Pyridine, adsorption Reaction rate

Investigation of template poly condensation kinetics has only been studied within a very narrow scope. Polymerization of dimethyl tartrate with hexamethylene diamine was found to be enhanced by using as a template poly(vinyl pyrrolidone), poly(2-vinyl pyridine), or polysaccharides and poly(vinyl alcohol), poly(4-vinyl pyridine). In this case, the template can be treated as a catalyst. No information exists on the influence of the template on the order of reaction. The increase in molecular weight of the polymerization product by the template can be induced by a shift of equilibrium or by an increase in the reaction rate. A similar increase in the reaction rate was observed when poly(4-vi-nyl pyridine) was used in the synthesis of poly(terephtalamides) activated by triphenyl phosphite.The authors suggested that a high molecular weight template was involved in the increase of the local concentration of the substrate (terephthalic acid) by adsorption and activation via N-phosphonium salt of poly(4- vinyl pyridine). 

The cumene cracking activities over zeolites with different amounts of pyridine, quinoline and aniline adsorption were studied. The reaction rate data of cumene cracking were treated by linearization of eq. (11) as follows ... 

Since silica-alumina contains Br nsted as well as Lewis acid sites, a clear correlation between rates of a heterogeneously catalyzed reaction and surface acidity as measured by pyridine adsorption is only possible if a distinction between PyH+ and PyL is made. This is possible by infrared spectroscopy as shown in this section. Thus, Ward and Hansford (226) found a good linear correlation between the percent conversion of o-xylene and the Br nsted acidity of synthetic silica-alumina catalysts. This correlation is shown in Fig. 4, where the Br nsted acidity is expressed as peak height of the band at 1545 cm-1 per unity of catalyst weight. 

The organic adsorbate in a small vessel was put into a phosphorous oxide desiccator and its vapor was allowed to adsorb on the clay at room temperature. When the adsorbate was solid, a clay sample was Immersed into the cyclohexane solution and dried in the desiccator. In the adsorption of pyridine, barium oxide was used as a drying agent. The formation rate of colored complexes was dependent on the adsorbate molecules and the dryness of montmorillonite. In the case of anisole or phenol, the color began to appear at once when the adsorbate was brought into contact with the dried montmorillonite, but it took about two weeks to finish the reaction in pyridine adsorption. 

Fig. 5. Correlation of the Taft reaction parameter for the dehydration of secondary alcohols (see Table 4) on four different oxide catalysts with the heat of adsorption, A//ads> °f water and diethylether, with the sensitivity of the rate to pyridine poisoning 7> [55] and with the value of the deuterium kinetic isotope effect [123] for the same catalysts.

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. 

The adsorption capacities of large pore zeolites for benzene and pyridine vapors are practically equal. The adsorption rate of pyridine is substantially lower than the adsorption rate of benzene due to its electronic structure. A comparison of the adsorption heats of pyridine and benzene makes it possible to conclude that the unshared pair of electrons and the large dipole moment of pyridine both make an important contribution to the energy of reaction of pyridine with zeolites [26]. Most linear and branched amines have also been used to titrate the acid sites in zeolites. 

---