Aminophosphine oxides in a pyridine series. Studies on the cleavage of pyridine-2- and pyridine-4-yl-(N-benzylamino)-methyldiphenylphosphine oxides in acidic solutions

The synthesis and reactions of 1-(N-benzylamino)-1-(2-pyridyl)- and 1-(N-benzylamino)-1-(4-pyridyl)-methyldiphenylphosphine oxides are described. It was found that these compounds were exceptionally easy to cleave in aqueous sulfuric acid solutions to form diphenylphosphinic acid and the corresponding N-(pyridylmethyl)-benzylamines. The structure of a single diastereoisomer, that is, the (R)-(+)-1-[N-(α-methylbenzylamino)]-1-(4-pyridyl)-(S)-methyldiphenylphosphine oxide was determined by X-ray crystallography. The acidic alcoholysis of the selected model chiral pyridine aminophosphine oxides was investigated by means of ³¹P NMR spectroscopy. The cleavage kinetics were also studied. On the basis of the obtained results, a mechanism of the cleavage was formulated.     

The first guaian-12-oic acid glucopyranosyl ester and other constituents from Picris rhagadioloides (L.) Desf. (Asteraceae)

The first guaian-12-oic acid glucopyranosyl ester was isolated from the roots of Picris rhagadioloides (L.) Desf. (Asteraceae), in addition to five costuslactone-type guaianolides, four germacranolides and three phenolic compounds. This is the first time that the known phenolics syringaldehyde and syringaresinol, as well as the known sesquiterpene lactones glucozaluzanin C, cichorioside C and hypochoeroside A have been described from a Picris species. The compounds were characterized on the basis of physicochemical, 1D- and 2D-NMR spectroscopic, and mass spectrometric data.     

Sterically crowded diolates of group 13 metals

The dependence of the structure of complexes of sterically crowded 2,4-dimethylpentane-2,4-diol with group 13 metals trialkyls on the kind of metal, as well as steric bulk of the substituents on the metal atoms is reported. The reaction of ^tBu₃Ga with 2,4-dimethylpentane-2,4-diol leads to the formation of an unstable dimeric product {^tBu₂Ga[(OC(CH₃)₂CH₂C(CH₃)₂OH]}₂ (1) possessing a four-membered Ga₂O₂ core and two unreacted hydroxyl groups. Compound 1 undergoes further intramolecular reaction to yield the unusual (monoalkyl)gallane O,O^′-chelate complex {^tBuGa[OC(CH₃)₂CH₂C(CH₃)₂O]}₂ (2). In contrast to ^tBu₃Ga, ^tBu₃In reacts with 2,4-dimethylpentane-2,4-diol to give the stable dimeric complex ^tBu₄In₂[OC(CH₃)₂CH₂C(CH₃)₂OH]₂ (4) stabilised by two intramolecular O-H?O bonds. At higher temperature compound 4 reacts with an excess of ^tBu₃In to form the trinuclear complex ^tBu₅In₃[OC(CH₃)₂CH₂C(CH₃)₂O]₂ (5). The reactions of 2,4-dimethylpentane-2,4-diol with trialkylmetallane with small alkyl groups, i.e. Me₃Ga and Me₃In allow for the isolation of the trinuclear diolates {Me₅M₃[OC(CH₃)₂CH₂C(CH₃)₂O]₂} [M=Ga (3), M=In (6)]. The crystal structures of 2, 3 and 4 have been determined by single crystal X-ray diffraction. The reactions of tert-butylmetallane diolates with trimethyl metallanes have been studied. The interaction of the allane complex {^tBuAl[OC(CH₃)₂CH₂C(CH₃)₂O]}₂ with Me₃Al results in the formation of the trialuminium mixed-ligand product {Me₃(^tBu)₂Al₃[OC(CH₃)₂CH₂C(CH₃)₂O]₂} (7). Compounds 2 and 4 undergo a total transmetallation reaction in the presence of Me₃M to yield [Me₅M₃(diol-(2H))₂] [M=Al, Ga] products.     

Ion exchange and ion transport properties of sulfonated organically modified silica hydrogels

Sulfonated ormosil hydrogels (~80% water) were prepared using tetramethyl orthosilicate as a silica precursor and 2(4-chlorosulfonylphenyl)ethyltrichlorosilane to provide sulfonate functionality for ion-exchange and ion conductivity. Ruthenium(III) hexamine was used as a redox probe in electrochemical studies performed on porous carbon fibre paper electrodes impregnated with the gel. The gel-modified electrodes extracted Ru(NH₃)₆³⁺ from solutions in 0.1 M CF₃CO₂Na_(aq) with a partition coefficient of ~36, and with ~100% of the sulfonate sites being accessible for ion exchange. The Ru(NH₃)₆^3+/2+ couple exhibited reversible and facile electrochemistry in the gel, with a Ru(NH₃)₆²⁺ diffusion coefficient of 4.9×10^–8 cm² s^–1 determined by chronoamperometry. This is an order of magnitude higher than the mobility of this complex in Nafion. The hydrogel-modified electrodes were stable for days, and could be repeatedly loaded with Ru(NH₃)₆³⁺.Special Issue to celebrate the 70^th birthday of Professor Zbigniew Galus     

Relativistic corrections in the multiple-scattering method

We show how to introduce the Foldy-Wouthuysen relativistic corrections in the multiple-scattering method, for the determination of the electronic energy levels of molecules. The present derivation begins from a variational expression where the Foldy-Wouthuysen hamiltonian is inserted, instead of the Schrödinger hamiltonian. The resulting secular equation becomes identical with the standard multiple-scattering secular equation, if one neglects the relativistic correction terms.     

(+)-(S)-α-diethoxyphosphorylvinyl p-tolyl sulfoxide: A new chiral Michael acceptor and dienophile

The tittle reagent, (+)-(S)-1, was prepared from (+)-(S)_s-α-diethoxy-phosphorylethyl p-tolyl sulfoxide 2 by phenylselenylation-deselenylation procedure. Its reactivity was demonstrated by diastereoselective Michael addition of ethanethiol giving rise to 3, tandem Michael addition/intramolecular Horner--Wittig reaction with 2-formyl pyrrole leading to the corresponding pyrrolizine sulfoxide 5 and cycloaddition with cyclopentadiene affording the diastereomeric adducts 6. The steric course of the Diels-Alder reaction is briefly discussed.     

Cross-linking of polytetrafluoroethylene during room-temperature irradiation

Exposure of polytetrafluoroethylene (PTFE) to α-radiation was investigated to determine the physical and chemical effects, as well as to compare and contrast the damage mechanisms with other radiation types (β, γ, or thermal neutron). A number of techniques were used to investigate the chemical and physical changes in PTFE after exposure to α-radiation. These techniques include: Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and fluorescence spectroscopy. Similar to other radiation types at low doses, the primary damage mechanism for the exposure of PTFE to α-radiation appears to be chain scission. Increased doses result in a change-over of the damage mechanism to cross-linking. This result is not observed for any radiation type other than α when irradiation is performed at room temperature. Finally, at high doses, PTFE undergoes mass-loss (via small-fluorocarbon species evolution) and defluorination. The amount and type of damage versus sample depth was also investigated. Other types of radiation yield damage at depths on the order of mm to cm into PTFE due to low linear energy transfer (LET) and the correspondingly large penetration depths. By contrast, the α-radiation employed in this study was shown to only induce damage to a depth of approximately 26 μm, except at very high doses.     

NHN]+ hydrogen bonding in protonated 1,8-bis(dimethylamino)-2,7-dimethoxynaphthalene. X-ray diffraction, infrared, and theoretical ab initio and DFT studies

Structural (X-ray diffraction), infrared spectroscopic, and theoretical MP2 and DFT studies on the HBr and DBr adducts of 1,8-bis(dimethylamino)2,7-dimethoxynaphthalene ((CH3O)2.DMAN) were performed. This particular proton sponge has been chosen for its strong basicity and display of the buttressing effect influencing the hydrogen bond dynamics and properties. The studies revealed a symmetric, planar DMAN.H+ cation with a short (NHN)+ hydrogen bond of 2.567(3) A. The X-ray diffraction results suggest that the proton is in the central position in the bridge, while the calculations show two potential energy minima with the zero point energy level close to the top of the barrier. The infrared spectra display an (NHN)+ band at 488 cm(-1) and an (NDN)+ band at 235 cm(-1), respectively. It gives the isotopic ratio of 2.08, the highest value reported to date. Such a result suggests a peculiar shape of the potential for the proton motion, characterized by an extremely high positive anharmonicity. The calculations reproduce this particular potential, yielding an ISR value displaying a very good agreement with the experimental one. The anharmonic frequencies, however, show the discrepancy between the observed and calculated transitions.