V Acetoxylation of camphene catalysed by beta zeolite

Acetoxylation of camphene catalysed by beta zeoliteJ.E.Castanheiro a,*,I.M.Fonseca b ,A.M.Ramos b ,J.Vital ba Centro de Química de Évora,Departamento de Química,Universidade de Évora,7000-671Évora,PortugalbREQUIMTE/CQFB,Faculdade de Ciências e Tecnologia,Universidade Nova de Lisboa,2829-516Caparica,Portugala r t i c l e i n f o Article history:Received 15January 2008Received in revised form 7May 2008Accepted 8May 2008Available online 15May 2008Keywords:CampheneIsobornyl acetate Acetoxylation Beta zeolitea b s t r a c tBeta zeolite with Si/Al ratio equal to 40was synthesised and used as solid catalyst in acetoxylation of camphene.The main product of camphene acetoxylation was isobornyl acetate being also formed bornyl acetate and fenchyl acetate.Effects of various parameters,such as reactant molar ratio,reaction temper-ature,catalysts loading and reusability of the catalyst were studied to optimise the reaction conditions.The catalytic stability of beta zeolite in the acetoxylation of camphene was studied by performing con-secutive batch runs with the same catalyst sample.After the third run,it was observed similar values of the catalytic activity.Ó2008Elsevier B.V.All rights reserved.1.IntroductionMonoterpenes are widely used in the pharmaceutical,cos-metic and food industry as active components of drugs and ingre-dients of artificial flavours and fragrances [1,2].Acid catalysed hydration and acetoxylation of terpenes are an important synthe-sis routes to valuable terpenic alcohols and esters with many applications in perfumery and pharmaceutical industry [1].Camphene is converted to isobornyl and bornyl acetate that are used in formulation of soap,cosmetic perfumes and medicines.Traditionally,strong homogeneous catalysts,e.g.sulphuric acid,are used,but the effluent disposal leads to environmental prob-lems and economical inconveniences.These problems can be overcome by the use of solid acid catalysts.Heteropolyacids [3],sulfonic acid surface-functionalised silica [4]and sulfonated cross-linked polystyrene [5]have been used as catalysts in the camphene acetoxylation.Beta zeolite has been used as acid catalyst in reactions where terpenes are involved,such as,hydration of a -pinene [6,7]and dihydromyrcene [8],isomerisation of a -pinene [9],acetoxylation of a -pinene [10]and alkoxylation of limonene [11,12]and a -pinene [11].This work reports the acetoxylation of camphene over beta zeolite.2.Experimental2.1.Preparation of the catalystBeta zeolite (Si/Al =40)was synthesised according to Wadlinger and Kerr [13].Briefly,3.0g of sodium aluminate (0.0365mol Na-AlO 2,Riedel-de-Haën),110g of 40%(w/w)tetraethylammonium hydroxide (0.299mol TEAOH,Aldrich)and 291.57g of silica sol (1.461mol Ludox LS (30%SiO 2))were mixed and transferred to a Teflon autoclave.After crystallisation (145h at 150°C),the zeolite was collected by filtration,dried at 115°C and calcined at 500°C to remove the organic template.2.2.Characterisation of the catalystThe textural characterisation of the catalysts was based on the nitrogen adsorption isotherm,determined at 77K with a Microm-eritics ASAP 2010apparatus.The amount of silica and aluminium in beta zeolite was measured by dissolving the catalyst in H 2SO 4/HF 1:1(v/v)and analysing the obtained solution using inductively coupled plasma analysis (ICP),which was carried out in a Jobin-Yvon ULTIMA instrument.The X-ray powder diffraction (XDR)of the zeolite was obtained on a Bruker powder diffractometer.2.3.Catalytic experimentsThe camphene acetoxylation reactions were carried out in a round bottom glass flask (50cm 3)fitted with a water-cooled con-denser in the temperature range 323–368K.In a typical experi-ment,the reactor was loaded with 30mL of acetic acid and1566-7367/$-see front matter Ó2008Elsevier B.V.All rights reserved.doi:10.1016/j.catcom.2008.05.009*Corresponding author.Tel.:+351266745311;fax:+351266744971.E-mail address:jefc@uevora.pt (J.E.Castanheiro).Catalysis Communications 9(2008)2205–2208Contents lists available at ScienceDirectCatalysis Communicationsjournal homepage:www.else v i e r.c o m /l o c a t e /c a t c om0.13g of the catalyst.Reactions were started by adding 1.76mmol of terpene.Stability tests of the beta zeolite were carried out by running five consecutive experiments,in the same reaction conditions.Samples were taken periodically and analysed by GC,using a KONIC HRGC-3000C instrument equipped with a 30m Â0.25mm DB-1column.3.Results and discussion3.1.Catalyst characterisationThe nitrogen adsorption–desorption isotherm of beta zeolite is type I (according to IUPAC nomenclature),characteristic of micro-porous zeolites,with a small type H4hysteresis loop.The specific surface area was determined using the BET method while micropo-rous volume and mesoporous surface area were determined by the t-method,using a standard isotherm proposed by Greeg and Sing [14].Table 1shows the values of BET specific area (S BET ),micropo-rous volume (V micro )and external surface area (S ext ).Fig.1shows the X-ray diffraction patterns obtained for the beta zeolite catalyst.It was not observed change of structure after syn-thesis and purification procedures.3.2.Catalytic experimentsThe main product of camphene (1)acetoxylation is isobornyl acetate (2)being also formed bornyl acetate (3),b -fenchyl acetate (4),pseudobornyl acetate (5)and tricyclene (6)(Scheme 1).Acetoxylation of camphene is an equilibrium-limited chemical reaction,so an excess of acetic acid is used in order to increase the amount of ester formed.The molar ratio of acetic acid:camph-ene was varied from 1:3.38Â10À3to 1:1.0Â10À2,while the cata-lyst amount and the temperature were kept constant.Fig.2shows the conversion of camphene versus time over beta zeolite,at 368K.After 5h of reaction,it was observed that the camphene conver-sion increases slightly from 85%to 89%at a molar ratio of acetic acid:camphene 1:3.38Â10À3and 1:1.0Â10À2,respectively.The selectivity to isobornyl acetate increases with the decrease of camphene concentration (Fig.3).These results can be explained probably due to the amount of camphene near the active sites.When the amount of camphene in the neighbour of actives sites is high,the possibility to occur parallel reactions is higher than if the amount of camphene is small.However,it is observed that the selectivity to isobornyl acetate has an increase at high values of camphene conversion.This behaviour can be explained due to the rearrange of bornyl acetate to isobornyl acetate.Table 1Physicochemical characterisation of beta zeolite catalyst Sample Si/Al ratio a Surface area b (m 2/g)External surface area c (m 2/g)Microporous volume c (cm 3/g)Beta40506100.185a ICP.b BET .ct Method.(2)OAcOAcOAcOAcAcOH+(3)(4)(5)(6)(1)Scheme 1.2206J.E.Castanheiro et al./Catalysis Communications 9(2008)2205–2208Fig.4shows the conversion of camphene versus time over beta zeolite,at different reaction temperatures in the range of323–368K,at a molar ratio of acetic acid:terpene1:3.38Â10À3and with0.13g catalyst loading.It was observed that the higher tem-perature yields the greater catalytic activity.The equilibrium con-versions of camphene were nearly equal(about87%)at353andJ.E.Castanheiro et al./Catalysis Communications9(2008)2205–22082207368K,afterfive hours of reaction.The selectivity to isobornyl ace-tate increases with the temperature(Fig.5).It is also observed an increase of the selectivity to isobornyl acetate at high values of camphene conversion,which can be explained due to the rear-range of bornyl acetate to isobornyl acetate.In order to study the effect of catalyst amount on the camphene conversion,different experiments were carried out.Catalyst load-ing was varied from0.37%to0.87%(w/w)(i.e.,weight of cata-lyst/total weight of reactants),while the molar ratio of acetic acid:camphene1:3.38Â10À3and the temperature were kept con-stant,at368K.The conversion equilibrium was reached quickly when higher catalysts loading were used,because there is an in-crease in the total number of available active catalytic sites for the reaction(Fig.6).Fig.7shows the dependence of the selectivity to isobornyl ace-tate on the amount of catalyst.It was observed that the selectivity to isobornyl acetate did not change with the amount of beta zeolite.Catalytic stability of the beta zeolite was evaluated by perform-ing consecutive batch runs with the same catalyst sample and in the same reaction conditions.Fig.8shows the initial catalytic activity of beta zeolite in the acetoxylation of camphene.After the third run,it was observed similar values of the catalytic activity.4.ConclusionsBeta zeolite with Si/Al ratio equal to40was synthesised and used as solid catalyst in the acetoxylation of camphene.The main product of camphene acetoxylation is isobornyl acetate being also formed bornyl acetate and fenchyl acetate.Effects of various parameters such as mole ratio of reactants, reaction temperature,catalysts loading and reusability of the cata-lyst were studied to optimise the reaction conditions.Catalytic sta-bility of beta zeolite was studied by performing consecutive batch runs with the same catalyst sample.Similar values of the catalytic activity were observed,after the third batch runs.References[1]D.Whittaker,in:A.A.Newman(Ed.),Chemistry of Terpenes and Terpenoids,Academic Press,London,1972,p.11.[2]J.O.Bledsoe,Terpenoids,in:J.I.Kroschwitz,M.Howe-Grant(Eds.),Kirk-Othmer Encyclopedia of Chemical Technology,fourth ed.,vol.23,Wiley,New York,1997,p.833.[3]K.A.da Silva,I.V.Kozhevnikov,E.V.Gusevskaya,J.Mol.Catal.A:Chem.192(2003)129.[4]I.J.Dijs,H.L.F.van Ochten,C.A.van Walree,J.W.Geus,L.W.Jenneskens,J.Mol.Catal.A:Chem.188(2002)209.[5]I.J.Dijs,H.L.F.van Ochten,A.J.M.van der Heijden,J.W.Geus,L.W.Jenneskens,Appl.Catal.A:Gen.241(2003)185.[6]J.van de Waal,H.van 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