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292 New J. Chem., 2011, 35, 292–298 This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011 Facile and efficient hydrolysis of organic halides, epoxides, and esters with water catalyzed by ferric sulfate in a PEG1000-DAIL[BF4]/toluene temperature-dependent biphasic system Yu Lin Hu, Hui Jiang, Jie Zhu and Ming Lu* Received (in Gainesville, FL, USA) 14th June 2010, Accepted 2nd November 2010 DOI: 10.1039/c0nj00454e An efficient and environmentally friendly procedure for the hydrolysis of organic halides, epoxides, and esters with water catalyzed by ferric sulfate in a PEG1000-DAIL[BF4]/toluene temperature-dependent biphasic system has been developed. The product can be easily isolated by a simple decantation, and the catalytic system can be recycled and reused without loss of catalytic activity. Hydrolysis of organic halides, epoxides, and esters is one of the most fundamental transformations both in laboratory synthesis and industrial production.1,2 The most commonly employed procedures for hydrolysis can be performed in acidic or alkaline media, with the use of enzymes or with the aid of metal ions.3–6 However, these described conditions are in most cases rather harsh. Moreover, long reaction times and high reaction temperatures are often required. To speed up the hydrolysis reactions, the use of micellar catalysis,7 phase transfer catalysis,8 ultrasonic irradiation,9 microwaves,10 and others11 have been applied to accomplish this transformation with different degrees of success. Transition metal-catalyzed hydrolysis of organic halides, epoxides, and esters has been developed with some innovative progress in recent years,12 whilst most of the reactions still require the use of expensive reagents, long reaction times of more than 24 hours, elevated reaction temperatures, and difficulties in recycling of the catalyst. Consequently, the search for new and environmen- tally benign catalytic hydrolysis systems that address these drawbacks remains to be of value and interest. Room temperature ionic liquids, a kind of environmental friendly solvents and catalysts, because of their adjustable physical and chemical properties, got broad attention of scholars from various fields such as synthesis, catalysis, separa- tion, and electrochemistry.13,14 Some novel ionic liquid–organ- ic solvent mixtures as temperature dependent biphasic systems have been reported.15 We as well as Luo and co-workers have described a new PEG1000-based dicationic ionic liquid (PEG1000-DAIL) exhibiting temperature-dependent phase behavior with toluene and applied it in one-pot synthesis of benzopyrans successfully.16 Utilization of such biphasic systems can improve product isolation as well as catalyst recovery. We herein report an efficient and environmentally friendly protocol for the hydrolysis of organic halides, epoxides, and esters with water catalyzed by ferric sulfate (Fe2(SO4)3) in the PEG1000-based dicationic ionic liquid (PEG1000-DAIL[BF4])/toluene temperature-dependent bipha- sic system (Scheme 1). It was determined during a preliminary survey of the reaction conditions that we should use 1-(chloromethyl)-4- methoxybenzene as the model substrate in the presence of copper(II) sulfate (Table 1). As H2O was used as the nucleophile, initial reaction screening led to disappointing results in the absence of an ionic liquid, the reaction proceeded very slowly, and the yield was only 29% after 7 h (Table 1, entry 1). The results mean that copper(II) sulfate alone does not work as an effective catalyst in the hydrolysis reaction. The effects of different ionic liquids such as PEG600- DAIL, PEG800-DAIL, PEG1000-DAIL, PEG1000-DAIL[BF4], PEG1000-DAIL[PF6], and PEG1000-DAIL[OTf] were then screened in this hydrolysis (Table 1, entries 2–7), and it was observed that PEG1000-DAIL[BF4] demonstrated the best performance. The different catalytic abilities of the ILs (PEG600-DAIL, PEG800-DAIL, and PEG1000-DAIL) should be attributed to their different abilities of forming homogeneous catalytic media by exhibiting a temperature- dependent phase behavior with toluene. This two phase medium is changed to a homogeneous one at elevated temperatures. Under the same conditions, the IL which forms a homogeneous catalytic medium in combination with toluene more easily will lead to a larger increase in the effective reactant concentration, which increases the encounter probability between the reactive species. Thus, the observed rate and yield of the reaction is PEG1000-DAIL > PEG800- DAIL > PEG600-DAIL. For a blank test (Table 1, entry 8), a lower yield of the product was obtained while the same reaction condition was carried out in the absence of copper(II) sulfate. The result indicates that this cocatalyst must play an important role in accelerating the rate of the reaction. Finally, we also tried to use other types of cocatalysts in the reaction (Table 1, entries 9–16), the results showed that FeSO4, Fe2(SO4)3, and Cu(OAc)2 were the same effective cocatalysts as CuSO4. Among them, Fe2(SO4)3 was found to be the most effective cocatalyst in terms of yield and reaction rate. Therefore, the optimal reaction conditions were observed in Table 1, entry 10. In addition, the catalytic system could be typically recovered and reused for subsequent reactions with no appreciable decrease in yields and reaction rates (Fig. 1). The recycling process involved the removal of the top oil layer (toluene containing product) by decantation. The bottom aqueous layer (catalytic system) was concentrated under vacuum to College of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, PR China. E-mail: luming1963@163.com; Fax: +86 025-84315030; Tel: +86 025-84315030 LETTER www.rsc.org/njc | New Journal of Chemistry D ow nl oa de d by U ni ve rs ity o f S ci en ce a nd T ec hn ol og y of C hi na o n 12 A pr il 20 12 Pu bl ish ed o n 22 N ov em be r 2 01 0 on h ttp :// pu bs .rs c. or g | do i:1 0.1 039 /C0 NJ 004 54E View Online / Journal Homepage / Table of Contents for this issue This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011 New J. Chem., 2011, 35, 292–298 293 remove the water and hydrogen chloride (the hydrolysis product). Fresh substrates and toluene were then recharged to the residual PEG1000-DAIL[BF4]/Fe2(SO4)3 and the mixture was heated to react once again. The procedure was repeated 8 times in the hydrolysis of 1-(chloromethyl)-4-methoxybenzene, and only 5.7% loss of weight was observed. The excellent reaction results of the catalytic system suggest that the hydrolysis reaction among 1-(chloromethyl)-4- methoxybenzene, water, Fe2(SO4)3, toluene and PEG1000- DAIL[BF4] has a particular catalytic process, which is schematically depicted in Fig. 2. Before the hydrolysis, there existed an obvious oil–water biphasic system, and the bottom layer (water phase) consisted of PEG1000-DAIL[BF4], Fe2(SO4)3, and water. The PEG1000-DAIL[BF4] and Fe2(SO4)3 were dissolved completely in the aqueous medium and the top layer (oil phase) consisted of toluene and 1-(chloromethyl)-4-methoxybenzene (substrate) (Fig. 2a). During the process of hydrolysis, the oil–water biphasic system disappeared and a homogeneous reaction medium was formed (Fig. 2b). After the completion of the reaction, the phase-separation appeared along with cooling (Fig. 2c), and a complete oil–water biphasic system was formed again after being cooled to room temperature (Fig. 2d). The PEG1000-DAIL[BF4] plays a very important role in the hydrolysis process to locally concentrate the reacting species near them by exhibiting a temperature-dependent phase behavior with toluene, which leads to a large increase in the effective reactant concentration and the excellent results of the hydrolysis reaction. With these results in hand, we subjected other organic halides to the hydrolysis reactions, and the results are listed in Table 2. It is clear that various types of benzylic, allylic, and aliphatic halides, both primary and secondary, can be efficiently converted to the corresponding alcohols in good to high yields (Table 2, entries 1–13). The reaction showed good functional group tolerance, thus benzylic halides with alkyl, Scheme 1 Hydrolysis of organic halides, epoxides, and esters and synthesis of PEGn-DAIL[anion]. D ow nl oa de d by U ni ve rs ity o f S ci en ce a nd T ec hn ol og y of C hi na o n 12 A pr il 20 12 Pu bl ish ed o n 22 N ov em be r 2 01 0 on h ttp :// pu bs .rs c. or g | do i:1 0.1 039 /C0 NJ 004 54E View Online 294 New J. Chem., 2011, 35, 292–298 This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011 alkoxy, fluoro and nitro groups all gave high yields of the corresponding alcohols (Table 2, entries 2–10). However, aryl halides were less reactive, even under more drastic reaction conditions, we did not obtain their corresponding phenols (Table 2, entries 14 and 15). It was also observed that the electronic nature of the substituents on the aromatic ring has some impact on the reaction rate. Substrates with electron- withdrawing groups (Table 2, entries 9 and 10) are less reactive than those with electron-donating groups (Table 2, entries 2–7). The next portion of this work involved the application of our catalytic protocol to prepare 1,2-diols by hydrolysis of epoxides with water. The optimal hydrolysis conditions were found to be the same as those in the case of hydrolysis of organic halides, and the desired 1,2-diol products were obtained in excellent yields (Table 3). Results revealed that our protocol can facilitate efficiently the hydrolysis reactions of various epoxides with water. Various epoxides were efficiently converted to the corresponding 1,2-diols in good to excellent isolated yields using the catalytic protocol (Table 3, entries 1–10). The epoxides such as 2-p-tolyloxirane and 2-(4- methoxyphenyl)oxirane gave products in higher yields under milder reaction conditions (Table 3, entries 2 and 3) than 4-(oxiran-2-yl)benzonitrile, 1-(4-(oxiran-2-yl)phenyl)ethanone, and 2-(4-fluorophenyl)oxirane (Table 3, entries 4–6), which was attributed to the electron-donating effect of alkyl group, that may explain why they showed more activity for the reactions. The final portion of this work involved the extension of our catalytic protocol to the hydrolysis of esters to carboxylic acids with water. As shown in Table 4, different esters were transformed into the corresponding carboxylic acids in good to excellent yields. Aryl esters containing electron-withdrawing substituents in the ortho and para positions reacted slowly (Table 4, entries 4–6) than those with electron-donating substituents (Table 4, entries 2 and 3). Moreover, longer reaction times or more harsh reaction conditions were required to reach good yields for benzoic acid long chain alkylesters (Table 4, entries 7–9), especially for entry 9. Obviously, the PEG1000-DAIL[BF4]/Fe2(SO4)3 catalytic system was found to be more effective in hydrolysis of organic halides than that of both epoxides and esters, which might be attributed to the different abilities of loss of the corresponding leaving groups when in the hydrolysis of organic halides, epoxides and esters with water (nucleophile). The reaction rate of hydrolysis depended upon what was being hydrolysed, under the same conditions, the substrate molecule which contained a better leaving group would lead to a much easier nucleophilic attack, and a faster reaction rate and a higher yield were obtained. In conclusion, we have successfully developed an efficient, experimentally simple, and environmentally friendly protocol for the hydrolysis of organic halides, epoxides, and esters with water catalyzed by ferric sulfate in a PEG1000-DAIL[BF4]/ toluene temperature-dependent biphasic system. Advantages of our protocol include simplicity of operation, high yields, easy isolation of products, good thermoregulated biphasic behavior of the IL, and excellent recyclability of the catalytic Table 1 Optimization of the conditions for hydrolysis of 1-(chloromethyl)-4-methoxybenzene with watera Entry Ionic liquid Cocatalyst Time/h %Yieldb 1 — CuSO4 7 29 2 PEG600-DAIL CuSO4 1 65 3 PEG800-DAIL CuSO4 1 73 4 PEG1000-DAIL CuSO4 1 78 5 PEG1000-DAIL[BF4] CuSO4 1 95 6 PEG1000-DAIL[PF6] CuSO4 1 92 7 PEG1000-DAIL[OTf] CuSO4 1 88 8 PEG1000-DAIL[BF4] — 2 81 9 PEG1000-DAIL[BF4] FeSO4 1 96 10 PEG1000-DAIL[BF4] Fe2(SO4)3 0.7 99 11 PEG1000-DAIL[BF4] CdSO4 2 80 12 PEG1000-DAIL[BF4] MnSO4 2 75 13 PEG1000-DAIL[BF4] ZnSO4 2 54 14 PEG1000-DAIL[BF4] Cu(OAc)2 2 91 15 PEG1000-DAIL[BF4] CuI 4 61 16 PEG1000-DAIL[BF4] FeCl3 4 66 a Reactions were carried out using 1-(chloromethyl)-4- methoxybenzene (2 mmol), H2O (2 mL), cocatalyst (0.05 mmol), and IL (2 mL) in toluene (2 mL) at 110 1C. b Isolated yield. Fig. 1 Repeating hydrolysis reactions using recovered PEG1000- DAIL[BF4]/Fe2(SO4)3. Fig. 2 Catalytic hydrolysis process in PEG1000-DAIL[BF4]/Fe2(SO4)3. D ow nl oa de d by U ni ve rs ity o f S ci en ce a nd T ec hn ol og y of C hi na o n 12 A pr il 20 12 Pu bl ish ed o n 22 N ov em be r 2 01 0 on h ttp :// pu bs .rs c. or g | do i:1 0.1 039 /C0 NJ 004 54E View Online This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011 New J. Chem., 2011, 35, 292–298 295 system. The scope, the definition of mechanism, and utility of the catalytic system to other organic syntheses are currently under study in our laboratory. Experimental All the chemicals were from commercial sources and used without any pretreatment. All reagents were of analytical grade. 1H NMR spectra were recorded on a Bruker 400 MHz spectrometer using CDCl3 as the solvent with tetramethylsilane (TMS) as an internal standard. High performance liquid chromatography (HPLC) experiments were performed on a liquid chromatograph (Dionex Softron GmbH, USA), consisting of a pump (P680) and an ultraviolet-visible light detector (UVD) system (170U). Elemental analysis was performed on a Vario EL III instrument (Elmentar Analysen Systeme GmbH, Germany). Typical procedure for the preparation of ionic liquid (PEG1000-DAIL[BF4]) (i) Preparation of intermediate 2 (according to ref. 13): a mixture of PEG-1000 (1, 0.1 mol), pyridine (0.25 mol), and toluene (80 mL) was stirred in a 250 mL round flask at 86 1C, then SOCl2 (0.105 mol) was added dropwise slowly, after that the mixture was stirred for another 18 h at 88 1C. Upon completion, the mixture was cooled to room temperature, then 10% HCl solution (40 mL) was added, the organic phase appeared and was then separated by decantation, the water phase (pyridine hydrochloride aqueous solution) was extracted with toluene (2 � 10 mL). The combined organic phases were washed with water (2 � 10 mL), then dried over anhydrous Na2SO4. The solvent was removed under reduced pressure to give 2. (ii) Preparation of intermediate 3 (according to ref. 13 and 16): a mixture of imidazole (0.1 mol), sodium Table 2 Hydrolysis of organic halides to alcohols with watera Entry Substrate Time/h Product %Yieldb 1 1 96 2 0.7 97 3 0.7 99 4 0.7 99 5 0.7 95 6 0.7 96 7 0.7 98 8 1 96 9 3 92 10 3 93 Table 2 (continued ) Entry Substrate Time/h Product %Yieldb 11 1 96 12 1 95 13 1 97 14 24 —c 0 15 24 —c 0 a Reactions were carried out using organic halides (2 mmol), H2O (2 mL), Fe2(SO4)3 (0.05 mmol), and PEG1000-DAIL[BF4] (2 mL) in toluene (2 mL) at 110 1C. b Isolated yield. c No product was detected. D ow nl oa de d by U ni ve rs ity o f S ci en ce a nd T ec hn ol og y of C hi na o n 12 A pr il 20 12 Pu bl ish ed o n 22 N ov em be r 2 01 0 on h ttp :// pu bs .rs c. or g | do i:1 0.1 039 /C0 NJ 004 54E View Online 296 New J. Chem., 2011, 35, 292–298 This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011 ethoxide (0.1 mol), and ethanol (10 mL) was stirred at 70 1C for 8 h, then 2 (0.05 mol) was added into the reaction solution. After that the mixture was stirred for another 20 h at 70 1C. Upon completion, the mixture was filtered, then the filtrate was extracted with ether (3 � 10 mL). The combined organic phases were concentrated under reduced pressure to give 3. (iii) Preparation of ionic liquid PEG1000-DAIL[BF4] 4 (according to ref. 13 and 16): 1,3-propanesultone (0.04 mol) was added dropwise into intermediate 3 (0.02 mol) over 20 min, with vigorous stirring, then the mixture was stirred for another 10 h at 50 1C. ThenHBF4 was added dropwise over 20 min. The final solution was stirred at 50 1C for another 8 h to give PEG1000-DAIL[BF4] as a viscous yellowish-brown liquid. Typical procedure for the hydrolysis reaction (Table 2, entry 3) To a stirred solution of 1-(chloromethyl)-4-methoxybenzene (2 mmol), H2O (2 mL), and PEG1000-DAIL[BF4] (2 mL) in toluene (2 mL) was added Fe2(SO4)3 (0.05 mmol) and then stirring was continued at 110 1C for 0.7 h, the reaction progress was monitored by HPLC. Upon completion, the mixture was cooled to room temperature. The organic phase was separated by decantation and dried with anhydrous sodium sulfate. Then the crude mixture was purified by column chromatography on silica gel to afford a colourless oil of 4-methoxybenzyl alcohol (273.3 mg, 99% yield). The next run was performed under identical reaction conditions. 1H-NMR (400 MHz, CDCl3): d/ppm = 1.86 (br, 1H, OH), 3.76 (s, 3H, CH3), 4.63 (s, 2H, CH2), 6.93–7.02 (m, 4H, Ar–H). Elemental analysis %calc. (%found): C 69.49 (69.54), H 7.31 (7.30), O 23.18 (23.16). Mesitylmethanol (Table 2, entry 7) 1H-NMR (400MHz, CDCl3): d/ppm= 1.85 (br, 1H, OH), 2.21 (s, 3H, CH3), 2.24 (s, 6H, CH3), 4.65 (s, 2H, CH2), 6.93–7.02 (s, 2H, Ar–H). Elemental analysis %calc. (%found): C 79.92 (79.96), H 9.42 (9.39), O 10.64 (10.65). 3-Phenoxypropane-1,2-diol (Table 3, entry 7) 1H-NMR (400 MHz, CDCl3): d/ppm = 3.62–3.78 (m, 5H, CH2, CH and OH), 4.29 (d, J = 7.0 Hz, 2H, CH2), 6.97–7.06 (m, 3H, Ar–H), 7.21 (m, 2H, Ar–H). Elemental analysis %calc. (%found): C 64.22 (64.27), H 7.20 (7.19), O 28.56 (28.54). 3-(4-Methoxyphenyl)acrylic acid (Table 4, entry 10) 1H-NMR (400MHz, CDCl3): d/ppm= 3.79 (s, 3H, CH3), 6.14 (d, J = 7.2 Hz, CH, 1H), 7.19 (d, J = 7.2 Hz, CH, 1H), 7.06 (m, Ar–H, 2H), 7.48 (m, Ar–H, 2H), 11.8–12.9 (br, COOH, 1H). Elemental analysis %calc. (%found): C 67.37 (67.41), H 5.67 (5.66), O 26.93 (26.94). Acknowledgements We thank the National Basic Research Program (973) of China (No. 613740101) and Natural Science Foundation of Jiangsu Province for support of this research. Table 3 Hydrolysis of epoxides to 1,2-diols with watera Entry Substrate Time/h Product %Yieldb 1 2.5 92 2 2 94 3 2 96 4 4.5 87 5 4.5 86 6 4.5 89 7 2.5 95 8 2 95 9 2 96 10 2 98 a Reactions were carried out using epoxides (2 mmol), H2O (2 mL), Fe2(SO4)3 (0.05 mmol), and PEG1000-DAIL[BF4] (2 mL) in toluene (2 mL) at 110 1C. b Isolated yield. D ow nl oa de d by U ni ve rs ity o f S ci en ce a nd T ec hn ol og y of C hi na o n 12 A pr il 20 12 Pu bl ish ed o n 22 N ov em be r 2 01 0 on h ttp :// pu bs .rs c. or g | do i:1 0.1 039 /C0 NJ 004 54E View Online This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011 New J. Chem., 2011, 35, 292–298 297 Table 4 Hydrolysis of esters to carboxylic acids with watera Entry Substrate Time/h Product %Yieldb 1 2 95 2 1.5 97 3 1.5 97 4 4 95 5 4 95 6 4 94