Oxidation of Vanillin by a New Oxidant Diperiodatoargentate (III) in

P.G. Department of Studies in Chemistry, Karnatak UniVersity, Dharwad-580 003, India. The kinetics of oxidation of vanillin (VAN) by diperiodatoargent...
0 downloads 0 Views 88KB Size
Download PDF
Ind. Eng. Chem. Res. 2007, 46, 1459-1464

1459

KINETICS, CATALYSIS, AND REACTION ENGINEERING Oxidation of Vanillin by a New Oxidant Diperiodatoargentate(III) in Aqueous Alkaline Medium Deepak S. Munavalli, Shivamurti A. Chimatadar, and Sharanappa T. Nandibewoor* P.G. Department of Studies in Chemistry, Karnatak UniVersity, Dharwad-580 003, India

The kinetics of oxidation of vanillin (VAN) by diperiodatoargentate (III) (DPA) in alkaline medium at a constant ionic strength of 1.0 mol dm-3 was studied spectrophotometrically. The reaction between DPA and vanillin in alkaline medium exhibits 1:1 stoichiometry (vanillin:DPA). The reaction is first order in [DPA] and has less than unit order both in [VAN] and [alkali]. A decrease in the dielectric constant of the medium increases the reaction rate. An increase in periodate concentration has no effect on the rate. The oxidation reaction in alkaline medium has been shown to proceed via a DPA-vanillin complex, which decomposes slowly in a rate-determining step to give the products. The main products were identified by spot test, IR, and MS studies. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed. Thermodynamic quantities are also determined. 1. Introduction 3-Methoxy-4-hydroxy benzaldehyde, commercially called p-vanillin and in general vanillin (VAN) occurs in nature as a glucoside, which hydrolyzes to vanillin and sugar. It is a very popular flavoring reagent in the food industry, and it is also useful in the synthesis of drugs. It is also used in the preparation of perfume and as a catalyst to polymerize methylacrylate.1 Vanillin has both phenolic and aldehydic groups and is capable of undergoing three different types of reactions: those of the aldehydic group, the phenolic hydroxyl, and aromatic nucleus. However, as a p-hydroxybenzaldehyde, vanillin does not undergo some common aldehyde reactions, such as Cannizzaro’s reaction and the benzoin condensation. If the hydroxyl group in vanillin is protected, it undergoes oxidation2 to vanillic acid. Similar to that of phenol, vanillin forms esters and ethers and the nucleus is easily substituted by halogen and nitro groups. In comparison with most other aldehydes, vanillin is noted for its stability. Only a few kinetic studies have been reported3,4 in the literature on the oxidation of vanillin. Diperiodatoargentate(III) (DPA) is a powerful oxidizing agent in alkaline medium with the reduction potential of 1.74 V.5a It is widely used as a volumetric reagent for the determination of various organic and inorganic species.6 Rao et al.7 have used DPA as an oxidizing agent for the kinetics of oxidation of various organic substrates. But, they did not indicate the possible active species of DPA in alkali, and on the other hand, they proposed mechanisms by generalizing the DPA as [Ag(HL)L](x+1)-. However, Kumar et al.8 made an effort to give evidence for the reactive form of DPA in the large scale of alkaline pH values. In the present investigation, we have obtained evidence for the reactive species for DPA in alkaline medium. A literature survey reveals that there are no reports on the kinetics of oxidation of vanillin by DPA. Hence, in order to understand the active species * To whom correspondence should be addressed. Tel.: +91-8362770524. Fax: +91-836-2747884. E-mail: [email protected].

of the oxidant and to propose a suitable mechanism based on experimental results, the title reaction is investigated. 2. Experimental Section 2.1. Materials and Reagents. All chemicals used were of reagent grade and double-distilled water was used throughout the work. A stock solution of vanillin (sd. fine chem.) was prepared by dissolving an appropriate amount of recrystallized sample in double-distilled water. The purity of the vanillin sample (99%) was checked by comparing its IR spectrum with literature data and with its melting point (mp), 81 °C (literature mp 81-83 °C). The required concentration of vanillin was used from its stock solution. An aqueous solution of AgNO3 was used to study the product effect, Ag(I). KNO3 (BDH) and KOH (BDH) were used to maintain ionic strength and alkalinity of the reaction, respectively. A stock solution of IO4- was prepared by dissolving a known weight of KIO4 (Riedel-de Haen) in hot water and was used after 24 h. Its concentration was ascertained iodometrically at neutral pH maintained by using phosphate buffer.9 2.1.1. Preparation of DPA. DPA was prepared by oxidizing Ag(I) in presence of KIO4 as described elsewhere:10 the mixture of 28 g of KOH and 23 g of KIO3 in 100 cm3 of water along with 8.5 g of AgNO3 was heated just to boiling, and 20 g of K2S2O8 was added in several lots with stirring; the mixture was then allowed to cool. It was filtered through a medium porosity fritted glass filter, and 40 g of NaOH was added slowly to the filtrate, whereupon a voluminous orange precipitate agglomerates. The precipitate is filtered as above and washed three to four times with cold water. The pure crystals were dissolved in 50 cm3 water and warmed to 80 °C with constant stirring, thereby some solid was dissolved to give a red solution. The resulting solution was filtered when it was hot, and on cooling at room temperature, the orange crystals separated out and were recrystallized from water.

10.1021/ie0613725 CCC: $37.00 © 2007 American Chemical Society Published on Web 02/02/2007

1460

Ind. Eng. Chem. Res., Vol. 46, No. 5, 2007 Table 1. Effect of Variation of [DPA], [VAN], [OH-], and [IO4-] on the Diperiodatoargentate(III) Oxidation of Vanillin in Alkaline Medium at 298 K and I ) 1.0 mol dm-3 kobs × 103 (s-1) [DPA] × 105 [VAN] × 104 [OH-] [IO4-] × 105 (mol dm-3) (mol dm-3) (mol dm-3) (mol dm-3)

Figure 1. First-order plots for the oxidation of vanillin by DPA in an aqueous alkaline medium at 298 K: [VAN] ) 5.0 × 10-4; [OH-]) 0.40 and I ) 1.0 mol dm-3; [DPA] × 10-5 (mol dm-3)s(1) 1.0, (2) 3.0, (3) 5.0, (4) 8.0, (5) 10.0.

1.0 3.0 5.0 8.0 10.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0

5.0 5.0 5.0 5.0 5.0 1.0 3.0 5.0 8.0 10.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0

0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.09 0.2 0.4 0.7 0.9 0.4 0.4 0.4 0.4 0.4

1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.6 0.8 1.0 3.0 5.0

found

calcd

2.26 2.34 2.27 2.35 2.35 1.00 2.02 2.27 2.67 3.15 1.11 1.74 2.27 2.56 2.94 2.12 2.23 2.20 2.18 2.22

2.36 2.36 2.36 2.36 2.36 0.99 1.83 2.36 2.67 2.85 1.14 1.75 2.36 2.66 2.78

Table 2. Effect of Added Products on the Oxidation of Vanillin by DPA at 298 Ka [Ag(I)] × 105 (mol dm-3)

kobs × 103 (s-1)

[vanillicacid] × 104 (mol dm-3)

kobs × 103 (s-1)

0.0 1.0 2.0 3.0 4.0 5.0

2.27 2.20 2.29 2.23 2.28 2.25

0.0 1.0 2.0 3.0 4.0 5.0

2.27 2.30 2.20 2.22 2.30 2.27

a [DPA] ) 5.0 × 10-5; [VAN] ) 5.0 × 10-4; [OH-] ) 0.40; [IO -] ) 4 1.0 × 10-5; I ) 1.0 mol dm-3.

Figure 2. Mass spectrum of reaction product, vanillic acid with its molecular ion peak at 168 amu.

The complex, characterized from its UV spectrum, exhibited three peaks at 216, 255, and 362 nm. These spectral features were identical to those reported10 earlier for DPA. The magnetic moment study revealed that the complex is diamagnetic. The compound prepared was analyzed11 for silver and periodate by acidifying a solution of the material with HCl, recovering and weighing the AgCl for Ag and titrating the iodine liberated when excess KI was added to the filtrate for IO4-. The aqueous solution of DPA was used for the required DPA concentration in the reaction mixture. 2.2. Kinetic Measurements. The kinetic measurements were performed on a Varian CARY 50 Bio UV-visible spectrophotometer. The kinetics was followed under pseudo-first-order conditions where [VAN] > [DPA] at 25 ( 0.1 °C, unless otherwise stated. The reaction was initiated by mixing the DPA to VAN solution, which also contained a required concentration of KNO3, KOH, and KIO4; the progress of reaction was followed spectrophotometrically at 360 nm by monitoring the decrease in absorbance of DPA. The molar absorbance index, at 360 nm, was found to be  )13900 ( 100 dm3 mol-1 cm-1. The pseudo-first-order rate constants, “kobs”, were determined from the log(absorbance) vs time plots and were reproducible to within (5%. The plots were linear up to 90% completion of reaction, as in Figure 1. During the kinetics, a constant concentration, viz., 1.0 × 10-5 mol dm-3 of KIO4 was used

throughout the study unless otherwise stated. Thus, the possibility of oxidation of VAN by periodate was checked, and it was found that there was no significant reaction under experimental conditions. The effect of dissolved oxygen on the rate of reaction was checked by preparing the reaction mixture and following the reaction in an atmosphere of nitrogen. No significant difference was obtained in the presence or absence of nitrogen. 3. Results 3.1. Stoichiometry and Product Analysis. Different sets of reaction mixtures containing varying ratios of DPA to vanillin in the presence of a constant amount of OH- and KNO3 were kept for 6 h in a closed vessel under a nitrogen atmosphere. The remaining concentration of DPA was estimated by spectrophotometer at 360 nm. The results indicated a (1:1) stoichiometry as given in eq 1.

The main reaction product was isolated by acidifying the reaction mixture with acetic acid followed by ether and ethyl acetate extraction. Each extract was dehydrated with anhydrous Na2SO4 and decanted, the solvent was removed by evaporation. The residue was recrystallized from warm glacial acetic acid.

Ind. Eng. Chem. Res., Vol. 46, No. 5, 2007 1461 Table 3. Thermodynamic Activation Parameters for the Oxidation of Vanillin by DPA in an Aqueous Alkaline Medium, with Respect to the Slow Step of Scheme 1 (A) Effect of Temperature temperature (K)

k × 103 (s-1)

298 303 308 313

3.7 7.2 10.8 17.2

(B) Activation Parameters (see Scheme 1) parameter Ea ∆H# ∆S# ∆G# log A Figure 3. Effect of dielectric constant (D) and ionic strength (I) on the oxidation of vanillin by diperiodatoargentate(III) in aqueous alkaline medium at 298 K: 3 + log kobs vs 1/D × 102 (-[-); 3 + log kobs vs I1/2 (-2-).

The main reaction product was identified as vanillic acid by spot test12 and by the IR spectrum (1686 cm-1 due to >CdO stretching and 3486 cm-1 due to OsH stretching). It was also confirmed by its melting point, 207 °C (literature mp 208 °C). Further, the reaction product was subjected to mass spectral analysis. MS data was obtained on a QP-5050A shimadzu mass spectrometer using the electron impact (EI) ionization technique. The mass spectrum showed a molecular ion peak at 168 amu confirming vanillic acid as in Figure 2. All other peaks observed in GC-MS can be interpreted in accordance with the observed structure of vanillic acid. The product, Ag+, in solution was identified by adding a KCl solution to the reaction mixture, which produced white precipitate due to the formation of AgCl. It was observed that the products formed did not undergo any further oxidation under the present kinetic conditions. 3.2. Reaction Orders. The reaction orders were determined from the slopes of log kobs vs log(concentration) plots by varying the concentration of the reductant and alkali in turn while keeping the other conditions constant. The DPA concentration was varied in the range of 1.0 × 10-5 to 1.0 × 10-4 mol dm-3, and the linearity of the plots, log(absorbance) vs time up to 90% completion of the reaction as in Figure 1, indicates a unit order dependence on DPA concentration. This was also confirmed by varying DPA concentration which did not result in any change in the pseudo-first-order rate constants, kobs, as reported in Table 1. The vanillin concentration was varied in the range 1.0 × 10-4 to 1.0 × 10-3 mol dm-3 at 25 °C while keeping other reactant concentrations and conditions constant. The kobs values increased with the increase in concentration of vanillin as reported in Table 1. From the slope of the plot of log kobs vs log [vanillin], less than unit order with respect to vanillin concentration was found. The effect of alkali on the reaction was studied in the range of 0.09 to 0.9 mol dm-3 at constant concentrations of vanillin, DPA, and a constant ionic strength of 1.0 mol dm-3. The rate constants increased with increasing alkali concentration, and the order was found to be less than unity. 3.3. Effect of [Periodate]. The periodate concentration was varied from 6.0 × 10-6 to 5.0 × 10-5 mol dm-3 at constant concentrations of DPA, VAN, and OH- and at constant ionic strength. It was observed that the periodate concentration had a negligible effect on the rate of reaction; the values are reported in Table 1.

value 78 ( 2 kJ mol-1 75 ( 1 kJ mol-1 -38.8 ( 0.5 J K-1 mol-1 87 ( 2 kJ mol-1 11.1 ( 0.2

(C) Effect of Temperature on Equilibrium Constants of Scheme 1 for the Oxidation of Vanillin by Diperiodatoargentate (III) in Alkaline Medium temperature (K)

K1 (dm3 mol-1)

K2 × 104 (mol dm-3)

298 303 308 313

0.58 ( 0.02 1.03 ( 0.05 2.10 ( 0.06 3.00 ( 0.08

1.71 ( 0.06 1.29 ( 0.04 0.71 ( 0.03 0.29 ( 0.01

(D) Thermodynamic Quantities Using K1 and K2 thermodynamic quantities

values from K1

values from K2

∆H ∆S ∆G298

88 ( 2 kJ mol-1 290 ( 8 J K-1 mol-1 1.34 ( 0.06 kJ mol-1

-76 ( 5 kJ mol-1 -177 ( 18 J K-1 mol-1 -24.1 ( 0.9 kJ mol-1

3.4. Effect of Products. Initially added products, Ag(I) and vanillic acid, had no effect on the rate of reaction (Table 2). 3.5. Effect of Ionic Strength (I) and Dielectric Constant of the Medium (D). The addition of KNO3, to increase the ionic strength of the reaction, increased the rate of reaction at constant DPA, VAN, OH-, and IO4- concentrations. The plot of log kobs vs I1/2 was found to be linear with a positive slope as given in Figure 3. The dielectric constant of the medium, D, was varied by varying the t-butyl alcohol-water percentage. The decrease in dielectric constant of the reaction medium increased the rate, and the plot of log kobs vs 1/D was linear with a positive slope as given in Figure 3. 3.6. Effect of Temperature (T). The effect of temperature on the rate of reaction was studied at 25, 30, 35, and 40 °C. The rate constants, k, of the slow step of Scheme 1 were obtained from the intercepts of the plots of 1/kobs vs 1/[VAN] at different temperatures. The values are given in Table 3. The activation energy was obtained from the plot of log k vs 1/T, from which activation parameters were calculated and are given in Table 3. 3.7. Test for Free Radicals (Polymerization Study). The intervention of free radicals was examined as follows: The reaction mixture, to which a known quantity of acrylonitrile scavenger had been added initially, was kept in an inert atmosphere for 2 h. Upon diluting the reaction mixture with methanol, no precipitate was observed. This indicates that the free radicals were absent in the reaction. 4. Discussion In the later period of 20th century, the kinetics of oxidation of various organic and inorganic substrates have been studied by Ag(III) species which may be due to the strong versatile nature of the two-electron oxidant. Among the various species

1462

Ind. Eng. Chem. Res., Vol. 46, No. 5, 2007 Scheme 1. Detailed Mechanism for the Oxidation of Vanillin by Alkaline DPA

Figure 4. Verification of rate law 5 in the form of eq 6 on the oxidation of vanillin by diperiodatoargentate(III) in aqueous alkaline medium at 298 K: 1/kobs vs 1/[OH-] (-[-); 1/kobs vs 1/[VAN] (-2-).

of Ag(III), Ag(OH)4-, diperiodatoargentate(III), and ethylenebis (biguanide) (EBS) silver(III) are of maximum attention to the researchers due to their relative stability.13 The stability of Ag(OH)4- is very sensitive toward traces of dissolved oxygen and other impurities in the reaction medium. Due to this, not much attention drawn to Ag(OH)4-. However, the other two forms of Ag(III)7,8,14 are considerably stable; DPA is used in highly alkaline medium, and EBS is used in highly acidic medium. The literature survey10 reveals that the water soluble diperiodatoargentate(III) (DPA) has a formula [Ag(IO6)2]7- with a dsp2 configuration of square planar structure, similar to the diperiodatocopper(III) complex with two bidentate ligands, periodate to form a planar molecule. When the same molecule is used in alkaline medium, it is unlikely to exist as [Ag(IO6)2]7-. The periodate is known to be in various protonated forms15 depending on the pH of the solution as given in the following multiple equilibria (2)-(4).

H5IO6 h H4IO6- + H+

(2)

H4IO6- h H3IO62- + H+

(3)

H3IO62- h H2IO63- + H+

(4)

Periodic acid exists in acid medium as H5IO6 and as H4IO6- at pH 7. Thus, under the present alkaline conditions, the main species are expected to be H3IO62- and H2IO63-. At higher concentrations, periodate also tends to dimerize.5b On the contrary, the authors in their recent studies7 proposed DPA as [Ag(HL)2]x-, in which L is a periodate with an uncertain number of protons and HL is a protonated periodate of an uncertain number of protons. This can be ruled out by considering the alternative form15 of IO4- at pH > 7 which is in the form H3IO62- or H2IO63-. Hence, DPA could be as [Ag(H3IO6)2]or [Ag(H2IO6)2]3- in alkaline medium. Therefore, under the present experimental conditions, diperiodatoargentate(III) may be depicted as [Ag(H3IO6)2]-. The similar speciation of periodate in alkali was proposed16 for diperiodatonickelate(IV). The added products did not have any significant effect on the rate of reaction. On the basis of these experimental results, the following mechanism has been proposed in the form of Scheme 1.

It is a well-known fact that vanillin exists in the anionic form in alkaline medium.17 In the first equilibrium step of Scheme 1, the [OH-] deprotonates the DPA to give a deprotonated diperiodatoargentate(III) (DPA). In the second equilibrium step of Scheme 1, diperiodatoargentate(III) (DPA) combines with a molecule of the anionic form of vanillin to give an intermediate complex. The complex decomposes in a rate-determining step to give the products, vanillic acid and Ag(I) species, by two equivalent change of Ag(III) in a single step as no intervention of free radicals has been observed. The plot of 1/kobs vs 1/[VAN] proved the complex formation between oxidant and reductant, which explains the less than unit order in [VAN]. On the basis of the square planar structure of DPA, the structure of complex may be proposed as given below

The oxygen atom of the aldehyde group of the vanillin is involved in the formation of the intermediate complex. Spectroscopic evidence for the complex formation between the oxidant and substrate was obtained from UV-vis spectra of vanillin (5.0 × 10-4), DPA (5.0 × 10-5), OH- (0.50 mol dm-3), and a mixture of both. A hypsochromic shift of about 5 nm from 291 to 286 nm in the spectra of DPA was observed. Scheme 1 leads to the following rate equation.

rate ) -

kK1K2[DPA][VAN][OH-] d[DPA] ) dt 1 + K1[OH-] + K1K2[OH-][VAN] or

kK1K2[VAN][OH-] rate ) kobs ) [DPA] 1 + K1[OH-] + K1K2[OH-][VAN]

(5)

Ind. Eng. Chem. Res., Vol. 46, No. 5, 2007 1463

The rate law (5) can be rearranged to eq 6, which is suitable for verification

1 1 1 1 ) + + kobs kK K [OH-][VAN] kK2[VAN] k 1 2

(6)

According to eq 6, the plots of 1/kobs vs 1/[OH-] and 1/kobs vs 1/[VAN] were expected to be linear and found to be so, as shown in Figure 4. From the intercepts and slopes of such plots, the equilibrium constants K1, K2, and k were calculated as (0.58 ( 0.02) dm3 mol-1, (1.71 ( 0.06) × 104 dm3 mol-1, and (3.7 ( 0.20) × 10-3 s-1, respectively, at 25 °C. The value of K1 obtained is in agreement with the earlier literature.18 Using these values, the rate constants under different experimental conditions were calculated. There was a good agreement between observed and calculated rate constants (Table 1), which fortifies Scheme 1. The effect of increasing ionic strength on the rate explains qualitatively the reaction between two negatively charged ions, as seen in Scheme 1. The effect of the solvent on the reaction rate has been described in detail in the literature.19 An increase in rate with an increase in the dielectric constant of the medium supports the involvement of similar charged species as shown in Scheme 1. The thermodynamic quantities for the different equilibrium steps of Scheme 1 can be evaluated as follows. The vanillin and hydroxide ion concentrations given in Table 1 were varied at different temperatures. The plots of 1/kobs vs 1/[VAN] and 1/kobs vs 1/[OH-] should be linear as shown in Figure 4. From the slopes and intercepts, the values of K1 and K2 were calculated at different temperatures. A vant Hoff’s plot was made for the variation of K1 with temperature [i.e., log K1 vs 1/T] and the values of the enthalpy of reaction ∆H, entropy of reaction ∆S, and free energy of reaction ∆G were calculated and are given in Table 2. A comparison of the latter values with those obtained for the slow step of the reaction shows that these values mainly refer to the rate-limiting step, supporting the fact that the reaction before the rate-determining step is fairly slow and involves high activation energy.20 In the same manner, K2 values were calculated at different temperatures and the corresponding values of thermodynamic quantities are given in Table 2. The negative value of ∆Sq suggests that the intermediate complex is more ordered than the reactants.21 The observed modest activation energy and sizable entropy of activation supports a complex transition state in the reaction. The observed modest enthalpy of activation and a relatively low value of the entropy of activation, as well as a higher rate constant for the slow step indicates that the oxidation presumably occurs via an innersphere mechanism. This conclusion is supported by the literature.21

Appendix According to Scheme 1

rate )

-d[DPA] ) k[c] ) kK2K1[DPA][VAN][OH-] dt

The total concentration of DPA is given by (where “T” and “f” refer to the total and free concentration, respectively)

[DPA]T ) [DPA]f + [Ag(H3IO6)]2- + C ) [DPA]f + K1 [DPA][OH-] + K2[VAN][Ag(H3IO6)(H2IO6)]2) [DPA]f + K1[DPA][OH-] + K1K2[VAN][DPA][OH-] [DPA]T ) [DPA]f{1 + K1[OH-] + K1K2[VAN][OH-]} [DPA]f )

Among various species of DPA in alkaline medium, diperiodatoargentate(III) (DPA), is considered to be an active species for the title reaction. The results demonstrate that, in carrying out this reaction, the role of pH in the reaction medium is crucial. The rate constant of the slow step and other equilibrium constants involved in the mechanism are evaluated and activation parameters with respect to the slow step of reaction were computed. The overall mechanistic sequence described here is consistent with product, kinetic, and mechanistic studies.

[DPA]T

(II)

-

{1 + K1[OH ] + K1K2[VAN][OH-]}

Similarly, the total concentration of vanillin is given by

[VAN]T ) [VAN]f + C ) [VAN]f + K1K2[VAN][DPA] [OH-] ) [VAN]f {1 + K1K2[DPA][OH-]} [VAN]f )

[VAN]T 1 + K1K2[DPA][OH-]

In view of the low concentrations of DPA and OH- used,

[VAN]f ) [VAN]T

(III)

Similarly,

[OH-]T ) [OH-]f + [Ag(H3IO6)]2- + C ) [OH]f + K1 [DPA][OH-] + K1K2[VAN][DPA][OH-] ) [OH-]f {1 + K1[DPA] + K1K2[VAN][DPA]} [OH-]f )

[OH-]T {1 + K1[DPA] + K1K2[VAN][DPA]}

In view of the low concentrations of DPA and VAN used,

[OH-]f ) [OH-]T

(IV)

Subustituting (II), (III), and (IV) in (I) and omitting the subscripts T and f, we get

rate ) Conclusion

(I)

kK1K2[VAN][OH-][DPA] 1 + K1[OH-] + K1K2[OH-][VAN]

Nomenclature and Abbreviations (DPA) ) diperiodatoargentate(III) (VAN) ) vanillin  ) molar absorption coefficient kobs ) observed rate constant k ) rate constant with respect to slow step of the mechanism K1, K2, and K3 ) equilibrium constants ∆H ) change in the enthalpy of reaction ∆S ) change in entropy of the reaction

1464

Ind. Eng. Chem. Res., Vol. 46, No. 5, 2007

∆G ) change in free energy of the reaction ∆Sq ) entropy of activation ∆Hq ) enthalpy of activation ∆Gq ) free energy of activation D ) dielectric constant of the medium I ) ionic strength of the medium T (K) ) absolute temperature in kelvin UV ) ultraviolet spectra IR ) infrared spectra MS ) mass spectra L ) ligand periodate EI ) electron impact Literature Cited (1) Imoto, M.; Maeda, T.; Ouchi, T. Chem. Lett. 1978, 2, 153. (2) Lange, G. Cleavage of alkyl O-Hydroxyphenyl Ethers. J. Org. Chem. 1962, 27, 2037. (3) Jose, T. P.; Nandibewoor, S. T.; Tuwar, S. M. Kinetics and mechanism of the oxidation of vanillin by hexacyanoferrate (III) in Aqueous Alkaline Medium. J. Solution Chem. 2006, 35, 51. (4) Kathari, C. P.; Pol, P. D.; Nandibewoor, S. T. The Kinetics and Mechanism of Oxidation of Vanillin by diperiodatonickelate(IV) in aqueous alkaline medium. Turk. J. Chem. 2002, 26, 229. (5) Sethuram, B. Some aspects of Electron - Transfer Reactions InVolVing Organic Molecules; Allied Publishers (P) Ltd.: New Delhi, 2003; (a) p 78 (b) 151. (6) (a) Jaiswal, P. K.; Yadava, K. L. Silver (III) as an oxidative Titrant Determination of Some Sugars, Carboxylic Acids and Inorganic Ions. Talanta 1970, 17, 236. (b) Jaiswal, P. K. Analyst 1972, 1, 503. (7) (a) Rao, J. P.; Sethuram, B.; Rao, N. T. Kinetics of Oxidative Deamination of Some Amino Acids by Diperiodatoargentate(III) in Alkaline Medium. React. Kinet. Catal. Letts. 1985, 29, 289. (b) Venkata Krishna, K.; Rao, J. P. Kinetics and Mechanism of Oxidation of Pyrimidine Nucleobases by Diperiodatoargentate(III) in Aqueous Alkaline Medium. Indian J. Chem. 1998, 37A, 1106 and references therein. (8) (a) Kumar, A.; Kumar, P.; Ramamurthy, P. Kinetics of Oxidation of Glysine and Related Substrates by Diperiodatoargentate(III). Polyhedron 1999, 18, 773. (b) Kumar, A.; Kumar, P. Kinetics and Mechanism of Oxidation of Nitrilotriacetic acid by Diperiodatoargentate(III) J. Phys. Org. Chem. 1999, 12, 79. (c) Kumar, A.; Vaishali; Ramamurthy, P. Kinetics and Mechanism of Oxidation of Ethylenediamine and Related compounds by Diperiodatoargentate(III) ion. Int. J. Chem. Kinet. 2000, 32, 286. (9) Panigrahi, G. P.; Misro, P. K. Kinetics and Mechanism of Oxidation of Os (VIII) Catalised Oxidation of Unsaturated Acids by Sodium Periodate. Indian J. Chem. 1978, 16A, 201. (10) Cohen, G. L.; Atkinson, G. The Chemistry of Argentic Oxide. The Formation of Silver(III) Complex with periodate in Basic Solution. Inorg. Chem. 1964, 3, 1741.

(11) Jeffery, G. H.; Bassett, J.; Mendham, J.; Denny, R. C. Vogel’s Textbook of QuantitatiVe Chemical Analysis, 5th ed.; ELBS, Longman: Essex U.K., 1996; pp 467 and 391. (12) Feigl, F. Spot Tests in Organic Analysis; Elsevier: New York, 1975; p 332. (13) Krishenbaum, L. J.; Mrozowski, L. Kinetics of Silver (III) Decomposition in Dilute Acid. Inorg. Chem. 1978, 17, 3718. (14) (a) Banerjee, R.; Das, K.; Das, A.; Dasgupta, S.; Kinetics of Silver (I)-Catalysed Oxidation of Formic Acid by the [Ethyienebis(biguanide)]Silver(III) Cation in Acid Perchlorate Media. Inorg. Chem. 1989, 28, 585. (b) Banerjee, R.; Das V.; Mukhopadhyay, S. Kinetics of Silver (I)-Catalysed Oxidation of H3PO2 with [Ethyienebis(biguanide)]-Silver(III) Cation in Aqueous Perchloric acid Solution. J. Chem. Soc., Dalton Trans. 1992, 1317. (15) Crouthamel, C. E.; Hayes, A. M.; Martin, D. S.; Ionization and Hydration Equilibria of Periodic Acid J. Am. Chem. Soc. 1951, 73, 82. Shetter, R.S.; Nandibewoor, S. T. Kinetic, Mechanistic and Spectral Investigations of Ruthenium(III) Catalysed Oxidation of 4-hydroxycoumarin by Alkaline Diperiodatonickelate (IV). J. Mol. Catal., A. 2005, 238, 137. (c) Bailar, J. C., Jr.; Emeleus, H. J.; Nyholm, S. R.; Trotman- Dikenson, A. F. ComprehensiVe Inorganic Chemistry; Pergamon Press: Oxford, 1975; Vol. 2, p 1456. (16) Bhattacharya, S.; Saha, B.; Datta, A.; Banerjee, P. Electron Transfer Reactions of Nickel(III) and Nickel(IV) Complexes. Coord. Chem. ReV. 1998, 170, 47. Haines, R. I.; McAuley, A. Synthesis and Reactions of Nickel(iii) Complexes. Coord. Chem. ReV. 1981, 39, 77. (17) Mahesh, R. T.; Bellakki, M. B.; Nandibewoor, S. T. Kinetics and Mechanism of Oxidation of L-proline by Heptavalent Manganese: A free Radical Intervention, and Decarboxylation. J. Chem. Res. 2005, 13. (18) Hiremath, C. V.; Kiran, T. S.; Nandibewoor, S. T. Os(VIII)/Ru(III) Catalysed Oxidation of Aspirin Drug by a New Oxidant, Diperiodatoargentate(III) in Aqueous Alkaline Medium: A Comparative Kinetic Study. J. Mol. Catal. A. 2006, 248, 163. (19) Moelwyn-Hughes, E. A. Physical Chemistry, 2nd ed.; Pergamon Press: New York, 1961. Amis, E. S. SolVent Effects on Reaction Rates and Mechanisms, Academic Press: New York, 1966. (20) Rangappa, K. S.; Raghavendra, M. P.; Mahadevappa, D. S.; Channegouda, D. Sodium N-Chlorobenzonesulfonamide as a Selective Oxidant for Hexasomines in Alkaline Medium: A Kinetic and Mechanistic Study. J. Org. Chem. 1998, 63, 531. (21) Martinez, M.; Pitarque, M. A.; Eldik, R. V. Outer-sphere Redox Reactions of [CoIII(NH3)5(HxPYOZ)](n-3)- Complexes. A Temperature and Pressure-Dependance Kinetic Study on the Influence of the Phosphorous Oxoanions. J. Chem. Soc., Dalton Trans. 1996, 2665. Farokhi, S. A.; Nandibewoor, S. T. Kinetic, Mechanistic and Spectrual Studies for the Oxidation of Alkaline Hexacyno Ferrate(III). Tetrahedron 2003, 59, 7595.

ReceiVed for reView October 25, 2006 ReVised manuscript receiVed December 2, 2006 Accepted December 23, 2006 IE0613725