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. 2020 Mar 25;5(13):7716–7721. doi: 10.1021/acsomega.0c00774

Sustainable and Efficient Route for the Regeneration of Carbonyl Compounds from Oximes Using Aqueous Extract of Sapindus laurifolia under Microwave Radiation

Debadutta Das †,*, Ranjan K Mohapatra ‡, Pankaj K Parhi §,∥, Ashish K Sarangi ∇, Raghaba Sahu ⊥, Soumya R Barik #
PMCID: PMC7144141  PMID: 32280915

Abstract

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The synthesis of organic compounds using aqueous medium has become an indispensable tool for modern chemical synthesis strategies because of its ability to produce pure products with higher yield at ambient temperature. The conversion of oxime group into carbonyl group serves as a key step for several organic syntheses. This article describes the regeneration of carbonyl compounds from the oxime group present in various carbon skeletons using I2 and aqueous extract of Sapindus laurifolia under microwave radiation. A correlation has been established between the critical micellar concentration of saponin extracted from Sapindous laurifolia and the yield percentage of regenerated different carbonyl compounds. An effortless, competent, and environmentally compassionate protocol for the regeneration of carbonyl compound with a high percent of yield in the range 45–95% could be achieved.

1. Introduction

Nowadays, a large amount of toxic materials are being produced due to the indiscriminate use of chemicals in different industries and chemical laboratories. These materials are causing serious health and environmental hazards thereby threatening living beings present in the ecosystem. The development of eco-friendly, pollution-free, and less cost-effective chemical methodology is therefore of dire need today for the sustainability of the biosystem. The sustainable methodology primarily means the involvement of green solvents,1 which in turn conserves the environment. Water is a nontoxic, nonflammable, inexpensive, benign, and abundantly available solvent. Therefore, considerable attentions are now being paid to organic reactions conducted in aqueous media.2−4 Many of the organic reactions like deoxygenation of nitrones to corresponding imines and oximes to nitriles have been carried out in hydrated media.5 Gogoi et al. reported the selective oxidation of alcohols and deprotonation of oximes and imines to carbonyl compounds in aqueous media.4,6 Surfactant aggregates have been found to be suitable biphase systems for carrying out a large number of reactions,7−9 and a substantial increase in the yield of products has been reported.

Oxime derivatives serve as an important synthetic intermediate in multistep organic synthesis10 as they are frequently used for the purification and protection of carbonyl compounds. Some reported methods are useful for the regeneration of carbonyl compounds from oximes, which are produced at nonactivated hydrocarbon sites.11 The literature enumerates a considerable number of methods in hydrolytic oxidative and reductive ways for the conversion of oximes into carbonyl groups. Some of the well-known deoximating agents are N2O4,12 pyridinium chlorochromate (PCC),13tert-butyl hydroperoxide (TBHP),14 KMnO4/alumina,15 (PhSeO)2O,16 TMSCl/NaNO2,17 Raney nickel,18 sodium perborate/HOAc,19 NaHSO3,20 etc., and several transition-metal salts involve Tl(NO3)3,21 Cr(OAc)2,22 Mn(OAc)3,23 trimethylsilyl chlorochromate,24 BiBr3/Bi(OTf)3,25 2-nitro-4,5-dichloropyridazin-3(2H)-one,26 and Al(NO3)3·9H2O in the presence of catalytic amounts of NaBr in CH2Cl2 at room temperature.27 Furthermore, tetraethyl ammonium chlorochromate (TEACC) in dimethylsulfoxide,28 potassium permanganate–graphite,29 citric acid,30 and many other reagents31−37 have recently been reported as deoximating agents. However, most of these reagents are toxic, corrosive, and expensive and take a longer reaction time for completion. Hence, an effortless, competent, and environmentally compassionate protocol for the regeneration of carbonyl compound with a high percent of yield within a few minutes using the microwave method38 is a big challenge for researchers.

Sapindous laurifolia is one type of soap nut tree mostly available in South Asia. Saponin isolated from S. laurifolia is a complicated mixture of saccharin derivatives and belongs to a class of naturally occurring nonionic surfactants.39,40 The hydrophilic part of the molecule called glycon consists of saccharides such as glucose, galactose, rhamnose, xylose, pentose, etc., and the hydrophobic part called aglycon consists of steroids or triterpene. The hydrophobic part is bonded through oxygen to the hemiketal or hemiacetal carbon of the saccharide residue, which in turn is linked through oxygen linkages to other saccharide residues. Due to its amphiphilic nature, it can solubilize organic molecules in water. Hence, it can be a suitable replacement for many organic solvents in chemical reactions. The general structure of saponin is shown in Figure 1.

Figure 1.

Figure 1

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Structure of saponin, where R = sugar unit.

Herein, we describe a simple and neutral method by which regeneration of carbonyls proceeds efficiently with good yield and reduced reaction time under mild reaction conditions. A method using iodine (I2) and an aqueous extract of natural surface active agent S. laurifolia under microwave radiation for the regeneration of carbonyl compounds from oxime is established.

2. Results and Discussion

2.1. Effect of S. Laurifolia Concentration on the Regeneration of Carbonyl Compounds

S. laurifolia is a saponin-rich plant that consists of two parts: one part is polar sugar chain and the other part is nonpolar triterpene ring. Due to the lipophilic nature of saponin, it can solubilize the nonpolar organic molecule in aqueous medium4,41−44 (Scheme 1). The rate enhancement in the aqueous extract of S. laurifolia pods might be attributed to its surfactant property and acidic pH. The saponins, which are acidic, solubilize the reactant species strongly by hydrogen-bond formation in aqueous medium. This increases the number of favorable collisions between the reactant species.

Scheme 1. Solubilization of Oxime and I2 in Micellar Core of S. laurifolia.

Scheme 1

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It has been observed from Figure 2 that the percentage of regeneration of carbonyl compounds increases with an increase in S. laurifolia concentration up to 0.017 g/cm3, which is the critical micellar concentration. Above the critical micelle concentration (CMC), there is no appreciable increase in the percentage of regeneration of carbonyl compounds, which may be due to the formation of micelles. Thus, the solubility of reactant species oxime and iodine reaches maximum at CMC. Therefore, 0.017 g/cm3 is the optimized concentration for the regeneration of carbonyl compounds from oxime.

Figure 2.

Figure 2

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Percentage of regeneration of carbonyl compounds.

2.2. Mechanism of Reaction

The electrophilic iodine forms an iodonium ion with the carbon–nitrogen double bond, which promotes the hydration of the carbon–nitrogen double bond of oxime (Scheme 2). This proposed mechanism involves dismutation of I2. Due to the formation of micelle by saponin of aqueous S. laurifolia, nonpolar I2 molecule and oxime are solubilized in the micellar core, which is nonpolar (hydrophobic). Therefore, aqueous extracts of S. laurifolia can solubilize both the reactants oxime and iodine. The low yield of the compound 1n (Table 1) may be due to its low solubility in the micellar core. This is because of the large number of nonpolar rings in the molecule. The time duration and yield percentage are given in Table 1.

Scheme 2. Mechanism for the Conversion of Oximes into Carbonyl Compounds. (Adapted with Permission from Gogoi et al.,4 2005, American Chemical Society.).

Scheme 2

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Table 1. Deprotection of Ketoxime and Aldoxime Using Iodinea,b.

2.2.

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a

Purification by distillation.

b

Purification by column chromatography.

The basic principle behind the microwave-assisted reaction is that the solvent molecule (here water) absorbs microwave energy and transfers heat energy to the reactant present in the medium. Thus, the transfer of oximes to corresponding carbonyl compounds enhanced efficiently within a few minutes with I2 in water under microwave irradiation. The conversion of oximes into carbonyl compounds catalyzed by iodine may be represented as follows (Scheme 2).

3. Conclusions

In a nutshell, a simple, green, and cost-effective protocol for the regeneration of carbonyl compounds using I2 and aqueous extract of S. laurifolia has been demonstrated. A salient feature of this method is that aqueous extracts of S. laurifolia effectively solubilize oxime and iodine in its micellar core, which can replace common commercial surfactants such as sodium dodecyl sulfate (SDS), cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl benzene sulfonate (SDBS), etc. in organic reactions. This work reports a useful, attractive, and alternative method for the conversion of oximes into corresponding carbonyl compounds with more efficiency compared to the existing conventional method. The activation energy required for the formation of transition state is achieved quickly due to the increase in the frequency of rotation of water molecules, which in turn increases the energy content of oxime molecule.

4. Materials and Methods

4.1. Isolation of Saponin from S. laurifolia

Dry fruit of S. laurifolia (10 g) was taken, and the pericarp of the fruit was removed, dried, and powdered. This powder was suspended in the desired volume (100 mL) of water. The aliquot was subjected to agitation for a time duration of 3 h by a magnetic stirrer. Then, the supernatant solution obtained was centrifuged and filtrated to extract out the active component as saponin into the corresponding aqueous medium. This extract was utilized as solvent for the regeneration of carbonyl compound.

4.2. Surface Activity of the Aqueous Extract of S. laurifolia

The surface tension of the aqueous extract was measured by a surface tensiometer (Kyowa-350, Japan). The surface tension of pure water is 72 mN/m, and it gets saturated until a minimum value of 40 mN/m when the concentration of the surfactant reaches 0.017 g/cm3 (1.7 wt %).33 It is reported that the minimum surface tension is achieved at 0.017 g/cm3, which may be the CMC of the dispersant.39,40 This is because, above this concentration, there is no further reduction in the surface tension value.

4.3. Preparation of Oxime and Carbonyl Compound

The chemicals are from Aldrich and purified by the standard procedure whenever necessary. Triple-distilled water is used throughout the experiment. Oxime derivatives are prepared from the corresponding carbonyl compounds. The products were characterized by elemental analyses; determination of melting point, boiling point, etc.; and direct comparison of the spectral data with those of the authentic samples. Infrared (IR) spectra and 1H NMR (in deuterio solvent chloroform) spectra were recorded on a JASCO FT/IR-530 spectrophotometer and JFAL FX-90 instrument, respectively.

4.4. Method of Regeneration of Carbonyl Compound

In a typical procedure, oxime derivatives (1 mmol) iodine (1.5 mmol) and S. laurifolia extract (5 mL) were taken in an Erlenmeyer flask and placed inside a microwave oven (2450 MHz frequency). The aliquots were irradiated at different currents (internal temperature ranging from 45 to 60 °C) for different time periods. The reaction mixture was cooled at room temperature, treated with water, and extracted with dichloromethane. The organic solvent layer was washed with sodium thiosulfate and then with water and dried over anhydrous sodium sulfate. Evaporation of the solvent followed by purification (distillation/chromatography on silica gel) produced the corresponding carbonyl compounds (Scheme 3).

Scheme 3. Regeneration of Carbonyl Compounds from Oxime.

Scheme 3

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Acknowledgments

D.D. would like to acknowledge Dr. N.B. Das, Scientist (retired) of CSIR-IMMT Bhubaneswar, for his technical expertise and discussions. R.K.M. is thankful to Principal, Government College of Engineering, Keonjhar, for providing necessary facilities. P.K.P. acknowledges KIGAM, South Korea, for awarding Visiting Scientist.

Glossary

Abbreviations

SDS

sodium dodecyl sulfate

CTAB

cetyl trimethyl ammonium bromide

SDBS

sodium dodecyl benzene sulfonate

CMC

critical micelle concentration

S. laurifolia

Sapindus laurifolia

Author Contributions

All authors have equally contributed and given approval to the final version of the manuscript.

The authors declare no competing financial interest.

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