Acetylene reduction test

This new assay technique was developed independently by American and Australian workers who first established the connection between nitrogenase and hydrogenase, and showed the former could reduce a number of substrates other than nitrogen, for example nitrous oxide, azide, cyanide and, most usefully, acetylene. The latter is reduced to ethylene and this forms the basis of the acetylene reduction test. The material to be examined is briefly gassed with acetylene and the ethylene formed measured by gas chromatography. While this technique was being refined,... 

A number of alternative multi-step procedures for the synthesis of a-tert-alkyl ketones are known, none of which possess wide generality. A previous synthesis of 2-tert-penty1cyclopentanone involved reaction of N-1-cyclopentenylpyrrol 1 dine with 3-chloro-3-methy1-l-butyne and reduction of the resulting acetylene (overall yield 46 ). However, all other enamines tested afford much lower yields. Cuprate addition to unsaturated ketones may be useful in certain cases. Other indirect methods have been briefly reviewed. ... 

We have also tested the effect of the matrix material on the activity of COj reduction. Figure 2 shows the catalytic activities of ACF/Ni comparing two carbon black matrix materials Vulcan XC-72 (Cabot Corp.) and Denka acetylene black (AB). When XC-72 was used, the partial current density for COj reduction saturated at -2.0 V vs SCE. However, in the case of AB, the partial current density continued to increase with increasing potential. The difference may be due to the fact that AB, being more hydrophobic than XC-72, allows more COj molecules to reach the catalyst pores. 

The influence of the reduction temperature, preparation method and type of support on the textural properties and on the activity, selectivity and coking formation on Ni-Ti02-Al20j catalysts, using acetylene hydrogenation as the test reaction, is investigated. 

It is known that nitrogenase reduces ethyne (acetylene) to ethene and ethane. This is also the case for Schrauzer s system mentioned above. Schrauzer (1975) tested his process with diazene, which may be an intermediate in the reduction of dinitrogen (see, however, the remark about diazene made earlier). Diazene decomposed, however, to hydrazine, following Scheme 3-28. The experiment neither supports nor contradicts the hypothesis of the intermediacy of diazene in nitrogen fixation, because it is known that hydrazine is reduced to ammonia if added to the natural nitrogenase system. 

With this key union effected, only a few operations separated 48 from the substrate needed to test enyne metathesis (i.e. 12, Scheme 9). First, the controlled exposure of this compound (48) to 2 equivalents of TBAF in THF at 0°C effected the lysis of both the phenolic silyl ether and the TMS group append onto the terminal position of the alkyne, but, importantly, not the TIPS group on the other acetylene group. As such, in the next operation partial reduction with Lindlar s catalyst (Pd on BaS04 poisoned with quinoline) was accomplished selectively on only one alkyne to provide the needed terminal olefin. Finally, cleavage of the alky-nyl TIPS moiety under more forcing conditions (TBAF, THF, 25 °C), followed by silylation of both the allylic hydroxy and the phenolic groups (TBSCl, imid, DMF), then completed the assembly of enyne metathesis precursor 12 in 62% overall yield from 48. 

Chitosan-modified silica aerogek have also been tested for chemical catalysis applications, for example, in Ref. [122]. After impregnation of the aerogel with Pd salts and chemical reduction, the resulting model catalyst was tested for the selective hydrogenation of acetylene in the presence of ethylene and superior selectivity for acetylene was found. Such a catalyst system can find use in the gas makeup for polyolefine production (e.g., ethylene purification). Removal of acetylene is important as it is a catalyst poison for commonly used olefin polymerization catalysts. A high selectivity in such a gas makeup catalyst is essential, so that the precious ethylene itself is not hydrogenated. 

We report here the preparation of precious metal catalysts by reduction-deposition, which meets all requirements for production on large scale. New Pd catalysts were tested in the semi-hydrogenation of substituted acetylenes. 

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