Nickel aqueous reactions

In the study of effects of ultrasound on the aqueous reactions of nickel, we found some interesting results, for example, the colloidal formation of Ni-DMG complex and degassing of NH3 during different experiments. When 25 ml of 0.001 M NiSC>4 solution was complexed with 5 ml of 1% dimethyl glyoxime (DMG) in faintly alkaline ammonia medium and sonicated for 30 minutes and compared with another set of 25 ml of complexed solution which was stirred mechanically, a colloidal solution of Ni-DMG complex was formed in sonicated condition. Particles of Ni-DMG complex did not settle even after keeping 3 1 h because of their smaller size, in sonicated solution, whereas in the unsonicated condition large particles of Ni-DMG complex settled down immediately. 

Novel transition metal-mediated strategies were also well represented this past year. Takahashi and co-workers reported a s nickel-catalyzed reaction between azaziconacyclopentadienes (9) and alkynes to form pyridines (10) of varying substitution patterns <00JA4994>. This methodology, a formal cyclotrimerization, is also noteworthy since two different alkynes can be used. In similar fashion, Eaton reported an aqueous, cobalt(II) catalyzed cyclotrimerization between two identical acetylenes and one nitrile to afford substituted pyridines . 

Greater durability of the colloidal Pd/C catalysts was also observed in this case. The catalytic activity was found to have declined much less than a conventionally manufactured Pd/C catalyst after recycling both catalysts 25 times under similar conditions. Obviously, the lipophilic (Oct)4NCl surfactant layer prevents the colloid particles from coagulating and being poisoned in the alkaline aqueous reaction medium. Shape-selective hydrocarbon oxidation catalysts have been described, where active Pt colloid particles are present exclusively in the pores of ultramicroscopic tungsten heteropoly compounds [162], Phosphine-free Suzuki and Heck reactions involving iodo-, bromo-or activated chloroatoms were performed catalytically with ammonium salt- or poly(vinylpyrroli-done)-stabilized palladium or palladium nickel colloids (Equation 3.9) [162, 163],... 

The diethyl ether extractions are carried out in the reaction vessel in the following manner. Diethyl ether (50 mL) is added by syringe to the aqueous reaction mixture and the two-phase mixture is vigorously stirred, still under argon, for a few minutes. The layers are allowed to separate and the organic layer is quickly cannulated into the nickel solution. The procedure is repeated twice. 

The battery electrolyte is aqueous KOH solution in a concentration range of 25-30% KOH by weight. The mechanism that best describes the overall nickel electrode reactions in aUcaline electrol3d e is given in Eqs. 13.1 and 13.2 below. 

However, in some cases (e.g. [38]) the model was not successful. This happened in the case of the extraction of zinc and nickel with HDEHP using the RDC technique, and this was interpreted as follows in the case of zinc the transfer was found to be controlled by mass transfer alone because the chemical reaction was too fast to limit the kinetics in the case of nickel the reaction was too slow and much extractant was partitioning to the aqueous phase without complexing the metal cation, thus making it impossible to use the MTWCR model of Rod [57] presented above. 

The introduction of hydrophobicity into the aqueous reaction system seems to be important to attain effective epimerization. Aggregation of complex and hydrophobic interaction due to amphiphilic properties plays a key role in the coordination of aldose. Possible reasons for the large epimerizing ability of amphiphilic nickel complexes include enhanced concentration of nickel ion and ethylenediamine in a metal complex core structure on the micelle surface, which enhances the coordination of the aldose to the nickel complex. The integrated effect of an active site is responsible for the pronounced degree of epimerization. 

The catalytic hydrogenation of alkenes can also be carried out with a finely dispersed form of nickel known as Raney nickel. It is prepared by treating a nickel—aluminum alloy with aqueous base, which reacts with the aluminum, leaving the finely divided nickel. Hydrogenation reactions using Raney nickel usually require higher temperatures or pressures than those required for palladium or platinum catalysts. However, nickel is less expensive than palladium or platinum, so it is used in industrial processes, such as the conversion of triolein, an od, into tristearin, a fat. 

The reactions of aqueous solutions of nickel(II) salts with hydroxide ions, with excess ammonia, with sulphide ion and with dimethyl-glyoxime (see above) all provide useful tests for nickel(II) ions. 

Fortunately, in the presence of excess copper(II)nitrate, the elimination reaction is an order of magnitude slower than the desired Diels-Alder reaction with cyclopentadiene, so that upon addition of an excess of cyclopentadiene and copper(II)nitrate, 4.51 is converted smoothly into copper complex 4.53. Removal of the copper ions by treatment with an aqueous EDTA solution afforded in 71% yield crude Diels-Alder adduct 4.54. Catalysis of the Diels-Alder reaction by nickel(II)nitrate is also... 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

Eye and Skin Contact. Some nickel salts and aqueous solutions of these salts, eg, the sulfate and chloride, may cause a primary irritant reaction of the eye and skin. The most common effect of dermal exposure to nickel is allergic contact dermatitis. Nickel dermatitis may occur in sensitized individuals following close and prolonged contact with nickel-containing solutions or metallic objects such as jewelry, particularly pierced earrings. It is estimated that 8—15% of the female human population and 0.2—2% of the male human population is nickel-sensitized (125). 

Pyrazole does not react with iodine although pyrazolylsilver is converted into 4-iodopyrazole. 3-Iodoindazole can be obtained by the reaction of iodine with the silver salt of indazole. Kinetic studies on pyrazole iodination have been carried out by Vaughan et al. (71PMH(4)55, B-76MI40402). Coordination of pyrazole by nickel(II) in aqueous solution increases the rate of iodination by factors of two at pH 6 and eight at pH 7.2 (72JA2460). 

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

Complexes o/M". The absence of any other oxidation state of comparable stability for nickel implies that compounds of Ni" are largely immune to normal redox reactions. Ni" forms salts with virtually every anion and has an extensive aqueous chemistry based on the green [Ni(H20)6] + ion which is always present in the absence of strongly complexing ligands. 

Two different sets of experimental conditions have been used. Buu-Hoi et al. and Hansen have employed the method introduced by Papa et using Raney nickel alloy directly for the desulfurization in an alkaline medium. Under these conditions most functional groups are removed and this method is most convenient for the preparation of aliphatic acids. The other method uses Raney nickel catalysts of different reactivity in various solvents such as aqueous ammonia, alcohol, ether, or acetone. The solvent and activity of the catalyst can have an appreciable influence on yields and types of compounds formed, but have not yet been investigated in detail. In acetic anhydride, for instance, desulfurization of thiophenes does not occur and these reaction conditions have been employed for reductive acetylation of nitrothiophenes. Even under the mildest conditions, all double bonds are hydrogenated and all halogens removed. Nitro and oxime groups are reduced to amines. 

From 13.1 g of N-preduction with Raney-nickel and hydrogen, in which reaction the substance may be suspended in methanol or dissolved in methanol-ethyl acetate at normal pressure and at about 40°C with combination of the theoretical quantity of hydrogen, 12.2 g are obtained of o-emino-N-pfrom aqueous methanol hasaMPof90°C. 

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