Pyridines and Derivatives

As a general trend, six-membered mononuclear N-heteroaromatics such as pyridine and derivatives are much less prone to undergo hydrogenation than bi-and trinuclear N-ring compounds (e.g., quinolines, benzoquinolines, acridines) due to their higher resonance stabilization energy. 

Mossbauer spectroscopy features relating to pyridine and derivatives complexed with Fe or certain other metallic ions in crystalline state1 ... 

We take up now the detailed question of how the chemical shifts correlate with structure, then consider relatively recent work on nuclear spin-spin coupling in pyridine and derivatives, and finally illustrate how external influences, solvent, complexation and so on, affect NMR patterns in this area. 

Protonated pyridines and derivatives readily undergo acylation at C-2 or C-4 (Table 28) (76MI20503). Acyl radicals are usually generated either by hydrogen abstraction from aldehydes (Scheme 210), or by oxidative decarboxylation of a-keto acids (Scheme 211). In the former case (Scheme 210) with acridine as the substrate, reduction can take place to give a dihydroacridine. 

Pyridine (and derivative) complexes [VL4(NCS)2] have been isolated from aqueous ethanol IR spectra indicated trans structures. On the other hand, [VL2(NCS)2] with L = phen or bipy exhibit split CN absorptions suggestive of cis structures.75... 

The extensive kinetic data available for quaternization of substituted pyridines and derivatives, such as benzologs and diazines, under a uniform set of conditions make possible the calculation of substituent rate factors that are of considerable value in dealing with new substrates. When a heteroaromatic molecule has two or more nucleophilic annular positions that can react, often it is possible to estimate, in some cases very accurately, the ratio of quaternized products using these rate factors. 

AZTNES. The products of the reaction between an aldehyde nr a ketone with hydrazine are termed azines. A number of dyestuffs and complex members of the pyridine family of compounds also are termed azines. See also Pyridine and Derivatives. 

The tar bases form water-soluble salts with mineral acids which are separated from the oil. They are recovered from their salts by contacting with aqueous alkali (springing) and separating the crude bases from the salt solution. The lutidines constilute the major part of the lower-boiling bases. See also Pyridine and Derivatives. 

METHY LISOBUTYL CARBINOI. (MIHC). Sec Ketones. METHYL1SOBUTYL KETONE (M1BKI. See Ketones. METHYLPR1D1NE. See Pyridine and Derivatives MEVALONIC ACID. See Steroids. 

Pyridine and derivatives of pyridine occur widely in nature as components of alkaloids, vitamins, and coenzymes. These compounds are of continuing interest to theoretical physical, organic, and biochemistry and to industrial chemistry. Pyridine and derivatives have many uses, e.g., herbicides and pesticides, pharmaceuticals, feed supplements, solvents and reagents, and chemicals for the polymer and textile industries. 

Kinetic results concerning catalytic hydrogenative destruction of heterocyclic nitrogen compounds have been published by Cox and Berg.21 In their operating condition (370°C, 17 atm, space velocity 0.5-20 h 1, which does not affect the rate of HDN, wt% N < 2.5%), they found that most of the five membered ring compounds (pyrrole derivatives and indole) follow a second-order law with respect to the amine pressure, while a first-order law is shown for six membered ring compounds (pyridine and derivatives). 

Asymmetric synthesis using W-acyl salts of pyridine and derivatives continues to be developed. The chiral. V-acylpyridinium salt 132 reacts with lithiated ethyl propiolate to provide the diastereomer 133 in 70% yield and... 

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