Dehydrogenation of aliphatics

Pincer-ligated iridium complexes have been used as homogeneous catalysts for the dehydrogenation of aliphatic polyalkenes to give partially unsaturated polymers. The catalyst appears to be selective for dehydrogenation in branches as compared with the backbone of the polymer.56 The mechanism shown in Scheme 1 has been suggested for an [IrCl(cod)]2-catalysed oxidative esterification reaction of aliphatic aldehydes and olefinic alcohols.57... 

Dehydrogenation of aliphatic hydrocarbons. A number of aliphatic hydrocarbons experience enhanced dehydrogenation conversions by carrying out the reactions in porous inorganic membranes. Most of the studies use porous alumina membrane tubes as the reactors. 

Scheme 19 DEAD-mediated dehydrogenation of aliphatic tertiary methylamines...

The author and Vasyunina (84, 85) investigated the kinetics of dehydrogenation of aliphatic amines into keti mines, a reaction found by them. 

The chemistry of pincer complexes of the group 9 has been dominated by the study of the derivatives with rhodium and iridium. To date, the reactivity of cobalt pincer compounds with carbon monoxide has not been reported, mainly due to the fact that the number of pincer complexes derived from cobalt is reduced [17]. Thus, the interest in the Rh and Ir PCP pincer complexes is mainly owing to the fact that they have been proved efficient in the catalytic dehydrogenation of aliphatic C—H bonds this is particularly true in the case of the iridium PCP pincer complexes [3j. 

The aliphatic diazo-compounds can also be prepared by careful dehydrogenation of the hydrazones (with HgO) (Curtius, Staudinger) and, conversely, they are converted into the latter by hydrogenation ... 

In heterogeneous metal catalysis alkanes, alkenes, and aromatics adsorbed on the metal surface rapidly exchange hydrogen and deuterium. The multiple adsorption of reactants and intermediates lowers the barriers for such exchange processes. Hydrogenation of unsaturated aliphatics and isomerisation can be accomplished under mild conditions. Catalytic dehydrogenation of alkanes to alkenes requires temperatures >200 °C, but this is because of the thermodynamics of this reaction. 

Numerous methods to prepare individual classes of aliphatic diazo compounds have been extensively developed. The major strategies for their synthesis involve the alkaline cleavage of N-alkyl-N-nitroso-ureas, -carboxamides and -sulfonamides, dehydrogenation of hydrazones, as well as diazo group transfer from sulfonyl and related azides to active methylene compounds, and electrophilic diazoalkane substitution reactions. These synthetic methods have been comprehensively reviewed (15,16). Useful information on the preparation of selected diazo compounds can be found elsewhere (6,17). 

In the petroleum (qv) industry hydrogen bromide can serve as an alkylation catalyst. It is claimed as a catalyst in the controlled oxidation of aliphatic and alicydic hydrocarbons to ketones, acids, and peroxides (7,8). Applications of HBr with NH4Br (9) or with H2S and HQ (10) as promoters for the dehydrogenation of butene to butadiene have been described, and either HBr or HQ can be used in the vapor-phase ortho methylation of phenol with methanol over alumina (11). Various patents dealing with catalytic activity of HQ also cover the use of HBr. An important reaction of HBr in organic syntheses is the replacement of aliphatic chlorine by bromine in the presence of an aluminum catalyst (12). Small quantities of hydrobromic acid are employed in analytical chemistry. 

Similar to the reforming of methane, the major product of aliphatic hydrocarbons reforming is syngas, although some dehydrogenated products such as olefins and alkynes may also be formed. Futamura et al. [49-51] reported the C02 reforming... 

Aromatization the conversion of nonaromatic hydrocarbons to aromatic hydrocarbons by (1) rearrangement of aliphatic (noncyclic) hydrocarbons (q.v.) into aromatic ring structures and (2) dehydrogenation of alicyclic hydrocarbons (naphthenes). 

For a lead reference and a particularly elegant example of the (site-directed) dehydrogenation of an aliphatic group incorporated into a complex organic synthesis see D. Sames in ... 

It can be presumed that under cold plasma conditions, the nitrogen and phosphorus containing polymers can lead also to the macroradicals through dehydrogenation of CH aromatic and aliphatic or NH groups. 

---