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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:
experimental study
Adequacy of study:
supporting study
Study period:
not reported.
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Experimental study that is well documented, and peer-reviewed but does not specify guidelines.

Data source

Reference
Reference Type:
publication
Title:
Rate constants for the reactions of OH with ethane and some halogen substituted ethanes at 296 K.
Author:
Howard, C.J. & Evenson, K.M.
Year:
1976
Bibliographic source:
The Journal of Chemical Physics. 64(11):4303-4306.

Materials and methods

Test guideline
Qualifier:
no guideline required
Principles of method if other than guideline:
A conventional discharge-flow system was used to generate OH radicals in helium carrier gas by reaction of H and NO2. Hydroxyl radicals are detected with a laser magnetic resonace spectrometer.
GLP compliance:
not specified
Remarks:
not specified
Type of study / information:
Atmospheric fate of volatised substance.

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
-Purity: >99% (analysed)

Results and discussion

Any other information on results incl. tables

Figure 1 shows a series of typical OH decay plots obtained for the OH reaction with CH2BrCH2Br. The concentration of the reactant gas, [CH2BRCH2BR], is shown on the right side of the figure for each set of points and has been varied over a range of about a factor of 5 in this series of experiments. The effective bimolecular rate coefficient for each line can be obtained by dividing the first-order rate constant from the slop of the line by the average linear flow velocity v and the reactant gas concentration. An alternative way to treat the data is shown in Fig. 2, where the first-order rate constants from Fig. 1 (in s-1) are plotted as a function of the reactant concentration. An average bimolecular rate coefficient for the whole set is given by the slope of the line through the data. Since the line very nearly goes through the origin, it is clear that the same result is obtained either averaging the individual bimolecular rate coefficients or using the set of first-order costants and concentrations as in Fig. 2. This is true of nearly all of the reactions reported here.

Bromine and chlorine substitution are roughly equivalent and both tend to weaken the remaining (C-H) bonds and increase the OH reactivity.

Table 1. Rate constant summary for this work and other measurements near 296 K.

Reactant

Number of measurements Average (s.d.) ± error (10-15cm3/molecule(s))
CH2BrCH2BR 19 250(18) ± 55

Applicant's summary and conclusion

Conclusions:
The rate constant for ethylene dibromide is 250 ± 55 x 10^-15cm^3/molecule·s.