Kinetics of the thermal decomposition of acetals. Part I

The kinetics of the thermal decomposition of ethylal, dimethyl acetal, and diethyl acetal have been studied over the range 389-530° in a static system, periodic quantitative analyses of the products being made By infrared spectrometry. The observed pressure increase may be accepted as a reasonable measure of the acetal decomposed. The reaction orders and the activation energies have been determined. Ethylal decomposes mainly By a chain mechanism, but rearrangement processes are probably more important with dimethyl and diethyl acetal. Inhibition By nitric oxide is transitory, which suggests incomplete suppression of chains in the presence of that inhibitor

Kinetics of the thermal decomposition of acetals. Part IV. Sensitized reactions

The influence of several sensitizers on the thermal decomposition of methylal and dimethyl acetal has been studied. Quantitative analyses of the products have been made by infrared spectrometry. If very small amounts of nitric oxide are added to a methylal-ethylene oxide mixture, the rate of the sensitized reaction is greatly reduced, the inhibition being transitory. Biacetyl seems to be efficient in sensitizing a reaction in a nitric oxide-inhibited methylal decomposition at 520°. Di-t-butyl peroxide has been tested over a wide temperature range (168-5-527°) but seems unsuitable as a sensitizer

Luminescence and triplet absorption of o-, m-, and p-methylbenzoic acids

The transient absorption spectra of flashed o-, m-, and p-methylbenzoic acids (o-MBOH, m-MBOH, and p-MBOH) in the 290-340-nm region are recorded and the transient is identified as the emitting lowest π,π* triplet state. The absorption and emission spectra of the three acids at room temperature and 77 K have been investigated and drastic solvent dependence of fluorescence and phosphorescence quantum yields has been found. These changes are attributed to different photophysic properties of monomeric and dimeric species. Glassy matrices containing either monomer or dimer MBOH were obtained by controlling solvent polarity and cooling rate. Thus the quantum yields and lifetimes of each species could be determined. The quenching of fluorescence in the monomer is interpreted in terms of strong coupling among n,π* and π,π* excited states, increasing the ISC process S1 /\/\/\> T. In the dimer, hydrogen bonding raises the energy of n,π* states and weakens the coupling allowing fluorescence to appear. Steric effects present in o-MBOH are also discussed

Luminescence of benzoic acid and methyl benzoate at 77 K

A method to obtain glassy matrices containing only dimer or monomer benzoic acid is described. Fluorescence and phosphorescence quantum yields of both forms of the acid are presented and compared with previous values. New data on the luminescence of methyl benzoate are also given

Kinetics of the thermal decomposition of acetals. Part III. The inhibited reactions of methylal and acetaldehyde dimethyl acetal

The influence of nitric oxide, propene, ethylene, toluene, and cyclohexene on the thermal decomposition of methylal and acetaldehyde dimethyl acetal in a static system has been studied. The reactions have been followed by observing the change of pressure with time and by infrared spectroscopy. Hydrogen cyanide, nitrous oxide, and probably a nitrite are produced from the nitric oxide, which is consumed during the transitory inhibition. The results obtained are discussed and it is shown that the normal methylal chain is several hundred steps long. A different behaviour is observed with unsaturated inhibitors. The pressure increase-time curves of the methylal decomposition are lowered by ethylene or propene below the limit reached with nitric oxide. Inhibition is not transitory. The amount of hydrogen in the products is preferentially diminished with any of either inhibitor. Ethylene or some of its products remaining adsorbed on the surface of the reaction vessel seem to have a specific influence on the decomposition of acetaldehyde dimethvl acetal

Gas phase oxidation of tetrahydrofuran

The slow gas‐phase oxidation of tetrahydrofuran was studied under static conditions at 220°C. The relative amounts of each product, if extrapolated to zero reaction time, show which are the primary reaction products, and the reaction stoichiometry was thus established. Rate constants for hydroperoxides production and consumption were calculated; these hydroperoxides are responsible for chain branching. Carbon monoxide and carbon dioxide have been shown to be formed in the early stages of the reaction and not simply as end products of oxidative degradation processes. It has been found that at reaction times close to zero one tetrahydrofuran molecule may be attacked in one or several carbon atoms. 65.9% of tetrahydrofuran consumed in the first stages of the reaction forms succinic acid through a mechanism in which one molecule of fuel is attacked by two molecules of oxygen. More than 20% of the tetrahydrofuran molecules are attacked at least by three molecules of oxygen. Copyright © 1988 John Wiley & Sons, Inc

Kinetics of the thermal decomposition of acetals. Part II. The methylal chain

The kinetics of the thermal decomposition of methylal has been studied over the range 472-520° and 50-450 mm. in a static system, By studying the change of pressure and By infrared analyses. The system of steadystate equations is too complex to have a straightforward solution but By means of them the experimental order is explained, several stoicheiometric relations among the products become amenable to experimental test, and ratios of elementary rate constants and changes of some radical concentrations have been calculated

Construcción de un sistema de fotólisis de destello

Trabajo presentado en la XV Reunión Bienal de la Real Sociedad Española de Física y Química, celebrada en Tarragona (España) del 27 de septiembre al 02 de octubre de 1971.Se describe un sistema de fotólisis de destello que utiliza destellos de hasta 2000 J generados por un banco de condesadores de 1 uF en paralelo, que se cargan con 20 KV. La detección se realiza con otro destello de 2 us de duración y 50 J de energía de una lámpara de Garton. Este instrumento permite trabajar con muestras líquidas y vidrios orgánicos en la zona de 77-300 K