Heterocycles, aromatic, nickel

Crude oil consists mainly of a mixture of paraffinic, naphthenic, and aromatic hydrocarbons with small amounts of metals-containing heterocyclic compounds. The most abundant metals found in oils are those contained in porphyrin or porphyrin-like complexes (nickel, copper, iron, and vanadium). These... 

Treatment of the silyl compound, 61, above with hydrogen peroxide leads to the diol 62 which formally constitutes an oxidation as well as an electrophilic attack on the carbon atom. Classically, oxidation of nonconjugated rings to furnish their conjugated (usually aromatic) analogues is achieved by treatment with nickel(ii) peroxide however, these reactions are common and have been extensively explored for a number of different heterocyclic systems in both GHEC(1984) and CHEC-II(1996) so are not discussed further here. 

Other methods for direct dueteration of aromatic and heterocyclic rings using platinum, rhodium, ruthenium, nickel, and cobalt catalysts are described by Ito et al. (1,2). 

The application of the displacement of halogen by nickel-aluminum alloy in aqueous alkali to the quantitative determination of halogens in organic compounds (115) is of considerable interest. Many of the above methods, when adapted for analysis, require the use of hydrogen gas, a prepared catalyst, and a hydrogenation apparatus of the conventional type. These requirements are obviated by the use of nickel-aluminum alloy in aqueous alkali, and the method is advantageously used for the quantitative determination of halogen in many aliphatic, aromatic, alicyclic, and heterocyclic compounds. 

Acid chlorides are suitable electrophiles. As aromatic and 1-alkenyl halides, bromides and iodides are generally good substrates. Until quite recently, the use of the corresponding chlorides, which are cheaper and often more readily accessible, had been limited to that bearing a strongly electron-withdrawing substituent at a proper position. The use of nickel catalyst [47], bulky phosphine [119], and heterocyclic carbene ligand (Scheme 23, Table 1) [116] enabled aryl chlorides to take part in the reaction. 

Certain amines are readily prepared by the reduction of aromatic, aryl aliphatic, and heterocyclic amines. For example, aniline is reduced to cyclohexylamine by high-pressure hydrogenation in the presence of Raney nickel catalyst or a cobalt oxide-calcium oxide catalyst. The reaction occurs at a temperature above 200°, where condensation of the primary amine also takes place, viz., 2CjHiiNHj — (CjHn),NH + NH,. If this side reaction is repressed by the presence of dicyclohexylamine at the start of the reaction, a 94% yield of cyclohexylamine is obtained. Hydrogenation of aryl aliphatic amines proceeds more readily, occurring at moderate temperatures and pressures over platinum catalyst in glacial acetic acid. Other reductions using this catalyst are best performed on the amines in the form of their hydrochlorides. ... 

The removal of a halogen from an aromatic heterocycle takes place more readily than the hydrogenolysis of a phenyl halide of the same type (Eqn. 20.61). 45 The relative difference between the ease of dehalogenation of a phenyl and a heterocyclic halide is more pronounced over Raney nickel in basic medium than it is over palladium (Eqn. 20.62). 46... 

Hydrogenation of Aromatic and Heterocyclic Compounds. In competitive experiments alkyl benzenes were hydrogenated (593 K, 50 atm) more rapidly than benzene over WS2 and sulphided Ni-W/Al203, whereas over metallic nickel, benzene hydrogenation was faster. Nickel sulphide was inactive. The active sites on Ni-promoted WS2 were therefore similar to those on WS2 their number or activity was modified by the presence of nickel sulphide, which itself is not a catalyst. 

From a retrosynfhetic viewpoint, N-aryl-l,2-diimine Ni precatalysts are synthesized by (i) reaction of 1,2 diimines with nickel halides from (ii) 1,2-diimine ligands which in turn are obtained by (iii) condensing 1,2-dicarbonyl substrates with two equivalents of primary aromatic amines, usually under acidic conditions [11]. In analogy, the synthesis of N-hetaryl 1,2 diimine catalysts starts from the corresponding substituted N-heterocyclic primary amines as the amine building blocks. The synthesis of three types of such heterocycles, N-amino-pyrroles, -indoles and -carbazoles, and their corresponding diimine derivatives is presented in the following sections. 

Figure 5. Separation of a variety of nitrogen bases and other aromatic heterocycles in the absence of (a) and presence of (b) nickel dipivoylmethane as a mobile phase additive in rp-hplc.

Aromatic heterocycles, nickel catalyst separation, >l6f Aromatic hydrocarbons,... 

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