Investigation of the Thermal and Photochemical Reactions of Ozone with 2,3-Dimethyl-2-butene

Abstract

The matrix isolation technique, combined with infrared spectroscopy and twin jet codeposition, has been used to characterize intermediates formed during the ozonolysis of 2,3-dimethyl-2-butene (DMB). Absorptions of early intermediates in the twin jet experiments grew up to 200% upon annealing to 35 K. A number of these absorptions have been assigned to the elusive Criegee intermediate (CI) and secondary ozonide (SOZ) of DMB, transient species not previously observed for this system. Also observed was the primary ozonide (POZ), in agreement with earlier studies. The wavelength dependence of the photodestruction of these product bands was explored with irradiation from λ ≥ 220 to ≥580 nm. Merged jet (flow reactor) experiments generated "late" stable oxidation products of DMB. A recently developed concentric jet method was also utilized to increase yields and monitor the concentration of intermediates and products formed at different times by varying the length of mixing distance (d = 0 to -11 cm) before reaching the cold cell for spectroscopic detection. Identification of intermediates formed during the ozonolysis of DMB was further supported by (18)O and scrambled (16,18)O isotopic labeling experiments as well as theoretical density functional calculations at the B3LYP/6-311++G(d,2p) level.

Investigation of the mechanism of ozonolysis of (Z)-3-methyl-2-pentene using matrix isolation infrared spectroscopy

“…The activation barrier for the reaction of MP and ozone has not been experimentally measured but it is anticipated to be similar to the E a for the reaction of ozone with acyclic alkenes such as cis-2-butene and 2-methyl-2-butene, both $2 kcal/mol [8], for which the room temperature rate constants are similar. The ozonolysis reaction for these two alkenes was observed [25,26] upon annealing to 35 K, so a similar reaction is likely here. Finally, the large number of product bands strongly suggests that more than a single product is formed under these conditions.…”

“…Additional reaction time is available in this mode compared to twin jet and has led to ''late'' thermal reaction products in previous studies [26,36,37]. Nonetheless, relatively stable ''early'' intermediates may survive through the reaction zone and be trapped in the argon matrix.…”

“…After several groups applied matrix isolation in an attempt to characterize the Criegee intermediate without success [19][20][21][22][23], the Ault laboratory succeeded in observing the three key intermediates (primary ozonide, Criegee intermediate and secondary ozonide) simultaneously in cryogenic matrices for several systems [24][25][26]. The study reported here continues this investigation with a single conformer (Z)-3-methyl-2-pentene (MP).…”

Peroxide intermediates of oxidation processes: Organic trioxides

“…The formation of a POZ was established or confirmed for some other examples, in particular, cis-but-2-ene 254 , tetramethylethylene (TME) 255,256 , hex-1-ene 255 , cyclopentene and cyclopentadiene 257 , and isoprene and methacrolein 258 . Kinetic studies on POZ stability are scarce.…”

Reaction Probability and Infrared Detection of the Primary Ozonide in Collisions of O3 with Surface-Bound C60

“…Therefore, several studies of the reaction between ozone and alkenes have been conducted in matrix isolation type experiments at low temperatures. [31][32][33] These studies have proven helpful in providing infrared spectroscopic characterization of the PO for a variety of unsaturated organic molecules. [31][32][33] Far fewer studies of the reaction between gas-phase ozone and solid or vaporous C 60 have been conducted.…”