SINGLE-PULSE SHOCK-TUBE STUDIES OF THE DECOMPOSITION OF ETHOXY COMPOUNDS

Tetraethyl orthocarbonate (TEOC), diethyl carbonate (DEC), and diethox ymethane (DEM) have been decomposed in single-pulse shock tube experim ents. TEOC decomposes to give DEC, ethylene, and ethanol as organic pr oducts, while DEC results in only the latter two, In both cases the et hylene to ethanol ratio is equal to 1, and the mechanisms appear to in volve molecular eliminations, The rate expressions for the initial pro cesses are the following: k(TEOC --> products) = 10(13.91+/-0.14) exp( (-27 529 +/- 348)K/T) s(-1), T = 1005-1180 K; k(DEC --> C2H5OCO2H + C2 H4) = 10(12.03+/-0.11) exp((-23 290 +/- 26 7 K/T) s(-1), T = 955-1095 K. The listed uncertainties are one standard deviation. DEM decomposes more slowly than the other two compounds. For each DEM reacted, 1.2 e thylene and 0.5 ethanol are produced. Methane and ethane are also obse rved as products. The mechanism is postulated to involve both molecula r and bond-breaking channels. It is concluded that ethanol arises only through the molecular channel, and on this basis the following rate e xpressions have been derived: k(DEM --> products) = 10(15.93+/-0.15) e xp((-36 179 +/- 403 K/T) s(-1), T = 1150-1260 K; k(DEM --> ethanol + p roducts) = 10(15.07+/-0.45) exp((-34 517 +/- 1090 K/T) s(-1); k(DEM -- > ethyl + OCH2OC2H5) = 10(16.32+/-0.45) exp((-38 214 +/- 1160 K/T) s(- 1). The results are compared with those dealing with the stability of analogous ethers, esters, and silicon compounds. For carbon compounds the addition of ethoxy groups to the compound destabilizes the molecul e. It is further concluded that rate data on the molecular decompositi ons of ethoxy carbon compounds cannot be easily extrapolated to silico n-containing species.