Atmospheric Chemistry of 1,3-Dioxolane:  Kinetic, Mechanistic, and Modeling Study of OH Radical Initiated Oxidation

Abstract

An absolute rate pulse radiolysis technique was used to measure k(OH + 1,3-dioxolane) ) (8.8 ( 0.9) × 10 -12 cm 3 molecule -1 s -1 at 295 K in 1000 mbar of Ar. Relative rate techniques were used to study the reactions of OH radicals and Cl atoms with 1,3-dioxolane and Cl atoms with ethylene carbonate and methylene glycol diformate at 300 K in 1 bar of synthetic air. Rate coefficients were k(OH + 1,3-dioxolane) ) (1.04 ( 0.16) × 10 -11 , k(Cl + 1,3-dioxolane) ) (1.6 ( 0.3) × 10 -10 , k(Cl + ethylene carbonate) ) (7.1 ( 1.7) × 10 -12 , and k(Cl + methylene glycol diformate) ) (5.6 ( 0.7) × 10 -13 cm 3 molecule -1 s -1 . OH radical and chlorine atom initiated oxidation of 1,3-dioxolane in 1 bar of N 2 /O 2 mixtures at 298 K in the presence of NO x gives ethylene carbonate and methylene glycol diformate. Molar yields of ethylene carbonate and methylene glycol diformate were 0.48 ( 0.07 and 0.50 ( 0.14 for OH radical initiation and 0.43 ( 0.07 and 0.53 ( 0.07 for Cl atom initiation. Product yields were independent of O 2 partial pressure over the range studied (60-800 mbar). A photochemical mechanism was developed to describe the OH-initiated degradation of 1,3-dioxolane in the presence of NO x . The results are discussed with respect to the available literature data concerning the atmospheric chemistry of ethers.

Product Study of the OH Radical and Cl Atom Initiated Oxidation of 1,3‐Dioxane

“…The sole cycloalkoxy radical produced during the atmospheric oxidation of 1,3,5-trioxane also undergoes CÀO bond cleavage rather than reaction with O 2 [8] and is thus consistent with the high strain energy of this triether ( % 30 kJ mol À1 ). In contrast, Sauer et al [7] reported that the cycloalkoxy radical generated by H-atom abstraction from the ÀOCH 2 OÀ group in 1,3-dioxolane preferentially reacts with molecular oxygen to form a cyclic carbonyl compound, despite having an estimated ring strain energy of around 30 kJ mol À1 . This is the only instance where reaction with O 2 appears to be a favourable reaction pathway for the highly strained C 5 cycloalkoxy radicals.…”

“…In the absence of authentic reference spectra for 3-oxopropyl formate or 2-oxoethyl formate it is not possible to confirm this. Although the formation of these formates cannot be ruled out, they are highly unlikely to be major products since attack at the ÀOCH 2 OÀ site is only expected to contribute less than 20 % to the overall reactivity of 1,3-dioxane, [4,7] . A number of reaction parameters were varied during the set of experiments, as indicated in Table 1.…”

“…These reaction schemes are based on the current knowledge on the reactivity of alkoxy radicals [14] and, in particular, on the observed reactivity of cyclic alkoxy radicals produced during the atmospheric oxidation of cyclic ethers. [2,[5][6][7][8][9] Previous studies of the atmospheric oxidation of ethers indicate that the reaction mainly proceeds by H-atom abstraction from a carbon atom in the a-position to the O atoms. [2] The reaction scheme for this pathway is shown in Figure 4.…”

“…In contrast, Sauer et al [7] reported that the cycloalkoxy radical generated by H-atom abstraction from the ÀOCH 2 OÀ group in 1,3-dioxolane preferentially reacts with molecular oxygen to form a cyclic carbonyl compound, despite having an estimated ring strain energy of around 30 kJ mol…”

“…[2] However, the cyclic ethers have received less attention. Although the kinetics of the OH reactions with cyclic ethers has been investigated in detail, [3,4] mechanistic studies have only been reported for 1,4-dioxane, [5,6] 1,3-dioxolane, [7] 1,3,5-trioxane [8] and tetrahydrofuran. [2] Ballesteros et al [9] have also investigated the kinetics and mechanisms for the reaction of chlorine (Cl) atoms with tetrahydropyran.…”