Side Chain Chlorination of 4- Methoxy Toluene by an Electro Chemical Method

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1 International Journal of Emerging Research in Management &Technology ISSN: (Volume-7, Issue-2) Research Article February 218 Side Chain Chlorination of 4- Methoxy Toluene by an Electro Chemical Method M. Surendra Varma *, S. Sivaji Ganesan, G. Muruganandam Department of Chemistry, A.V.V.M Sri Puspham College (Autonomous), Thanjavur , Tamil Nadu, India - Abstract: A simple method for the preparation of 4- Methoxy Benzylchloride from 4- Methoxy Toluene is reported. The electrolysis was carried out at room temperature in a divided electrochemical cell fitted with graphite electrodes. The conversion of 4- Methoxy Toluene varies from 8 to 85 and the selectivity observed is above as 99. The effects of different electrode, solvent, current densities are studied and reported. Keywords: Electrochemistry, Chlorination, Two Compartment divided electrochemical cell, Emulsion electrolysis, 4- Methoxy Benzylchloride. I. INTRODUCTION The conversion of methoxy group in 4- methoxy toluene is a fundamental reaction in the synthesis of a variety of organic compounds.[1,2] The α-halogenated carbonyl compounds are valuable intermediate in synthetic organic chemistry[3]. These compounds are useful synthetic intermediates for various transformations and employed in the synthesis of biological active substrates such as antiviral, antifungal, antineoplastic, antibacterial, antitumor compounds[4]. Some of the reagents proclaimed for chlorination are often very toxic, not readily available, hazardous, expensive, prolonged reaction time, need to freshly prepared and involve hard work-ups[5]. The electrochemical method avoids the above mentioned problem as the electrons are used as the environment friendly reagent. The instrumentation and experimental procedure adopted for the present investigation is quite conventional in nature and well known in electro organic synthesis laboratories[6]. In continuation of our work on the electrochemical halogenation of aromatic compounds, α-halogenation of aromatic compounds have been studied and optimized. The α chlorination of 4- Methoxy Toluene to 4- Methoxy Benzylchloride was carried out by two phase electrolysis [7] using an aqueous 33 percentage of NaCl solution as the supporting electrolyte at room temperature in a H type cell. Electrochemical chlorination has been investigated in different solvents [8-14] and Electrochemical reaction has an advantage over regular homogenous processes in as much as they do not require the use of large quantities of noxious or corrosive reagents as in this case with elemental chlorine and sulphuric acid. Electrochemical chlorination produces chlorine in vivo as intermediate from non-corrosive chlorides and it can be easily controlled. Selective chlorination can be achieved in electrochemical technique[15]. Similarly this kind of work chlorination has been carried out by [16-2]. We observed formation of side chain chlorination without formation of any poly chlorinated product. OCH 3 OCH 3 CH 3 Pt/Pt, NaCl, RT, -e - CH 2 Cl 4- Methoxy Toluene 4- Methoxy Benzylchloride All Rights Reserved Page 39

2 First Author et al., International Journal of Emerging Research in Management &Technology II. EXPERIMENTAL GALVANOSTATIC ELECTROLYSIS FOR THE ELECTROCHEMICAL CHLORINATION OF 4- METHOXY TOLUENE 2.1 The Instrumentation The electrochemical chlorination of 4- Methoxy Toluene was carried out in 15 ml capacity two-compartment glass divided electrochemical cell with porous glass frit as separator. The cell was placed on a magnetic stirring unit. The electrolyte was stirred throughout the electrolysis using Teflon magnetic stirrer. The platinum (4 x 2.5 cm 2 ) and graphite (4 x 2.5 cm 2 ) electrodes were commonly used as anode and cathode. D.C.Power source is used for the supply of current (Aplab, India) in preparative electrolysis. 2.2 Experimental Procedure In a 15 ml capacity two compartment divided glass cell, 31.5ml of 2M H 2 SO 4, 5 ml of saturated solution of NaCl and 7 ml of Acetonitrile containing 1.5 g of 4- Methoxy Toluene (.1M) were taken as anolyte and the catholyte was the equal volume of solution as mentioned above without depolariser. The graphite electrode was used as anode (4 x 2.5 cm 2 ) and a charge of 2F was. In some cases more amount of current (4F, 6F) was to get maximum conversion. After electrolysis the aqueous electrolyte solution was extracted twice with 25ml of diethyl either in order to remove the organic phase. The ether layer was then washed with water (2X1 ml) and dried over anhydrous sodium sulphate. Then the filtered organic extract was distilled to get the crude product. The material yield and current were calculated for the isolated products based on HPLC, IR and NMR analysis. III. PRODUCT ANALYSIS The product analysis was carried out by high performance liquid chromatography using Shimadzu Model LC8A preparative liquid chromatography along with Shimadzu SPD6A UV detector. 1 methanol was used as the eluent. ODS (Octa Dodoecyl Silance) column was used as stationary phase. Chromatograms of the experimental samples were compared with authentic samples. The product identification was also confirmed by FT-IR spectrophotometer using Perkin Elmer model paragon 5. Neat liquid was used for recording FT-IR measurements in the range of 4-4cm -1. Product analysis was also done by recording proton NMR spectra using 4 MHz Bruker NMR spectrometer. 3.1 Chemicals and Solvents Used The following chemicals and solvents were used for the present study Methoxy Toluene, (AR) 2. Sulphuric acid (LR) 3. Diethyl ether (LR) 4. Acetonitrile (LR) 5. n-hexane (LR) 6. Anhydrous sodium sulphate (LR) 7. TLC Silica gel 6 F 254 plates. IV. RESULTS AND DISCUSSION Galvanostatic electrolysis was carried out for the synthesis of 4- Methoxy Benzylchloride from 4- Methoxy Toluene. The experimental parameters such as current, solvent, current (F /mol) and anode material for the chlorination of 4- Methoxy Toluene to 4- Methoxy Benzylchloride was carried out and the results are summarized in Table. At the optimum electrolytic condition platinum electrodes were used at a current of 5mA/cm 2 in acetonitrile solvent medium. 4.1 Effect of Solvent: A total charge of 2F/mol was at different current densities of 3, 5 and 7mA/cm 2 using graphite electrode and acetonitrile as a solvent. The yield of product 4- Methoxy Benzylchloride obtained is of 75, 88, and 64 with 3, 5,7mA/cm 2 respectively. When the electrolysis was carried out using Dichloromethane as a solvent with a current of 3, 5 &7mA/cm 2 and the product is obtained with an yield of 63, 71 & 56 respectively. All Rights Reserved Page 4

3 percentage of yield First Author et al., International Journal of Emerging Research in Management &Technology In the case of 1-Butanol as a solvent, with a current of 3, 5 &7mA/cm 2 the product is obtained with an yield of 52, 62 & 4 respectively. From the above set of experiments the maximum yield of product 88 is obtained when the acetonitrile was used as the solvent. 4.2 Effect of Electrode: The electrochemical chlorination of 4- Methoxy Toluene was carried out using different electrodes of platinum and graphite under various solvents of acetonitrile, Dichloromethane and 1 Butanol as solvent the following results are observed. When the electrolysis was carried out with platinum as electrode and acetonitrile as solvent, the product 4- Methoxy Benzylchloride was obtained with a yield of 81, 99, and 72 at different current densities of 3, 5 and 7mA/cm 2 respectively. In the case of Dichloromethane as a solvent, the yield obtained was 77, 84, and 68 at the current densities of 3, 5 and 7mA/cm 2 respectively. Similarly when 1-Butanol was used as solvent, the yield obtained was 55, 69, and 43 at the current densities of 3, 5 and 7mA/cm 2 respectively. From the above results it is concluded that usage of platinum electrode gives a maximum yield of 99 product. Electrochemical chlorination of 4- Methoxy Toluene to 4- Methoxy Benzylchloride Effect of current using Graphite electrode in Acetonitrile Electrolyte : 31.5ml of 2M H 2 SO 4 + 7ml of acetonitrile Electrode : Graphite (Area = 4 x 2.5 cm 2 ) No. 4- methoxy toluene taken for chlorination (g) Table 1 the product yield Density 5 A/dm 2 7 Effect of current using Graphite electrode in Dichloromethane Electrolyte : 31.5ml of 2M H 2 SO ml of dichloro Methane Electrode : Graphite (Area = 4 x 2.5 cm 2 ) All Rights Reserved Page 41

4 percentage of yield percentage of yield First Author et al., International Journal of Emerging Research in Management &Technology Table 2 No. 4- methoxy toluene the product taken for chlorination (A/dm 2 yield ) (g) Density A/dm 2 Effect of current using Graphite electrode in 1- Butanol Electrolyte : 31.5ml of 2MH 2 SO 4 + 7ml of 1- butanol Electrode : Graphite (Area = 4 x 2.5 cm 2 ) No. 4- methoxy toluene taken for chlorination(g) Table 3 the product yield Density A/dm 2 All Rights Reserved Page 42

5 percentage of yield percentage of yield First Author et al., International Journal of Emerging Research in Management &Technology Effect of current using Platinum electrode in Acetonitrile Electrolyte : 31.5ml of 2M H 2 SO 4 + 7ml of acetonitrile Electrode : Platinum (Area = 4 x 2.5 cm 2 ) No 4- methoxy toluene taken for chlorination(g) Table 4 the product yield Density A/dm 2 Effect of current using Platinum electrode in Dichloromethane Electrolyte : 31.5ml of 2M H 2 SO ml of dichloromethane Electrode : Platinum (Area = 4 x 2.5 cm 2 ) No. 4- methoxy toluene taken for chlorination (g) Table - 5 the product yield Density A/dm 2 All Rights Reserved Page 43

6 percentage of yield First Author et al., International Journal of Emerging Research in Management &Technology Effect of current using Platinum electrode in 1- Butanol Electrolyte : 31.5ml of 2M H 2 SO ml of 1- Butanol Electrode : Platinum (Area = 4 x 2.5 cm 2 ) No 4- methoxy Toluene taken for chlorination(g) Table - 6 the product yield * Experiment carried out in an undivided glass cell Density A/dm Effect of (F / mol) The electrochemical chlorination of 4- Methoxy Toluene is found to be quite facile, the theoretically required current of 2F/mole is quite sufficient for the conversion of 4- Methoxy Toluene with maximum yield of 4- Methoxy Benzylchloride. When more than theoretical amount of current, 4F/ mole and 6F/mole were for electrolysis, low yield was obtained due to competitive O 2 evolution. Hence the optimum conditions for the direct anodic oxidation of 4- Methoxy Toluene to 4- Methoxy Benzylchloride is found to be 5. A/dm 2 current, platinum electrodein acetonitrile solvent medium with theoretical amount of current. V. PRODUCT ANALYSIS 5.1 High performance liquid chromatography (HPLC) Typical HPLC graphs of standard 4- Methoxy Benzylchloride prepared are given in figure. The retention times of 4- Methoxy Benzyl chloride in the synthesized product mixture was The percentage purity of 4- Methoxy Benzyl chloride in the product mixture was found out by HPLC as above 99 and the material yield of 4- Methoxy Benzyl chloride was calculated. 5.2 FTIR Spectroscopy The FT-IR Spectrum of synthesized 4- Methoxy Benzylchloride is presented in figure. The characteristic aliphatic absorption is found at 1176 cm -1 and C-Cl absorption of alkyl halide function is found at 659 cm -1. These values coincide well with the literature value and hence the 4- methoxy benzyl chloride presence is confirmed. 5.3 Proton NMR Spectrum Proton NMR Spectrum of prepared 4- Methoxy Benzylchloride is presented in Figure. The chemical shift values ( ) obtained in the product spectrum are compared with the literature value. All Rights Reserved Page 44

7 First Author et al., International Journal of Emerging Research in Management &Technology Compound Name Chemical Shift values H 1 C 13 OCH 3 CH 2 Cl 4- Methoxy Benzylchloride Observed Reported Observed Reported The values of aromatic protons are observed at ( ), Methoxy protons at 3.84 and two benzylic protons at 4.6 are observed in our products compares well with the literature value. The absence of proton signal at 1.61 ppm indicates the complete conversion of the methyl group which is present in the starting material 4- Methoxy Toluene. The values C 13 of aromatic protons are observed at ( ), Methoxy protons at 56. and two benzylic protons at 5.5 are observed in our products compares well with the literature value. VI. CONCLUSION The present research investigation has established a very good method for the anodic chlorination 4- Methoxy Toluene using platinum electrode in a divided cell with aqueous sulphuric acid medium containing a solvent of acetonitrile gave product 4-Methoxy Benzyl chloride in excellent yield (99). The optimum current for the chlorination of 4- Methoxy Toluene was found to be at 5. A/dm 2. Usage of Dichloromethane and 1- Butanol as solvents in the galvanostatic electrolyses did not give better yields. Platinum electrode gave maximum material yield than the graphite. ACKNOWLEDGEMENTS The authors are thankful to Dr. K. Kulangiappar, Electro Organic Division, Central Electrochemical Research Institute, Karaikudi-636, India, he dedicated their precious time, gave insightful comments and valuable suggestions to carry out this work. REFERENCES [1] Y.C. Chen, T.-F. Wu, J.-G. Deng, F. Liu, Y.Z. Jiang, M.C.K. Chai, A.S.C. Chan, Chem. Commun. (21) [2] H. Otsuka, H. Matsumoto, T. Harada, S. Shinkai, J. Org. Chem. 6 (1995) [3] Veisi, H.curr. org. chem. 211,15, [4] Butler, A. Walker, J.V. chem.. Rev 1993,93,1937 [5] T. Raju, K.Kulangiappar, M. Anbu Kulandainathan, A. Muthukumuran Tetrahedron lett. 46(25) [6] Kyriacou, D.Basics of electro organic synthesis. Wiley-interscience, New York, 1981, p-16 [7] T. Raju,G. Kalpana Devi, K.KulangiapparElectrochemical Acta 26, [8] Toni, T. Inokuchi, S. Matsumoto, T. Saeki, T. Oki, Bull. Chem. Soc. Jpn. 63 (199) 852. [9] Casalbore, G.;Mastragostino, M.;Valcher, S. J. Electroanal. Chem. 1975, 61, 33. [1] Casalbore, G.;Mastragostino, M.;Valcher, S. J. Electroanal.Chem. 1976, 68, 123. [11] Casalbore, G.;Mastragostino, M.;Valcher, S. J. Electroanal.Chem. 1977, 77, 373. [12] Mastragostino, M.;Valcher, S.; Lazzari, P. J. Electroanal.Chem. 1981, 126, 189. [13] Mastragostino, M.;Valcher, S.;Biserni, M. J. Electroanal.Chem. 1983, 158, 369. [14] Nematollahi, D.;Akaberi, N. Molecules 21, 6, 639. [15] Nematollahi, D.;Akaberi, N. J. Electroanal. Chem. 2,481, 28. [16] Toni, T. Inokuchi, S. Matsumoto, T. Saeki, T. Oki, Bull. Chem. Soc. Jpn. 63 (199) All Rights Reserved Page 45

8 First Author et al., International Journal of Emerging Research in Management &Technology [17] M. Mastragostino, G. Casalbore, S. Valcher, J. Electroanal. Chem. 56 (1974) 117. [18] J. Gourcy, J.S. Simonet, M. Jaccaud, Electrochim. Acta 24 (1979) 139. [19] Y. Matsuda, A. Terashima, K. Nakagawa, Denki Kagaku 51 (1983) 79. [2] S.R. Forsyth, D. Pletcher, Extended Abstracts of the Ist International Symposium on Electroorganic Synthesis, Kurashiki, 1986, p. 35. [21] M. Mortita, S. Yamamoto, Y. Matsuda, J. Appl. Electrochem. 18 (1988) All Rights Reserved Page 46