Dehydrogenation bimolecular

The importance of an energized reaction complex in bimolecular reactions is illustrated by considering in more detail the termination step in the ethane dehydrogenation mechanism of Section 6.1.2 ... 

The next basic aspect in the studies of dehydrogenation mechanism is the determination of the H202 interaction type with hydrocarbons. Under high-temperature oxidation conditions this interaction produces unsaturated compounds. Is this reaction the chain of a simple bimolecular type If the process is chain, variations of experimental conditions (presence of inert diluters, small additives, treatment of the reactor surface by various salts, the effect of the surfaceireaction zone volume ratio—the so-called SIV factor, etc.) must significantly change the initiation and chain termination rates. 

Dihydroxy acids, preparation, 179 Dihydroxy compounds, alkylation in the Williamson reaction, 227 dehydration, 33, 236 dehydrogenation to lactones, 336 esterification, 481 preparation, by bimolecular reduction of ketones, 134 by cleavage of oxides, 172 by hydrolysis of esters, 169 by reduction of dihydric phenols, 138... 

Formic acid decomposition has been studied on the (110), (001), and (100) surfaces of Ti02 [23-25,40-51]. The degree to which surface reducibility influences the reaction paths e.g., dehydrogenation vs. dehydration unimolecular reactions vs. bimolecular ones) will be explored in more detail... 

It should not be surprising that, except in those cases where the coordination environment around the cation is suitable for bimolecular coupling reactions, UHV decomposition reactions tend toward unimolecular processes. The bimolecular dehydrogenation process that occurs during steady-state reaction on the single crystal TiOafOOl) surface should serve as a reminder that steady-state processes involve interaction between the surface, surface species, and vapor phase components, and that it is not appropriate to attribute product selectivity exclusively to oxide characteristics. 

Qualitatively similar results were obtained for reaction and desorption of normal and iso-propanol on the 011 [-faceted TiO2(001) surface. In the case of normal propanol, almost half of the molecules initially adsorbed desorbed as the parent molecule at 370 K, while half of the remaining surface species reacted to form propanol at 580 K. The ratio of propene to propionaldehyde generated at 580 K was 10 1. Desorption of isopropanol quantitatively mirrored the desorption of normal propanol in two desorption states at 365 and 512 K. Isopropanol did not generate any dehydrogenation products (e.g., acetone), and the surface did not generate any bimolecular coupling products for any of the probe alcohol molecules. The absence of ether formation on the (Oil [-faceted surface is consistent with the need for double-coordination vacancies to facilitate that reaction, and the absence of such sites on this surface of titanium dioxide [80]. 

Interactions with other molecules can affect the ultimate reaction selectivity of the process. For example, the catalytic dehydration of formic acid on TiO2(001) occurred as a unimolecular process at high temperatures and low formate coverage, while a bimolecular dehydrogenation process dominated at near-saturation coverage of the titania crystal. 

An answer to the puzzling problem of the kinetics of skeletal isomerization may be found in a recent proposal, by Frennet and his co-workers (62), that hydrocarbon adsorption involves not a single site but an ensemble of several contiguous sites of the surface (seven to eight). When using the model of bimolecular dehydrogenation steps, one should always replace the first equation in Scheme 15 by... 

Chen et al. [118] showed for CH3OH vapor adsorbed on a Pd(lll) surface that the dissociation of the C-O bond requires methanol coverages close to one mono-layer Upon heating, most of the methanol (75%) desorbs, but the remaining part (25%) becomes partially dehydrogenated, while some other fraction of CH3OH molecules undergo a bimolecular reaction via... 

Uses of Formic Acid, Formamide, and DMF. Traditional markets for formic acid developed as a result of some of the unusual properties of this inexpensive, volatile carboxylic acid. It is nearly as acidic as sulfuric acid but may react either as an acid or an aldehyde because the carboxyl group is bound to a hydrogen rather than an alkyl group. It decomposes readily by dehydration, dehydrogenation, or through a bimolecular reaction (15]. 

The equations shown in Table 3.2 deal with variants on monomolecular or bimolecular reaction rate equations in general A to D terms. For a more concrete example in terms of chemical species, let us consider the speeifie ease of the dehydrogenation of butene to butadiene over a chromia/alumina eatalyst as detailed by Dumez and Froment [F.J. Dumez and G.F. Froment, Ind. Eng. Chem. Proc. Design Devel., 15, 291 (1976)]. In Table 3.3a is a number of reaetion sehemes for dehydrogenation classified as to atomic or molecular with the various possibilities listed as to the nature of the hydrogen recombination, (a)-(e), and with subdivisions as to... 

This group of alkaloids is formed in the plant (Faltis theory) by a double enzymatic dehydrogenation of two molecules of norcoclaurine (II). It is necessary to perform this bimolecular dehydrogenation in three different ways in order to provide correct skeletal structures for the known bis-benzylisoquinoline alkaloids of this group. First, the two diphenyl ether linkages may be formed by the dehydrogenation occurring between the... 

Secondly, the bimolecular dehydrogenation of norcoclaurine (II) can take place between the 12-hydroxyl groups and the 8-hydrogens to form the symmetrical structure XXIII. The alkaloids isochondodendrine,... 

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