Aqueous Phase Photolysis of Succinic Acid : Effect of Hydrogen Peroxide Concentration on Product Composition
- Paula Hudson, Assistant Professor of Analytical Chemistry, California State University Fullerton
- Peter de Lijser, Professor of Organic Chemistry, California State University Fullerton
Tropospheric aerosol directly affect the earth’s climate by reflecting and scattering incoming solar radiation, and indirectly by acting as cloud condensation nuclei. One source of tropospheric aerosol are low molecular weight α,ω-dicarboxylic acids, such as succinic acid (SA), a C4 diacid. It is established that SA does not exhibit hygroscopic growth, however oxidation reactions of SA produce other compounds that are hygroscopic, and in turn can act as cloud condensation nuclei. In this study, we conducted photochemical reactions of SA and hydrogen peroxide (H2O2) in the aqueous phase. The effect of H2O2 concentration on the product formation was observed in order to better understand the different photochemical reaction pathways of SA. Seven major reaction products were observed which included malonic acid, oxalic acid, 1,2,3,4-butantetetracarboxylic acid, malic acid, tricarballylic acid, and adipic acid. At higher H2O2 concentrations where the H2O2:SA ratio was greater than or equal to five, photooxidation took precedence over other photochemical pathways. SA reacted first to form malonic acid, and then oxalic acid, both highly hygroscopic compounds. At lower H2O2 concentrations, reaction intermediates began to recombine in radical-radical termination steps which led to the formation of 1,2,3,4-butanetetracarboxylic acid and tricarballylic acid. When no H2O2 was present α-β carbon-carbon bond cleavage took place followed by radical-radical termination. These processes led to the formation of adipic acid, a C6 diacid that does not exhibit hygroscopic growth. This study provides an insight on some of the photochemical reactions of succinic acid that take place in the atmosphere, and demonstrates the effect they can have on climate change.