Acetylene, hydrogenation studies

Bilimoria, M. R., and Bailey, J. E. Dynamic studies of acetylene hydrogenation on nickel catalysts. ACS Symp. Ser. 

Replacing the hydrogen in 68 with a phenyl group leads to the secondary acetylenic monomer 70. It was believed that this disubstituted acetylene would suppress the reaction of acetylene with itself and insure that there was an acetylene functionality available for reaction with the o-quinodimethane at 200 °G The DSC of 68 showed the presence of a single exothermic peak at 263 °C which the authors felt was adequate evidence for the occurrence of a Diels-Alder reaction between the acetylene and benzocyclobutene. Unfortunately they did not report on any control experiments such as that between diphenylacetylene and simple benzocyclobutene hydrocarbon or a monofunctional benzocyclobutene in order to isolate the low molecular weight cycloaddition product for subsequent characterization. The resulting homopolymer of 68 had a Tg of 274 °C and also had the best thermooxidative stability of all of the acetylenic benzocyclobutenes studied (84% weight retention after 200 h at 343 °C in air). 

Other chemicals present in acrylonitrile production or in other non-acrylonitrile operations on sites of the companies in the epidemiological study by Blair et al. (1998) include acetylene, hydrogen cyanide, propylene, ammonia, acetic acid, phosphoric acid, lactonitrile, hydroquinone, sodium hydroxide, sulfuric acid, acrylamide, acetone cyanohydrin, melamine, methyl methaciydate, zweto-methylstyrene, urea, methacrylonitrile, butadiene, ammonium hydroxide and ammonium sulfate (Zey et al., 1989, 1990a,b Zey McCammon, 1990). 

Alkynes. Because of their less nucleophilic character, alkynes react less readily with hydrogen halides than do alkenes and often require the use a metal halide catalyst. Vinyl halides are formed in the reaction with one equivalent of HHlg. They may react further in an excess of the reagent to yield geminal dihalides. High yields of these compounds can be achieved. The addition of HC1 to acetylene was studied in detail because of the practical importance of the product vinyl chloride (see Section 6.2.4). 

Pyrrol-2-one (71) has been studied under matrix isolation conditions (95JPC15870). It is converted photochemically into acetylene, hydrogen cyanide, and carbon monoxide. 

The fruitfulness of the idea of a stepwise addition with an independent variation of the addends was brilliantly illustrated by Normant s studies, which resulted in the elaboration of a general method of alkene synthesis based on the reaction of alkyne carbometallation. Basically this reaction represents a case of the well-known nucleophilic addition to a carbon-carbon triple bond. In the Normant reaction, however, the initial addition of a nucleophile (an organome-tallic reagent) across the triple bond results in the formation of a stabilized carbanion-like intermediate equivalent to a vinyl carbanion. This intermediate can similarly be further reacted with an external electrophile. Most typically, copper-modified Mg or Li reagents, which are unable to react with acidic acetylenic hydrogens, are used in this sequence. 

Yasunobi T, Yasumoii I (1971) Pressure jump and isotope replacement studies of acetylene hydrogenation on palladium surface. J Phys Chem 75 880... 

Shvo has used complex 7 in eq 46 to catalyse the ionic hydrogenation of ketones, olefins, and acetylenes at moderate temperature and pressure [83]. A mononuclear hydride with a tethered hydroxyl group (8) is believed to be the active catalyst, so dissociation of 7 is necessary [84]. Ru(Ph4C50)(CO)2 (9) can be converted to the active catalyst under H. The ionic hycfrogenation of alkynes occurs with few turnovers because free alkyne coordinates irreversibly to the catalyst precursor (9) [85] similar alkyne complexes have been observed in other hydrogenation studies [86]. 

Since no intermediates could be detected in the in vitro studies of the oxidation of acetylenic derivatives, it was assumed that very short-lived intermediates were probably formed. In order to further characterize this pathyway, studies with deuterium and labeled biphenylacetylene (acetylenic hydrogen and internal acetylenic carbon, respectively) were initiated. The mass and nuclear magnetic resonance spectra of the resulting biphenyl acetic acid derivative showed that ... 

The commercial catalyst studied in this work was palladium (0.03w%) supported in a-alumina with less than 10 m /g of surface. Spent samples of catalyst were taken from industrial reactors after a 7 years run. The industrial unit correspond to a front end acetylene hydrogenation scheme comprising three reactors in series. The design of the unit is such that in normal operation the first reactor decrease acetylene concentration from 2700 ppm to 270 ppm, the second one from 270 ppm to 27 ppm and the last one from 27 to less than 3 ppm. 

The acetylene-hydrogen cyanide complex is of particular interest in view of the fact that the C-H stretches of both monomers can be probed using the F-center laser. Earlier microwave studies of this system showed the existence of a T-shaped isomer S shown in Figure 3, in which the acetylene acts as the proton acceptor. During our infrared investigation of this species, a linear isomer was also found in which the acetylene now acts as the acid. By studying the two C-H stretch vibrational modes of these two isomers it is possible to learn a great deal about the anisotropy of the vibrational... 

Dynamic Studies of Acetylene Hydrogenation on Nickel Catalysts... 

We have already discussed one important chemical property of alkynes the acidity of acetylene and terminal alkynes In the remaining sections of this chapter several other reactions of alkynes will be explored Most of them will be similar to reactions of alkenes Like alkenes alkynes undergo addition reactions We 11 begin with a reaction familiar to us from our study of alkenes namely catalytic hydrogenation... 

Dia ene deductions. Olefins, acetylenes, and azo-compounds are reduced by hydrazine in the presence of an oxidizing agent. Stereochemical studies of alkene and alkyne reductions suggest that hydrazine is partially oxidized to the transient diazene [3618-05-1] (diimide, diimine) (9) and that the cis-isomer of diazene is the actual hydrogenating agent, acting by a concerted attack on the unsaturated bond ... 

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