Sequential dehydrogenation

Fig. XVni-4. HREELS vibrational spectra from ethylene chemisorbed on Rh(lll). There is a sequential dehydrogenation on heating. (From Ref. 13, p. 64.)...

It was clearly important to drive adduct formation to completion any unreacted starting material 32 was not rejected in isolation of the product 33 and the result was an impurity in the finasteride product. Excess DDQ was required to ensure complete conversion of 32, but any DDQ remaining after adduct formation produced over-oxidation products in the thermolysis. The three over-oxidation products shown in Figure 3.4 were identified. Sequential dehydrogenation in the B-ring... 

Aromatization of alicyclic compounds. Cyclohexane carboxylic acids maybe metabolized by a mitochondrial enzyme system to an aromatic acid such as benzoic acid. This enzyme system requires CoA, ATP, and oxygen and is thought to involve three sequential dehydrogenation steps after the initial formation of the cyclohexanoyl CoA (Fig. 4.36). The aromatase enzyme also requires the cofactor FAD. 

Significant yields of products heavier than the starting olefin are observed only for 1-butene. Traces of C5+ are observed from 2-butenes at the highest conversion levels. While the total yields of the C5 products correlate satisfactorily with feed conversion, distribution of the components within this fraction is strongly influenced by both temperature and contact time in a manner that suggests that the initially formed C5 products undergo sequential dehydrogenation reactions. 

Figure 2.25. Vibrational spectra from chemisorbed ethylene on Rh(lll) at different temperatures obtained by HREELS. Note the sequential dehydrogenation process.

This is a multistep reaction, which probably proceeds through a sequential dehydrogenation that can produce several intermediates, as indicated in the general scheme proposed by Bagotzky and coworkers [86]. Details of the dehydrogenation of methanol on Pt have not been established. From kinetic isotope measurements of CD3OH and CH3OH oxidation, it was shown that the first removal of H in the reaction... 

The activation of methane or methane formation on metal surfaces is a cataly tically critical reaction. The sequential dehydrogenation of methane is important for CO production and the sequential hydrogenation of carbon are essential parts of the Fisher-TVopsch mechanism. 

Fig. 31. Hydrogen thermal desorption spectra illustrating the sequential dehydrogenation of ethylene, propylene, and cis-2-butene chemisorbed on the Pt(lll) crystal surface at 120 K. The rate of heating is 12 K/sec...

Scheme 3.8 The one-pot process of sequential dehydrogenation-oxidative Heck cyclization.

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