Pyridine

About: Pyridine is a research topic. Over the lifetime, 39783 publications have been published within this topic receiving 561908 citations. The topic is also known as: azabenzene & azine.

Raman spectra of pyridine adsorbed at a silver electrode

Abstract: Raman spectroscopy has been employed for the first time to study the role of adsorption at electrodes. It has been possible to distinguish two types of pyridine adsorption at a silver electrode. The variation in intensity and frequency of some of the bands with potential in the region of the point of zero charge has given further evidence as to the structure of the electrical double layer; it is shown that the interaction of adsorbed pyridine and water must be taken into account.

Surface raman spectroelectrochemistry: Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized silver electrode

Abstract: In this work we have verified the remarkable sensitivity of Raman spectroscopy for the study of adsorbed pyridine on a silver surface, and extended its applicability to other nitrogen heterocycles and amines. New bands in the scattering spectrum of adsorbed pyridine have been characterized, which were not previously reported, as well as the Raman intensity response of all the surface pyridine bands as a function of electrode potential. As a result of these experiments, we have proposed a model of the adsorbed species for pyridine in which the adsorption is anion induced, leading to an axial end-on attachment to the electrode surface. The ability to obtain resonance Raman spectra with good signal-to-noise with laser powers less than 1.0 mW, reported here for the first time, opens up possibilities of surface Raman studies with relatively inexpensive laser systems. As laser power requirements are relaxed, reliability is improved, and greater tuning ranges can be achieved for wavelength dependent studies. We previously demonstrated the potential of resonance Raman spectroscopy for monitoring solution kinetic behavior [2], and now have shown that NR as well as RR spectroscopy has sufficient sensitivity to extend the studies of kinetic processes to include those occurring at electrode surfaces.

Determination of integrated molar extinction coefficients for infrared absorption bands of pyridine adsorbed on solid acid catalysts

Abstract: Integrated molar extinction coefficients were determined for infrared absorption bands of pyridine adsorbed on acid sites in Si/Al-based catalysts. The infrared spectra of five zeolites and two amorphous silica-aluminas were recorded during quantitative dosing of pyridine gas at 150°C. The integrated molar extinction coefficients were calculated assuming that they did not depend on the catalyst or the strength of the acid site. The resulting values were 1.67 cm/μmol for the 1545-cm−1 band characteristic of pyridine on a Bronsted acid site and 2.22 cm/μmol for the 1455-cm−1 band of pyridine on a Lewis acid site. The 95% confidence limits were estimated at ±15%. Subsequent analysis of the data provided no evidence for a dependence of the integrated coefficients on the catalyst or the strength of the site. The measurements gave indications for differences between the rates of reaction of Bronsted and Lewis acid sites with pyridine.

Palladium- and Copper-Catalyzed Arylation of Carbon-Hydrogen Bonds

Abstract: The transition-metal-catalyzed functionalization of C-H bonds is a powerful method for generating carbon-carbon bonds. Although significant advances to this field have been reported during the past decade, many challenges remain. First, most of the methods are substrate-specific and thus cannot be generalized. Second, conversions of unactivated (i.e., not benzylic or alpha to heteroatom) sp(3) C-H bonds to C-C bonds are rare, with most examples limited to t-butyl groups, a conversion that is inherently simple because there are no beta-hydrogens that can be eliminated. Finally, the palladium, rhodium, and ruthenium catalysts routinely used for the conversion of C-H bonds to C-C bonds are expensive. Catalytically active metals that are cheaper and less exotic (e.g., copper, iron, and manganese) are rarely used. This Account describes our attempts to provide solutions to these three problems. We have developed a general method for directing-group-containing arene arylation by aryl iodides. Using palladium acetate as the catalyst, we arylated anilides, benzamides, benzoic acids, benzylamines, and 2-substituted pyridine derivatives under nearly identical conditions. We have also developed a method for the palladium-catalyzed auxiliary-assisted arylation of unactivated sp(3) C-H bonds. This procedure allows for the beta-arylation of carboxylic acid derivatives and the gamma-arylation of amine derivatives. Furthermore, copper catalysis can be used to mediate the arylation of acidic arene C-H bonds (i.e., those with pK(a) values <35 in DMSO). Using a copper iodide catalyst in combination with a base and a phenanthroline ligand, we successfully arylated electron-rich and electron-deficient heterocycles and electron-poor arenes possessing at least two electron-withdrawing groups. The reaction exhibits unusual regioselectivity: arylation occurs at the most hindered position. This copper-catalyzed method supplements the well-known C-H activation/borylation methodology, in which functionalization usually occurs at the least hindered position. We also describe preliminary investigations to determine the mechanisms of these transformations. We anticipate that other transition metals, including iron, nickel, cobalt, and silver, will also be able to facilitate deprotonation/arylation reaction sequences.

An infrared study of pyridine adsorbed on acidic solids. Characterization of surface acidity

Abstract: The infrared spectrum in the 1400 to 1700 cm−1 region has been determined for pyridine adsorbed on acidic solids. The spectrum of pyridine coordinately bonded to the surface is markedly different from that of the pyridinium ion. This permits the differentiation of acid type on the surface of acidic solids. From the frequency shift of one of the bands of coordinately bonded pyridine over that found in the liquid phase, and from the relative retention of the band upon evacuation and heating, a very rough estimate of the strength of surface Lewis sites can be inferred. It is shown that a silica surface hydrogen bonds pyridine only. Alumina has considerable strong Lewis acidity but no proton acidity while a cracking catalyst has both. The effect on the acidity of sodium poisoning a cracking catalyst is discussed.