Combinatorial synthesis and screening of polystyrene-supported quaternary ammonium salt phase transfer catalysts

Transcription

1 Rective & Functionl Polymers 48 (2001) Combintoril synthesis nd screening of polystyrene-supported quternry mmonium slt phse trnsfer ctlysts *,b, b b Mnci Xu, Zhize Ou, Zuoqing Shi, Mincheng Xu, Hito Li, b Shnxin Yu, Binglin He Deprtment of Chemistry, Hunn Norml University, Chngsh , PR Chin b The Stte Key Lbortory of Functionl Polymer Mterils for Adsorption nd Seprtion, Institute of Polymer Chemistry, Nnki University, Tinjin , PR Chin Received 1 July 2000; received in revised form 27 December 2000; ccepted 5 Jnury 2001 Abstrct A phse trnsfer ctlyst librry with 50 kinds of polystyrene-supported quternry mmonium slt ctlyst ws synthesized by the rection of 10 kinds of chloromethylted crosslinked polystyrene with five tert-mines using the portioning-mixing method. The Br/ I nion exchnge rection of hexyl-bromide nd borohydride reduction of cetophenone were used s the probing rections to screen out the most ctive ctlysts for ech rection using the itertive deconvolution method. For the Br/ I nion exchnge rection of hexyl-bromide, the ctlytic ctivity of the phse trnsfer ctlyst ws minly ffected by the lipophilicity of the ctive sites, nd the most ctive ctlyst ws mcroporous strongly bsic nion exchnge resin (1). However, for the borohydride reduction of cetophenone, gel-type (microporous) strongly bsic nion exchnge resin (2) ws the most ctive ctlyst, nd hydrogen bonding promoted ctlytic mechnism ws proposed to explin the high ctlytic ctivity of the ctlyst Elsevier Science B.V. All rights reserved. Keywords: Polystyrene-supported quternry mmonium slt; Phse trnsfer ctlysis; Combintoril chemistry; Nucleophilic substitution; Borohydride reduction 1. Introduction orgnic synthesis [1], such s nucleophilic substitution [2], oxidtion [3], nd reduction [4]. Polystyrene-supported quternry mmonium The ctlytic ctivity of the polymer-supported slts re often used s phse trnsfer ctlysts in phse trnsfer ctlyst is ffected by mny fctors, such s loding extent nd topology of ctive sites, crosslinking degree, porosity, surfce re, nd prticle size [1]. Furthermore, the *Corresponding uthor. Deprtment of Chemistry, Hunn Norml University, Chngsh , PR Chin / 01/ $ see front mtter 2001 Elsevier Science B.V. All rights reserved. PII: S (01) 转载

2 86 M. Xu et l. / Rective & Functionl Polymers 48 (2001) ctivity of the sme ctlyst vries for different tioning-mixing method. There re two routes to rections. Therefore, it is time-consuming synthesize the librry. The first route is to mke business to discover nd optimize phse five portions of the 10 kinds of chlorotrnsfer ctlyst with high ctivity using trdi- methylted crosslinked polystyrene mixtures tionl methods. rect with ech one of the five tert-mines, Combintoril chemistry is new strtegy for respectively, to obtin five 10-membered subthe discovery nd optimiztion of mterils with librries. The second route is to mke 10 specil functions [5]. It mkes big difference portions of the five tert-mine mixtures rect from trditionl method in which trget mteri- with ech one of the 10 kinds of chlorols re synthesized, purified nd screened one methylted crosslinked polystyrenes, respectiveby one. Combintoril chemistry is type of ly, to obtin 10 five-membered sub-librries. synthetic nd screening strtegy which leds to The rectivities of the five tert-mines re lrge chemicl librries nd significntly ccel- different, nd excess mines need be dded in ertes the rte of discovery nd optimiztion of order to obtin the ctlyst with the highest new led mterils [6]. Menger et l. reported exchnge cpcity tht cn be reched. So the the development of ctlysts for the hydrolysis second route is not fesible due to the lck of of bis( p-nitrophenol) vi combintoril chemis- polystyrene-supported quternry mmonium try [7], nd rpidly found some effective slt ctlyst mde from inctive tert-mines. ctlysts. However, there does not seem to be Therefore, we chose the first route to synthesize ny literture on the combintoril synthesis nd the librry (Fig. 1). First, we synthesized 10 screening of polymer-supported phse trnsfer kinds of chloromethylted crosslinked polyctlysts. Hence, the present investigtion ws styrene resins. Second, the resins were uniformdirected towrds introducing the combintoril ly mixed with isodose, nd then the mixture ws strtegy into the synthesis nd screening of divided into five portions. Third, ech portion polymer-supported quternry mmonium slt ws mde to rect with only one of the five phse trnsfer ctlysts in order to estblish tert-mines. Thus, librry with five sub-lirpid method to synthesize nd screen phse brries ws synthesized, nd ech sub-librry trnsfer ctlysts. contined 10 kinds of polystyrene-supported The portioning-mixing method is one of the quternry mmonium slt ctlyst. most influentil methods in the synthesis of We designed the polystyrene-supported combintoril librries [8]. This method is bsed quternry mmonium slt phse trnsfer cton Merrifield s solid phse procedure. The lyst librry bsed on the literture [9] nd our principle of the portioning-mixing synthesis is previous work [10]. With respect to the polymer executed by repetition of the following three bckbone, the crosslinking degree of the gelsimple opertions: dividing the solid support type polystyrene should be reltively low in into equl portions; coupling ech portion in- order to be esily nd fully functionlized, but it dividully with only one of the regents; should lso be high enough to ensure mechnihomogeneously mixing the portions. The key cl strength in use. Thus, gel-type polystyrenes feture of the portioning-mixing synthesis is its with crosslinking degrees of 2 nd 4% were high efficiency in ppliction. The number of synthesized. The crosslinking degree of mcroproducts is multiplied fter ech coupling step. porous polystyrene should be reltively high in In our pproch, phse trnsfer ctlyst librry order to possess permnent mcropores. Thereof polystyrene-supported quternry mmonium fore, we designed nd synthesized eight kinds of slt ctlyst ws synthesized by the rection of mcroporous polystyrenes with vrious cross- 10 kinds of chloromethylted crosslinked poly- linking degrees nd pores. With respect to the styrene with five tert-mines using the por- selection of the tert-mines to synthesize the

3 M. Xu et l. / Rective & Functionl Polymers 48 (2001) Fig. 1. Scheme of the portioning-mixing synthesis of the ctlyst librry. librry, the hydrophobicity nd hydrophilicity of the mines should be considered. We used trimethylmine, triethylmine, tributylmine, dimethylethnolmine, nd triethnolmine to build the librry. Other tert-mines with longer hydrocrbon chins would be hrd to rect with the chloromethylted resins due to steric hindrnce. The itertive deconvolution method is usully used to screen out the most ctive smples from combintoril librries. The principle is outlined in Fig. 2, demonstrting the method for determintion of the most ctive ctlysts for probing rection. First, ech sub-librry is pplied to ctlyze the probing rection in order to select the most ctive sub-librry, nd the tertmine recting with the chloromethylted resin is determined. If the sub-librry mrked 1 is the most ctive, the components of the 10 smples re re-synthesized seprtely, nd ech Fig. 2. The itertion deconvolution method pplied to screen the librry. smple is used to ctlyze the probing rection. The most ctive smple is considered s the most ctive ctlyst in the librry. Although the

4 88 M. Xu et l. / Rective & Functionl Polymers 48 (2001) itertive deconvolution method ws used suc- cntly lower thn tht produced by smll moleculr cessfully to determine the most ctive comof tetr-lkylmmonium borohydrides becuse pounds from combintoril librries [11], it ws the low ctlytic ctivity of the ctlysts. If once criticized s n ineffective method since it phse trnsfer ctlyst with high ctlytic ctivi- ws considered tht the most ctive sub-librry ty for the reduction rection were found, the perhps did not contin the most ctive smple rection rte nd yield would be improved in the librry. However, perfect theory proby gretly. Hence, the reduction of cetophenone posed by Freier et l. showed tht the most sodium borohydride ws lso selected s one ctive smples in combintoril librries could of the probing rections to screen out the most be determined lmost ll the time by using the ctive polymer-supported quternry mmo- itertive deconvolution method [12]. In this nium slt phse trnsfer ctlyst for reduction study, we used the method to screen out the by sodium borohydride. most ctive ctlyst in the librry. We used the Br/I nion exchnge rection of hexyl-bromide nd the borohydride reduction of cetophenone s the probing rections to screen 2. Experimentl out the most ctive ctlysts for ech rection Building the polystyrene-supported phse Usully, the Br/ I nion exchnge rection is trnsfer ctlyst librry used s the probing rection to investigte the phse trnsfer ctlysis ctivity of nion ex Preprtion of chloromethylted chnge-type resins for nucleophilic substitution crosslinked polystyrene [13]. Hence, we first selected the Br/ I nion Ten kinds of styrene divinylbenzene copolyexchnge rection of hexyl-bromide s one of mer of mesh were synthesized using the probing rections to screen out the most suspension polymeriztion, nd ll were chloroctive polymer-supported quternry mmo- methylted seprtely ccording to Ref. [16]. nium slt phse trnsfer ctlyst for nucleophilic The crosslinking degree of the copolymer, the substitution. mounts of porogen used in the polymeriztion Borohydride reduction of orgnic compounds nd the chlorine contents of the chloroby sodium borohydride is often used in orgnic methylted crosslinked polystyrenes re shown synthesis. The rection only proceeds in the in Tble 1. interfce between the orgnic phse nd the wter phse becuse of the low solubility of Tble 1 sodium borohydride in orgnic compounds, nd Chloromethylted crosslinked polystyrene resins this results in slow rection rte nd low yield. Resin Crosslinking Amount of Chlorine code degree (%) porogen content (%) In order to increse the rection rte nd yield, sodium borohydride is converted into smll moleculr tetr-lkylmmonium borohydrides [14] or nion exchnge resin-supported boro hydride [15], nd this mkes the operting process complex nd gret mount of quter nry mmonium slt is needed. Polymer-sup ported quternry mmonium slts hve been used s phse trnsfer ctlysts to ctlyze the rection [4], nd the rection ws improved Note: the crosslinking degree is the mss percentge of di- vinylbenzene in the monomers. The porogen used is mixture of somewht. However, the yield of the phse toluene nd liquid prffin with mss rtio of 2:1, nd the trnsfer ctlyst ctlyzed rection ws signifi- mount of porogen is the mss rtio of the porogen to monomers.

5 M. Xu et l. / Rective & Functionl Polymers 48 (2001) Synthesis of the phse trnsfer ctlyst trnsfer ctlyst of ech sub-librry, nd 20 ml librry of chlorobenzene ws then dded to ech flsk. The 10 kinds of chloromethylted crosslinked After the ctlysts hd been llowed to swell for polystyrenes synthesized were uniformly mixed 2 h, 17.0 g (0.1 mol) of KI, 10 ml of wter nd with isodose, nd the mixture ws then divided 7.8 ml (0.05 mol) of hexyl-bromide were dded into five portions. The five portions were mde to ech flsk. The rection ws llowed to to rect with trimethylmine, triethylmine, proceed t 1008C under stirring with the speed tributylmine, dimethylethnolmine, nd tri- of the gittor greter thn 600 r/ h. During the ethnolmine, respectively. Thus polystyrene- first 2 h of the rection, smples were tken supported quternry mmonium slt phse every 0.5 h. The smples were nlyzed by gs trnsfer ctlyst librry with five sub-librries chromtogrphy to determine the yield t the ws obtined. The codes of the five mines re corresponding time. The rection ws stopped shown in Tble 2, nd the five sub-librries re fter 4 h, nd smple ws tken to determine nmed by the code of the corresponding mine. the yield of the rection. The corresponding Rection with trimethylmine ws crried out sub-librry of the rection with the highest yield ccording to Ref. [17]. Rections with the other ws selected s the most ctive sub-librry. mines were performed s follows. Twenty milliliters of N,N-dimethylformmide nd Screening out the most ctive ctlyst g mixture of chloromethylted polystyrene resin in the librry were dded to round-bottom flsk. Two hours The corresponding mine of the most ctive lter, 20 ml of mine ws dded to the flsk, nd sub-librry ws rected with the 10 kinds of the rectnts were then heted for 24 h under chloromethylted crosslinked polystyrenes prestirring. After cooling, the resin ws wshed pred to synthesize the 10 ctlysts of the most with wter nd lcohol, distilled with lcohol ctive sub-librry. The ctlysts re nmed by for 10 h, nd then dried under vcuum. combining the code of the corresponding mine nd tht of the corresponding chloromethylted 2.2. Screening of the phse trnsfer ctlyst polystyrene. The rection conditions were the for nucleophilic substitution sme s those for the synthesis of the most ctive sub-librry. The strongly bsic nion The Br/ I nion exchnge rection of hexyl- exchnge cpcity of ech ctlyst ws mebromide ws used s the probing rection to sured ccording to Ref. [9]. The most ctive select the most ctive ctlyst for nucleophilic ctlyst ws selected using the sme method s substitution from the librry. for selecting the most ctive sub-librry Screening out the most ctive sub Comprison of the most ctive ctlyst librry with other phse trnsfer ctlysts To ech of five 100 ml three-necked flsks The Br/I nion exchnge rection of hexylws dded 1.0 g mixture of polystyrene- bromide ws crried out with the most ctive supported quternry mmonium slt phse ctlyst under the sme conditions s for Ref. Tble 2 The tert-mines used in the synthesis of the combintoril librry Amine NMe3 NEt3 NBu3 Me2NCH2CH2OH N(CH2CH2OH) 3 Code of mine A B C D E

6 90 M. Xu et l. / Rective & Functionl Polymers 48 (2001) [4] in order to compre the ctlytic ctivity 3. Results nd discussion with other phse trnsfer ctlysts Screening phse trnsfer ctlysts for 2.3. Screening of the phse trnsfer ctlyst nucleophilic substitution for borohydride reduction Screening of the librry Yields of the Br/I nion exchnge rection of Screening out the most ctive subhexyl-bromide ctlyzed by different sub-lilibrry brries re listed in Tble 3. Sub-librry C ws The reduction of cetophenone by sodium the most ctive sub-librry, nd ws prepred by borohydride ws used s the probing rection to rection of chloromethylted polystyrenes with select the most ctive sub-librry in the librry. tributylmine. It cn be seen from Tble 3 tht To ech of five 100 ml three-necked flsks ws the ctlytic ctivity of the sub-librries indded 1.0 g mixture of polystyrene-supcresed with incresing sub-librry lipophilicity, ported quternry mmonium slt phse trnsfer which is in ccordnce with the literture [13]. ctlyst of ech sub-librry, nd 20 ml of The influence of vrying the quternry mtoluene ws then dded to ech flsk. After the monium ction on the ctlytic ctivity is ctlysts hd been llowed to swell for 2 h, 2.4 through the vrition of the interction between g (0.02 mol) cetophenone, 2.2 g (0.069 mol) ctions nd nions, nd tht of the environment NBH4 nd 10 ml wter were dded to ech of the ctive sites. The more lipophilic the flsk. The reduction rection proceeded t 508C ction the weker the interction between ction under stirring with stirring rte greter thn nd nion, nd the greter the nucleophilic 600 rpm. The nlysis procedure ws the sme ctivity of the nion, the more ctive the s tht for screening out the most ctive ctlyst ctlyst. sub-librry for nucleophilic substitution. The The yields of the Br/ I nion exchnge recorresponding sub-librry of the rection with ction of hexyl-bromide ctlyzed by polymerthe highest yield ws selected s the most ctive supported quternry mmonium slts of the sub-librry. most ctive sub-librry re listed in Tble 4. It cn be seen from Tble 4 tht C5 ws the most Screening out the most ctive ctlyst ctive ctlyst in the most ctive sub-librry, in the librry which ws the mcroporous strongly bsic The experimentl method ws the sme s nion exchnge resin of structure 1. It ws tht for the screening out of the most ctive reported in Ref. [1] tht the ctlytic ctivity of ctlyst for nucleophilic substitution, but the polymer-supported ctlysts my depend heviprobing rection vried. Tble 3 Yields of the Br/ I nion exchnge rection ctlyzed by different ctlyst sub-librries (%) Comprison of the most ctive ctlyst with other phse trnsfer ctlysts Time Ctlyst sub-librry Reductions of cyclohexnone, benzldehyde (h) A B C D E nd benzophenone by sodium borohydride were crried out with the most ctive ctlyst under the sme conditions s for screening out the most ctive sub-librry, nd the results of these rections were compred with tht ctlyzed by other phse trnsfer ctlysts in the literture. Yield of the rection with no ctlyst t 4 h ws less thn 5%.

7 M. Xu et l. / Rective & Functionl Polymers 48 (2001) Tble 4 Yields of the Br/ I nion exchnge rection ctlyzed by different ctlysts of sub-librry C (%) Time (h) Ctlyst C1 C2 C3 C4 C5 C6 C7 C8 C9 C ,10,10 Exchnge cpcity (mmol/ g) ly on both the crosslinking degree nd the polymer, nd thus the ctlyst with both higher polymer morphology, nd microporous resins reltive diffusionl efficiency nd nion exre more ctive thn the corresponding mcro- chnge cpcity, which ws C5, showed the porous resins. Contrry to the results of Ref. [1], highest ctlytic ctivity. the results in Tble 4 indicte tht mcroporous resins re more ctive thn microporous resins Comprison of C5 with other phse In fct, the rection rte my be controlled trnsfer ctlysts minly by the mss trnsport rte from bulk Results of the Br/ I nion exchnge rection solution to the polymer surfce, diffusion within of hexyl-bromide ctlyzed by C5 nd one of the polymer mtrix, or the intrinsic rection. In the most ctive phse trnsfer ctlysts reported order to revel the reson for the different in the literture, which is ctlyst T [4], re ctivities reported in the literture nd the listed in Tble 6. It cn be seen from Tble 6 results presented in Tble 4, the rection t tht the ctivity of C5 ws greter thn tht of stirring rte of 300 rpm ws investigted, nd ctlyst T, lthough ctlyst T is n ctive the results re listed in Tble 5. At stirring rte polystyrene-supported ctlyst with n rm of of 300 rpm, the rection rte ws minly limited 12 crbon toms. This results from the differby trnsport of rectnts onto the polymer ence of the pore structure between the two surfce. In this cse the ctlytic ctivity ws ctlysts. C5 is mcroporous nion exchnge minly effected by the nion exchnge cpcity resin with both high diffusionl efficiency nd of the ctlyst, nd thus the ctlyst with the nion exchnge cpcity, while ctlyst T is lrgest nion exchnge cpcity, which ws C1, microporous nion exchnge resin with relshowed the highest ctlytic ctivity. As the tively low diffusionl efficiency. Hence the stirring rte ws incresed to.600 rpm, the ctlytic ctivity of C5 is greter thn tht of rection ws minly limited by diffusion of the rectnts within the pore nd surfce of the Tble 6 Yields of the Br/ I nion exchnge rection ctlyzed by vrious phse trnsfer ctlysts Tble 5 Yields of the Br/I nion exchnge rection ctlyzed by some of Rectnt Product Ctlyst Yield (%) Ref. the ctlysts t different stirring rtes (%) Hexyl bromide Hexyl iodide C Stirring Ctlyst T 87.0 [4] rte (rpm) C1 C2 C3 C4 C $ The structure of ctlyst T:.

8 92 M. Xu et l. / Rective & Functionl Polymers 48 (2001) ctlyst T. The synthetic route for C5 is much duction ws different from tht for ctlytic simpler thn tht for ctlyst T. Therefore, C5 nucleophilic substitution. This resulted from would be more useful for the ctlysis of differences in the ctlytic mechnism. ordinry nucleophilic substitution. C5 ws lso Yields of the borohydride reduction of used to ctlyze the Cl/ OAc nion exchnge cetophenone ctlyzed by different ctlysts in rection nd the ldol condenstion of benzl- the most ctive sub-librry re listed in Tble 8. dehyde nd cetone, nd showed high ctlytic It cn be seen tht E1 ws the most ctive ctivity [18,19]. Hence, C5 is polymer-sup- ctlyst in the most ctive sub-librry, which ported quternry mmonium slt phse trnsfer ws the gel-type strongly bsic nion exchnge ctlyst with high ctlytic ctivity for nu- resin of structure 2. In contrst to the mcrocleophilic substitution. porous nion exchnge resin which ws the most ctive ctlyst in nucleophilic substitution, 3.2. Screening phse trnsfer ctlysts for the microporous resin ws the most ctive borohydride reduction ctlyst in borohydride reduction. This lso resulted from differences in the ctlytic mech Screening of the librry nism. Yields for the ctlytic reduction of cetophenone by sodium borohydride using Ctlytic mechnism of borohydride different ctlyst sub-librries re listed in Tble reduction ctlyzed by the most ctive ctlyst 7. As cn be seen from Tble 7, sub-librry E As cn be seen from Tble 8, the strong bsic ws the most ctive sub-librry, which ws the exchnge cpcities of E1, E3 nd E5 were triethnolmine minting strongly bsic nion reltively high, nd the ctivity of the three exchnge resin ctlyst sub-librry. The most ctlysts ws lso reltively high. Although E1 ctive sub-librry for ctlytic borohydride re- ws the gel-type (microporous) resin in contrst to the mcroporous resins E3 nd E5, the yield Tble 7 of the rection ctlyzed by E1 ws slightly Yields of borohydride reduction ctlyzed by different ctlyst sub-librries (%) higher thn those ctlyzed by E3 nd E5 since the exchnge cpcity of E1 is slightly lrger Time Ctlyst sub-librry (h) thn tht of E3 nd E4. This indictes tht the A B C D E rection rte ws not limited by diffusion, but controlled by the intrinsic rection. The inver sion of the exchnge cpcity nd yields of the ctlytic rection between E2 nd E6 my result from differences in the ccessibility to the Yield of the rection with no ctlyst t 4 h ws 35.7%. ctive site between the two ctlysts. Tble 8 Yields of borohydride reduction ctlyzed by ctlysts of the most ctive sub-librry (%) Time (h) Ctlyst E1 E2 E3 E4 E5 E6 E7 E8 E9 E Exchnge cpcity (mmol/ g)

9 M. Xu et l. / Rective & Functionl Polymers 48 (2001) For ctlytic rection controlled by the bonding nd dihydrogen bonding with two of intrinsic rection, the lipophilic or hydrophilic the three hydroxyl groups in ech ctive site. properties of the ctive sites re one of the min The neighboring effect gretly enhnced the rte fctors determining the ctivity of phse trnsfer of reduction (Fig. 3). Thus, E1 is hydrogen ctlysts with similr chemicl structure. The bonding promoted phse trnsfer ctlyst with structures of ll the ctlyst sub-librries were high ctivity for the borohydride reduction of similr. As shown in Tble 7, the ctivity of crbonyl compounds. sub-librry E ws higher thn tht of sub-librry B, nd the ctivity of sub-librry B ws higher Comprison of E1 with other phse thn tht of sub-librry A. As we know, the trnsfer ctlysts hydrophilicity of sub-librry E is much stronger Results of the borohydride reduction of thn tht of sub-librry B, nd the hydrophilicity cetophenone, cyclohexnone, benzldehyde of sub-librry B is weker thn tht of sub- nd benzophenone with the ctlyst E1 nd librry A. Therefore, it cn be concluded tht other phse trnsfer ctlysts reported in the the high ctlytic ctivity of sub-librry E did literture [4,20] re listed in Tble 9. It cn be not result from its hydrophilicity or lipophilic- seen tht the ctivity of E1 ws higher thn tht ity. of ctlyst T, lthough ctlyst T is the most Colonn et l. [20] reported tht the presence ctive polymer-supported phse trnsfer ctlyst of hydroxyl group in smll moleculr quternry mmonium phse trnsfer ctlyst enhnces the rte of reduction, nd this provides possible explntion of why the crbonyl group is ctivted towrds borohydride ttck through hydrogen bonding with the ctlyst. However, the result of our study shows tht the presence of only one hydroxyl group in the ctive site of polymer-supported quternry mmonium slt ctlyst pprently does not enhnce the rte of reduction, s shown in the cse of sub-librry A nd sub-librry D in Tble 7. This my be the result of nchoring the ctlytic ctive site onto the polymer. The presence of three hydroxyl groups in the ctive site gretly enhnces the rte of reduction, s shown in the cse of sub-librry B nd sublibrry E in Tble 7. An explntion for this is tht the rectnts were held together through intercting with the hydroxyl groups of the ctive sites. The crbonyl group of cetophenone is bound to the ctive sites nd ctivted through hydrogen bonding with the ctlyst. The borohydride ion intercts with the hydroxyl groups of the ctive sites of the ctlyst through new intermoleculr interction: dihydrogen bonding [21]. Thus the two Fig. 3. Ctlytic rectnts were held together through hydrogen cetophenone. mechnism of borohydride reduction of

10 94 M. Xu et l. / Rective & Functionl Polymers 48 (2001) Tble 9 Yields of borohydride reduction ctlyzed by vrious phse trnsfer ctlysts Rectnt Product Ctlyst Rection Rection Yield Ref. time (h) temp. (8C) (%) E T [4] b S [20] E T [4] Ph2C=O Ph2CH2OH E S [20] PhCHO PhCH2OH E S [20] Ctlyst T is the sme ctlyst s tht in Tble 6. b The structure of ctlyst S:. for borohydride reduction reported in the literture, possessing ctive sites with n rm of 12 crbon toms. However, the ctlytic ctivity of E1 ws lower thn tht of ctlyst S, one of the most ctive smll moleculr phse trnsfer ctlysts for borohydride reduction reported in the literture, nd this my result from the non-homogeneity of the rection system s ctlyzed by polymer-supported ctlysts. Acknowledgements Support of this work by the Ntionl Nturl Science Foundtion of Chin, under grnt No , nd by the Eduction Committee of Hunn Province, is grtefully cknowledged. References 4. Conclusion [1] R. Solro, S. D Antone, E. Chiellini, Rect. Polym. 9 (1988) 155. [2] S.L. Regen, J. Am. Chem. Soc. 97 (1975) [3] N. Kobyshi, K. Iwi, Mkromol. Chem., Rpid Commun. 2 (1981) 105. Combintoril chemistry is n effective [4] Hung Jinxi, Chen Jiwei, Jing Jilong, Cuihu Xuebo 9 strtegy for the synthesis nd screening of (1994) 399. polymer-supported phse trnsfer ctlysts. [5] F. Blkenhold, A. Lnsky, C. Zechel, Angew. Chem. Int. Ed. Engl. 35 (1996) For nucleophilic substitution, the gel-type [6] R.A. Houghten, C.T. Dooley, J.H. Cuervo, Nture 354 (microporous) strongly bsic nion exchnge (1991) 84. resin of structure 1 is the most ctive polymer- [7] F.M. Menger, A.V. Eliseev, V.A. Migulin, J. Org. Chem. 60 (1995) supported quternry mmonium slt phse [8] A. Furk, F. Sebestyen, G. Dibo, Int. J. Pept. Protein Res. 37 trnsfer ctlyst in the librry synthesized here. (1991) 487. However, with respect to borohydride reduction [9] He Binglin, Hung Wenqing, Resins for Ion Exchnge nd Adsorption, Shnghi Science nd Eduction Press, Shngof crbonyl compounds, the most ctive ctlyst hi, Chin, 1995, p in the librry is the mcroporous strongly bsic [10] S. Yu, Z. Ou, C. Wng, L. Zhng, S. Zhng, Hecheng Huxue nion exchnge resin of structure 2. The most 7 (1997) 98. ctive polymer-supported phse trnsfer ctlyst [11] E. Erb, K.D. Jnd, S. Brenner, Proc. Ntl. Acd. Sci. USA 91 (1994) in the librry vries s the ctlytic mechnism [12] S.M. Freier, D.A.M. Konings, J.R. Wytt, D.J. Ecker, J. Med. vries. Chem. 38 (1995) 344.

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