SEC-MALLS analysis of softwood kraft pulp using LiCl/1,3-dimethyl-2-imidazolidinone as an eluent

Various cellulose and pulp samples including softwood bleached kraft pulp (SBKP) were dissolved in 8% lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) and 8% LiCl/N,N-dimethylacetamide (DMAc), and the obtained solutions were subjected to size-exclusion chromatographic analysis with multi-angle light scattering detection (SEC-MALLS). Although SBKP was not completely soluble in 8% LiCl/DMAc, 1% LiCl/DMI always gave a clear solution of SBKP without centrifugation. Molecular mass (MM) and MM distribution measurements using 1% LiCl/DMI as an eluent for the SEC-MALLS analysis revealed that SBKP had MM higher than those of the other cellulose and pulp samples at the same elution volume. The slope of the conformation plots for SBKP showed an anomalously low value of 0.41, while those for other cellulose and pulp samples were in the range of 0.57–0.59, which corresponds to the normal random coil conformations. These results indicate that some compact structures like branches or cross-linkages other than molecular-dispersed states are present in the high MM region of SBKP, which can be detected when the LiCl/DMI solvent system is used as the solvent as well as the eluent for the SEC-MALLS analysis. On the other hand, no such structures were observed for the other cellulose and pulp samples including softwood bleached sulfite pulps. Thus, the compact structures present in SBKP are likely to be susceptible to acid treatments.     

Kinetics and thermodynamics of the attack of a phosphate ore by acid solutions at different temperatures

A calorimetric study of the kinetics and thermodynamics of the attack of a phosphate ore from Gafsa region (Tunisia) by phosphoric acid and by a mixture of phosphoric acid and sulfuric acids is undertaken at different temperatures. Two samples of the same ore having different grain size have been used. At 25 °C, the dissolution enthalpy in phosphoric acid solution equals −233.6 ± 2.2 J/g for both of the samples. Attack by the mixture of acids is strongly dependent on the solid granulometry. Interpretation of the calorimetric results by Avrami model shows the existence of three domains attributed to phosphate ore dissolution/H₂PO₄⁻ neutralisation, hemihydrate (HH) precipitation and hemihydrate/dihydrate (DH) transformation. The attack by the acid mixture was performed at higher temperatures and showed in addition the transitional formation of the anhydrous sulfate (AH) at T ≥ 55 °C, which transforms into dihydrate after the HH/DH transformation.     

Use of CaH2 as a reductive hydride source: reduction of ketones and imines with CaH2/ZnX2 in the presence of a Lewis acid

A new combination reagent of CaH₂/ZnX₂ effectively reduced a variety of ketones and imines to the corresponding alcohols and amines, respectively, in the presence of a catalytic amount of a Lewis acid such as Ti(O-i-Pr)₄, Al(O-i-Pr)₃, B(O-i-Pr)₃ and ZnF₂.     

Qualitative and quantitative 1H NMR spectroscopy for determination of divalent metal cation concentration in model salt solutions,food supplements,and pharmaceutical products by using EDTA as chelating agent

This paper introduces an ¹H NMR method to identify individual divalent metal cations Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Sn²⁺, and Pb²⁺ in aqueous salt solutions through their unique signal shift and coupling after complexation with the salt of ethylenediaminetetraacetic acid (EDTA). Furthermore, quantitative determination applied for the divalent metal cations Ca²⁺, Mg²⁺, Hg²⁺, Sn²⁺, Pb²⁺, and Zn²⁺ (limit of quantification: 5–22 μg/ml) can be achieved using an excess of EDTA with aqueous model salt solutions. An internal standard is not required because a known excess of EDTA is added and the remaining free EDTA can be used to recalculate the quantity of chelated metal cations. The utility of the method is demonstrated for the analysis of divalent cations in some food supplements and in pharmaceutical products.     

Preparative synthesis of 2,2-dimethyl-5-(trifluoroacetyl)-1,3-dioxane-4,6-dione (2-trifluoroacetyl Meldrum's acid) and 2,2-dimethyl-6-(trifluoromethyl)-4H-1,3-dioxin-4-one and their synthetic usefulness as (trifluoroacetyl)ketene precursors

A simple and reliable method for the preparation of 2,2-dimethyl-5-(trifluoroacetyl)-1,3-dioxane-4,6-dione and 2,2-dimethyl-6-(trifluoromethyl)-4H-1,3-dioxin-4-one on a multigram scale was developed. These (trifluoroacetyl)ketene precursors were used in the hetero-Diels-Alder reaction with dialkylcyanamides and 1-ethoxyprop-1-yne, as well as in some reactions with nucleophiles.     

Consequences of the formation of 3,4-dimethyl-5-phenyl-1,3-oxazolidine on the analysis of ephedrines in urine by gas chromatography and a new method for confirmation as N-trifluoroacetyl-O-t-butyldimethylsilyl ether derivatives

The compound 3,4-dimethyl-5-phenyl-1,3-oxazolidine can appear as an artifact during the gas chromatographic analysis of ephedrines. Its presence is a risk for doping control and forensic analyses. An evaluation about the consequences of its formation showed the possibility of a false positive for ephedrine, a false negative for pseudophedrine and increased uncertainty in the quantitative approach. Misinterpretations can be avoided with the observation of fragments m/z 56 and 71 in the ephedrine mass spectrum during GC-MS analysis and also by the formation of N-TFA-O-TBDMS derivatives prior to GC analysis. These N-TFA-O-TBDMS derivatives lead to an increase in the number and mass of diagnostic ions, meet the identification criteria, and provide an improvement in chromatographic resolution, allowing the separation of the ephedrines.     

Study of NaCl solutions in a mixed solvent H2O−CH3OH: Experimental densities and comparison with calculated values obtained with a modified Pitzer's model

Densities at 25°C and atmospheric pressure were measured using a densimeter for several aqueous sodium chloride+methanol mixtures. The experimental results were then compared with data calculated using a modified Pitzer's model.     

Biodiesel production via esterification of oleic acid catalyzed by MnO2@Mn(btc) as a novel and heterogeneous catalyst

The main objective of this study is to develop efficient and environmentally benign heterogeneous catalysts for biodiesel production. For this purpose, a heterogeneous MnO₂@Mn(btc) catalyst was prepared by the solvothermal method, and the prepared catalyst was tested for the esterification of oleic acid. Various techniques such as X‐ray diffraction, scanning and transmission electron microscopy, Brunauer–Emmett–Teller (BET) method, infrared spectroscopy, thermogravimetry, and NH₃‐TPD (temperature programmed desorption) analysis were employed for the characterization of the solid catalyst. The solid catalyst with MnO₂@Mn(btc) loading of 15% showed high catalytic activity and long durability in the esterification of oleic acid, in which the fatty acid methyl ester yield reached 98% consecutively for at least five cycles under mild conditions.     

A new [2 + 2] photodimerization of 5-chloro- and 5-methyl-2-pyridone in their inclusion complexes with 1,1'-biphenyl-2,2'-dicarboxylic acid as a model for DNA damage by photodimerization of its thymine component

As a model for DNA damage by photodimerization of its thymine component, a new [2 + 2] photodimerization of 5-chloro and 5-methyl-2-pyridone to the corresponding cis-anti-dimers as their inclusion complexes with 1,1'-biphenyl-2,2'-dicarboxylic acid was found, and the mechanism of this stereoselective solid state reaction was studied by X-ray analysis.     

Selectivity and efficiency enhancement of supercritical fluid extraction by application of reactive additives. I. The analysis of calcium montanate using citric acid as a complexing agent

It has been demonstrated that calcium montanate (a mixture of aliphatic hydrocarbons, fatty acid esters of C₂₈–C₃₂ acids, the calcium salts of these fatty acids, and the acids themselves) can be selectively extracted with supercritical fluids. By use of carbon dioxide, carbon dioxide containing 10% methanol, and carbon dioxide containing 10% methanol and citric acid (as a further additive), the various compound classes could be isolated with high selectivity. The addition of citric acid results in the complexation of Ca²⁺ and the simultaneous formation of the free fatty acids, which are soluble in the extractant.     

Selective and sensitive extraction spectrophotometric method for the determination of vanadium (V) as a mixed ligand complex withN-phenyl benzohydroxamic acid and 4-(2-pyridylazo)resorcinol in non-aqueous media

A selective, sensitive and direct method for the spectrophotometric determination of vanadium in steels is developed in which vanadium is extracted withN-phenyl benzohydroxamic acid (PBHA) into chloroform from 5M hydrochloric acid medium followed by colour development by addition of 4-(2-pyridylazo)resorcinol (PAR) inN,N-dimethyl formamide (DMF). The vanadium(V)-PBHA-PAR mixed ligand complex shows maximum absorbance at 560 nm with a molar absorptivity 3.6 × 10⁴ l mol^–1 cm^–1 and obeys Beer's law up to 2.0 g/ml of vanadium. The composition of the mixed ligand complex is determined by Job's method of continuous variations which revealed a 1 1 1 ratio for V(V) PBHA PAR. This method can be directly applied for the determination of vanadium in steels, while in the case of titanium base alloys, after separation of titanium matrix it gives good results even at 50–200 g of vanadium per gram level.     

Study on ketalization reaction of poly(vinyl alcohol) by ketones. IX. Kinetic study on acetalization and ketalization reaction of 1,3-butanediol as a model compound for poly(vinyl alcohol)

A kinetic study was carried out on the acetalization reaction of 1,3-butanediol, as a model compound for poly(vinyl alcohol) (PVA), in water, under acidic conditions. Since these equilibrium constants of ketalization reaction of 1,3-butanediol and ethylene glycol are so small, the kinetic parameters were estimated from the hydrolysis reactions of the corresponding ketals. It was made clear that these reactions proceed in the reversible bimolecular reaction, and the heat of reaction and activation energy are nearly equal to that of PVA. The rate constants of hydrolysis reaction (k′s) of model compounds were calculated on the basis of value of acetone ketal, Hammett-Taft's equation log k′s/k′so – 0.54(n – 6) = ρ^*σ^* was established, and the value of ρ^* was obtained (3.60), which coincided with the value of PVA. Therefore, it was made clear that the hydrolysis reactions of acetals and ketals are electrophilic reaction (SE II reaction) and the step of rate determination is the formation of hemiacetal and hemiketal. The rate constants of hydrolysis reaction of 1,3-butanediol acetals and ketals were approximately 10–20 larger, and those of ethylene glycol were approximetly 50–80 larger except for ketals, and those of ethanol were roughly 2000–10,000 larger compared with that of high-molecular weight compound (PVA). It can be well explained that these differences in the rate constant depend on their entropy and the mobility of molecules. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1719–1931, 1997     

Efficient atom-economic one-pot multicomponent synthesis of benzylpyrazolyl coumarins and novel pyrano[2,3-c]pyrazoles catalysed by 2-aminoethanesulfonic acid (taurine) as a bio-organic catalyst

The present work describes eco-friendly multicomponent protocol for the synthesis in excellent yields of structurally diverse benzylpyrazolyl coumarin 5 (a–s) involving the reaction of 4-hydroxycoumarin, ethyl acetoacetate, hydrazine hydrate/phenyl hydrazine hydrate and aldehydes, also novel pyrano[2,3-c]pyrazole derivatives 8 (a–k) integrated by isonicotinic acid hydrazide from reaction of aldehyde, ethyl acetoacetate, malononitrile with isoniazid, employing water as a reaction medium and 2-aminoethanesulfonic acid (taurine) as the catalyst. This new methodology endowed the advantages such as short reaction time, recovery of catalysts after catalytic reaction and reusing them without losing their activity and alleviate of operation.     

NaY zeolite functionalized by sulfamic acid/Cu(OAc)2 as a new and reusable heterogeneous hybrid catalyst for efficient solvent-free formylation of amines

NaY zeolite functionalized by sulfamic acid/Cu(OAc)_2[NaY/SA/Cu(Ⅱ)] was synthesized and used as a new,efficient and recyclable catalyst for preparation of formamides. This novel organic-inorganic hybrid catalyst was characterized by several techniques such as FT-IR, XRD, SEM, EDX and TG analysis.Chemoselectivity, easy procedure, excellent yields, very short reaction times, solvent-free and mild reaction conditions are some benefits of this new protocol.