4-cyanopyridinium salts

The rates of radical additions to protonated heteroarenes correlate with the nucleophihcities of the attacking radicals [112] for example, electrophihc radicals such as CH2C02H, CH2CN and CH2N02 do not react with protonated pyridines. Furthermore, the reactivity towards aromatic substitution depends on the electro-philicity of the arene moiety, with the highest rates being observed for addition to the electron-poor 4-cyanopyridinium salts (Scheme 13.15). Similar reactions with the para-methoxy derivative may be up to 3.5 x 10 times slower [112, 113]. 

An interesting kinetic study was carried out under pseudo-first-order conditions for the base hydrolysis of the three isomeric N-methyl-cyanopyridinium salts, a reaction that leads partly to CN replacement and partly to the formation of a carboxamido derivative. ... 

Dipole moments have indicated that the oxidation of l-phenethyI-3-phenoxy-pyridinium salts by alkaline ferricyanide givesthe 6-pyridone (XII-399) and that the corresponding 3-bromo- and 3-cyanopyridinium salts (R = Br, CN) form the... 

The homopolymer of the pyridinium salt monomer readily initiates the cationic polymerization of BOE upon heating to around 120 °C, to yield grafted copolymers. The copolymer with styrene similarly catalyzed the polymerization to form the corresponding grafted copolymers. The initiation activity of the copolymer in the polymerization was higher than that of the homopolymer but lower than that of the low-molar mass analogue, N-benzyl-p-cyanopyridinium hexafluoroantimonate. 

Figure 5. Intimate donor-acceptor orientation in the inner-sphere CT salts of (A) quinolinium with tetracarbonylcobaltate [118], (B) A-methyl-4-cyanopyridinium with tetracarbonylcobaltate [118], (C) A-methyl-3-cyanopyridinium with tetraphenylborate [65], and (D) iV-methyl-4-cyanopyr-idinium with TpMo(CO)j [127].

The reduction of l-methyl-4-cyanopyridinium iodide (72) in aqueous methanol gave solely the tetrahydropyridine 73. However, in methanol/ sodium hydroxide two different temperature-dependent products could be isolated. The [4 + 2] product 74 predominated above — 20°C, whereas the [2 -I- 2] adduct75 was the sole product at or below —45° C. Similar behavior is observed with the 2-cyano derivative 76 (R = H) again, the initially formed [2 + 2] adduct 79 (R = H) thermally rearranges to the [4 -I- 2] product 80 (R = H). In this case pH and temperature control are not as important because enamine reactivity is diminished by the presence of the cyano group. Other pyridinium salts behave similarly in strong base. Reduction... 

Notably, some reactive monomers such as isobutylvinylether and /V-vinylcarbazol are observed to polymerize even in dark when used in conjunction with /V-ethoxy-4 cyanopyridinium (EPP) and /V-ethoxyisoquinolinium (EIQ) salts. An electron transfer from the monomer to these initiators can be proposed as an explanation for the observed reactivity in the absence of light (Scheme 11.11). 

Ricinus communis.—The specific intermediates between nicotinic acid and ricinine are unknown a reasonable biosynthetic pathway is illustrated in Scheme 10. Robinson and co-workers have obtained a crude enzyme from R. communis seedlings, and resolved it by chromatography on DEAE-cellulose into three components, all of which catalysed the oxidation of 3-cyano-l-methylpyridinium perchlorate (43) to the pyridones (46) and (47). The optimum activity for ail these fractions was between pH 9.S and 10.S. The enzymes were relatively non-specific. All the following pyridinium salts were oxidized 3-formyl-l-methylpyridinium iodide, 3-nitro-l-methylpyridinium iodide, 3-acetyl-l-methylpyridinium iodide, 3-cyano-l-ethylpyridinium iodide, and l-benzyl-3-cyanopyridinium chloride. N-Methylnicotinamide, trigonelline sulphate, 1-methylpyridinium iodide, nicotinic acid, 1-methylquinolinium iodide, and 3-cyanopyridine, were not oxidized to any appreciable extent. 

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