Induced electron transfer reaction of Cobalt (III) complexes of α–Hydroxy acids by 2, 2ââ

IJSRD - International Journal for Scientific Research & Development| Vol. 3, Issue 11, 2016 | ISSN (online): 2321-0613

Induced Electron Transfer Reaction of Cobalt (III) Complexes of α– Hydroxy Acids by 2, 2’-Bipyridinium Bromo Chromate (BPBC) in the Presence of Surfactant Medium C.Vijayakumar1 K. Subramani2 1,2 Department of Chemistry 1,2 Islamiah College, Vaniyambadi – 635752 (T.N.) India Abstract— The kinetics mechanistic studied of BPBC with Cobalt (III) bound and unbound complexes of α-hydroxy acid in micellar medium at 323 K in 50% acetic acid 50 % water. In this reaction the rate of oxidation shows pseudo first order kinetics each in Cobalt (III)] and BPBC. It rules out the synchronous C-C bond fission and electron transfer to Cobalt (III) centre. With increasing micelles concentration an increase in the rate is observed. Oxidation of Cobalt (III) complexes increases with increase in temperature. The kinetic and stoichiometric results have been accounted by a suitable mechanism.

Key words: α – Hydroxy Acids, 2,2’–Bipyridinium Bromochromate, Sodium Lauryl Sulphate, Cetyl Trimethyl Ammonium Bromide, TRITON-X100

cleavage accompanied by an induced electron transfer to the Co (III) in the complex and one electron transfer to the oxidant. The contest between the two mechanisms became interesting and produced definite results when mild oxidizing agents like BPBC were kinetically followed. The structure of BPBC is given below O -

N

O

+

NH

Cr Br

O

Fig. 1: Structure of BPBC II. EXPERIMENTAL

2,2´-Bipyridine (A.R. Qualigens, India), HBr, chromium trioxide from (SD Fine chemicals. India 95%) Preparation of BPBC to 16.75 ml of 6 M hydrobromic acid (0.11mole) is added 10.0g.

I. INTRODUCTION (0.11mole) of chromium trioxide rapidly while stirring. After Chromium (VI) reagents have been widely used in organic dissolution of the chromium trioxide is complete, 15.6 g. chemistry for the oxidation of primary and secondary alcohols to (0.1mole) of 2, 2’-bipyridine is added in portions while stirring carbonyl compounds. Pyridine chromium trioxide complexes vigorously. A yellow slurry results which is stirred for 1 hour at and pyridinium bromo chromate have been especially useful room temperature. The slurry is then collected on a sintered reagents for the mild oxidation of primary alcohols to aldehydes. glass funnel and washed with two 15 ml portions of cold There are, however, some significant difficulties associated with distilled water. The resulting solid yellow filter cake is dried for the reagents. For instance, chromium containing by-products 3 hours in vacuum at room temperature.The resulting product is often contaminate the desired products, requiring time 2,2’-bipyridinium bromochromate, its purity was checked by an consuming purifications. A novel compound 2, 2’-bipyridinium iodometric method and is obtained in a typical yield of 26.8 g. chlorochromate, 2, 2’-bipyridinium bromo chromate has been which is 92% of the theoretical yield. Mandelic, lactic and discovered which is useful as an oxidizing agent. The compound glycolic acids from (SD Fine chemicals. India 95%) is especially useful as an oxidizing agent in reactions which HClO4 (Merck, India 95%) was standardized using require relatively mild oxidizing conditions, such as the standard sodium carbonate (BDH.AR) solution with methyl conversion of primary or secondary alcohols to carbonyl orange as an indicator. Acetic acid was purified by standard compounds. Evolution 60 thermo spectrophotometer has been method and the fraction distilling at 1180C was collected. The utilize to study the oxidation of α-hydroxyacids1 such as cobalt (III) complexes of alpha-hydroxy acids were prepared as mandelic acid, lactic acid, glycolic acid and their Cobalt (III) their perchlorates using the method of Fau and Gould 4. The Complexes using Pyridinium dichromate as an oxidant in the surfactants used in the present work are sodium lauryl sulphate presence of surfactant. Surfactants are often used in the (NaLS) and cetyl trimethylammonium bromide5 (CTAB).The formulations of pesticides and herbicides2. They have also found surfactants are purified by adopting earlier procedure 6 Kinetic a wide range of applications because of their unique solution measurements of the oxidation of cobalt (III) complexes of α properties such as detergency, solubilisation, and surface hydroxy acids and unbound ligands were carried out under wetting capabilities in diverse areas such as chemical as well as pseudo first order conditions in 50% acetic acid 50% water at 55 biochemical research3. Surface active materials are major ± 2oC by following the concentration of BPCC at 365 nm with building blocks of many physical, chemical, anti-biological the help of an UV visible spectrophotometer. The total volume systems. They have been introduced into several commercial of reaction mixture in the spectrophotometric cell was kept as products such as antiseptic agents in cosmetics and as 2.5 ml in each kinetic run all the solutions for the experiments germicides7, and have also found a wide range of applications in were maintained at the specified temperature in an electrically diverse areas such as mining, petroleum, and pharmaceutical operated thermo stated bath. Perchloric acid was used as the industries. A mechanism involving the C-C bond cleavage source of H+ ions and ionic strength was maintained by leading to the formation of aldehydes as the product was NaClO .Stoichiometric studies for the oxidation of Penta 4 proposed. The formation of keto acids by the C-H cleavage of ammine cobalt (III) complexes of alpha-hydroxy acids and the alpha-hydroxy acids was reported with many chromium (VI) unbound ligands by BPBC were carried out with the oxidant in oxidant3. In the case of complexes, the hydroxyl group of the excess. The [H+] and ionic strength were maintained as such in bound ligand is free for oxidation with C-H cleavage leading to the corresponding rate measurements. After ten half-lives when the formation of keto complexes. Formation of aldehydes as a the reaction was nearing 80% completion the concentration of product is possible with decarboxylation and synchronous C-C

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Induced Electron Transfer Reaction of Cobalt (III) Complexes of α–Hydroxy Acids by 2, 2’-Bipyridinium Bromo Chromate (BPBC) in the Presence of Surfactant Medium (IJSRD/Vol. 3/Issue 11/2016/037)

unreacted BPBC was determined spectrophotometrically.The B. Rate Dependence of Bound Co (III) of α–Hydroxy Acids difference in the concentration of the oxidant [BPBC] was in Micellar Medium measured and then the stoichiometry was calculated from the The reaction proposes that BPBC oxidizes OH centre of the ratio between reacted [oxidant] and [substrate]. The amount of cobalt (III) bound α - hydroxy acids at a rate comparable to cobalt (III) reduced was also calculated from the decrease in the that of the unbound ligand and there is 99 % reduction at the absorbance measured for the Co (III) complex (Table 1).All cobalt(III) centre The kinetic data for the oxidation of the kinetic measurements were carried out by the spectro pentaamminecobalt (III) complexes by BPBC in presence of photometer. The spectrophotometer was kept at 365 nm the Perchloric acid catalyst and maintained temperature 55± monitoring changes the absorbance of the progress reaction.502 0.20C is given in the Table 2.The behaviour of the nm was set for remaining Cr (VI) by monitoring changes of the complexes were similar to the free ligands and the reaction cobalt (III) complexes. The required α-hydroxy acid, HClO4 and showed a total pseudo first order dependence on them and BPBC were premixed in a reaction vessel, thermostated in an oil the reagent. The rates of oxidation of complexes were found bath, and BPBC solution (thermally equilibrated) was then to be higher than the corresponding free ligands showing added prior to the absorbance measurements. that the oxidation was facilitated by complexation. Further the absence of keto complexes in the product and formation A. Product Analysis of aldehydes as the only organic product confirm the C-C Co (II) was estimated after the completion of reaction, by cleavage. The reduction of Co (III) to Co (II) to an extent of diluting the reaction mixture 10-fold with concentrated HCl, 99% showed an induced electron transfer from the ligand to allowing evolution of chlorine to cease, and then measuring the the metal due to decarboxylation and synchronous cleavage absorbance at 692 nm. The amount of Co (II) estimated to of the C-C bond in the complexes. BPBC undergoes a one nearly 40% of [Co (II)] initial. After 48h, the product was electron change and the overall reaction between BPBC and extracted with ether and analysed iodoimetrically for the the complexes could be written as: amount of aldehyde formed in the case of the [Mandelato] and [C6H5CH (OH) COO – CoIII] +O2CrBrO-bPyH+ → [Lactato] Cobalt (III) complexes, the dimeric Co (III) complex, C6H5CHO + CrV+ CoII + CO2 and unbound mandaleic acid. The yield of aldehyde in all these The rate equation for this reaction could be deduced as cases is nearly 60% [Co (III)] initial. After neutralization of the Rate = K [CoIII – Complex] [BPBC] reaction mixture with sodium bicarbonate, the pH of the Table-1 shows the Stoichiometric Data of 2,2aqueous layer was adjusted to about 6.5 and the aqueous layer biPyridinium bromo Chromate oxidation of pentaammine was separated by filtration in the case of both free ligands and cobalt (III) complexes of bound and unbound alpha– corresponding complexes. On evaporation of water under hydroxy acids in presence NaLS at maintained temperature reduced pressure, the product separated and the percentage 55±0.2OC and alternatively changed micelles such as Cetyl yield was calculated. Though the yield of mandelic acid was Trimethyl ammonium Bromide (CTAB) and TRITON-X100 nearly quantitative, the estimation of mandaleic acid complex respectively. was less nearly quantitative. In both the cases the IR spectra of 102 the product agreed with that of authentic samples of mandalic 102 102 BPBC BPBC 102 [Compound] acid or the [mandelato] cobalt (III) complex.

[Compound] Final Initial BPBC :  [ BPBC] mol dm-3 III. RESULT AND DISCUSSION Mandelic acid A. Rate Dependence of Free Ligand of α –Hydroxy Acids in 1.0 1.0 9.30 0.70 1.00:0.70 Micellar Medium 2.0 10.0 8.50 1.50 1.00:0.75 3.0 20.0 17.5 2.25 1.00:0.75 The rate of BPBC oxidation of alpha-hydroxy acids had been followed under pseudo first order condition by keeping excess of Lactic acid the alpha-hydroxy acid concentration than the reagent 1.0 1.0 9.28 0.72 1.00 : 0.72 summarized kinetic data for the oxidation of α-hydroxy acids 2.0 10.0 8.52 1.48 1.00 : 0.74 and their CoIII complexes by BPBC in presence of perchloric 3.0 20.0 17.78 2.22 1.00 : 0.74 acid of anionic and cationic micells at 55±0.2°C.BPBC induced Glycolic acid electron transfer in pentaammine cobalt(III) complexes of alpha1.0 1.0 9.24 0.76 1.00 : 0.76 hydroxy acids seems to involve nearly synchronous C-C fission 2.0 10.0 8.52 1.48 1.00 : 0.74 and reduction at cobalt(III)centre. An explanation for the higher 3.0 20.0 17.72 2.28 1.00 : 0.70 reactivity of lactic acid involving C-H cleavage was given based CoIII Mandelato on the higher acidity of C-H proton. In the present investigation, 1.0 1.0 9.64 0.36 1.00 : 0.36 the absence of such an observation leads to C-C cleavage.

2.0 10.0 9.30 0.70 1.00 : 0.35 Finally product analysis confirmed the formation of aldehydes 3.0 20.0 18.98 1.02 1.00 : 0.34 due to C-C cleavage and not formed keto acids.

CoIII Lactato Stoichiometric analysis showed that the following 1.0 1.0 9.65 0.35 1.00 : 0.35 overall reaction 2.0 10.0 9.26 0.74 1.00 : 0.37 C6H5CH (OH) COOH + O2CrBrO-bPyH+ + H+ → 3.0 20.0 18.89 1.11 1.00 : 0.37 C6H5CHO + H2O + OCrCO-bPyH+ CoIII Glycolato The rate equation for this reaction could be 1.0 1.0 9.62 0.38 1.00 : 0.38 deduced as 2.0 10.0 9.26 0.74 1.00 : 0.37 Rate = K [alpha-hydroxy acid] [BPBC]

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Induced Electron Transfer Reaction of Cobalt (III) Complexes of α–Hydroxy Acids by 2, 2’-Bipyridinium Bromo Chromate (BPBC) in the Presence of Surfactant Medium (IJSRD/Vol. 3/Issue 11/2016/037)

3.0 20.0 18.92 1.08 1.00 : 0.36 Table 1: Stoichiometric Data for BPBC oxidation of Co (III) bound and unbound α –hydroxy acids in presence of Sodium Lauryl Sulphate (NaLS) at 55 ± 0.2 ºC [HClO4] = 1.00x10-1 mol dm-3 [NaLS] = 1.00x10-2 mol dm-3 Temperature = 55 ± 0.2ºC

0.5 1.0 1.5 2.0 2.5

1.210 1.441 1.587 2.423 2.885 3.173 3.637 4.330 4.762 4.852 5.772 6.352 6.067 7.222 7.942 Lactic acid 0.5 1.556 1.731 1.905 1.0 3.114 3.465 3.814 C. Effect varying of Temperature 1.5 4.677 5.200 5.724 The reaction has been carried out at four different temperatures 2.0 6.238 6.932 7.634 -3 -3 -2 keeping [BPBC] =10 mol dm Mandellic Acid =1.00 x10 mol 2.5 7.792 8.660 9.545 -3 dm (Table 2).Absorbance decrease the while reaction time of Table 3: Kinetic data for the oxidation of alpha-hydroxy BPBC with alpha hydroxy acid. The rate constants were acids free ligands by BPBC calculated by the integrated rate equation. The graph of = 10-3mol dm-3 logarithm of absorbance versus time was linear and the rate [BPBC] = 0.1 mol dm-3 constants calculated from the slope of the graph. Temperature [HClO4] Temperature = 55 ± 0.2°C increases rate also increased.

[Micelles] = 1.00x10-2 mol dm-3 4 -1 Time(s) log(Absorbance) 10 k s 1

Fig 1: First order dependence plot 104k1s-1 102[α-hydroxyacids] -3 mol dm NaLS Triton CTAB Glycolic acid 0.5 0.916 1.111 1.306 1.0 1.831 2.224 2.617 1.5 2.751 3.339 3.922 2.0 3.674 4.456 5.232 2.5 4.595 5.572 6.547 Mandelic acid

Glycolic acid Mandelic acid Lactic acid

5.0

9 .99 = 0 000 e . p = 1 000 slo pe 1. slo e = p slo

4.9 4.8 4.7

4+logk1

0 -0.18111 0.00 306 -0.21396 2.513 604 -0.24642 2.308 902 -0.27819 2.242 1203 -0.30980 2.146 1505 -0.33363 2.284 1807 -0.36856 2.396 2106 -0.40012 2.468 2409 -0.43063 2.577 2708 -0.45967 2.644 3004 -0.49214 2.675 Table 2: Kinetic data on the effect of Temperature [BPBC] = 10-3mol dm-3 [HClO4] = 0.1 mol dm-3 Temperature = 55 ± 0.2°C Mandellic Acid = 1.00 x10-2 mol dm-3 [NaLS] = 1.00x10-2 mol dm-3

4.6 4.5 4.4 4.3 4.2 4.1 1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2+log[alpha-Hydroxy acids]

Fig 2: Dependence of rate on α-hydroxy acid with CTAB 104k1s-1 102[(NH3)5Co(III)-L] -3 mol dm NaLS Triton CTAB Glycolic acid 0.5 1.216 1.357 1.588 1.0 2.430 2.713 3.173 1.5 3.647 4.073 4.764 2.0 4.864 5.434 6.344 2.5 6.085 6.790 7.935 Mandelic acid 0.5 1.306 1.615 1.905 1.0 2.615 3.234 3.811 1.5 3.912 4.853 5.721 2.0 5.230 6.474 7.630 2.5 6.548 8.095 9.540 Lactic acid 0.5 1.806 2.006 2.207 1.0 3.614 4.014 4.412 1.5 5.423 6.026 6.621 2.0 7.232 8.030 8.832 2.5 9.048 10.043 11.045 Table 4: Kinetic data for the oxidation of CoIII complexes of alpha-hydroxy acids and bound ligands by BPBC [BPBC] = 2.00x10-1mol dm-3 [HClO4] = 0.1mol dm-3 Temperature = 55 ± 0.2°C [Micelles] = 1.00 x10-2 mol dm-3

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Induced Electron Transfer Reaction of Cobalt (III) Complexes of α–Hydroxy Acids by 2, 2’-Bipyridinium Bromo Chromate (BPBC) in the Presence of Surfactant Medium (IJSRD/Vol. 3/Issue 11/2016/037)

IV. CONCLUSION

Glycolato & CTAB Mandelato & CTAB Lactato & CTAB

5.1 5.0

9 .99 0 = 0 1.00 9 pe 9 = slo ope = 0.9 l s pe slo

4.9 4.8

The kinetics and oxidation cobalt (III) of α-Hydroxy acids viz, glycolic acid, mandelic acid, lactic acid by 2,2’bipyridinium bromo chromate in surfactant medium have been using a novel chromium (VI) oxidant. In this reaction C-C cleavage occurs leading reduction at CoIII centre. In this reaction C-C cleavage occurs leading reduction at Co III centre. The rate of the increase the observed presence surfactant NaLS, CTAB and TRITON. Among the surfactant which CTAB enhances the rate much more than the TRITON, NaLS. Temperature increases the rate of the reaction increases with micelles CTAB higher than the TRITON, NaLS.

4+logk1

4.7 4.6 4.5 4.4 4.3 4.2 4.1 1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

III

2+log[Co ]

Fig 3: Dependence of rate on [Co (III)] with CTAB

D. Mechanism The reaction was show that pseudo first order dependence on the ACKNOWLEDGEMENT BPCC with CoIII α-Hydroxy acids and alpha-Hydroxy acids. It involve two steps. Mechanism proposes that BPBC oxidizes OH We express sincere thanks to Department of Chemistry, centre of the cobalt (III) bound alpha - hydroxy acids at a rate Islamiah College Vaniyambadi and VME society for comparable to that of the unbound ligand and there is 100 % providing the necessary facilities for the successful reduction at the cobalt (III) centre, forms a chromate ester with completion of this research work. cobalt (III) Mandelato complex which can decompose in a slow REFERENCES step, proceeds through C-C bond fission leading to the formation of cobalt (II), carbonyl compounds and carbon dioxide as [1] Anbuselvan, C., and Sankaran, K.R., (1998) Oxidation products. The kinetic results and absence of keto acids as a Communications, 21, 257-260. product leads to a mechanism involving one electron transfer to [2] Scramm, L. LStasiuk., E. N., and Marangoni Annu, D. Cr (VI) with C-C cleavage and decarboxylation Scheme 1.In the G., (2003) Rep. Prog. Chem. Sect., 3, 99. oxidation of the complexes a mechanism involving one electron [3] M. J. Rosen (2004) Surfactants and Interfacial transfer to Cr (VI) and an induced electron transfer to Co (III) by Phenomenon, 3rd Edn.Wiley, New Jersey, 25,569. the decarboxylation and synchronous cleavage of C-C was [4] Fan, R. F, and Gould, E. S., (1974), Inorg. Chem.,13, proposed.

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Induced Electron Transfer Reaction of Cobalt (III) Complexes of α–Hydroxy Acids by 2, 2’-Bipyridinium Bromo Chromate (BPBC) in the Presence of Surfactant Medium (IJSRD/Vol. 3/Issue 11/2016/037)

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