A quantum-chemical study of alternative chlorotropic isomerization mechanisms for bis(diethylamino)-chlorophosphonium methylide

The MNDO-PM3 method has been used in the supermolecular approximation to examine alternative mechanisms for the chlorotropic isomerization of unsolvated bis(diethylamino)chlorophosphonium methylide and solvated forms of it containing chloroform of 1∶1 and 1∶2 compositions. It is shown that the most favorable channel for the chlorotropic rearrangement of unsolvated P-chloroylide corresponds to the sigmatropic mechanism. There are effects from specific interactions with the chloroform that make themselves felt in the preferential chlorotropic transformation of the isomers by the dissociation-recombination mechanism, whose activation energy E_1∶2 ^≠=kcal/mol is comparable with the observed activation barrier for the 1,2-shift of the chlorine atom in the related P-chloroylide. Institute for Bioorganic Chemistry and Petroleum Chemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya ul., Kiev 253094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 215–221, July–August, 1999.     

The chlorotropic isomerization mechanism for amidinium tetrachlorophosphorates

MNDO-PM3 quantum-chemical calculations have been combined with³⁵Cl NQR spectroscopy in research on the thermodynamic and kinetic stability of chlorotropic isomers in the Cl₄P(NCH₃)₂CR amidinium tetrachlorophosphorate series, in which R=C₆H₅, CCl₃, CF₃, Cl; the relative thermodynamic stability of the phosphorate P^VI isomer is higher than that of the phosphetidine P^V one and has a minimum in the series for the CF₃ derivative. The chlorotropic P→C transformation of the isomeric forms of the amidinium tetrachlorophosphorates occurs in liquid solutions and in melts by an intramolecular sigmatropic mechanism, not by the formation of a contact ion pair. Institute of Bioorganic Chemistry and Petroleum Chemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya ul., Kiev 253094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 3, pp. 155–161, May–June, 1999.     

Peculiarities of the mechanism of chlorotropic and conformational isomerism in a series of chloromethyl isocyanates

The thermodynamic and kinetic stability of chlorotropic isomers in a series of chloromethyl isocyanates Cl_3−nH_nC−N=C=O, where n=0, 1, 2, has been shown by quantum chemical calculations, using the MNDO method, and by³⁵Cl NQR spectroscopy. The phase transformations of two polymorphic modifications of N-chlorocarbonyl dichloride, which is a stable iminocarbonyl form of trichloromethyl isocyanate with small conformational activation barriers, have been studied. Institute of Bioorganic and Petrochemistry, National Academy of Sciences of Ukraine, 1 Murmansk ul., Kiev-94 252660, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 164–169, May–June, 1998.     

Reactivity of macroheterocycles with respect to sulfamic acid

It has been established, on the basis of the formation of a 1∶1∶1 inclusion compound of 18,19-benz-1,16-diaza-4,7,10,13-tetraoxoeicosa-17,20-dione with sulfamic acid and water from the interaction of 11–20-membered macrocyclic oxyethyleneamides of phthalic acid with sulfamic acid, that 18–20-membered oxyethylene macrocycles containing six oxygen donor atoms in the macrocycle are effective in the formation of “host-guest” complexes. Physicochemical Institute for the Preservation of the Environment and Mankind, Ministry of Education and Ukraine National Academy of Sciences of Ukraine, Odessa 270100. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1571–1573 November, 1997.     

Conformational Isomerism and Chlorotropy Mechanisms of Chloromethyl- and Trichloromethyldichlorophosphines

³⁵Cl NQR spectroscopy and MP2//RHF/6-31⁺⁺G(d,p) and MNDO-PM3 calculations were used to study the conformational and chlorotropic isomerism of chlorodimethyldichlorophosphine (I) and trichloromethyldichlorophosphine (II). The experimental ³⁵Cl NQR spectrum is in complete accord with the staggered conformation of phosphine II obtained using an RHF/6-31⁺⁺G(d,p) calculation. The rotational barrier of the CCl₃ group is 38.1 kJ/mol. On the other hand, the spectrum of phosphine I is in accord with a gauche conformation, which agrees with experiment only upon taking account of electron correlation (MP2). The ylide and phosphinic chlorotropic isomers for I and II are thermodynamically stable with greater stability found for II. The chlorotropic phosphine–ylide conversion in system I proceeds exclusively through a sigmatropic transition state in qualitative accord with nonempirical and semiempirical calculations. Such a conversion is theoretically possible in system II by means of dissociation of the P⁺—C^– ylide bond.     

Influence of hydrothermal treatment conditions on the formation and breakdown of phosphates with zeolitic structure

In a study of certain features of the formation and breakdown of phosphates with zeolitic structure, manifested when the reaction mixtures and detemplated products are subjected to various schedules of heating, cooling, and holding at constant temperature, it has been shown that these features are related to a change in coordination state of the aluminum atoms in the presence of water molecules and to the transition of the aluminum atoms into an octahedral environment, with subsequent hydrolysis and breakdown. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Nauka Prospect, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 3, pp. 170–174, May–June, 1997.     

Specific Features of Chlorotropism in the ENC Triad (E = PIV-PVI,C) of High-Coordination Phosphorus Chlorides and Trichloromethyl Isocyanate

The semiempirical MNDO method and its parametrized PM3 version in supermolecular approximation was used for a comparative study of the structure and alternative mechanisms of chlorotropism in the ENC triad (E = P^{I V - V I}, C) of amidinium tetrachlorophosphorate Cl₄P(NCH₃)₂CCCl₃ (I), phosphazopentachloroethane Cl₅C₂NPO₂C₆H₄, (II), trichloromethyl isocyanate Cl₃CNCO (III), and their 1:2 chloroform solvates. The absence of the thermodynamically stable intermediate as a separated ion pair in the chlorotropic transformations of structures I, III and the high enthalpy of the substrate-intermediate transformation for structure II show that the sigmatropic mechanism of chlorotropism in compounds under study is the only probable one. The activation barrier of chlorotropism in phosphorus systems I, II is much reduced. In the case of specific solvation, a weak tendency to further reduction of the activation barrier for structures I-III is observed, and the equilibrium for phosphorus systems I, II, is appreciably shifted, unlike system III, where, according to experimental data, the equilibrium is fully to the side of the carbamoyl isomer Cl₂C = NC(O)Cl.     

The effect of nitrogen in the carbon matrix on the donor-acceptor and catalytic activity of activated carbons in electron transfer reactions

The effect of the position of the nitrogen atoms in the π-conjugated system of condensed rings on the width of the forbidden band of carbon as a semiconductor was investigated by the semiempirical AM1 molecular orbital method. A correlation was found between the position of the nitrogen atoms in nitrogen-containing carbon, the catalytic activity in electron transfer reactions, and the width of the forbidden band of such semiconductors. Institute of Sorption and Problems of Endoecology, National Academy of Sciences of Ukraine, 13 Generala Naumova ul., Kiev 252680, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 6, pp. 338–342, November–December, 1999.     

Morpholine adducts of Co, Ni, and Mn benzoylacetonates: isostructurality and C–H···O hydrogen bonding

Morpholine adducts of nickel(II), cobalt(II), and manganese(II) benzoylacetonates, as well as a morpholine solvate of manganese(II) benzoylacetonate, were prepared and characterized by X-ray diffraction and thermal analysis. All four compounds crystallize in the P2₁/c space group with two complex molecules per unit cell. The morpholine solvate, along with the two adduct molecules, also contains four solvent morpholine molecules in the unit cell. The non-solvate compounds are isostructural, with crystal structures comprising 2D networks formed by C–H···O hydrogen bonding between phenyl rings and morpholine oxygen atoms. The topology of these networks can be described as intersecting C₂²(24) chains forming R₄⁴(48) rings. Networks with the same topology are also present in the solvate, but they are heavily distorted due to the presence of solvent morpholine molecules. Thermogravimetric analysis shows similar behavior of the non-solvate compounds upon thermal decomposition, with three degradation steps which can be related to gradual loss of morpholine molecules and subsequent overall decomposition. Decomposition of the solvate also proceeds in several steps, the first of which can be related to loss of solvent morpholine molecules and the further steps are analogous to those in the non-solvate compounds.     

P(IV)-P(V) Coordinational Isomerism of Phosphorus N-α-Haloethylimines

The semiempirical MNDO-PM3 method in supramolecular approximation was used to study the structure of (N--haloethylimino)chloro(o-phenylenedioxy)phosphoranes R¹ ₃CR²X-N-P(Cl)O₂C₆H₂(R³-m)₂, where R¹ = H, Cl, F, R² = R³ = H, Cl, and X = F, Cl, Br, and of their 1:2 solvates with chloroform, as well as alternative mechanisms of the P(IV)-P(V) holotropic rearrangement. It was found that the activation barrier of the sigmatropic rearrangement increases in the order Br < Cl < F, in parallel with increasing thermodynamic stability of a more stable phosphorane isomer with an axial-equatorial arrangement of the dioxaphos- phole ring. It was shown that the most favorable pathway of the phosphorus-carbon halotropic rearrangement of a phosphorus N--haloethylimine, both nonsolvated and solvated with two molecules of chloroform, is the sigmatropic transformation.     

Sorption of heavy-metal ions and radioactive cesium by “Ultrasorb” composite sorbent

Data are given on the sorption of heavy-metal ions (Fe³⁺, Co²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cu²⁺ and Ni²⁺) and radioactive isotope¹³⁷Cs from Ringer salt solution by Ultrasorb composite sorbent, which has two components: the modified clay mineral palygorskite (palygorskite-M) and a modified fibrous carbon sorbent of AUT-M type (UVM-Ts). Selectivity series have been determined for the sorption of these toxic metals on the basis of the calculated distribution coefficients K_d under standard conditions. It is shown that the properties of the components combine well in the material, and it is proposed for use as a treatment agent (enterosorbent) having a selective action in the treatment of diseases due to the accumulation of heavy metals and radionuclides in the body. Institute for Sorption and Endoecological Problems, National Academy of Sciences of Ukraine, 13 ul. Generala Naumova, Kiev 03164, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 1, pp. 53–57, January–February, 2000.     

Hydro­gen bonding in bis­(tri­phenyl­phosphine‐P)­iminium hydrogen­sulfate chloro­form solvate

The title compound, C₃₆H₃₀NP₂⁺·HSO₄^?·CHCl₃, consists of discrete ions and well separated chloroform solvate molecules. The central feature of the structure is O—H?O hydrogen bonding between two hydrogensulfate ions related by a crystallographic inversion centre. The chloroform solvate molecule takes part in a well defined C—H?O hydrogen bond.     

Atomic ordering in CuGeO3 during the spin-Peierls transition: Calculation of63Cu NQR frequencies

The X_α discrete variation (X_α-DV) method is used to calculate the electronic structures of the clusters modeling the spin-Peierls transition in CuGeO₃. The⁶³Cu NQR frequencies of two centers that fall within the simulated supercell are calculated. It is shown that the nature of the forbidden gap and the⁶³Cu NQR spectral parameters depend on the motion of copper atoms in the chains. Some assumptions are made to explain the fact that dimerization in chains of Cu atoms is experimentally unobservable. Translated from Zhurnal Strukturnoi Khimii, Vol. 38, No. 1, pp. 43–50, January–February, 1997.     

Crystallization kinetics of zeolite-like phosphates AIPO4-5 and SAPO-5

We show that the crystallization rate of isostructural zeolite-like phosphates AlPO₄-5 and SAPO-5 is considerably higher than for zeolites and polysilicates. We analyze the kinetic and energy parameters, taking into account the high structural lability of aluminophosphates, the effect of limiting processes of dissolution of the original pseudoboehmite and conversion of the intermediates, and also isomorphic inclusion of silicon atoms. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Nauki Prospekt, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 3, pp. 184–187. May–June, 1997.     

Halogenotropy in the CNC Triad of Trihalomethyl Isocyanates and Conformational Lability of Their Iminocarbonyl Isomers

According to the MNDO calculations, halotropic transformation of trihalomethyl isocyanates X₃CNCO (X = F, Cl, Br) follows sigmatropic mechanism with formation of a contact ion pair. In keeping with the experimental data, the isocyanate structure of the fluorine derivative and carbamoyl structure of the chlorine and bromine analogs are determined by the relative stabilities of isomeric forms. Specific solvation gives rise to a weak tendency to reduction of the activation energy of chlorotropy and leveling of the stability of chlorotropic isomers.     

Solvent-induced allylic rearrangements in poly(trichlorobutadiene) chains

It was established by Fourier-transform IR and¹H NMR spectroscopy that a portion of the units of poly(1,1,2- and 1,2,3-trichlorobuta-1,3-diene) chains rearrange with migration of the allylic chlorine (1–4%) and allylic hydrogen (3–10%) under the influence of chloroform. Rearrangement with the migration of hydrogen under the influence of CDCl₃, CCl₄, and THF was also observed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 763–768, April, 1997.     

Role of dimethylformamide in generating the active form of platinum for catalyzing the synthesis of diaryls from aryl iodides

A mechanism is proposed for the reaction of aryl iodides with platinum(II) tetrachloride complexes in dimethylformamide including formation of PtCl₃(CONMe₂)²⁻ in the first step through activation of a dimethylformamide C−H bond by platinum(II) and subsequent oxidative addition of ArI to this species. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 4, pp. 244–246, July–August, 1998.     

Selenomethionine content of candidate reference materials

Selenium has been identified as an antioxidant of importance in the diet. Accurate determination of its chemical forms depends on the availability of suitable reference materials (RMs). Two candidate reference materials for determination of selenomethionine (Semet) in food-related materials, a standard wheat gluten sample (NIST RM 8418 Wheat Gluten) and a commercial selenium enriched yeast, have been examined by use of a gas chromatography–isotope dilution mass spectrometry (IDMS) procedure, after treatment of the matrix with 0.1 mol L^–1 hydrochloric acid containing stannous chloride, addition of CNBr, and extraction with chloroform. This procedure results in cleavage of the CH₃Se group to form volatile CH₃SeCN. Addition of isotopically enriched ⁷⁴Semet to an analytical sample enables estimation of the naturally occurring protein-bound ⁸⁰Semet by IDMS without a protein-digestion process. We found that the Wheat Gluten RM contains a significant amount of Semet as a portion of its assigned value of 2.58 μg Se_total g^–1. Commercial selenium yeast tablets are labeled as containing an elevated level of “organic selenium”, usually as Semet. The sample we investigated contained 210 μg Se_total g^–1 sample as determined separately by IDMS, measuring elemental selenium after digestion. 73% of this total (153±21 μg Se_Semet g^–1; n = 23) was present as Semet. Thus, these two materials contain significant amounts of their total selenium content as Semet and would be good candidates for further study and characterization as reference materials for determining this important food component. The CNBr reaction used will also enable the determination of Se-(methyl)selenocysteine, the biological role of which is of recent interest. In addition to matrix RMs for Semet, it is important to have standard materials of the pure substance. We have examined a sample of a candidate standard material of selenomethionine being prepared by the USP. It was confirmed that this material is pure selenomethionine. Received: 13 December 2000 / Revised: 5 March 2001 / Accepted: 12 March 2001     

Degradation of an ether–alcohol (3-ethoxypropan-1-ol) by photo-Fenton-generated <Superscript>•</Superscript>OH radicals: products analysis and formation pathways; relevance to atmospheric water-phase chemistry

We have chosen 3-ethoxypropan-1-ol (EtOPrOH) as a typical short-carbon-chain ether–alcohol used as industrial solvent and have analyzed the degradation products resulting from its attack by ^•OH radicals generated by the photo-Fenton reaction. The laboratory conditions were representative of those found in tropospheric water droplets. Twelve products have been identified by use of GC–MS analysis, either directly or after extraction by SPME fibers, and by HPLC–UV analysis with a special column for carboxylic acids and after reaction of carbonyl groups with 2,4-dinitrophenylhydrazine. These products contain one to three carbon atoms (instead of five in EtOPrOH), among which one or two are oxidized. According to the reaction pathways proposed, seven products—including methanal—can result from attack by one ^•OH only, three products imply attack by a second ^•OH, as expected from their higher oxidation number, and it is suggested that reaction between two organic radicals is needed for formation of only two products. The relevance of this investigation to the fate of EtOPrOH and similar ether–alcohols in the troposphere is briefly discussed.     

Quantity of sorbed ions and forms of their binding to carbon surface as factors influencing catalytic activity in esterification and hydrolysis reactions

Results are summarized and correlated from studies of how the quantity and nature of sorbed ions and the forms of their binding with the surface of carbon materials (CM) differing in structure and origin will influence the catalytic activity in acid-type reactions. It has been shown that of all of the methods of incorporating metals into the CM surface, the most effective is the ion-exchange modification. It is suggested that the mechanisms of catalysis of protolytic reactions by various ion-exchanged forms of CM are all quite similar. “Sonar” Scientific and Engineering-Technological Center of Biotechnical Systems, National Academy of Sciences of Ukraine, 52/2 Victory Prospect, Kiev 252057, Ukraine. Affiliation of second author: Institute of Sorption and Problems in Endoecology, National Academy of Sciences of Ukraine, 32/34 Academician Palladin Prospect, Kiev-142 252680, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 3, pp. 175–179, May–June, 1997.