An Energy Efficient Sonochemical Selective Oxidation of Benzyl

Research Note pubs.acs.org/IECR

An Energy Efficient Sonochemical Selective Oxidation of Benzyl Alcohols to Benzaldehydes by Using Bio-TSIL Choline Peroxydisulfate Balu L. Gadilohar,† Dipak V. Pinjari,*,‡ and Ganapati S. Shankarling*,† †

Department of Dyestuff Technology, and ‡Department of Chemical Engineering, Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai, 400 019, India S Supporting Information *

ABSTRACT: The present work deals with effective combination of ultrasonication (US) and biodegradable oxidizing task specific ionic liquid (bio-TSIL) choline peroxydisulfate monohydrate (ChPS·H2O) for the selective oxidation of alcohols to aldehydes/ketones. The reactions were also conducted by using a thermal heating method (TH), and the comparative studies are provided to understand the effectiveness of the ultrasound process; it was observed that the use of ultrasound significantly reduces the reaction time from 30 to 5 min. Also, a substantial energy saving (>86%) was observed when the US method (0.125 kJ/g) was compared with the TH method (0.958 kJ/g). Bio-TSIL ChPS in water as an oxidant is found to be advantageous, as it is synthesized from biodegradable and nontoxic raw materials. Incorporation of an ultrasonic energy source along with the use of biodegradable raw materials for bio-TSIL makes the process not only green but also energy efficient.

1. INTRODUCTION Development of organic reactions in environmental friendly media with high energy efficiency and process safety are the current challenges in the chemical research community and industry. Energy conservation is one of the most ignored of the 12 principles of green chemistry.1 To develop environmentally benign chemical reactions, it is necessary that any process in addition to being high yielding and facile, should consume minimum energy, preferably from renewable sources.2 Ultrasonic energy3 has already proved its usefulness as a reaction aid which promotes organic transformations.4−6 Sonochemical energy delivery has been used as an excellent alternative to thermal energy in promoting organic reactions, especially those requiring harsh conditions in terms of pressure and temperature. The use of ultrasound has also been known to improve the rate of reaction and yield, thereby saving tremendous amounts of energy required for synthetic purpose.7 The source of this energy lies in the cavitation phenomenon that includes sequential formation, growth, and collapse of several millions of microscopic vapor bubbles (voids) in the liquid.8,9 Earlier, we have also reported the use of ultrasound (US) in energy efficient chalcone synthesis10 and oxazole synthesis.11 Selective oxidation of benzyl alcohols to benzaldehyde derivatives is an important facet in industrial production of pharmaceuticals, pesticides, and perfumery-flavoring agents as its derivatives are widely used in the manufacture of pharmaceuticals,12,13 pesticides (dibenzoquat), dyes (triphenylmethane green), perfumes and flavoring agents14 (cinnamalde© XXXX American Chemical Society

hyde, amyl cinnamaldehyde, hexyl cinnamaldehyde), and fireproof structural foam (phenol benzaldehyde resins).15 Thus, oxidation is an important reaction, and so discovering a new oxidizing agent is always necessary. Traditional reagents contains metals, such as Cr(VI), Mn(VII) and halogen derivatives, namely, O-iodoxybenzoic acid,16 IBX-tetrabutylammonium bromide17 have been introduced as oxidizing agents, but these are expensive, hazardous, and generate large quantities of heavy metal wastes which are environmentally detrimental. Ionic liquids18 (ILs) and deep eutectic solvents (DESs)19 are the key classes of green media which have gained vast attention over the past few years in chemistry as environmentally friendly or “green” alternatives to conventional molecular solvent systems. DESs exhibit similar physicochemical properties as that of traditionally used ILs. DESs can be achieved by simply mixing two or more inexpensive and safe components (renewable and biodegradable), which are capable of forming a eutectic mixture. DESs are generally liquid at temperatures lower than 100 °C. Many ILs are hazardous environmental contaminants,20,21 and a number of results22,23 documenting the toxicity of ILs to the aquatic ecosystem highlight a real cause for concern. Therefore, it is desired to develop alternate Received: February 23, 2016 Revised: March 31, 2016 Accepted: April 14, 2016

A

DOI: 10.1021/acs.iecr.6b00731 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

diameter of stainless steel tip of horn, 1.3 × 10−2 m; surface area of ultrasound irradiating face, 1.32 × 10−4 m2; intensity, 3.4 × 105 W/m2. 2.2. Experimental Setup for US Method. Ultrasound for sonochemical synthesis is generated with the help of ultrasonic instrument setup (horn type). The animated representation of the setup is given in Figure 2, which consists of generator, transducer, and ultrasonic probe with temperature controller.

ILs from components which are inexpensive, nontoxic toward the environment, and biodegradable to overcome these drawbacks. Their success as environmentally benign solvents or catalysts is described in numerous reactions, such as Diels− Alder,24 Friedel−Crafts,25,26 esterification27,28 and so on. In the case of ILs synthesis, the selection of the cation has influence on the physicochemical properties and will often define it is stability. The chemistry and functionality of the IL is controlled by the choice of the anion, so the polarity of an IL can be tuned by a suitable choice of cation/anion using metathesis or an ion exchange reaction. In continuation to the development of green solvents and an energy efficient organic process in organic synthesis29−32 we began to explore the oxidizing activity of the recently reported environmentally friendly biodegradable oxidizing task specific ionic liquid (TSIL) choline persulfate (ChPS)29 (Figure 1);

Figure 1. Structure of bio-TSIL ChPS. Figure 2. Experimental setup of oxidation using ultrasonic probe (US method).

specifically its use in ultrasonically assisted energy efficient selective oxidation of primary and secondary alcohols to the corresponding carbonyl compounds, without further oxidation to acids, with good to excellent yields. The ultrasonic energy has been applied for the oxidation of alcohols using ChPS as a bio-oxidizing TSIL. Energy calculations of the US method for the oxidation of alcohols show that the US method is more efficient as compared to the conventional thermal heating (TH) method (Scheme 1).

2.3. Procedure for Choline Peroxydisulfate (ChPS) Synthesis. {2-Hydroxy-N,N,N-Trimethyl Ethanaminium Peroxydisulfate [NMe3CH2CH2OH] 2[S2O8]}. ChPS was prepared as discussed in the previous research paper.29 Choline peroxydisulfate (ChPS·H2O) was synthesized by the metathesis/ion exchange reaction of the choline chloride (2 mol) with potassium peroxydisulfate (1 mol) in 100 mL of acetone stirring at room temperature (RT). The byproduct, KCl, is insoluble in acetone and spontaneously separated from the reaction system as a precipitate, which also promoted the formation of a yellow color viscous liquid. The mixture was further dried under a high vacuum for 4−5 h and stored at 0−5 °C. The yield was 88%. 2.4. Oxidation of alcohols using ChPS in neat condition under conventional (TH) method. Oxidation of benzyl alcohols using ChPS·H2O under conventional (TH) method was discussed in the previous research paper.29 In a 25 mL round-bottom flask (RBF), mixture of benzyl alcohol (0.01 mol) and choline peroxydisulfate (0.02 mol) were charged at room temperature (RT). The reaction mixture was heated at 70 °C for 30 min. The completion of the reaction was monitored by TLC using 10% ethyl acetate in hexane as eluent. After completion of the reaction, the mixture was cooled and extracted with ethyl acetate and the TSIL layer was separated as thick liquid settled at bottom. The ethyl acetate layer was washed with water, dried (anhyd. Na2SO4), and concentrated. It was purified by column chromatography (silica gel, hexane/ ethyl acetate, 9:1) to give the corresponding pure aldehydes and ketones. 2.5. Oxidation of Alcohols Using ChPS·H2O under Sonochemical (US) Method. In a 10 mL beaker (placed in jacketed reaction flask) a mixture of benzyl alcohol (0.01 mol) and choline peroxydisulfate monohydrate (0.02 mol) was charged at room temperature (RT) in water (5 mL). Reaction was monitored under sonication using an ultrasonic horn (ACE horn, 22 kHz frequency) at 40% amplitude for 5 min with a 5 s ON and 5 s OFF cycle from time t = 0 h. The temperature of the process was maintained at 35 ± 2 °C by means of supplying

Scheme 1. Oxidation of Alcohols Using ChPS·H2O under Ultrasound Conditions

2. EXPERIMENTAL SECTION 2.1. Materials. Choline chloride, potassium peroxydisulfate, and benzyl alcohol derivatives were procured from M/s. S. D. Fine Chemical Ltd. Mumbai (India). Reagents were used without further purification. All organic solvents were obtained from commercial sources and were distilled prior to use. All melting points/boiling points are measured by melting point apparatus M/s. Sundar Industrial Products, Mumbai (India), and are uncorrected and presented in degrees Celsius. IR spectra were recorded on a JASCO-FT/IR-4100 LE with attenuated total reflection (ATR) method. 1H and 13C NMR spectra were recorded on a Varian 400 MHz mercury plus spectrometer, and chemical shifts are expressed in δ ppm using TMS as an internal standard. The specification and details of the ultrasonic setup and processing parameters used during the experiments are as follows: make, Vibra Cell, Sonics, USA; operating frequency, 20 kHz; rated output power, 750 W; B


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water was selected as a model reaction (Scheme 1). The reaction was found to be complete (yield 90%) in 0.5 h thermally in water at 70 °C (Table 2, entry 3). We also tried

water to the beaker used for the synthesis. The reaction progress was monitored by using thin layer chromatography (TLC). After 5 min of completion of reaction, the mixture was cooled and extracted with ethyl acetate and the TSIL layer was separated as a thick liquid at bottom of the flask. The ethyl acetate layer was washed with water, dried (anhyd. Na2SO4), and concentrated. It was purified by column chromatography (silica gel, hexane/ethyl acetate, 9:1) to give the corresponding pure aldehydes and ketones. 2.6. Selected Spectral Data. Benzaldehyde (Table 3, entry 1). 1H NMR (CDCl3, 400 MHz) δ/ppm: 7.46−7.54 (2H, m, aromatic H), 7.60−7.64 (1H, m, aromatic H), 7.85−7.88 (2H, m, aromatic H), 10.0 (1H, s, CHO). GC−MS (EI, 70 eV) m/z (%): 106 (M+, 85), 105 (100), 77 (54). 4-Chlorobenzaldehyde (Table 3, entry 4). 1H NMR (CDCl3, 400 MHz) δ/ppm: 7.59−7.65 (2H, m, aromatic H), 7.70−7.72 (2H, m, aromatic H), 9.94 (1H, s, CHO). GC−MS (EI, 70 eV) m/z (%): 140 (M+, 87), 139 (100), 111 (58), 75 (40). Acetophenone (Table 3, entry 6). 1H NMR (CDCl3, 400 MHz) δ/ppm: 2.58 (3H, s, CH3CO), 7.42−7.46 (2H, m, aromatic H), 7.52−7.56 (1H, m, aromatic H), 7.92−7.95 (2H, m, aromatic H). GC−MS (EI, 70 eV) m/z (%): 120 (M+, 32), 105 (100), 77 (73). Benzophenone (Table 3, entry 12). 1H NMR (CDCl3, 400 MHz) δ/ppm 7.45−7.48 (4H, m, aromatic H), 7.55−7.59 (2H, m, aromatic H), 7.78−7.80 (4H, m, aromatic H). GC−MS (EI, 70 eV) m/z (%): 182 (M+, 52), 105 (100), 77 (68), 51 (23).

Table 2. Optimization of Reaction Parameters for Oxidation of Benzyl Alcohol Using ChPS·H2O by the TH or US Method entry 1. 2. 3. 4. 5. 6. 7.

1. 2. 3. 4. 5. 6. a

ultrasound bath ultrasound bath ultrasound bath ultrasound bath ultrasound bath ultrasonic probe

time (min)

yield (%)

H2O2, Fe(DS)3, 90 °C

360

100

33

graphite oxide (200 wt %), toluene, 80 °C NaOCl (20 equiv), acetonitrile KMnO4, CuSO4·5H2O, dichloromethane, RT FeCl3/HNO3, acetone, RT

120

98

34

120

22a

35

60

81

36

10

94

37

5

97

this work

catalyst/reagent, condition

ChPS·H2O, water, RT

reaction condition

temp (°C)

yield (%)a

water water water

THb THb TH

70 70 70

25 54 90

neat

TH

70

93

water water water

US US US

RT RT RT

40 65 97

Isolated yields. bSeveral hours heating; reaction conditions: TH (thermal method); benzyl alcohol (0.01 mol), oxidizing agent (0.02 mol), water (5 mL), reaction time = 30 min. Reaction conditions: US (ultrasound method), benzyl alcohol (0.01 mol), oxidizing agent (0.02 mol), water (5 mL), reaction time = 5 min.

sonochemical synthesis by oxidation using ChPS·H2O in water as a solvent. The reaction was found to be complete (yield 97%) in 5 min in water as solvent (ultrasonically assisted) at RT. (Table 2, entry 7). The possible reason for completion of the reaction in less than 5 min may be due to the collapse cavities in the water medium, the free radicals generation rate has been enhanced thus effectively enhancing the overall reaction rate. The use of water as solvent in ultrasonic method enhances the yield of the reaction as compared to neat condition because of the viscosity of medium. To check the effect of other metal peroxydisulfates, we carried out reactions thermally and ultrasonically using potassium persulfate (KPS) and ammonium persulfate (APS) based oxidizing agents. Very low yields (25% and 54%) were obtained even after heating and refluxing the reaction mixture for several hours in water using metal peroxydisulfate (Table 2, entries 1, 2), while ultrasonically, 40% and 65%, respectively, were obtained (Table 2, entries 5, 6). Bio-TSIL ChPS·H2O was found to be the most effective among all the reagents employed for the reaction (Table 2, entries 3, 4, 7). Thus, the results obtained, demonstrate the usefulness of the combinative technique of using ultrasound and bio-TSIL ChPS·H2O. Also because of its green character and easy separation from the reaction media, it represents a convenient and environmentally friendly alternative to the traditional oxidants. Thus, the results obtained, demonstrate the effectiveness of the choline peroxydisulfate over other metal peroxydisulfates in the US method. After completion of the reaction, ChPS·H2O will dissociate as a cholinium (NMe3CH2CH2OH)+ and bisulfate/hydrogen sulfate (HSO4−) or sulfate (SO4−2) ion, and it is expected not to accumulate in the soil leading to any environmental hazards. But in the case of use of other metal oxidants or halogenated oxidants, generation of large amounts of residual effluents subsequently leads to its treatment to minimize their environmental impact, whereas it is totally avoided in the case of ChPS·H2O. Thus, the use of novel choline based

Table 1. A Comparative Overview of Previous Work for the Oxidation of Benzyl Alcohols Using Ultrasound with Current Work method

KPS (2 equiv) APS (2 equiv) ChPS·H2O (2 equiv) ChPS·H2O (2 equiv) KPS (2 equiv) APS (2 equiv) ChPS·H2O (2 equiv)

solvent

a

3. RESULTS AND DISCUSSIONS 3.1. Study of Significance of bio-TSIL ChPS in Oxidation of Benzyl Alcohol by Thermal (TH) and Ultrasound (US) Method. Previous results, which are tabulated in Table 1, show the use of ultrasound waves which

entry no.

oxidizing agent

ref

Starting material is benzyl chloride.

require a longer time (10 to 360 min) and use of expensive catalyst (FeDS3, graphite oxide, KMnO4, CuSO4, FeCl3, HNO3)33−37 and solvents (toluene, dichloromethane, acetonitrile, acetone) for the oxidation of benzyl alcohols to aldehydes (Table 1, entry 1−5). On the other hand in this work using an ultrasonic probe the reaction time is reduced drastically, with high yields in water as solvent using bio-TSIL ChPS·H2O (Table 1, entry 6). To optimize the reaction parameters, the reaction of benzyl alcohol (0.01 mol) in the presence of ChPS·H2O (0.02 mol) in C


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Industrial & Engineering Chemistry Research oxidizing TSIL along with ultrasound method can be the best alternative for oxidation of alcohols which occur thermally. 3.2. Energy Efficacy of ChPS in TH, US Methods. Energy efficiency has been calculated and compared using ChPS·H2O in the conventional (TH) and ultrasound (US) methods. The methods for energy calculation have been reported by Jarag et al.10 Appendix A (see Supporting Information) shows the calculation of the energy of the two methods: conventional (TH) and ultrasound (US) method used for oxidation of benzyl alcohol. The data for energy utilization in kJ/g during reaction is depicted in (Figure 3).

Table 3. Oxidation of Benzyl Alcohols in the Presence of ChPS Using the US Methoda

Figure 3. Yield (%) and energy (kJ/g) comparison of ChPS·H2O using conventional (TH) and ultrasound (US) methods. a

Reaction conditions: US (ultrasound method); aryl alcohol (0.01 mol), ChPS (0.02 mol), water (5 mL), time 5 min, temp = RT. b Isolated yields. cSigma-Aldrich.

The energy utilized for the oxidation of benzyl alcohol is the total energy supplied (kJ) per unit weight of the material processed/obtained (g). The reaction time of benzyl alcohol oxidation was 30 min for the TH method and 5 min for the US method. Total energy required per unit weight of the material processed to synthesize benzaldehyde is 0.958 kJ/g for the TH method and 0.125 kJ/g for the US method. It was observed that the US method saved more than 86% energy as compared to the TH method as shown in (Figure 3). 3.3. Derivative Studies and Energy Calculations. Table 3 shows the synthesis and energy calculations of various aldehydes and ketones using number of various substrates of aromatic alcohols under US method. Most alcohols underwent oxidation to afford the corresponding aldehydes or ketones in good to excellent yield using ChPS·H2O by ultrasound system. The following data are indicative of the merit of using the US method. The reaction of primary alcohols (Table 3, entries 1− 5) and secondary alcohols (Table 3, entries 6−12) was completed and provided yields from 88% to 93% in the TH method,29 while it was 90% to 97% in the US method in a shorter reaction time (shortened from 30 to 5 min). Benzylic alcohols underwent smooth oxidation; no noticeable overoxidation of aldehydes to carboxylic acids was detected. The ultrasound method was found to be energy efficient, and the energy requirement found for 12 derivatives of benzyl alcohols was from 0.1134 kJ/g to 0.1681 kJ/g. However, such calculations are reported for the first time in the bio-TSIL− US blended method. The data for energy utilization in kJ/g during the reaction for all the derivatives is depicted in Table 3 as per the energy calculations specified in Appendix A (see Supporting Information). It was observed that the ultrasound (US)

method saved more than 86% energy with much reduced reaction time compared to the conventional (TH) method.

4. PLAUSIBLE MECHANISM FOR OXIDANT ACTIVITY OF CHPS·H2O TSIL The influence of ultrasound on the reactivity of ChPS·H2O is not clear; however, we think that hydrogen bonding of choline cation of ChPS·H2O with the alcohol and excitation of persulfate to more powerful sulfate anion radical (SO4−•) under ultrasound accelerates the oxidation process. The reaction mechanism of the oxidation using a ChPS·H2O involved a decomposition of ChPS·H2O to choline bisulfate ([Ch]+HSO4−) under ultrasonic waves in the presence of water via sulfate anion radical (SO4−•) and hydroxyl radical (•OH) formation38,39 to give oxygen. Alcohols reacted with in situ generated oxygen from ChPS·H2O in aqueous condition at RT in US to form aldehydes (Scheme 2). It is recognizable that the use of ultrasound leads to the generation of microscopic internal pressure within the cavitation bubbles, which causes extreme microscopic conditions within these bubbles such that substrates entering them are converted to highly reactive species (persulfate to •OH radical),40,41 thereby supporting a faster oxidation reaction. Such postulation has also been done in earlier reports wherein ultrasound is used to accelerate reactions in ionic liquids.42,43 5. CONCLUSIONS The blending of bio-TSIL ChPS·H2O with ultrasound energy facilitated the oxidation of aryl alcohols with less reaction time D


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(5) Tabassum, S.; Govindaraju, S.; Khan, R.-R.; Pasha, M. A. Ultrasound Mediated, Iodine Catalyzed Green Synthesis of Novel 2Amino-3-Cyano-4H-Pyran Derivatives. Ultrason. Sonochem. 2015, 24, 1. (6) Chen, B.-H.; Li, J.-T.; Chen, G.-F. Efficient Synthesis of 2,3Disubstituted-2,3-Dihydroquinazolin-4(1H)-Ones Catalyzed by Dodecylbenzenesulfonic Acid in Aqueous Media under Ultrasound Irradiation. Ultrason. Sonochem. 2015, 23, 59. (7) Mason, T. J. Ultrasound in Synthetic Organic Chemistry. Chem. Soc. Rev. 1997, 26 (6), 443. (8) Mahulkar, A. V.; Riedel, C.; Gogate, P. R.; Neis, U.; Pandit, A. B. Effect of Dissolved Gas on Efficacy of Sonochemical Reactors for Microbial Cell Disruption: Experimental and Numerical Analysis. Ultrason. Sonochem. 2009, 16 (5), 635. (9) Moholkar, V. S.; Sable, S. P.; Pandit, A. B. Mapping the Cavitation Intensity in an Ultrasonic Bath Using the Acoustic Emission. AIChE J. 2000, 46 (4), 684. (10) Jarag, K. J.; Pinjari, D. V.; Pandit, A. B.; Shankarling, G. S. Synthesis of Chalcone (3-(4-Fluorophenyl)-1-(4-Methoxyphenyl)prop-2-En-1-One): Advantage of Sonochemical Method over Conventional Method. Ultrason. Sonochem. 2011, 18 (2), 617. (11) Singh, B. S.; Lobo, H. R.; Pinjari, D. V.; Jarag, K. J.; Pandit, A. B.; Shankarling, G. S. Ultrasound and Deep Eutectic Solvent (DES): A Novel Blend of Techniques for Rapid and Energy Efficient Synthesis of Oxazoles. Ultrason. Sonochem. 2013, 20 (1), 287. (12) Popp, F. D. Synthesis of Potential Anticancer Agents. VIII. Benzaldehyde Mustard Derivatives and Related Compounds. J. Med. Pharm. Chem. 1962, 5 (3), 627. (13) Choudhary, V. R.; Dumbre, D. K.; Narkhede, V. S.; Jana, S. K. Solvent-Free Selective Oxidation of Benzyl Alcohol and Benzaldehyde by Tert-Butyl Hydroperoxide Using MnO- 4-Exchanged Mg−Al− Hydrotalcite Catalysts. Catal. Lett. 2003, 86 (4), 229. (14) Ajaikumar, S.; Pandurangan, A. Reaction of Benzaldehyde with Various Aliphatic Glycols in the Presence of Hydrophobic Al-MCM41: A Convenient Synthesis of Cyclic Acetals. J. Mol. Catal. A: Chem. 2008, 290 (1−2), 35. (15) Backvall, J. E. Modern Oxidation Methods; Wiley-VCH: Weinheim, Germany, 2004. (16) Duschek, A.; Kirsch, S. F. 2-Iodoxybenzoic AcidA Simple Oxidant with a Dazzling Array of Potential Applications. Angew. Chem., Int. Ed. 2011, 50 (7), 1524. (17) Shukla, V. G.; Salgaonkar, P. D.; Akamanchi, K. G. A Mild, Chemoselective Oxidation of Sulfides to Sulfoxides Using OIodoxybenzoic Acid and Tetraethylammonium Bromide as Catalyst. J. Org. Chem. 2003, 68 (13), 5422. (18) Wasserscheid, P.; Welton, T. Ionic Liquids in Synthesis, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2007. (19) Zhang, Q.; De Oliveira Vigier, K.; Royer, S.; Jerome, F. Deep Eutectic Solvents: Syntheses, Properties and Applications. Chem. Soc. Rev. 2012, 41 (21), 7108. (20) Stolte, S.; Bottin-weber, U.; Matzke, M.; Stock, F.; Thiele, K.; Uerdingen, M.; Welz-biermann, U.; Ranke, J. Anion Effects on the Cytotoxicity of Ionic Liquids. Green Chem. 2006, 8, 621. (21) Ranke, J.; Mölter, K.; Stock, F.; Bottin-Weber, U.; Poczobutt, J.; Hoffmann, J.; Ondruschka, B.; Filser, J.; Jastorff, B. Biological Effects of Imidazolium Ionic Liquids with Varying Chain Lengths in Acute Vibrio Fischeri and WST-1 Cell Viability Assays. Ecotoxicol. Environ. Saf. 2004, 58 (3), 396. (22) Thuy Pham, T. P.; Cho, C. W.; Yun, Y. S. Environmental Fate and Toxicity of Ionic Liquids: A Review. Water Res. 2010, 44 (2), 352. (23) Docherty, K. M.; Kulpa, C. F., Jr. Toxicity and Antimicrobial Activity of Imidazolium and Pyridinium Ionic Liquids. Green Chem. 2005, 7 (4), 185. (24) Fischer, T.; Sethi, A.; Welton, T.; Woolf, J. Diels-Alder Reactions in Room-Temperature Ionic Liquids. Tetrahedron Lett. 1999, 40 (4), 793. (25) Earle, M. J.; Seddon, K. R.; Adams, C. J.; Roberts, G. FriedelCrafts Reactions in Room Temperature Ionic Liquids. Chem. Commun. 1998, 19, 2097.

Scheme 2. A Plausible Oxidation Reaction Mechanism Using Bio-TSIL ChPS·H2O

at RT accompanied by high to excellent yield. Bio-TSIL ChPS· H2O is synthesized from simple and cost-effective raw materials that are biodegradable. Energy utilized for the ultrasound method was found to be much lower than the thermal method for oxidation. Use of ultrasound for the oxidation of alcohols using environmentally benign and cost-effective TSIL makes the process greener, safer, and energy efficient (more than 86% energy saving) and shortens the reaction time (from 30 to 5 min) as compared to the thermal method. Thus, from the viewpoint of greener chemical processes, a combination of bioTSIL ChPS·H2O and ultrasound for oxidation makes it more attractive and ecofriendly as well as time and energy-saving with extreme efficiency.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b00731. Detailed energy calculations (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS B.L.G. is thankful to DST under INSPIRE Fellowship for providing financial support and to SAIF IIT Bombay for recording 1H-NMR and mass spectra.

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REFERENCES

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An Energy Efficient Sonochemical Selective Oxidation of Benzyl

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