Novel Method of Synthesis of Quaternary Ammonium

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Novel Method of Synthesis of Quaternary Ammonium Tribromides and Investigation of Catalytic Role of Benzyltrimethylammonium Tribromide in Oxidation of Alcohols to Carbonyl Compounds a

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Madhudeepa Dey , Siddhartha Sankar Dhar & Mukul Kalita

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Department of Chemistry, National Institute of Technology, Silchar, Silchar, Assam, India Accepted author version posted online: 08 Aug 2012.Version of record first published: 06 Mar 2013.

To cite this article: Madhudeepa Dey , Siddhartha Sankar Dhar & Mukul Kalita (2013): Novel Method of Synthesis of Quaternary Ammonium Tribromides and Investigation of Catalytic Role of Benzyltrimethylammonium Tribromide in Oxidation of Alcohols to Carbonyl Compounds, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 43:12, 1734-1742 To link to this article: http://dx.doi.org/10.1080/00397911.2012.666694

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Synthetic Communications1, 43: 1734–1742, 2013 Copyright # Taylor & Francis Group, LLC ISSN: 0039-7911 print=1532-2432 online DOI: 10.1080/00397911.2012.666694


NOVEL METHOD OF SYNTHESIS OF QUATERNARY AMMONIUM TRIBROMIDES AND INVESTIGATION OF CATALYTIC ROLE OF BENZYLTRIMETHYLAMMONIUM TRIBROMIDE IN OXIDATION OF ALCOHOLS TO CARBONYL COMPOUNDS Madhudeepa Dey, Siddhartha Sankar Dhar, and Mukul Kalita Department of Chemistry, National Institute of Technology, Silchar, Silchar, Assam, India

GRAPHICAL ABSTRACT

Abstract Stable crystalline organic quaternary ammonium tribromides (QATBs) have been easily synthesized by the oxidation of the corresponding organic ammonium bromides (QABs) with ammonium persulfate. The reactions have been performed under solvent-free conditions in the presence of sulfuric acid and silica as supporting agent. Two equivalents of potassium bromide have been used as the source of additional bromides for quantitative conversion of QABs to QATBs. Ammonium persulfate, a cheap and readily available oxidant, carries out the bromide oxidation to tribromide very effectively under solvent-free conditions. The synthesized QATBs have been shown to catalyze the oxidation of alcohols to carbonyl compounds with hydrogen peroxide as oxidant in good yields under mild reaction conditions. Keywords Ammonium persulfate; green synthesis; organic ammonium tribromides; oxidation

INTRODUCTION Classical bromination involves the direct or indirect use of elemental bromine under harsh conditions.[1] However, handling of liquid bromine is cumbersome because of its hazardous nature, and special care is required for its storage and transport.[2–6] Moreover reactions carried out with elemental bromine reduce the atom efficiency to 50%.[7] Environmental legislation against the use of detrimental chemicals and solvents causes major concern for the use of liquid bromine in classical Received January 11, 2012. Address correspondence to S. S. Dhar, NIT Silchar, Silchar 788010, Assam, India. E-mail: ssd_ [email protected]

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QUATERNARY AMMONIUM TRIBROMIDES

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brominations.[8–11] Therefore, some environmentally safer procedures have been envisioned. Taking cues from various literatures, it is seen that organic ammonium tribromides constitute a convenient source of bromine and find increasing applications as substituents for molecular bromine for a variety of organic transformation reactions.[12–14] Hence, they are regarded as highly efficient, versatile brominating and oxidizing agents.[15–17] However, most of their preparations invariably involve elemental bromine and in some cases HBr, which leads to environmental pollution.[12–14,18,19] In the recent past, a few environmentally benign syntheses of tribromides have been documented, including contributions from our own group.[12,15,16] Despite the plethora of methods available in the literature, the search for a simple, convenient, and environmentally safer synthesis of tribromides is still a challenge. Therefore, as part of our research interest aimed towards the development of greener synthetic protocols in organic synthesis, we report herein the syntheses of quaternary ammonium tribromides (QATBs) using a benign oxidant ammonium persulfate and application of one of the QATBs viz., BTMATB for carrying out the oxidation of a number of primary and secondary alcohols. Ammonium persulfate is relatively strong oxidant in comparison to most oxidants employed for bringing out organic transformation reactions.[20] It is inexpensive, stable, and easily handled. Its use as an oxidant is also safe from environmental point of view, and it is readily commercially available, which makes ammonium persulfate attractive for carrying out organic syntheses. Moreover, its use as an oxidant for tribromide syntheses is hitherto unknown, which prompted us to utilize it for the oxidative transformation of ammonium bromides to ammonium tribromides. The most common application of this reagent in the chemical industry is for bleaching, for alkene oxidation[21] and substituted aromatics,[22] for cyclization, and for deoximation of steroidal oximes,[23] but its general applicability in organic syntheses has largely been unexplored.[24–26]

RESULTS AND DISCUSSION The syntheses of QATBs involve the grinding of benzyltrimethylammonium bromide (BTMAB) together with potassium bromide and ammonium persulfate as oxidant in the presence of dilute sulfuric acid. A little amount of silica was used as a supporting agent (Scheme 1). The color of the mixture changed from white to orange-yellow, indicating the formation of tribromide. The UV-Visible spectrum of the product showed an intense absorption peak at 279 nm, typical of the tribromide (Br3 ) anion (Fig. 1).[13] Similar methodology was applied for the preparation of other tribromides viz., tetrabutylammonium tribromide TBATB (87%), cetyltrimethylammonium tribromide (CTMATB) (85%), tetramethylammonium tribromide (TMATB) (81%), and tetraethylammonium tribromide (TEATB) (87%). The plausible mechanistic pathway for the oxidative transformation of bromides to tribromides by persulfate under acidic condition may be rationalized from the reaction shown in Scheme 2. It is evident from the reaction that the amount of sulfuric acid required is twice the amount of the oxidant used for carrying out the reaction. Selective oxidation of alcohols is a fundamental reaction in organic chemistry.[27–29] A variety of transition-metal-based[30–32] as well as metal-free oxidation

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M. DEY, S. S. DHAR, AND M. KALITA


Scheme 1. Oxidation of ammonium bromides to ammonium tribromides using (NH4)2S2O8.

methodologies have been reported in the literature as alternative efficient routes to accomplish this transformation. In this context, the importance of bromine catalysis in the auto-oxidation for a variety of industrial processes is well documented.[33,34] In one of the reported methodologies, liquid bromine is used for the catalytic oxidation of alcohols to carbonyl compounds with H2O2 as the oxidant.[35] A recent report showed use of N-methylpyrrodin-2-one hydrotribromide (MPHT) as a catalyst for carrying out the oxidation of alcohols with H2O2.[36] However, the preparation of MPHT itself requires bromine,[37] which

Figure 1. UV-Visible spectrum of Br3 . (Figure is provided in color online.)

Scheme 2. Proposed mechanism of formation of Br3 from Br using ammonium persulfate.


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Table 1. Benzyltrimethylammonium tribromide–catalyzed oxidation of alcohols to carbonyl compoundsa Reaction time (h)

Yield (%)b

1

1

97

2

2

88

3

1.75

90

4

1.5

93

5

2.5

72c

6

4

78c

7

3.5

78c

8

6

72

9

3

88

10

2.5

85


Entry

Substrate

Product

a Reaction conditions: Substrate (1 mmol), BTMATB (10 mol%), aqueous hydrogen peroxide (2 mmol, 30 wt%), acetonitrile (5 mL) at 60 C. b Isolated yields. c Experiment carried out using (50 mol%) of BTMATB in the presence of hydrogen peroxide (2 mmol, 30 wt%) at 60 C.


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does not comply with the norms of green chemistry. In another similar work, poly(ethylene glycol)–embedded potassium tribromide (PEG KBr3) has been used as a catalyst for oxidation of alcohols,[38] but according to this protocol the regeneration of the catalyst involves the addition of molecular bromine, thereby making the protocol unfavorable from environmental viewpoints. This has prompted us to explore the effectiveness of one of the synthesized tribromides (BTMATB) as catalyst=oxidant in transformation of alcohols to carbonyl compounds in the presence of H2O2. The results of oxidation of a variety of alcohols, their reactions conditions, and yields are summarized in Table 1. When the oxidation of alcohols was carried out at room temperature, the reaction took longer to complete and the yield of the product was very low. For example, yield of the product for oxidation of 4-methoxybenzylalcohol was only 20%. Also dropwise addition of hydrogen peroxide resulted in better yield than addition of all at a time. During the course of the investigation, it was further observed that if the reaction was carried out in the absence of the catalyst, no product was isolated. It may be further mentioned that when oxidation of alcohols was carried out with only catalytic amount of BTMATB in the absence of the oxidant (30% aqueous hydrogen peroxide), only a trace amount of the corresponding aldehydes were obtained in some cases, whereas for others the reaction did not take place at all. Similarly the reaction of the alcohols with a stoichiometric amount of BTMATB without using hydrogen peroxide did not occur effectively, indicating that BTMATB=H2O2 is an efficient catalytic system for this transformation. Acetonitrile proved to be the best solvent for this oxidative transformation. Among the various benzyl alcohols studied, unsubstituted benzyl alcohol (Table 1, entry 1) was found to be more reactive than the others. Furthermore, it was observed that aromatic-substituted alcohols (Table 1, entries 1–6) were more reactive than the aliphatic or alicyclic alcohols (Table 1, entries 7–11). Again, alcohols substituted with electron-donating groups (Table 1, entries 2–4) were more reactive than alcohols bearing electron-withdrawing groups, as they facilitate attack of electrophile on the alcoholic carbon (Table 1, entries 5 and 6). However, for some of the substrates (Table 1, entries 5–7) that comparatively afforded lower yields, the catalyst amount was increased to 50 mol% to obtain substantial amounts of the product.

Scheme 3. Proposed mechanism for Br3 -catalyzed transformation of alcohols to carbonyl compounds. (Figure is provided in color online.)


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Although the exact mechanism is not comprehensible at this stage, it probably involves the in situ generation of molecular Br2 from tribromide Br3 , which then reacts with hydrogen peroxide to give hypobromous acid. The generated hypobromous acid subsequently reacts with the alcoholic group to form the reactive hypobromite species, which finally gets converted to the desired carbonyl compound. The proposed mechanism is depicted in Scheme 3.


CONCLUSION Thus in conclusion, a simple and useful method has been devised for the synthesis of QATBs from quaternary ammonium bromides by employing ammonium persulfate as oxidant under very mild and environmentally safe reaction conditions. Its role as an effective catalyst has been utilized in the oxidation of alcohols to carbonyl compounds. This methodology for the quaternary ammonium tribromides synthesis represents an easy and alternative route to the rather hazardous classical preparation of such reagents. EXPERIMENTAL All the alcohols were purchased from Fisher Scientific and used without further purification. Melting points were determined in open capillaries and are uncorrected. The completion of the reaction was monitored by thin-layer chromatography (TLC). Infrared (IR) spectra were recorded on KBr matrix with Perkin-Elmer BX-FTIR spectrometer. 1H NMR spectra were recorded in dimethylsulfoxide (DMSO-d6)= CDCl3 using tetramethylsilane (TMS) as internal standard on a 400 MHz Varian spectrometer. Synthesis of Quaternary Ammonium Tribromides Typical methodology of synthesis of QATBs involves the grinding of BTMAB (1 mmol, 0.23 g), KBr (2 mmol, 0.24 g), ammonium persulfate (1 mmol, 0.23 g), 4 N sulfuric acid (0.1 mL), and a little silica in a motor for ca. 5–10 min at room temperature (Scheme 1). The color of the mixture changed from white to orange-yellow, indicating the formation of the tribromide salt. The product was extracted with ethyl acetate (5 mL) and concentrated under reduced pressure to get the tribromide in excellent yield (88%) with high purity. Analytical data for benzyltrimetylammonium tribromide: C10H16NBr3, mp: 99 C, lit.[15](99–101 C), Calc: C, 30.8; H, 4.14; N, 3.59%. Found: C, 30.6; H, 4.19; N, 3.61%. General Procedure for the Oxidation of Alcohols Substrate (1 mmol) was added to a solution of 5 mL of acetonitrile and magnetically stirred, followed by the addition of BTMATB (10 mol%).Hydrogen peroxide (30%, 0.3 mL, 2 mmol) was then added dropwise, and the resulting mixture was heated at 60 C. The progress of the reaction was monitored by TLC using ethyl acetate–hexane (6:4) as eluent. After the completion of the reaction, the reaction mixture was extracted with diethyl ether to get the corresponding carbonyl compound.

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The ether layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to give the desired oxidized products.

ACKNOWLEDGMENT S. S. Dhar acknowledges the Department of Science and Technology (DST), New Delhi, for funding the work through DST-SERC Fast Track Project No. SR=FTP=CS-100=2007.


REFERENCES 1. Kumar, L.; Sharma, V.; Mahajan, T.; Agarwal, D. D. Instantaneous, facile, and selective synthesis of tertabromobisphenol a using potassium tribromide: An efficient and renewable brominating agent. Org. Proc. Res. Devel. 2010, 14, 174–179. 2. Chiappe, C.; Leandri, E.; Pieraccini, D. Highly efficient bromination of aromatic compounds using 3-methylimidazilium tribromide as reagent=solvent. Chem. Commun. 2004, 2536–2537. 3. Tajik, H.; Shirini, F.; Zadeh, P. H.; Rashtabadi, H. R. Bromination of aromatic compounds with potassium bromide in the presence of poly(4-vinylpyridine)-supported bromate in nonaqueous solution. Synth. Commun. 2005, 35, 1942–1947. 4. Rahman, H.; Mahood, T.; Maryam, M.; Zahra, L. An efficient and regioselective bromination of aromatic compounds with ethylene bis(N-methylimidazolium)ditribromide (EBMIDEB). Synth. Commun. 2010, 40, 868–876. 5. Raju, T.; Kalangiappar, K.; Kulandainathan, A. M.; Uma, U.; Malini, R.; Muthukumaran, A. Site-directed nuclear bromination of aromatic compounds by an electrochemical method. Tetrahedron Lett. 2006, 47, 4581–4584. 6. Sels, B. F.; Devos, E. D.; Jacobs, P. A. Use of WO42 on layered double hydroxides for mild oxidative bromination and bromide-assisted epoxidation with H2O2. J. Am. Chem. Soc. 2001, 123, 8350–8359. 7. Kavala, V.; Naik, S.; Patel, B. K. A new recyclable ditribromide reagent for efficient bromination under solvent-free condition. J. Org. Chem. 2005, 70, 4267–4271. 8. Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University Press: Oxford, 2000; p. 20. 9. Metzger, J. O. Solvent-free organic syntheses. Angew. Chem. Int. Ed. 1998, 37, 2975–2978. 10. Clark, J. H. Green chemistry: Challenges and opportunities. Green Chem. 1999, 1, 1–8. 11. Tanaka, K.; Toda, F. Solvent-free organic synthesis. Chem. Rev. 2000, 100, 1025–1074. 12. Bora, U.; Bose, G.; Chaudhuri, M. K.; Dhar, S. S.; Gopinath, R.; Khan, A. T.; Patel, B. K. Regioselective bromination of organic substrates by tetrabutylammoniumbromidepromoted by V2O2-H2O2: An environmentally favorable synthetic protocol. Org. Lett. 2000, 2, 247–249. 13. Chaudhuri, M. K.; Khan, A. T.; Patel, B. K. An environmentally benign synthesis of organic ammonium tribromides (QATB) and bromination of selected organic substrates by tetrabutylammonium tribromide (TBATB). Tetrahedron Lett. 1998, 39, 8163–8166. 14. Borah, R.; Thakur, A. J. Green synthesis of tetraalkylammonium tribromide using cerium(IV) ammonium nitrate (CAN) as oxidant. Synth. Commun. 2007, 37, 933–939. 15. Chaudhuri, M. K.; Bora, U.; Dehury, S. K.; Dey, D.; Dhar, S. S.; Kharmawphlang, W.; Choudhary, B. M.; Mannepalli, L. K. Process for preparation of quaternary ammonium tribromides. US Patent No. 7005548, 2006.



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16. Bora, U.; Chaudhuri, M. K.; Dey, D.; Dhar, S. S. Peroxometal-mediated environmentally favorable route to brominating agents and protocols for bromination of organics. Pure Appl. Chem. 2001, 73, 93–102. 17. Pravst, I.; Zupan, M.; Stavber, S. Introduction of halogen atoms into organic compounds under solvent-free reaction conditions. Curr. Org. Chem. 2009, 13, 47–70. 18. Adimurthy, S.; Ghosh, S.; Patoliya, P. U.; Ramachandraiah, G.; Agarwal, M.; Gandhi, M. R.; Upadhyay, S. C.; Ghosh, S.; Ranu, B. C. An alternative method for the region- and stereoselective bromination of alkenes, alkynes, toluene derivatives, and ketones using a bromide=bromated couple. Green Chem. 2008, 10, 232–237. 19. Wu, L. Q.; Wang, C.-G.; Wu, Y. F.; Yang, L. M. Synthesis of 6-bromocoumarins using tetrabutylammonium tribromide as a selective brominating agent and an efficient generator of HBr. J. Chin. Chem. Soc. 2009, 56, 606–608. 20. Varma, S. R.; Meshram, M. H.; Dahiya, R. Solid-state oxidation of thiols to disulfides using ammonium persulfate. Synth. Commun. 2000, 30, 1249–1255. 21. Fristad, W. E.; Peterson, J. R. Iron(II)-catalyzed persulfate oxidation of alkenes to vicinal diacetates. Tetrahedron Lett. 1983, 24, 4547–4550. 22. Angelo, C.; Ombretta, P. Oxidation of substituted aromatic compounds by peroxydisulphate: Homolytic benzylation and oxidative coupling reaction. Can. J. Chem. 1980, 58, 2117–2119. 23. Brooks, S. G.; Evans, R. M.; Green, G. F. H.; Hunt, J. S.; Long, A. G.; Mooney, B.; Wyman, L. J. Use of 20-oximes and 20-semicarbazones in making cortisol and 4:5adihydrocortisol. J. Chem. Soc. 1958, 4614–4628. 24. Chaveliar, J.-W.; Bergeron, J.-Y.; Dao, L. H. Synthesis, characterization, and properties of poly(N-alkylanilines). Macromolecules 1992, 25, 3325–3331. 25. Lee, J.-Y; Song, K. T.; Kim, S. Y.; Kim, Y. C.; Kim, D. Y.; Kim, C. Y. Synthesis and characterization of soluble polypyrrole. Synth. Met. 1997, 84, 137–140. 26. Imanzadeh, G. H.; Zamanloo, M. R.; Eskandari, H.; Banaei, D. R. Aqueous media deprotection of ketoximes with ammonium persulfate. Bull. Korean Chem. Soc. 2006, 27, 119–120. 27. Nishiyama, Y.; Nakagawa, Y.; Mizuno, N. High turnover numbers for the catalytic selective oxidation of alkenes with 1 atm of molecular oxygen. Angew. Chem. Int. Ed. 2001, 40, 3639–3641. 28. Ley, S. V.; Madin, A. In Comprehensive Organic Synthesis; B. M. Trost and I. Fleming (Eds.); Pergamon: Oxford, 1991; vol. 7, pp. 305–327. 29. Arterburn, J. B. Selective oxidation of secondary alcohols. Tetrahedron 2001, 57, 9765–9788. 30. Schultz, M. J.; Sigman, M. S. Recent advances in homogeneous transition metal– catalyzed aerobic alcohol oxidations. Tetrahedron 2006, 62, 8227–8241. 31. Zhan, B.-Z.; Thompson, A. Recent developments in the aerobic oxidation of alcohols. Tetrahedron 2004, 60, 2917–2935. 32. Punniyamurthy, T.; Velusami, S.; Iqbal, J. Recent advances in transition metal–catalyzed oxidation of organic substrates with molecular oxygen. J. Chem. Rev. 2005, 105, 2329–2364. 33. Bjorsvik, H.; Fontana, F.; Liguori, L.; Minisci, F. A bromine-catalysed free-radical oxidation of acetamides from primary and secondary alkylamines by H2O2. Chem. Commun. 2001, 523–524. 34. Bravo, A.; Dordi, B.; Fontana, F.; Minisci, F. Oxidation of organic sulfides by Br2 and H2O2 elecrophilic and free-radical process. J. Org. Chem. 2001, 66, 3232–3234. 35. Amati, A.; Dosualdo, G.; Zhao, L.; Bravo, A.; Fontana, F.; Minisci, F. Catalytic processes of oxidation by hydrogen peroxide in the presence of Br2 or HBr: Mechanism and synthetic applications. Org. Proc. Res. Devel. 1998, 2, 261–269.

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36. Joseph, K. J.; Jain, L. S. Oxidation of alcohols and vic-diols with H2O2 by using catalytic amounts of N-methylpyrrolidin-2-one hydrotribromide. Eur. J. Org. Chem. 2006, 590–594. 37. Bekaert, A.; Provot, O.; Rasolojaona, O.; Alami, M.; Brion, J.-D. N-Methylpyrrolidin2-one hydrotribromide (MPHT), a mild reagent for selective bromination of carbonyl compounds: Synthesis of substituted 2-bromo-1-naphtols. Tetrahedron Lett. 2005, 46, 4187–4191. 38. Verma, S.; Jain, L. S.; Sain, B. Poly(ethylene glycol)–embedded potassium tribromide (PEG KBr3) as a recyclable catalyst for oxidation of alcohols. Ind. Eng. Chem. Res. 2011, 50, 5862–5865.