Rapid and Selective Oxidation of Alcohols in Deep Eutectic Solvent

Article pubs.acs.org/IECR

Rapid and Selective Oxidation of Alcohols in Deep Eutectic Solvent Najmedin Azizi,* Meysam Khajeh, and Masoumeh Alipour Chemistry and Chemical Engineering Research Center of Iran, P.O. Box 14335-186, Tehran, Iran S Supporting Information *

ABSTRACT: Deep eutectic solvent (DES) has been identified as a highly efficient catalyst and reaction medium, for rapid oxidation of alcohols to aldehydes and ketones using N-bromosuccinimide as the oxidant. This mild procedure utilizes biodegradable and readily available choline chloride/urea-based DES for high-yield oxidation at room temperature or at 60 °C. Selective oxidation of secondary alcohols in the presence of primary alcohols can be achieved. Furthermore, the catalyst-free synthesis of 2-bromoacetophenone was achieved through DES-mediated tandem oxidation and bromination of alcohol.

1. INTRODUCTION In this era of green chemistry, solvents occupy a strategic place. In this sense, some green solvents such as supercritical fluids, ionic liquids (ILs), and water have been paid great attention to replace conventional hazardous volatile organic solvents in industry and laboratory.1 Among them, ILs have received increasing attention for different applications for the chemical process because of a negligible vapor pressure, their solubility factor, their good thermal stability, and nonflammability.2,3 However, despite all of the valuable properties of ILs, their cost due to expensive raw materials, tedious preparation, and purification, toxicity, and very poor biodegradability have prevented their widespread usage in the chemical process. Deep eutectic solvents (DESs) have emerged as advanced neoteric ionic solvents for industrial reactions with some additional advantages such as a chemical inertness with water, low cost, high atom economy, and environmental impact. DESs result from the association of a cheap and biodegradable choline chloride with a hydrogen-bond donor such as alcohol, acid, or amide, and they are now of growing interest in many possible applications because of their potential use as alternative environmentally friendly solvents.4−16 Oxidation of alcohols to the corresponding aldehydes and ketones is considered a most important transformation in organic synthesis, and a wide variety of reagents and catalysts have been developed at the laboratory-scale and industrial process. 17−21 Oxidation of alcohols with a variety of N-halogenated reagents such as N-bromoacetamide (NBA), N-chlorosuccinimide (NCS), and N-bromosuccinimide (NBS) and other halogen sources has been known for a long time, and the reactions proceed in rather demanding conditions for the absence of any catalyst.22−25

Buchi 535 melting point apparatus and were uncorrected. Fourier transform infrared (FTIR) spectra were determined on a Bruker Vector-22 IR spectrometer using KBr disks. 1H NMR spectra were recorded at room temperature on a Bruker Ultra Shield (500 MHz) FT-NMR spectrometer. Gas chromatography (GC) was performed on a Varian CP-3800 GC-FID, and analytical conditions are included in Table 5 (Supporting Information, SI). 2.2. DES Preparation. According to the literature,4 100 mmol of choline chloride and 200 mmol of urea were mixed in a 250 mL round-bottomed flask and were heated for 40 min at 60 °C until a clear liquid appeared. 2.3. General Procedure. A test tube, equipped with a magnetic stirring bar and septum, was charged with DES (0.5 mL), alcohols (1 mmol), and NBS (1 mmol), and the mixture was heated at 60 °C with stirring until the reaction was complete. The reaction was cooled to room temperature, quenched with water (10 mL), and extracted with ethyl acetate (5 mL). The organic layer was dried over Na2SO4, and the solvent was removed under vacuum. In most cases, the reaction products were obtained in high purity and did not require further purification by distillation or column chromatography. All compounds were known and were characterized by melting and boiling points found to be identical with the ones described in the literature. In a few cases, crude products were further purified by silica column chromatography using ethyl acetate/ petroleum ether.

3. RESULTS AND DISCUSSION As part of an ongoing research program on the development of green solvents in organic synthesis,26−28 we envisaged to explore selective oxidation of a wide range of primary and secondary alcohols into the corresponding carbonyl compounds with NBS in DES under catalyst-free conditions. In our preliminary studies to optimize the best reaction conditions, 1-phenylethanol (1 mmol) was treated with NBS (1 mmol) as a model reaction in the absence of any added catalyst using

2. EXPRIMENTAL SECTION 2.1. Materials and Instrumentation. All chemicals and solvents were commercially available and were used as purchased. All products were confirmed by melting point and 1 H NMR spectroscopy. 1H NMR spectra were recorded on 500 and 80 MHz NMR spectrometers using CDCl3 as the solvent, and chemical shifts were expressed in (ppm) downfield from tetramethylsilane. Water and other solvents were distilled before use. Melting and boiling points were recorded on a © 2014 American Chemical Society

Received: Revised: Accepted: Published: 15561

May 20, 2014 September 3, 2014 September 8, 2014 September 8, 2014 dx.doi.org/10.1021/ie502019z | Ind. Eng. Chem. Res. 2014, 53, 15561−15565

Industrial & Engineering Chemistry Research

Article

electron-rich and electron-withdrawing ring substituents underwent oxidation with NBS under similar reaction conditions to give the corresponding carbonyl compounds within 5−60 min. Oxidation of aliphatic alcohols to the corresponding aldehydes and ketones was also possible, albeit with extended reaction times and diminished efficiency. Many common functional and protecting groups such as methoxy, halo, alkyl, and alkene double bonds were shown to be compatible with the present reaction conditions. A highly deactivated alcohol such as 3-pyridinemethanol proved inert to the reaction conditions, and only the starting material was recovered after 24 h. 4-Nitrobenzyl alcohol was consumed within 5 min to give 4-nitrobenzaldehyde with 20% conversion and the other three unknown products. Primary alcohols are oxidized to aldehydes without the formation of any undesired side products such as overoxidation to carboxylic acids even with an excess of NBS. Oxidative decarboxylation of mandelic acid under the above reaction conditions affords only benzaldehyde in good yield. Selective oxidation of secondary alcohols over primary alcohols is a formidable challenge that offers a desirable alternative to the use of protecting groups, especially in the natural product’s synthesis.29−33 Having demonstrated the efficiency of DES in the oxidation of a variety of alcohols, we examined the chemoselective oxidation of secondary alcohols in the presence of primary alcohols. Excellent chemoselectivities were observed for oxidation of secondary alcohols. Parallel experiments were performed using benzyl alcohol and 1-phenylethanol using NBS as the oxidant under different reaction conditions, and the results are shown in Table 3. 1-Phenylethanol underwent selective oxidation to the corresponding acetophenone, with benzyl alcohol remaining untouched with 1 equiv of NBS at room temperature or at 60 °C (Table 3, entries 1 and 2). However, slow oxidation of benzyl alcohol was observed in DES with an excess of NBS with long reaction time (Table 3, entries 3 and 4). To further illustrate the applicability of this economical and environmental solvent, the tandem synthesis of 2-bromoacetophenone from secondary alcohols under optimized conditions was studied. DES promoted the facile conversion of 1phenylethanol to the corresponding 2-bromoacetophenone using 3 equiv of NBS with 68% isolated yield within 1 h (Scheme 1). Finally, the efficiency of urea/choline chloride-based DES, compared to data reported in the literature for oxidation of alcohols with NBS, is collected in Table 4 in the SI. It was found that DES is an efficient and green reaction medium compared to the reported procedure with respect to the time and yield of the product in the absence of catalysts and additives without overoxidation to carboxylic acids. The mechanism of NBS oxidation of alcohols in DES has been suggested as follows. Although NBS is a versatile oxidizing agent, the exact mechanism of oxidation has not yet been established. It is supposed that the considerably enhanced reaction rates could possibly be due to increased polarization of the N−Br bond in the more polar DES.22,34 Another activation of DES, with the Lewis basic oxygen center of urea, can engage the reaction carried out without an additive such as a base, which is common in imidazolium-based ILs and organic solvents. We tentatively propose the mechanism of oxidation with NBS to proceed via the formation of a hypobromite intermediate that accelerated in DES, which readily loses hydrogen bromide to form the corresponding carbonyl product (Figure 1).

Table 1. Optimization of the Reaction Conditions

entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

solvent urea/choline chloride 2:1 urea/choline chloride 2:1 urea/choline chloride 2:1 urea/choline chloride 2:1 urea/choline chloride 2:1 urea/choline chloride 2:1 urea/choline chloride 2:1 urea/choline chloride 2:1 choline chloride/SnCl2 (1:2) choline chloride/ZnCl2 (1:2) choline chloride/ZnCl2/SnCl2 (1:1:1) choline chloride/LaCl3 (1:2) choline chloride/PTSA (1:1) choline chloride/glycerol(1:1) dichloromethane ethanol methanol acetonitrile water ethyl acetate without solvent

time (min)

temp (°C)

yield (%)a,b

40 120 25 5 5 5 5 5 5 5 5

25 0c 40 60 80 120 60 60 60 60 60

100 50 100 100 100 75 68d 45e 58 62 55

5 5 5 80 80 80 80 80 80 80

60 60 60 60 60 60 60 60 60 60

68 64 88 45 65 65 55 80 65 40

a

Reactions were carried out with 1-phenylethanol (1 mmol) and NBS (1 mmol) in the solvent (0.5 mL). bGC yields. cReactions were carried out at zero deg. dNCS was used as the halogen source. eNIS was used as the halogen source.

various solvents (Table 1). The reaction requires only 5 min at 60 °C (Table 1, entry 4) or 40 min at room temperature (Table 1, entry 1) in choline chloride based DES (0.5 mL) to give a quantitative yield of acetophenone. On the other hand, it has been found that other choline chloride based DESs, such as choline chloride/ZnCl2, choline chloride/SnCl2, choline chloride/ p-Toluenesulfonic acid (PTSA), and choline chloride/LaCl3 (Table 1, entries 9−13), give lower yields of products because of the side bromination reactions. However, choline chloride glycerol based DES offers good yields of the products under identical reaction condition (Table 1, entry 14). The replacement of DES with organic solvent, such as methanol, ethanol, acetonitrile, dichloromethane, and ethyl acetate, and solvent-free conditions decreased the yields significantly under optimized reaction conditions (Table 1, entries 15−21). Other commercial halogen sources such as NCS and N-iodosuccinimide (NIS) did not perform better than NBS under otherwise identical conditions. With optimized conditions in hand, the fast oxidation of a variety of activated and nonactivated alcohols, including alkyl, cyclic, and aryl alcohols with NBS in choline chloride/urea was carried out to study the scope and functional group compatibility of DES, and the results are summarized in Table 2. Under the above conditions, most primary and secondary alcohols studied were smoothly converted to the corresponding aldehydes and ketones in good-to-excellent yields and short reaction times. A wide range of benzylic primary and secondary alcohols with different steric and electronic environments gave good-to-excellent yields of the corresponding aldehydes and ketones in short reaction times. Benzylic alcohols with both 15562

dx.doi.org/10.1021/ie502019z | Ind. Eng. Chem. Res. 2014, 53, 15561−15565


Article

Table 2. Oxidation of Alcohols to Carbonyl Compounds in DES

a

Isolated yields.

Table 3. Chemoselective Oxidation of Secondary Alcohols in DES

a

GC yields. bAnalytical conditions are reported in Table 5 in the SI. 15563



Article

chemical methodologies in organic synthesis. Chem. Soc. Rev. 2013, 42, 5522−5551. (4) Abbott, A. P.; Capper, G.; Davies, D. L.; Rasheed, R. K.; Tambyrajah, V. Novel solvent properties of choline chloride/urea mixtures. Chem. Commun. 2003, 70−71. (5) Hayyan, A.; Hashim, M. A.; Mjalli, F. S.; Hayyan, M.; AlNashef, I. M. A novel phosphonium-based deep eutectic catalyst for biodiesel production from industrial low grade crude palm oil. Chem. Eng. Sci. 2013, 92, 81−89. (6) Zhang, Q.; Vigier, K. D. O.; Royer, S.; Jérôme, F. Deep eutectic solvents: syntheses, properties and applications. Chem. Soc. Rev. 2012, 41, 7108−7146. (7) Hayyan, A.; Hashim, M. A.; Hayyan, M.; Mjalli, F. S.; AlNashef, I. M. A novel ammonium based eutectic solvent for the treatment of free fatty acid and synthesis of biodiesel fuel. Ind. Crops Prod. 2013, 46, 392−398. (8) Phadtare, S. B.; Shankarling, G. S. Halogenation reactions in biodegradable solvent: Efficient bromination of substituted 1-aminoanthra-9,10-quinone in deep eutectic solvent (choline chloride: urea). Green Chem. 2010, 12, 458−462. (9) Huang, W.; Tang, S.; Zhao, H.; Tian, S. Activation of Commercial CaO for Biodiesel Production from Rapeseed Oil Using a Novel Deep Eutectic Solvent. Ind. Eng. Chem. Res. 2013, 52, 11943− 11947. (10) Liu, T.; Li, S.; Zhou, R.; Jia, D.; Tian, S. Solubility of Triphenylmethyl Chloride and Triphenyltin Chloride in Supercritical Carbon Dioxide. J. Chem. Eng. Data 2009, 54, 1913−1915. (11) Paiva, A.; Craveiro, R.; Aroso, I.; Martins, M.; Reis, R. L.; Duarte, A. R. C. Natural Deep Eutectic SolventsSolvents for the 21st Century. ACS Sustainable Chem. Eng. 2014, 2, 1063−1071. (12) Abbott, A. P.; Boothby, D.; Capper, G.; Davies, D. L.; Rasheed, R. K. Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids. J. Am. Chem. Soc. 2004, 126, 9142−9147. (13) Gutiérrez, M. C.; Rubio, F.; del Monte, F. Resorcinol− Formaldehyde Polycondensation in Deep Eutectic Solvents for the Preparation of Carbons and Carbon−Carbon Nanotube Composites. Chem. Mater. 2010, 22, 2711−2719. (14) Carriazo, D.; Serrano, M. C.; Gutierrez, M. C.; Ferrer, M. L.; del Monte, F. Deep Eutectic Solvents Playing Multiple Roles in the Synthesis of Polymers and Related Materials. Chem. Soc. Rev. 2012, 41, 4996−5014. (15) Gutierrez, M. C.; Ferrer, M. L.; Yuste, L.; Rojo, F.; del Monte, F. Bacteria Incorporation in Deep Eutectic Solvents via Freeze-Drying. Angew. Chem. 2010, 49, 2158−2162. (16) Saadat Ghareh Bagh, F.; Mjalli, F. S.; Ali Hashim, M.; Hadj-Kali, M. K. O.; AlNashef, I. M. Solubility of Sodium Salts in AmmoniumBased Deep Eutectic Solvents. J. Chem. Eng. Data 2013, 58, 2154− 2162. (17) White, R. J.; Luque, R.; Budarin, V. L.; Clark, J. H.; Macquarrie, D. J. Supported metal nanoparticles on porous materials. Methods and applications. Chem. Soc. Rev. 2009, 38, 481−494. (18) Rajabi, F.; Pineda, A.; Naserian, S.; Mariana Balu, A.; Luque, R.; Romero, A. A. Aqueous oxidation of alcohols catalysed by recoverable iron oxide nanoparticles supported on aluminosilicates. Green Chem. 2013, 15, 1232−1237. (19) Zhu, Y.; Zhao, B.; Shi, Y. Highly Efficient Cu(I)-Catalyzed Oxidation of Alcohols to Ketones and Aldehydes with Diaziridinone. Org. Lett. 2013, 15, 992−995. (20) Wang, X.; Zhang, B.; Wang, D. Z. Reductive and TransitionMetal-Free: Oxidation of Secondary Alcohols by Sodium Hydride. J. Am. Chem. Soc. 2010, 132, 890−890. (21) De Luca, L.; Giacomelli, G.; Porcheddu, A. A Very Mild and Chemoselective Oxidation of Alcohols to Carbonyl Compounds. Org. Lett. 2001, 3, 3041−3043. (22) Bhushan Tripathi, C.; Mukherjee, S. Lewis Base Catalysis by Thiourea: N-Bromosuccinimide-Mediated Oxidation of Alcohols. J. Org. Chem. 2012, 77, 1592−1598.

Scheme 1. Direct Conversion of Alcohol to Bromoacetophenone

Figure 1. Proposed reaction mechanism.22,34

4. CONCLUSION In this work, for the first time, urea/choline chloride-based DES was used to a straightforward and green catalyst and reaction medium for selective oxidation of various alcohols using NBS under mild reaction conditions. A broad range of aliphatic alcohols were tolerated in this method with good-to-excellent yields and short reaction times. Because of the mild reaction conditions, selective oxidation of secondary alcohols in the presence of primary alcohols was also possible. In addition, the catalyst-free synthesis of 2-bromoacetophenone was achieved through DES-mediated tandem oxidation and bromination of alcohol.

■

ASSOCIATED CONTENT

S Supporting Information *

Experimental procedures, product characterization, and 1H NMR, FTIR, and GC spectra of relevant compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■ ■

ACKNOWLEDGMENTS Financial support of this work by the Chemistry and Chemical Engineering Research Center of Iran is greatly appreciated. REFERENCES

(1) Welton, T. Room-Temperature Ionic Liquids. Solvents for Synthesis and Catalysis. Chem. Rev. 1999, 99, 2071−2084. (2) Sheldon, R. A. Fundamentals of green chemistry: efficiency in reaction design. Chem. Soc. Rev. 2012, 41, 1437−1451. (3) Gawande, M. B.; Bonifácio, V. D. B.; Luque, R.; Branco, P. S.; Varma, R. S. Benign by design: catalyst-free in-water, on-water green 15564



Article

(23) Fan, J.-C.; Shang, Z.-C.; Liang, J.; Liu, X.-H.; Liu, Y. J. The oxidation of alcohols to aldehydes and ketones with N-bromosuccinimide in polyethylene glycol: an experimental and theoretical study. Phys. Org. Chem. 2008, 21, 945−953. (24) Krishnaveni, N. S.; Surendra, K.; Rao, K. R. A Simple and Highly Selective Biomimetic Oxidation of Alcohols and Epoxides with N-Bromosuccinimide in the Presence of β-Cyclodextrin in Water. Adv. Synth. Catal. 2004, 346, 346−350. (25) Einhorn, J.; Einhorn, C.; Ratajczak, F.; Pierre, J. L. Efficient and Highly Selective Oxidation of Primary Alcohols to Aldehydes by NChlorosuccinimide Mediated by Oxoammonium Salts. J. Org. Chem. 1996, 61, 7452−7454. (26) Azizi, N.; Batebi, E. Highly efficient deep eutectic solvent catalyzed ring opening of epoxides. Catal. Sci. Technol. 2012, 2, 2445− 2448. (27) Azizi, N.; Batebi, E.; Bagherpour, S.; Ghafuri, H. Natural deep eutectic salt promoted regioselective reduction of epoxides and carbonyl compounds. RSC Adv. 2012, 2, 2289−2293. (28) Azizi, N.; Yadollahy, Z.; Rahimzadeh-Oskooee, A. An atomeconomic and odorless thia-Michael addition in a deep eutectic solvent. Tetrahedron Lett. 2014, 55, 1722−1725. (29) Lenze, M.; Bauer, E. B. Chemoselective, iron(II)-catalyzed oxidation of a variety of secondary alcohols over primary alcohols utilizing H2O2 as the oxidant. Chem. Commun. 2013, 49, 5889−5891. (30) Arterburn, J. B. Selective oxidation of secondary alcohols. Tetrahedron 2001, 57, 9765−9788. (31) Davis, S. E.; Ide, M. S.; Davis, R. J. Selective oxidation of alcohols and aldehydes over supported metal nanoparticles. Green Chem. 2013, 15, 17−45. (32) Qian, W.; Jin, E.; Bao, W.; Zhang, Y. Clean and Highly Selective Oxidation of Alcohols in an Ionic Liquid by Using an Ion-Supported Hypervalent Iodine(III) Reagent. Angew. Chem., Int. Ed. 2005, 44, 952−955. (33) Liu, C.; Tang, S.; Lei, A. Oxidant controlled Pd-catalysed selective oxidation of primary alcohols. Chem. Commun. 2013, 49, 1324−1326. (34) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G. Halogen Bonding in Supramolecular Chemistry. Angew. Chem., Int. Ed. 2008, 47, 6114−6127.

15565


Rapid and Selective Oxidation of Alcohols in Deep Eutectic Solvent

Recommend Documents