Ethene reactions

Alcohols undergo dehydration in supercritical and hot water (41). Tertiary alcohols require no catalyst, but secondary and primary alcohols require an acid catalyst. With 0.01 MH2SO4 as a catalyst, ethanol eliminates water at 385°C and 34.5 MPa to form ethene. Reaction occurs in tens of seconds. Only a small amount of diethyl ether forms as a side reaction. 

In the case of the stabilized alkoxy radical formed in the ethene reaction, decomposition and reaction with... 

While it is often assumed that only the stabilized form of the Criegee intermediate undergoes such reactions, Moortgat and co-workers (Horie et al., 1994) have suggested that in the ethene reaction, it is the excited form that reacts with water vapor to form the acid, while the reaction of the stabilized Criegee intermediate leads to a hydroxyhydroperoxide, corresponding to reaction (48b). 

The addition of carbon-centered radicals to C-C double bonds (for a review see Giese 1983) is the key reaction in the free-radical-induced polymerization. In general, the rate constants of these reactions are only moderately high, but this process becomes fast and efficient, because in technical applications the polymerizing olefin is usually present at high concentrations. In aqueous solutions, the rate constant of the addition of the hydroxyethyl radical to ethene [reaction (29)], a non-activated C-C double bond, has been determined at 3 x 104 dm3 mol1 s1 (Soylemez and von Sonntag 1980). 

The Diels-Alder reaction and related pericyclic reactions, which can be treated qualitatively by the Woodward-Hoffmann rules (Section 4.3.5), have been reviewed in the context of computational chemistry [39]. The reaction is clearly nonionic, and the main controversy was whether it proceeds in a concerted fashion as indicated in Fig. 9.5 or through a diradical, in which one bond has formed and two unpaired electrons have yet to form the other bond. A subtler question was whether the reaction, if concerted, was synchronous or asynchronous whether both new bonds were formed to the same extent as reaction proceeded, or whether the formation of one ran ahead of the formation of the other. Using the CASSCF method (Section 5.4.3), Li and Houk [40] concluded that the butadiene-ethene reaction is concerted and synchronous, and chided Dewar and Jie [41] for stubbornly adhering to the diradical (biradical) mechanism. 

Problem 10.29 What is the Diels-Alder addition product of anthracene and ethene Reaction occurs at the (most reactive) and positions. 

The behaviour of pent-l-ene is typical of that of terminal olefins. Its metathesis to form oct-4-ene and ethene, reaction (9), is most readily achieved with high... 

The observed pressure independence of the product distribution in the ozone-ethene reaction between 100 and 1030 mbar indicates that the branching ratio may not be pressure dependent, in this pressure region. The pressure independence of the H2 yield has been shown, even down to 1 mbar (Becker). These findings are not in agreement with reaction step (3) by which excited Criegee intermediates are stabilised. 

Motivated by this proposal, Sabbah et al. performed low temperature measurements of the rate coefficients for these reactions. 0( P) atoms were generated in the cold CRESU flow via 355 nm laser photolysis of NO2, and their concentration followed using chemiluminescence from excited NO2, formed in the association of 0( P) with NO, as a marker for the oxygen atom concentrations, which decayed exponentially as a result of reaction with the added alkene. Results were obtained in most cases down to 23 K or 27 K, except for the 0( P) + ethene reaction, for which only an upper limit to the rate coefficient could be measured at 39 K. 

Theoretical calculations on T)2-ethyne complexes of second row transition metals and their insertion products have been reported362. it was found that for most atoms the 7C-coordinated complexes are thermodynamically favoured, just as in the case of the corresponding ethene reaction. The barrier height for the ethyne reaction was found to increase significantly between niobium and molybdenum, associated with the absence of vacant d orbitals in the latter atom. 

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