硝酸-硫酸硝化

NITRATION OF AROMATIC HYDROCARBONS ANDHALOBENZENES USING NOx CATALYZED BYSOLID ACID CATALYSTSManoj A.Pande and Shriniwas D.SamantDepartment of Chemistry,Institute of Chemical Technology,Matunga,Mumbai,IndiaThe nitration of aromatics using zeolite as a solid inorganic catalyst and nitric oxides asnitrating agents is a relatively clean process for aromatic nitration.Keywords :Aromatic nitration;nitrogen oxides;zeolitesINTRODUCTIONAromatic nitration reaction is an important unit chemical process as theresulting aromatic nitro compounds find diverse applications;main being pre-paration of primary amines through reduction.[1]Classically nitration is carriedout using mixed acid (HNO 3þH 2SO 4).This nitration is a hazardous processwith very high E factor.It is a run-away reaction (D H ¼À110kJ =mol for benzene)and is probably the most potentially hazardous industrial process.This is due tothe heat generated during the reaction which can trigger the power of nitric acidto degrade organic material exothermically to gaseous products with explosiveviolence.The reaction can be carried out in batch mode or continuous mode;the latter is more suitable for large tonnage intermediates,like nitrobenzene andnitrotoluene and is attractive for reasons of safety as well as obvious economicconsideration.For large scale mononitration 20=60=20mixed acid system isemployed i.e.,20%HNO 3,60%H 2SO 4,20%H 2O.Thus a large excess of sulfuricacid is required as the water formed as a by product slows the reaction by dilutingthe acid.At the end of the reaction,a large amount of ‘spent acid’is obtainedwhich increases the E-factor of the reaction.Moreover,Sulfuric acid is corrosiveand is dangerous to transport and handle.Hence,nitration of aromatics avoidingsulfuric acid appears to be an attractive alternative.The use of zeolites in aromaticnitration is a subject of increasing interest,particularly with regards to unusualReceived August 28,2009.Address correspondence to Shriniwas D.Samant,Organic Chemistry Research Laboratory,University Institute of Chemical Technology,N.M.Parekh Road,Mantunga,Mumbai 400019,India.E-mail:samantsd@Synthetic Communications 1,40:3734–3738,2010Copyright #Taylor &Francis Group,LLCISSN:0039-7911print =1532-2432onlineDOI:10.1080/003979109035317633734regioselectivity.[2]At present,best combination of high yield,high para selectivity and low solvent use is achieved using a nitric acid,zeolite H b as catalyst,and acetic anhydride(for moderately active aromatics)[3]or trifluroacetic anhydride (for deactivated aromatics)[2]as activator.However,carboxylic acid is formed as a by product.The nitration using nitrogen oxides has been attempted using solid acid catalysts like zeolites.In some cases oxidant like oxygen or ozone is required.[4]The method where ozone is employed most likely involves dinitrogen pentoxide,as this is known to be a highly active nitrating agent.The nonacid method for aromatic nitration using NO2=O3gives excellent conversion of a wide variety of aromatic compounds under mild conditions(Kyodai nitration).[5]How-ever,use of ozone adds to the cost of the process.Fe(III)-catalyzed nitration using NO2-O2system requires a long reaction time(12to36h)and large amount of nitrogen dioxide and catalyst.[6]Vapor phase nitration of benzene over mixed metal oxides(silica-alumina,zinc oxide-titania,tungsten oxide-molybdenum oxide)using NO2is carried out at high temperature and give around25%of nitrobenzene.[7] Nitration of halobenzenes using NO2–O2-zeolite system gives good conversion with enhanced para selectivity after48h of reaction time.[8]Thus,nitration using NOx in presence of suitable acid catalyst appears to be promising.In our efforts to develop an atom-economic and eco-friendly process for aromatic nitration,we attempted nitration of aromatic compounds using NOx in the presence of zeolites.Zeolite b and zeolite Y have3-dimensional channels and large pore sizes.Zeolite H b is a strong bronsted acid and is known to catalyze nitration reaction.Nitration of chlorobenzene was attempted as the products are commercially important[1b,9]and has been studied earlier under different reaction conditions.[10] The nitration of chlorobenzene was carried out in the presence of different amount of zeolite H b at40 C.The NOx was generated by reacting HNO3with P2O5with some modification in reported method.[11]The amount of P2O5was taken intentionally excess.The gas so generated was passed through the reaction mixture using N2as carrier gas.After the complete addition of HNO3to P2O5,theflow of nitrogen was continued to ensure the purging of NOx from the generator. In the absence of catalyst33%conversion of chlorobenzene was obtained,and the conversion increased with increasing quantity of the catalyst(Table1).There was Table1.The effect of catalyst amount(zeolite H b)on the nitration of chlorobenzene(CB)using NOxCatalyst amount(wt%) wrt wt of CB Selectivity(%)aEntry Conversion CB(%)a o-m-p-o=p a1033.231.020.068.970.44 30.7542.433.49 1.6565.090.51 4168.135.530.5863.870.55 5571.827.420.4472.080.38Reaction conditions:Chlorobenzene(30mmol),catalyst zeolite H b,1,2-dichloroethane(30ml),HNO3 4ml,P2O510g;temperature40 C,reaction time240min.a GC.AROMATIC NITRATION37353736M.A.PANDE AND S.D.SAMANTTable2.The effect of different catalysts on the nitration of chlorobenzene using NOxSelectivity(%)aEntry Catalyst Conversion CB(%)o-m-p-o=p a1Zeolite H b68.135.530.5863.870.55 2Zeolite Y-H47.4348.61 1.6649.710.97 3ZSM-5Na41.3349.84 1.4748.68 1.02 4Mont K-1046.1240.02 1.2158.780.68Reaction conditions:Chlorobenzene(30mmol),catalyst1wt%wrt wt.of CB,dichloroethane(30ml), HNO34ml,P2O510g;temperature40 C,reaction time240min.a GC.no remarkable difference in conversion from1wt%to5wt%H b.Hence1wt%of catalyst amount was used for further study.The reaction was carried out using 1wt%of different zeolites and Mont K-10(Table2).Among the catalysts,Zeolite H b was found to give maximum conversion of chlorobenzene and gave higher selectivity for para nitrochlorobenzene.For Zeolite H-Y and ZSM-5Na no selectivity was observed.Under the optimized conditions different less activated aromatics were nitrated (Table3).After240min.of reaction time,toluene was completely consumed,however a range of products including isomers of mononitrotoluene,dinitrotoluene,and oxidized products were found.When nitration of aniline and benzaldehyde was tried under the same conditions,oxidation products were observed.Nitration of para-dichlorobenzene gave2,5-dichloro-1-nitrobenzene in a trace quantity.Table3.Nitration of aromatic hydrocarbons and halobenzenes using NOx in presence of zeolite H bSelectivity(%)bEntry Substrate Conversion of substrate(%)b o-m-p-1Benzene a37–––2Benzene48–––3Chlorobenzene68.135.530.5863.874Naphthalene98c–––5Toluene100231196Iodobenzene1530–707Bromo b enzene4240–608Orthodichloro Benzene1212d(2,3DCNB)88e(3,4DC4NB)Reaction conditions:substrate(30mmol),catalyst zeolite H b1wt%wrt wt.of substrate,dichloroethane (30mL),HNO34ml,P2O510g;temperature40 C,reaction time240min.a Without catalyst.b GC and GC-MS.c Exclusive1-nitronaphthalene.d2,3-Dichloro-1-nitrobenzene.e3,4-Dichloro-1-nitrobenzene.CONCLUSIONIn conclusion we have developed a potentially clean nitration process for weakly activated aromatics using NOx and solid acid zeolite H b.Sulfuric acid is totally eliminated in the process.The process is environmentally benign and has potential for commercialization.EXPERIMENTALGeneralSolvents:All the solvents were of LR-grade and were purified and dried by the known procedures before use.Chemicals:The chemicals were of LR or sometimes AR grade and procured from M=s s.dfine chemicals,Mumbai;LOBA Chemie,Mumbai;Fluka Chemicals, A.G,Switzerland;E.Merck(India)Ltd.,Mumbai;Aldrich Chemical Company, Inc.,and Lancaster,PA,USA.Analytical Methods:The progress of the reaction and simultaneous product formation was carried out by external standard method using a gas chromatographic technique.For this purpose,Chemito8610gas chromatograph withflame ionizationdetector and stainless steel column(OV17,12in.Â2m)was used.GC-MS spectra were recorded on a Shimatzu GC-MS QP2010(RTX-WAX, capillary column,30m,0.25mm)equipped with an electron capture detector.All the products reported here are known compounds and their identity was determined with authentic samples using GC and GC-MS.Preparation of NOxPhosphorus pentoxide(10g)was taken in a three-necked round bottom flask(100ml).Theflask was kept in an electrically heated oil bath and heated at60–65 C.A slow stream of nitrogen gas was passed through the side neck, to drive the NOx formed.Concentrated nitric acid(70%,4ml)was added at a slow rate(1drop=min)through a dropping funnel.The gas which evolved was introduced through a glass tube into theflask containing substrate dissolved in ethylenedichloride(EDC).General Procedure of NitrationSubstrate(30mmol)was taken in a three-necked round bottomflask(50ml) and dissolved in ethylenedichloride(30ml).Theflask was kept in an oil bath main-tained at40–45 C.The solution was stirred magnetically.The NOx from the NOx generator was bubbled through a glass tube in the solution containing substrate. 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