Acidic catalysis of microporous polyoxometalate H3PW12O40/SiO2 in acetal reaction between benzaldehy

PROGRESS IN NATURAL SCIENCEVol 12, No. 2, February 2002Acidic catalysis of microporous polyoxometalate H3PW 12O40/ SiO2in acetal reaction between benzaldehyde and ethylene glycol^YANG Yuir, GuO Yihang', WANG Yonghuil, HU Changwent". 0b AWANG Enbo' and FENG Shouhusa21 Insitule of Polyoxonetalate Cherstry. Faculy of Chemistr. Norheast Normal University. (Changchun 130024, Chin;2. Stare Key Laboratory of Inorganic Synthesis eand Preparative Chermustry. Jjlin University, Changchun 130023. (Chna)Received.1. 2001:lber 28, 2001AbstrnctMrcroporous Kegin-lype polyoxometalate maleral was synubesised by supporting H;PW 12040 intu a silica mnatix via 日sol. gel technique. The siasupported 12- tungstophnxphonrc secid (H;PW 120w/Si02) ohtained is insoluble and readly separable porousmatenals with uniform micropores (0. 57 nm) and a high specic surface area (350. 5 m/g) in oxygen- containing polar solvents. HyPW20n/ SIO2 was caraterzed by nrared spectrophoromeer (IR), ulrevidler visible spetrophotometer (UV vs)，idutively couple plas.me (ICP),. ternmgraviertie analysis (TGA) and Brunner Enmet-Teler merhod (BET) measurenents. HjPW2On/ SIO2 obrainedcatalyzed the aceral reaction belwee benaidehyde and ethylene glycxl to pruduce 2-pheny-1.3. doxolane moe eficinlt then the typrelsold aeids such a sU; /ZrO2, Nafion H and H.2SM.5. Conversion was 93. 8% for benzaldehyde during the Tecton perixd of 2 h.HgPWr2Oo/ SiO2 kept its itial actviy durng three timnes of reuse. The inital acetal reetion fllows a second order kineis model at 298Keywords; sisupportede 12-tungstophnosphoric acid, catalyze, acetal reaction,Keggin type polyoxometalates (POMs) repre- basic solids like MgO tend to decompose POMslb!.sented by H;PW I2O4o(PW12) exhibit a unique combi-Acetalization is a general method of protecting thenation of physical and chemical properties. PW12 pos-aldehyde group in synthetic organic chemistry. Thissessesa very strong acidity"i. This alws it 10 beis achieved by a nurber of methods using HCI，p-widely used as an acid catalyst in homogeneous andtoluene sulfonic acid, FeCl3, ZnC2, montmoilloniteheterogeneous systems for various organic reactionsclays, lanthanidest12: and Mg-Al or Zn- Al hydrotal-such as esterification,, ester exchangel2l, acylation[3l,cites-3.1， etc.. In this paper. we synthesizedhydration'，etc. at moderate temperatures with8.1% mass fraction( w )Hz PW1z O4o1 SiO2 withmicro-yields higher than those of other currently used acidsporous structure according to a modified literaturesuch as sulfuric and p-toluene sulfonic acids. Howev-merthod'4l. PW 12/ SiO2 obtained catalyzed acetal reac-er, the catalytic activity and application of the PW12tion between benzaldehyde and ethylene glycol. Con-are greatly limited due to its very low specific surfaceversion was 93.8 % for benaldehyde during the re-areas (PW1p≤9 m2/g)5, so polar molecules can on-action period of 2 h.ly react on its surface. Therefore, many attemptshave been made to enhance the specific surface area of1 ExperimentalPW12. Acidic or neutral substances such as SiO2, active carbon, acidie ion exchange reinshI, Zr0{7,Synthesis of the PW 12/SiO2: a mixture of H2Olayer double hydroxides ( L.DHs) obtained by interca-(1.00 mol), nC4Hg0H (0.20 mol) and HsPW 12040lating POMs into LDHs8- l0， and organic polymer●7H2O (5.0X 10~4 mol) was added 10 Si(OCHs)4(poly( I, 4-phenylenemethylidynenitrilo-1, 4-phenyle-(TEOS) (0.21 mol) and strred at 75C for3h. Thenenitrilomethylidyne))6)， etc. are suitable as sup-hydrogel obtained was dehydrated slowly at 55T for.ports, among which the most often used is Si21.8h to give PWn2/SiO2(8.1 % PW12 included estiHowever, the acid strength o[ POMs can be greatlymated by ICP). The dried gel was calcined in vacuurmreduced when they are loaded on activated carbon and中國煤化工network and then :Suppored by the National Nartural Sciencee Foundation of Chine (Grant SoTHCN M H Gauly Key Techer oif theMnistry of Education of China，. To whom crrspondenren should be adresed. E mail: hurhw@ nenu. edu. cn .154Progress in Aatural SrenreVol.12Xn: 2002extracted with water at 90t until the filrale wasThe PW1z/ SiO2 has a maximum lV abyurptionneutral. The silica supported PW12 was dried in vacu-peakat 263- 266 nm, similar to that