P. Geneste

BIOCHEMICAL PROPERTIES OF THE BRAIN PHENCYCLIDINE RECEPTOR

This paper gives a detailed account of techniques which can be used to measure [3H]phencyclidine binding to its receptor. The main properties of the binding component are the following: (i) It is rapidly heat-inactivated at temperatures over 50 degrees C. (ii) It is destroyed by proteases like trypsin, pronase or papain suggesting that it is of a protein nature. The receptor structure is resistant to chymotrypsin. (iii) A good correlation was found between the pharmacological activity of 30 different analogs as measured by the rotarod assay and the affinity of these different molecules for the phencyclidine receptor. (iv) Monovalent and divalent cations antagonize [3H]phencyclidine binding to its receptor. The dissociation constant is 15 mM, the same for Na+, Li+, K+, cholinium or Tris. Na+ (and other monovalent cations) and phencyclidines bind to distinct sites. The saturation of the Na+ site by Na+ modulates the affinity of phencyclidine for its receptor. Divalent cations antagonize [3H]phencyclidine binding in the absence of Na+. This antagonism is of the non-competitive type. (v) [3H]phencyclidine binding is also antagonized by histrionicotoxin and by local anaesthetics.

Selective isopropylation of naphthalene over zeolites

The isopropylation of naphthalene with isopropylbromide over a series of H mordenites and Y zeolites has been studied. In both cases, a high β-selectivity is observed in the monoalkylation and dialkylation reactions (selective formation of 2-isopropylnaphthalene and a mixture of 2,6- and 2,7-iisopropylnaphthalenes, respectively). Over H mordenites, the β-selectivity is explained as the result of transition-state shape selectivity. Over Y zeolites, the β-selectivity is due to a thermodynamic equilibrium favorable to the formation of 2-isopropylnaphthalene from 1-isopropylnaphthalene. The use of zeolites modified by silanation using chemical vapor deposition leads to an improvement of the β-selectivity by reducing the amount of trialkyl derivatives that are formed on the external surface.

Influence of acidity in friedel-crafts acylation catalyzed by zeolites

The activity of various cation-exchanged Y-type zeolites is investigated in the acylation of toluene with octanoic acid for which the yield in acylated product is 75% and the selectivity in para isomer 94%. The most efficient catalysts are the rare earth-exchanged zeolites (70% exchange). The following order of activity is observed: Cr3+, Zr4+ < Mg2+, Cu2+, Co2+ ⪡ H+ ⪡ Pr3+, La3+, Gd3+, Yb3+, Ce3+. A parallel drawn between the acylation reaction and the cyclohexanol dehydration suggests that the active centers are Bronsted sites. This result is confirmed by the study of the influence of the pretreatment temperature on the catalytic activity.

Acylation over cation-exchanged montmorillonite

The Friedel-Crafts acylation of aromatic compounds (benzene, toluene, xylene) with carboxylic acids (CH3(CH2)n COOH, n = 0–14) was performed over cation-exchanged montmorillonites (H+, Al3+, Ni2+, Zr4+, Ce3+, Cu2+, La3+). Yields in ketones were found to be dependent upon the nature of the interlayer cation and on the acid chain length.

Structure-activity relationships in hydroprocessing of aromatic and heteroaromatic model compounds over sulphided NiO-MoO3/γ-Al2O3 and NiO-WO3/γ-Al2O3 catalysts: chemical evidence for the existence of two types of catalytic sites

Abstract The hydroprocessing of nitrogen-containing model compounds such as pyridine, quinoline, acridine, pyrrole and carbazole was studied using a batch method at 340°C and 70 bar H 2 over sulphided NiO-MoO 3 /Al 2 O 3 and NiO-WO 3 /Al 2 O 3 catalysts, where it was found that saturation of the heteroaromatic rings always occurs prior to any cleavage of C-N bonds, generally C sp3 -N bonds. The rates of hydrogenation of the heteroaromatic rings were shown to be mostly influenced by the aromaticity of these rings (π-electron delocalization) and not by the basicity of the nitrogen atom. On the other hand, the basicity of nitrogen atoms considerably influences the cleavage of C sp3 -N bonds in the absence of steric effects. The hydroprocessing of substrates of general formula C 6 H 5 X, where X is an electronegative atom (OR, NHR, SR, Br, Cl, F) was also studied under the same experimental conditions. The rates of hydrogenation of the phenyl moiety and the rates of hydrogenolysis of the C sp2 -X bond are both correlated with the same substituent constant, σ o R , which represents the delocalization of π-electrons in the molecule by resonance. Hydrogenation is favoured over hydrogenolysis for highly electron-donating substituents such as NHR and OR (R=H, C 6 H 5 ); conversely, hydrogenolysis is favoured over hydrogenation for slightly electron-donating substituents such as SR (R=H, C 6 H 5 ) or halogens (Cl, Br). The presence of such correlations constitutes chemical evidence for the existence of two distinct catalytic sites, one responsible for hydrogenation associated with an electron-withdrawing character and the other responsible for the hydrogenolysis of C sp2 -X bonds associated with an electron-donating character.

Cesium oxide encapsulation in faujasite zeolites effect of framework composition on the nature and basicity of intrazeolitic species

Abstract Post-synthetic modification of basic CsNaX and CsNaY zeolites was performed by impregnation with cesium acetate at varoous loadings followed by thermal decomposition of the cesium acetate into oxide. A comparative study of the nature and basic character of intrazeolitic species in CsNaX and CsNaY zeolites is reported. Crystallinities of modified X zeolites are largely retained after activation at 550°C for six hours. Under the same activation conditions modified Y zeoolites are less stable as evidenced by XRD, N 2 sorption, 27 Al and 29 Si MAS NMR and stepwise thermal desorption of CO 2 (TPD). The modified CsNaY zeolite crystallinities were largely maintained when the activation temperature was lowered to 400°C. The TPD of CO 2 below 500°C allows the differentiation of the structures of guest cesium species occluded in the host CsNaX or CsNaY zeolites. A shift of the desorption peak maximum from 250 to 150°C accounts for a higher basicity of the species within the pores of the CsNaX host than in the CsNaY one. Linear correlations between the amount of desorbed CO 2 and the cesium loading suggest a homogeneously dispersed loading up to 16 and 24 cesium atoms per unit cell for the modified X and Y zeolites, respectively. The formation of oxide (Cs 2 O) inside the cages of the CsNaX zeolite is proposed. In the case of the modification of the CsNaY zeolite various structures are discussed involving either the formation of local lattice cesium silicate or aluminate defects or the encapsulation of cesium oxide.

Hydrodesulfurization of oxidized sulfur compounds in benzothiophene, methylbenzothiophene, and dibenzothiophene series over CoOMoO3Al2O3 catalyst

Hydrodesulfurization experiments were carried out with a sulfided CoOMoO3Al2O3 catalyst at various elevated pressures (30 to 70 atm) and temperatures (200 to 300 °C) under stirred batch reactor conditions. The reactants were hydrogen and pure sulfur compounds including dibenzothiophene, benzothiophene and its methyl derivatives, and their oxidized products, sulfoxides and sulfones. In the case of dibenzothiophene the reaction is the CS bond scission without any observed hydrogenation of the aromatic ring. For the S-oxidized compounds a deoxygenation takes place first and the sulfide reacts as before. For benzothiophene (BT) and its methyl derivatives there is first a hydrogenation of the C2–3 thiophenic double bond and then desulfurization leading to ethylbenzene derivatives. For the sulfoxides a deoxygenation takes place first but for the sulfones (BTO2) as for the sulfide the hydrogenation is operative. Methyl substitution leads to a decrease in the rate of the hydrogenation step in the BT and BTO2 series. A correlation, related to the overall aromaticity of the system, between the rate constants and the vertical ionization potential of the molecules, suggests that electronic effects may be preponderant.

Characterization of basicity in alkaline cesium-exchanged X zeolites post-synthetically modified by impregnation: A TPD study using carbon dioxide as a probe molecule

Interesting basic zeolites have been prepared by impregnating CsNaX zeolite with various loadings of cesium acetate in order to improve, after calcination, the basic character of the solid and to benefit from the cage effect in fine chemistry. In the range of 0 up to 26 cesium atoms per unit cell, X-ray powder diffraction shows that the crystallinity is largely retained after the generation of the basic species. The microporous volume values indicate that an interesting space is available for fine chemistry. For characterizing the surface chemical properties of the basic post-synthetically modified CsNaX zeolites, the stepwise thermodesorption of CO2 (TPD) has been studied. Experimental conditions allowing an accurate determination of the basic species are described. The modified zeolites with various loadings have been compared under these conditions. For loadings below 16 cesium atoms per unit cell, a linear relationship is established between the amount of desorbed CO2 (molecules per unit cell), up to 550°C, and the impregnated cesium loading (atoms per unit cell). This result supports the hypothesis that the active cesium species are homogeneously located inside the cages of the CsNaX zeofite. The slope of the straight line (0.44) indicates that one cesium oxide per zeolite cage is generated, leading upon CO2 adsorption to a carbonate species (Cs2CO3). For loadings higher than 16 cesium atoms per unit cell, a saturation is observed for the amount of desorbed CO2 up to 550°C along with an increase of the amount of desorbed CO2 above 550°C corresponding to a deposition of basic species on the external surface of the solids.

Factors affecting the hydrogenation of substituted benzenes and phenols over a sulfided NiOMoO3γ-Al2O3 catalyst☆

Abstract The hydrogenation of substituted benzenes ( R = Et, Ph, c -C 6 H 11 , PhCH 2 , c -C 6 H 11 CH 2 ), of ortho - and para -substituted phenols ( R = Et, Ph, c -C 6 H 11 , PhCH 2 ) was studied by a batch method at 340 °C and 70 bar H 2 over a sulfided NiOMoO 3 / γ -Al 2 O 3 catalyst. The rates of hydrogenation are always higher for phenols than for benzenes and can be related to differences in the π-electron delocalization between the two series of organic compounds. The rates of hydrogenation of ortho - and para -substituted phenols are similar to one another and generally lower than those for phenol alone, thus suggesting a predominant role of electronic factors over steric ones.

Hydroprocessing of dibenzothiophene, phenothiazine, phenoxathiin, thianthrene, and thioxanthene on a sulfided NiOMoO3γ-Al2O3 catalyst

Abstract The hydroprocessing of phenothiazine, phenoxathiin, thianthrene, and thioxanthene was studied by a batch method at 340°C and 70 bar H2 over a sulfided NiOMoO 3 γ-Al 2 O 3 catalyst. The hydrodesulfurization (HDS) rate constants are similar to one another and about tenfold higher than that of dibenzothiophene. The presence of a second heteroatom or a methylene group does not play an important role on the removal of sulfur. The differences of reactivity could rather result from geometrical considerations in relation with the ease of adsorption on the catalyst surface. The cleavage patterns and reaction networks for the hydroprocessing of compounds dibenzothiophene, phenothiazine, phenoxathiin, thianthrene, and thioxanthene are discussed. The product distribution allows, in particular, an estimate to be made of the rates of hydrogenation and hydrogenolysis in HDS, hydrodenitrogenation (HDN), and hydrodeoxygenation (HDO) processes.