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1、Oxidation of Neopentyl glycol by Diperodatocuprate( ) in Alkaline Medium-A Kinetic and Mechanistic Study JINHUANSHAN, QIANQIAN WANG, ZIWEIZHANGandJIN HANCollege of Chemistry and Environmental Science, Hebei University, Baoding 071002, P.R.ChinaCorresponding author: Fax: +86-0312-5079386; E-mail: hbu
2、shanjh163. com.ABSTRACT The kinetic of oxidation of Neopentyl glycol by Diperodatocuprate() (DPC) in alkaline medium had been studied spectrophtometrically in the different of temperature range of 25 -45. The reaction of Neopentyl glycol is the first order in each DPC by experiment determination. Th
3、e rate constant kobsincreased with increase in OH- and neopentyl glycol. However, with the increase of the temperature, the kobs decreased with increase in IO4-. The reaction constants which involved in the different steps of the mechanisms are calculated. Activation parameters which controlled by s
4、low step of the mechanism are discussed and thermodynamic quantities are determined. Therefore, the activation parameters at 298.2K were calculated. Key Words: Kinetics; Diperodatocuprate( ); Oxidation; Neopentyl glycol; Corresponding author. E-mail: ; fax: 86-0312-5079386INTRODUCTION Diperodatocupr
5、ate( ) (DPC)1,2has been reported by many researches. 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
6、. As the kinetics of self-decomposition, these complexes were studied in some details and it was well recognized3 as an analytical reagent. Diperiodatocuprate(III) is square-planar d8 complex, it is because Cu() is an high oxidation state that its significance to have a further study. Alcohols have
7、been oxidized by diperiodatocuprate(III) (DPC) 4, We report here the kinetics of the oxidation of Neopentyl glycol by diperiodatocuprate(III) (DPC). Neopentyl glycol becomes important because of the widely of applications in industrial production. Such as Neopentyl glycol can be used for production
8、of plasticizers, resins, high lubricant additive and as well as in organic synthesis. In addition, Neopentyl glycol is a better solvent, it can be used to select the separation of aromatic and naphthenic hydrocarbons. Due to no hydrogen atom at the position on neopentyl glycol, so that it has high c
9、hemical stability and thermal stability. It also can be used as analgesic ibuprofen synthesis in the pharmaceutical industry. EXPERIMENTAL All chemicals used were of reagent A.R. grade. Double distilled water was prepared and used throughout the work. The diperiodatocuprate(III) (DPC) crystals is pr
10、epared5,6 by oxidizing Cu(II) in the alkaline medium and standardized reported by the method7 of Jaiswal and Yadava. 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
11、reducing agent need to extemporaneous so that to maintain always freshly daily. KOH and KNO3were employed to maintain the required alkalinity and ionic strength in reaction solutions, respectively. Kinetics measurements and apparatus:All kinetics measurements were performed on under pseudo-first ord
12、er conditions. The reaction containing required quantities of concentration of DPC (2mL), OH-, IO 4-and ionic strength and reductant solution (2mL) of maintain the required concentration were transferred separately to the upper and lower branch tubes of a type two-cell reactor. The results obtained
13、the absorption spectra of the diperiodatocuprate(III) well agree with those observed by L. Jensovsky8. The first peak is observed at 415nm and the second at 265nm for the diperiodatocuprate(III) respectively. The concentration of the diperiodatocuprate(III) has an absorption peak at 415nm，as a funct
14、ion of time. The ionic strength was controlled by KNO3solution and the PH was maintained by adding KOH solution. The kinetic measurements were performed on a UV-visible spectrophotometer (TU-1901, Beijing Puxi Inc., China), which had a cell holder kept at constant temperature ( 0.1o C) by circulatin
15、g water from a thermostat (DC-2006, Baoding, China). Other agents did not affect at the wavelength. product analysis: When the complete disappearance of the color of the diperiodatocuprate(III) and marked the reaction was terminated. The main product of oxidation was identified as corresponding aldo
16、l by its spot test 9. RESULTS AND DISCUSSION Under the conditions of reductant020Cu(III)0 , the plots of ln(At-A) versus time were straight lines, indicating the reaction is the first order in DPC, which using the equation ln(At-A)=-kobst+b(constant). The pseudo-first-order rate constants kobswere calculated by the method of least-squares. The kobsvalues were the average value of at least three independent experiments, and reproducibility is withi
