| Abstract |
In this Thesis, the kinetic and mechanistic studies of a series of reactions of atomic chlorine in the gas phase with partially halogenated ethers and sulfur compounds are described. The measured rate parameters (units in cm3 molecule-1 s-1) are: CHF2OCHF2 k=(5.24±0.84)x10-13 exp[-(698.5±45.2)/T], CF3CH2OCH2CF3 k=(7.77±2.70)x10-12 exp[-(939.7±110.5)/T], CF3CH2OCHF2 k=(4.63±0.92)x10-12 exp[-(1502.5±35.2)/T], CF3CH2OCH3 k=(1.49±0.3)x10-11 exp[0/T], CHF2CF2OCH3 k=(2.65±0.9)x10-12 exp[-(603±57.8)/T], CF3CHFCF2OCH3 k=(1.75±0.21)x10-13 exp[-(397±20.1)/T], CF3CH2OCF2CHF2 k=(1.59±0.56)x10-12 exp[-(1547.7±50.2)/T], CH2=CHCH2OCF2CHF2 k=(1.55±1.11)x10-13 exp[+(1190.95±110.55)/T], ICH2OCH3 k=(1.53±0.82)x10-11 exp[+(748.7±301.5)/T], BrCH2OCH3 k=(2.61±0.46)x10-11 exp[0/T], CH3SSCH3 kabstraction=(1.83±0.08)x10-10 exp[-(291.4±25)/T], kobservable=(5.17±0.32)x10-11 exp[+(406.6±34.8)/T] . All the above measurements were performed in the temperature range T = 273-363 K by using the VLPR (Very Low Pressure Reactor) technique. The reaction mechanism of partially fluorinated ethers involves the direct metathesis of atomic hydrogen, leading to the formation of hydrogen chloride (HCl) and the corresponding organic free radical, except in the case of CH2=CHCH2OCF2CHF2 where the mechanism involves the initial addition of atomic chlorine to the double bond leading to the formation of an unstable intermediate. Under the experimental conditions used, the fate of this intermediate could be the dissociation into the initial reactants (reverse reaction) or the unimolecular dissociation into products (CH2=CHCl + CH2OCF2CHF2). The reaction of ICH2OCH3 is taking place via the formation of an intermediate complex (adduct) which further decomposes into the final products. The formation of this adduct is confirmed on the basis of the negative activation energy in the temperature range used, but is also assisted by ab initio calculations. In the case of BrCH2OCH3 the final products are HCl + BrCHOCH3/BrCH2OCH2 without evidence of formation of intermediate complex. Nevertheless, a complex reaction mechanism can't be excluded because the formation of such a complex is predicted theoretically for the similar system Cl + CH3Br. Finally, in the case of CH3SSCH3 the reaction mechanism involves two pathways, the direct metathesis of atomic hydrogen, and the formation of an intermediate complex which is further decomposes into the final products, CH3SCl + CH3S. The operation of the addition mechanism was confirmed by both the negative activation energy and the appearance of the parent peak of CH3SCl (m/z = 82, 84) in the mass spectrum of the reaction mixture.
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Κινητική μελέτη των αντιδράσεων του ατομικού χλωρίου με μία σειρά μερικώς αλογονωμένων αιθέρων και τις αντιδράσεις με το διμεθυλοδισουλφίδιο
