The isomerization of α-pinene in the vapor phase over alumina catalysts of varying acid strength has been studied. The isomerization proceeds via two parallel paths, one giving bi- and tricyclic products such as camphene, β-pinene, tricyclene, and bornylene and the other giving rise to monocyclic compounds such as dipentene, terpinolene, α-terpinene, γ-terpinene, p-cymene, and p-menthene. Dependence of the distribution of reaction products on space time reveals that camphene, β-pinene, tricyclene, dipentene, and terpinolene are the primary products. The acid strength of alumina catalysts has a remarkable influence on the selectivity ratio of bi- and tricyclic to monocyclic products, the strong acid sites favoring the formation of monocyclic products. From the study of the reactions of camphene and tricyclene over the same catalysts under similar conditions it has been concluded that the decrease in the selectivity ratio with increasing acid strength of the catalysts is mainly due to the further isomerization of the bi- and tricyclic compounds to monocyclic products which takes place only on the strong acid sites.
The vapour phase dehydrogenation of 3-carene has been studied over chromia, chromia–alumina, chromia doped with potassium, and chromia–alumina doped with potassium and fluoride ions. Addition of potassium to chromia and chromia–alumina up to 1% by weight does not significantly affect the overall conversion of 3-carene whereas it increases its dehydrogenation to p- and m-cymenes. Potassium ions above 1% lower both the total conversion and dehydrogenation of 3-carene to cymenes. The ratio of p- to m-cymene over chromia–alumina is enhanced by added potassium ions up to 2%, but over chromia it remains unaffected. Addition of potassium to chromia decreases the formation of menthanes and menthadienes but its addition to chromia–alumina reduces the formation of menthanes and increases that of menthadienes. Impregnation of chromia–alumina with hydrofluoric acid suppresses the formation of menthadienes and increases that of menthanes. All these are explained in terms of the effect of added potassium and fluoride ions on the acidity of the catalysts.
I n view of the differences in the positional reactivities, reported by different authors, in phenol and methylol phenols, an exhaustive kinetic study using quantitative paper chromatography has been carried out not only on phenol and methylol phenols hut also on phenols with methyl group and chlorine atom substituents.The o-position is less reactive than thep-position in phenol and substituted phenols forthe addition of formaldehyde in the presence of alkali catalyst, with a correspondingly higher activation energy. The effect of the methylol group appears to be intermediate between the activating effect of the electron repelling methyl group and the deactivating effect of the electron attracting chlorine atom. But the marked activating effect of the methyl and methylol group in the o-position is tried to be accounted for by intra-molecular hydrogen bonding. The activating effect of chlorine atom in the o-position is explained in terms of the electron repulsion between chlorine atom and the phenoxide anion.The few characteristic differences in the positional reactivities observed in the results of earlier workers are not found in the results obtained in the present investigation. Z U S A M M E N F A S S U N G :Im Hinblick auf die Unterschiede der durch die Stellung bedingten Reaktivititen bei Phenolen und Methylolphenol en, iiber die verschiedene Autoren berichteten, wurde eine erschopfende kinetische Untersuchung mit Hilfe der quantitativen Papierchromatographie durchgefuhrt. Dabei wurden auner dem Phenol und Methylolphenolen auch methyl-und chlorsubstituierte Phenole untersucht. I m Phenol und in substituierten Phenolen ist entsprechend einer hoheren Aktivierungsenergie die o-Stellung fur die Anlagerung von Formaldehyd in Gegenwart von alkalischen Katalysatoren weniger reaktionsfreudig als die p-Stellung. Die Wirkung der Methylolgruppe scheint zwischen dem Aktivierungseffekt der Elektronen abstofienden Methylgruppe und dem Inaktivierungseffekt des elektronenanziehenden Chloratoms zu liegen. Hingegen wird versucht, den ausgepragten Aktivierungs-ef€ekt der Methyl-und Methylolgruppe in o-Stellung auf eine intramolekulare Wasserstoffbindung zuriickzufiihren. Der Aktivierungseffekt des Chlors in o-Stellung wird durch die Elektronenabstofiung zwischen dem Chloratom und dem Phenoxidanion erklart.Die wenigen charakteristischen Unterschiede in den durch die Stellung bedingten Reaktivitaten, die von andern Forschern beohachtet wnrden, konnten durch die vorliegenden Untcrsuchungen nicht bestatigt werden.
The kinetics of the alkali-catalysed condensation of ortho and para nlethylol phenols, each by itself and with phenol has been studied under various experimental conditions with the help of quantitative paper chromatography. At low concentrations of the reactants and catalyst, the self-condensation of saligenin gives mainly 3-methyl01 2',4-dihydroxy diphenyl methane (DPM) and that of p-methylol phenol 5-methyl01 2,4'-DPM, the apparent first-order rate constant a t 80°C. and activation energy being 1.60.10-5 sec-l and 16.0 kcal./mole for the former and for the latter 1.67.10-5 sec-l and 17.3 kcal./mole However at higher concentrations, p-methylol phenol gives also p,p'-DPM, 2,4-dimethylol phenol, and small amounts of 3-methyl01 4,4'-DPM.When phenol and one of the methylol phenols are made to react, both the self-condensation and the inter-condensation take place, the former much more rapidly than the latter. A large excess of phenol is needed to suppress the self-condensation. The apparent energies of activation for the formation of o,o'-, 09'and p,p'-DPMs are 21.4, 18.7, and 17.0 kcal./mole respectively. Evidence is presented for the probable mode of formation of monomethylol dinuclear compounds in the alkaliLcatalysed phenol-formaldehyde reaction. ZUSAMMENFASSUNG:Die Kinetik der alkalikatalysierten Kondensation von 0-und p-Methylol-phenol mit sich selber oder mit Phenol unter verschiedenen experimentellen Bedingungen wurde mit Hilfe der quantitativen Papierchromatographie untersucht. Bei niedriger Konzentration der Reaktionsteilnehmer und des Katalysators ergibt die Selbstkondensation von Saligenin hauptsachlich 3-Methylol-2',4-dihydroxy-diphenyl-methan (DPM), wahrend die Selbstkondensation von p-Methylol-phenol zu 5-Methylol-2,4'-DPM fiihrt. Die scheinbare Geschwindigkeitskonstante der Reaktion l. Ordnung bei 80°C ist 1,6.10-5 sec-l und die scheinbare Aktivierungsenergie betragt 16,O kcal/Mol; fur p-Methylol-phenol liegen diese Werte bei 1,67.10-5 sec-' und 17,3 kcal/Mol. Bei hoheren Konzentrationen fiihrt die Kondensation von p-Methylol-phenol aber auch zur Bildung von p,p'-DPM, 2,4-Dimethylolphenol und geringen Mengen 3-Methylol-4,4'-DPM.Wenn ein Gemisch von Phenol mit einem der Methylol-phenole reagiert, findet sowohl Selbstkondensation des Methyl-phenols als auch Cokondensation statt, und zwar die erstere vie1 schneller als die letztere. Ein groOer PhenoluberschuO ist erforderlich, urn die Selbstkondensation zu unterdriicken. Die scheinbaren Aktivierungsenergien fur die Bildung van o,o'-, o,p'-und p,p'-DPM betragen 21,4, 18,7 bzw. 17 kcal/Mol. Es werden Hinweise fur den wahrscheinlichen Bildungsmechanismus einer zweikernigen Monomethylolverbindung bei der alkalikatalysierten Phenol-Formaldehyd-Kondensation gegeben.
Chemisorption of H2 on MoS2‐Al2O3 catalyst was studied at different temperatures and initial pressures. The results when analysed according to the Elovich equation revealed multiple kinetic stages. Assigning two sets of boundary conditions to the equation, a statistical procedure employing least square analysis has been applied for the evaluation of the Elovich parameters a and α and their temperature dependence has also been followed. A comparison is made with the parameters derived by the graphical method. The role of initial surface saturation q0 on the sequence of the multiple kinetic stages is discussed. Excepting for descriptive purposes, the kinetic stage connotation is not strictly followed. On the other hand, all the first straight line portions of the Elovich plots for a given initial pressure including the single stage plots have been grouped together and the corresponding a and α were calculated. The merits of deriving the apparent activation energies from the initial rates rather than from α are discussed.
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