Cyclobutadieneiron tricarbonyl carboxylic acids: Synthesis and acidity

Two carboxylic acid derivatives of the cyclobutadieneiron tricarbonyl (I) system have been synthesized and their pK_a values determined. It appears that I tends to be electron withdrawing by induction and electron releasing by resonance.     

Reaction of pentadienyliron tricarbonyl cations with hydride donors

A series of pentadienyliron tricarbonyl cations has been prepared and reacted with the hydride ion donors sodium borohydride, sodium cyanoborohydride, and lithium triethylborohydride in order to determine steric and electronic effects in these reduction reactions. Sodium cyanoborohydride yields products of retained configuration whereas lithium triethylborohydride yields dieneiron tricarbonyl compounds of inverted configuration. Kinetic and thermodynamic considerations are used to account for these results.     

Synthesis of ketobemidone precursors via phase-transfer catalysis

Hydrochloride salts of N-substituted-bis-(2-chloroethyl)amines can be condensed with m-methoxyphenyl-acetonitrile or 1-phenyl-2-alkanones under phase-transfer conditions to yield precursors of the powerful analgesic compounds - the ketobemidones.     

Pyrolysis/gas chromatography/ion-trap detection of polyphenols (vegetable tannins): Preliminary results

Tannins from sorghum grains with high and low tannin content, from grape skins and seeds and from apple pomace were analysed by pyrolysis/gas chromatography/ion-trap detector mass spectrometry. Pyrolysis at 600°C produced catechol as a characteristic fragment of condensed tannins, and other phenolic compounds related to the lignified tissues. Catechol was also the main fragment in the pyrogram of catechin, a monomeric constituent of condensed tannins. Mass spectral data and relative quantifications of the pyrograms of several samples are provided. Quantitative data are discussed in terms of reproducibility and linearity of response and are compared with the results of a spectrophotometric assay for tannins.     

Non-atomic absorption from matrix salts volatilized from graphite atomizers in atomic absorption spectrometry

The non-atomic absorption signals obtained from alkali halides atomized from three types of graphite atomizer are examined. The wavelength dependence of the signals identifies the absorption as that of charge-transfer transitions of the alkali halide molecules. The contribution of light scattering to the total non-atomic absorption signal is shown to be of small significance; the observed light-scattering is not Rayleigh scattering. The temperature dependence of the loss of sodium chloride from a rod atomizer is studied experimentally and compared with calculated vaporization rates based on the kinetic theory of gases.     

Adsorption of urea at the mercury—water interface

The adsorption of urea on mercury from aqueous 1 M KNO₃ has been determined from capacity and electrocapillary measurements. A Langmuir isotherm is obeyed with a saturation molecular area of 24 × 10^?10 m² per molecule. The standard free energy of adsorption is a quadratic function of charge with maximum adsorption occurring at a charge of +8 μC cm^?2. These data are interpreted in terms of the partially oriented urea dipole, the contribution of water dipoles and nitrate ions also being considered.     

Asymmetric hydrogenation of unsaturated ureas with the BIPI ligands

Asymmetric hydrogenation of unsaturated urea esters with the BIPI Ligands has been examined. Optimization of the P-N ligand structure has led to the development of chiral rhodium catalysts capable of producing the targets with >99% ee. The critical phosphine borane SNAr reaction needed for ligand synthesis has been optimized to give the adducts in high yield at ambient temperature with no racemization. An extremely concise, economical, and scalable sequence to these important new ligands for catalysis of asymmetric hydrogenation has been developed.     

A 13C nuclear magnetic resonance study of cyclobutadieneirontricarbonyl-substituted carbonium ions

The ¹³C NMR spectra of (hydroxymethyl)-, (α-hydroxyethyl)- and (α-hydroxybenzyl)cyclobutadieneiron tricarbonyl (in CDCl₃) and of their derived carbonium ions (in concentrated H₂SO₄) are reported. The data suggest extensive donation of electron density from the metal, via the cyclobutadiene unit, to the exocyclic, electron-deficient carbon atom, thus giving highly stabilized carbonium ions.