THEORETICAL AND EXPERIMENTAL STUDY OF THE DEGRADATION OF MALONIC ACID DIESTERS IN GAS PHASE

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Simposio; Terceiro Simposio Iberoamericano de Qui­mica Organica (SIBEAQO3); 2016

Malonic acid diesters are widely used in the chemical industry as intermediates for the synthesis of a variety of organic chemicals and as the building blocks of different processes in which malonates are used as intermediates, such as pharmaceuticals, agrochemicals, vitamins, fragrances, and dyes. Until now, data atmospheric degradation of these compounds is not available in literature. To improve our knowledge of the atmospheric chemistry of malonic acid diesters, we report here the rate coefficients for the reaction between chlorine atom and a series of malonic acid diesters: di-methyl malonate (CH3OC(O)CH2C(O)OCH3, DMM), di-ethyl malonate (CH3CH2OC(O)CH2C(O)OCH2CH3, DEM), di-isopropyl malonate ((CH3)2CHOC(O)CH2C(O)OCH(CH3)2, DIPM), and di-tert-butyl malonate ((CH3)3COC(O)CH2C(O)OC(CH3)3, DTBM). Additionally, we present the fotooxidation mechanism of DMM and DTBM in absence and presence of NO2, supporting both by experimental and theoretical calculations.The rate constant for the reaction between malonic acid diesters and chlorine atom in gas phase were measured relative to cyclohexane, pentane and acetone. Photolyses were carried out in a photo-reactor using black lamps. Identification and quantification of reactants and products were performed by infrared spectroscopy. The rate coefficients measured for DEM, DIPM, and DTBM with chlorine atoms resulted to be approximately one order of magnitude higher than the corresponding for DMM (kDMM << kDIPM ¡Ö kDEM < kDTBM). This is in agreement with the expected results due to the structure of the molecules. For DMM and DTBM chlorine atom initiate the photooxidation mainly by the abstraction of the H-atom of methyl group, followed by the reaction of radicals formed with molecular oxygen to form the peroxy radical and subsequently the corresponding oxy radical (RO?: CH3OC(O)CH2C(O)OCH2O? and (CH3)3COC(O)CH2C(O)OC(CH3)2O?, respectively). The RO? radical react by two different ways: decomposition and migration of hydrogen atom from methylene group to terminal oxygen atom. The activation energy for the low steps are in agreement with the percentage of products obtaining in the two main paths supporting experimental results. The geometric parameters of the reactants, transition states, and products were fully optimized using density functional theory (Gaussian09, B3LYP/6-311+G(d,p)). Mechanism reaction for DMM and DTBM are proposed. AcknowledgmentsFinancial support from CONICET, ANPCYT, and SECyT-UNC is gratefully acknowledged. This work used computational resources from CCAD ? Universidad Nacional de C¨®rdoba (http://ccad.unc.edu.ar/), in particular the Mendieta Cluster, which is part of SNCAD ? MinCyT, Rep¨²blica Argentina.