Comparative Study of Solvent Effect for Mandelic Acid Oxidation by Different Oxidants

Introduction

α- Hydroxy acids are chemical molecules that include hydroxyl and carboxylic groups. Some important members of α-hydroxy acids like glycolic acid, mandelic acid, lactic acid, malic acid, citric acid and tartaric acid are obtained from sugarcane, milk, apple, citrus fruits, grape wine and bitter almonds, respectively. These α-hydroxy acids and their derivatives have a large application area like biological, vital, cosmetic and organic synthesis. We have used mandelic acid for our oxidation study. Studying various organic compounds’ oxidation in non-aqueous environments is crucial in synthetic organic chemistry. For this study, many Cr (VI) derivatives have been reported^1-5. The oxidation study of α-hydroxy acids by PBC⁶, PDC⁷, PCC⁸, IDC⁹, QCC¹⁰, PzCC¹¹, MCC¹², TEACC¹³,IFC¹⁴, PipCC¹⁵, MFC¹⁶, BIDC¹⁷ etc. has been reported in DMSO. We have studied oxidation reactions of mandelic acid by BIFC, MFC, BIDC, MCC and TEACC in 6 different solvents as dimethyl sulphoxide (DMSO), dimethyl formamide (DMF), chloroform (CF), acetone, dichloromethane (DCM) and 1,2-dichloroethane (DCE) at temperature 308K. α-Hydroxy acids either oxidised as alcohols, which results in the formation of corresponding oxoacids or undergo oxidative decarboxylation, which gives ketone.  We have identified the best solvent under the different alternatives using the TOPSIS method18 and proposed a suitable mechanism.

Hwang and Yoon¹⁹ invented the TOPSIS approach, which Yoon20 subsequently enhanced. Hwang et al. ²¹ also published a new approach to multi-objective decision-making.

Material and Method

Material

We have used A. R. (analytical reagent) grade mandelic acid. The reported method was used to prepare BIFC²², MFC²³, BIDC²⁴, MCC²⁵ and TEACC²⁶ and their purity was determined using an iodometric approach. Solvents were purified using standard procedures²⁷.

Kinetic Experiments

Pseudo, first-order constant, was obtained using a significant excess (*15 times or more) of the substrate over oxidants. For our research, we used six different solvents. The study of reactions was done at a constant temperature of 308K. The reaction mixtures were prepared by mixing the appropriate amount of solvent, substrate etc. and keeping them at a constant temperature in a thermostatic water bath. The reaction was started by introducing an oxidant solution previously stored in the water bath. The decrease in the concentration of oxidants was monitored spectrophotometrically. For carrying out our experiments, we have used the UV-Vis spectrophotometer model (AIMIL India model MK2) in which we have selected λ_max 364 nm, 356 nm, 365 nm, 350 nm and 352 nm, respectively, for BIFC, MFC, BIDC, MCC and TEACC as these oxidants showed (absorbance) λ_max at 364 nm, 356 nm, 365 nm, 350 nm and 352 nm.           

Results and Discussion

We have done the oxidation of mandelic acid by different oxidants using six solvents, which results in the formation of corresponding oxoacids. The product is also confirmed by spectral analysis. FTIR spectra of mandelic acid oxidation by BIFC in DMSO solvent have been given, and similar results have been obtained with other oxidants and solvents. A suitable mechanism has been proposed which involves the formation of a chromate ester in a fast pre-equilibrium and then the decomposition of the ester in a subsequent slow step via a cyclic concerted symmetrical transition state leading to the formation of corresponding oxo acid in all the cases. A suitable mechanism for all the oxidants has been given. We have used the TOPSIS approach to compare the rate constants k₂ in six solvents for specific oxidants to find out which solvent is best suited for the oxidation of mandelic acid.

Graph 1: FTIR Spectrum of mandelic acid Click here to View Figure

Figure 2: FTIR Spectrum of corresponding oxyacids formed by oxidation of  mandelic acid by BIFC in DMSO. Click here to View Figure

Mechanism

Scheme 1: Acid Dependent Path Mechanism 1 Click here to View Scheme

Scheme 2: Acid Dependent Path Mechanism 2 Click here to View Scheme

Where B = BI-Benzimidazolium, M-Morpholinium, TEA-Tetraethylammonium

TOPSIS Study

Table 1: At 308 K decision matrix of rate constants (10⁴ k₂ s^-1) for the mandelic acid oxidation by given oxidants

Oxidant/ Solvent	BIFC	MFC	BIDC	MCC	TEACC
DMSO	62.9	72.4	52.4	74.6	68.2
DMF	31.7	46.6	28.9	40.4	39.2
CF	20.5	23.4	15.0	19.9	19.2
ACETONE	22.8	25.1	16.3	24.1	25.8
DCM	21.6	30.3	17.2	22.8	23.6
DCE	23.8	27.8	19.1	26.5	28.9

Figure 3: Decision matrix of the rate constants for mandelic acid oxidation by given oxidants Click here to View Figure

Calculations of the Normalized Matrix

Calculations of the Normalized matrix X_ij done by this formula:

i = 1, 2,…, m

 j = 1, 2,…, n

Table 2: Normalized matrix calculated using rate constants (10⁴ k₂ s^-1) for the mandelic acid oxidation by given oxidants at 308 K

 

Oxidant/ Solvent	BIFC	MFC	BIDC	MCC	TEACC
DMSO	0.0091	0.0070	0.0111	0.0079	0.0079
DMF	0.0045	0.0045	0.0061	0.0043	0.0046
CF	0.0029	0.0023	0.0032	0.0021	0.0022
ACETONE	0.0033	0.0024	0.0034	0.0026	0.0029
DCM	0.0031	0.0029	0.0036	0.0024	0.0027
DCE	0.0034	0.0027	0.0040	0.0028	0.0034

Calculations of the weighted normalized matrix

Calculations of the weighted normalized matrix V_ij done through this formula:

i = 1, 2,…, m

 j = 1, 2,…, n

Table 3: Weighted normalized matrix calculated using normalized matrix for the mandelic acid oxidation by given oxidants at 308 K

Oxidant/ Solvent	BIFC	MFC	BIDC	MCC	TEACC
DMSO	0.0018	0.0014	0.0022	0.0016	0.0016
DMF	0.0009	0.0009	0.0012	0.0009	0.0009
CF	0.0006	0.0005	0.0006	0.0004	0.0004
ACETONE	0.0007	0.0005	0.0007	0.0005	0.0006
DCM	0.0006	0.0006	0.0007	0.0005	0.0005
DCE	0.0007	0.0005	0.0008	0.0006	0.0007

 

Figure 4: Weighted normalised matrix of the rate constants for mandelic acid oxidation by given oxidants Click here to View Figure

oxidation by given oxidants

Calculations of the positive ideal and negative ideal values

Max V_ij is V⁺ (positive ideal value), and Min V_ij is V ^– (negative ideal value).

Positive Ideal Values V⁺:

0.0018

0.0014

0.0022

0.0016

0.0016

 

Negative Ideal Values V^–:

0.0006

0.0005

0.0006

0.0004

0.0004

 

Calculations of the Euclidean distance from positive ideal values and negative ideal values

Calculations of the Euclidean distance from positive ideal values (S_i⁺) done by this formula

DMSO	DMF	CF	ACETONE	DCM	DCE
0	0.0017	0.0028	0.0025	0.0026	0.0024

 

Calculations of the Euclidean distance from negative ideal values (S_i^–) done by this formula:

DMSO	DMF	CF	ACETONE	DCM	DCE
0.0028	0.0011	0	0.0003	0.0002	0.0004

 

Calculate the performance score

Calculations of Performance score P_i done as follows:

DMSO	DMF	CF	ACETONE	DCM	DCE
1	0.393	0	0.11	0.07	0.14

 

Table 4: Rank by the performance score of the solvents

Solvent	Pi	Rank
DMSO	1	1
DMF	0.393	2
CF	0	6
ACETONE	0.11	4
DCM	0.07	5
DCE	0.14	3

 

Figure 5: Rank by the performance score of the solvents Click here to View Figure

Conclusion

In this study, we have done the oxidation of mandelic acid by different oxidants. The resultant product was corresponding oxoacids. The mechanism involved the formation of a cyclic chromate ester in a fast pre-equilibrium and then the decomposition of the ester in a subsequent slow step via a cyclic concerted symmetrical transition state leading to the formation of corresponding oxo acid in all the cases. The comparative study of the solvent effect is an essential concept of physical organic chemistry. The TOPSIS method is helpful for this study. This is the multiple criteria decision-making method. In this study, we have done the oxidation of mandelic acid by different oxidants and solvents and based on the TOPSIS method, the following order by the performance score of the solvents for the reaction- DMSO>DMF>DCE>ACETONE>DCM>CFwas obtained. Thus it was concluded that the oxidation of mandelic acid by different oxidants gives the best results when DMSO is used as a solvent.

Acknowledgement

We are thankful to HOD, Chemistry, Jai Narain Vyas University, Jodhpur, India, for providing us with valuable lab facilities to conduct our research work.

Conflict of Interest

The authors declare no conflict of interest in the present work.

References

1. Corey, E.J.; Suggs W.J., Tetrahedron Lett, 1975, 16(31),2647-2650.
2. Bhattacharya, M.N.; Chaudhuri, M.K.; Dasgupta, H.S.; Roy, N.; Kathing, D.T., Synthesis, 1982, 1982(07), 588-590.
3. Balasubramanian, K.; Prathiba, V., Indian J. Chem., 1986, 25B, 326-327.
4. Li, M.; Johnson, M.E., Synth Commun, 1995, 25, 533-537.
5. Pandurangan, A.; Murugesan, V.; Palamichamy, P., J. Indian Chem. Soc., 1995, 72, 479.
6. Aparna, P.; Kothari, S.; Banerji, K.K., J. Chem. Res., V, 1994, 367-367.
7. Sundaram, S.M.; Amutha, M.; Sockalingam, R.M., Chem. & Env. Res., 1996, 5,229-234.
8. Sethumathavan, D.; Sankaran, K.R., Oxid. Commun, 1997, 20, 587-591.
9. Meenakshisundaram, S.; Sathiyendiran, V., Oxid. Commun., 1998, 21, 71-76.
10. Gurumurthy, R.; Karthikeyan, B., Orient. J. Chem., 1998, 14, 435-437.
11. Sekar, K.G.; Prabakaran, A., Oxid. Commun., 2008, 31, 879-884.
12. Malani, N.; Pohani, S.; Baghmar, M.; Sharma, P.K., Ind. J. Chem., 2008, 47A, 1373-1376.
13. Swami, P.; Yajurvedi, D.; Mishra P.; Sharma, P.K., Int. J. Chem. Kinet., 2009, 1-6.
14. Sekar, K.G.; Anbarasu, K., Oxid. Commun., 2013, 36, 979-983.
15. Anbarasu, K.; Selvi, P., Rasayan J. Chem., 2014, 7, 365-369.
16. Purohit, V.; Mishra, P., Int. J. Innov. Res. Rev., 2018, 6(1),27-37.
17. Pandey, D.; Kachawa, T.; Kothari, S., Prog. React. Kinet. Mech., 2018, 43(3-4), 300-314.
18. Rao, A.; Kumar, G., J. Appl. Chem., 2019, 8(4), 1798-1804.
19. Hwang, C.L.; Yoon, K., Multiple Attribute Decision Making: Methods and Applications, New York, Springer-Verlag, 1981.
20. Yoon, K., Journal of Operational Research Society, 1987, 38(3), 277-286.
21. Hwang, C.L.; Lai, Y.J.; Liu, T.Y., Computer and Operational research, 1993, 20, 889-899.
22. Sivamurugan, V.; Rajkumar, G.A.; Arabindoo, B.; Murugesan, V., Ind. J. Chem., 2005, 44B, 144-147.
23. Zahra, S.; Alangi, S.; Ghotbabadi, H.S.; Baei, M.T.; Naderi, S., E-J. Chem, 2011, 8(2), 815-818.
24. Meng, Q.H.; Feng, J.C.; Bian, N.S.; Liu, B.; Li, C.C., Syn. Commun., 1998, 28(6), 1097-1102.
25. Sheikh, H.N.; Sharma, M.; Hussain, A.; Kalsotra, B.L., Oxid. Commun., 2005, 28(4), 887-893.
26. Pandurangan, A.; Murugesan, V., J. Indian Chem. Soc., 1996, 73, 484-486.
27. Perrin, D.D.; Armarego, W.L.; Perrin, D.R.; Pergamon Press, Oxford, 1966.

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