ZnCl 2 supported on Fe 3 O 4 @SiO 2 core–shell nanocatalyst for the synthesis of quinolines via Fri

FULLPAPER

ZnCl2supportedonFe3O4@SiO2core–shellnanocatalystforthe

synthesisofquinolinesviaFriedländersynthesisundersolvent‐free

condition

EbrahimSoleimani*|MahbobehNaderiNamivandi|HeshmatollahSepahvand

DepartmentofChemistry,RaziUniversity,Kermanshah67149‐67346,Iran

CorrespondenceEbrahimSoleimani,DepartmentofChemistry,RaziUniversity,Kermanshah67149‐67346,Iran.E‐mail:e_soleimanirazi@yahoo.comAmagneticnanocatalystofFe3O4@SiO2/ZnCl2waspreparedbysupportingZnCl2onsilica‐coatedmagneticnanoparticlesofFe3O4.Thisrecoverablecatalystwas

usedforthesynthesisofquinolinesviaFriedländersynthesisfrom2‐aminoaryl

ketonesandα‐methyleneketonesundersolvent‐freecondition.Thepreparedcata-

lystwascharacterizedbyFT‐IR,TEM,SEM,XRD,EDX,ICP‐OES,VSMand

BET.ItwasfoundthatFe3O4@SiO2/ZnCl2showedhighercatalyticactivitythan

homogenousZnCl2,andcouldbereusedseveraltimeswithoutsignificantlossof

activity.

KEYWORDS

magnetitenanocatalyst,ZnCl2,quinolines,Friedländer

1|INTRODUCTION

Inrecentyears,muchattentionhasbeenfocusedonheteroge-

neouscatalystsduetotheirpotentialapplicationsforreplac-

inghomogenouscatalystsinorganicchemistryand

industry;theyexhibitadvantagesofeasyseparationofthe

catalystfromthereactionmedium,minimalcorrosion,

simplifyrecovery,reusability,greenchemicalprocesses,

andenhancedproductselectivity.[1]Amongheterogeneous

catalysts,supportedcatalystsonasolidsupporthasattracted

significantattentionduetoanumberofadvantagesastheir

availableactivesites,stability,andproductseparationand

theirrecovery,whichareallimportantfactorsinorganic

chemistryandindustry.[2]Althoughsupportedcatalystsare

availableondifferentsupportssuchascharcoal,alumina,sil-

icaandpolymers,sincesilicadisplaysmanyadvantages

propertiessuchasexcellentstability(chemicalaswellas

thermal),noswelling,highsurfacearea,goodaccessibility

andinadditionorganicgroupscanberobustlyanchoredto

thesurfacetoprovidecatalyticcenter.[3]

Magneticsilicananoparticleshaverecentlyreceivedsig-

nificantattentionduetotheirchemicalinertness,magnetic

properties,notoxicity,andexcellentthermalstability.[4]

Thesefavorablepropertiesallownanoparticles(NPs)tobe

widelyusedasacatalystorsupportedcatalystfororganicsyntheses.[5]Ithasbeenreportedthattheheterogeneouscat-

alystssupportedonMNPsrevealexcellentperformancein

manyreactionse.g.,hydrolysis,hydrogenation,oxidation,

carbon–carboncouplingandreduction.[6]

TheuseofZnCl2hasreceivedconsiderableattentionas

aninexpensive,nontoxic,commerciallyavailablecatalyst

forvariousorganictransformations.Duetothenumerous

advantagesassociatedwiththiseco‐friendlycompound,

ZnCl2hasbeenexploredasapowerfulLewisacidcatalyst

fordifferentreactions.[7]However,inspiteoftheirpotential

utility,thishomogeneouscatalystpresentlimitationsdueto

theuseoftoxicandcorrosivereagentsandthetedious

work‐upprocedurethatthusmakingtheprocesseconomi-

callyandenvironmentallyundesirable.Therefore,inthis

research,ZnCl2wasimmobilizedonthesurfaceof

Fe3O4@SiO2core–shellnanoparticles,andthenusedamag-

neticheterogeneousnanocatalystforthesynthesisofquino-

linesviaFriedlanderannulationreactionundersolvent‐free

conditions.Advantagesandnoveltyofthisnewcatalystis

easyseparationoffromreactionmediumbyapplyingexter-

nalmagneticfieldandreusedseveraltimes.

Itiswellknownthatquinolinesexhibitawiderangeof

biologicalactivities,[8–10]andarevaluablereagentsforthe

synthesisofnano‐andmesostructureswithenhancedelec-

tronicandphotonicproperties.[11]Theclassicversionof

theReceived:25May2016Revised:26June2016Accepted:1July2016

DOI10.1002/aoc.3566

Appl.Organometal.Chem.2016;1–8Copyright©2016JohnWiley&Sons,Ltd.wileyonlinelibrary.com/journal/aoc1Friedländerquinolinesynthesis,whichcombinesa2‐

aminoarylketoneandacarbonylcompoundcontainingan

activatedα‐CHacidunderacidicorbasicconditionsby

refluxinginanaqueousoralcoholicsolutiontogivequino-

line,hasbeenextensivelyexplored.[12]Inatypicalprocedure,

thecatalystisvariedfromstrongproticinorganicliquid

acids,[13]suchasHCl,H2SO4,andpolyphosphoricacid,to

Lewisacids,[14]suchasNaAuCl6,andAuCl3.3H2O,and

transition‐metals,[15]suchasrutheniumandpalladium.More-

over,thesynthesisoftheseheterocycleshasbeenusuallycar-

riedoutinapolarsolventsuchasTHF,DMF,orDMSO

leadingtocomplexisolationandrecoveryprocedures.There-

fore,thediscoveryofanovelandinexpensivecatalyst,which

canbeeasilyseparatedandreused,withoutundesirablecon-

tamination,isofprimeimportance.Therefore,wehavepre-

paredamagneticheterogeneouscatalystofFe3O4@SiO2/

ZnCl2bysupportingZnCl2onsilica‐coatedmagnetic

nanoparticlesofFe3O4.

Incontinuationofoureffortstodevelopnewmethodsin

thesynthesisofquinolines,[16]andmagnetic

nanocatalysts,[17]herein,wewishtoreportamildandeffi-

cientapproachforthesynthesisofpolysubstitutedquinolines

viaFriedländerannulationusingacatalyticamountof