Kinetic study of the reaction between sodium ethyl xanthogenacetate and alkylamine

Abstract

In this work kinetics investigation of the reaction between sodium ethyl xantogenacetate (NaEtXAc) and primary as well as secondary alkylamines, for each pair NaEtXAc-amine, was performed. Firstly, in order to determine the wavelength for following the reaction, the influence of the structures of reactants on the absorption was investigated. Absorption of the system was followed at l = 280 nm. The values of rate constants for 16 selected amines, at the different temperatures, were determined. Considering high correlations coefficients, r > 0.988, it was confirmed that investigated reactions are the second-order. On the basis of reaction constants, at the different temperatures, several thermodynamic parameters were calculated such as the energy of activation Ea,, frequency factor A, the entropy of activation DS#2S, Gibbs’s free-energy of activation DG#2S and enthalpy of activation DH#2S. By evaluation of the obtained results some assumptions, that refer to the reaction mechanisms of nucleophilic attack of the amine on the thiocarbonyl carbon, were made. Following the proposed mechanism activated complex, as a critical step, is formed in this reaction.

U cilju ispitivanja kinetike reakcije natrijum-etilksantogenacetata (NaEtXAc) sa primarnim i sekundarnim alkilaminima za svaki par NaEtXAc-amin ispitan je prvo uticaj strukture ovih jedinjenja na apsorpciju kako bi se odredila talasna dužina na kojoj će se pratiti reakcija. Praćena je promena apsorpcije sistema na l= 280nm. Određene su konstante brzina reakcija za šesnaest odabranih amina na različitim temperaturama. Na osnovu visokih vrednosti korelacionih koeficijenata r > 0,988, potvrđeno je da ispitivane reakcije slede kinetiku reakcije drugog reda. Na osnovu vrednosti reakcionih konstanti na različitim temperaturama izračunato je nekoliko termodinamičkih parametara ispitivanih reakcija: energija aktivacije Ea, faktor učestanosti A, entropija aktivacije ΔS#25, Gibsova slobodna energija aktivacije ΔG#25 i entalpija aktivacije ΔH#25. Obradom dobijenih rezultata pretpostavljen je reakcioni mehanizam nukleofilnog napada amina na tiokarbonilni ugljenik, pri čemu kao limitirajući korak nastaje aktivirani kompleks.