J. Iran. Chem. Soc., Vol. 6, No. 4, December 2009, pp JOURNAL OF THE Iranian Chemical Society

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1 J. Iran. Chem. Soc., Vol., o., December 00, pp. 0. JURAL F THE Iranian Chemical Society Poly(,'dibromoethylbenzene,disulfonamide) and,,',' Tetrabromobenzene,disulfonamide as Effective Catalysts for Conversion of Aldehydes to,diacetates and Acetals R. GhorbaniVaghei*, M. Amiri,. Moshfeghifar, H. Veisi and S. Akbari Dadamahaleh Department of rganic Chemistry, Faculty of Chemistry, BuAli Sina University, Hamadan, Iran (Received ctober 00, Accepted ctober 00) Poly(,'dibromoethylbenzene,disulfonamide) [] and,,','tetrabromobenzene,disulfonamide [] are effective catalysts for easy preparation of,diacetates from aldehydes and acetic anhydride, and for easy preparation of acetals using diols under microwave irradiation in the presence of Si. Keywords: Aldehydes, Acetic anhydride, Diols, Microwave irradiation,, ITRDUCTI The protection of aldehydes as acetates is an interesting feature in organic chemistry []. They are stable in neutral and basic media [], and can be used as starting materials for the synthesis of valuable intermediates for DilsAlder cycloaddition reactions [], acetoxydienes from α,βunsaturated aldehydes [,], and vinyl acetates such as, dichlorovinylacetate [a,b]. The preparation of,diacetates is carried out under the catalysis of strong protic acids such as H P and CH S H [], and afionh [], or Lewis acids, such as Me S + [], In /Al [], Bi(Tf) [], I [], Fe []. In recent years, several catalysts have been employed for this reaction such as Zeolites [], CA [], clay [a,b], BS [], Ti (Tf) [], and dodecatungstophosphate (AlPW 0 ) []. Acetalization is a wellknown synthetic procedure for the protection of carbonyl groups in multistage synthesis [], and is achieved by treatment of aldehydes or ketones with alcohols or diols and dehydrating agents in the presence of onsted or Lewis acids such as In(Tf) [], ammonium triflate [0], *Corresponding author. rgvaghei@yahoo.com H PW 0 [], novel brønsted acid (PDA) [],,' bis[,bis(trifluoromethyl)phenyl]thiourea [], butyl methylimidazolium tetrachlorogallate [], Zr(HS ) [],,,,tetrabromo,cyclohexadienone (TABC) [], Si [], LiTf [], Ti + Montmorillonite [] and I [0]. In this work, we used poly(,'dibromoethylbenzene,disulfonamide) [] and,,','tetrabromobenzene,disulfonamide [] as effective catalysts for easy preparation of,diacetates from aldehydes and acetic anhydride, and for easy preparation of acetals using diols under microwave irradiation in the presence of Si. EXPERIMETAL Typical Procedure for Conversion of Benzaldehyde to,diacetates Using under Reflux Condition To a magnetically stirred solution of benzaldehyde ( mmol) and freshly distilled acetic anhydride (. mmol), ( mmol) was added and the mixture was stirred under reflux condition untile complete disappearance of the aldehyde starting material (as monitored by TLC). After completion, the reaction was quenched with water ( ml),

2 ) GhorbaniVaghei et al. and the mixture was extracted with CH ( ml). The organic layer was separated, and dried over a S. Evaporation of the solvent under reduced pressure gave the pure,diacetate (Table ). General Procedure for Conversion of Aldehydes to Acetals Using under Microwave Irradiation and Reflux Conditions Aldehydes ( mmol), 0.0 g (0. mmol),, ethane diol ( mmol) and Si ( g) were mixed together and irradiated with microwaves for the appropriate reaction times as indicated in Table. After completion of the reaction, CH ( ml) was added to the reaction mixture and Si was separated by simple filtration followed by the addition of H (0 ml) to the mixture. rganic layer was separated and dried over anhydrous a S ( g) which, after evaporation of the solvent under vacuum, gave the desired acetals in high yields (Table ). RESULTS AD DISCUSSI ur interest in the application of poly(,'dibromoethylbenzene,disulfonamide), [] and,,',' tetrabromobenzene,disulfonamide [] [], in organic synthesis has been previously reported []. We now report a mild and efficient method for conversion of aldehydes to,diacetates, in the presence of and with acetic anhydride. Both and bear bromine atoms which are attached to nitrogen atoms adjacent to S groups. This generating + in situ, a strong Lewis acid, or an electrophilic species can catalyze generation of,diacetate from aldehydes and acetals from carbonyl compounds (Scheme ). By using or as catalysts, various aromatic and aliphatic aldehydes were acylated to,diacetates in good to high yields under reflux conditions without byproducts (Table ). S S H C S S CH ) n R R= Alkyl, aryle,, CH, reflux CCCH RCH(CCH ) Scheme Table. Acylation of Carbonyl Compounds Catalyzed by and in CH under Reflux Condition Product CH(CCH ) CH(CCH ) (h) (%) a (h) (%) a.. CH(CCH ). 0 H CH(CCH ) CCH.. CH(CCH ).

3 Poly(,'dibromoethylbenzene,disulfonamide) Table. Continued H C CH(CCH ) CH(CCH ) CH(CCH ) CH(CCH ) CH(CCH ) CH(CCH ). 0 a Products were characterizied by their physical properties, comparison with authentic samples, and by spectroscopic methods (IR, H MR). Table. Comparison of the Effect of Catalysts for GemDiacetate Synthesis from Methylbenzaldehyde and Chlorobenzaldehyde Catalysts a b BS Bi(Tf) (CA) c Time (h).. Yield (%) Ref. [] [] [] Me S +. []. b a,,','tetrabromobenzene,disulfonamid. b Poly(,'dibromoethylbenzene,disulfonamide). c Ceric ammonium nitrate.

4 GhorbaniVaghei et al. The advantages of or over reported catalysts for the acylation of pchlorobenzaldehyde, and p methylbenzaldehyde are shown in Table. It is noteworthy that some of the previously reported methods require longer reaction times. We found that aliphatic aldehydes acylated slower than aromatic aldehydes. Therefore, the method was selective for aromatic aldehydes in the presence of aliphatic aldehydes. From a mixture of benzaldehyde ( mmol) and noctanal ( mmol) with acetic anhydride (. mmol) in the presence of catalysts under reflux condition, 0% of benzaldehyde and % of noctanal were acylated to,diacetates (Scheme ). It was also found that and were efficient (mmol) + (mmol) (mmol), acetic anhydryde (. mmol) H R + H R= Alkyl, aryle reflux, h Scheme catalysts for the conversion of aldehydes to their acetals in the presence of Si under microwave irradiation (Scheme ). ur experiments showed that acetalization of aldehydes in the presence of Si, and in the absence of and under microwave irradiation, afforded low yields of acetals (0%). It is noteworthy that various types of aromatic aldehydes, either electeronwithdrawing or electronreleasing, were converted to their acetals with high chemoselectivity without overoxidation of aldehydes to carboxylic acids (Table ). Aliphatic aldehydes also produced their corresponding acetals in good yields under the same reaction condition (Table, entry ). or MW Scheme (0%) + R CH(CCH ) CH(CCH ) Table. Acetalization of Aldehydes Using and in the Presence of Diols under Microwave Irradiation and Reflux Condition (0%) Product (min/h) (%) a (min/h) (%) a 0

5 Poly(,'dibromoethylbenzene,disulfonamide) Table. Continued H () H CH H H () H CH H h. h h 0 b h 0 b a Products were characterizied by their physical properties, comparison with authentic samples, and by spectroscopic methods (IR, H MR). b Aldehydes ( mmol), or (0. mmol, 0. g),,butanediol ( mmol), C ( ml), under reflux condition. CCLUSIS In this study, we have introduced other useful catalytic applications of and for the generation of, diacetates from aromatic aldehydes under reflux conditions, and acetals from carbonyl compounds in the presence of Si under microwave irradiation. Preparation of the catalysts is easy and not a time consuming process. Workup of the reaction mixture was also easy and yields of the products are high. ACKWLEDGMETS We are thankful to BuAli Sina University, Center of Excellence and Development of Chemical Methods (CEDCM) for financial support.

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