Suchergebnisse

Department of Chemistry, Government Raza P. G. College, Rampur-244 901, Uttar Pradesh, India E-mail : bhadanaadesh@ yahoo.co.in Manuscript received 9 November 2006, revised 7 May 2007, accepted 18 July 2007 Hydrolysis of mono 4-methyl phenyl phosphate and 4-ethyl phenyl phosphate ester has been studied with CTAB, a cationic surfactant at 40 ± 1: 1.0°C in borate buffers solutions of pH= 8.0, 9.0 and 10.0. Absorbances of them were mcasurcd spectrophotomdrically and used to calculate rate constant of the hydrolysis, which found to be pseudo-first order. The process was run with and without CTAB with Kψ and K'w as rate constants respectively and the concentration of phosphate was restricted to 5.0 x 10-4 mol dm-3 and CTAB varied in between 0.2 x 10-1 to 2 x 10-3 mol dm-3. Rate constanls increase with concentrations of CTAB, giving as rate maximum Kψ = 67.3 x 105 S-1 at 18 x 103 mol dm-3 CTAB and Kψ = 58.3 X 105 S-1 at 16 x 103 mol dm-3 CTAB respectively at pH= 8.0 and pH= 9.0 for dianions of 4- mpp. But 4-EPP giving as rate maximum Kψ = 69.5 x 105 S-1 at 18 x 103 mol dm-3 CTAB and K'w= 60.8 x 10-3 S-1 at 16 x 10-3 mol dm-3 CTAB respectively at pH= 8.0 and pH= 9.0, it is concluded that the contribution of methylene group towards dcphosphorylation has been found to he 2.2 x 10-5 S-1 and 2.5 x 10-5 S-1 with respect to 18 x 10-3 mol dm-3 CTAB and 16 x 10-3 mol dm-3. The values of ion exchange parameters calculated at pH 8.0 and 9.0 by using various ion exchange equation have been summarized and found mSOH (concentration of reaction ion in Stern layer) 0.14, 0.452. Ks (binding constant) in 103 mol dm-3 is 1.06, 3.64. Kw (second order rate constant of water) in 105 mol dm-3 S-1 is 215,396. [OH-w](ion concentration in water) in 103 mol dm-3 is 3.76, 20.43. [OH-m] (ion concentration in micelle) in 104 mol dm-3 is 1.32, 3.70 at borate buffer 3.9 x 103 mol dm-3 [OH-], 20.3 x JO'l mol dm-3 [OH-]. Activation enerqy is 7.64 kca/mol and entropy is 32.06 [-∆S ± (eu)] at pH = 8 and used borate buffer 3.9 x 103 mol dm-3 [OH-].

7 páginas, 2 figuras ; In this letter we show that closed reversible chemical reaction networks with independent elementary reactions admit a global pseudo- Hamiltonian structure which is at least locally dissipative around any equilibrium point. The structure matrix of the Hamiltonian description reflects the graph topology of the reaction network and it is a smooth function of the concentrations of the chemical species in the positive orthant. The physical interpretation of the description is briefly explained and two illustrative examples are presented for global and local dissipative Hamiltonian description, respectively. ; The authors acknowledge financial support received from the Spanish Government (MCyT Projects PPQ2001-3643 & DPI2004-07444-C04-03) and Xunta de Galicia (PGIDIT02- PXIC40209PN). This research was partially supported by the Hungarian grant nos. K67625, F046223, which are gratefully acknowledged. The second author is a grantee of the Bolyai J´anos Research Scholarship of the Hungarian Academy of Sciences. ; Peer reviewed

Mechanochemistry has attracted a lot of attention over the last few decades with a rapid growth in the number of publications due to its unique features. However, very little is known about how mechanical energy is converted into chemical energy. Most of the published works using mechanochemistry neglect the required attention to the experimental parameters and their effect over the resulting products, what makes extremely difficult to reproduce the results from lab to lab. Moreover, if it is taken into consideration the broad range of experimental conditions used in different studies, it is quite difficult to compare results and set optimum conditions. As a result, mechanochemistry is generally viewed as a "black box". The aim of this work is to provide some insight into mechanochemistry. Thus, a simple kinematic-kinetic approach that allows the full parametrization of mechanically induced reactions is proposed. In an analogous way to thermally activated process, it is shown that kinetic modeling can serve to parametrize and model mechanically induced reactions as a function of the milling parameters with great reliability, thereby gaining prediction capability. As a way of example, this methodology has been applied for the first time to the mechanochemical reaction of Co and Sb to form CoSb3, a skutterudite-type thermoelectric material. Moreover, the universality of this methodology has also been validated with data from the literature. A key feature of the proposed kinematic-kinetic approach is that it can be extrapolated to other mechanically induced reactions, either inorganic or organic. ; Spanish Government Agency Ministerio de Economı́a y Competitividad and FEDER CTQ2017–83602-C2–1-R ; Junta de Andalucı́a-Consejerı́a de Economı́a, Conocimiento, Empresas y Universidad and FEDER P18-FR-1087 ; Junta de Andalucı́a-Consejerı́a de Economı́a, Conocimiento, Empresas y Universidad and FEDER US-1262507 ; INTRAMURAL-CSIC 201960E092