Revealing structural effects: electrochemical reactions of butanols on platinum

Spectroelectrochemical studies on the reactivity of butanol isomers on Pt electrodes in perchloric acid medium led to the observation of structural effects that result from the different arrangements of atoms in the organic molecules. The use of differential electrochemical mass spectrometry (DEMS) to detect volatile products showed that all four isomers react on the electrode, though different product yields were observed for each compound. In spite of the differences in the electrochemical behaviour of the butanol isomers, a series of general processes accounts for the results obtained. The formation of strongly adsorbed residues by a dehydration process leading to the formation of a C=C bond was proposed for all isomers. Electroreduction of the adsorbates produces C(4) and C(3) alkanes, and the latter reveal the existence of a fragmentation process. The C(4) hydrocarbons can be formed by hydrogenation of these residues and by hydrogenolysis of alcohol molecules in the bulk solution which react at the electrode with adsorbed hydrogen. On the other hand, CO(2) is formed during electrooxidation of the adsorbed species. Partial-oxidation products containing a carbonyl group were detected from 0.2 M solutions of 1-butanol, isobutyl alcohol and sec-butyl alcohol. The tertiary alcohol tert-butyl alcohol only reacts in its adsorbed state.     

Flow injection system with gas diffusion for the sequential determination of total nitrogen and phosphorus in vegetables

 A flow injection system was developed for the sequential determination of total nitrogen and phosphorus in digests of vegetables using potentiometric and spectrophotometric detection systems, respectively. A tubular ammonium selective electrode with a sensor system composed of nonactin/monactin in tris(2-ethylhexyl) phosphate was used. The selectivity limitations of this electrode were overcome by the inclusion of a gas-diffusion unit in the system that separated ammonium from the rest of the sample matrix and allowed the determination of total nitrogen and phosphorus by the partition of the sample plug between two streams. The results obtained with the developed FIA system were in good agreement with those of the reference methods. Sampling rates from 40 to 60 samples per hour and relative standard deviations below 3.5% were achieved. Received: 17 October 1996/Revised: 21 November 1996/Accepted: 27 November 1996     

Flow injection system with gas diffusion for the sequential determination of total nitrogen and phosphorus in vegetables

 A flow injection system was developed for the sequential determination of total nitrogen and phosphorus in digests of vegetables using potentiometric and spectrophotometric detection systems, respectively. A tubular ammonium selective electrode with a sensor system composed of nonactin/monactin in tris(2-ethylhexyl) phosphate was used. The selectivity limitations of this electrode were overcome by the inclusion of a gas-diffusion unit in the system that separated ammonium from the rest of the sample matrix and allowed the determination of total nitrogen and phosphorus by the partition of the sample plug between two streams. The results obtained with the developed FIA system were in good agreement with those of the reference methods. Sampling rates from 40 to 60 samples per hour and relative standard deviations below 3.5% were achieved. Received: 17 October 1996/Revised: 21 November 1996/Accepted: 27 November 1996     

A comparison of cellactose with two ad hoc processed lactose-cellulose blends as direct compression excipients

Three processed lactose-cellulose blends of similar composition, particle size and true density were compared as direct compression excipients: one was prepared by dry granulation, one by extrusion-spheronization, and the commercial product Cellactose. Differences among their flow properties depended solely on their different sphericities. Unlike those of the other blends, Cellactose particles exhibited numerous macropores. The mean yield pressures of all three blends were similar to those of direct compression lactoses. Cellactose tablets prepared at a punch pressure that largely eliminated macropores (pores >1 microm) had better mechanical properties but much poorer disintegration than tablets of the other blends prepared at the same punch pressure. However, the tensile strength and disintegration time of Cellactose tablets both fell rapidly as macropore volume was increased by reducing punch pressure, while the enthalpy of wetting/dissolution rose. The strength and water-resistance of well-compacted Cellactose tablets is attributed to the spatial distribution of lactose and cellulose in Cellactose particles, rather than to beta-lactose content or extra-particular structural features.     

Synthesis in Water and Antimicrobial Activity of 5-Trichloromethyl-4,5-dihydroisoxazoles

Two series of 5-trichloromethylisoxazoles were synthesized from the cyclocondensation of 1,1,1-trichloro-4-methoxy-3-alken-2-ones [Cl₃CC(O)C(R²) = C(R¹)OMe, where R¹ = H, Me, Et, Pr, iso-Pr, cyclo-Pr, Bu, terc-Bu, CH₂Br, CHBr₂, CH(Me)SMe, (CH₂)₂Ph, and Ph, and R² = H; R¹ = H and R² = Me and Et; R¹ and R² = -(CH₂)₄- and -(CH₂)₅-; and R¹ = Et and Ph and R² = Me] with hydroxylamine hydrochloride through a rapid one-pot reaction in water. The 5-trichloromethyl-4,5-dihydroisoxazoles were aromatized by reaction with concentrated sulfuric acid to obtain the respective 5-trichloromethylisoxazoles. Their structures were confirmed by elemental analysis, ¹H/¹³C nuclear magnetic resonance, and electron impact mass spectroscopy. Crystal structure analysis for 5-triclhoromethyl-5-hydroxy-3-propyl-4,5-dihydroisoxazole (2d) and 5-trichloromethyl-5-hydroxy-3,4-hexamethylene-4,5-dihydroisoxazole (2o) is presented. The antimicrobial activities of the 5-trichloromethyl-4,5-dihydroisoxazole derivatives were examined using the standard twofold dilution method against Gram-positive bacteria (Staphylococcus aureus), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), and yeasts (Candida spp. and Cryptococcus neoformans). All of the tested 5-trichloromethyldihydroisoxazoles exhibited antibacterial and antifungal activities at the tested concentrations.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Versatile chelating behavior of benzil bis(thiosemicarbazone) in zinc, cadmium, and nickel complexes

Reactions of benzil bis(thiosemicarbazone), LH(6), with M(NO(3))(2).nH(2)O (M = Zn, Cd, and Ni), in the presence of LiOH.H(2)O, show the versatile behavior of this molecule. The structure of the ligand, with the thiosemicarbazone moieties on opposite sides of the carbon backbone, changes to form complexes by acting as a chelating molecule. Complexes of these metal ions with empirical formula [MLH(4)] were obtained, although they show different molecular structures depending on their coordinating preferences. The zinc complex is the first example of a crystalline coordination polymer in which a bis(thiosemicarbazone) acts as bridging ligand, through a nitrogen atom, giving a 1D polymeric structure. The coordination sphere is formed by the imine nitrogen and sulfur atoms, and the remaining position, in a square-based pyramid, is occupied by an amine group of another ligand. The cadmium derivative shows the same geometry around the metal ion but consists of a dinuclear structure with sulfur atoms acting as a bridge between the metal ions. However, in the nickel complex LH(6) acts as a N(2)S(2) ligand yielding a planar structure for the nickel atom. The ligand and its complexes have been characterized by X-ray crystallography, microanalysis, mass spectrometry, IR, (1)H, and (13)C NMR spectroscopies and for the cadmium complex by (113)Cd NMR in solution and in the solid state.     

Unexpected single-step formation of 1,2-anti-heterodisubstituted calix[4]arenes upon alkylation of a tribenzoyl precursor

The selective preparation and complete structural characterization of a small series of 1,2-anti-heterodisubstituted calix[4]arenes has been accomplished. These compounds were obtained in two steps from unsubstituted p-tert-butylcalix[4]arene by tribenzoylation and a subsequent one-pot, two-step sequence involving alkylation with simultaneous partial deacylation, resulting in heterodisubstituted calixarenes carrying an alkyl and an aroyl group. The monoalkyl-tribenzoyl intermediate, prior to in situ deprotection, could also be isolated.