Hydrogenation examples

A wide variety of process-induced defects in Si are passivated by reaction with atomic hydrogen. Examples of process steps in which electrically active defects may be introduced include reactive ion etching (RIE), sputter etching, laser annealing, ion implantation, thermal quenching and any form of irradiation with photons or particles wih energies above the threshold value for atomic displacement. In this section we will discuss the interaction of atomic hydrogen with the various defects introduced by these procedures. 

Hydrogen is produced in microoiganisms by enzymes capable of ledncing free protons to molecular hydrogen. Examples of these enzymes inclnde hydrogenases and the nitrogenases. The production of hydrogen by these enzymes is nsnally cou-... 

The effect which amino functionality has on the thermal and impact sensitivity of polyni-troarylenes (Section 4.8.1.4) makes amination by VNS a method with much future potential for energetic materials synthesis. Other carbon, nitrogen, oxygen and sulfur nucleophiles can displace aromatic hydrogen examples with 1,3-dinitrobenzene and 1,3,5-trinitrobenzene are extensive. 

A Du Pont patent " reports that tungsten nitride preferably supported on alumina or titania is an active catalyst for amination by reaction of an alcohol with an amine in the presence of hydrogen. Examples are given of the amination of monoethanolamine by diethylenetriamine and amination of mon-oethanolamine by ethylenediamine. 

Metals that remain ductile at very low temperatures are preferred for use with liquid hydrogen. Examples include aluminum, copper, Monel, Inconel, titanium, austenitic stainless steels, brass, and bronze [3.19]. 

A variety of metal hydrides react with water at ambient temperature to produce high purity hydrogen. Examples of reactions are ... 

Hydride complexes of palladium and platinum are almost invariably stabilized by phosphine ligands and play an important role in catalytic processes such as hydrogenation. Examples are Pt(H)ClL2 and Pt(H)2L2, as well as hydrido alkyls and aryls, trans,-Pt(H)(R)L2. There are cis and trans isomers. A typical reaction is the insertion of alkenes and alkynes into the Pt—H bond 33... 

In the case of mixed Claisen condensations, a mixture of products is commonly avoided by using an acceptor ester that has no a-hydrogen. Examples of such reactants are ethyl formate... 

In contrast to asymmetric hydrogenation, examples of stereoselective reduction of functionalized ketones are rare. Scheme 43 illustrates the highly enantioselec-tive reduction of methyl benzoylformate in 2-propanol containing KOH using a catalyst prepared in situ from [RhCl(CgHjo)]2 and (S,S)-3 [101]. With the same catalyst, methyl pyruvate is reduced in 5% optical yield. 

More recently, chromium-promoted sponge cobalt has been found to be an active catalyst for nitrile hydrogenation. Examples of nitriles which have been successfully hydrogenated using this catalyst include 2-methylglutaronitrile [6], nitrilotriacetonitrile [7], and adiponitrile [8]. Hydrogenation of the latter nitriles typically is complicated by intramolecular cyclization reactions of the feedstocks. Use of the chromium-promoted sponge cobalt catalyst results in improved selectivities to linear products. 

Neither of the two types of chain termination reactions mentioned above in the isotopic hydrogen example is a fast reaction by these standards. Heterogeneous removal of chain centres requires as a minimum their delivery to a phase boundary, and at typical molecular speeds near 10 cm sec quite small apparatus dimensions would be necessary to yield a 10 sec reaction rate even under high vacuum conditions. This argument can be extended to the general observation that heterogeneous steps play no direct part in the interior of the shortlived experiments in shock tubes. 

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