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Author(s):   Imrik, K.; Sarzynski, D.; Dobe, S.; Berces, T.; Marta, F.
Title:   Competitive bromination kinetics of CH3Br and CH2ClBr
Journal:   React. Kinet. Catal. Lett.
Volume:   78
Page(s):   309 - 314
Year:   2003
Reference type:   Journal article
Squib:   2003IMR/SAR309-314

Reaction:   CH3Br + Br·HBr + ·CH2Br
Reaction order:   2
Reference reaction:   CH2ClBr + Br·HBr + ·CHBrCl
Reference reaction order:   2
Temperature:   353 - 410 K
Pressure:  9.00E-2 - 0.39 bar
Rate expression:   1.6±2.0x10-1 e-15200 [±300 J/mole]/RT
Bath gas:   He
Category:  Experiment
Data type:   Relative rate value measured
Pressure dependence:   Rate constant is pressure independent
Experimental procedure:   Static or low flow - Data taken vs time
Excitation technique:   Direct photolysis
Time resolution:   By end product analysis
Analytical technique:   Gas chromatography
Comments:   Experimental study measuring relative rates of reaction for CH3Br + Br -> CH2Br + HBr versusCH2ClBr + Br -> CHClBr + HBr. Br produced by UV photolysis (mercury lamp) of Br2. Ultimate products CH2Br2 and CHClBr2 (from rxn of halomethyl rads with Br2) were detected with GC/FID. Typical total pressure 90-390 mbar He. 50-200 mbar CH3Br. 5-20 mbar CH2ClBr. Br2 3 mbar. Temperature 353-410 K.

Ratio of rate constants is about 110 at lower temperature (353 K) and about 55 at higher temperature (410) in measured range. These measurements combined with estimated barriers for the reverse reaction, suggest that C-H BDE in CH3Br is about 10 kJ/mol stronger than in CH2ClBr.

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Rate constant values calculated from the Arrhenius expression:

T (K)k(T) []
353 9.02E-3
375 1.22E-2
400 1.66E-2
410 1.85E-2