Efficient and Facile Chlorination of Industrially-Important Aromatic

Feb 10, 2012 - ... Chlorination of Industrially-Important Aromatic. Compounds using NaCl/p-TsOH/NCS in Aqueous Media. Tanu Mahajan,*. ,†. Lalit Kuma...
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Efficient and Facile Chlorination of Industrially-Important Aromatic Compounds using NaCl/p-TsOH/NCS in Aqueous Media Tanu Mahajan,*,† Lalit Kumar,† K. Dwivedi,‡ and D. D. Agarwal† †

Department of Industrial Chemistry, and ‡School of Studies in Chemistry, Jiwaji University, Gwalior-474011, Madhya Pradesh, India ABSTRACT: A simple and efficient process for the chlorination of industrially important aromatic compounds using NaCl/pTsOH/NCS in aqueous media under mild conditions is described. The addition of NaCl increases the yield of chlorinated product and decreases the reaction time in the presence of p-toluenesulphonic acid (p-TsOH) and N-chlorosuccinimide (NCS). The present method furnishes higher selectivities and yields of chlorinated products under mild reaction conditions in a short reaction time. Organic solvent-free conditions, a feature of green chemistry, was successively used not only for the reactions but also for the isolation of products at the end of the reaction, which seems to be the most promising methodology from the viewpoint of a green approach to organic synthesis.

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INTRODUCTION Electrophilic aromatic halogenation is one of the most important basic reactions in organic chemistry,1,2 since haloarenes are the key intermediates in the preparation of organometallic reagents3,4 and play vital roles in transition metal mediated coupling reactions.5−7 Numerous industrially valuable products such as pesticides, insecticides, pharmaceutically- and medicinally active molecules, pigments, dye-stuffs, and other newer materials carry halogen functionality.8−10 Recently, several methods have been reported in literature for the chlorination of aromatic compounds. The reported methods for preparing the chlorinated aromatic compounds were based on molecular Cl2/1°,2°,3° amines,11 H2O2− HCl,12−16 SnCl4/Pb(OAc)4,17 InCl3/NaClO,18 tetraalkylphosphonium trihalides,19 KCl/oxone,20 sulfuryl chloride in presence of amine catalysts,21 metal chloride-H2O2 in acidaqueous medium,22 etc. However, developing selective monochlorination reactions or selective dichlorination reactions still remains a challenge, since these reactions in many cases always result in a complex mixture of mono- and dichlorinated products.23 There are some methods that have been reported earlier to solve this challenge.24−27 Novel methods of halogenation with high selectivity and replacement of hazardous solvents with environmentally benign solvents that satisfy the requirement of green chemistry have attracted a lot of attention.28 Water is the most promising solvent because it is readily available, nonflammable, nontoxic, and could offer the easy separation of reagents or catalysts from many organic products. The present system involves the use of NaCl/pTsOH/NCS in water for the chlorination of aromatic compounds and has also been developed to solve the above problems (Scheme 1). The use of p-TsOH23,24 and NCS27,29 is reported in literature for chlorination; however, the disadvantages of these methods involve the use of organic solvents24,26 which have serious environmental impacts, poor yield and selectivities, solvent-free conditions operating at high temperature (up to 80 °C) and in long durations, use of expensive catalyst (gold, etc.),26,27,29 and use of microwave conditions which are not suitable for large scale processes.30 The present © 2012 American Chemical Society

Scheme 1. Chlorination of Aromatic Substrates in Water

system overcomes all these disadvantages of recently reported systems and has the advantages of higher yields, higher selectivities, and elimination of catalyst and organic solvent and is easy to scale-up under mild reaction conditions.

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EXPERIMENTAL SECTION Materials and Instrumentation. Starting materials and other reagents were obtained from commercial suppliers and used without further purification. Granular and scaly substrates were crushed to a fine powder prior to reactions using mortar and pestle. 1H NMR spectra were recorded on a Bruker Avance II 400 MHz spectrometer in DMSO and CDCl3 using tetramethylsilane (TMS) as an internal standard. Mass spectra were recorded on Micromass Quattro Micro API triple quadrupole MS equipped with a standard APCI ion source. HPLC analyses were conducted using a Waters 2695 instrument with PDA detector, column C18 (250 mm × 4.6 mm × 5 μm), solvent system of 70% CH3OH + 30% H2O and flow rate of 1 mL/min. HPLC purity is reported by area percent. General Procedure for the Chlorination of Aromatic Compounds. Monochlorination. Water (8 mL) was added to a finely crushed powder of aromatic compound (0.01 mol) taken in a 100 mL round-bottom flask equipped with a Received: Revised: Accepted: Published: 3881

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The study began first by using NCS in water (Table 1, entry 1) for the chlorination of 4-hydroxybenzonitrile. No chlorinated

magnetic stirring bar at room temperature. To this was added NaCl (0.015 mol), p-TsOH (0.01 mol), and NCS (0.01 mol). The reaction completion was monitored with thin layer chromatography (TLC). After completion of the reaction, 5 mL of water was added to separate the precipitated mass; precipitates were filtered and dried in oven. The structures of products were confirmed by 1H NMR and mass spectra and compared with authentic samples. Dichlorination. The process for synthesis of dichlorinated product was the same as that given in the monochlorination, except 0.03 mol of NaCl, 0.02 mol of p-TsOH, and 0.02 mol of NCS were used with respect to 0.01 mol of substrate. Spectroscopic Data of Some Chlorinated Aromatic Compounds. 2,6-Dichloro-4-nitroaniline (2). Yellow powder. 1H NMR (400 MHz, DMSO): δ 8.1 (s, 2H, Ar), δ 6.08 (s, 2H, NH2) ppm. MS (APCI): calcd for C6H4Cl2N2O2; 207.0; found, 205.0 [M − 2]+. 2,6-Dichloro-4-nitrophenol (5). Light yellow crystals. 1H NMR (400 MHz, DMSO): δ 8.22 (s, 2H, Ar), δ 6.6 (br, 1H, OH) ppm. MS (APCI): calcd for C6H3Cl2NO3, 208; found, 207 [M − 1]+. 2,4,6-Trichlorophenol (6). Brownish white needles. 1H NMR (400 MHz, CDCl3): δ 5.78 (s, 1H, OH), δ 7.16 (s, 2H, Ar). MS (APCI): calcd for C6H3Cl3O, 197.45; found, 196 [M − 1]+. 3-Chloro-4-hydroxybenzaldehyde (7). Light brown powder. 1 H NMR (400 MHz, DMSO): δ 9.78 (s, 1H, CHO), δ 7.81 (d, 1H, Ar), δ 7.64 (dd, 1H, Ar), δ 7.12 (d, 1H, Ar) ppm. MS (APCI): calcd for C7H5ClO2 156.5; found, 157.5 [M + 1]+. 5-Chlorosalicylic acid (10). White crystals. 1H NMR (400 MHz, DMSO): δ 9.05 (s, 1H, OH), δ 7.79 (d, 1H, Ar), δ 7.38 (dd, 1H, Ar), δ 6.91 (d, 1H, Ar) ppm. MS (APCI): calcd for C7H5ClO3, 172; found, 173 [M + 1]+. 3,5-Dichlorosalicylic acid (11). White crystals. 1H NMR (400 MHz, DMSO): δ 7.81 (d, 1H, Ar), δ 7.72 (d, 1H, Ar) ppm. MS (APCI): calcd for C7H4Cl2O3, 207.01; found, 206 [M − 1]+. 4-Chlorobenzanilide (14). White powder. 1H NMR (400 MHz, CDCl3): δ 7.19−7.80 (m, 9H, Ar) ppm. MS (APCI): calcd for C13H10ClNO, 231; found, 232 [M + 1]+. 3-Chloro-4-hydroxybenzonitrile (15). White needles. 1H NMR (400 MHz, DMSO): δ 7.12 (d, 1H, Ar), δ 7.77 (dd, 1H, Ar), δ 7.95 (d, 1H, Ar) ppm. MS (APCI): calcd for C7H4ClNO, 153.56; found, 152.9 [M]+. 3,5-Dichloro-4-hydroxybenzonitrile (16). White needles. 1H NMR (400 MHz, DMSO): δ 7.91 (s, 2H, Ar) ppm. MS (APCI): calcd for C7H3Cl2NO, 187; found, 187 [M]+.

Table 1. Optimization of Reaction Conditions for Chlorination in Water Using 4-Hydroxybenzonitrile as a Target Substratea entry

reagent system

reaction conditions

yield (%)

mp (°C) (lit.)

1 2 3 4

NCS NCS/p-TsOH NCS/p-TsOH NaCl/p-TsOH/NCS

24 h at r.t. 3 h at r.t. 3 h at 40 °C 1 h at 40 °C

S 29 40 95

146 (15331) 149 (15331) 151 (15331)

a

S = substrate (4-hydroxybenzonitrile); r.t. = room temperature. Reaction conditions: 4-hydroxybenzonitrile, 0.01 mol; NCS, 0.01 mol; p-TsOH, 0.01 mol; NaCl, 0.015 mol; H2O, 8 mL.

product was obtained even up to 24 h of reaction time. With the intention to obtain the chlorinated product, we used paratoluenesulphonic acid (p-TsOH) and studied the effect of acids on the reaction rate and yield. It was observed that addition of small amount of acid afforded 40% yield of chlorinated product within 3 h (Table 1, entry 3) at slightly higher temperature (40 °C), while at room temperature a very small amount of product was formed (29% yield) (Table 1, entry 2). The yield became static after 3 h and no effect on yield of chlorinated product was observed up to 6 h of reaction time at 40 °C. Therefore, it can be concluded that presence of acid is necessary to activate the N-chlorosuccinimide. Now, to increase the yield of chlorinated product, different types of salts were used along with p-TsOH (Table 2). Table 2 Table 2. Effect of Changing the Salts on the Yield of 3Chloro-4-hydroxybenzonitrilea

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RESULTS AND DISCUSSION To optimize the reaction conditions, first of all we studied the effect of substrate particle size on reaction rate and then we varied several reaction parameters including the absence or presence of different acids and salts, when the reaction was carried out in water. Therefore, granules and scaly substrates were crushed before carrying out the reaction using mortar and pestle and it was concluded experimentally that the smaller the particle size of the reactant is, the more efficient will be the reaction. The smaller reactant particles provide greater surface area which further increases the chances for the particle collision and hence reaction rate increases. Also, the smaller reactants particles get easily solubilized or dispersed in the reaction medium. 4-Hydroxybenzonitrile was used as a target substrate to study the effect of changing different parameters.

a

Reaction conditions: 4-hydroxybenzonitrile, 0.01 mol; NCS, 0.01 mol; p-TsOH, 0.01 mol; H2O, 8 mL at 40 °C for 1 h.

shows that NaCl afforded the best results and 3-chloro-4hydroxybenzonitrile was obtained as a chlorinated product from 4-hydroxybenzonitrile within 1 h, having 95% yield and 99% selectivity (Table 4, entry 5). It was also observed that NaCl addition enhanced the yield of chlorinated product in water, while in solvent (CH3CN) the presence of NaCl declined the yield. However, replacing NaCl with KBr leads to a brominated product rather than chlorinated product and employing salts other than metal chloride showed no significant effect on yield. Therefore, from experimental results it can be concluded that NCS in the presence of p-TsOH acid may react with KBr to 3882

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form BrCl, which further furnishes the Br+ electrophile to brominate the aromatic compound rather than chlorination. Similarly, NCS in the presence of p-TsOH reacts with NaCl to give Cl2, which then reacts with substrate to furnish the chlorinated product. This observation further suggests that NaCl plays a major role in the chlorination of aromatic substrates. In an attempt to optimize the amount of p-TsOH, we repeated the experiments again using 4-hydroxybenzonitrile as a target substrate at 40 °C. The results showed that decreasing the moles of p-TsOH from 0.01 to 0.005 (Figure 1) decreased

Figure 2. Effect of changing the type of acid on reaction time and yield of 3-chloro-4-hydroxybenzonitrile. Reaction conditions: 4-hydroxybenzonitrile, 0.01 mol; NCS, 0.01 mol; NaCl, 0.015 mol; H2O, 8 mL at 40 °C.

Figure 1. Effect of amount of p-TsOH on yield and melting point of 3chloro-4-hydroxybenzonitrile. Reaction conditions: 4-hydroxybenzonitrile, 0.01 mol; NCS, 0.01 mol; NaCl, 0.03 mol; H2O, 8 mL at 40 °C for 1 h.

the yield of chlorinated product. Also, depression in melting point of product from its actual value indicates that impure or underchlorinated product is being formed when we decrease the amount of p-TsOH below its optimal quantity. On increasing the amount of p-TsOH (from 0.01 to 0.02 mol) there was no effect on yield. Therefore, the optimum amount of p-TsOH is 0.01 mol, which gave the best results of monochlorination. To study the influence of using different types of acids (H2SO4, HCl, and CH3COOH) in place of pTsOH and results of changing the amount of NaCl on the yield and reaction rate at the same temperature (40 °C), the graphs have been plotted between % yield and reaction time. Figure 2 depicts that among the different types of acids, ptoluenesulfonic acid gave the best yield of chlorinated product (95%) in less reaction time (1 h). Acetic acid gave poor yield (60%) in 1 h which further increased up to 73% in 5 h, and after that no effect on yield was observed even up to 10 h of reaction time. HCl showed better results than acetic acid but poorer results than H2SO4 and p-TsOH. Among the different acids, H2SO4 showed results very much closer to p-TsOH, but yield (95%) and purity (99%) were better with p-TsOH. Therefore, it can be concluded that the presence of p-TsOH gave the best results and increased the yield and reaction rate while other acids showed increase in reaction time with decrease in yield. These results were also in accordance with an earlier method25 which employed CH3CN as a solvent. Figure 3 shows the effect of changing the amount of NaCl on reaction time and yield. It is clear from Figure 3 that the best results of chlorination were obtained with 0.015 mol of NaCl in 1 h, and after that no effect on yield was observed even up to 5−10 h of reaction time. Reducing the amount of NaCl below 0.015 mol reduced the yield of chlorinated product and increased the reaction time. However, increasing the amount of NaCl above

Figure 3. Effect of changing the amount of NaCl on reaction time and yield of 3-chloro-4-hydroxybenzonitrile. Reaction conditions: 4hydroxybenzonitrile, 0.01 mol; NCS, 0.01 mol; p-TsOH, 0.01 mol; H2O, 8 mL at 40 °C.

0.015 mol causes no effect on yield and reaction time. Therefore, 0.015 mol of NaCl is the optimal amount which gave best results of monochlorination. Since chlorination also occurred even in the absence of NaCl, its role may be kinetic. However, NaCl along with NCS plays a very important role in the chlorination reaction, since reducing the amount of either NaCl or NCS reduced the yield of product and increased the reaction time. It was also observed that dichlorination can be achieved merely by doubling the amount of NCS, p-TsOH and NaCl. Hence, 0.01 mol of NCS, 0.01 mol of p-TsOH, and 0.015 mol of NaCl furnish the best results of monochlorinated product while 0.02 mol of NCS, 0.02 mol of p-TsOH, and 0.03 mol of NaCl furnish the best results of dichlorinated product in water at 40 °C. After confirming the synthesis of 3-chloro-4hydroxybenzonitrile from 4-hydroxybenzonitrile, we extended our study to a large variety of industrially important aromatic compounds, and the results are shown in Table 3. The results 3883

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Table 3. Chlorination of Aromatic Compounds Using NaCl/p-TsOH/NCS in Water

a Reaction conditions: substrate, 0.01 mol; NCS, 0.01 mol; p-TsOH, 0.01 mol; NaCl, 0.015 mol; H2O, 8 mL at 40 °C. bReaction conditions: substrate, 0.01 mol; NCS, 0.02 mol; p-TsOH, 0.02 mol; NaCl, 0.03 mol; H2O, 8 mL at 40 °C.

either through Cl• or Cl+ or Cl2.24,27,30,36 However, in the

signify that most of the substrates are chlorinated in good yields and higher selectivity in shorter reaction duration under mild reaction conditions. Table 4 confirms that 4-hydroxybenzonitrile afforded the best yield of 3-chloro-4-hydroxybenzonitrile (95%) with an HPLC purity of 99% (Table 4, entry 5). The dichlorinated product of 4-hydroxybenzonitrile (Table 3, entry 16) which is used as a pesticide31 was also synthesized in 93% yield within 1.5 h. Another industrially important chlorinated products like 2,6-dichloro-4-nitroaniline,32 2,6-dichloro-4-nitrophenol,11 5-chlorosalicylic acid,33 3-chloro-4-hydroxybenzaldehyde,34 and 5-chloroisatin35 were produced under mild conditions, thus, affording the chlorinated products in excellent yields in short reaction durations (1−2 h). 2,6-Dichloro-4nitroaniline (Table 3, entry 2) which is known to be active against certain soil, foliar, and fruit pathogens on ornamental and agricultural crops was obtained in 94% yield and 98.8% HPLC purity. It was synthesized earlier by Smythe et al.32 using Cl2 gas in 92% yield within 4 h. 2,6-Dichloro-4-nitrophenol which is also a valuable chemical intermediate useful in agrochemistry and can be used as an enzyme inhibitor was obtained in 90% yield (Table 3, entry 5). Earlier, Desmurs et al.11 synthesized this compound at a high temperature (120 °C) using molecular chlorine as a chlorinating agent. 5-Chlorosalicylic acid (85% yield, Table 3, entry 10) used as an intermediate of pesticide, medicine and dyes was also synthesized earlier by H. A. Muathen17 using SnCl4/ Pb(OAc)4 in ethyl acetate in 77% yield. Plausible Mechanism. Generally, in the chlorination reaction involving the use of NCS, chlorination can proceed

present method there is no involvement of free radical since use Table 4. Product Selectivity in Chlorination of Various Aromatic Substrates

a Isolated yield. bPurity determined by HPLC. cReaction conditions: substrate, 0.01 mol; NCS, 0.02 mol; p-TsOH, 0.02 mol; NaCl, 0.03 mol; H2O, 8 mL at 40 °C. dReaction conditions: substrate, 0.01 mol; NCS, 0.01 mol; p-TsOH, 0.01 mol; NaCl, 0.015 mol; H2O, 8 mL at 40 °C.

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Facility, Punjab University, Chandigarh, in carrying out the spectral analysis of the compounds. The authors thanks the School of Studies in Chemistry, Jiwaji University, for providing a University Research Fellowship.

of a free radical initiator and inhibitor showed no effect on reaction rate. In our experimental study, the attacking species may be Cl+ when NCS was used as a chlorinating agent in the presence of acid and absence of NaCl using water as a solvent (Table 1). However, the addition of NaCl enhanced the yield of chlorinated product and minimized the reaction time. When NaCl was replaced with KBr, a brominated product was obtained rather than chlorination. Therefore, it can be concluded from present results that KBr along with NCS generates BrCl which further polarizes to give bromonium ion (Br+). This Br+ then brominates the aromatic compound. In the present work, NaCl plays an important role in the process of chlorination. Hence, a different mechanism will operate for the chlorination of aromatic compounds where NaCl was added along with NCS and p-TsOH. Cl2 can be generated from NCS in presence of acid and Cl−. The idea of generation of Cl2 from NCS and Cl− ions in the presence of acid can also be obtained from literature reports.36−38 Also, from experimental results we found that even chlorination takes place in the absence of NaCl, so its role may be kinetic but both NaCl and NCS plays a very important role in increasing the reaction rate, yield, and generation of Cl2. Thus, on the basis of experimental results, a plausible mechanism of chlorination of aromatic compounds is given in Scheme 2 where the function of the acid is to activate

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(1) De la Mare, P. B. Electrophilic Halogenation; Cambridge University Press: Cambridge, UK, 1976. (2) Taylor, R. Electrophilic Aromatic Substitution; Wiley: Chichester, UK, 1990. (3) Davis, S. G. Organotransition Metal Chemistry: Applications to Organic Synthesis; Pergamon Press: Oxford, UK, 1982. (4) Cannon, K. C.; Krow, G. R. Handbook of Grignard Reagents; Dekker: New York, 1996. (5) Miyaura, N.; Suzuki, A. Palladium-catalyzed cross-coupling reactions of organoboron compounds. Chem. Rev. 1995, 95, 2457. (6) Beletskaya, I. P.; Cheprakov, A. V. The Heck reaction as a sharpening stone of palladium catalysis. Chem. Rev. 2000, 100, 3009. (7) Meijere, A.; Meyer, F. E. Fine feathers make fine birdsThe Heck reaction in modern garb. Angew. Chem., Int. Ed. Engl. 1994, 33, 2379. (8) Mais, F. J.; Fiege, H. Process for the preparation of 2-chloro-4methylphenol. U.S. Patent 5,847,236, 1998. (9) YipengChemical. http://www.yipengchem.com/in/2315-81-3. htm (accessed Jan 15, 2011). (10) Chemcalland21. http://www.chemicalland21.com/lifescience/ agro/2,4,6-TRICHLOROPHENOL.htm (accessed Feb 27, 2011). (11) Desmurs, J. R.; Jouve, I. Chlorination of nitrophenols. U.S. Patent 4,827,047, 1989. (12) Barhate, N. B.; Gajare, A. S.; Wakharkar, R. D.; Bedekar, A. V. Simple and practical halogenation of arenes, alkenes and alkynes with hydrohalic acid/H2O2 (or TBHP). Tetrahedron 1999, 55, 11127. (13) Vyas, P. V.; Bhatt, A. K.; Ramachandraiah, G.; Bedekar, A. V. Environmentally benign chlorination and bromination of aromatic amines, hydrocarbons and naphthols. Tetrahedron Lett. 2003, 44, 4085. (14) Bogdal, D.; Lukasiewicz, M.; Pielichowski, J. Halogenation of carbazole and other aromatic compounds with hydrohalic acids and hydrogen peroxide under microwave irradiation. Green Chem. 2004, 6, 110. (15) Mukhopadhyay, S.; Mukhopadhyaya, J. K.; Ponde, D. E.; Cohen, S.; Kurkalli, B. G. S. Kinetics and process parameter studies in oxidative chlorination of 4-methylphenol under phase-transfer conditions. Org. Process Res. Dev. 2000, 4, 509. (16) Daniel, R. B.; de Visser, S. P.; Shaik, S.; Neumann, R. Electrophilic aromatic chlorination and haloperoxidation of chloride catalyzed by polyfluorinated alcohols: A new manifestation of template catalysis. J. Am. Chem. Soc. 2003, 125, 12116. (17) Muathen, H. A. Mild chlorination of aromatic compounds with tin(IV) chloride and lead tetraacetate. Tetrahedron 1996, 52, 8863. (18) Pisoni, D. S.; Gamba, D.; Fonseca, C. V.; de Costa, J. S.; Petzhold, C. L.; de Oliveria, E. R.; Ceschi, M. A. InCl3/NaClO: A reagent for allylic chlorination of terminal olefins. J. Braz. Chem. Soc. 2006, 17, 321. (19) Cristiano, R.; Ma, K.; Pottanat, G.; Weiss, R. G. Tetraalkylphosphonium trihalides. Room temperature ionic liquids as halogenation reagents. J. Org. Chem. 2009, 74, 9027. (20) Narender, N.; Srinivasu, P.; Kulkarni, S. J.; Raghavan, K. V. Highly efficient, para-selective oxychlorination of aromatic compounds using potassium chloride and oxone. Synth. Commun. 2002, 32, 279. (21) Yu, G.; Mason, H. J.; Wu, X.; Endo, M.; Douglas, J.; Macor, J. E. A mild and efficient method for aromatic chlorination of electron-rich arylalkyl amines. Tetrahedron Lett. 2001, 42, 3247. (22) Jerzy, G.; Slawomir, Z. Oxidative chlorination of acetanilides by metal chloridesHydrogen peroxide in acid−aqueous medium systems. Synth. Commun. 1997, 27, 3291. (23) Hoffman, R. V.; Weiner, W. S.; Maslouh, N. Highly stereoselective synthesis of anti-n-protected-α-amino epoxides. J. Org. Chem. 2001, 66, 5790.

Scheme 2. Plausible Mechanism of Chlorination

the N-chlorosuccinimide to give intermediate (2). The Cl+ electrophile generated from the activated intermediate (2) will then combine with the chloride ion from NaCl, which may then ultimately lead to the generation of Cl2. This Cl2 when reacted with aromatic substrate affords the corresponding chlorinated product.

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CONCLUSION A number of industrially important aromatic compounds were chlorinated in good yields and selectivity with NaCl/p-TsOH/ NCS in aqueous medium under mild conditions. The present system involves the elimination of organic solvent, no use of any expensive catalyst except the use of stoichiometric amount of acid promoter, higher yields, and selectivities under mild conditions which make the present system economical, clean, efficient, and easy to scale-up. Thus, this system can be used for the commercial production of industrially important chlorinated aromatic compounds.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Tel.: +91-9752643903. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors express their sincere thanks to Kapil Kumar, SRF Ltd., and Director of Sophisticated Analytical Instrumentation 3885

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