Laboratory studies of the OH-initiated photooxidation of di-n-propyl ether

The OH-initiated photooxidation of di-n-propyl ether was investigated in this study. Di-n-propyl ether was mixed with nitric oxide and a hydroxyl radical precursor and irradiated using UV black lamps in a glass environmental chamber. Mass spectrometry was used as the primary analytical technique to monitor the reactants and products. FTIR spectroscopy was used to monitor formaldehyde. The products observed were propyl formate, acetaldehyde, propionaldehyde, and propyl propionate, with molar yields relative to di-n-propyl ether concentration loss of 0.61±0.044, 0.60±0.057, 0.15±0.062, and 0.043±0.015, respectively. Errors represent ±2σ. Nitrates could not be quantified because of a lack of commercially available standards. However, evidence exists for nitrate formation from the photooxidation of di-n-propyl ether. Formaldehyde concentrations were negligible. Mechanism predictions were performed on the di-n-propyl ether/OH system using the Carter kinetic software. Propyl formate and acetaldehyde yields were reasonably predicted (under 11.7% error). However, propionaldehyde and propyl propionate yields were vastly underpredicted, and examination of the experimental data suggested secondary production of both propionaldehyde and propyl propionate. Reactions were proposed for the photolysis and OH-initiated photooxidation of a primary nitrate product (1-propoxy propyl nitrate) that resulted in the formation of propionaldehyde and propyl propionate. Basic semiempirical computational chemistry calculations at the UHF/PM3 level of theory were performed using Hyperchem to investigate pathways for the secondary formation of propionaldehyde in particular.