Gas chromatography of trimethylsilyl derivatives of α-methoxyalkyl hydroperoxides formed in alkene–O3 reactions

The synthesis of trimethylsilyl (TMS) hydroperoxide derivatives for gas chromatography (GC) was studied using N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) for derivatization of cumene hydroperoxide (CMOOH) (α,α′-dimethylbenzyl hydroperoxide) and α-methoxyalkyl hydroperoxides formed by liquid- and gas-phase ozonolysis of a series of terminal alkenes in the presence of methanol (CH3OH). Derivatization efficiencies >90% were achieved over a wide range of solution concentrations. The major compounds identified by GC–mass spectrometry of the derivatized products of alkene–O3 reactions were α-methoxyalkyl hydroperoxides, methyl esters, and aldehydes. Yields of α-methoxyalkyl hydroperoxides and methyl esters were quantified using effective carbon numbers (ECNs) and used to determine the yields of stabilized Criegee intermediates (SCIs) from gas-phase ozonolysis reactions. Such measurements are important for understanding the atmospheric chemistry of alkene emissions. SCI yields measured for the reactions of 1-octene [CH3(CH2)5CHCH2], 1-nonene [CH3(CH2)6CHCH2], and 2-methyl-1-octene [CH3(CH2)5C(CH3)CH2] are consistent with previous measurements or predictions based on literature data. SCI yields measured for the reactions of 1-decene [CH3(CH2)7CHCH2], 1-dodecene [CH3(CH2)9CHCH2], and 1-tetradecene [CH3(CH2)11CHCH2] are much lower than expected, apparently due to side reactions with low volatility aldehydes that form peroxyhemiacetals, which are not amenable to GC analysis. In general, the results indicate that off-line MSTFA derivatization can be an efficient means for increasing the stability of thermally labile hydroperoxides for identification and quantitation by GC, and offers a new approach for the analysis of these environmentally important compounds.