Phosphinerhodium complexes as homogeneous catalysts : VIII. Enantioselective hydrogenation of ketones: evidence for several mechanisms with catalysts containing diop

Optical yields obtained in the hydrogenation of acetophenone with cationic and in situ rhodium complex catalysts depend on the P/Rh ratio and on the ionic or non-ionic character of the active species. The enantioselectivity of the in situ catalyst containing (+)-DIOP is reversed by addition of achiral tri-n-alkyl-phosphines. On the basis of these observations and the amount of H₂ consumed in preforming the catalysts, several different mechanisms are suggested: for example: cycles involving cationic rhodium complexes containing two (or three) phosphorus ligands and cycles involving non-ionic rhodium complexes with two phosphorus ligands in cis or trans positions. In the in situ catalyst with a Rh/(+)-DIOP/P-n-Bu₃  1/1/1 ratio (+)-DIOP functions as a monodentate ligand.     

Mikrobestimmung von Quecksilber in organischen Verbindungen

Zusammenfassung Eine Methode zur Mikrobestimmung von Quecksilber in organischen Verbindungen wurde beschrieben. 3–5 mg Substanz werden in einem Sauerstoffkolben verbrannt und die Produkte in 4 ml konz. Salpetersäure absorbiert. Die Absorptionslösung wird dann für 6 min gekocht, wobei die vollständige Oxydation zu Quecksilber(II) abläuft. Dieses wird mit 0,005 M Kaliumjodidlösung potentiometrisch titriert. Zur Indikation des Endpunktes wird eine Meßkette aus einer ionenselektiven Elektrode für Jodid und einer Referenzelektrode mit KNO₃-Zwischenelektrolyt verwendet. Die Resultate liegen innerhalb der üblichen Fehlergrenze von ± 0,30%.

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Microassay of mercury in organic substances

Summary A method for microassay of mercury in organic compounds was described. 3–5 mg substance are combusted in an oxygen flask and the products absorbed in 4 ml conc. nitric acid. The absorption solution is then boiled for 6 minutes, during which complete oxidation to mercury(II) occurs. This is titrated potentiometrically with 0.005M potassium iodide solution. A measuring chain consisting of an ion-selective electrode for iodide and a reference electrode with KNO₃ intermediate electrode was used to indicate the endpoint. The results are within the usual ±0.30% limit of error.

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Herrn Prof. Dr. Hans Lieb zum 90. Geburtstag gewidmet.

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Frl. Mirella Piccinini hat an dem experimentellen Teil dieser Arbeit mitgeholfen, wofür ich bestens danke.     

New Furano-sesquiterpenoids from Mediterranean Sponges

A mixture of sponges of the East Pyrenean Mediterranean is shown to contain the known sponge products longifolin ( 1 ), avarol ((+)- 3 ), and avarone ( 4 ) and the terrestrial-plant product sesquirosefuran ( 2 ), besides to the new furano-sesquiterpenoids tavacfuran (= 3-methyl-2-[(3′Z)-3′-methyl-4″-methyl-2″-furyl-3′-butenyl]furan; ( 5 ) and tavacpallescensin (= 5,10-dihydro-6,9-dimethyl-4H-benzo[5,6]cyclohepta[1,2-b]furan; 6 ) and the new furano-butenolide sesquiterpenoids tavacbutenolide-1 (= (±-4-ethoxy-2-methyl-4-)[(2′E)-2′-methyl-4′-(3″-methyl-2″-furyl)-2′-butenyl]-2-buten-4-olide; (±)- 7 ) and tavacbutenolide-2 (= (±)-4-ethoxy-3-methyl-4-[2′E)-3′-methyl-4′-(4″-methyl-2″-furyl)-2′-butenyl]-2-buten-4-olide; (±)- 8 ). Structural assignments are based on NMR data and on the synthesis of the (E)-isomer of 5 . The sponge Dysidea tupha of the same area is also shown to contain the two sesquiterpenoids ent-furodysinin ((?)- 14 ), which is enantiomeric to a product of a Dysidea sp. of Australian waters, and tuphabutenolide ((+)- 15 ).     

Infrared study of adsorption of methanol,deuterated methanol and ethylene on the surface of ZSM-5 type zeolite

The surface species resulting in exposing of the ZSM-5 zeolite at elevated temperatures to methanol, deuterated methanol or ethylene have been studied by IR method.The three-step adsorption at 150°, 300°, 420° C or one-step adsorption at 420° C have been carried out in order to prepare the samples for IR. In all cases the most prominent band appeared in the range 1495–1515 cm^?1; besides two bands at about 1470 and 1370 cm^?1 have been observed. On the basis of Greenler's results and of the shift values of the bands in our spectrum of adsorbed deuterated methanol it was supposed that the band 1495–1515 cm^?1 is due to the OCO group from the surface species. Moreover these species would involve both oxygen atoms from the surface of zeolite but not from OH groups of methanol.     

Determination of lanthanum in large steel samples by the neutron activation method

In view of the inhomogeneous distribution of lanthanum in steel, large samples should be used for the determination of this element. The method elaborated consists in the preparation of an average samople by dissolving 50 g steel and analysing an aliquot of the obtained solution corresponding to 0.5 g of steel. In order to reduce the activity of the sample, iron and some other elements are separated from the steel solution by electrolysis prior to irradiation. The amount of lanthanum contamination introduced during the pre-irradiation treatment of the sample is relatively low (10^?10–10^?9 g) if the treatment is carried out under suitable conditions. The post-irradiation treatment consists in the separation of²⁴Na by shaking the sample solution with Sb₂O₅. The¹⁴⁰La-activity is measured by means of a γ-spectrometer (1.6 MeV photopeak).     

A two-dimensional (magnetic field and concentration) electron paramagnetic resonance method for analysis of multispecies complex equilibrium systems. information content of EPR spectra

A two-dimensional simulation method has been developed for the interpretation of electron paramagnetic resonance (EPR) spectra consisting of a multitude of strongly overlapping signal components. The set of EPR spectra for complex equilibrium systems is analyzed simultaneously as a function of metal and ligand concentrations and pH. The formation constants of the various species are adjusted together with the magnetic parameters of the component EPR spectra. At most 10 EPR-active and 5 EPR-silent species can be involved to simulate a maximum of 36 experimental spectra, while the number of adjusted parameters is at most 100. Statistical parameters are suggested to give the confidence intervals for parameter estimation and to distinguish alternative speciation models. The efficiency of the program is demonstrated for the copper(II)--L-asparagine system, in which 10 species, including 3 pairs of isomers, are characterized with magnetic parameters and formation constants. On the basis of the magnetic parameters, a structural assignment is made for the detected species. The two-dimensional approach can also supply the formation constant of the EPR-silent species, as demonstrated for the copper(II)--glycyl-L-serine system.     

Paired electrosynthesis of cyanoacetic acid

Cyanoacetic acid is formed by cathodic reduction of CO(2) and anodic oxidation of the tetraalkylammonium salt anion; the process is conduced in acetonitrile using a divided cell with a medium porosity glass-frit diaphragm. A mechanism for this paired electrochemical reaction is proposed.     

Template-assisted self assembly of two lipophilic polyion aggregates derived from sodium tetraphenyl imidodiphosphinate-complexes containing sodium ions in four different coordination environments

The molecular structures of two lipophilic polyion aggregates derived from tetraphenyl imidodiphosphinate are described: [Na(crown ether)][MNa(2)[Ph(2)P(O)NP(O)Ph(2)](4)] with crown ether = 15-crown-5 for 1and benzo-15-crown-5 for (M = Na(+) for 1 and Na(H(2)O)(+) for 2).     

Linear free-energy relationships and the density functional theory: an analog of the hammett equation

Density functional theory has been applied to describe electronic substituent effects, especially in the pursuit of linear relationships similar to those observed from physical organic chemistry experiments. In particular, analogues for the Hammett equation parameters (sigma, rho) have been developed. Theoretical calculations were performed on several series of organic molecules in order to validate our model and for comparison with experimental results. The trends obtained by Hammett-like relations predicted by the model were found to be in qualitative agreement with the experimental data. The results obtained in this study suggest the applicability of similar correlation analysis based on theoretical methodologies that do not make use of empirical fits to experimental data can be useful in the study of substituent effects in organic chemistry.