Combination of microwave heating extraction and dispersive liquid-liquid microextraction for the determination of nitrosoamines in foods using gas-liquid chromatography with a mass-spectrometric detector

A method has been developed for the determination of trace amounts of seven nitrosoamines (N-nitrosodimethylamine, N-nitrosomethylethylamine, N-nitrosodiethylamine, N-nitrosopyrrolidine, N-nitrosodipropylamine, N-nitrosopiperidine, and N-nitrosodibutylamine) in food using gas-liquid chromatography with a mass-spectrometric detector. The optimum chromatographic conditions were selected: a DB-5MS column, temperature ramp rate 10 K/min from 40 to 250°C, carrier gas flow rate 1 mL/min. Conditions of the extraction of nitrosoamines from samples using microwave heating extraction followed by dispersive liquid-liquid microextraction, ensuring sufficient preconcentration and additional purification of the extract, have been optimized. The linearity ranges for nitrosoamines were (0.5–2.5)–25 µg/kg; the limits of detection were 0.1–0.5 µg/kg (signal-tonoise ratio 3). The method has been applied to the analysis of samples of sausage, smoked chicken meat, and smoked pork. The time of analysis is 1.5–2 h, the relative standard deviation of the results of analysis does not exceed 10%.     

Thermodynamics of the dissociation of aminomethanesulfonic acid and its <Emphasis Type="Italic">N</Emphasis>-substituted derivatives in aqueous solutions at 293–313 K

ΔG, ΔH, and ΔS of the second dissociation step of aminomethanesulfonic acid and its N-methyl, N-hydroxyethyl, N-(tert-butyl), N-benzyl derivatives in aqueous solutions (at the isoelectric point where the ionic strength is 4.75 × 10^–4 М) are determined on basis of pH measurements at 293–313 K. It is found that an increase of the electron-acceptor properties of the substituents at nitrogen atom reduces the effect temperature has on the thermodynamic functions of dissociation. Enthalpy–enthropy compensation at an isothermodynamic temperature of 303 K is recorded.     

Enantioselective hydrogen transfer hydrogenation on rhodium colloid systems with optically active stabilizers

Hydrogen transfer hydrogenation of acetophenone and methyl benzoylformate with 2-propanol was studied on colloidal systems obtained by reduction of rhodium complexes in the presence of optically active compounds: chiral diamines, quaternary salt (4S,5S)-(–)-N¹,N⁴-dibenzylene-2,3-dihydroxy-N¹,N¹,N⁴,N⁴-tetramethylbutane-1,4-diammonium dichloride and (8S,9R)-(–)-cinchonidine. The increase in the molar ratio modifier/Rh leads to the increase in the enantioneric excess (ee) of the reaction products. The largest ee [43.8% of (R)-1-phenylethanol and 58.2% of methyl ester of (R)-mandelic acid] were achieved for the ratios (8S,9R)-(–)-cinchonadine: Rh = 9: 1 and 3: 1, respectively. The catalyst was characterized by the high-resolution transmission electron microscopy, X-ray diffraction analysis, and thermal analysis.     

3-(1-Methyl-1-nitroethyl-1-<Emphasis Type="Italic">ONN</Emphasis>-azoxy)-4-aminofuroxan. Synthesis and transformations of the amino group

A four-step procedure to convert 4-(1-methyl-1-nitroethyl-1-ONN-azoxy)-3-cyanofuroxan into 3-(1-methyl-1-nitroethyl-1-ONN-azoxy)-4-aminofuroxan was developed. The pathways of transformation of the amino group of the synthesized compound into N-nitramino-, N-alkyl-N-nitramino-, N,N’-methylenediamino-, N,N’-methylene-N,N’-dinitramino-, and azo groups were studied.     

1,3-Dipolar cycloaddition of 3-phenylamino-5-phenylimino-1,2,4-dithiazole to 1-acyl-2-phenylacetylenes—A new route to functionalized 1,3-thiazole derivatives

3-Phenylamino-5-phenylimino-1,2,4-dithiazole reacted with 1-acyl-2-phenylacetylenes in ethanol or toluene on heating (78–80°C, 1 h) in chemo- and regioselective fashion to give previously unknown N-[5-acyl-3,4-diphenyl-1,3-thiazol-2(3H)-ylidene]-N′-phenylthioureas (yield 57–60%). The structure of N-[5-benzoyl-3,4-diphenyl-1,3-thiazol-2(3H)-ylidene]-N′-phenylthiourea was proved by X-ray analysis.     

Effect of solvent nature on the photoreduction kinetics of substituted benzoquinones

Effect of the solvent nature on the kinetics of photoreduction of substituted benzoquinones in the presence of hydrogen donors has been studied. It has been found that the effective photoreduction rate constant (k_H) for quinones decreases with an increase in solvent polarity. For the 3,6-di-tert-butylbenzoquinone–1,2-N,N-dimethylaniline pair, the dependence of ln k_H on the difference of the reciprocals of optical and static solvent permitivities (1/ε _∞–1/ε₀) is stepwise with a break point corresponding to CH₂Cl₂. A similar relationship lnk_H = f(1/ε _∞–1/ε₀) is observed for the p-chloranil–mesitylene pair. In the study of the photoreduction kinetics for a series of seven o-benzoquinones in the presence of p-derivatives of N,N-dimethylaniline in CH₂Cl₂, it has been found that the dependence of k_H on the free energy of electron transfer (ΔG_e) has a maximum for the 3,6-di-tert-butylquinone-1,2–N,N-dimethylaniline pair at ΔG_e = 0.11 eV.     

Rearrangements of <Emphasis Type="Italic">N</Emphasis>-ethoxycarbonylmethyl-1,2,3,4-tetrahydroquinolinium halogenalkylates effected by sodium hydride. Synthesis of 2,3,4,5-tetrahydro-1<Emphasis Type="Italic">H</Emphasis>-3-benzazepines

Quaternary salts obtained from N-alkyl-1,2,3,4-tetrahydroisoquinolines and ethyl haloacetates or diethyl bromomalonate under the action of sodium hydride in boiling 1,4-dioxane were converted into N-alkyl-N-ethoxycarbonyl-2,3,4,5-tetrahydro-1H-3-benzazepines in 49–60% yield. From the reaction mixture by column chromatography products of β-elimination by Hofmann reaction, 2-(N-methyl-N-ethoxycarbonylmethyl)-aminomethylstyrenes were also isolated (yield 0.6–16%).     

Reaction of <Emphasis Type="Italic">N</Emphasis>-chloroamines with carbanions derived from ethyl acetoacetate and diethyl malonate

Carbanions derived from ethyl 3-oxobutanoate and diethyl malonate reacted with an equimolar amount of N-chloro-N-ethylethanamine, N-chloromorpholine, or N-chloropiperidine to give diethyl 2,3-diacetylbutanedioate and tetraethyl ethane-1,1,2,2-tetracarboxylate in 68–83% yield. The possibility of heterocoupling of ethyl 3-oxobutanoate and diethyl malonate carbanions by the action of N-chloro-N-ethylethanamine and the effect of the molar reactant ratio on the selectivity of oxidative homo- and heterocoupling were studied.     

<Emphasis Type="Italic">N</Emphasis>′-tetrazolylmethoxyl derivatives of <Emphasis Type="Italic">N</Emphasis>-methyldiazene <Emphasis Type="Italic">N</Emphasis>-oxides

A preparation method was developed for previously unknown tetrazole derivatives containing in the 1, 2, and/or 5 positions of the tetrazole ring N-methyldiazene-N-oxide-N′-oxymethyl groups.     

Solubility enhancement of phenanthrene using novel chelating surfactant

A novel chelating surfactant denoted as sodium N-lauroyl ethylenediamine triacetate (N-LED3A) with both surface activity and chelation functions was studied for phenanthrene (PHE) solubilisation ability. The critical micelle concentration (CMC) of N-LED3A was measured, and the effects of the initial N-LED3A concentration, temperature, pH value and coexisting ions (Na⁺, Ca²⁺ and Cu²⁺) on PHE solubilisation by N-LED3A were investigated. The results demonstrated that PHE solubility was efficiently enhanced by N-LED3A, especially with N-LED3A concentrations above the CMC, which was 707 mg L^?1 when measured at 25°C. The temperature influenced the apparent PHE solubility slightly and the apparent solubility of PHE was significantly affected by the pH. Na and Ca were shown to increase the PHE solubility, while Ca exhibited a better promoting ability than Na⁺. A suitable quantity of Cu could significantly enhance the solubilisation capacities of N-LED3A at pH 5. The mechanism of the interaction between Cu⁺ and N-LED3A was further confirmed by Fourier transform infrared spectroscopy (FTIR). These results reveal that Cu²⁺ can be chelated with N-LED3A to form a chelate complex. The results implied that N-LED3A had the potential to remediate soils contaminated by both organics and heavy metals.     

Ultrafiltration membranes based on interpolyelectrolyte complexes: Adsorption and mass-exchange properties

Ultrafiltration membranes based on interpolyelectrolyte complexes of a sulfonated aromatic copolyamide, an acrylonitrile–N,N-dimethyl-N,N-diallylammonium chloride copolymer, and poly-N,N-dimethyl-N,N-diallylammonium chloride were prepared. The adsorption (in batch experiments and under conditions of ultrafiltration of myoglobin, lysozyme, and bovine serum albumin solutions) and mass-exchange properties of the membranes were studied. Correlation between the procedure for performing the interpolymer reaction, the composition of the complexes formed, and the characteristics of the membranes prepared was found. The protein/membrane interaction in the system studied is mainly due to Coulomb forces. The effect of the protein adsorption on the separation and transport properties of the membranes was considered. The general level of the mass-exchange properties of the membranes based on the interpolyelectrolyte complexes is higher compared to the samples containing ionic groups of like charge.     

Free-Radical Co-Oligomerization of <Emphasis Type="Italic">N</Emphasis>-Vinylpyrroles with <Emphasis Type="Italic">N</Emphasis>-Vinylpyrrolidone: A Route to New Bioactive Oligomers

Co-oligomerization of N-vinylpyrroles (N-vinyl-2,3-dimethylpyrrole, N-vinyl-2-phenylpyrrole, N-vinyl-2,3-diphenylpyrrole, N-vinyl-2-(2-thienyl)pyrrole, and N-vinyl-2-[1-(4,5,6,7-tetrahydroindolyl) ethyl]-4,5,6,7-tetrahydroidole) with N-vinylpyrrolidone in the presence of a radical initiator (AIBN) gives co-oligomers with molecular masses of 1600–5200 in up to 87% yield. The products are readily soluble in organic solvents (benzene, 1,4_dioxane, and chloroform), and in the case of high N-vinylpyrrolidone content, also in ethanol and in water. The co-oligomers are non-toxic or have low toxicity (the lethal dose LD₅₀ = 1300–2000) and possess biological activity.     

Quantitative analysis of amphiphilic <Emphasis Type="Italic">N</Emphasis>-alkyloxypyridinecarboximidamide by liquid chromatography–tandem mass spectrometry

LC–MS/MS method to determine hydrophobic N-alkyloxy substituted amidines: N-(2-ethylhexyloxy)pyridine-2-carboximidamide, N-(2-ethylhexyloxy)pyridine-3-carboximidamide, N-(2-ethylhexyloxy)pyridine-4-carboximidamide, N-decyloxy pyridine-2-carboximidamide, N-decyloxypyridine-3-carboximidamide and N-decyloxypyridine-4-carboximidamide was developed and validated in terms of linearity, precision and accuracy. The developed method was successfully applied to monitor and control the synthesis process. The experimental data points indicated that the straight chain alkyl bromide reacted most rapidly than branched alkyl bromide and the enhancement of the reaction efficiency strongly depended on reaction temperature.     

Graphene oxide promoted synthesis of <Emphasis Type="Italic">p</Emphasis>-phenylenediamine antioxidants

Three p-phenylenediamine antioxidants (p-phenylenediamine-N,N,N′,N′-tetrapropionic acid tetramethyl ester, p-phenylenediamine-N,N,N′-tripropionic acid trimethyl ester, and p-phenylenediamine-N, N′-dipropionic acid dimethyl ester) were successfully synthesized via atom-economic aza-Michael addition of pphenylenediamine to methyl acrylate p-romoted by graphene oxide in water. The synthesized compounds were characterized by NMR, ESI-MS spectra, and elemental analyses. The effects of the solvent and graphene oxide on the reaction were investigated.     

Arylation of adamantanamines: VIII. Optimization of the catalytic system for copper-catalyzed arylation of adamantane-containing amines

Arylation of adamantane-containing amines with iodobenzene in the presence of copper(I) and copper(II) compounds and various N,N-, N,O- and O,O-bidentate ligands was studied. The best results were obtained using the catalytic system CuI–rac-BINOL [1,1′-bi(naphthalen-2-ol)] (10/20 mol %). Reactions with iodobenzene derivatives containing electron-donor and electron-withdrawing substituents in the para position to the iodine atom were carried out under the optimal conditions.     

Oligomerization of <Emphasis Type="Italic">N</Emphasis>-vinylpyrroles under the action of iodine

The oligomerization of N-vinylpyrroles (N-vinyl-4,5,6,7-tetrahydroindole, N-vinyl-2-[1-(1-4,5,6,7-tetrahydroindole)ethyl]-4,5,6,7-tetrahydroindole, N-vinyl-2-phenylpyrrole, N-vinyl-3-heptyl-2-phenylpyrrole, N-vinyl-2,3-diphenylpyrrole, and N-vinyl-2-(2-naphthyl)pyrrole) under the action of iodine vapor leads to the formation of iodine-containing oligomers with an iodine content of 17–52% and a yield of up to 99%. The oligomers are paramagnetic and possess conductivity; they are readily soluble in organic solvents (benzene, dioxane, and chloroform) and are stable up to 110–260°C.     

Transformations of <Emphasis Type="Italic">N</Emphasis>-(2-acylaryl)benzamides and their analogs under the Camps cyclization conditions

N-(2-Acylaryl)benzamides and analogous N-substituted furan-2-, thiophene-2-, and cyclopropane-carboxamides in the systems EtONa–EtOH, EtONa–THF, and t-BuOK–t-BuOH undergo Camps cyclization to 2-aryl-, 2-hetaryl-, and 2-cyclopropylquinolin-4(1H)-ones with high yields. The same substrates in the system t-BuOK (5 equiv)–THF are converted mainly to the corresponding N-(2-hydroxyaryl) amides as a result of oxidative transformation of the acyl fragment into hydroxy group.     

Reaction of <Emphasis Type="Italic">N</Emphasis>-phenyltriflamide with 1,2-dibromoethane and propargyl bromide. Unexpected cleavage of С–С and С–N bonds

Reaction of N-phenyltriflamide with 1,2-dibromoethane under basic conditions in DMSO unexpectedly results in N-methyl-N-phenyltriflamide and 1,3-diphenylurea. The presumed reaction mechanism includes the formation of unstable intermediate disubstitution product TfN(Ph)CH₂CH2N(Ph)Tf that suffers the the С–С bond cleavage resulting in TfN(Me)Ph and N,N′-methanediylbis(N-phenyltriflamide). The latter reacts with K₂CO₃ releasing two molecules of potassium triflinate and after hydrolysis of diphenylcarbodiimide PhN=C=NPh gives 1,3-diphenylurea. With propargyl bromide, N-phenyltriflamide affords N-propargyl-Nphenyltriflamide in high yield. The bromination of the latter results in a mixture of Z,E-isomers of N-(2,3-dibromoprop-2-en-1-yl)-N-phenyltriflamide which undergo dehydrobromination giving first N-(3-bromopropanedienyl)-N-phenyltriflamide and then the products of the C–N bond cleavage: N-phenyltriflamide and 3,3-dimethoxyprop-1-yne.     

Electron density distribution in crystals of the antimony(V) spiroendoperoxide complexes

The experimental and theoretical electron densities in complexes [6-(2,6-di-iso-propylphenyl)imino-2,4-di-tert-butylcyclohexa-2,4-diene-1-peroxo-1-olato-N,O,O′]tris(p-chlorophenyl)antimony(V), (p-Cl–C₆H₄)₃Sb(2,6-iso-Pr–Ph–AP) · O₂ (I), and [6-(2,6-dimethylphenyl)imino-2,4-di-tert-butylcyclohexa-2,4-diene-1-peroxo-1-olato-N,O,O′]tris(p-chlorophenyl)antimony(V), (p-Cl–C₆H₄)₃Sb(2,6-Me–Ph–AP) · O₂ (II), where AP is 4,6-di-tert-butyl-N-o-iminobenzoquinone dianion, are studied on the basis of high-resolution X-ray diffraction data and theoretical calculations using the density functional theory (B3LYP/DGDZVP). The nature of chemical bonds and the charge distribution on atoms are studied, and the energy of molecular oxygen addition to the Sb(V) o-aminophenolate complexes is estimated. The structures are deposited with the Cambridge Crystallographic Data Centre (CIF files CCDC nos. 1560600 (spherical refinement) and 1560601 (multipole refinement) for complex I; 1560602 (spherical) and 1560603 (multipole) for complex II).     

Alkylation of 2-(methylsulfanyl)-6-polyfluoroalkylpyrimidin-4(3<Emphasis Type="Italic">H</Emphasis>)-ones with haloalkanes

The alkylation of ambident anions of 2-(methylsulfanyl)-6-(polyfluoroalkyl)pyrimidin-4(3H)-ones with 4-bromobutyl acetate leads to concurrent formation of O- and N-(4-acetoxybutyl) derivatives. Polar aprotic solvents favor formation of the O-isomer, and weakly polar dioxane favors N-alkylation. The reaction of 2-(methylsulfanyl)-6-(trifluoromethyl)pyrimidin-4(3H)-one with an equimolar amount of 1,2-dibromoethane in polar acetonitrile gives a mixture of N,N-, O,O-, and N,O-bridged bis-pyrimidines, as well as N- and O-[2-(methylsulfanyl)ethyl] derivatives, whereas in the presence of 10 equiv of 1,2-dibromoethane the N,O-isomer is formed as the only product. The reaction in weakly polar tetrahydrofuran yields N,N- and N,O-bispyrimidines.