO
[Tea]HSO
[BSMin]HSO
[BSTea]HSO
[BSTma]HSO
[BSTma]H PO
[BSTma]p‐TAꢀ
4
ꢀ
cyclohexanoneꢀtoꢀCLꢀ(Fig.ꢀ3).ꢀInꢀtheꢀabsenceꢀofꢀ[BSTma]HSO
theꢀyieldsꢀofꢀCLꢀandꢀCHOꢀwereꢀ62.7%ꢀandꢀ26.8%,ꢀrespectively.ꢀ
TheꢀyieldꢀofꢀCLꢀincreasedꢀasꢀtheꢀmolarꢀratioꢀofꢀcyclohexanoneꢀtoꢀ
4
,ꢀ
3
ꢀ
4
ꢀ
98.8ꢀ
98.2ꢀ
98.5ꢀ
98.3ꢀ
93.6ꢀ
98.1ꢀ
4
ꢀ
4
ꢀ
5
ꢀ
4
ꢀ
[BSTma]HSO ꢀ increasedꢀ fromꢀ 1:0.04ꢀ toꢀ 1:0.08.ꢀ However,ꢀ fur‐
4
6
ꢀ
4
ꢀ
ꢀ
ꢀ
therꢀ increasingꢀ theꢀ molarꢀ ratioꢀ toꢀ 1:0.16ꢀ didꢀ notꢀ leadꢀ toꢀ anyꢀ
furtherꢀchangesꢀinꢀtheꢀyieldꢀofꢀCLꢀandꢀtheꢀcarbonꢀbalanceꢀgrad‐
uallyꢀ decreased,ꢀ whichꢀ wasꢀ attributedꢀ toꢀ theꢀ formationꢀ ofꢀ aꢀ
highꢀboilingꢀcondensationꢀby‐product.ꢀTheꢀone‐potꢀconversionꢀ
ofꢀ cyclohexanoneꢀ toꢀ CLꢀ mostꢀ likelyꢀ proceedsꢀ viaꢀ theꢀ
non‐catalyticꢀoximationꢀofꢀcyclohexanoneꢀtoꢀCHO,ꢀfollowedꢀbyꢀ
theꢀBeckmannꢀrearrangementꢀofꢀCHOꢀtoꢀCL.ꢀTheꢀmechanismꢀforꢀ
7
ꢀ
4
8ꢀ
4
9
ꢀ
2
4
ꢀ
99.0ꢀ
99.2ꢀ
10ꢀ
Reactionꢀ conditions:ꢀ cyclohexanol:H
2 2 2 4 2
O :Na WO ·2H O:ionicꢀ liquidꢀ
(
molarꢀratio)ꢀ=ꢀ1.00:1.50:0.06:0.04,ꢀ80ꢀ°C,ꢀoxidationꢀtimeꢀ5ꢀh.ꢀ
Yieldꢀofꢀcyclohexanone.ꢀ
aꢀ

ꢀ
HefangꢀWangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ58–64ꢀ
61ꢀ
hexanoneꢀtoꢀCL.ꢀ
100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
3
.3.ꢀ ꢀ One‐potꢀconversionꢀofꢀcyclohexanolꢀtoꢀCLꢀ
Finally,ꢀ weꢀ investigatedꢀ theꢀ one‐potꢀ conversionꢀ ofꢀ cyclo‐
hexanolꢀtoꢀCLꢀusingꢀNa
2).ꢀInꢀtheꢀabsenceꢀofꢀaꢀcatalyst,ꢀthisꢀreactionꢀdidꢀnotꢀaffordꢀanyꢀ
CLꢀ(Tableꢀ2,ꢀentryꢀ1).ꢀWhenꢀtheꢀsameꢀreactionꢀwasꢀconductedꢀinꢀ
theꢀpresenceꢀofꢀNa
4
usedꢀ asꢀ aꢀ catalystꢀ inꢀ theꢀ one‐potꢀ synthesisꢀ ofꢀ CL.ꢀ Duringꢀ theꢀ
oxidationꢀprocess,ꢀtheꢀcatalystꢀactedꢀasꢀaꢀphase‐transferꢀcata‐
lystꢀbasedꢀonꢀitsꢀionꢀexchangeꢀbehavior,ꢀandꢀtheꢀacidityꢀofꢀtheꢀ
catalystꢀsystemꢀimprovedꢀtheꢀcoordinationꢀofꢀtheꢀsubstrateꢀtoꢀ
bisperoxotungstate.ꢀOurꢀnewlyꢀdevelopedꢀcatalystꢀalsoꢀloweredꢀ
theꢀactivationꢀenergyꢀforꢀtheꢀBeckmannꢀrearrangementꢀbyꢀsta‐
bilizingꢀ theꢀ chargedꢀ intermediateꢀ formedꢀ duringꢀ theꢀ rear‐
rangement,ꢀtoꢀultimatelyꢀaffordꢀCLꢀ[14].ꢀ
2
WO
4
‐[BSTma]HSO ꢀasꢀaꢀcatalystꢀ(Tableꢀ
4
Conversion of cyclohexanone
Selectivity for cyclohexanone oxime
Selectivity for caprolactam
Carbon balance
2 4 4
WO ‐[BSTma]HSO ,ꢀtheꢀyieldꢀofꢀCLꢀreachedꢀ
9.1%ꢀ(Tableꢀ2,ꢀentryꢀ3).ꢀNa
2
WO ‐[BSTma]HSO
4
4
ꢀwasꢀthereforeꢀ
1
:0.00
1:0.04
Cyclohexanone/IL7 molar ratio
Fig.ꢀ3.ꢀEffectꢀofꢀtheꢀmolarꢀratioꢀofꢀcyclohexanoneꢀtoꢀ[BSTma]HSO
theꢀ one‐potꢀ conversionꢀ ofꢀ cyclohexanoneꢀ toꢀ CL.ꢀ Reactionꢀ conditions:
cyclohexanone:H O:(NH OH) ·H SO :Na WO ·2H Oꢀ (molarꢀ ratio)ꢀ =
.00:6.60:0.50:0.06,ꢀ80ꢀ°C,ꢀoximationꢀandꢀarrangementꢀtimeꢀ2.5ꢀh.ꢀ
1:0.08
1:0.12
1:0.16
4
ꢀonꢀ
2
2
2
2
4
2
4
2
1
Weꢀ subsequentlyꢀ proceededꢀ toꢀ investigateꢀ theꢀ effectsꢀ ofꢀ
severalꢀ keyꢀ parameters,ꢀ includingꢀ theꢀ reactionꢀ temperature,ꢀ
reactionꢀ timeꢀ andꢀ theꢀ molarꢀ ratioꢀ ofꢀ cyclohexanoneꢀ toꢀ
theꢀrearrangementꢀofꢀCHOꢀinvolvesꢀtheꢀBrønstedꢀacid‐mediatedꢀ
protonationꢀofꢀ theꢀnitrogenꢀ atomꢀofꢀtheꢀoxime,ꢀfollowedꢀ byꢀ aꢀ
protonꢀtransferꢀfromꢀtheꢀnitrogenꢀatomꢀtoꢀtheꢀoxygenꢀatomꢀofꢀ
theꢀoximeꢀ[31,32].ꢀTheꢀformationꢀofꢀanꢀO‐protonatedꢀoximeꢀinꢀ
thisꢀ wayꢀ isꢀ aꢀ 1,2‐H‐shiftꢀ reaction,ꢀ andꢀ reactionsꢀ ofꢀ thisꢀ typeꢀ
generallyꢀrequireꢀaꢀhighꢀactivationꢀenergy.ꢀForꢀthisꢀreason,ꢀthisꢀ
stepꢀisꢀconsideredꢀtoꢀbeꢀtheꢀrate‐determiningꢀstepꢀinꢀtheꢀBeck‐
mannꢀrearrangement.ꢀ
Accordingꢀtoꢀpreviousꢀreportsꢀfromꢀtheꢀliterature,ꢀsolventsꢀ
withꢀhighꢀdielectricꢀconstantsꢀsuchꢀasꢀbenzonitrile,ꢀDMSOꢀandꢀ
MeCNꢀ canꢀ playꢀ anꢀ importantꢀ roleꢀ inꢀ loweringꢀ theꢀ activationꢀ
energyꢀofꢀaꢀBeckmannꢀreactionꢀbyꢀinteractingꢀdirectlyꢀwithꢀtheꢀ
N‐protonatedꢀoximeꢀtoꢀformꢀaꢀcyclicꢀtransitionꢀstateꢀ[33–35].ꢀInꢀ
theꢀone‐potꢀsolventꢀfreeꢀconversionꢀofꢀcyclohexanoneꢀtoꢀCL,ꢀtheꢀ
sulfonicꢀacidꢀgroupsꢀassociatedꢀwithꢀtheꢀcationsꢀonꢀtheꢀsulfonicꢀ
acid‐functionalizedꢀ ionicꢀ liquidꢀ couldꢀ facilitateꢀ theꢀ formationꢀ
andꢀstabilizationꢀofꢀtheꢀpositivelyꢀchargedꢀintermediateꢀbasedꢀ
onꢀtheirꢀstrongꢀacidityꢀandꢀhighꢀpolarityꢀ[36].ꢀAꢀcyclohexanoneꢀ
[BSTma]HSO
4
ꢀ onꢀ theꢀ outcomeꢀ ofꢀ theꢀ Na
2
WO
4
‐[BSTma]HSO
4
‐
ꢀ
catalyzedꢀ one‐potꢀ conversionꢀ ofꢀ cyclohexanolꢀ toꢀ CL.ꢀ Theꢀ tan‐
demꢀ reactionꢀ wasꢀ dividedꢀ intoꢀ threeꢀ steps.ꢀ Theꢀ firstꢀ andꢀ theꢀ
thirdꢀ stepsꢀ wereꢀ determinedꢀ toꢀ beꢀ exothermic,ꢀ whereasꢀ theꢀ
secondꢀoneꢀwasꢀslightlyꢀexothermic.ꢀTheꢀcyclohexanolꢀconver‐
sionꢀ andꢀ yieldꢀ ofꢀ CLꢀ increasedꢀ withꢀ increasingꢀ temperatureꢀ
fromꢀ70ꢀtoꢀ80ꢀ°C,ꢀwhereꢀtheꢀyieldꢀofꢀCLꢀreachedꢀitsꢀmaximumꢀ
valueꢀofꢀ49.1%ꢀ(Tableꢀ2,ꢀentriesꢀ2ꢀandꢀ3).ꢀAlthoughꢀfurtherꢀin‐
creasesꢀinꢀtheꢀtemperatureꢀresultedꢀinꢀaꢀdecreaseꢀinꢀtheꢀyieldꢀofꢀ
CLꢀ(Tableꢀ2,ꢀentriesꢀ4ꢀandꢀ5),ꢀtheꢀselectivityꢀforꢀcyclohexanoneꢀ
continuedꢀtoꢀincrease.ꢀTheꢀhighꢀselectivityꢀforꢀcyclohexanone,ꢀ
whichꢀwasꢀformedꢀbyꢀtheꢀhydrolysisꢀofꢀtheꢀCHO,ꢀresultedꢀinꢀaꢀ
decreaseꢀ inꢀ theꢀ selectivityꢀ forꢀ CLꢀ forꢀ reactionꢀ temperaturesꢀ
aboveꢀ80ꢀ°C.ꢀ
Theꢀcyclohexanolꢀconversionꢀremainedꢀunchangedꢀforꢀoxi‐
mationꢀandꢀrearrangementꢀreactionꢀtimesꢀinꢀtheꢀrangeꢀofꢀ60ꢀtoꢀ
180ꢀmin.ꢀTheꢀCLꢀyieldꢀinitiallyꢀincreasedꢀandꢀreachedꢀitsꢀmaxi‐
mumꢀvalueꢀofꢀ49.1%ꢀ(Tableꢀ2,ꢀentriesꢀ3,ꢀ6,ꢀandꢀ7),ꢀbeforeꢀde‐
creasingꢀtoꢀ41.4%ꢀafterꢀextendingꢀtheꢀreactionꢀtimeꢀbyꢀ30ꢀminꢀ
toꢀ[BSTma]HSO
ꢀmolarꢀratioꢀofꢀ1:0.08ꢀwasꢀthereforeꢀselectedꢀasꢀ
4
theꢀoptimumꢀmolarꢀratioꢀforꢀtheꢀone‐potꢀconversionꢀofꢀcyclo‐
Tableꢀ2ꢀ
One‐potꢀconversionꢀofꢀcyclohexanolꢀtoꢀCLꢀusingꢀNa
2
WO
4
‐[BSTma]HSO .ꢀ
4
ꢀ
a
Selectivityꢀ(%)ꢀ
Time ꢀ
(
Cyclohexanolꢀtoꢀ
Entryꢀ
Tꢀ(°C)ꢀ
X
ANOLꢀ(%)ꢀ
Carbonꢀbalanceꢀ(%)
min)ꢀ
150ꢀ
150ꢀ
150ꢀ
150ꢀ
150ꢀ
ꢀ 60ꢀ
120ꢀ
180ꢀ
150ꢀ
150ꢀ
150ꢀ
4
[BSTma]HSO ꢀmolarꢀratio
Ketoneꢀ
ꢀ ꢀ 5.67ꢀ
23.2ꢀ
10.3ꢀ
32.4ꢀ
31.4ꢀ
23.1ꢀ
15.4ꢀ
Oximeꢀ
41.9ꢀ
49.8ꢀ
36.6ꢀ
39.4ꢀ
39.5ꢀ
50.2ꢀ
37.2ꢀ
31.5ꢀ
ꢀ 9.6ꢀ
42.0ꢀ
40.0ꢀ
Amideꢀ
ꢀ 0.5ꢀ
24.2ꢀ
49.1ꢀ
23.0ꢀ
21.6ꢀ
23.0ꢀ
44.3ꢀ
41.4ꢀ
76.0ꢀ
46.7ꢀ
32.0ꢀ
1
ꢀ
ꢀ 80ꢀ
ꢀ 70ꢀ
ꢀ 80ꢀ
ꢀ 90ꢀ
100ꢀ
ꢀ 80ꢀ
ꢀ 80ꢀ
ꢀ 80ꢀ
ꢀ 80ꢀ
ꢀ 80ꢀ
ꢀ 80ꢀ
—ꢀ
1.58ꢀ
96.1ꢀ
100ꢀ
100ꢀ
100ꢀ
100ꢀ
100ꢀ
100ꢀ
97.3ꢀ
96.0ꢀ
52.5ꢀ
96.8ꢀ
93.3ꢀ
93.7ꢀ
92.5ꢀ
90.1ꢀ
93.8ꢀ
94.0ꢀ
90.1ꢀ
93.3ꢀ
92.4ꢀ
85.4ꢀ
2
ꢀ
1:0.04ꢀ
1:0.04ꢀ
1:0.04ꢀ
1:0.04ꢀ
1:0.04ꢀ
1:0.04ꢀ
1:0.04ꢀ
1:0.08ꢀ
1:0.12ꢀ
1:0.16ꢀ
3
ꢀ
4
ꢀ
5
ꢀ
6
ꢀ
7ꢀ
8
ꢀ
19.1ꢀ
11.0ꢀ
ꢀ ꢀ 7.88ꢀ
13.4ꢀ
9
ꢀ
1
1
0ꢀ
1ꢀ
Reactionꢀconditions:ꢀcyclohexanol:H
2
O
2
:(NH
2
OH)
2
·H
2
SO
4
:Na
2
WO
4
·2H Oꢀ(molarꢀratio)ꢀ=ꢀ1.00:1.50:0.50:0.06,ꢀoxidationꢀtimeꢀ5ꢀh.ꢀ
2
a
ꢀOximationꢀandꢀarrangementꢀtime.ꢀ

62ꢀ
HefangꢀWangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ58–64ꢀ
(
Tableꢀ 2,ꢀentryꢀ 8).ꢀFurthermore,ꢀtheꢀ selectivityꢀforꢀcyclohexa‐
Tableꢀ3ꢀ
Directꢀ conversionꢀ ofꢀ variousꢀ alcoholsꢀ toꢀ amidesꢀ usingꢀ Na WO ‐
noneꢀincreasedꢀfromꢀ10.3%ꢀtoꢀ19.1%ꢀduringꢀthisꢀperiod.ꢀThisꢀ
resultꢀindicatedꢀthatꢀtheꢀCHOꢀformedꢀduringꢀtheꢀreactionꢀwasꢀ
ꢀ
2
4
4
[BSTma]HSO ꢀasꢀaꢀcatalyst.ꢀ
beingꢀ hydrolyzedꢀ inꢀ theꢀ presenceꢀ ofꢀ [BSTma]HSO
duringꢀtheꢀprolongedꢀreactionꢀtimesꢀ[37].ꢀWhenꢀtheꢀmolarꢀratioꢀ
ofꢀ cyclohexanoneꢀ toꢀ IL7ꢀ wasꢀ 1:0.08,ꢀ Na WO ‐[BSTma]HSO
showedꢀ highꢀ catalyticꢀ activity,ꢀ withꢀ theꢀ conversionꢀ ofꢀ cyclo‐
hexanolꢀandꢀyieldꢀofꢀCLꢀreachingꢀ97.3%ꢀandꢀ76%,ꢀrespectively.ꢀ ꢀ
4
ꢀandꢀwaterꢀ
Sectivity
Ketoneꢀ Oxime Amide
ꢀ
(%)ꢀ
Entryꢀ
Substrateꢀ
X
Alcoholꢀ(%)ꢀ
OH
CH
2
4
4
ꢀ
1ꢀ
100ꢀ
0ꢀ
18.0ꢀ
12.2ꢀ
80.8ꢀ
80.1ꢀ
OH
2ꢀ
100ꢀ
7.39ꢀ
3.4.ꢀ ꢀ One‐potꢀconversionꢀofꢀvariousꢀalcoholsꢀtoꢀamidesꢀusingꢀ
Na WO ‐[BSTma]HSO ꢀasꢀaꢀcatalystꢀ ꢀ
2
4
4
OH
3
ꢀ
ꢀ
97.3ꢀ
91.5ꢀ
11.0ꢀ
26.7ꢀ
9.6ꢀ
76.0ꢀ
36.3ꢀ
Withꢀtheꢀoptimizedꢀreactionꢀconditionsꢀinꢀhand,ꢀweꢀproceedꢀ
OH
toꢀinvestigateꢀtheꢀscopeꢀofꢀthisꢀreactionꢀbyꢀsynthesizingꢀaꢀseriesꢀ
ofꢀN‐substitutedꢀamidesꢀ(Tableꢀ3).ꢀPleasingly,ꢀaꢀwideꢀrangeꢀofꢀ
alcoholꢀsubstrates,ꢀincludingꢀvariousꢀaromaticꢀandꢀcyclicꢀalco‐
hols,ꢀreactedꢀsmoothlyꢀunderꢀtheꢀoptimizedꢀconditionsꢀtoꢀgiveꢀ
theꢀ desiredꢀ productsꢀ inꢀ excellentꢀ yields.ꢀ Furthermore,ꢀ theseꢀ
resultsꢀcomparedꢀwellꢀwithꢀthoseꢀpreviouslyꢀreportedꢀforꢀtheꢀ
reactionsꢀ ofꢀ theꢀ correspondingꢀ ketoximesꢀ usingꢀ
4
36.0ꢀ
OH
OH
5
ꢀ
ꢀ
100ꢀ
100ꢀ
38.9ꢀ
31.5ꢀ
37.0ꢀ
65.6ꢀ
20.1ꢀ
1.33ꢀ
6
Reactionꢀ conditions:ꢀ cyclohexanol:H
molarꢀratio)ꢀ=ꢀ1.00:1.50:0.50:0.06,ꢀoxidationꢀatꢀ80ꢀ°Cꢀforꢀ6ꢀh,ꢀoximationꢀ
andꢀrearrangementꢀatꢀ80ꢀ°Cꢀforꢀ5ꢀh.ꢀ
2
O
2
2
:(NH OH)
·H
2 2
4
SO :Na
2
WO
4
·2H Oꢀ
2
(
[
n‐C16
H
33N(CH
3
)
3
]H
2
PW12
O
40ꢀ [17],ꢀ Cs H3‐xPW12O40ꢀ [33],ꢀ pro‐
x
paneꢀsulfonicꢀacid‐functionalizedꢀimidazoliumꢀsaltꢀofꢀphospho‐
tungstateꢀ[34],ꢀCL‐basedꢀBrønstedꢀacidicꢀionicꢀliquidꢀ[38],ꢀhet‐
6
([bmim]PF )ꢀ wasꢀ usedꢀ asꢀ anꢀ additive.ꢀ Theꢀ yieldꢀ ofꢀ CLꢀ overꢀ
3
eropolyanion‐basedꢀ ionicꢀ liquidꢀ [39]ꢀ andꢀ H PW12O40ꢀ [40]ꢀ asꢀ
Na WO ‐[BSTma]HSO
2
4
4
ꢀwasꢀmuchꢀlowerꢀthanꢀthatꢀofꢀcyclohex‐
catalystsꢀ(shownꢀinꢀTableꢀ3).ꢀ
anoneꢀ whenꢀ cyclohexanoneꢀ wasꢀ usedꢀ asꢀ aꢀ reactantꢀ (Tableꢀ 4,ꢀ
entryꢀ4).ꢀHowever,ꢀtheꢀapplicationꢀofꢀthisꢀprocessꢀisꢀlimitedꢀbyꢀ
theꢀdifficultiesꢀassociatedꢀwithꢀtheꢀrecoveryꢀofꢀtheꢀhomogene‐
Notably,ꢀ ourꢀ newlyꢀ developedꢀ catalystꢀ gaveꢀ anꢀ excellentꢀ
performanceꢀforꢀtheꢀconversationꢀofꢀisopropanolꢀandꢀsec‐butylꢀ
alcohol.ꢀThisꢀresultꢀwasꢀparticularlyꢀimpressiveꢀbecauseꢀprevi‐
ousꢀreportsꢀhadꢀsuggestedꢀthatꢀitꢀwasꢀnotꢀpossibleꢀtoꢀconvertꢀ
theseꢀ substratesꢀ toꢀ amidesꢀ usingꢀ novelꢀ Brønstedꢀ acidicꢀ ILsꢀ
3
ousꢀ CF COOHꢀ catalystꢀ fromꢀ theꢀ reactionꢀ mixture.ꢀ
Na WO ‐[BSTma]HSO
2
4
4
ꢀ exhibitedꢀ comparableꢀ catalyticꢀ activityꢀ
toꢀallꢀofꢀtheꢀotherꢀcatalystsꢀusingꢀCHOꢀasꢀaꢀreactantꢀ(Tableꢀ4,ꢀ
entriesꢀ 5–10).ꢀ Theseꢀ resultsꢀ thereforeꢀ demonstrateꢀ thatꢀ
bearingꢀ doubleꢀ –SO
thisꢀ workꢀ wasꢀ lowerꢀ thanꢀ thatꢀ reportedꢀ byꢀ Zhangꢀ etꢀ al.ꢀ [29]ꢀ
99%),ꢀwhereꢀcyclohexanoneꢀwasꢀdirectlyꢀconvertedꢀtoꢀCLꢀus‐
3
Hꢀ cationsꢀ [41].ꢀ Theꢀ CLꢀ yieldꢀ achievedꢀ inꢀ
Na
2
WO
4
‐[BSTma]HSO ꢀ isꢀ anꢀ efficientꢀ catalystꢀ forꢀ theꢀ one‐potꢀ
4
(
conversionꢀofꢀcyclohexanolꢀtoꢀCL.ꢀ
ingꢀtrifluoroaceticꢀacidꢀasꢀaꢀcatalystꢀwithꢀacetonitrileꢀasꢀanꢀad‐
ditive.ꢀ
3.5.ꢀ ꢀ Catalystꢀrecyclingꢀ
Tableꢀ 4ꢀ summarizesꢀ theꢀ catalyticꢀ performanceꢀ ofꢀ variousꢀ
catalystsꢀpreviouslyꢀreportedꢀforꢀtheꢀsynthesisꢀofꢀCL.ꢀTheꢀyieldꢀ
Uponꢀcompletionꢀofꢀtheꢀreaction,ꢀtheꢀmixtureꢀwasꢀallowedꢀtoꢀ
settleꢀtoꢀformꢀtwoꢀdistinctꢀphases.ꢀTheꢀaqueousꢀphaseꢀwasꢀcol‐
lectedꢀ andꢀ extractedꢀ withꢀ dichloromethane,ꢀ withꢀ theꢀ ILsꢀ andꢀ
ofꢀCLꢀoverꢀNa
Nb‐MCM‐41ꢀusingꢀcyclohexanoneꢀasꢀaꢀreactantꢀ(Tableꢀ4,ꢀentryꢀ
).ꢀTheꢀyieldꢀofꢀCLꢀoverꢀNa WO ‐[BSTma]HSO ꢀwasꢀhigherꢀthanꢀ
thatꢀ ofꢀ Pd‐Sc(OTf) /[bmim]PF ꢀ(Tableꢀ4,ꢀentryꢀ2),ꢀwhereꢀ300ꢀ
1‐butyl‐methylimidazoliumꢀ hexafluorophosphateꢀ
2
WO
4
‐[BSTma]HSO ꢀwasꢀmuchꢀhigherꢀthanꢀthatꢀofꢀ
4
1
2
4
4
Na
2
WO ꢀcompletelyꢀdissolvingꢀinꢀtheꢀaqueousꢀphase.ꢀToꢀinves‐
4
3
6
tigateꢀ theꢀ reusabilityꢀ ofꢀ theꢀ catalyst,ꢀ theꢀ aqueousꢀ phaseꢀ fromꢀ
theꢀfirstꢀrunꢀwasꢀconcentratedꢀtoꢀdrynessꢀusingꢀaꢀrotaryꢀevap‐
mol%ꢀ
Tableꢀ4ꢀ
ComparisonꢀofꢀtheꢀcatalyticꢀperformancesꢀofꢀvariousꢀcatalystsꢀforꢀsynthesisꢀofꢀCL.ꢀ
Entryꢀ
Catalystꢀ
Nb‐MCM‐41ꢀ
Reactionꢀconditionsꢀ
1ꢀatmꢀofꢀH
,ꢀ20ꢀ°C,ꢀHONH +
:NH :cyclohexanoneꢀ=ꢀ1.32:1.5:1ꢀ
Oxidationꢀatꢀ80ꢀ°Cꢀforꢀ6ꢀh,ꢀ ꢀ
Reactantꢀ
Cyclohexanoneꢀ
Phenolꢀ
Yieldꢀ(%)
4.82ꢀ
67.0ꢀ
Ref.ꢀ
[11]ꢀ
[14]ꢀ
[17]ꢀ

1
ꢀ
2
3
Cl ꢀ
2
ꢀ
Pd−Sc(OTf)
3
/[bmim]PF
]H
6
ꢀ
H O
2 2
3
3ꢀ
[n‐C16
H
33N(CH
3
)
3
2
PW12
O
40
ꢀ
Cyclohexanolꢀ
73.9ꢀ
oximationꢀandꢀrearrangementꢀatꢀ80ꢀ°Cꢀforꢀ5ꢀhꢀ
Solventꢀacetonitrile,ꢀ70ꢀ°C,ꢀ4ꢀhꢀ
Solventꢀbenzonitrile,ꢀ130ꢀ°C,ꢀ6ꢀhꢀ
Solventꢀacetonitrile,ꢀ90ꢀ°C,ꢀ1ꢀhꢀ
100ꢀ°C,ꢀ4ꢀhꢀ
4
5
6
7
8
9
1
1
ꢀ ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0ꢀ
1ꢀ
CF
3
COOHꢀ
Cyclohexanoneꢀ
Cyclohexanoneꢀoximeꢀ
Cyclohexanoneꢀoximeꢀ
Cyclohexanoneꢀoximeꢀ
Cyclohexanoneꢀoximeꢀ
Cyclohexanoneꢀoximeꢀ
Cyclohexanoneꢀoximeꢀ
Cyclohexanolꢀ
99.0ꢀ
56.0ꢀ
83.0ꢀ
82.3ꢀ
73.0ꢀ
89.0ꢀ
37.0ꢀ
76.0ꢀ
[29]ꢀ
[33]ꢀ
[34]ꢀ
[38]ꢀ
[39]ꢀ
[40]ꢀ
[41]ꢀ
thisꢀwork
Cs
[MIMPS]
[NHC]BF
[DPySO
x
H3‐xPW12
O ꢀ
40
3
PW12
O40ꢀ+ꢀZnCl
2
ꢀ
4
ꢀ
3
H]1.5PW12
O
40
ꢀ
Solventꢀbenzonitrile,ꢀ130ꢀ°C,ꢀ2ꢀhꢀ
Solventꢀacetonitrile,ꢀreflux,ꢀ2ꢀhꢀ
Solventꢀacetonitrile,ꢀ5ꢀhꢀ
3
H PW12
O
40
ꢀ
[Bis‐BsImD][OTf]
Na WO
2
‐ZnCl
2
ꢀ
2
4
‐[BSTma]HSO
4
ꢀ
2 2 2 2 2 4 2 4 2
Cyclohexanol:H O :(NH OH) ·H SO :Na WO ·2H Oꢀ=ꢀ
1.00:1.50:0.50:0.06,ꢀ5ꢀh,ꢀoximationꢀandꢀrearrangementꢀfor5ꢀhꢀ

ꢀ
HefangꢀWangꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ38ꢀ(2017)ꢀ58–64ꢀ
63ꢀ
orator,ꢀ andꢀ theꢀ resultingꢀ residueꢀ wasꢀ storedꢀ atꢀ 60ꢀ °Cꢀ underꢀ
vacuumꢀ toꢀ obtainꢀ theꢀ recycledꢀ catalyst.ꢀ Thisꢀ processꢀ wasꢀ re‐
peatedꢀforꢀfourꢀcycles.ꢀNotably,ꢀtheꢀyieldꢀofꢀCLꢀobtainedꢀusingꢀ
theꢀrecycledꢀcatalystꢀdecreasedꢀonlyꢀslightlyꢀ(3.5%)ꢀafterꢀfourꢀ
runs.ꢀThisꢀlossꢀinꢀactivityꢀcanꢀmostꢀlikelyꢀbeꢀattributedꢀtoꢀtheꢀ
physicalꢀlossesꢀincurredꢀduringꢀtheꢀrecyclingꢀprocess.ꢀ
Catal.ꢀA,ꢀ2011,ꢀ351,ꢀ210–216.ꢀ
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[
[
3
2
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2
presenceꢀofꢀaꢀ Na
id‐functionalizedꢀ ionicꢀ liquidsꢀ bearingꢀ HSO
2
WO
4
‐acidicꢀionicꢀliquidꢀcatalyst.ꢀ Sulfonicꢀ ac‐
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GraphicalꢀAbstractꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2017,ꢀ38:ꢀ58–64ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(16)62563‐9
One‐potꢀconversionꢀofꢀcyclohexanolꢀtoꢀε‐caprolactamꢀusingꢀaꢀ
One-pot conversion of cyclohexanol to ε-caprolactam
OH
O
2 4
multifunctionalꢀNa WO ‐acidicꢀionicꢀliquidꢀcatalyticꢀsystemꢀ
NH
ꢀ
Na WO -Acidic Ionic Liquid
2 4
HefangꢀWang,ꢀLiyuanꢀJia,ꢀRongbinꢀHu,ꢀMeidanꢀGao,ꢀYanjiꢀWang*ꢀ ꢀ
HebeiꢀUniversityꢀofꢀTechnologyꢀ
ꢀ
ꢀ
ꢀ
2 4
Na WO ‐acidicꢀionicꢀliquidꢀwasꢀusedꢀasꢀaꢀsimple,ꢀecofriendly,ꢀrecy‐
O
NOH
clableꢀ andꢀ efficientꢀ catalyticꢀ systemꢀ inꢀ theꢀ one‐potꢀ synthesisꢀ ofꢀ
ε‐caprolactamꢀfromꢀcyclohexanol,ꢀhydrogenꢀperoxide,ꢀandꢀhydrox‐
ylamine.ꢀ
(
2 2 2 4
NH OH) ·H SO

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