Nickel compounds, activated

There is a dramatic difference between the behavior of CeFe2 and ThFes and that of RNis, ThNis, and other nickel compounds in that the activity of the iron strongly decreases with time whereas with the nickel compounds activity increased with time. The behavior of the nickel compounds is undoubtedly a consequence of the progressive transformation of ThNis, UNis, or RNis into nickel plus an oxide, the mixture being the active catalyst. In the case of the iron compounds, the decline in activity is caused by carbon deposition and perhaps the formation of small amounts of waxes since it was observed that the reactor tended to plug up. 

Copper sulfate, in small amounts, activates the zinc dust by forming zinc—copper couples. Arsenic(III) and antimony(TTT) oxides are used to remove cobalt and nickel they activate the zinc and form intermetaUic compounds such as CoAs (49). Antimony is less toxic than arsenic and its hydride, stibine, is less stable than arsine and does not form as readily. Hydrogen, formed in the purification tanks, may give these hydrides and venting and surveillance is mandatory. The reverse antimony procedure gives a good separation of cadmium and cobalt. 

In 1968, Eisch and Foxton showed that nickel(II) salts enhance the rate of BU2AIH addition to internal alkynes by a factor of ca. 1000 compared to the process in the absence of a catalyst [26]. Similar catalytic activity of nickel compounds was found for the addihon of aluminum hydrides to alkenes. 

These catalysts should be clearly distinguished from those active for the cyclooligomerization of conjugated dienes, etc., which are based on zero-valent nickel compounds... 

There can be little doubt that the active species involved in most or even all of the various combinations described in Section II is HNi(L)Y (see below), because the different catalysts prepared by activating the nickel with Lewis acids have been shown to produce, under comparable conditions, dimers and codimers which have not only identical structures but identical compositions. On modification of these catalysts by phosphines, the composition of dimers and codimers changes in a characteristic manner independent of both the method of preparation and the nickel compound (2, 4, 7, 16, 17, 26, 29, 42, 47, 76). Similar catalysts are formed when organometallic or zero-valent nickel complexes are activated with strong Lewis acids other than aluminum halides or alkylaluminum halides, e.g., BFS. 

The following conclusions can be drawn (a) ir-Allylnickel compounds are probably not involved in the catalytic dimerization of cyclooctene, because the highest reaction rate occurs when only traces of these compounds can be detected further, the concentration of the new 7r-allyl-nickel compound (19) becomes significant only after the catalytic reaction has ceased, (b) The complex formed between the original 7r-allylnickel compound (11) and the Lewis acid is transformed immediately upon addition of cyclooctene to the catalytically active nickel complex or complexes. In contrast to 7r-allylnickel compounds, this species decomposes to give metallic nickel on treatment of the catalyst solution with ammonia, (c) The transformation of the catalytically active nickel complex to the more stable 7r-allylnickel complex occurs parallel with the catalytic dimerization reaction. This process is obviously of importance in stabilizing the catalyst system in the absence of reactive olefins. In... 

Animal experimental models of nickel-induced skin sensitivity are few and have been conducted only under very specialized conditions (USEPA 1986). Studies examining the mechanism of nickel contact sensitization and its extent in wildlife are needed (USPHS 1993). The importance of the surface properties and crystalline structure of nickel compounds in relation to their reactivity and protein-binding activities is well documented. It is therefore necessary to identify clearly the nickel compounds to which exposure occurs (Sunderman etal. 1984). Acute and chronic dermal and... 

Costa, M., Simmons-Hansen, J., Bedrossian, C. W. M., Bonura, J. and Caprioli, R. M. (1981). Phagocytosis, cellular distribution, and carcinogenic activity of particulate nickel compounds in tissue culture, Cancer Res., 41, 2868-2876. 

The transition group compound (catalyst) and the metal alkyl compound (activator) form an organometallic complex through alkylation of the transition metal by the activator which is the active center of polymerization (Cat). With these catalysts not only can ethylene be polymerized but also a-olefins (propylene, 1-butylene, styrene) and dienes. In these cases the polymerization can be regio- and stereoselective so that tactic polymers are obtained. The possibilities of combination between catalyst and activator are limited because the catalytic systems are specific to a certain substrate. This means that a given combination is mostly useful only for a certain monomer. Thus conjugated dienes can be polymerized by catalyst systems containing cobalt or nickel, whereas those systems... 

Gilman JPW. 1962. Metal carcinogenesis. 11. A study on the carcinogenic activity of cobalt, copper, iron and nickel compounds. Cancer Res 22 159-162. 

Carbonylation of methanol to form acetic acid has been performed industrially using carbonyl complexes of cobalt ( ) or rhodium (2 ) and iodide promoter in the liquid phase. Recently, it has been claimed that nickel carbonyl or other nickel compounds are effective catalysts for the reaction at pressure as low as 30 atm (2/4), For the rhodium catalyst, the conditions are fairly mild (175 C and 28 atm) and the product selectivity is excellent (99% based on methanol). However, the process has the disadvantages that the proven reserves of rhodium are quite limited in both location and quantity and that the reaction medium is highly corrosive. It is highly desirable, therefore, to develop a vapor phase process, which is free from the corrosion problem, utilizing a base metal catalyst. The authors have already reported that nickel on activated carbon exhibits excellent catalytic activity for the carbonylation of... 

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