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Iranica, Vol. 14, No. 4, pp 297{302 Scientia c Sharif University of Technology, August 2007 y-Supp orted Quaternary Ammonium and Cla Cations in Triphase Catalysis and Phosphonium E ect of Cosolvent in Catalytic Activity the 1 1 1 B.L. Cutts D. Dutko and S. Khazaeli , Shab estary , N. this research, a naturally o ccurring clay mineral, hectorite, was used as the supp ort for several In ry ammonium and phosphonium cations to measure and compare their catalytic activity quaterna a triphase catalytic system. The intercalation of the catalysts in the clay has the advantage in easy catalyst recovery; the catalyst can b e removed by a simple separation technique, such of ltration or centrifugation, up on completion of the reaction. The rate of conversion of n- as yl bromide to n-butyl chloride was measured in the presence of two classes of phase transfer but Quaternary ammonium and quaternary phosphonium cations. The rate of the reaction catalyst: as measured for the biphase reactions (no supp orting clay) and for the triphase catalytic system w supp orting clay). The results have shown that quaternary phosphonium catalysts ar e (with more reactive than the corresponding quaternary ammonium catalysts. It wa s also somewhat that the intercalated catalysts could be used several times b efore losing their catalytic found y. Also, a remarkable increase in catalytic activity has b een observed using a co-solvent. activit wever, it app ears that there is a limit for the co-solvent concentration to b e e ective. Ho Based on this technique, synthetic metho ds phases. ODUCTION INTR ve b een developed for aqueous-organic phase reac- ha application of Phase-Transfer Catalysis (PTC) in The using solid catalysts, such as synthetic p olymers tions past few decades has b ecome prevalent in academic the various clay minerals. TC shows considerable p oten- or h, as well as in commercial pro cesses [1-4]. researc for commercial application. Several commercially tial of the advantages that this technique o ers Some vailable ion-exchange resins, such as Dowex resins, a increased reaction yield, requirement of only mild are taining quaternary ammonium groups, h ave b een con conditions, safety, requirement of inexp ensive reaction as triphase catalysts [9]. Also, quaternary am- studied ents and reagents and the ability to conduct reac- solv salts immobilized on insoluble p olymers and monium on a commercial scale. However, the recovery tions oxides, such as silica and alumina, have b een inorganic recycling of relatively exp ensive phase transfer and ely explored in TC. However, silica, alumina extensiv catalysts from the liquid phase has b een a challenge for p olymers are relatively unstable in strong acidic and technique. The treatment of the reaction mixture this alkaline environments and they normally su er from or ciated with soluble catalysts imp oses limitations on asso oor physical strength. In contrast, clays h ave b et- p applicability and usefulness of PTC as an industrial the physical strength, b etter resistance towards alkali ter hnique of synthesis. Recently, Triphase Catalysis tec t and are relatively inexp ensive. Recently, treatmen has b een introduced by Regen [5-8] as a unique (TC) investigations have app eared on the application some yp e of heterogeneous catalysis, in which the catalyst t clays as solid supp orts for quaternary salts [10-16]. of each of a pair of reactants are lo cated in di erent and the present investigation, a study on the use In clay of the smectite family, hectorite, is rep orted as of ort for quaternary ammonium and phosphonium supp Corresponding Author, Department of Chemistry, Col- *. salts. Smectite clay minerals are among members of ge of Arts and Sciences, Southern Il linois University le arious layered silicates with 2:1 mica-like layer lattice v at Edwardsville, Il linois, P.O. Box 62026-1652, USA. Naturally o ccurring negative charges on structures. 1. Department of Chemistry, Col lege of Arts and Sciences, Southern Il linois University at Edwardsville, Il linois, clay layers are balanced by interlayer cations that the P.O. Box 62026-1652, USA. ccupy intercalated p ositions b etween the interlayers. o N. Shab estary, S. Khazaeli, D. Dutko and B.L. Cutts 298 so dium acetate bu ered to pH 5 with Adding o ccurring alkali and alkaline earth cations in Naturally acid converts calcium carb onate to carb on diox- acetic pristine clay minerals can b e replaced by almost any the 10 g which is removed when heated to 70 C. ide, cation. Cation exchange in this type of clay desirable of clay were used to remove carb onates and samples is relatively rapid. Smectite or swelling clay mineral salts. First, 100 mL of 1 N so dium acetate soluble a great anity towards water, as well as organic has to pH 5 with acetic acid was added to the clay bu ered ts. This unique wetting prop erty makes the clay reagen a blender. The clay susp ension was then heated for in attractive for catalysis. Earlier work [17,18] has quite with o ccasional stirring. The solution hour at 70 C 1 that alkyl ammonium ions intercalated demonstrated as then centrifuged and the sup ernatant was analyzed w smectite clay pro duce ordered structures, in which in an atomic absorption sp ectrophotometer (Varian on alkyl chains and the ammonium groups form a the ectra AA-10) for the amount of calcium. Standards Sp eci c orientation, with resp ect to the clay layers. sp ere prepared from 1000 ppm Fisher standards. The w us, these structures dep end on the length of the alkyl Th steps were rep eated until the amount of previous hains and the charge density of the clay layers. Chi-Li c was less than 2 ppm. calcium et al. [19] h ave indicated that onium ions within Lin ree iron oxides are removed by the addition of a F clay have an emulsion-forming ability, which, most the dium citrate/so dium bicarb onate solution and with so ely, is related to the amphiphilic nature of onium ions lik 80 mL t by so dium hydrosul te (Na S O ). treatmen the external surfaces of the clay tactoids. Thus, on 2 2 4 ere 0.3 N so dium citrate and 10 mL of 1N NaHCO w of y adopting parallel or p erp endicular orientations at b 3 to the clay susp ension in water. The mixture was added clay-liquid interface, the onium ions may show the and 2 g of so dium hydrosul te heated to 75-80 C then ydrophilic or organophilic wetting prop erties. h wa s slowly added. Care was taken not to heat a b ove The rate of conversion of n-butyl bromide to to prevent FeS precipitation. The clay susp ension 80 C -butyl chloride wa s measured in the presence of n as heated for 15 minutes. The resulting solution was w wo classes of phase transfer catalysts: Quaternary t trifuged and the sup ernatant was analyzed for the cen and quaternary phosphonium salts. The ammonium t of iron. A typical atomic absorption calibra- amoun of the reaction was measured for the biphase cat- rate curve was constructed to measure the amount of tion system (no supp orting clay) and for the triphase alytic in ppm. iron system (with supp orting clay). The results catalytic p eroxide wa s employed to digest or- Hydrogen ve shown that quaternary phosphonium catalysts ha matter in the clay. A 30% solution of hydrogen ganic more e ective than the corresp onding quaternary are eroxide (150 mL for 10 g clay) wa s mixed with the p catalysts. It wa s also found that the ammonium y slurry for 15 minutes at ro om temp erature. Then, cla tercalated catalysts could be recycled several times in clay wa s saturated with so dium by addition of the signi cantly losing their activities. without dium chloride (10% solution, 200 mL). The mixture so as stirred for another 15 minutes, then centrifuged. w AL EXPERIMENT clay was then washed four to 5 times until free of The hloride ions (test with silver nitrate solution). After c stated otherwise, all reagents were obtained Unless pro cess, the clay wa s freeze-dried using a VirTis this and used without further puri cation. commercially ench top freeze-dryer. Typically, the freeze-drying is b overnight. done Hectorite Natural o ccurring so dium hectorite, with particle size Naturally Preparation of Clay Intercalates 2 m, was obtained in the precentrifuged and spray- < tercalation reactions of all cations were p erformed In form. The idealized anhydrous unit-cell formula dried similar conditions, since all the quaternary under hectorite is Na of (Si [Li Mg ] )O (OH, :66 :66 :34 0 :00 0 5 8 20 salts were quite stable and also soluble in water. onium the exp erimentally determined cation-exchange F) ; 4 a typical exp eriment, a 1.0 wt% aqueous susp ension In y is ab out 73 meq/100 g and the surface area is capacit 2 was added to 0.1 g of the mineral in 10 mL H O) (e.g. of air-dried clay. The clay contains two out 750 m /g ab 2 vigorously stirred aqueous solution of the quaternary a jor impurities that may interfere with the catalytic ma salt containing ab out 1.2 meq/meq of clay. The onium These are calcium carb onate and free (non- reactions. mixture was stirred for over an hour. After an reaction iron oxides, which can inhibit intercalation of lattice) time of 24 hours, the clay was rep eatedly equilibration clay, b ecause they act as cementing agents, which the washed with deionized water and then collected by prevent o cculation from o ccurring.

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