Dynamic properties of water in silicalite-1 powder

Self-diffusion of D₂O in partially filled silicalite-1 crystals was studied at 25°C by ²H nuclear magnetic resonance (NMR) with bipolar field gradient pulses and longitudinal Eddy-current-delay. For the first time, reliable experimental diffusion data for this system were obtained. Analysis of NMR diffusion decays revealed the presence of a continuous distribution of apparent self-diffusion coefficients (SDCs) of water, ranging from 10⁻⁷ to ∼10⁻¹⁰ m²/s, which include values much higher and lower than that of bulk water (∼10⁻⁹ m²/s) in liquid phase. The observed distribution of SDC changes with variation of the diffusion time in the range of 10–200 ms. A two-site Kärger exchange model was successfully fitted to the data. Finally, the water distribution and exchange in silicalite-1 pores were described by taking into account (a) a gas-like phase in the zeolite pores, a gas-like phase in mesopores and an intercrystalline gas-like phase and (b) intercrystalline liquid droplets with intermediate exchange rate with the other phases. The other phases experience fast exchange on the NMR diffusion time scale. Diffusion coefficients and mean residence times of water in some of these states were estimated.     

Kinetic and quantum chemical studies of the mechanism of formation of 1,2-dialkyldiaziridines

The regularities of AlkNHBr consumption in the reaction of formation of 1,2-dialkyldiaziridines in aqueous media were studied for the first time by UV spectrometry. The rate constants of particular steps of the reaction were estimated starting from the possibility of formation of the precursor of 1,2-dialkyldiaziridine, N-halogenaminal, due to the amination of the intermediate iminium cation along with the parallel halogenation of the intermediate gem-diamine. The quantum chemical calculations (DFT, B3LYP, 6–31++G(d,p) and 3–21G basis sets) were performed for the spatial and electronic structures of the compounds and indices of the local reactivity and global electrophilicity of the key intermediates of the reactions. The results of the calculations allowed us to explain the retardation of the reaction when using EtNHBr instead of MeNHBr.     

Reaction of 1,2‐Dialkyldiaziridines and 1,2,3‐Trialkyldiaziridines with Methyl Propiolate in Ionic Liquids and in Organic Solvents

An interaction of 1,2‐dialkyldiaziridine and 1,2,3‐trialkyldiaziridine with methyl propiolate was studied both in organic solvent (MeCN, CH₂Cl₂, C₆H₆) and in ionic liquids. Earlier unknown linear structures, in which three molecules of methyl propiolate were suited to one diaziridine molecule (adducts 1 : 3), were obtained in MeCN. The diaziridine ring expansion products 1,2,3,4‐tetrahydropyrimidine derivatives (adducts 1 : 2) and, along with them in some cases, the same linear structures were obtained in ionic liquids. A mechanism of reactions found was offered. The regioselectivity of reactions was supposed to determine by the structure of substituents in initial diaziridines. This conclusion was supported by quantum chemical calculations.     

Transformations of 3(4)-amino-4(3)-(<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">NNO</Emphasis>-azoxy)furoxans in the annulation reactions into 1,2,3,4-tetrazine 1,3-dioxides

Reactions of 3(4)-amino-4(3)-(tert-butyl-NNO-azoxy)furoxans with excess (NO₂)₂S₂O₇ or with a HNO₃—H₂SO₄—Ac₂O mixture unexpectedly produce [1,2,5]oxadiazolo[3,4-e]?[1,2,3,4]tetrazine 4,6-di-N-oxide (furazanotetrazine dioxide) and products of amino group oxidation (mainly to the corresponding azofuroxans) instead of the expected furoxanotetrazine dioxides. In some cases, individual (Z)-3,3´-((E)-diazene-1,2-diyl)-bis-((Z)-2-tert-butyl-1-oxidodiazenyl)-1,2,5-oxadiazole 2-oxide) was isolated. Formation of furazanotetrazine dioxides was observed in the reaction of 3-nitramino-4-(tert-butyl-NNO-azoxy)furoxan sodium salt with H₂SO₄ in Ac₂O. Quantum chemical calculation at the DFT/B3LYP/6-31G(d) level of theory was used to estimate several aspects of the reactivity of 3(4)-nitramino-4(3)-(tert-butyl-NNO-azoxy)furoxans in a comparison with 3(4)-nitramino-4(3)-phenylfuroxans and the possible causes of the observed transformations were revealed.     

<Emphasis Type="Italic">p</Emphasis>-Adic solid-on-solid model on a Cayley tree

We consider a p-adic solid-on-solid (SOS) model with a nearest-neighbor coupling, m+1 spins, and a coupling constant J ∈ Q _p on a Cayley tree. We find conditions under which a phase transition does not occur in the model. We show that if p | m + 1 for some J, then a phase transition occurs. Moreover, we formulate a criterion for the boundedness of p-adic Gibbs measures for the (m+1)-state SOS model.     

Chiral crystallization of cis-2,3-dichloro-buth-2-ene-1,4-diol

The X-ray diffraction study of cis-2,3-dichlorobuth-2-ene-1,4-diol (3) obtained by the reduction of 3,4-dichloro-5-ethoxy- and 5-isopropoxi-2(5H)-furanones with lithium aluminum hydride is performed. The crystals of compound 3 are trigonal: a = b = 15.746(9) Å, c = 6.848(4) Å; V = 1470.5(15) ų, space group P3₁, Z = 9 (three independent molecules). Independent molecules have identical planar conformation, and hydroxyl groups are located on different sides of the multiple bond plane. The supramolecular motif of the crystal is spirals about the threefold screw axes; the neighboring spirals are linked by OH…O hydrogen bonds.     

Computer simulation of the crystal structure of tetrazino-tetrazine tetraoxide (TTTO) isomers with one and two independent molecules in the unit cell

Russian Chemical Bulletin - The crystal structure prediction for two isomeric forms of tetrazino-tetrazine tetraoxide (TTTO), viz., [1,2,3,4]tetrazino[5,6-e][1,2,3,4]tetrazine 1,3,6,8-tetraoxide...     

New solutions in the technology of chlorine-free bleaching of cellulose

Sequence for hydrogen peroxide bleaching of sulfite cellulose without use of chlorine-containing compounds was developed. It is shown that alternation of acid and alkaline stages of bleaching leads to swelling or contraction of cellulose fibers, depending on the pH of the medium, and, accordingly, to a change of the microstructure of the fibers, and just this circumstance improves the bleaching efficiency. An important specific feature of the bleaching with hydrogen peroxide by the suggested technique, compared with the conventional methods using chlorine-containing reagents, is the mild oxidative effect on cellulose and substantial decrease in the mass fraction of tars and fats in cellulose, which favors practical solution of tar problems in paper industries.     

Crystal structures of mucochloric and mucobromic acids: pseudosymmetry,polymorphism, and intermolecular interactions

Russian Chemical Bulletin - The crystal structure of the known triclinic modification of mucochloric acid (MCA) was refined significantly, as well as its earlier unknown orthorhombic modification...     

Spectra of pressure relaxation times of polymer and copolymer melts and their practical use

The possibility of using pressure relaxation of melted polymers for the investigation of the structure of three types of polymers and their compositions and the analysis of the change of their molecular characteristics during aging is shown.Kazan State Technological University, Tatarstan, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 531–538, July–August, 1998.