Greener protocol for one pot synthesis of coumarin styryl dy(2)

106S.B.Phadtareetal./DyesandPigments97(2013)105e112

thecomponentsofDESarebiodegradableandapproximatelyten-foldlessexpensivethanthoserequiredforionicliquids.Theirsynthesisisalsosimplerandmerelyrequiresthemixingoftwoormorecomponentsinproperratios.

Ofthefourcategories[17]ofeutecticsolvents,especiallyattrac-tiveisthecholinechloride:ureamixture.Aeutecticmixtureofcholinechloride:ureacanactasacatalystaswellassolventinthe eldoforganicsynthesisandisthusapowerfulreplacementforthemostcommonlyemployedbaseoracid-catalyzedreactionsthatinvolvetheuseofstrongacid,strongalkali,andcarcinogenicbaseslikepiperidine,pyridine,etc.AtypeIIIeutectic,cholinechloride:urea-basedDEShasbeensuccessfullyusedforionothermalmaterialsynthesis[18],chemical xationofCO2[19],lipasecatalyzedtrans-esteri cation[20],synthesisofdihydropyrimidin-2(1H)-ones[21],etc.Higherconcentrationofureacanbeirritatingtoskin,eyes,andtherespiratorytract(LD50is15g/kgforrat).Ingestionoflowconcentrationsofurea,suchasarefoundintypicallyhumanurine,isnon-toxicwithadditionalwateringestionwithinareasonabletime-frame.

Inthepresentstudy,wereportforthe rsttimethesynthesisofnovel uorescentcolorantsbasedoncyanocoumarininaonepotmethodusingcholinechlorideandureamixtureasDES.Goodyieldsofthenoveldyescouldbeobtained;theseexhibitedremarkablethermalstabilityaswellasbrilliant uorescence.Wecarriedoutspectroscopicstudiesinvarioussolventswithincreasingpolarityandobservedthebathochromicshiftassolventpolarityincreased.TheDEScouldberecycledthreetimeswithoutlosingitssigni cantactivity.DESbasedoncholinechlorideandureachosenherewasespeciallyattractivebecauseboththeingredientswereinexpensive,thuscontributingtotheeconomicviabilityoftheentireprocess.Theabilityofadeepeutecticmixturetoserveasasolventhasbeenexploredinsomeofourrecentpapersinorganicchemistry[22].2.Experimental

2.1.Materialsandequipments

Allproductswerecon rmedbymeltingpoint,FT-IRspectros-copy,CHNSanalysis,1HNMR,COSY,13CNMRspectroscopyandmassspectrometry.PuritywascheckedbyHPLCusingAcetonitrile:Methanol(75:25)mobilephaseandsilicacolumnC18.AllmeltingpointsareuncorrectedandarepresentedindegreeCelsius.1HNMR,COSYand13CNMRspectrumswererecordedon300,500MHzand100MHzmercuryplusspectrometerrespectively,andchemicalshiftsareexpressedindppmusingTMSasaninternalstandard.Massspectraldatawereobtainedwithamicromass-Q-TOFspectrometer.2.2.Generalprocedure

Added1mmolof4-(diethylamino)-2-hydroxybenzaldehydeand1mmolofethylacetoacetateinDES(7w/v)to100mlroundbottom askequippedwiththermowellandcondenserarrangedonmagneticstirrer.Stirredreactionmixtureat70e75 Cfor1e2h.ReactionwasmonitoredbyTLCshowed.Added1mmolofmalo-nonitrile4slowlyandagainstirredfor70e75 Cfor1e2h.ThisreactionwasalsomonitoredbyTLC.Added1mmolofaromaticaldehyde6a-6handstirredfor30e40 Cfor1e2h.DESismisciblewithwaterandalltheproductsareinsolidformthusproductwasseparatedfromaqueousphasebyphaseseparation.Afterreactionforisolationofproduct,mixturewaspouredinto10mlofwaterand ltered,washedwith4mlofwatertwice,driedinoventillconstantweightisobtained.

2.3.Scaleupandrecycling

ForscaleupandrecyclingofDES,added5mmolof4-(dieth-ylamino)-2-hydroxybenzaldehydeand5mmolofethylacetoace-tateinDES(7w/v)to250mlroundbottom askequippedwiththermowellandcondenserarrangedonmagneticstirrer.Stirredreactionmixtureat70e75 Cfor1e2h.ReactionwasmonitoredbyTLCshowed.Added5mmolofmalononitrile4slowlyandagainstirredfor70e75 Cfor1e2h.ThisreactionwasalsomonitoredbyTLC.Added5mmolofaromaticbenzaldehyde6aandstirredfor30e40 Cfor1e2h.Aftercompletionofthereaction,waterwasadded,andthemixture lteredandresiduedriedinanoventoisolatetheproduct7a.TheDESwasrecoveredfromthe ltratebyevaporatingthewaterphaseat80 Cundervacuum.TherecycledDESwasusedforthenextbatchandrecycledagain.Sameproce-durefollowedforconsecutiverecycling.

2.4.Spectraldata

2-(1-(7-(Diethylamino)-2-oxo-2H-chromen-3-yl)ethylidene)malononitrile5:browncoloredsolid.Yield:1.4g(88%).Meltingpoint(measured)166e168 C;nmax/cmÀ1:2982,2224,1579,1502,1134,767;1HNMR(300MHz;CDCl3;TMS)1.25(6H,t,J¼7.0Hz,(eCH3)2)"and"3.45(4H,q,J¼7.0Hz,(eCH2)2),6.55(3H,m),7.6(1H,s,vinylproton).13CNMR(100MHz,CDCl3,TMS)d13.7,14.2,52.5,62.5,77.5,113.7,114.2,116.2,127.9,130.7,136.9,148.6,154.5,164.6,169.3;m/z:(EI)308(Mþ1);Mol.Wt.307.35;Anal.CalcdforC18H17N3O2:70.34;H,5.58;N,13.67.Found:C,70.12;H,5.43;N,13.56.

Table1

Condensationreaction.Product

Ar

Yielda%,time(h)

HPLCpurity

7a78(4)98.8

7a*

60(12)

86.5

7b75(3)99.2

7c84(5)97.8

7d71(3.5)98.1

7e85(6)99.0

7f

86(4)

97.9

7g80(5)98.2

7arefersreactionwith0.1mol%Piperidineascatalystinethanol.a

Isolatedyield.