Transferable potentials for phase equilibria. 7. Primary, secondary, and tertiary amines, nitroalkanes and nitrobenzene, nitriles, amides, pyridine, and pyrimidine

The transferable potentials for phase equilibria (TraPPE) force fields are extended to amine, nitro, nitrile, and amide functionalities and to pyridine and pyrimidine. In many cases, the same parameters for a functional group are used for both united-atom and explicit-hydrogen representations of alkyl tails. Following the TraPPE philosophy, the nonbonded interaction parameters were fitted to the vapor-liquid coexistence curves for selected one-component systems. Coupled-decoupled configurational-bias Monte Carlo simulations in the Gibbs ensemble were applied to neat (methyl-, dimethyl-, trimethyl-, ethyl-, diethyl-, or triethyl-)amine, nitromethane, nitroethane, nitrobenzene, acetonitrile, propionitrile, acetamide, propanamide, butanamide, pyridine, and pyrimidine. Excellent agreement with experimental results was found, with the mean unsigned errors being less than 1% for both the critical temperature and the normal boiling temperature. Similarly, the liquid densities at low reduced temperatures are reproduced to within 1%, and the deviation for the critical densities is about 4%. Additional simulations were performed for the binary mixtures of methylamine + n-hexane, diethyl ether + acetonitrile, 1-propanol + acetonitrile, and nitroethane + ethanol. With the exception of the methylamine/n-hexane mixture for which the separation factor is substantially overestimated, agreement with experiment for the other three mixtures is very satisfactory.     

Determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in Milk, Cheese and Chocolate

 Combined analytical procedures consisting of wet digestion step followed by instrumental determination – differential pulse cathodic stripping voltammetry (DPCSV) or electrothermal atomic absorption spectrometry (ETAAS) – as well as a direct analysis method – slurry sampling ETAAS – for the determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in milk, cheese and chocolate are described and compared. Wet digestion using a mixture of HNO₃-HClO₄-H₂O₂ is proposed for complete matrix decomposition prior to trace analyte determinati on by DPCSV or ETAAS. A mixture of HNO₃-H₂O₂ is used for slurry preparation. Optimal instrumental parameters for trace analyte measurements are presented. The reliability of the procedures has been verified by analyzing standard reference materials. Results obtained are in good agreement with the certified values and the relative standard deviations (for these results) are in the range 5–10% for wet digestion DPCSV or ETAAS and 3–9% for slurry sampling ETAAS in the range of 2 μgċg⁻¹ (Cd) to 12 μgċg⁻¹ (Fe). Received August 24, 1999. Revision January 20, 2000.     

Mild, powerful, and robust methods for esterification, amide formation, and thioesterification between acid chlorides and alcohols, amines, thiols, respectively

We developed two efficient practical methods for esterification, amide formation, and thioesterification between acid chlorides and alcohols, amines, thiols, respectively. The present mild and robust reaction was performed by two separate methods both by combining cheap and readily available amines, N-methylimidazole, and N,N,N′,N′-tetramethylethylenediamine (TMEDA). Method A uses catalytic N-methylimidazole and TMEDA with an equimolar amount of K₂CO₃, whereas Method B uses equimolar amounts of N-methylimidazole and TMEDA. The salient features are as follows. (i) With regard to reactivity, Method B was superior to Method A for esterification and thioesterification, whereas cost-effective Method A was superior to Method B for amide formation. (ii) Amide formation proceeded smoothly between acid chlorides and less nucleophilic and stereocongested amines such as 2,6-dichloroaniline. (iii) This protocol was applied to the successful synthesis of two agrochemicals, bromobutide and carpropamid.     

Intermetallic compounds of the heaviest elements and their homologs: the electronic structure and bonding of MM', where M=Ge, Sn, Pb, and element 114, and M'=Ni, Pd, Pt, Cu, Ag, Au, Sn, Pb, and element 114

Fully relativistic (four-component) density-functional theory calculations were performed for intermetallic dimers MM', where M=Ge, Sn, Pb, and element 114, and MM'=group 10 elements (Ni, Pd, and Pt) and group 11 elements (Cu, Ag, and Au). PbM and 114M, where M are group 14 elements, were also considered. The results have shown that trends in spectroscopic properties-atomization energies D(e), vibrational frequencies omega(e), and bond lengths R(e), as a function of MM', are similar for compounds of Ge, Sn, Pb, and element 114, except for D(e) of PbNi and 114Ni. They were shown to be determined by trends in the energies and space distribution of the valence ns(MM')atomic orbitals (AOs). According to the results, element 114 should form the weakest bonding with Ni and Ag, while the strongest with Pt due to the largest involvement of the 5d(Pt) AOs. In turn, trends in the spectroscopic properties of MM' as a function of M were shown to be determined by the behavior of the np(1/2)(M) AOs. Overall, D(e) of the element 114 dimers are about 1 eV smaller and R(e) are about 0.2 a.u. larger than those of the corresponding Pb compounds. Such a decrease in bonding of the element 114 dimers is caused by the large SO splitting of the 7p orbitals and a decreasing contribution of the relativistically stabilized 7p(1/2)(114) AO. On the basis of the calculated D(e) for the dimers, adsorption enthalpies of element 114 on the corresponding metal surfaces were estimated: They were shown to be about 100-150 kJ/mol smaller than those of Pb.     

Thermodynamics of water,vapor, ice,and seawater

The SCOR/IAPSO Working Group 127 was founded in 2005 and charged with the development of a new, comprehensive, highly accurate, and consistent standard formulation of seawater thermodynamics for oceanography. This task was approached in cooperation with the International Association for the Properties of Water and Steam (IAPWS) for a joint standard with industrial applications. In addition to the available standard for fluid water, IAPWS-95, new formulations for ice, IAPWS-06, and the thermodynamics of seawater, IAPWS-08, have been developed, supplemented by a redefinition of salinity, the Reference-Composition Salinity Scale 2008. In this paper the starting situation is described, the requirements to be met during the development process are studied, and the properties of the final formulations are briefly characterized.

Cubane, cuneane, and their carboxylates: a calorimetric, crystallographic, calculational, and conceptual coinvestigation

[reaction: see text] This study is a multinational, multidisciplinary contribution to the thermochemistry of dimethyl1,4-cubanedicarboxylate and the corresponding isomeric, cuneane derivative and provides both structural and thermochemical information regarding the rearrangement of dimethyl 1,4-cubanedicarboxylate to dimethyl 2,6-cuneanedicarboxylate. The enthalpies of formation in the condensed phase at T = 298.15 K of dimethyl 1,4-cubanedicarboxylate (dimethyl pentacyclo[4.2.0.0.(2,5)0.(3,8)0(4,7)]octane-1,4-dicarboxylate) and dimethyl 2,6-cuneanedicarboxylate (dimethyl pentacyclo[3.3.0.0.(2,4)0.(3,7)0(6,8)]octane-2,6-dicarboxylate) have been determined by combustion calorimetry, delta(f) H(o)m (cr)/kJ x mol(-1) = -232.62 +/- 5.84 and -413.02 +/- 5.16, respectively. The enthalpies of sublimation have been evaluated by combining vaporization enthalpies evaluated by correlation-gas chromatography and fusion enthalpies measured by differential scanning calorimetry and adjusted to T = 298.15 K, delta(cr) (g)Hm (298.15 K)/kJ x mol(-1) = 117.2 +/- 3.9 and 106.8 +/- 3.0, respectively. Combination of these two enthalpies resulted in delta(f) H(o)m (g., 298.15 K)/kJ x mol(-1) of -115.4 +/- 7.0 for dimethyl 1,4-cubanedicarboxylate and -306.2 +/- 6.0 for dimethyl 2,6-cuneanedicarboxylate. These measurements, accompanied by quantum chemical calculations, resulted in values of delta(f) Hm (g, 298.15 K) = 613.0 +/- 9.5 kJ x mol(-1) for cubane and 436.4 +/- 8.8 kJ x mol(-1) for cuneane. From these enthalpies of formation, strain enthalpies of 681.0 +/- 9.8 and 504.4 +/- 9.1 kJ x mol(-1) were calculated for cubane and cuneane by means of isodesmic reactions, respectively. Crystals of dimethyl 2,6-cuneanedicarboxylate are disordered; the substitution pattern and structure have been confirmed by determination of the X-ray crystal structure of the corresponding diacid.     

Co-precipitative pre-concentration with sodium diethyldithiocarbamate and ICP-AES determination of Se, Cu, Pb, Zn, Fe, Co, Ni, Mn, Cr and Cd in water

Sodium diethyldithiocarbamate in the presence of a weak oxidizing agent is used as a co-precipitative agent for the pre-concentration of Se, Cu, Pb, Zn, Fe, Co, Ni, Mn, Cr and Cd. A procedure was developed for ICP-AES determination of these elements after pre-concentration in river and waste water (an enrichment factor of 40). The recovery of all the elements tested for was more than 98%. The limits of determination (mg l⁻¹) (10 S.D. blank) are 0.001 (Cu, Co, Cr, Mn), 0.0007 (Zn, Cd), 0.003 (Se), 0.004 (Fe), 0.007 (Ni), and 0.01 (Pb).     

Electronic structure, spectra, and magnetic circular dichroism of cyclohexa-, cyclohepta-, and cyclooctapyrrole

Three recently obtained expanded porphyrins represent nice examples of compounds for which the electronic and spectral properties can be predicted from symmetry considerations alone. Perimeter-model-based theoretical analysis of the electronic structure of doubly protonated cyclo[6], cyclo[7], and cyclo[8]pyrrole leads to the anticipation of qualitatively the same electronic absorption and magnetic circular dichroism patterns for all three compounds. These predictions are fully confirmed by experiments, as well as DFT and INDO/S calculations. Due to a characteristic pattern of frontier molecular orbitals, a degenerate HOMO and a strongly split LUMO pair, the three cyclopyrroles show comparable absorption intensity in the Q and Soret regions. Magnetic circular dichroism spectra reveal both A and B Faraday terms, of which the signs and magnitudes are in remarkably good agreement with theoretical expectations. The values of the magnetic moments of the two lowest degenerate excited states have also been obtained.     

Polarization, steric, and focusing micro-thermal field-flow fractionation principles, theory, instrumentation, and applications in polymers and particles analysis

The benefits of the miniaturization of the separation channel for Thermal field-flow fractionation (TFFF) are analyzed theoretically and studied experimentally. It is found that the operational variables influencing the efficiency and resolution of the separation can be optimized and that the concept of a micro-TFFF is meaningful. A miniaturized TFFF channel was proposed and constructed. It has been demonstrated experimentally that micro-TFFF allows one to carry out high-performance separations under carefully chosen experimental conditions. This new technique is highly competitive in comparison with size-exclusion chromatography (SEC) of macromolecules with molar masses up to roughly one million gram per mole. However, the versatility of micro-TFFF is superior to SEC for macromolecules of ultra-high molar masses, as well as colloidal sub-micron, and micron-sized particles of synthetic, natural, or biological origin. The free choice of the carrier liquids without any modification of the separation system affords an advantage to micro-TFFF. The experimental implementation and application to polymer and particle analysis confirmed the potential of micro-TFFF.     

Transition-metal-free O-, S-, and N-arylation of alcohols, thiols, amides, amines, and related heterocycles

A new protocol for the Ullmann-type arylation process of different aromatic heterocycles without any transition-metal catalyst, implying the use of a combination of an excess of potassium hydroxide and dimethyl sulfoxide, is described. The reaction can be performed between a broad range of starting nucleophiles including phenol, alcohols, amines, nitrogen-containing five-membered systems such as pyrazoles, imidazoles, and indoles, and amides with haloarenes, iodide and bromide derivatives giving the best results, the possible pathway involving the in situ generation of the corresponding benzyne intermediate. When the reaction was performed with 2-iodoaniline and either carboxamides or isothiocyanato derivatives, the corresponding benzoazole derivatives were obtained.     

Enthalpies of formation, bond dissociation energies, and molecular structures of the n-aldehydes (acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal) and their radicals

Aldehydes are important intermediates and products in a variety of combustion and gas-phase oxidation processes, such as in low-temperature combustion, in the atmosphere, and in interstellar media. Despite their importance, the enthalpies of formation and bond dissociation energies (BDEs) for the aldehydes are not accurately known. We have determined enthalpies of formation for acetaldehyde, propanal, and butanal from thermodynamic cycles, using experimentally measured reaction and formation enthalpies. All enthalpy values used for reference molecules and reactions were first verified to be accurate to within around 1 kcal mol-1 using high-level ab initio calculations. Enthalpies of formation were found to be -39.72 +/- 0.16 kcal mol-1 for acetaldehyde, -45.18 +/- 1.1 kcal mol-1 for propanal, and -49.27 +/- 0.16 kcal mol-1 for butanal. Enthalpies of formation for these three aldehydes, as well as for pentanal, hexanal, and heptanal, were calculated using the G3, G3B3, and CBS-APNO theoretical methods, in conjunction with bond-isodesmic work reactions. On the basis of the results of our thermodynamic cycles, theoretical calculations using isodesmic work reactions, and existing experimental measurements, we suggest that the best available formation enthalpies for the aldehydes acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal are -39.72, -45.18, -50.0, -54.61, -59.37, and -64.2 kcal mol-1, respectively. Our calculations also identify that the literature enthalpy of formation of crotonaldehyde is in error by as much as 1 kcal mol-1, and we suggest a value of -25.1 kcal mol-1, which we calculate using isodesmic work reactions. Bond energies for each of the bonds in the aldehydes up to pentanal were calculated at the CBS-APNO level. Analysis of the BDEs reveals the R-CH(2)CH=O to be the weakest bond in all aldehydes larger than acetaldehyde, due to formation of the resonantly stabilized vinoxy radical (vinyloxy radical/formyl methyl radical). It is proposed that the vinoxy radical as well as the more commonly considered formyl and acetyl radicals are important products of aldehyde combustion and oxidation, and the reaction pathways of the vinoxy, formyl, and acetyl radicals are discussed. Group additivity values for the carbon-oxygen-hydrogen groups common to the aldehydes are also determined. Internal rotor profiles and electrostatic potential surfaces are used to study the dipole induced dipole-dipole interaction in the synperiplanar conformation of propanal. It is proposed that the loss of this dipole-dipole interaction in RC(.-)HCH(2)CH=O radicals causes a ca. 1-2 kcal mol-1 decrease in the aldehyde C-H and C-C bond energies corresponding to RC(.-)HCH(2)CH=O radical formation.     

Borinium, borenium, and boronium ions: synthesis, reactivity, and applications

Boron cations are elusive and highly electrophilic species that play a key role in the chemistry of boron. Despite early interest in the chemistry of boron cations, until recently they have largely remained chemical curiosities. However, hints at harnessing their potential as potent electrophiles have begun to appear and developments in weakly coordinating anion technology suggest that this is an area of research that is ripe for exploration. It has been nearly 20 years since the last major review on boron cations; herein we summarize the progress in the area since that time.     

Structure and properties of HOO,HOS, HSO,HSS, FSO,FOS and FSS

High quality SCF-MO calculations are reported for the title molecules, including geometry optimization. One-electron properties are presented and discussed, and relative stabilities of (HOS, HSO) and (FOS, FSO) compared. Little experimental geometric data are available at present, but the calculated and experimental geometries of HO₂ agree well.     

Periodicity, visualization, and design

This paper explores the development of the chemical table as a tool designed for chemical information visualization. It uses a historical context to investigate the purpose of chemical tables and charts, analyzing them from the perspective of theory of tables, cartography, and design. It suggests reasons why the two-dimensional periodic table remains the de facto standard for chemical information display.     

Synthesis, photophysical, electrochemical, and electrogenerated chemiluminescence studies. Multiple sequential electron transfers in BODIPY monomers, dimers, trimers, and polymer

Synthesis of the C(8) BODIPY monomers, dimers, and trimers, a C(8) polymer, and N(8) aza-BODIPY monomer and dimer was carried out. Methyl and mesityl C(8)-substituted monomers, dimers, and trimers were used. Dimers, trimers, and polymer were formed chemically through the β-β (2/6) positions by oxidative coupling using FeCl(3). A red shift of the absorbance and fluorescence is observed with addition of monomer units from monomer to polymer for C(8) dyes. The aza-BODIPY dye shows red-shifted absorbance and fluorescence compared with the C(8) analogue. Cyclic voltammetry shows one, two, and three one-electron waves on both reduction and oxidation for the monomer, dimer, and trimer, respectively, for the C(8) BODIPYs. The separation for the reduction peaks for the C(8) dimers is 0.12 V compared with 0.22 V for the oxidation, while the trimers show separations of 0.09 V between reduction peaks and 0.13 V for oxidation peaks. The larger separations between the second and third peaks, 0.25 V for the oxidation and 0.2 V for the reduction, are consistent with a larger energy to remove or add a third electron compared with the second one. The BODIPY polymer shows the presence of many sequential one-electron waves with a small separation. These results provide evidence for significant electronic interactions between different monomer units. The aza-BODIPY dye shows a reduction peak 0.8 V more positive compared to the C(8) compound. Aza-BODIPY dimer shows the appearance of four waves in dichloromethane. The separation between two consecutive waves is around 0.12 V for reduction compared with 0.2 V for oxidation, which is comparable with the results for the C(8) dyes. Electrogenerated chemiluminescence (ECL) of the different species was obtained, including weak ECL of the polymer.     

Structural, magnetic, and spectroscopic studies of YAgSn, TmAgSn, and LuAgSn

The rare earth-silver-stannides YAgSn, TmAgSn, and LuAgSn were synthesized from the elements by arc-melting and subsequent annealing. The three stannides were investigated by X-ray powder and single-crystal diffraction: NdPtSb type, P6₃mc, Z=2, a=468.3(1), pm, wR₂=0.0343, 353 F² values, 12 variables for YAgSn, and ZrNiAl type, P6¯2 m, a=726.4(2), , wR₂=0.0399, 659 F² values, 15 variables for TmAgSn, and a=723.8(2), , wR₂=0.0674, 364 F² values, 15 variables for LuAgSn. Besides conventional laboratory X-ray data with monochromatized Mo radiation, the structures were also refined on the basis of synchrotron data with , in order to clarify the silver-tin ordering more precisely. YAgSn has puckered, two-dimensional [AgSn] networks with Ag-Sn distances of 278 pm, while the [AgSn] networks of TmAgSn and LuAgSn are three-dimensional with Ag-Sn distances of 279 and 284 pm for LuAgSn. Susceptibility measurements indicate Pauli paramagnetism for YAgSn and LuAgSn. TmAgSn is a Curie-Weiss paramagnet with an experimental magnetic moment of 7.2 μ_B/Tm. No magnetic ordering is evident down to 2 K. The local environments of the tin sites in these compounds were characterized by ¹¹⁹Sn Mössbauer spectroscopy and solid-state NMR (in YAgSn and LuAgSn), confirming the tin site multiplicities proposed from the structure solutions and the absence of Sn/Ag site disordering. Mössbauer quadrupolar splittings were found in good agreement with calculated electric field gradients predicted quantum chemically by the WIEN2k code. Furthermore, an excellent correlation was found between experimental ¹¹⁹Sn nuclear magnetic shielding anisotropies (determined via MAS-NMR) and calculated electric field gradients. Electronic structure calculations predict metallic properties with strong Ag-Sn bonds and also significant Ag-Ag bonding in LuAgSn.     

Determination of Lead,Copper, and Iron in Cosmetics,Water, Soil,and Food Using Polyhydroxybutyrate-B-polydimethyl Siloxane Preconcentration and Flame Atomic Absorption Spectrometry

A separation and preconcentration method has been established based on solid phase extraction of Fe(III), Cu(II) and Pb(II) as their 2-(5-Bromo-2-pyridylazo)-5-diethylamino-phenol (5-Br-PADAP) chelates adsorbed on polyhydroxybutyrate-b-polydimethyl siloxane. Several analytical conditions including pH, amount of (5-Br-PADAP), eluent type and volume, sample volume, and flow rates were investigated. The effects of foreign ions on the recovery of the analytes were also studied. The detection limits for Cu(II), Fe(III), and Pb(II) were 1.9, 2.2, and 2.5 µg per liter, respectively. Enrichment factors for Cu(II), Fe(III), and Pb(II) were 150, 200, and 80, respectively. The adsorption capacity of the polymer for Cu(II) and Pb(II) studied was 10.2 and 17.2 milligrams per gram respectively. Relative standard deviation was 4%. Standard Reference Material (SRM 1577B Bovine liver), International Atomic Energy Agency (IAEA 336 Lichen), and Certified Reference Waters for Trace Elements (TMDA 51.3 Fortified lake water) were used for the validation of the method. Optimized procedure was applied for the determination of analyte elements in various cosmetic products, hair brilliantine and gel, water, soil, and food samples from Turkey.     

Rearrangements and interconversions of heteroatom-substituted isocyanates, isothiocyanates, nitrile oxides, and nitrile sulfides, RX-NCY and RY-CNX

Isocyanates and isothiocyanates of the type RX-NCY (X and Y = O or S) and the isomeric nitrile oxides and nitrile sulfides RY-CNX are highly reactive compounds. A number of potential 1,4-shifts of substituent groups of the type R-Y-CNX → R-X-N═C═Y, 1,3-shifts R-C(═Y)-N═X → R-X-N═C═Y, and 1,2-shifts R-C(═Y)-N═X → R-Y-CNX have been evaluated computationally. The results obtained for the relatively new functional MPW1K and the well-established B3LYP, together with a triple-ζ quality basis set, are very similar. The 1,3- and 1,4-halogen shifts in the title compounds are usually highly exothermic and possess low activation barriers. 1,3-Aryl shifts are feasible for for 5e → 6e (Ar-CO-NSO(2) → Ar-SO(2)-NCO) with activation barriers of less than 40 kcal/mol. Additionally, several 1,3- and 1,4-hydrogen shifts and the 1,4-methyl-shift in methoxynitrile sulfide MeO-CNS to methylsulfenyl isocyanate MeS-NCO (4c → 6c) are potentially feasible. The 1,2-shift reactions 4b → 5b (HO-NCS → H-CS-NO) and 4c → 5c (Ar-O-CNS→ Ar-CO-NS) are good candidates for experimental observation with activation energies around 30 kcal/mol.