Scholarly article on topic 'Kinetic, mechanistic, and spectroscopic studies of permanganate oxidation of azinylformamidines in acidic medium, with autocatalytic behavior of manganese(II)'

Kinetic, mechanistic, and spectroscopic studies of permanganate oxidation of azinylformamidines in acidic medium, with autocatalytic behavior of manganese(II) Academic research paper on "Chemical sciences"

CC BY-NC-ND
0
0
Share paper
Academic journal
Journal of Saudi Chemical Society
OECD Field of science
Keywords
{Kinetics / Mechanism / Permanganate / Oxidation / Azinylformamidines / Manganese(II)}

Abstract of research paper on Chemical sciences, author of scientific article — Basim H. Asghar, Ahmed Fawzy

Abstract The kinetics of permanganate oxidation of two substituted azinylformamidines (Azn-Fs), namely N,N-dimethyl-N′-(pyridin-2-yl)formamidine (Py) and N,N-dimethyl-N′-(pyrimidin-2-yl)formamidine (Pym), in sulfuric acid were investigated using conventional spectrophotometry. Kinetic evidence for the formation of 1:1 intermediate complexes between the oxidant and substrates was obtained. The reactions of both substrates with permanganate showed similar kinetics, i.e. first order in [MnO4 −]0 and fractional-first-order with respect to both [Azn-F]0 and [H+]. The initial product, Mn2+, was found to autocatalyze the oxidation process. Changes in the ionic strength and dielectric constant of the medium had no significant effect on the rate. The final oxidation products of Py and Pym were identified as 2-aminopyridine and 2-aminopyrimidine, respectively, in addition to dimethylamine and carbon dioxide. A plausible reaction mechanism is suggested and the reaction constants involved in the mechanism were evaluated.

Academic research paper on topic "Kinetic, mechanistic, and spectroscopic studies of permanganate oxidation of azinylformamidines in acidic medium, with autocatalytic behavior of manganese(II)"

Accepted Manuscript

Original article

Kinetic, mechanistic, and spectroscopic studies of permanganate oxidation of azinylformamidines in acidic medium, with autocatalytic behavior of manga-nese(II)

Basim H. Asghar, Ahmed Fawzy

PII: DOI:

Reference:

S1319-6103(14)00180-X http://dx.doi.org/10.1016/joscs.2014.12.001 JSCS 700

To appear in:

Journal of Saudi Chemical Society

Received Date: Revised Date: Accepted Date:

28 August 2014

29 November 2014 2 December 2014

Please cite this article as: B.H. Asghar, A. Fawzy, Kinetic, mechanistic, and spectroscopic studies of permanganate oxidation of azinylformamidines in acidic medium, with autocatalytic behavior of manganese(II), Journal of Saudi Chemical Society (2014), doi: http://dx.doi.org/10.1016/jjscs.2014.12.001

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Kinetic, mechanistic, and spectroscopic studies of permanganate oxidation of azinylformamidines in acidic medium, with autocatalytic behavior of manganese(II)

Basim H. Asgharb'*, Ahmed Fawzy a'b

a Chemistry Department, Faculty of Applied Sciences, Umm Al-Qura University, Makkah, Saudi An b Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt

Abstract The kinetics of permanganate oxidation of two substituted azinylformamidines (Azn-Fs), namely N,N-dimethyl-.W-(pyridin-2-yl)formamidine (Py) and ^,^-dimethyl-^'-(pyrimidin-2-yl)formamidine (Pym), in sulfuric acid were

substitut

investigated using conventional spectrophotometry. Kinetic evidence for the formation of 1:1 intermediate complexes between the oxidant and substrates was obtained. The reactions of both substrates with permanganate showed similar kinetics, i.e. first order in [MnO4-]0 and fractional-first-order with respect to both [Azn-F]0 and [H+]. The initial product, Mn2+, was found to autocatalyze the oxidation process. Changes in the ionic strength and dielectric constant of the medium had no significant effect on the rate. The final oxidation products of Py and Pym were identified as 2-aminopyridine and 2-aminopyrimidine, respectively, in addition to dimethylamine and carbon dioxide. A plausible reaction mechanism is suggested and the reaction constants involved in the mechanism were evaluated.

Keywords: Kinetics, Mechanism, Permanganate, Oxidation, Azinylformamidines, Manganese(II)

*Corresponding author. Tel.: +966 555511003. E-mail address: bhasghar@uqu.edu.sa

Kinetic, mechanistic, and spectroscopic studies of permanganate oxidation of azinylformamidines in acidic medium, with autocatalytic behavior of manganese(II)

b Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt

Basim H. Asgharb'*, Ahmed Fawzy a'b

Chemistry Department, Faculty of Applied Sciences, Umm Al-Qura University, Makkah, Saudi Arabia

Abstract The kinetics of permanganate oxidation of two substituted azinylformamidines (Azn-Fs), namely N,N-dimethyl-.W-(pyridin-2-yl)formamidine (Py) and ^,^-dimethyl-^'-(pyrimidin-2-yl)formamidine (Pym), in sulfuric acid were investigated using conventional spectrophotometry. Kinetic evidence for the formation of 1:1 intermediate complexes between the oxidant and substrates was obtained. The reactions of both substrates with permanganate showed similar kinetics, i.e. first order in [MnO4-]0 and fractional-first-order with respect to both [Azn-F]0 and [H+]. The initial product, Mn2+, was found to autocatalyze the oxidation process. Changes in the ionic strength and dielectric constant of the medium had no significant effect on the rate. The final oxidation products of Py and Pym were identified as 2-aminopyridine and 2-aminopyrimidine, respectively, in addition to dimethylamine and carbon dioxide. A plausible reaction mechanism is suggested and the reaction constants involved in the mechanism were evaluated.

Keywords: Kinetics, Mechanism, Permanganate, Oxidation, Azinylformamidines, Manganese(II)

• Corresponding author. Tel.: +966 555511003.

E-mail address: bhasghar@uqu.edu.sa 1. Introduction

The permanganate ion is an important oxidizing agent in neutral, alkaline, and acidic media. It is one of the most versatile and vigorous oxidants and is extensively used for oxidation of organic [1-9] and inorganic [10-22] compounds in acidic media, and is an important source of mechanistic information [23]. It is stable in neutral and slightly alkaline solutions, but it decomposes in strongly alkaline media to form blue hypomanganate(V) and green manganate(VI), which are short-lived transient species [24,25]. In alkaline, neutral, or weakly acidic solutions, MnVI1 is reduced to MnIV. In acidic media, the permanganate ion can exit in several different forms, namely HMnO4, H2MnO4+, and Mn2O7. The redox reaction mechanism is inner-sphere or outer-sphere [26,27], depending on the nature of the reductant. In general, the reduction of permanganate ion in an acidic medium gives either MnIV or Mnn; the reduction potential of the MnVII/MnIV couple is 1.695 V and that of the MnVII/Mnn couple is 1.51 V [28]. In strongly acidic media, MnVn is reduced, ultimately forming MnII, but the species that has the main role as a potential oxidant depends on the nature of the substrate and the pH of the medium [22,24,29-37].

Trisubstituted formamidines have attracted increasing interest in recent decades, because of their very broad spectrum of biological activities. The biochemical roles of formamidines include monoamine oxidase inhibitors [38,39], adrenergic and neurochemical receptors [40,41], and participation in prostaglandin E2 synthesis [42]. The N,N-dialkyl derivatives are highly effective acaricides, and the most important result was the discovery of the acaricide insecticide chlordimeform. The oxidative cleavage of formamidines is important, because the N,N-dialkylformamidine group is one of the most versatile protecting groups, especially in biosynthetic applications.

The azine moiety is a common structural subunit in a large number of natural products and synthetic compounds with important biological activities [43].

Although the kinetics of the oxidation of the azinylformamidine (Azn-F) derivatives N,N-dimethyl-.W-(pyridin-2-yl)formamidine (Py) and N,N-dimethyl-.W-(pyrimidin-2-yl)formamidine (Pym) by permanganate ions have been studied in aqueous alkaline solution [44], there are no reports describing their oxidation kinetics when other oxidants are used. A detailed study of the title reaction was therefore undertaken in order to understand the effect of the medium on the kinetics, with a view to assigning a mechanistic pathway for the reactions.

ck solu

2. Experimental

2.1. Materials

Reagent-grade chemicals were used. Stock solutions of Azn-Fs were synthesized and identified as described elsewhere [44]. A permanganate stock solution was prepared by dissolving potassium permanganate in water, and it was standardized by titration against oxalic acid. Stock solutions of other reagents were prepared by dissolving the appropriate amounts of the samples in the required volumes of double-distilled water. Sulfuric acid and sodium sulfate were used to provide the required acidity and ionic strength, respectively. The reaction temperature was controlled within ±0.1 °C.

2.2. Kinetic measurements

Kinetic measurements were conducted under pseudo-first-order conditions; a large excess of Azn-F over permanganate ion concentration was maintained. The ionic strength, I, of the reaction mixture was adjusted to 0.3 mol dm-3. Solutions of permanganate and the mixture containing Azn-F and acid were separately

thermostated for about 2 h. The permanganate solution was then added to the mixture. Absorbance measurements were performed using a Shimadzu UV-1800 PC automatic scanning double-beam instrument, which had a cell compartment kept at constant temperature. The reactions were followed by measuring the absorbance of permanganate in the reaction mixture at its absorption maximum, I = 525 nm, as a function of time. The kinetic runs monitored up to at least three half-lives of the reactions completion. The effect of dissolved oxygen on the reaction rate was checked by monitoring the reaction in a nitrogen atmosphere. No significant difference between the results obtained under nitrogen and in the presence of air was observed.

3. Results

3.1. Stoichiometry and identification of products

esence o

-oducts

Different reaction mixtures containing an excess of Azn-Fs over permanganate were mixed at [H+] = 0.1 and I = 0.3 mol d m , and allowed to react in the dark for about 6

h at 20 °C. The remaining MnO4- concentration was determined spectrophotometrically at 525 nm. The results confirm that the stoichiometry of the overall reaction holds for the following stoichiometric equations:

5R-N=CH-NMe2 + 2MnO4- + 6H+ = 5R-NH(CO)NMe2 + 2 Mn2+ + 3H2O (1)

R-NH(CO)NMe2 + H2O = R-NH2 + HNMe2 + CO2 (2)

here R-N=CH-NMe2 is the Azn-F, R-NH(CO)NMe2 is an intermediate product, i.e. 1,1-dimethyl-3-(azin-2-yl)urea, and R-NH2 is the corresponding 2-aminoazine. The above stoichiometric equations are consistent with the results of product analysis. The presence of the intermediate product 1,1-dimethyl-3-(azin-2-yl)urea was confirmed by the 1H NMR spectrum shown in Fig. 1(a). Furthermore, the IR spectrum showed an NH band at ca. 3320 cm-1 (spectrum not shown). The final 2-aminoazine products

were isolated after completion of the reaction and identified based on their XH NMR spectra (Fig. 1b). In addition, the IR spectrum showed two bands assigned to the NH2 group, at 3420 and 3380 cm-1. Dimethylamine and carbon dioxide were identified using a spot test [45] and lime water [46], respectively.

u „ 1 t i > 1 « I t l

Fig. 1. 1H NMR spectra of formed intermediate (a) and azine products (b).

3.2. Spectroscopic changes

Figure 2(a, b) shows the spectral scans during acidic permanganate oxidation of Azn-Fs; gradual disappearance of the MnO4- bands at k = 525 nm was observed. Previous studies [47-49] showed that manganese(IV) ions absorb in the region 400-650 nm. Figure 1 shows no features in this wavelength area, meaning that MnO2 is no reaction product. Furthermore, as no absorption increases and decreases were observed at 418 nm, it is concluded that MnIV ions do not act as an oxidizing agent.

■Q <

200 300 400 500 600 700

Wavelength, nm

200 300 400 500 600 700 Wavelength, nm

Figure 2(a,b) Spectroscopic changes in oxidation of Azn-Fs by permanganate in sulfuric acid medium; [Azn-F] = 0.01, [MnO4-] = 4 x 10-4, [H+] = 0.1, and I = 0.3 mol dm-3, at 20 °C. Scanning time interval = 1 min.

3.3. Reaction-time curves

The reaction-time curves for the overall reactions were sigmoid, as shown by the example in Fig. 3. The initial rates were slow, followed by an increase in the oxidation rates over longer time periods. The pseudo-first-order rate constants, kobs, were calculated as the slopes of the plots by considering the initial straight line region. The values of kobs were reproducible to within 4% and were the average of at least three to four kinetic runs.

— -3

Figure 3 ln(abs

rbance) ^

Time, s

versus time curves for oxidation of Pym by permanganate in

sulfuric acid medium. [Pym] = 0.01, [MnO^] = 4 x 10-4, [H+] = 0.1, and I = 0.3 mol dm-3, at

acid med t 20 °C.

dependence on oxidant concentration

he order with respect to permanganate ion concentration was determined by studying the reaction rate at different initial permanganate ion concentrations, [MnO4-]0, in the range (1-6) x 10-4 mol dm-3, at constant concentrations of both

substrate and sulfuric acid, and fixed ionic strength and temperature. The observed

pseudo-first-order rate constants, kobs, were almost constant (Table 1), indicating firstorder dependence with respect to permanganate ion concentration.

3.5. Rate dependence on reductant concentration

The effect of changing the reductant (Azn-F) concentration on the reaction r;

ion rate w a, consta

studied in the concentration range 4.0 x 10-3 to 1.4 x 10-2 mol dm-3, at constant concentrations of permanganate and acid, and at constant ionic strength. It was observed that kobs increases with increasing reductant concentration (Table 1). The slopes of the linear plots of ln kobs versus ln [S] (Fig. 4) were less than unity (0.96 and 0.98), which indicates that the reactions are fractional-first-order with respect to Azn-F concentration.

3.6. Rate dependence on acid concentration

Kinetic measurements were performed in sulfuric acid solutions with different [H+] and constant [MnO4-], [Azn-F], ionic strength, and temperature, to clarify the influence of [H+] on the reaction and to elucidate the reaction mechanisms. An increase in acid concentration accelerated the reactions, suggesting that the oxidation reactions were acid catalyzed. Under our experimental conditions, the plots of kobs us [H+] were linear, with positive intercepts on the kobs axes, as shown in Fig. 5, confirming that the reaction order with respect to [H+] was less than unity. Some experiments were performed in perchloric acid solutions, but the reactions were very slow.

3.7. Rate dependence on manganese(II) concentration

Mn2+ is one of the oxidation products, therefore its effects on the reaction rates were investigated in the concentration range (2-10) x 10-3 mol dm-3, with other reagent

concentrations and conditions kept constant. The kobs values increased with increasing [Mn2+]. The orders with respect to [Mn2+] were less than unity, as shown in Fig. 6.

Table 1 Influence of [MnO4 ], [Azn-F], and [H+] on the first-order rate constants, kobs, in the oxidation of Azn-Fs by permanganate in sulfuric acid medium at 20 °C and I =

0.3 mol dm-3.*

104 [MnO4-], 102 [Azn-F], [H+], 104 fcobs, s 1

mol dm mol dm-3 mol dm 3 Py Pym

1.0 1.0 0.10 24.1 20.8

2.0 3.0 4.0 5.0 1.0 1.0 1.0 1.0 s 0.10 24.7 23.4 24.5 24.9 21.9 21.3 21.5 22.1

6.0 1.0 0.10 25.6 21.9

4.0 0.4 0.10 11.4 9.6

4.0 0.6 0.10 15.4 12.8

4.0 0.8 0.10 19.8 17.1

4.0 1.0 0.10 24.5 21.6

4.0 1.2 0.10 29.2 25.9

4.0 1.4 0.10 34.3 28.7

4.0 1.0 0.01 3.9 3.1

4.0 1.0 0.02 6.2 5.6

4.0 1.0 0.05 13.2 11.4

4.0 1.0 0.10 24.5 21.6

4.0 1.0 0.15 33.6 32.2

4.0 1.0 0.20 43.1 41.4

* Experimental error ± 4%.

Je -6.4 -

Figure 4 Plots of lnkobs versus ln[S] in the oxidation of Azn-Fs by permanganate in sulfuric acid medium. [MnO4-] = 4 x 10-4, [H+] = 0.1, and I = 0.3 mol dm-3, at 20 °C.

[H+], mol dm-

Figure 5 Plots of kobs versus [H+] in oxidation of Azn-Fs by permanganate in sulfuric

acid medium. [Azn-F] = 0.01, [MnO^f] = 4 x 10-4, and I = 0.3 mol dm-3, at 20 °C.

103 [Mn2+], mol dm-3 2+

Figure 6 Plots of kobs versus [Mn ] in oxidation of Azn-Fs by permanganate in sulfuric acid medium. [Azn-F] = 0.01, [MnO4-] = 4 x 10-4, [H+] = 0.1, and I = 0.3 mol

dm-3, at 20 °C.

stant 1.0 mol dm-3, d MnO4-, and at

3.8. Influences of ionic strength and dielectric const The ionic strength was varied from 0.3 to 1.0 mol dm", using sodium sulfate, at constant concentrations of Azn-F and MO.-, a ind at constant pH and temperature. Increasing the ionic strength had a negligible effect on the reaction rate. Similarly, at constant concentrations of reactants and with other conditions constant, the concentration of t-butyl alcohol was varied from 0% to 40% (v/v) in the reaction medium. Changing the dielectric constant of the medium did not have any significant effect on the reaction rate.

anging t "ect on the reactioi

3.9. Free-radical tests

To test for the participation of free radicals in these reactions, the reaction mixtures were mixed with known quantities of acrylonitrile monomer and kept for 6 h under nitrogen. On dilution with methanol, a white precipitate formed, indicating the participation of free radicals in the oxidation reactions. Blank experiments carried out with either MnO4- or Azn-Fs alone with acrylonitrile did not induce polymerization under the same experimental conditions.

4. Discussion

The reaction rate enhancement with increasing acid concentration, with an apparent order of less than unity in [H+], suggests the formation of a more powerful oxidant, namely permanganic acid [50-52], by the following equilibrium:

+ Kl-MnO4- + H+ - HMnO4

where Ki is the protonation constant of permanganate ion.

The negligible effects of both the ionic strength and the dielectric constant of the

ic con

medium on the rates indicate that the reactions occur between two neutral molecules [53], i.e. between Azn-F substrates and permanganic acid. However, the linearity of the plots of 1/kobs versus 1/[S] (Fig. 7) is considered to be kinetic evidence of possible formation of an intermediate complex between the oxidant and the substrates, similar to the well-known Michaelis-Menten [54] mechanism for enzyme-substrate reactions. The failure to detect such an intermediate complex spectrophotometrically may be due to low concentration of the reactants used, leading to lower absorptivity of the formed complex, and/or fast subsequent decomposition of the intermediate compared with its formation.

Based on the experimental observations, a mechanism can be suggested that involves attack of the powerful oxidant, HMnO4, on the Azn-F substrate (S), leading to formation of a complex (C) prior to the rate-determining step: K

S + HMnO4 [S- HMnO4] (C) (4)

followed by cleavage of the complex to form a free-radical substrate and

manganate(VI) intermediates:

[S-HMnO4] —^ S' + HMnVIO4- + H+ (5)

The intermediate (S') is rapidly attacked by the manganate(VI) ion of the oxidant to yield an intermediate product, 1,1-dimethyl-3-(azin-2-yl)urea, as follows:

_ fast _

S'+ HMnO4 -intermediate product + MnO3 (6)

In a further fast step, the intermediate product is hydrolyzed to give the final oxidation

products:

fast .... (

MnV is very unstable in strong acidic media, therefore it will be converted to MnII and

Intermediate product + H2O -final products (7)

MnVI1 by rapid disproportionation, as follows:

5Mn03" + 6 H+ . 3Mn04~ + 2 Mn2+ + 3H20 (8)

id then sui

Multiplying Eqs. (3) to (7) by a factor of five and then summing them with Eq. (8) results in an overall reaction with the stoichiometry satisfied.

According to this mechanism, the relationship between the reaction rate and the substrate, hydrogen ion, and oxidant concentrations can be deduced (see the Appendix), to give the following equation:

Rate = ¿i^2[MnO4-][S][H+ ] 1 + KJH+] + ^[S][H+]

Under pseudo-first-order conditions, the rate law can be expressed as [MnO

Rate = d[Mn° ] = kobs [MnO4-] (10)

Comparing Eqs. (9) and (10) and rearrangement gives the following relationship:

1 ( 1 + ^[H+] ^ 11

+ ~ (11)

k1K1K 2[H+]) [S] k

As predicted by Eq. (11), the plots of 1/kobs against 1/[S] for the two substrates are linear (Fig. 7). The reciprocals of the intercepts of the plots yield k1 values of 0.014 dm3 mol-1 s-1 for both substrates.

1/[S], dm3 mo!"1

Figure 7 Plots of 1/kobs versus 1/[S] in the oxidation of Azn-Fs by permanganate in sulfuric acid medium. [MnO4-] = 4 x 10-4, [H+] = 0.1 and I = 0.3 mol dm-3, at 20 oC.

Because the intercepts observed in Fig. 7 are small, Eq. (11) can be simplified to

uitable rate-l

Eq. (12), which is considered to be a suitable rate-law expression:

IS!=I_L +1

kobs k '[H+] k"

are the

where k' and k" are the apparent rate constants and are equal k1K1K2 and k1K2, Accor

respectively.

vely. A

)rding to Eq. (12), the plots of [S]/kobs versus 1/[H ] gave good

straight lines confirming the suggested mechanism and rate law (Fig. 8); the slopes and intercepts of such plots can be used to calculate the apparent rate constants, k' and k". The protonation constants of the permanganate ion can be evaluated by dividing k'

by k" (Ki = k'/k''), and were found to equal 0.73 and 0.87 dm3 mol-1 at 20 °C for Pym and Py, respectively, in good agreement with the literature values [55] (0.62 dm3 mol-1 at 25 °C), indicating the validity of the proposed mechanism. The value of the formation constant of the intermediate complex, K2, was also calculated as 71.42 dm3 mol-1.

Fs by p

1/[H+], dm3 mol-1

Figure 8 Plots of [S]/kobs versus 1/[H+] in oxidation of Azn sulfuric acid medium. [MnO4-] = 4 x 10-4 and I = 0.3 mol dm-3, at 20 °C.

ermanganate in

+ o=Mn—oh

N N^ NNMe,

Permanganic acid

^N^N^NH

Intermediate product

CO2 + HNMe2

5MnVÜ3- + 6 H+

N N^NMe2

Complex (C)

HMnVIO4-

N N^ NMe;

Free radical (X ) +

HMnVIO4- +H+

HO NMe2

3Mnvll04~ + 2Mn2+ + 3H20

where X = N for Pym-F and X = CH for Py-F

Scheme 1. Mechanism of oxidation of Azn-Fs by permanganate in aqueous acidic medium.

4.1. Mechanism of autocatalysis by manganese(II)

The addition of Mn2+ ions led to a significant increase in the reaction rates (Fig. 6),

suggesting autocatalysis of the oxidation reactions by Mn2+. The catalytic effect of

Mn2+ can be interpreted in one of two ways: (a) Mn2+ may form a complex with the substrate, which is then oxidized by HMnO4, or (b) Mn2+ first reduces MnVI1 to Mn111 and MnIV, which then accelerate the reaction. The less-than-unity orders in [Mn2+] (Fig. 6) suggest that a complex (C1) might be formed between the Azn-F substrate and Mn2+ in a fast step. The complex is then oxidized by HMnO4 in a slow step [56], according to the following scheme:

S + Mn2+ ^^ Ci (13)

Ci + HMnÜ4 now HMnÜ4- + Mn2+ + H+ . IT (14)

e final pi

The remaining steps, leading to the final products, resemble those presented in Scheme 1.

According to this mechanism, the relationship between the reaction rate and the

mechanis gen ion, o ' " following equation:

substrate, hydrogen ion, oxidant, and Mn2+ concentrations can be expressed by the

Rate = k2 ^i^3[Mnü;][S][H+][Mn2+] (1 + ^1[H+])(1 + K3[S] + K3[Mn2+])

Under pseudo-first-order conditions, the rate law can be expressed by Eq. (10).

Rate = - d[Mn<° ] = kobs [MnÜ4-] (10)

A comparison of Eqs. (10) and (15), and rearrangement, gives the following relationship:

f 1 + K1[H+] ^ v k2K^H ]

2+ + K ' (16)

[Mn2+]

As predicted by Eq. (16), the plots of [S]/&obs against 1/[Mn2+] for the two substrates are linear (Fig. 9), supporting the validity of the proposed mechanism.

-o 3 -

1/[Mn2+], dm3

Figure 9 Verification of rate law (15) in the form of Eq. (16) in the oxidation of Azn-Fs by permanganate in sulfuric acid medium. [MnÜ4-] = 4 x 10-4, [H+] = 0.1, and I = 0.3 mol dm-3, at 20 °C.

5. References

1. K.W. Hicks, J.R. Sutter, J. Phys. Chem. 75 (1971)1107-1113.

2. K.W. Hicks, G.A. Chappele, Inorg. Chem. 19 (1980)1623-1625.

3. K.W. Hicks, Inorg. Nucl. Chem. 38 (1976) 381-1383.

4. R.M.C. Allister, K.W. Hicks, M.A. Hurless, Inorg. Chem. 21 (1982) 4098-41°0.

5. M.A. Rawoof, J.R. Sutter, J. Phys. Chem. 71 (1967) 2767-2771.

-3866.

6. L.J. Kirshenbaum, J.R. Sutter, J. Phys. Chem. 70 (1966) 3863-3

7. S.A. Lawni, J.R. Sutter, J. Phys. Chem. 77 (1973)

8. R.M. Hassan, M.A. Mousa, S.A. El-Shatoury, J. Chem. Soc., Dalton Trans. 1988 601-603.

9. R.M. Hassan, S.A. El-Gaiar, A.M. El-Samman, Collect. Czech. Chem. Commun. 58 (1993) 538-546.

10. M.S. Manhas, F. Mohamed, Z. Khan, A kinetic study of oxidation of P-cyclodextrin bypermanganate in aqueous media, Coll. Surf. 295 (2007) 165171.

ry, J. Chem r, A.M. El-Sam

ermanga

11. S.M.Z. Andrabi, M.A. Malik, Z. Khan, Colloids Surf., A 299 (2007) 58-64.

12. M.A. Malik, S.A. Al-Thabiti, Z. Khan, Colloids Surf., A 377 (2009) 9-14.

13. M.A. Malik, Z. Khan, Submicellar catalytic effect of cetyltrimethylammonium bromide in the oxidation of ethylenediaminetetraacetic acid by MnO4 , Coll. Surf. B Biointerfaces, 64 (2008) 42-48.

14. S.A. Farokhi, S.T. Nandibewoor, Can. J. Chem. 82 (2004) 1372-1380.

15. R.M. Hassan, M.A. Mousa, M.H. Wahdan, Chem. Soc., Dalton Trans. 1988 605-609.

16. R.M. Hassan, Acta Chim. Hung. 129 (1992) 661-669.

woor, Polyhedrc

(1976)179-184 norganic Chem

(2009) 1

31. M.

17. M. Jaky, J. Szammer, T.J. Simon, Chem. Soc., Perkin Trans. 2000 1597-1602.

18. M. Jaky, J. Szammer, E.S. Trompler, Int. J. Chem. Kinet. 38 (2006) 444-450.

19. L.I. Simandi, M. Jaky, M.A. Khenin, Inorg. Chim. Acta 134 (1987) 187-192.

20. D.G. Lee, J.R. Browndridge, J. Am. Chem. Soc. 98 (1973) 3033-3037.

21. D.G. Lee, T.J. Chen, J. Am. Chem. Soc. 111 (1989) 7534-7535.

22. F. Freeman, D.K. Lin, G.R. Moore, J. Org. Chem. 47 (1982) 56-59.

23. K.A. Thabaj, S.G. Kulkarni, S.A. Chimatadar, S.T. Nandibewoor, Polyhedron 26 (2007)4877-4885.

24. F. Freeman, Rev. React. Species Chem. React. 1 (1976) 179-184.

25. F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 4th ed., John Wiley & Sons, New York, 1980, p 747.

26. J.F. Perez-Benito, J. Phys. Chem. 2113 (2009) 15982-15991.

27. Ü.A. Babatunde, World J. Chem. 3 (2008) 27-31.

28. M.C. Day, J. Selbin, Theoretical Inorganic Chemistry, Reinhold Publishing Corporation, New York, 1985, p. 344.

29. R. Stewart, in: K.B. Wiberg (Ed.), Üxidation in Ürganic Chemistry. Part A, Academic Press, New York, 1965.

30. A.J. Fataidi, Synthesis 2 (1987) 85-127. . M. Jaky, L.I. Simandi, J. Chem. Soc. Perkin II (1972) 1481-1486; (1973)

1565-1569;(1976) 939-943.

32. F. Freeman, J.C. Kappos, J. Ürg. Chem. 51 (1986) 1654-1657; F. Freeman, J.C. Kappos, J. Am. Chem. Soc. 107 (1985) 6628-6633.

33. D. Bilehal, R. Kulkarni, S.T. Nandibewoor, J. Mol. Catal. 223 (2005) 21-28.

34. K.A. Thabaj, S.G. Kulkarni, S.A. Chimatadar, S.T. Nandibewoor, Polyhedron 26 (2007)4877-4885.

D.J. Lee, J.F.P. Benito, Can. J. Chem. 63 (1985) 1275-1279. Z. Khan, R.M. Akram, K. ud-Din, Int. J. Chem. Kinet. 36 (2004) 345-358. K. ud-Din, W. Fatma, Z. Khan, Colloids Surf. 234 (2004) 159-164. R.W. Beeman, F. Matsumura, Chlordimeform: A Pesticide Acting upon Amine Regulatory Mechanisms, Nature 242 (1973) 273-274. S.A. Aziz, C.O Knowles, Inhibition of monoamine oxidase by the pesticide chlordimeform and related compounds, Nature 242 (1973) 417-418. V.S. K Leung, T.Y.K. Chan, V.T.F. Yeung, Amitraz poisoning in humans, J. Toxicol. Clin. Toxicol. 37 (1999) 513-514. A. Nakayama, M. Sukekawa, Y. Eguchi, Stereochemistry and active conformation of a novel insecticide, acetamiprid, Pesticide Science, 51 (1997) 157-164.

G.K.W. Yim, M.P. Holsapple, W.R. Pfister, R.M Hollingworth, Prostaglandin Synthesis Inhebited by Formamidine Pesticides, Life Sci. 23 (1978) 25092515.

I.M. Lagoja, Pyrimidines as constituent of natural biologically active compounds, Chem. Biodiversity, 2 (2005) 1-50. A. Fawzy, M.R. Shaaban, Kinetic and mechanistic investigations on the oxidation of N'-heteroaryl unsymmetrical formamidines by permanganate in aqueous alkaline medium, Transition Met. Chem. 39 (2014) 379-386. F. Feigl, Spot tests in organic analysis, Elsevier, New York, 1975, p 195. Vogel AI (1978) A text book of quantitative inorganic analysis. 4th ed ELBS and Longman, New York p 352.

J.F. Perez Benito, F. Mata Perez, E. Brillas, Can. J. Chem. 65 (1987) 23292337.

48. E. Brillas, J.A Garrido, J.F. Perez Benito, Collect. Czech. Chem. Commun. 53 (1988) 479-486.

49. J. De Andrés, E. Brillas, J.A. Garrido, J.F. Perez Benito, J. Chem. Soc., Perkin

50. N. Bailey, A. Carrington, A.K. Lon, M.C.R. Symons, J. Chem. Soc. (1960)

290-297; A. Carrington, M.C.R. Symons, Chem. Rev. 63 (1963) 443-460

51. S.A. Chimatadar, S.C. Hiremath, J.R. Raju, Ind. J. Chem 30A (1990) 190-192.

52. M. Zahedi, H. Bahrami, Kinet. Catal. 45 (2004)351-358.

53. C.H. Rochester, Progress in Reaction Kinetics, Pergamon Press, Oxford, 1971, p. 145.

54. L. Michaelis, M.L. Menten, Biochem Z. 1918, 49 (1918) 333-338.

55. S.A. Farokhi, S.T. Nandibewoor, Can. J. Chem. 82 (2004) 1372-1380.

56. F.J. Andres Ordax, A. Arrizabalaga, J.I. Martinez de Ilarduya, An. Quim. 80

Trans. 2 (1988) 107-112.

Appendix

According to the suggested mechanism,

Rate = ki[C] (A1)

From reaction (3), Ki =

[HMnO4]

[MnO4"][H+]

Therefore, [HMnO4] = Ki[MnO4-][H+] ^ ^^ (A3)

From reaction (4),

K2 =-—--(A4)

[S][HMnO4]

Therefore, [C] = K2[S][HMnO4] (A5)

Substituting Eq. (A3) into Eq. (A5) leads to

[C] = №[S][H+][MnO4-] r (A6)

Substituting Eq. (A6) into Eq. (A1) yield Rate = kiKiK2[S][H+][MnO4-] (A7)

The total concentration of the substrate is given by

[S]t = [S]f + [C] (A8)

where [S]T and [S]F stand for total and free concentrations of the substrate. Substituting Eq. (A6) into Eq. (A8) gives

f + KiK2[S]F[H+][MnO4-] (A9)

t = [S]f (i+ KiK2[H+][MnO4-]) (Ai0)

Therefore,

■ [C]

[S]t and [S]f

[S]t = [S] [S]t

[S]f =-[S]t--(Aii)

i + KiK2[H+ ][MnO4-]

Similarly,

[MnO4-]T = [MnO4-]F + [HMnO4] + [C] (Ai2)

Substituting Eqs. (A3) and (A6) into Eq. (A12) gives [MnO4-]T = [MnO4-]p + ^i[MnO4-]p[H+] + J№[S][H+][MnO4-]p

[MnO4"]r

[MnÜ4-]F =—

1 + K^H+] + K1K 2[S][H+] and [H+]t = [H+]f + [HMnÜ4]

[H+]f =-

[H+ ]t

1 + K:[MnO4~]

Substituting Eqs. (A11), (A14), and (A16) into Eq. (A7) (and omitting the subscripts "T" and "F") we get

k1K1K 2[S][H+][MnO4-]

Rate =-

omitting

(1 + K1K 2[H][MnO/])(1 + K1[MnO^])(1 + K:[H+] + K1K 2[S][H+]) In view of the low concentration of [MnO4-] used, the first and second terms in the denominator of Eq. (A17) both approximate to unity. Therefore, Eq. (17) becomes

Rate = klKlK2[S][H+ ][MnO/]

1 + K1[H+] + K1K2[S][H+ ]

Under pseudo-first-order conditions, the rate law can be expressed as

Rate = - i[Mn°4~] = Us[MnO4-] dt

Comparing Eqs. (A18) and (A19), the following relationship is obtained:

kb = kKK 2[S][H+] obs 1 + K1[H+] + K1K 2[S][H+]

and with rearrangement it becomes

1 ( 1 + K^H+ ] ^ 11

klKlK2[H + ] J [S] k,

- + —

Figure, table, and scheme captions

Figure 1 iH NMR spectra of formed intermediate (a) and azine product (b).

Figure 2(a,b) Spectroscopic changes in oxidation of Azn-Fs by permanganate in sulfuric acid medium; [Azn-F] = 0.01, [MnO4-] = 4 x 10-4, [H+] = 0.1, and I =

mol dm , at 20 °C. Scanning time interval = 1 min.

Figure 3 Ln(absorbance) versus time curves for oxidation of Pym by perm iganate in sulfuric acid medium. [Pym] = 0.0i, [MnO4-] = 4 x iO-4, [H+] = 0.i, and = 0.3 mol dm-3, at 20 °C.

Figure 4 Plots of ln^bs versus ln[S] in the oxidation of As i-Fs by permanganate in

sulfuric acid medium. [MnÜ4 ] = 4 x 10 , [H+] = 0.1,

0.3 mol dm-3, at 20 °C.

Figure 5 Plots of kobs versus [H+] in oxidation of Azn-Fs by permanganate in sulfuric acid medium. [Azn-F] = 0.0i, [MnO4-] = 4 x i0-4, and I = 0.3 mol dm-3, at 20 °C.

Figure 6 Plots of kobs versus [Mn2+] in oxidation of Azn-Fs by permanganate in sulfuric acid medium. [Azn-F] = 0.0i, [MnO4-] = 4 x i0-4, [H+] = 0.i, and I = 0.3 mol dm-3, at 20 °C.

Figure 7 Plots of 1/kobs versus 1/[S] in the oxidation of Azn-Fs by permanganate in sulfuric acid medium. [MnO4-] = 4 x 10-4, [H+] = 0.1 and I = 0.3 mol dm-3, at 20 oC.

Figure 8 Plots of [S]/kobs versus i/[H+] in oxidation of Azn-Fs by permanganate in sulfuric acid medium. [MnO4-] = 4 x i0-4 and I = 0.3 mol dm-3, at 20 °C.

re 9 Verification of rate law (15) in the form of Eq. (16) in the oxidation of Azn-by permanganate in sulfuric acid medium. [MnÜ4-] = 4 x 10-4, [H+] = 0.1, and I = 0.3 mol dm-3, at 20 °C.

Scheme 1. Mechanism of oxidation of Azn-Fs by permanganate in aqueous acidic medium.

Table 1 Influence of [MnO4 ], [Azn-F], and [H+] on the first-order rate constants, kobs, in the oxidation of Azn-Fs by permanganate in sulfuric acid medium at 20 °C and I =

0.3 mol dm .