To prepare Silica Aerogel the Sol-gel process is used. The chemical step is the first one to obtain a gel in alcoholic or acetonic medium. The aim of this work is the study of the influence ofsuch physico-chemical parameters on gel preparation and specially the acido-basic catalyst which gaverns the two steps of sol-gel process. For all precursors used (TMOS, TEOS et PEDS-Px) a reactionnal mecanism was given. Eventually the gelation time and the ageig of the gel were studied.
E. El Aloui, G.M. Pajonk
Sol-gel process, Silica, catalyst, precursors
Pages 607-620
5-amino-1-phenyl-1,2,4-triazoles 1, obtained by condensation of cyanamide with hydrazonate, react with ethoxymethylene derivatives of diethyl malonate 2, ethyl cyanoacetate 3 and malononitrile 4, to yield a new class of triazolopyrimidines.
F. Chabchoub, M. Kossentini, M. Salem
Hydrazonates, aminotriazoles, triazolopyrimidines
Pages 621-630
The condensation of hydrazine with 2-dialcoylaminomethylpropenenitriles constitute a highly regiospecific reaction and an original route for synthesis of new 2-cyano-3-dialcoylarnino-propylhydrazines.
F. Yaccoubi, M.L. El Efrit, H. Zantour
hydrazine, dialcoylaminornethylpropenenitriles
Pages 631-638
Aminopyrazolo[1,5-a]pyrimidines and aminopyrimido[1,2-b]pyrydazines were synthesized respectively by the condensation of 2-cyano-3-morpholinopropylhydrazine with α-ketonitriles and 2-cyano-3-dialcoylaminopropylhydrazines with β-ketonitriles in refluxing ethanol.
F. Yaccoubi, M.L. El Efrit, H. Zantour
2-cyano-3-dialcoylaminopropylhydrazines, ketonitriles
Pages 639-645
Six products have been isolated for the first time from the leaves and flowers of Hyparrhenia hirta (L.) Stapf (Andropogon hirtus) : tricosane; vanillin; 4-hydroxybenzaldehyde; 12,14-tritriacontandione; β-sitosterol and 3-O-β-D-glucoside sitosterol. Their structures were determined by spectroscopic methods.
H. Ben Salah, M. Bouaziz, A. Bahroun, M. Damak, A. Mc Killop, M. Simmonds
Hyparrhenia hirta, Gramineae, leaves, flowers, tricosane, 12,14- tritriacontandione, vanillin, 4-hydroxybenzaldehyde, β-sitosterol, 3-O-β-D-glucoside sitosterol
Pages 647-652
Three extracts from flowers and stems of Centaurea dimorpha showed anti-Giardia, anti-oxydant, anti-inflammatory and anti H.I.V. activities. Two lignans, one alcane and four triterpens have been isolated from flowers and leaves of Centaurea dimorpha (Asteraceae). By means of spectroscopic methods (MS, IR, UV, 1H and 13C NMR and NOE difference sequence), their structures were established as arctigenin, arctigenin-4'-glucoside, tricosane, (β-amyrin, taraxasterol, sitosterol-3-O-β-D-glucoside and poriferasterol.
N. Damak, H. Ghorbel, A. Bahroun, M. Damak, A. Mc Killop, M. Simmonds
Centaurea dimorpha, Asteraceae, flowers, leaves, stems, lignans, alcane, triter-pens
Pages 653-658
[1,3]Dipolar cycloaddtion of 2-diazopropane on 2,6-dibenzylidenecyclohexanone 2 done at 0°C lead to tow bis-spiro-Δ1-pyrazolines: diastereoisomers 3 and 4. The same addition reaction carried out at -50°C gave in addition to adducts 3 and 4 and for the first time a new spiro-Δ3-(1,3,4)oxadiazoline with an inverse regiochemical way. The pyrolysis of 3 and 4 gave the ethylenic derivatives 6 and 7.
N. Boukamcha, M.T. Martin , A. Khemiss
2-diazopropane, bis-spiro-Δ1-pyrazolines, spiro-Δ3-(1,3,4)oxadiazoline
Pages 659-670
Conjugated addition of nitroalkanes to the Baylis-Hillman acetates 1b and 2b in the presence of NaOH (0.45N) in THF gave 2-alkylidene-4-nitronitriles 3-(Z,E) and -4-nitroesters 4-(Z,E) which were further converted via the Nef reaction into the corresponging 2-alkylidene-4-ketonitriles 5(Z,E) and -4-ketoesters 6-(Z,E) in high stereoselectivity and good yields.
S. Hbaïeb, H. Amri
Pages 671-681
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