Kinetics of the transesterification of para-nitrophenyl esters of phosphorus acids in water and aqueous hexamethylphosphorotriamide

The rate constants for the substitution of the para-nitrophenoxide ion by the phenoxide and hydroxide ions in phosphates and phosphonates are enhanced upon the addition of hexamethylphosphorotriamide (HMPTA) to water. The lack of alkaline hydrolysis of the esters in 90% aqueous HMPTA containing PhONa is a consequence of the formation of the PhOH... OH complex, which is nonreactive.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Science Center, Russian Academy of Sciences, 420083 Kazan. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 456–459, February, 1992.     

Entropy‐Driven Selectivity for Chain Scission: Where Macromolecules Cleave

We show that, all other conditions being equal, bond cleavage in the middle of molecules is entropically much more favored than bond cleavage at the end. Multiple experimental and theoretical approaches have been used to study the selectivity for bond cleavage or dissociation in the middle versus the end of both covalent and supramolecular adducts and the extensive implications for other fields of chemistry including, e.g., chain transfer, polymer degradation, and control agent addition are discussed. The observed effects, which are a consequence of the underlying entropic factors, were predicted on the basis of simple theoretical models and demonstrated via high‐temperature (HT) NMR spectroscopy of self‐assembled supramolecular diblock systems as well as temperature‐dependent size‐exclusion chromatography (TD SEC) of covalently bonded Diels–Alder step‐growth polymers.     

Kinetics of alkaline hydrolysis of ethylp-nitrophenyl ethylphosphonate in the reverse micellar system: sodium dodecyl sulfate-hexanol-water

The kinetics of alkaline hydrolysis of ethylp-nitrophenyl ethylphosphonate in the reverse micellar system sodium dodecyl sulfate—hexanol—water was studied. At high pH and low water content, the process occurs at the surface layer and can satisfactorily be described by the pseudo-phase model equation. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp 262–266, February, 2000.     

Color center formation by synchrotron radiation in the Na6Al6Si6O24(Nal)1.6 optical ceramic

The spectrum of F-center excitation by 5-to 27-eV photons in the Na₆Al₆Si₆O₂₄(NaI)_2x sodalite optical ceramic (x=0.8) was measured at 80 K by high-sensitivity photoexcited luminescence techniques. The F-centers are created by photons with an energy of 5.6-to 8.5 eV through the excitation and ionization of iodine centers of two types; in the 8.2-to 27-eV region, through the generation of electronic excitations in the aluminosilicate framework of alternating Al³⁺ and Si⁴⁺ ions, each coordinated tetrahedrally by oxygen ions. At the low irradiation doses used, the F centers are created primarily through photoelectron capture by the iodine vacancies which exist before irradiation. In the 23-to 25-eV region, the efficiency of F-center formation doubles as a result of the multiplication of electron-hole pairs.     

Aggregation behavior and catalytic properties of systems based on aminomethylated calix[4]resorcinarenes and poly(ethylene) imines

Self-assembling in systems poly(ethylene) imine-aminomethylated calix[4]resorcinarene-water-DMF (30 vol%) and catalytic properties of these compositions in hydrolysis of 4-nitrophenylbis (chloromethyl)phosphinate are studied. Critical concentrations of association, aggregates radii, and kinetic parameters of the reaction are established.     

Carbon-based leaving group in substitution reactions: functionalization of sp3-hybridized quaternary and tertiary benzylic carbon centers

Lewis acid promoted substitution reactions employing Meldrum's acid and 5-methyl Meldrum's acid as carbon-based leaving groups are described which transform unstrained quaternary and tertiary benzylic C(sp(3))-C(sp(3)) bonds into C(sp(3))-X bonds (X = C, H, N). Importantly, this reaction has a broad scope in terms of both suitable substrates and nucleophiles with good to excellent yields obtained (typically >90%).     

Hydrogen diffusion constants in stainless steel and Pd60Ag40 alloy, and permeability of diaphragms made of these metals

Hydrogen permeability through diaphragms made of 12X18H12T stainless steel and Pd₆₀Ag₄₀ alloy under electrolytic hydrogen saturation has been studied with an electrolytic cell with a vacuum chamber. Hydrogen diffusion constants D _H = 3.86 × 10⁻¹⁰ cm² s⁻¹ for stainless steel and D _H = 4.36 × 10⁻⁸ cm² s⁻¹ for Pd₆₀Ag₄₀ alloy have been determined at a temperature of 40°C using the Berrer relations.     

A nonparametric scaling equation of state,developed on the basis of the Migdal’s phenomenological theory and Benedek’s hypothesis

A new nonparametric scaling equation with density and temperature as variables is proposed using the phenomenological theory of critical phenomena and the experimentally confirmed Benedek’s hypothesis, on the basis of which we assume that the behavior of a number of thermodynamic functions for the critical and near-critical isochores in the neighborhood of an asymptotic critical point is similar. In comparison to Scofield’s linear model (LM), the proposed scale equation is not inferior to known nonparametric equations of the same type; in contrast to the latter, however, its physical grounds are just as valid as the LM equation.     

Study of coatings based on titanium oxides and oxynitrides using a set of methods

A set of methods has been applied to study the properties of titanium oxide and oxynitride coatings on steel. It is established that the coatings consist of two phases with a nanocrystalline and an amorphous structure with a high proportion (～50 %) of grain boundaries; anatase is the dominant crystalline phase. The obtained results can be applied in the development of coatings for stents as well as for manufacturing hydrogen accumulators.