Gas-phase reactions of brominated diphenyl ethers with OH radicals

A small volume reaction chamber coupled to a mass spectrometer was used to study the gas-phase kinetics and mechanism of the reaction of OH radicals with diphenyl ether and seven polybrominated diphenyl ethers (PBDEs) with 1-2 bromines. Relative rate constants for these reactions were determined using isopropyl nitrite photolysis in He-air mixtures at approximately 740 Torr between the temperatures of 326-388 K. The Arrhenius expression for each compound was used to extrapolate the following OH rate constants at 298 K (in units of 10(-12) cm3 molecule(-1) s(-1), with 95% confidence intervals): diphenyl ether, 7.45 +/- 0.13; 2-bromodiphenyl ether, 4.7; 3-bromodiphenyl ether, 4.6; 4-bromodiphenyl ether, 5.7; 2,2'-dibromodiphenyl ether, 1.3; 2,4-dibromodiphenyl ether, 3.8; 3,3-dibromodiphenyl ether, 3.2; and 4,4'-bromodiphenyl ether, 5.1. The measured OH rate constants are in reasonable agreement with those predicted by structure activity relationships. Positive temperature dependences of these OH rate constants are observed for all compounds measured except for diphenyl ether and 4,4'-dibromodiphenyl ether. Bromophenols (in yields up to 20% relative to the amount of PBDE consumed) and Br2 were characterized as products of these reactions, suggesting that OH addition to ipso positions of these brominated aryls may be an important reaction pathway.