Enantioselective separations by capillary GC on derivatized cyclodextrins. Part 2: Determination of enantiomeric excess of some racemic 2,3-isopropylidene-1,2,3-cyclohexanetriol derivatives on permethyl α-, β-, and γ-cyclodextrins

Capillary GC on permethyl α-, β-, and γ-cyclodextrins has been applied to separate and quantify the enantiomers of some 2,3-iso-propylidene-1,2,3-cyclohexanetriol derivatives. Quantitative CGC data are compared to those obtained with chiral shift ¹H NMR.     

The Azo(Azoxy) Functionality as a π2 Component in Photo [2+2] cycloadditions ‘syn’- and ‘anti’-3,4-diazatricyclo[4.2.2.22,5]dodeca-3,7-diene,syntheses, photolyses,X-ray-structure analysis,and PE spectra

The propensity of the N?N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1–3 , no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray ( 1 : d = 2.71 Å, ω = 129°) and PE measurements ( 1 : I₁ = 8.0₀, I₂ = 9.0₅ eV; 2 ; I₁ = 8.0₀, I₂ = 9.2₅eV). The steric/stereoelectronic demands for the participation of the N?N bond in pericyclic reactions are clearly more stringent than those for the C?C bond.     

Halogenation of 2-Hydroxynicotinic Acid

A convenient method to prepare 5-halo-2-hydroxy-nicotinic acid is described.     

Synthesis of tribenzyl D-gluco- and D-galactopyranosides

The synthesis of ethyl-3,4,6-tri-O-benzyl-D -glucopyranoside and of ethyl-3,4,6-tri-O-benzyl-D -galactopyranoside is described. These compounds are isomers of ethyl-3,5,6-tri-O-benzyl-D -glucofuranoside, GLYVENOL ®, a substance displaying interesting pharmacological actions.     

Membrane bioprocesses for the denitrification of drinking water supplies

A membrane bioreactor (MBR) system, consisting of a bioreactor coupled to a hollow fiber ultrafiltration membrane module, has been developed at the Centre International de Recherche sur l'Eau et l'Environnement (CIRSEE). This process combines the advantages of biological conversion of nitrate to nitrogen with that of hollow fiber ultrafiltration technology to produce high quality drinking water. The influence of several parameters, both biological and hydraulic, on the overall performance of the process has been investigated. With adequate membrane backwashing frequency an crossflow velocity, we were able to obtain, and to maintain for more than two months, a net permeate flow rate of over 100 1-hr⁻¹-m⁻². It has also been found that such a high permeate flow rate was not detrimental to the overall denitrification process, since permeate nitrate and nitrite concentration remained below 20 and 0.1 mg-l⁻¹, respectively, for a nitrate volumetric loading rate of 2.8 kg-m⁻³-day⁻¹ at a hydraulic retention time of either 60 or 30 minutes.     

A 13C?{1H} double resonance study of the signs of 1H?19F and 13C?19F spin coupling constants in fluorobenzenes and 2-fluoropyridine

The signs of all ¹³C? ¹⁹F and ¹H–¹⁹F coupling constants in fluorobenzene, some substituted derivatives, and in 2-fluoropyridine have been related using single-frequency ¹³C? {¹H} double resonance techniques. All ¹³C? ¹⁹F couplings in these compounds are shown to be positive. Direct experimental proof is given for a positive sign for the small five-bond ¹H? ¹⁹F coupling constant (=0.2—0.3 Hz) in fluorobenzene. The positive sign for ⁴J(C-4, F) in fluorobenzene is in accord with a positive π-electron contribution to this coupling.     

A synthesis of isoindoles and isoindolines via aryne intermediates

The intramolecular cyclization of the tertiary amines (3) with potassium amide in liquid ammonia affords a variety of unsymmetrical isoindolines (5) and isoindoles (6).