Ethanol, also known as vinyl alcohol, hydroxyethylene, or hydroxyethylene, is an alcohol with the chemical formula C2H4O (H2C=CHOH) and CAS number 557-75-5. Under normal conditions, it tautomerizes to acetaldehyde. For this reason, thermoplastic polyvinyl alcohol (PVA or PVOH) derived from this monomer is produced indirectly by polymerization of vinyl acetate followed by hydrolysis of ester linkages.
Before the recent discovery of enols as intermediates in many flames, they appeared in non-combustion models. Furthermore, the flame chemistry of enols is poorly understood. Enol formation in a low-pressure flame occurs in the preheat zone, and its precursors are likely to be fuel species or early products of fuel decomposition. The OH + ethylene reaction has been shown to dominate vinyl alcohol production in ethylene flames, although this reaction appears to be underpowered to describe vinyl alcohol formation in all hydrocarbon oxidation systems. In this work, the mole fraction distributions of vinyl alcohol in several representative low-pressure flames were correlated with those of possible precursor species as a means of judging possible formation pathways in the flames. These correlations and modeling suggest that the reaction of OH with ethenol is in fact the main source of vinyl alcohol in many hydrocarbon flames, and that addition-elimination reactions of OH with other alkenes may also be responsible for the formation of enols in flames. On this basis, enols are expected to be minor intermediates in most flames and should be most prevalent in olefinic flames, where the reaction of fuel with OH can directly produce enols.
