Hydrogenation of pyridines

The Hydrogenation of Pyridine-3-Carbonitrile and Valeronitrile. Table 57.4 displays the effect of FT on the 1° amine yields and reaction rates of pyridine-3-carbonitrile (P3C) and valeronitrile (VN). Unlike with the hydrogenation of BN,... 

Scheme 52 explains the [(Cp )Rh(MeCN)3]2+-assisted regioselective hydrogenation of pyridines, benzoquinolines, acridines as well as indoles and benzothiophene.258 The relative hydrogenation rates were attributed to both electronic and steric effects, the rate generally decreasing with increasing basicity and steric hindrance at the nitrogen atom. 

According to Hales and Herington [8], the equilibrium constant K for the hydrogenation of pyridine (C5H5N) to piperidine (C5H11N),... 

Piperidine is obtained commercially by the catalytic hydrogenation of pyridine over a nickel catalyst at about 200 C. A-Substituted derivatives are formed by reduction of the corresponding pyridinium salts. 

Catalytic hydrogenation of pyridine 2-isoxazolones gives, surprisingly, a mixture of [l,8]naphthyridine and [l,8]tet-rahydronaphthyridine, the exact ratio depending upon the solvent used to perform the hydrogenation (Scheme 25) <2003T9887>. 

Enantiomerically-enriched piperidines can also be prepared by hydrogenation of pyridine derivatives. Andrd Charette of the University de Montreal found (J. Am. Chem. Soc. 2005,127,8966) that ylids such as 5, prepared directly from the pyridine 4, gave the highest ee s on lr -catalyzed hydrogenation. An advantage of this approach is that the piperidine derivatives 6 are crystalline, and arc easily recrystallized to higher . 

Hydrogenation of pyridines and their benzoderivatives can be carried out with various catalysts. Pyridines are readily hydrogenated to piperidines over Raney nickel at 120°C. The optimal pressure for... 

Pipendine. the hydrogenation product of pyridine, is used as an intermediate for drugs and for making rubber-vulcanization accelerators, e.g., piperidinium pentamechylenedithiocarbamate (also known as Accelerator 552 ). On a commercial scale, piperidine (hexahydropyridine) is prepared by the catalytic hydrogenation of pyridine, e.g., with nickel catalysts at from 68 to 136 atmospheres pressure and at l50-20C,c,C. or under milder conditions with noble-metal catalysts. Pyridine derivatives can be similarly reduced to substitute piperidines. See formulas below. 

Application of Spectrophotometry to the Study of Catalytic Systems H. P. LeftinandM. C, Hobson,Jr. Hydrogenation of Pyridines and Quinolines Morris Freifelder Modern Methods in Surface Kinetics Flash, Desorption, Field Emission Microscopy, and Ultrahigh Vacuum Techniques Gert Ehrlich... 

Oxidative reactions of pyridines are commercially more interesting than reductive ones because catalytic hydrogenation of pyridines is a generally useful method, whereas catalytic oxidation is not. In contrast, anodic oxidation of pyridines is widely applicable and can replace methods that use expensive oxidants such as permanganate salts or chromic oxide. Consider, as an example, oxidation of a methylpyridine to produce 1 kg of the pyr-idinecarboxylic acid this process would consume about 3 worth of potassium permanganate at 100% efficiency and would produce 0.7 kg of byproduct Mn02 for disposal or recycle. The same anodic reaction would consume only 0.30 of electrical power (for oxidation) and would not produce a significant amount of material for disposal. 

A native of Long Island, New York, Timothy P. Meagher received his B.A. from SUNY Potsdam, Potsdam, New York, in 1981. Following a brief stint in industry, he earned his Ph.D. at Ohio State University in 1988. He joined the research department at Reilly Industries, Inc. in 1988. During his tenure there he worked in the area of pyridine chemistry. In particular, projects involved gas phase synthesis, ammoxidation, chlorination, and hydrogenation of pyridine compounds. Publications include contribution to Chemistry of Heterocyclic Compounds II and a patent on hydrogenation of 2-ethanol pyridine. He left Reilly Industries, Inc. in 2001 and is currently a consultant for TEKA Consulting. 

The study of pyridine HDN indicates that the hydrogenation of pyridine to piperidine is of first order with respect to H2 at 250 °C and 1.5 at 300-375 °C and of first order with respect to the pyridine partial pressure. The strong adsorption of NH3 proposed by Mcllvried220 was not observed and the deviation from the first-order rate is explained because the reverse reaction of piperidine to pyridine, thermodynamically favoured at 315°C, was neglected. The order in H2 of the ring opening was found to be near zero. 

In recent years, a few stereoselective methods for the asymmetric hydrogenation of pyridines and related heterocycles have been developed <20050BC4171>. A chiral auxiliary method starts with an oxazolidinone-substituted pyridine which on reduction with H2/Pd(OH)2 in acetic acid affords the corresponding piperidine in good yield and high enantiopurity. The chiral auxiliary is cleaved during the reaction and can be recovered (Equation 100) <2004AGE2850>. 

Corrected for hydrogenation of pyridine that was determined separately. 

Rylander and Rakoncza compared the rates of hydrogenation of pyridine V-oxide over 5% palladium-, platinum-, rhodium-, and ruthenium-on-carbon in methanol, water, and acetic acid.224 Rhodium was always the most active, although the pyridine ring was hydrogenated concomitantly with the reduction of the V-oxide group. 

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