untitled European Journal of Chemistry 6 (2) (2015) 174‐177 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2015 Atlanta Publishing House LLC ‐ All rights reserved ‐ Printed in the USA http://dx.doi.org/10.5155/eurjchem.6.2.174‐177.1232 European Journal of Chemistry Journal webpage: www.eurjchem.com Oxidation of butylamine and isobutylamine by diperodatocuprate(III) in alkaline medium ‐ A kinetic and mechanistic study Jinhuan Shan * and Qianqian Wang College of Chemistry and Environmental Science, Hebei University, Key Laboratory of Analytical Science and Technology of Hebei Province, Baoding, 071002, China * Corresponding author at: College of Chemistry and Environmental Science, Hebei University, Key Laboratory of Analytical Science and Technology of Hebei Province, Baoding, 071002, China. Tel.: +86.0312.5971129. Fax: +86.0312.5079386. E‐mail address: hbushanjh@163.com (J. Shan). ARTICLE INFORMATION ABSTRACT DOI: 10.5155/eurjchem.6.2.174‐177.1232 Received: 12 December 2014 Received in revised form: 05 February 2015 Accepted: 07 February 2015 Published online: 30 June 2015 Printed: 30 June 2015 The kinetics of oxidation of butylamine and isobutylamine by diperodatocuprate(III) (DPC) in alkaline medium has been studied spectrophotometrically in the temperatures range of 20‐40 . All data follow pseudo‐first order reaction in [DPC] under experimental conditions. It was found that the reaction showed pseudo‐first order with respect to DPC and 1 < nap < 2 to reductant. The rate constant kobs increased with increase in [reductant], however, the kobs decreased with increase in [IO4‐] and [OH‐]. In addition, there was a negative salt effect. Through the determined experimentally found that the rate of isobutylamine was higher than butylamine. The reaction constants involved in the different steps of the mechanisms are calculated. Activation parameters, which were controlled by slow step of the mechanism are discussed and thermodynamic quantities are determined. Therefore, the activation parameters at 298.2 K were calculated. KEYWORDS Oxidation Butylamine Isobutylamine Mechanistic study Diperodatocuprate(III) Kinetics and mechanism Cite this: Eur. J. Chem. 2015, 6(2), 174‐177 1. Introduction It is well known that the studies of the supernormal oxidation states of transition metals were initially done in United States and India. Diperodatocuprate(III) had been reported by many researches [1‐3]. It is one‐electron oxidants in the study of kinetics and mechanism of various compounds in alkaline medium. In recent years, the periodate complexes of copper in its trivalent state has been widely used in the analysis of several organic compounds. As the kinetics of self‐ decomposition, these complexes were studied in some details and it was well recognized as an analytical reagent [4]. Diperiodatocuprate(III) is square‐planar d8 complex, so Cu(III) is a high oxidation state that its significance to have a further study. Amine had been oxidized by diperiodatocuprate(III) [5,6], we report here the kinetics of the oxidation of butylamine and isobutylamine by diperiodatocuprate(III). Butylamine becomes important because of the widely of applications in production, such as butylamine applied in pharmaceutical intermediates which can be used for production of anti‐diabetic drug and applied in pesticide intermediates which can be used for production of herbicide and insecticide. It is also applied in intermediates of rubber accelerator. In addition, butylamine is the developer of color photograph. Isobutylamine applied in synthetic intermediate of insecticide, corrosion inhibitor and rubber processing chemicals, it is also used as neutralizing agent and stabilizer which applied for mineral flotation agent, gasoline antiknock agent, polymerization catalyst and sulfobenzoic acid alkyl ester thirteen. 2. Experimental 2.1. Materials All chemicals used were of reagent analytical reagent grade. Double distilled water was prepared and used throughout the work. The diperiodatocuprate(III) crystals is prepared [7,8] by oxidizing Cu(II) in the alkaline medium and standardized reported by the method of Chandra and Yadava [9]. The crystals dissolving into a solution, then the purity of the complex was characterized by its UV/Visible spectrum, which showed a broad absorption peak at 415 nm. However, DPC and reducing agent need to extemporaneous so that to maintain always freshly daily. KOH and KNO3 were employed to maintain the required alkalinity and ionic strength in reaction solutions, respectively. Shan and Wang / European Journal of Chemistry 6 (2) (2015) 174‐177 175 2.2. Instrumentations The kinetic measurements were performed on a UV‐visible spectrophotometer (TU‐1950, Beijing Puxi Inc., China), which had a cell holder kept at constant temperature (±0.1 ) by circulating water from a thermostat (RA8, Germany). Other agents did not affect at the wavelength. 2.3. Kinetics measurements All kinetics measurements were performed under pseudo‐ first order conditions. The reaction containing required quantities of concentration of DPC (2 mL), OH‐, IO4‐, ionic strength and reductant solution (2 mL) of maintain the required concentration were transferred separately to the upper and lower branch tubes of a λ type two‐cell reactor. The results obtained the absorption spectra of the diperiodato cuprate(III) well agree with those observed by L. Jensovsky [10]. The first peak is observed at 415 nm and the second at 265 nm for the diperiodatocuprate(III), respectively. The concentration of the diperiodatocuprate(III) has an absorption peak at 415 nm, as a function of time. The ionic strength was controlled by KNO3 solution and the pH was maintained by adding KOH solution. 3. Results and discussion 3.1. Evaluation of pseudo‐first order rate constants Under the conditions of [reductant]0 >> 20 [Cu(III)]0 , the plots of ln(At‐A∞) versus time were straight lines, indicating that the reaction is the first order in DPC, which using the equation ln(At‐A∞) = ‐kobs×t + b (Constant). The pseudo‐first‐ order rate constants kobs were calculated by the method of least‐squares. The kobs values were the average value of at least three independent experiments, and reproducibility is within ±5%. 3.2. Rate dependence on the [reductant] At fixed [DPC], [OH‐], [IO4‐] and μ, the [butylamine] was varied in the range of 5.00×10‐2 to 25.00×10‐2 mol/L and the [isobutylamine] was varied in the range of 1.00×10‐2 to 5.00×10‐2 mol/L at different temperatures. The plots of ln kobs versus ln c (reductant) were linear (r ≥ 0.999), according to the slopes of five plots showing that the reaction order 1 < nap < 2 dependence in reductant. Moreover, the kobs increase with the increase of reactant concentration. The plots of [reductant]/kobs vs 1/[reductant] were straight line with a positive intercept (Figure 1 and 2). Figure 1. Plots of [butylamine]/kobs vs. 1/[butylamine] (r ≥ 0.999). [DPC] = 8.61×10‐5 mol/L, [IO4‐] = 1.00×10‐3 mol/L, [OH‐] = 1.00×10‐2 mol/L, µ = 3.00×10‐2 mol/L. Figure 2. Plots of [isobutylamine]/kobs vs. 1/[isobutylamine] (r ≥ 0.999). [DPC] = 8.61×10‐5 mol/L, [IO4‐] = 1.00×10‐3 mol/L, [OH‐] = 1.00×10‐2 mol/L, µ = 3.00×10‐2 mol/L. 3.3. Rate dependence on the [IO4‐] At fixed [DPC], [OH‐], [reductant], µ and temperature, the [IO4‐] was varied in the range of 0.50×10‐3 to 2.50×10‐3 mol/L. It is found to be the plots of 1/kobs versus [IO4‐] were straight line with a positive intercept (Figure 3). The experimental results showing that the kobs decreased with increase in [IO4‐]. Figure 3. Plots of 1/kobs vs. [IO4‐] at 303.2 K. [DPC] = 8.61×10‐5 mol/L, [OH‐] = 1.00×10‐2 mol/L, µ = 3.00×10‐2 mol/L. (1) [Butylamine] = 15.00×10‐2 mol/L, (r ≥ 0.999) (2) [Isobutylamine] = 3.00×10‐2 mol/L, ( r ≥ 0.999) 3.4. Rate dependence on the [OH‐] The [OH‐] was varied in the range of 5.00×10‐3 to 25.00×10‐3 mol/L, the kobs decreased with increasing [OH‐] at constant [DPC], [reductant], [IO4‐], µ and temperature. The plots of 1/kobs versus [OH‐] proved to be straight line with a positive intercept (Figure 4). 3.5. Rate dependence on ionic strength µ The ionic strength of the concentration was varied from 1.50×10‐2 to 7.50×10‐2 mol/L at constant [DPC], [reductant], [OH‐], [IO4‐] and temperature, It was found that the reaction of [reductant] was a negative salt effect, thus indicate that the kobs was decreased with the ionic strength [11] (Table 1). 4. Reaction mechanism In the alkaline medium, periodate acid radical of equilibrium constants was given earlier at 298.2 K by Aveston [11]. 176 Shan and Wang / European Journal of Chemistry 6 (2) (2015) 174‐177 Table 1. Influence of variation ionic strength µ at 303.2 K. μ×102, mol/L 1.50 3.00 4.50 6.00 7.50 kobs×102, s‐1 Butylamine 4.67 3.41 2.72 2.46 2.28 Isobutylamine 10.33 6.60 4.97 3.92 3.64 [DPC] = 8.61×10‐5 mol/L, [OH‐] = 1.00×10‐2 mol/L, [IO4‐] = 1.00×10‐3 mol/L. (1) [Butylamine] = 15.00×10‐2 mol/L (2) [Isobutylamine] = 3.00×10‐2 mol/L. Table 2. Rate constants (k) and the activation parameters for the rate‐determining step at 298.2 K. T, K 293.2 298.2 303.2 308.2 313.2 k×10, mol‐1.L.s‐1 Butylamine 5.59 7.03 8.88 10.27 12.47 K, mol‐1.L.s‐1 Isobutylamine 8.57 14.92 24.53 40.19 76.17 Thermodynamic activation parameters Butylamine Ea (kJ·mol‐1) = 30.05, ΔH≠ (kJ·mol‐1) = 27.57, ΔS≠ (J·K‐1·mol‐1) = ‐155.55 Isobutylamine Ea (kJ·mol‐1) = 80.98, ΔH≠ (kJ·mol‐1) = 78.51, ΔS≠ (J·K‐1·mol‐1) = 40.38 The plot of ln k vs 1/T have following intercept (a) slope (b) and relative coefficient (r). Butylamine: a = 11.75, b = ‐3614.89, r = ‐0.999; Isobutylamine: a = 35.32, b = ‐9740.79, r = ‐0.998. 2IO4‐ + 2OH‐ ⇌ H2I2O104‐ log β1 = 15.05 (1) IO4‐ + OH‐ + H2O ⇌ H3IO62‐ log β2 = 6.21 (2) IO4‐ + 2OH‐ ⇌ H2IO63‐ log β3 = 8.67 (3) The distribution of all the species of periodate in aqueous alkaline solution can be calculated from Equation (1‐3). In an alkaline medium such as [OH‐] = 1.00×10‐2 mol/L, [H2IO63‐ ]:[H3IO62‐]:[H2I2O104‐]:[IO4‐] = 2.9:1.0:0.02:6×10‐5, and at the OH‐ employed in this study, H2I2O104‐and IO4‐ can be neglected, so the main periodate species exists as [H2IO63‐] and [H3IO62‐], we chose the former and this conclusion has supported by literature [12]. It is known that [H2IO63‐] was protonated and coordinated with central ion to form [Cu(H2IO6)2]3‐. Based on the experimental results and discussion, the mechanism was proposed as follows (R stands for butylamine and isobutylamine, R′ stands for CH3(CH2)2 and (CH3)2CH, respectively).    3 2 2 6 2 2 6 3 62 Cu H IO H O Cu H IO H IO OH1 K          (4)    2 2 6 2 2 2 6 2 2Cu H IO R 'CH NH Cu H IO R 'CH NH K       (5)  2 6 2 2 2 2 slow Cu H IO R 'CH NH R 'CH NH    k 2 2 2Cu(II) R 'CH NH R 'CH NH   (6)    fast 2 3Cu * III R 'CH NH OH Cu II NH R 'CHO      (7) The Cu*(III) stand for any kind of which Cu3+ existed in Equilibrium (4‐7)，subscripts T and e represents the total concentration and at equilibrium concentration respectively. The total concentration of Cu(III) can be written as:        3 2 6 2 6 2 6 2 22T e ee Cu III Cu H IO Cu H IO Cu H IO R 'CH NH                 (8) Due to Equation (6) was the rate‐determining step, the rate law of the reaction was derived as follows:           2 1 2T obs2 T T 1 3 6 1 2 d Cu(III) 2 R Cu III Cu III dt OH H IO R kK K - k K K K                 (9)     2 1 2 obs 2 3 6 1 2 2 R OH H IO R1 kK K k K K K           (10) The Equation (10) deformation can be obtained to Equation (11) and (12): 2 1 3 6 obs 1 2 OH H IO[R] 1 1 2 2 [R] K k k kK K            (11)       1 2 1 2 3 62 2 obs 1 2 1 2 OHR1 H IO 2 R 2 R K K K k kK K kK K             (12) From the Equation (9) can be knows the reaction showed the first order dependence in DPC and the Equation (11) showed 1 < nap < 2 dependence in reductant, which the plots [reductant]/kobs vs 1/[reductant] was straight lines with a positive intercept. The Equation (12) suggest that the plots of 1/kobs vs [OH‐] and 1/kobs vs [IO4‐] were also straight lines, in addition, the kobs decreased with increase in [OH‐] and [IO4‐]. Activation energy and the thermodynamic parameters were evaluated at 298.2 K by the method given earlier [13] (Table 2). Figure 4. Plots of 1/kobs vs. [OH‐] at 303.2 K. [DPC] = 8.61×10‐5 mol/L, [IO4‐] = 1.00×10‐3 mol/L, µ = 3.00×10‐2 mol/L, (1) [Butylamine] = 15.00×10‐2 mol/L, (r ≥ 0.999) (2) [Isobutylamine] = 3.00×10‐2 mol/L, (r ≥ 0.999). 5. Conclusion On the bases of above discussion and results, we can know that the rate constant of the rate‐determining step and activation parameters with respect to the rate‐determining step of the reaction were computed. Through the deep study of the reaction system, it can be good to verify the extraordinary of the transition metal complexes present with low protonated form. According to the experimental determination, we can be found that the rate constants and the rate‐determining step constants of isobutylamine are larger than butylamine, this is because of the complex formed with isobutylamine of the space steric hindrance is smaller than with butylamine so that increasing the reaction rate. In addition, there is an obvious negative salt effect in reductant, which is because of the “ion Shan and Wang / European Journal of Chemistry 6 (2) (2015) 174‐177 177 atmosphere” can be contain the effects between ions of the reaction, it makes activated complex more unstable. For isobutylamine experimental values for ΔS≠ > 0, it may be related to the structure of the transition state is relatively loose. All the mechanism described is consistent with mechanistic and kinetic studies. Acknowledgement I sincerely thank my teacher Jinhuan Shan, who has spent much of her precious time and not to mind taking the trouble to guide me whenever I have questions in writing. In addition, my teacher carefully correcting thesis and put forward many pertinent guidance after the completion of my thesis. Had she not devoted her painstaking efforts to reading patiently each draft and making critical comments, the completion of this article would have been impossible. Also thank teachers who giving the selfless help and guidance for me and I learned a lot from them. References [1]. Shan, J. H.; Li, Huo, S. Y., Yin, C. H. J. Chem. 2013, 2013, Article ID 627324. [2]. Shan, J. H.; Li, Y. Eur. J. Chem. 2013, 4(3), 203‐206. [3]. Shan, J. H.; Wang, X. Q.; Shen, H. X. Asian J. Chem. 2011, 23, 180‐182. [4]. Shan, J. H.; Wei, H. Y., Liu, B. S. Indian J. Chem. 2001, 40A, 865‐869. [5]. Shan, J. H.; Wang, X. Q.; Han, C.; Wang, F. J. Hebei Univ. (Nat. Sci. Ed.) 2010, 30(1), 43‐44. [6]. Wang, L. 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