Extensive literature survey Essay

The kinetic methods of analysis are highly sensitive, selective, simple, accurate and less expensive. Extensive literature survey reported oxidation of paracetamol[70-72], D-glucose[73-83] and chloramphenicol[84-86] by various oxidant and their kinetic investigations.

A] Oxidation of Inorganic substrate by POM anion:-

The survey of the literature showed that oxidation of various inorganic substrates was studied kinetically by using POM as oxidant or catalyst under mild conditions. Kinetic study of Oxidation of Platinum(II) [87], hydroxylamine[88-89], hydrophosphite and phosphate [90-91] thiourea[92], thalium(I) [93-94], permagnate ion[95], carbohydrazide[96] by POM have also been reported. POM’s efficient catalytic property was reported by oxidation of Hexacyanoferrate(III)[97], Benzyl alcohol [98",99].

B] Oxidation of Organic substrate by POM anion:-

POM anions have been used as well-defined outer sphere electron transfer agents. The oxidation of numerous Organic substrates such as amines, alcohols, ketones [100], Phenols[101], alkyl aromatics[102], dienes[103], alkanes[104], pyridine [105] is reported by various researchers. Ayoko and Olatunji [106] reported that the rates of oxidations of thiourea and 1",1",3",3-tetramethyl-2-thiourea is independent of [H+] ions. The oxidation of aliphatic alcohols by [CoIIIW12O40]5- at very high ionic strength was investigated by Ayoko and Olatunji [107] over a wide [H+] range. POM catalyzed oxidations of thioesters by t-butyl hydroperoxide was studied by Gall and co-worker [108]. The Keggin structure of 12-tungstocobaltate(III) anion is substitution inert and precluded inner sphere mechanism because the central CoIII atom is protected by a sheath of chemically inert oxygen atoms. Electron exchange between the CoIII and CoII compounds in solution is relatively rapid which support outer-sphere electron transfer. In comparison with Keggin and Dawson types of salts, 6-molybdocobaltate(III) salts are substitution inert and are compact. It belongs to Anderson-Evans structure and contains six non-ionisable proton. To the best of our knowledge, very limited study is available on kinetic and mechanistic study of oxidation by 6-molybdocobaltate(III) anion[117-119].

POM anions have been used as well-defined outer sphere electron transfer agents. Few among them with the corresponding rate laws of oxidation reactions have been included in table 1

Oxidant Substrate Rate law Ref

[CoIIIW12O40]-5 Platinum(II) k1 +K k2[Cl-] [PtCl4-2] [CoIIIW12O40]-5 37


[CoIIIW12O40]-5 NH3OH+ 2 k[CoIIIW12O40]-5 [NH3OH+] 27


(NH4)6[MnIVMo9O32] Hydroxyl amine ( k1 [H+] + k2 / ([ H+] + Ka) 39


[CoIIIW12O40]-5 H3PO2 2 k [CoIIIW12O40]-5 [H3PO2] 30


(NH4)6[MnIVMo9O32] H3PO2 k1K2[H+][H3PO2] / (H+]+K1)(1+K2[H3PO2] 41


[CoIIIW12O40]-5 Thiourea kobs = ( kc Kc +kc2 Kc[H2NCSNH2] 38


[CoIIIW12O40]-5 TlI k [CoIIIW12O40]-5 [TlCl3] 34


[CoIIIW12O40]-5 TlI 2 k1 K [CoIIIW12O40]-5 [TlCl3] [RuCl6 3-] [Cl-] 35


[CoIIIW12O40]-5 Pyridine kobs (1 + Kb [H+]) = ket [Pyridine]T 105

[CoIIIW12O40]-5 N2H5+ 2 k[CoIIIW12O40]-5 [N2H5+] 28


[CoIIIW12O40]-5 HNO2 2 k [CoIIIW12O40]-5 [HNO2] 29


[CoIIIW12O40]-5 H3AsO3 2 k [CoIIIW12O40]-5 [H3AsO3] 31


[CoIIIW12O40]-5 H3AsO3 2 k[CoIIIW12O40]-5 32


[CoIIIW12O40]-5 SCN- 2 k [CoIIIW12O40]-5 [SCN-] 33


[CoIIIW12O40]-5 SbIII k [CoIIIW12O40]-5 [SbCl6 3- ] 36


(NH4)6[MnIVMo9O32] Arsenous acid kK1K2 [H+]2/ 1+ k1[H+] + K1K2 [H+]2 40


(NH4)6[MnIVMo9O32] L- Methionine k1KcK3[ Mn IV M]-[(CH3)2SR+H2][H+]

/ (1+K3[H+]) 44


[CoIIIMo] Phenanthro

line iron(II) (k+k1[Co III Mo]3-)⤬[CoIIIMo]3-[H]+ 45


[CoIIIMo] Ethane Diol kKc[H+]2/{[H+]2+K1[H+]2[HMoO4]- +K2[Co III Mo]2-} 46


[CoIIIMo] H3PO3 or H3PO2 k1[RP(OH)2] [H+]2/

[H+]2 +K1[H2MoO4][H+]+K2[CoIIIMo]2- 47


Table 1: Oxidation of Inorganic and Organic substrate by POM anion as efficient Oxidant

POM’s have relatively low toxicity as compared to chromates; they accept electrons without major changes of their structures and form insoluble salts with large cations. POM represents thermodynamically stable structural arrangements. They characteristically maintain their identities in aqueous and non-aqueous solution as well as in ionic crystal [120]. These properties make POM attractive as oxidant. The POM compounds are active as oxidation-reduction catalysts with wide range of organic / inorganic substrates and mostly provide higher activities and selectivity and allow for cleaner processing compared to conventional catalysts. The use of variety of multi-component redox systems based on POM’s greatly enhances the scope of possible oxidations.

POM’s are the promising acid, redox and bifunctional (acid/ redox) catalysts, as they have high thermal stability in solid state and high solubility in a polar solvent. Literature survey concluded that the majority of the applications of POM’s are found in the area of the catalysis. Carboxylic acid hydrazides are pharmaceutically important organic compounds pertaining anti-tubercular and antibacterial properties. Some POM’s like Anderson type Hexamolybdochromate(III) [123",124], 13-Vanadomagnate(IV) [125], Octamolybdomagnatate(II) [126], have reported as catalyst for oxidation of hydrazides more effectively than metal ion.

Substrate Catalyst Oxidant Ref

Hexacyanoferrate(III) [CoIIIW12O40]-5 Perborate 97

Benzyl alcohol [CoIIIW12O40]-5 Oxone 98

sulfides [CoIIW12O40]-6 Hydrogen peroxide 121

Alcohols Hexamolybdochromate(III) Hydrogen peroxide 122

Acetic acid hydrazide Hexamolybdochromate(III) KBrO3 123

Benzoic acid hydrazide Hexamolybdochromate(III) KBrO3 124

Benzoic acid hydrazide 13-Vanadomagnate(IV) Bromatein 125

Benzoic acid hydrazide Octamolybdomagnate(II) KBrO3 126

Table 3: Oxidation of Inorganic and Organic substrate by using POM anion as catalyst

C] Oxidation of Pharmaceutically Important organic compounds by using POM:- The study of oxidation mechanism involving drugs was well documented [127-132] in case of 12-Tungstocabaltate(III). While comparatively very few studies are reported on other POM’s [133-134]. Recent study focuses on study of electron-transfer processes for pharmaceutical and biological investigations.

Oxidant Pharmaceutically Important substrate Rate law Ref

[CoIIIW12O40]-5 L-cystine kobs = [LH3+]T (k1[H+] + k2 K2 ) /

([H+] + K2) 127

[CoIIIW12O40]-5 Pyridoxine k Kc [H+] [Pyridoxine]

/ ([H+] +K1 )(1+Kc[Pyridoxine]) 128

[CoIIIW12O40]-5 Semicarbazide kobs = (K1 k1 〖[semicarbazide]〗^2)/((K_1+ [H^+])) 129

[CoIIIW12O40]-5 Guaifenesin kobs = (K_1 k_1 〖[Guaifenesin]〗_T)/((K_1+ [H^+])) 130

[CoIIIW12O40]-5 Atenolol kobs = ( K 〖[ATN]〗_T k_1 k_2 [ H^+] )/((K_1+ [H^+])) 131

[CoIIIW12O40]-5 Levosalbutamol kobs = (K_1 k_1 〖[L]〗_T)/((K_1+ [H^+])) 132

(NH4)6[MnIVMo9O32] pyridoxine kcKc [H+] [Pyridoxine]

/ ([H+] +K1 )(1+Kc[Pyridoxine]) 133

[CoIIIMo] Paracetamol k1[Paracetamol] [H+]2/

[H+]2 +K1[H2MoO4][H+]+K2[CoIIIMo]2- 62


Table 4: Oxidation of Pharmaceutically Important organic compounds by using POM

The oxidation of organic compounds generally proceeds with very low rates and they require rather drastic conditions. POM show good selectivity and high yields. Due to high selectivity, POM’s are also useful for clean synthesis of fine and specific chemicals having industrial importance. Consequently, current research is centered on oxidation of pharmaceutically important organic compounds. Herein we report “KINETICS AND MECHANISM OF OXIDATION OF PHARMACEUTICALLY IMPORTANT ORGANIC COMPOUNDS BY POLYOXOMETALATES.”

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