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Diss Factsheets

Environmental fate & pathways

Additional information on environmental fate and behaviour

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Administrative data

Endpoint:
additional information on environmental fate and behaviour
Type of information:
other: overview
Adequacy of study:
other information
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Several studies, published in peer reviewed literature, adequate for assessment

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
Photolysis of 1,1,1-difluorochloroethane, Internal Journal of Chemical Kinetics, vol. IX, 697-703.
Author:
Ichimura T, Kirk, AW and Tschuikow-roux, E
Year:
1977
Bibliographic source:
Internal Journal of Chemical Kinetics, vol. IX, 697-703.
Reference Type:
publication
Title:
Products of the tropospheric reactions of hydrochlorofluorocarbons (HCFCs-225ca -225cb -141b and -142b
Author:
Tuazon EC and Atkinson R
Year:
1994
Bibliographic source:
Environmental Science and Technology
Reference Type:
publication
Title:
The environmental impact of CFC replacements - HFCs and HCFCs
Author:
Wallington TJ, Schneider WF, Worsnop DR, Nielsen OJ, Sehested J, DeBruyn WJ, Shorter JA
Year:
1994
Bibliographic source:
Environmental Science and Technology 28:320A-326A
Reference Type:
publication
Title:
Rate constants for the reactions of OH with HC3CFCl2 (HCFC-141b), CH3CF2Cl (HCFC-142b), and CH2FCF3 (HFC-134a)
Author:
Zhang Z, Huie RE and Kurylo MJ
Year:
1992
Bibliographic source:
Journal Physics and Chemical 96: 1533-1535

Materials and methods

Test material

Constituent 1
Chemical structure
Reference substance name:
1-chloro-1,1-difluoroethane
EC Number:
200-891-8
EC Name:
1-chloro-1,1-difluoroethane
Cas Number:
75-68-3
Molecular formula:
C2H3ClF2
IUPAC Name:
1-chloro-1,1-difluoroethane

Results and discussion

Applicant's summary and conclusion

Executive summary:

Degradation products of HCFC 142 (Cas no. 75-68-3)

Summaries of studies

1,1,1-Difluorochloroethane was photolyzed at 147 nm in the pressure range of 3.6-20.6 torr (Ichimura et al. 1977). The effects of added NO, H2S, and CF4were investigated. The extinction coefficient at 147 nm and 296 °K was determined to be 64 ± 8 atm-1·cm-1. The molecule photodecomposes largely bya,ßelimination of HCl to give 1,1 -difluoroethylene (F0.74 ± 0.06). There is no observable elimination of HF, but there is strong evidence for the elimination of the elements of FCl though the relative importance of this process is minor, as are contributions from carbon-carbon and carbon-halogen bond fission. There were no significant variations in the quantum yields of the principal products with time in the range of 40-180 minutes. The major observed product was 1,1-difluoroethylene (CH2CF2). The quantum yields of all other products were between one and two orders of magnitude lower than those of CH2CF2. Since CH2CF2is the major product with a quantum yield unaffected by the addition of NO, the most important primary process is molecular elimination of HCI [reaction (2)]:

(1) CH3CF2Cl + hvàCH3CF2Cl

(2) CH3CF2ClàCH2CF2+ HCl; ¿H = 21.9 kcal/mol

The rate constants for the reaction of OH with CH3CFCl2(HCFC-141b) over the temperature range 250-297 K were measured with improved detection sensitivity as a function of flash energy and concentration of OH radical precursor (H2O)(Zhang et al. 1992). The rate constants were reduced at the lower OH concentrations employed, suggesting complications due to secondary reactions. The new values disagree with the low-temperature values reported earlier but agree with the values extrapolated from the higher temperature results (T> 298 K). In contrast, rate constants for CH3CFCl2(HCFC-142b) and CH2FCF3(HFC-134a), re-measured at the lower flash energy at 270 K, were found to agree with those reported earlier at higher flash energy. The diagnostic rate constant measurement for reactions of OH with CH3CFCl2was:

OH + CH3CFCl2àH2O + CH2CFCl2

An evaluation of the environmental impact of HFCs and HCFCs is given in terms of their ozone depletion potentials, global warming potentials, and ability to form noxious degradation products (Wallington et al. 1994). This evaluation is based on an overview of their atmospheric chemistry and the gas- and liquid-phase loss processes of their halocarbonvl decomposition products. The atmospheric fate of the alkoxy radical is either decomposition or reaction with O2. For HCFC-142b reaction with O2dominates giving CF2ClCHO.

The Cl atom-initiated photooxidation of CF3CF2CHCl2(HCFC-225ca) produced CF3CF2C(O)Cl in 100% yield, while CF2ClCF~HFCl(HCFC-225cb) yielded CF2ClCF2-C(O)F (99%) and C(O)FCl (1 %). The two-carbon aldehydes CFCl2CHO and CF2ClCHOwere positively observed as photooxidation products of CFCl2CH3(HCFC-141b) and CF2ClCH3(HCFC-142b), respectively. Their calculated 100%formation yields show conclusively that under lower tropospheric conditions the alkoxy radicals CFCl2-CH2O and CF2ClCH2O do not undergo C-C bond scission, but rather react with O2to form the aldehydes and HO2.

The contributions of two competing reaction pathways for the acyl radicals formed from the OH radical-initiated reactions of halogenated aldehydes, CX3COàCX3+ CO (a) and CX3CO + O2àCX3C(O)OO (b), were determined as 79±7% (a) and 21± 5% (b) for the acyl radical CFCl2-CO and 39±3% (a) and 61±5% (b) for CF2ClCO at 298 K and 740 Torr of air. These results are intermediate and consistent with those reported in the literature for the corresponding reactions of CCl3CO and CF3CO radicals.

References

Ichimura T, Kirk, AW and Tschuikow-roux, E (1977) Photolysis of 1,1,1-difluorochloroethane, Internal journal of chemical kinetics, vol. IX, 697-703.

Tuazon, EC., and Atkinson R, Products of the tropospheric reactions of hydrochlorofluorocarbons (HCFCs-225ca -225cb -141b and -142b, Env.Science and Technology, 1994.

Wallington TJ, Schneider WF, Worsnop DR, Nielsen OJ, Sehested J, DeBruyn WJ, Shorter JA (1994) The environmental impact of CFC replacements - HFCs and HCFCs, Environmental Science and Technology 28:320A-326A.

Zhang Z, Huie RE and Kurylo MJ (1992) Rate constants for the reactions of OH with HC3CFCl2 (HCFC-141b), CH3CF2Cl (HCFC-142b), and CH2FCF3 (HFC-134a), Journal Physics and Chemical 96: 1533-1535.