Redox reactions in non-aqueous media: determination of organic isothiocyanates alone, in formulations and in important mixtures

A simple potentiometric method for the determination of organoisothiocyanates is described. The isothiocyanate is treated in acetonitrile medium with an excess of primary amine to convert it into a substituted thiourea and the surplus amine is converted into a dithiocarbamate by addition of carbon disulphide. The solution is then titrated with a copper(II) solution in acetonitrile. The three-step titration curve enables the results to be calculated on the bash of the dithiocarbamate and/or thiourea formed. The method has been successfully applied to the analysis of a commercial insecticide formulation based on isothiocyanate and important mixtures containing isothiocyanates.     

Determination of Pd and Co as Their Dithiocarbamate Complexes by Liquid Chromatography without Solvent Extraction

Abstract

High performance reverse-phase liquid chromatography with UV-detection can be used to determine trace levels of Pd and Co as their dithiocarbamate complexes by direct injection of aqueous acetonitrile solutions of the metal containing dithiocarbamate. An excess of ligand, at least four times that required to form the neutral metal complex, was necessary for complete metal-complex formation. The presence of other metal species and the solution acidity depleted the amount of ligand available for complexation. Detection limits for Pd(II) and Co(III) from aqueous solution as their dithiocarbamate complexes were 2.7 ng/mL and 9.5 ng/mL respectively. Trace levels of Pd in Platinum powder (62 ug/g)have been determined. A solution of cobalt platonic chloride was analyzed for cobalt content.     

Synthesis,Spectroscopic Characterization,DFT Calculations,and Dynamic Behavior of Mononuclear Macrocyclic Diorganotin(IV) Bis‐Dithiocarbamate Complexes

Nine mononuclear diorganotin(IV) dithiocarbamate complexes 1 – 9 with 19‐, 20‐ and 21‐membered macrocyclic structures were synthesized from dimethyl, di‐n‐butyl, and diphenyltin(IV) dichloride and three bis‐dithiocarbamate ligands derived from secondary bis‐amines having aromatic spacer groups. All compounds were characterized by elemental analysis, mass spectrometry, and spectroscopic methods (IR and ¹H, ¹³C, and ¹¹⁹Sn NMR). Additionally, quantum chemical DFT calculations were performed for the dimethyltin(IV) derivatives in order to model the molecular structures. For one compound series the NMR spectra showed a concentration‐dependent behavior in solution, which was analyzed in detail and permitted to postulate the existence of an equilibrium with the corresponding [2+2] macrocycles.     

Diorganotin(IV) dithiocarbamate complexes as chromogenic sensors of anion binding

One dinuclear chlorodiphenyltin (IV) dithiocarbamate complex (1) and four mononuclear complexes of general formula Ph₂Sn(S₂CNR)Cl (2, 3, 5, and 6) have been synthesized and characterized both in solid-state and solution. X-ray structures for complexes 1, 3 and 6 demonstrated a five-coordination geometry around of tin atoms, in which dithiocarbamate ligand chelates asymmetrically the metal center. As shown by ¹¹⁹Sn NMR spectroscopy, five-coordination geometry observed in the solid-state remains in solution. The stability of these chlorodiphenyltin(IV) dithiocarbamate complexes in the presence of biologically relevant anions such as acetate, dicarboxylates of general formula ^?OOC-(CH₂)_n-COO^? (n = 2–8), dihydrogenphosphate, hydrogensulfate, and halides has been examined in acetonitrile solutions. For all of these organotin(IV) complexes the displacement of the coordinated ligands (i.e., chloride and dithiocarbamate) from the organotin(IV) moiety occurred in the presence of monoanions like acetate, dihydrogenphosphate, hydrogensulfate and fluoride. A stepwise mechanism for ligand exchange is proposed based on UV–Vis, ¹H, ¹³C and ¹¹⁹Sn spectroscopic data, as well as mass spectrometry. From UV–Vis titration experiments it was found that dicarboxylates with small spacers like malonate and succinate, acted differently in the exchange of the dithiocarbamate group in comparison to other monoanionic O donor ligands or dicarboxylates with longer chains, perhaps by following an intramolecular displacement of the coordinated ligand.The lability of these organotin(IV) dithiocarbamate compounds in solution hampers their use as stably host for anions, however, by taking advantage of the intrinsic chromogenic properties of free dithiocarbamate anions, or by attaching dithiocarbamate groups to well-known fluorescent moieties such as antracene, these complexes can sense the presence of O-donor anions at very low concentrations by displacement of the metal-coordinated dithiocarbamate.     

Determination of methylmercury in natural waters by headspace gas chromatography with microwave-induced plasma detection after preconcentration on a resin containing dithiocarbamate groups

A method for the determination of methylmercury at ng l^?1 levels in natural waters is described. Methylmercury present in a sample is first preconcentrated on a column of a resin containing dithiocarbamate groups and eluted quantitatively with acidic thiourea solution. Methylmercury in the effluent is then converted to the iodide by addition of sulphuric acid and iodoacetic acid and determined by headspace gas chromatography with microwave-induced plasma detection. The adsorption properties of the resin are discussed.     

Thermodynamics of Organic Mixtures Containing Amines. II. Excess Molar Volumes at 25°C for Methylbutylamine + Alkane Systems and Eras Characterization of Linear Secondary Amine + Alkane Mixtures

Excess molar volumes, at 25°C and atmospheric pressure for methylbutyl amine + n-hexane; + cyclohexane; + n-octane; n-decane; + n-dodecane; + n-tetradecane, or + n-hexadecane systems are reported from densities measured with a vibrating-tube densimeter. The excess functions, molar enthalpy, and volume, for linear secondary amine + n-alkane systems are discussed in terms of interactional and structural effects. In addition, these solutions, which include amines from dimethyl to dioctylamine, are studied in the framework of the ERAS model. The corresponding ERAS parameters are reported. The agreement between experimental data and ERAS results is good for excess enthalpies, excess Gibbs energies, and excess molar volumes. The larger discrepancies are found for the excess volumes when strong free-volume effects are present in the investigated mixtures. The variation with temperature of the thermodynamic properties is well described by ERAS.     

Thermodynamics of complex formation in ternary liquid mixtures containing acetonitrile

Vapor—liquid and liquid—liquid equilibria and excess enthalpies for ternary mixtures formed from acetonitrile, benzene, n-heptane, toluene, and carbon tetrachloride are successfully correlated with a modified version of the associated solution theory proposed by Lorimer and Jones in 1977, which assumes two types of self-association for acetonitrile and binary complexes between acetonitrile and unsaturated hydrocarbons and does not include any ternary parameters.     

Thermodynamics of n-alkane systems and the solution theories of flory and prigogine

The partial molar excess free enthalpies and enthalpies as well as the molar excess enthalpies of a number of n-alkane systems were reexamined within the scope of the polymer solution theory of Flory, Orwoll, and Vrij and that of Prigogine in the version after Delmas, Patterson, and Somcynsky. A semiempirical method was used to obtain characteristic n-alkane data, which obey the principle of corresponding states. By using these data (instead of those from the partition function after Flory and collaborators), a physically realistic interpretation of the excess free enthalpies over the whole concentration range is possible if the combinatorial contribution is purely athermal in nature. Both theories give an enthalpy interaction parameter near zero as expected, whereas neither a significant end effect nor an entropic interaction contribution is apparent from the analyses of the excess free enthalpies. The poor results obtained for the partial excess enthalpies and the enthalpies of mixing reflect the inadequacy of the partition functions on which these modern solution theories are based.     

Selective liquid sorption properties of hydrophobized graphite oxide nanostructures

 Hydrophilic graphite oxide (GO) of lamellar structure was prepared by oxidation of graphite; the thickness of the individual lamellae was 6.1 Å. GO was hydrophobized by n-alkylammonium cations, and the GO-organocomplex nanocomposites were swollen in organic solvents of various polarities (ethanol, toluene, cyclohexane, n-heptane) and their binary mixtures. The binary liquid composition determined the size (15–45 Å) of the lamellar GO nanostructures. Interlamellar swelling was quantitatively characterized by XRD experiments, determination of liquid sorption excess isotherms and flow microcalorimetry. Received: 12 November 1997 Accepted: 12 February 1998     

Separation of molybdenum (VI) by extraction withn-octylaniline from hydrochloric acid medium

n-Octylaniline in bezene was used for the extractive separation of molybdenum (VI) from hydrochloric acid medium. Molybdenum(VI) was extracted quantitatively from 10 ml aqueous solution 1.5M in hydrochloric acid and 10M in lithium chloride into 10 ml of 10%n-octylaninline in benzene. It was stripped from the organic phase with 5% aqueous ammonia solution and estimated spectrophotometrically with thiocyanate at 465 nm. The interference of various ions has been studied in detail and conditions have been established for the determination of molybdenum(VI) in synthetic mixtures and alloy samples.     

A new photoiniferter/RAFT agent for ambient temperature rapid and well‐controlled radical polymerization

Phenacyl morpholine‐4‐dithiocarbamate is synthesized and characterized. Its capability to act as both a photoiniferter and reversible addition fragmentation chain transfer agent for the polymerization of styrene is examined. Polymerization carried out in bulk under ultra violet irradiation at above 300 nm at room temperature shows controlled free radical polymerization characteristics up to 50% conversions and produces well‐defined polymers with molecular weights close to those predicted from theory and relatively narrow poyldispersities (M_w/M_n ～ 1.30). End group determination and block copolymerization with methyl acrylate suggest that morpholino dithiocarbamate groups were attained at the end of the polymer. Photolysis and polymerization studies revealed that polymerization proceeds via both reversible termination and RAFT mechanisms. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3387–3395, 2008     

Synthesis and characterization of stannacyclododecane-yl-dithiocarbamates

Thirteen new stannacyclododecane dithiocarbamate complexes have been prepared by reacting 12-chloro-12-n-butyl-1,11-dioxa-4,8-dithia-12-stannacyclododecane (1) and 12-chloro-12-n-butyl-1,4,8,11-tetrathia-12-stannacyclododecane (2) with pyrrolidine-, morpholine-, thiomorpholine-, piperidine-, piperazinebis-, and 3-pyrroline-carbodithioates, respectively, as well as with diethyl-dithiocarbamate. All complexes were characterized by elemental analyses, IR, EI-MS, and NMR (¹H, ¹³C, and ¹¹⁹Sn) studies. The spectroscopic data suggest the replacement of the chlorides by the corresponding dithiocarbamates with monodentate coordination, leading to six-coordinate tin atoms in all the cases.     

Excess Molar Volumes of Binary Mixtures of Acetonitrile with n-Alkanols at 25°C

Molar excess volumes of acetonitrile with ten n-alkanols (from methanol to decanol) were determined from density measurements at 25°C and normal atmospheric pressure, using a vibrating-tube densimeter. V ^E for acetonitrile + methanol mixtures are negative over the entire range of mole fractions. The ethanol and propanol mixtures exhibit sigmoidal curves and positive values are obtained for all remaining mixtures. The results for V ^E were compared with those obtained using several theoretical models.     

Colorimetric determination of manganese(II) in natural and waste waters after preconcentration on a polymeric adsorbent

A combined procedure has been developed for the colorimetric determination of manganese(II) in natural and waste waters based on the selective preconcentration of metal ions on a polymer complexing adsorbent,—polystyrene-2-oxy-〈1-azo-1′〉-2′-oxy-3′-sulfo-5′-nitrobenzene, followed by the digital detection of the analytical signal. Manganese(II) is extracted (95–100%) in the batch mode in the pH range from 4.9 to 6.8. The determination is not interfered by n × 10⁵-fold excess (by weight) of K, Na; n × 10⁴-fold excess of Ca, Mg; n × 10³-fold excess of Ba, Sr, Al, Fe(III); n × 10²-fold excess of Ti(IV), Ni, Co, Zn, Pb, Cu. The accuracy of the procedure has been examined by the standard addition method. The relative standard deviation varies from 9 to 16%. The advantages of the procedure include simplicity, availability of the apparatus, rapidity, and the possibility of its application in field conditions.     

High Tg microspheres by dispersion copolymerization of N‐phenylmaleimide with styrenic or alkyl vinyl ether monomers

Solution and dispersion copolymerizations of N‐phenylmaleimide (PMI) with either styrenics or alkyl vinyl ethers (AVEs), systems with a tendency to give alternating polymers, were investigated with the goal of producing high glass transition particles. Equimolar solution copolymerization of PMI with styrenics gave alternating copolymers, whereas AVEs gave PMI‐rich copolymers (～65:35) except for t‐butyl vinyl ether, which gave copolymers with only a slight excess of PMI. These copolymers had glass transition temperatures (T_gs) ranging from 115 to 225 °C depending on comonomer(s). Dispersion copolymerization in ethanol‐based solvents in the presence of poly(vinylpyrrolidone) as steric stabilizer led to narrow‐disperse microspheres for many copolymers studied. Dispersion copolymeriations of PMI with styrenics required good cosolvents such as acetonitrile or methyl ethyl ketone as plasticizers during particle initiation and growth. Dispersion copolymerizations generally resulted in copolymer particles with compositions and T_gs very similar to those of the corresponding copolymers formed by solution polymerization, with the exception of t‐butyl vinyl ether (tBVE), which now behaved like the other AVEs. Dispersion terpolymerizations of PMI (50 mol %) with different ratios of either n‐butylstyrene and t‐butylstyrene or n‐butyl vinyl ether and tBVE led to polymer particles with T_gs that depended on the ratio of the two butyl monomers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Determination of strobilurin fungicides in cotton seed by combination of acetonitrile extraction and dispersive liquid−liquid microextraction coupled with gas chromatography

The simultaneous determination of four strobilurin fungicides (picoxystrobin, kresoxim‐methyl, trifloxystrobin, and azoxystrobin) in cotton seed by combining acetonitrile extraction and dispersive liquid?liquid microextraction was developed prior to GC with electron capture detection. Several factors, including the type and volume of the extraction and dispersive solvents, extraction condition and time, and salt addition, were optimized. The analytes were extracted with acetonitrile from cotton seed and the clean‐up was carried out by primary secondary amine. Afterwards, 60 μL of n‐hexane/toluene (1:1, v/v) with a lower density than water was mixed with 1 mL of the acetonitrile extract, then the mixture was injected into 7 mL of distilled water. A 0.1 mL pipette was used to collect a few microliters of n‐hexane/toluene from the top of the aqueous solution. The enrichment factors of the analytes ranged from 36 to 67. The LODs were in the range of 0.1 × 10^?3?2 × 10^?3 mg/kg. The relative recoveries varied from 87.7 to 95.2% with RSDs of 4.1?8.5% for the four fungicides. The good performance of the method, compared with the conventional pretreatments, has demonstrated it is suitable for determining low concentrations of strobilurin fungicide residues in cotton seed.     

Precolumn derivatization with glyoxal as a new approach to the highly sensitive HPLC-UV determination of unsymmetrical dimethylhydrazine

A procedure has been developed for the determination of unsymmetrical dimethylhydrazine (UDMH) based on precolumn derivatization with glyoxal and determination of the produced derivative, mono-1,1-dimethylhydrazone of glyoxal, by reversed-phase HPLC (RP-HPLC) with UV detection at 305 nm. It has been demonstrated that the reaction of UDMH with an excess of glyoxal in solution quantitatively yields one stable product within 20 min at 25°C at pH 3.5. To increase the sensitivity of UDMH determination it has been proposed to perform solid-phase extraction preconcentration of the derivative from a 25-mL sample portion on cartridges containing Strata SDB-L polymer adsorbent. The analytical range of UDMH determination in water is 0.5–10000 μg/L or 0.01–20 μg/L using preconcentration. The relative standard deviations of UDMH determination (n = 3) do not exceed 0.12 and 0.25 without and with preconcentration, respectively. The accuracy of UDMH determination is confirmed by the analysis of spiked samples and by RP-HPLC determination with preliminary derivatization with 4-nitrobenzaldehyde as independent method.     

Features of the initiated oxidation mechanism of n-heptadecane at low concentrations of oxygen

The oxidation of n-heptadecane was studied at various partial pressures of oxygen in an oxygen-argon mixture from 100 to 10% and various initiation rates W _i in the range (1–5)·10⁻⁶ mol L⁻¹ s⁻¹ at 413 K. The kinetic curves of oxygen uptake and hydroperoxide buildup were obtained under the indicated conditions. The observed features of n-heptadecane oxidation at low concentrations of oxygen may qualitatively be explained and quantitatively described if the oxidation scheme takes into account the cross termination of alkyl and peroxyl radicals R · + RO₂ · \underrightarrow k₅ \underrightarrow {k_5 } ROOR along with the square termination of peroxyl radicals. A method for determination of the corresponding kinetic parameter by the dependence of the initial oxidation rate on the partial oxygen pressure was proposed. A method for identification of the key reactions and determination of the kinetic parameters by the kinetics of oxygen uptake at lowered oxygen concentrations was developed. The kinetic model of the process was obtained, which quantitatively describes the kinetic curves of oxygen uptake and hydroperoxide buildup at the initial steps of initiated oxidation of n-heptadecane.     

Pesticides Residues Rapid Extraction from Panax Ginseng Using a Modified QuEChERS Method for GC–MS

A modified quick, easy, cheap, effective, rugged and safe (QuEChERS) rapid detection method followed by gas chromatography–tandem mass spectrometry (GC–MS) has been developed for the simultaneous determination of 42 pesticides in Panax ginseng. This method can be different from the other QuEChERS methods in the sense that it uses acetone and n-hexane solution rather than acetonitrile to extract and partition pesticides. This acetone, water and n-hexane solution QuEChERS method consists essentially of two steps: extraction/partitioning and purification. In step 1, P. ginseng was mixed with acetone, water and n-hexane solution, and then partitioned by vortex. In step 2, the top layer (n-hexane) was transferred into a centrifuge tube containing primary secondary amine, activated carbon and C₁₈ for purification. After the centrifuge supernatant was injected into GC–MS. The QuEChERS method was applied in P. ginseng detection and we confirmed that this method can easily extract various types of pesticides from P. ginseng. The rates of recovery for pesticides studied were satisfactory, ranging from 75.3 to 119.4 % for most of the pesticides with a relative standard deviation of less than 13 %. The LOQs ranged between 0.5 and 1.2 µg kg⁻¹. The modified QuEChERS method and GC–MS could enable complex pretreatment in P. ginseng analysis quickly and easily.

     

Neighboring effect of thiol group in acyl transfer reaction on a polymer with a lipoic acid structure

Reductive S-monoacylation of lipoamide with some carboxylic acids and tri-n-butylphosphine was carried out in acetonitrile to obtain the corresponding S-monoacylated compounds in excellent yield. This method was applied to the preparation of S-monoacylated dihydrolipoyl polymer with a neighboring thiol group. The acyl transfer from the polymer to cyclohexylamine was enhanced as much as 64 times by adding silver perchlorate.