SciELO - Scientific Electronic Library Online

 
vol.54 número1STUDY OF THE COPPER, CHROMIUM AND LEAD CONTENT IN MUGIL CEPHALUS AND ELEGINOPS MACLOVINUS OBTAINED IN THE MOUTHS OF THE MAULE AND MATAQUITO RTVERS (MAULE REGION, CHILE)IMPROPER HYDROGEN BONDS - A THEORETICAL STUDY ABOUT THE MOLECULAR STRUCTURE OF INTERMOLECULAR SYSTEMS FORMED BY H3C-H+Δ...X AND H3C+Δ...H-Y WITH X = CL- OR F- AND Y = CL OR F índice de autoresíndice de materiabúsqueda de artículos
Home Pagelista alfabética de revistas  

Journal of the Chilean Chemical Society

versión On-line ISSN 0717-9707

J. Chil. Chem. Soc. v.54 n.1 Concepción  2009

http://dx.doi.org/10.4067/S0717-97072009000100009 

J. Chil. Chem. Soc, 54, N° 1 (2009); págs: 40-42

 

THE SYNTHESIS OF SALICYLATE PROMPTED BY BR0NSTED ACIDIC IONIC LIQUIDS

 

DONG JIANG, JIE LIU, YUAN YUAN WANG, LI YI DAI*

Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, Shanghai 200062, P. R. China. *e-mail: lydai@chem.ecnu.edu.cn


ABSTRACT

Brønsted acidic ionic liquids based on imidazolium cation were employed as a series of efficient and environmentally benign catalysts and solvents for the synthesis of salicylate, the yields could reach 76%-96%. The optimal reaction conditions were determined. The results showed that Brønsted acidic ionic liquids were efficient catalysts and solvents which could be recycled easily without obvious decline in catalytic activities.

Key words: Ionic liquid, esterification, salicylate


INTRODUCTION

Salicylate was a kind of very useful organic compound, which could be used as essence, medicine, solvent and so on. The traditional catalysts used for the synthesis of salicylate were concentrated sulfuric acid and phosphoric acid which were strongly corrosive, harmful to environment and unreusable. When using concentrated sulfuric acid and phosphoric acid as catalysts, it also brought difficulty to the final treatment of the synthesis of salicylate1. Toluene-p-sulfonic acid, sodium acid sulfate and solid acid had been used as substitute catalysts for the synthesis of salicylate, butthe recovery of them was difficult1-3.

Brønsted acidic ionic liquids (ILs) 1 -butyl-3-methyl-imidazolium hydrogen sulphate ([bmim]HSO4), l-butyl-3-methyl-imidazolium dihydogen phosphate ([bmim]H2PO4), 1-methyl-3-hydro-imidazolium tetrafluoroborate ([Hmim] BF4), 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulphate ([HS03-pmim]HSO4), 1-methyl-3-(3-sulfopropyl)-imidazolium tetrafluoroborate ([HS03-pmim]BF4) and 1-methyl-3-(3-sulfopropyl)-imidazolium 4-methylbenzenesulfonate ([HS03-pmim][pTSA]) had received vast research interests in recent years which had been used as satisfactory acidic catalysts and solvents for many organic reactions4-6, due to their particular properties, such as high thermal stability, reusability, miscibility with organic compounds and so on7-9. In this paper, an efficient and feasible procedure for the synthesis of salicylate was reported, using Brønsted acidic ILs [bmim]HSO4, [bmim] H2PO4, [Hmim]BF4, [HS03-pmim]HSO4, [HS03-pmim]BF4 and [HS03-prnim] [pTSA] (Figure 1) as recyclable catalysts and solvents (Scheme 1). The optimal reaction conditions were determined and the results showed that Brønsted acidic ILs were efficient catalysts and solvents for the synthesis of salicylate. ILs used could be recycled easily without obvious decline in catalytic activities.



EXPERIMENTAL

N-methylimidazole and 1-butylbromide were purchased and distilled before using. All the other reagents used were purchased and used without any further purification.

The synthesized salicylates were characterized by FT-IR (Nicolet Nexus 670) and GC (Agilent 6890-5973N). The results of GC showed that the purities of salicylates were higher than 99%10-14.

Preparation of ILs: ILs used were synthesized according to the previously published papers4-6,15.

Typical esterification procedure: Alcohol (20 mmol), salicylic acid (20 mmol) and IL (20 mmol) were added into a flask and stirred at 115°C for lOh. Upon completion of the reaction, the reaction mixture became biphasic. The upper phase was salicylate and the lower phase was IL. The upper phase was separated, washed with water and saturated solution of sodium hydrogen carbonate, and dried over anhydrous sodium sulfate. Then salicylate was characterized by FT-IR and GC. The lower phase was rotatory evaporated and IL was reused after removal of water under vacuum (O.OlTorr) at 80°C for 6h.

RESULTS AND DISCUSSION

1. The optimization of reaction conditions

The results of the optimization of reaction conditions were listed in Table 1. The effect of reaction temperature onthe yield was shown in entries 1, 2 and 3. When the reaction temperature was 100°C, the yield was only 28% (entry 1). However, when the reaction temperature was higher than 115°C, the increase in the yield was slightly, 51% for 115°C and 53% for 130°C (entries 2 and 3). So the optimal reaction temperature was 115°C.


The effect of molar ratio on the yield was shown in entries 2, 4 and 5, the optimal molar ratio (acid: alcohol: IL) was 1: 1: 1. When the molar ratio was higher than 1: 1: 1, the increase in the yield was also slightly, 51% for 1: 1: 1 and 52% for 1: 1: 1.5 (entries 2 and 5).

As can be seen, the yields of salicylate for 4h and 7h were not satisfactory, 51% for 4h and 64% for 7h (entries 2 and 6). When the reaction time reached lOh, the yield could reach 86% (entry 7). Then prolonging the reaction time, there was no obvious increase in the yield, 88% for 12h (entry 8). So the optimal reaction time was lOh.

Therefore, the optimal reaction conditions were: molar ratio (acid: alcohol: IL), 1: 1: 1; reaction time, 1 Oh; reaction temperature, 115°C.

2. The synthesis of salicylate in Brønsted acidic ILs

The synthesis of salicylate was carried out in Brønsted acidic ILs [bmim] HSO4, [bmim]H2PO4, [Hmim]BF4, [HS03-pmim]HSO4, [HS03-pmim]BF4 and [HS03-pmim][pTSA]. The results were listed in Table 2 showing good yields. The reactants had good solubilities in Brønsted acidic ILs while salicylate was almost immiscible with ILs. Therefore, the esterification started as a homogeneous process and ended as biphasic which could facilítate the separation of salicylate from the reaction mixture and promote the forward reaction of the synthesis of salicylate. Upon completion of the reaction, the upper phase was salicylate and the lower phase was IL, so salicylate could be separated easily. No volatile ILs as catalysts and solvents for the synthesis of salicylate could be reused easily after removal of water under vacuum.


The results of the synthesis of salicylate in Brønsted acidic ILs were shown in Table 2, the catalytic activities of Brønsted acidic ILs were decreased over thefollowing series: [bmim]HSO4> [Hmim]BF4> [bmim]H2PO4; [HS03-pmim] HSO4> [HS03-pmim]BF4> [HS03-pmim][pTSA]. Y. L. Gu had indicated that the acidity sequence of Brønsted acidic ILs [bmim]HSO4, [Hmim]BF4 and [bmim]H2PO4 was [bmim]HSO4> [Hmim]BF4> [bmim]H2PO416. The acidity sequence and the catalytic activity sequence of [bmim]HSO4, [Hmim]BF4 and [bmim]H2PO4 revealed that the catalytic activities of Brønsted acidic ILs were related to their acidities, the strong acidic IL had higher catalytic activity than the weak acidic IL. From the mechanism of the synthesis of salicylate (Scheme 2), it also could find that when using the strong acidic IL as catalyst and solvent, the synthesis of salicylate from alcohol and salicylic acid was easier. For the catalytic activity sequence of Brønsted acidic ILs containing sulfonic acid groups was [HS03-pmim]HSO4> [HS03-pmim]BF4> [HS03-pmim][pTSA], the acidity sequence of them should be [HS03-pmim]HSO4> [HS03-pmim]BF4>[HS03-pmim][pTSA].


In the synthesis of salicylate using Brønsted acidic ILs as catalysts and solvents, the yields increased from methyl alcohol to n-octyl alcohol orderly (82%, 85%, 86%, 88% and 90%, entries 1-5). For the boiling points of alcohols increased from methyl alcohol to n-octyl alcohol orderly, the amounts of alcohols in the gas phase decreased from methyl alcohol to n-octyl alcohol during the reaction process. Therefore, the yield of salicylate using the high-boiling alcohol was higher than that using the low-boiling alcohol.

One important advantage of using Brønsted acidic ILs as efficient catalysts and solvents was the possibihty of recycling. We examined the synthesis of n-butyl salicylate in [Hmim]BF4. The results of recycling experiments were summarized in Table 3. For each cycling reaction, n-butyl alcohol (20mmol), salicylic acid (20mmol) and recovered [Hmim]BF4 were added into a flask successively and stirred at 115°C for lOh. Upon completion of the reaction, salicylate was separated and [Hmim]BF4 was reused after removal of water. The results of recycling use of [Hmim]BF4 revealed that Brønsted acidic ILs as catalysts and solvents for the synthesis of salicylate were recyclable. The slightly decline in the yield should be ascribed to the slightly lose of IL.


CONCLUSIONS

In summary, a procedure for the synthesis of salicylate in Brønsted acidic ILs has been developed. The synthesis of salicylate, using Brønsted acidic ILs [bmim]HSO4, [bmim]H2PO4, [Hmim]BF4, [HS03-pmim]HSO4, [HS03-prnim] BF4 and [HSO3-pmim][pTSÁ] as catalysts and solvents, has several advantages: (1) ILs as catalysts show good catalytic activities, the yields could reach 76%-96%, except [bmim]H2PO4; (2) For salicylate could not dissolve in ILs, ILs as solvents could promote the forward reaction and facilítate the separation of salicylate from the reaction mixture; (3) ILs could be reused easily after removal of water without obvious decline in catalytic activities.

ACKNOWLEDGEMENTS

This project was supported by the Key Project of Chinese Ministry of Education (No. 105075).

 

REFERENCES

1. D. Y. Yu, T. Q. Ren, T. Z. Ma, Ind. Catal. 14, 42, (2006)        [ Links ]

2. M. M. Tang, Q. Y. Lai, K. Liu, M. Liang, Tech. & Dev. Chem. Ind. 32, 6, (2003)        [ Links ]

3. L. B. Peng, A. H. Shi, W. C. Fu, Fine Chem. Intermed. 33, 18, (2003)        [ Links ]

4. J. Fraga-Dubreuil, K. Bourahla, M. Rahmouni, J. P. Bazureau, J. Hamelin, Catal. Commun. 3, 185, (2002)        [ Links ]

5. H. P. Zhu, F. Yang, J. Tang, M. Y. He, Green Chem. 5, 38, (2003)        [ Links ]

6. H. L. Li, S. T. Yu, F. S. Liu, C. X. Xie, L. Li, Catal. Commun. 8, 1759, (2007)        [ Links ]

7. J. G. Huddleston, R. D. Rogers, Chem. Commun, 1765, (1998)        [ Links ]

8. D. Jiang, Y. Y. Wang, H. Sun, L. Y. Dai, J. Chil. Chem. Soc. 52, 1302, (2007)        [ Links ]

9. A. J. Carmichael, D. M. Haddleton, S. A. F. Bon, Chem. Commun, 1237, (2000)        [ Links ]

10. F. Toribio, J. Catalán, F. Amat, A. U. Acuna, J. Phys. Chem. 87, 817, (1983)        [ Links ]

11. M. M. Radhi, M. F. El-Bermani, Spectrochim. Acta Part A 46, 33, (1990)        [ Links ]

12. R. S. Rasmussen, R. R. Brattain, J. Am. Chem. Soc. 71, 1073, (1949)        [ Links ]

13. P. R. Jones, C. E. Malmberg, C. McGrattan, J. Pharm. Sci. 64, 1240, (1975)        [ Links ]

14. T. Maki, K. Ishihara, H. Yamamoto, Org. Lett. 7, 5047, (2005)        [ Links ]

15. H. B. Xing, T. Wang, Z. H. Zhou, Y. Y. Dai., J. Mol. Catal. A: Chem. 264, 53, (2007)        [ Links ]

16. Y. L. Gu, J. Zhang, Z. Y. Duan, Y. Q. Deng, Adv. Synth. Catal. 347, 512, (2005)        [ Links ]

 

(Received 7 March 2008 - Accepted 24 October 2008)