Carbon-nitrogen dimers

Under ordinary conditions, reduction of these imines in dimethylformamide is a two-electron process involving saturation of the carbon-nitrogen double bond [181] because the radical from protonation of the radical-anion is more easily reduced than the starting imine. Immonium salts with two or more phenyl substituents are reduced reversibly in acetonitrile to the radical-zwitterion such as 42. Other immo-niura salts, e.g. 43, are reduced irreversibly to the dimer [182]. Radical-zwitterion intermediates generated from immonium salts exhibit nucleophilic character on carbon. Intramolecular interaction between the reduced immonium function and a... 

Azo compounds may be considered to have the carbon-nitrogen framework of dimeric nitroso compounds. The oxidation of one of the nitrogen atoms of an azo compound to an azoxy compound has been discussed in Chapter 15. The oxidation of the second nitrogen would give rise to one of the resonance forms of a nitroso dimer. Indeed, on oxidation of 4-methylcinnoline with hydrogen... 

Nitro-compounds fRNOj) are isomeric with nitrites, but their electronic structure, excited states and photochemistry are very different. There is no very low-lying (n.jt ) state, and nitroalkanes show n — 3i absorption with a maximum around 275 nm ( —201 mol - cm In cyclohexane solution, nitromethane (CH1NOi) is photoreduced to nitrosomethane(CH,NO, but nitroethane under the same conditions gives rise to a nitroso-dimer derived from the solvent CS.47). The latter process is probably initiated by cleavage of the carbon-nitrogen bond in the nitroalkane. In basic solution (when the nitroalkane is converted to a nitronate anion) irradiation can lead to efficient formation of a hydroxamic acid (S.48), and this reaction most likely proceeds through formation of an intermediate three-mem bered cyclic species. 

There has been a short review of the oxidative nucleophilic substitution of hydrogen in nitroarenes in which recent results with carbon, nitrogen, and oxygen nucleophiles are summarized and the preferred oxidants are discussed.11 The oxidative substitution of nitroarenes with carbanions of isopropyl phenylacetate in liquid ammonia-KMn04 initially yields products (4) which may suffer hydroxylation at the o -position, and dimeric and trimeric products may be formed by couplings of nitrobenzylic radicals formed during the reaction.12... 

The fluid dimer polyamides and fatty amido amines also react with phenolic resins (23). These reactions are significantly different from those of epoxy resins. With the heat-reactive phenolic resins, the aminopolyamide portions react with methylol groups. A carbon-nitrogen bond or cross-link is formed and a volatile byproduct, water, is produced. This reaction requires external heat to remove water. At temperatures near 150 °C the reaction proceeds smoothly. Since curing at elevated temperatures is required, the pot life or shelf life at room temperature is relatively long. The liquid dimer polyamide and fatty amido amines also react with alpha, beta unsaturated acids and esters (29) and with polyesters (30). The unsaturated esters reduce viscosity, lengthen useful pot life, and reduce heat of reaction. Thus, they are useful diluents when low viscosity is desired. 

Products arising by carbon-nitrogen bond homolysis have been obtained on irradiation of iV-benzyldiphenylamine, dimers of 2,4,5-triphenylimidazolyl, and A -alkyl-4-(carboalkoxy)pyridinyl radicals. The pyrazoline carbonyl ylides... 

The carbon monoxide dimer 0=C=C=0, ethenedione, appears to dififer fundamentally from dimers etc. (oligomers and polymers) based on nitrogen, on carbon... 

Peroxy-linked dimers are also formed from linoleate hydroperoxides in the presence of free radical initiators and copper palmitate, and carbon-carbon linked dimers in the presence of copper catalysts. Decomposition of methyl linoleate hydroperoxides at 210°C under nitrogen produces mainly carbon-carbon linked dimers (82%), monomers with loss of diene conjugation, volatile compounds (4-5%) and water. The resulting dimers contain carbonyl and hydroxyl groups and double bonds scattered between carbon 8 and carbon 10. Linoleate hydroperoxides can dimerize by one of the termination reactions discussed in Chapter 1. The termination reactions involving combination of alkyl, alkoxyl, or peroxyl radical intermediates produce dimers with carbon-carbon, carbon ether, or peroxy links. The carbon-carbon and carbon-oxygen linked dimers are favored at elevated temperatures and the peroxy-linked dimers at ambient temperatures. The peroxy-linked dimers may also decompose to the ether-linked and carbon-carbon linked dimers via the corresponding alkyl and alkoxyl radical intermediates. 

When the isomers 11 and 12 were oxidized in acetonitrile in the presence of base, contrary to expectations, carbon-oxygen dimers were formed because of nitrogen participation as indicated in Scheme 1.4. However, when the nitrogen is protonated (acid medium), or acylated, the products are all carbon-carbon dimers. 

Effect of various concentrations of inorganic phosphate, microelements, temperature, pH, and sources of carbon, nitrogen on the yield of epoxyagroclavine-I dimer was studied in P. sizovae (Kozlovsky et al., 1995). Active biosynthesis of the dimer occurred upon the cultivation on the media containing mannitol, a-ketoglutarate, ammonium, KH2PO4 in concentration of 0.1 g L, and microelements (Fe, Mn ) at 28°C and initial pH 7.0. 

A molecule of [Cp2YCH=NBu-t]2 is a dimer in which each yttrium atom is T -bonded to two Cp rings and bonded to a formimidoyl carbon-nitrogen unit and a carbon atom of the other formimidoyl ligand in the dimer (Fig. 1.24) [188]. The Y-C(Cp) distances range from 2.659 to 2.697 A, the average value is 2.68 A. The central fragment of the... 

The stepwise formation of tropones upon insertion of GO into alkyne dimers coordinated to diiron centers is a commonly found process in iron carbonyl chemistry no triiron complexes are isolated during these processes (e.g., see Refs 14 and 14a). Finally, GO insertion is observed when diiron dimers linked by diacetylene moieties are reacted with diethylamine to give the complexes 6 and 7 (Figure 2) these complexes also contain iron-carbon-nitrogen and iron-carbon-phosphorus bonds. 

From an analysis of the product obtained in preparative electrolysis of pyrimidone, in conjunction with other data, it has been suggested that a dimer with the carbon-nitrogen double bond of the pyrimidone rings hydrogenated is formed as a result of the electrode reaction [58]. 

Stainless steel or epoxy-lined tank cars and tank tmcks are recommended for shipping. Aluminum also has been used. The tank can be flushed with carbon dioxide before loading and blanketed with nitrogen after loading. Dmm shipments are recommended in epoxy-lined open-head dmms fitted with a bung. Dimer acids and their by-products contaminated with iron or copper show accelerated color deterioration. Exposure to these metals or their salts should be minimised. 

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