Kinetics and Mechanisms of CF3CHFOCH3, CF3CHFOC(O)H, and FC(O)OCH3 Reactions with OH Radicals

Kinetics of CF3CH2OCH3 (HFE-263fb2), CHF2CF2CH2OCH3 (HFE-374pcf), and CF3CF2CH2OCH3 (HFE-365mcf3) with OH radicals, IR absorption cross sections, and global warming potentials

Hydrofluoroethers (HFEs), like CF3CH2OCH3 (HFE-263fb2), CHF2CF2CH2OCH3 (HFE-374pcf), and CF3CF2CH2OCH3 (HFE-365mcf3), have been proposed in the last decades as the third-generation replacements of perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs) because of their...

Computational study on the thermal decomposition and isomerization of the CH3OCF2O• radical

The geometries of the reactant, products, and transition states involved in the decomposition pathways of the CH3OCF2O• radical formed during the photooxidation of CH3OCHF2 (HFE-152a) have been optimized and characterized at the DFT-B3LYP level of theory using the 6–311G(d,p) basis set. Single-point energy calculations have been made at the G2M (CC,MP2) level of theory. Out of the four prominent decomposition channels considered, the β-C–O bond scission is found to be the dominant path involving a barrier height of 9.78 kcal mol–1 (1 cal = 4.184 J). The thermal rate constant for the above decomposition pathway is evaluated using canonical transition state theory (CTST) and was found to be 5.27 × 104 s–1 at 298 K and 1 atm (1 atm = 101.325 kPa).

Atmospheric photooxidation of fluoroacetates as a source of fluorocarboxylic acids

A 1080 L environmental chamber with in situ FTIR spectroscopy detection was used to study the product distribution and the mechanism of the Cl-initiated photooxidation of a series of fluoroacetates. The gas-phase reactions of Cl atoms with ethyl trifluoroacetate (CF(3)C(O)OCH(2)CH(3)), methyl trifluoroacetate (CF(3)C(O)OCH(3)), and methyl difluoroacetate (CF(2)HC(O)OCH(3)) were investigated at 296 +/- 2 K and atmospheric pressure (approximately 760 Torr) of synthetic air. The fate of the fluoroalkoxy radicals formed in the reaction with Cl atoms mainly occurs through (i) an H-atom abstraction by reaction with O(2,) to produce the corresponding fluoroanhydride and (ii) an alpha-ester rearrangement via a five-membered ring intermediate to give the corresponding fluoroacetic acid. The yields of fluoroacids (CF(2)XC(O)OH, with X = H, F) obtained were as follows: 78 +/- 5, 23 +/- 2, and 30 +/- 5% for CF(3)C(O)OCH(2)CH(3), CF(3)C(O)OCH(3), and CF(2)HC(O)OCH(3,), respectively. Yields of <or=20, <or= 80, and <or=55% have been estimated for the anhydride formation from CF(3)C(O)OCH(2)CH(3), CF(3)C(O)OCH(3), and CF(2)HC(O)OCH(3), respectively. Formation of CF(2)O, with yield of 13 +/- 2% has been observed for the reaction of Cl with CF(2)HC(O)OCH(3). The measured yields are rationalized in terms of mechanisms consisting of competitive reaction channels for the radicals formed in the oxidation, that is, reaction with O(2), alpha-ester rearrangement and a decomposition pathway. The stability of the five-membered transition state of the alpha-ester rearrangement is correlated with the acid yields observed for the different fluoroacetates. Atmospheric implications, especially with regard to the fluorocarboxylic acid formation, are discussed.

Flammability assessment of CH2CFCF3: comparison with fluoroalkenes and fluoroalkanes

The burning velocity, flammability limits, and heat of combustion of CH(2)CF=CF(3) (1234yf) have been studied to elucidate the fundamental flammability properties of this new alternative refrigerant with low global-warming potential. The burning velocity of 1234yf was measured independently by schlieren photography and the spherical vessel method. In the spherical vessel method, the burning velocities of 1234yf and its analogues CH(2)=CFCHF(2) (1243yf) and CH(2)=CHCF(3) (1243zf) as well as those of typical fluoroalkanes CH(2)F(2) (HFC-32) and CH(3)=CHF(2) (HFC-152a) were measured in mixtures of air at various O(2)/(N(2)+O(2)) ratios. The maximum burning velocity of 1234yf was found to be 1.2+/-0.3 cm s(-1), which was approximately one-fifth that of HFC-32 (6.7 cm s(-1)) and one order of magnitude less than those of 1243yf (19.8 cm s(-1)) and 1243zf (14.1 cm s(-1)). The flame propagation of 1234yf was highly sensitive to flame temperature compared to that of the other compounds. The measured flammability limits and calculated heat of combustion of 1234yf were also determined.