Kinetics and products of the gas-phase reaction of OH radicals with 5-hydroxy-2-pentanone at 296 ± 2 K

The 1,4-hydroxycarbonyl 5-hydroxy-2-pentanone is an important product of the gas-phase reaction of OH radicals with n-pentane in the presence of NO. We have used a relative rate method with 4-methyl-2-pentanone as the reference compound to measure the rate constant for the reaction of OH radicals with 5-hydroxy-2-pentanone at 296 +/- 2 K. The carbonyls were sampled by on-fiber derivatization using a Solid Phase Micro Extraction (SPME) fiber coated with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride with subsequent thermal desorption of the oxime derivatives and quantification by gas chromatography with flame ionization detection. For comparison, the reference compound was also analyzed following sample collection onto a Tenax adsorbent cartridge. Products of the reaction were investigated using coated-fiber SPME sampling with gas chromatography-mass spectrometry analysis as well as by using in situ atmospheric pressure ionization mass spectrometry. A rate constant for the reaction of OH radicals with 5-hydroxy-2-pentanone of (1.6 +/- 0.4) x 10(-11) cm(3) molecule(-1) s(-1) was obtained at 296 +/- 2 K. Two dicarbonyl products, of molecular weight 86 and 100, were observed and are attributed to CH3C(O)CH2CHO and CH3C(O)CH2CH2CHO, respectively. Reaction schemes leading to these products are presented.