Kinetics of the Reactions of OH Radicals with 2- and 3-Methylfuran, 2,3- and 2,5-Dimethylfuran, and E- and Z-3-Hexene-2,5-dione, and Products of OH + 2,5-Dimethylfuran

Furan and alkylfurans are present in the atmosphere from direct emissions and in situ formation from other volatile organic compounds. The OH radical-initiated reactions of furan and alkylfurans have been proposed as relatively clean in situ sources of unsaturated 1,4-dicarbonyls, some of which are otherwise not readily available. Using a relative rate method, rate constants at 296 2 K for the gas-phase reactions of OH radicals with 2- and 3-methrlfuran, 2,3- and 2,5-dimethylfuran, and Z- and E-3-hexene-2,5-dione have been measured, of (in units of 10(-11) cm(3) molecule(-1) s(-1)): 2-methylfuran, 7.31 +/- 0.35; 3-methylfuran, 8.73 +/- 0.18; 2,3-dimethylfuran, 12.6 +/- 0.4; 2,5-dimethylfuran, 12.5 +/- 0.4; Z-3-hexene-2,5-dione, 5.90 +/- 0.57; and E-3-hexene-2,5-dione, 4.14 +/- 0.02. Products of the OH radical-initiated reaction of 2,5-dimethylfuran were investigated, with 3-heliene-2,5-dione being formed with molar yields of 24 +/- 3% in the presence of NO and 34 +/- 3% in the absence of NO. Direct air sampling atmospheric pressure ionization mass spectrometry showed the formation of additional products of molecular weight 114, attributed to CH3C(O)CH=CHC(O)OH and/or 5-hydroxy-5-methyl-2-furanone, and 128, attributed to CH3C(O)OC(CH3)=CHCHO.