Display omitted
▶ Quantification of both Lewis and Brønsted acid sites by combined FTIR and gravimetric measurement. ▶ Three nitrogen bases describe the distribution of sites of different acid ...strength and accessibility. ▶ Correlation between site density and activity for acetone condensation show the latter to be catalysed by Lewis acid sites.
The density of acid sites on amorphous silica alumina has been determined using a combination of gravimetric and spectroscopic analysis using pyridine and 2,4-lutidine and 2,6-lutidine for surfaces treated at different calcination temperatures. An attempt was made to correlate the number of acid sites determined by the different base molecules with the activity for liquid phase reaction of acetone to produce diacetone alcohol at 298
K. The best correlation was obtained with the number of Lewis acid sites which were able to retain pyridine after evacuation at 473
K. The lutidines underestimated the number of Lewis sites on the oxide surface. In particular, 2-6-lutidine was only able to detect Lewis acid sites in geometries at edges and other geometric imperfections on the solid and these were mainly generated after low temperature (573
K) calcination treatment.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The synthesis of 3,5-lutidine N-oxide dehydrate, 1, was achieved in the synthesis route of 2-amino-pyridine-3,5-dicarboxylic acid. Ochiai first used the methodology for non-substituted pyridines in ...1957 in a 12 h process, but no X-ray suitable crystals were obtained. The substituted ring used in the methodology presented here clearly influenced the addition of water molecules into the asymmetric unit, which confers a different nucleophilic strength in 1. The X-ray suitable crystal compound 1 was possible due to the stabilization of the negative charge in the oxygen by the presence of two water molecules where the hydrogen atoms donate positive charge into the ring; such water molecules serve well to construct a supramolecular interaction. The hydrated molecules may be possible for the alkaline system that is reached by adjusting the pH to 10. Importantly, the double methyl substituted ring and a reaction time of 5 h, makes it a more versatile method and with wider chemical applications for future ring insertions.
The vapour pressures of liquid mixtures 3,5- and 2,6-dimethylpyridine (or lutidines) with cyclohexane were measured by a static method in the range of 283.15–353.15K. The pure components vapour ...pressures data and those of corresponding mixtures were correlated using Antoine type equation. Data reduction by Barker's method provides correlation for excess molar Gibbs energy GE.
The excess molar enthalpies HE of binary liquid mixtures of 3,5- and 2,6-dimethylpyridine with cyclohexane were measured at 303.15K using a Calvet type microcalorimeter, C80 Setaram.
The experimental results, along with our previous data of GE and HE1,2 are used for estimating interaction parameters in DISQUAC, an extended quasi-chemical group contribution model 3.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The heterogeneous catalytic synthesis of pyridine and methylpyridines (picolines) was carried out by the reaction of ethanol with formaldehyde and ammonia over aluminosilicates with different acidic ...properties and textural characteristics: zeolite framework-type FAU in H-form with microporous (H-Y) and micro-meso-macroporous structure (H-Y-mmm) and mesoporous aluminosilicates, obtained by sol-gel synthesis in an alkaline medium (ASM-1) and under variable pH (ASM-2). It is shown that the highest catalytic activity is characteristic of ASM-2 (Si/Al = 40) with a narrow pore size distribution within the range 2 to 5 nm and containing strongly acidic bridging Si–OH–Al groups on the surface. The products of the reaction of ethanol with formaldehyde and ammonia on the catalysts studied are dominated by picolines; the maximum amount of picolines (60%) is formed on the H-Y-mmm and aluminosilicate ASM-2 samples.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Development of catalysts based on modified zeolites with a microporous or micro/mesoporous structure and on microporous metallosilicates is aimed at creating high-selectivity method of obtaining ...pyridine and alkylpyridines. In this study, pyridine and methylpyridines have been synthesized for the first time via the heterogeneous catalytic reaction of ethanol with formaldehyde and ammonia catalyzed by the microporous zeolites Y, Beta, ZSM-12, and ZSM-5 in the H-form and by a granular zeolite Y with a combined, micro-meso-macroporous structure (HY-MMM). The latter zeolite is particularly effective in the synthesis of picolines, affording a picoline selectivity of 46–63% at an ethanol conversion of 70–80%. Among the microporous catalysts, the most active ones are the highly decationized zeolites H-Y and H-Beta. The major products of the reaction occurring over H-Beta and H-ZSM-5 are pyridine (up to 50%) and picolines (up to 40%), and the main products of the same reaction carried out over H-Y and H-ZSM-12 are picolines (45–52%) and lutidines (19–25%). For zeolite H-Y-MMM, the ethanol conversion and the composition of pyridines depend on the reaction conditions.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The influence of acid and salt concentration in the mobile phase on the retention of basic analytes has been studied. An increase in the retention of fully protonated analytes with increasing the ...concentration of inorganic additives was found. The addition of salt, such as perchlorate, trifluoroacetate, and phosphate, leads to the increase of retention for fully protonated analytes while mobile phase pH remains constant. The observed effect was attributed to the interaction of protonated analytes with the counter-anion of acid or salt, which leads to the disruption of the analyte solvation shell and the increase of its hydrophobicity and corresponding increase of retention. A mathematical model for the description of the influence of counter-anion concentration on analyte retention is proposed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Mono(6-deoxy-dimethylpyridinium)-β-cyclodextrins have been synthesized in reaction of mono (p-toluenesulfonyl) derivative of β cyclodextrin with the appropriate lutidine under microwave irradiation ...and conventional conditions. The results indicate that the mechanism consists of inclusion complex formation.
The vapour pressures of liquid (3,5; 2,6)-dimethylpyridine
+
n-hexane; +
n-heptane and +
n-octane mixtures were measured by a statistic method, respectively, between 263.15–353.15
K at 10
K ...intervals. The pure component vapour pressures data and those of mixtures were correlated with the Antoine equation. The excess enthalpies, at 303.15
K for those mixtures were measured by an isothermal calorimeter model C80 SETARAM. The molar excess Gibbs energies, calculated from the vapour liquid equilibrium data and the molar excess enthalpies compared satisfactorily with group contribution method (DISQUAC).
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A series of poly(norborn-2-ene) (poly-NBE), poly(7-oxanorborne-2-ene-5,6-dicarboxylic acid) (poly-ONDCA), as well as poly(norborn-2-ene-
co-7-oxanorborne-2-ene-5,6-dicarboxylic acid) (poly-NBE-
...co-ONDCA) based silica supports were prepared via ring-opening metathesis polymerization (ROMP) using both coating and grafting techniques. Poly-NBE-grafted and poly-NBE-coated supports were used for the reversed-phase separation of phenols; poly-NBE, poly-ONDCA as well as poly-NBE-
co-ONDCA-grafted supports were used for comparative studies on the separation of a series of anilines and lutidines. As expected, grafted supports possess superior separation capabilities compared to their coated analogues. Compared to pure poly-NBE- and poly-ONDCA-grafted stationary phases, supports consisting of poly-NBE-
co-ONDCA block-copolymers possess both hydrophobic and ion-exchange sites and represent optimum stationary phases for the separation of isomeric basic analytes.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The vapour pressures of liquid (3,5; 2,6)-dimethylpyridine with toluene mixtures were measured by a static method in the range of 263.15–353.15
K. The pure components vapour pressures data and those ...of the mixtures were correlated with the Antoine equation. The excess enthalpies were measured at 303.15
K, by means of an isothermal calorimeter (C80 SETARAM model). The molar excess Gibbs energies, calculated from the vapour–liquid equilibrium data and the molar excess enthalpies compared satisfactorily with group contribution method (DISQUAC).
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
PDF
