Study On The Reaction Kinetics Of Trans-sobrerol And 8-p-menthen-1,2-diol With Hydroxyl Radical In Aqueous Solution

Alcohols, being widely used in medical and chemical industry, are important volatile organic compounds(VOCs) in the atmosphere. Natural and anthropogenic activities emit a large amount of alcohols into the atmosphere. In the atmosphere, gaseous alcohols are removed by their reactions with the atmospheric oxidants such as OH, O3, and NO3, forming products aldehydes, ketones, and organic acids, which might contribute to the formation of ozone and second organic aerosols(SOAs). Therefore, it is essential to study the atmospheric reaction mechanisms of alcohols.Atmospheric oxidation reaction of gaseous alcohols is primary initiated by hydroxide radical(OH), and the reaction rate is much higher than those of other radicals. Alternatively, with relatively high solubility in water, the alcohols can also easily dissolve in atmospheric liquid phase particles, including clouds, fogs, and wet aerosols, where the alcohols are also subject to aqueous-phase oxidation. Aqueous-phase oxidation is also an important process in the formation of SOA in the atmosphere. The studies in this dissertation focus on the reaction of two unsaturated alcohols with the hydroxyl radical in aqueous phase by using experimental and theoretical methods. Main results are summarized as followed.1. We have set up an aqueous-phase reaction system, which consists of a reaction vassal, a low voltage mercury lamp(λ = 254 nm, 313 nm), a quartz reactor, a circulation water system, and a stirring device. At different time intervals, samples are taken from the reactor and subsequently transferred to HPCL(High Performance Liquid Chromatography) analysis. The rate constants for the reactions of hydroxyl radicals with Trans-sobrerol(Sob) and 8-p-menthen-1,2-diol(Limo-diol) are measured by using p CBA(p-chlorobenzoic acid) and DMP(dimethyl phthalate) as references, for which the reaction rate constants are known already. The hydroxyl radical are generated from the UV photolysis of hydroperoxide. Limo-diol is obtained from hydrolysis of limonene oxide and presents as a mixture of three conformers. The rate constants of Trans-sobrerol(Sob) and 8-p-menthen-1,2-diol(Limo-diol) are obtained as(3.05 ± 0.5) × 109 M-1 s-1 and(4.57 ± 0.2) × 109 M-1 s-1 respectively.2. The reaction mechanisms of the unsaturated alcohols reacting with OH have been studied theoretically by using quantum chemistry and transition state theory calculations. All quantum chemistry calculations are performed by using Gaussian 09 suite of programs. M06-2X/6-311++G(2df,2p) are used to optimize equilibrium geometries and calculate vibrational frequencies and single point energies. The solvent effect was estimated with the polarizable continuum model(PCM) and with radii and non-electrostatic terms by SMD model. The reactions are assumed to proceed via OH additions to the unsaturated >C=C< double bonds, and the rate constants are estimated as 1.28 × 1010 M-1 s-1 and 2.56 × 1010 M-1 s-1 for Sob and Limo-diol, respectively.