Enzymatic kinetic resolution of tropic acid

A new strategy has been developed for the CAL-B catalysed kinetic resolution of tropic acid by which both enantiomers of tropic acid can be obtained in good enantiomeric excess. (R)-Tropic acid was synthesised with 90% ee and (S)-tropic acid butyl ester in 99% ee by the hydrolysis of tropic acid butyl ester. The other enantiomers were available through the enzymatically catalysed reaction of tropic acid lactone with butanol to give (S)-tropic acid lactone and (R)-tropic acid ester in >98% ee.     

Thermodynamic excess properties for binary mixtures of (butanenitrile + a carboxylic acid) atT = 298.15 K

Excess molar enthalpies and excess molar volumes for (butanenitrile  +  acetic acid, or propanoic acid, or butanoic acid, or 2-methylpropanoic acid, or pentanoic acid, or 3-me thylbutanoic acid) atT =  298.15 K are presented. The excess molar enthalpy values are found to be positive for all six systems, whereas the excess molar volumes are found to be negative. The excess molar enthalpy values are correlated by the UNIQUAC and NRTL models and also by the Redlich–Kister polynomial.     

Kinetics of benzene nitration by nitric acid

The kinetics of benzene mononitration in excess of 45–70 wt % nitric acid in a homogeneous liquid phase was studied. The data on the effects of temperature and nitric acid concentration on the reaction rate were obtained.     

Benzohydroxamic acid as a reductometric titrant: Determination of thorium

Milligram quantities of thorium can be accurately determined by precipitating it as oxalate, dissolving the precipitate in 11 sulphuric acid and oxidizing the liberated oxalic acid with a known excess of standard permanganate solution above 60 °C in sulphuric acid medium, and finally estimating the excess permanganate by titrating with a standard solution of benzohydroxamic acid either visually or potentiometrically. 10 mg quantities of thorium has been estimated with an error not exceeding 0.12%. The coefficient of variation for 10 estimations is found to be 0.06% and 0.12% for potentiometric and visual methods, resp.     

Density,speed of sound,and refractive index measurements for the binary systems (butanoic acid + propanoic acid,or 2-methyl-propanoic acid) at T = (293.15 to 313.15) K

Density, speed of sound, and refractive index for the binary systems (butanoic acid + propanoic acid, or 2-methyl-propanoic acid) were measured over the whole composition range and at T = (293.15, 298.15, 303.15, 308.15, and 313.15) K. The excess molar volumes, isentropic compressibilities, excess isentropic compressibilities, molar refractions, and deviation in refractive indices were also calculated by using the experimental densities, speed of sound, and refractive indices data, respectively. The Redlich–Kister smoothing polynomial equation was used to fit the excess molar volume, excess isentropic compressibility and deviation in refractive index data. The thermodynamic properties have been discussed in terms of intermolecular interactions between the components of the mixtures.     

Colorimetric enantiodiscrimination of mandelic acid by indicator displacement assay

The colorimetric enantiodiscrimination between mandelic acid and L-proline-Cu(II) is exploited to develop enantioselective indicator displacement assays. The sensitivity of the assay could be tuned by using a colorimetric indicator. The chromophoric ligand, pyrocatechol violet, effectively competes with the mandelic acid guest for open coordination sites on L-proline-Cu(II). The DA could be increased to 0.12 by changing the ratio of(+)- and(à)-mandelic acid concentrations that were found to be optimal from the displacement experiments. The resultant enantiomer excess versus DA relationship is linear. From the calibration curves, the absorbance values of the unknowns may be calculated for the enantiomeric excess value and the colorimetric enantiodiscrimination of mandelic acid can thus be obtained.     

Carbon isotope effect studies in the mechanism of reactions of alkynes with formic acid

Carbon-13 fractionation observed in the course of carbon monoxide formation in the reaction of phenylacetylene with the large excess of liquid formic acid in the temperature interval 20–100°C has been investigated and compared with the¹³C fractionation in the dehydration of pure liquid formic acid. The anomalous temperature dependence of the¹³C fractionation has been interpreted as caused by the change of the kinetics and of the mechanism of CO formation from the one involving¹³C–H bond rupture rate determining step (operating in the presence of phenylacetylene) to the mechanism according to which HCOOH decarbonylates in liquid state. No large increase of the¹³C fractionation with rising of the reaction temperature from 70 to 134°C has been found in the case of decarbonylation of F.A. in the presence of large excess of phenylacetylene. The¹³C KIE was of 1.020 in the temperature interval 90–133.7°C in this case.     

Determination of bismuth by selenious acid

Summary Bismuth is shown to be precipitated quantitatively as bismuth selenite by boiling an almost neutral solution of bismuth nitrate and excess selenious acid. The excess H₂SeO₃ is determined iodometrically by standard thiosulphate or arsenious oxide solution. Alternatively, the precipitated selenite may be dried at 105–110° C and weighed as Bi₂(SeO₃)₃.Sincere thanks of the authors are due to Prof. S. S. Joshi for research facilities and to Dr. G. S. Deshmukh for keen interest in the work.     

Extractive photometric determination of palladium with o-mercaptobenzoic acid

A procedure is described for the extractive photometric determination of palladium(II) with o-mercaptobenzoic acid. The reagent forms a yellow complex having maximum absorption at 365–370 mμ. The complex is quantitatively extractable with chloroform in the presence of pyridine at pH 5.2–7.2. The color develops immediately at room temperature and is very stable. Beer's law conforms over the range of 0.37–5.86 ppm of palladium. Most of the cations do not interfere in the presence of ascorbic acid and EDTA. Gold and silver are effectively masked with excess of thiocyanate prior to the addition of ascorbic acid and EDTA. Many common anions do not interfere. The molar absorptivity and Sandell sensitivity are 16.7 × 10³ and 0.0065 μg/cm². The reagent forms a 2:1 complex with palladium. The proposed method is simple, rapid, and selective for the determination of palladium(II).     

Excess molar enthalpies of binary systems containing 2-octanone,hexanoic acid,or octanoic acid at T = 298.15 K

An isothermal titration calorimeter was used to measure the excess molar enthalpies (H^E) of six binary systems at T = 298.15 K under atmospheric pressure. The systems investigated include (1-hexanol + 2-octanone), (1-octanol + 2-octanone), (1-hexanol + octanoic acid), (1-hexanol + hexanoic acid), {N,N-dimethylformamide (DMF) + hexanoic acid}, and {dimethyl sulfoxide (DMSO) + hexanoic acid}. The values of excess molar enthalpies are all positive except for the DMSO- and the DMF-containing systems. In the 1-hexanol with hexanoic acid or octanoic acid systems, the maximum values of H^E are located around the mole fraction of 0.4 of 1-hexanol, but the H^E vary nearly symmetrically with composition for other four systems. In addition to the modified Redlich–Kister and the NRTL models, the Peng–Robinson (PR) and the Patel–Teja (PT) equations of state were used to correlate the excess molar enthalpy data. The modified Redlich–Kister equation correlates the H^E data to within about experimental uncertainty. The calculated results from the PR and the PT are comparable. It is indicated that the overall average absolute relative deviations (AARD) of the excess enthalpy calculations are reduced from 18.8% and 18.8% to 6.6% and 7.0%, respectively, as the second adjustable binary interaction parameter, k_bij, is added in the PR and the PT equations. Also, the NRTL model correlates the H^E data to an overall AARD of 10.8% by using two adjustable model parameters.     

Excess molar volumes of formic acid + water acetic acid + water and propionic acid + water systems at 288.15, 298.15 and 308.15 K

Densities and excess molar volumes were determined in the formic acid + water, acetic acid + water and propionic acid + water systems at 288.15, 298.15 and 308.15 K. The results are satisfactorily described using the ideal association model of the type A + B + A₂ for the system with formic acid. The Mecke—Kempter model is adequate for the acetic acid + water and propionic acid + water systems. In both models the formation of open dimers and open higher associates is postulated for the self-association of carboxylic acids in water.     

Oligomeric bishydroxybutyl terephthalates from terephthalic acid

A process that uses terephthalic acid and excess 1,4-butanediol for the production of polybutylene terephthalate was investigated and the reaction conditions were maximized for fast reaction and minimal loss of butanediol by dehydration to tetrahydrofuran. For best results a mixed catalyst was selected: butylstannoic acid and titanium tetrabutoxide (0.05 and 0.025 mole %, respectively, versus terephthalic acid) with a starting material ratio of butanediol: terephthalic acid of 1.7 at 210°C. The mixture cleared at 2.5 hr with a loss of 6% of butanediol. HPLC analysis showed that the clearing point corresponds to the disappearance of terephthalic acid and monohydroxybutyl terephthalate from the reaction mixture. Thus the polycondensation conditions can be applied before the clearing point with the result that the reaction is faster and tetrahydrofuran formation is minimized. Tetrahydrofuran is formed from butanediol in the reaction mixture by acid catalysis. Excess butanediol results in the formation of larger amounts. End group cyclization of terephthalate esters accounts for the slow tetrahydrofuran formation in the absence of excess butanediol.     

Microdetermination of histamine and serotonin drugs using bromine monochloride in water-acetic acid medium

A micromethod for the determination of histamine, serotonin drugs has been developed. A 2–10 mg sample dissolved in glacial acetic acid is reacted with a known excess of bromine monochloride at ice-bath temperature and the excess reagent is back titrated iodometrically. The maximum deviation in the results is ±1.41%.     

Flow injection amperometric sensing of uric acid and ascorbic acid using the self-assembly of heterocyclic thiol on Au electrode

Au electrode modified with the self-assembled monolayer of a heterocyclic thiol, mercaptotriazole (MTz), is used for the electroanalysis of uric acid (UA) and ascorbic acid (AA). MTz forms a less compact self-assembly on Au electrode. The self-assembly of MTz on Au electrode favors the oxidation of UA and AA at less positive potential. Significant decrease (∼400 mV) in the overpotential and enhancement in the peak current for the oxidation of interfering AA with respect to the unmodified electrode is observed. The negative shift in the oxidation peak potential of AA favors electrochemical sensing of UA without any interference. Two well-separated voltammetric peaks for AA and UA are observed in their coexistence. The large separation between the two voltammetric peaks allows the simultaneous or selective sensing of the analytes without compromising the sensitivity. Linear response is obtained for a wide concentration range. This electrode could sense as low as 1 μM of UA in the presence of 10-fold excess of interfering AA. No change in the sensitivity (0.012 μA/μM) of the electrode toward UA in the presence and absence of AA is observed. Reproducible and stable amperometric flow injection response was obtained upon repetitive injection.     

Use of thiopropyl sepharose for preparation of 2-nitro-5-thiobenzoic acid

A simple method is described for preparation of 2-nitro-5-thiobenzoic acid (NTB), a compound with versatile applications but is commercially unavailable. In this method, NTB is produced by the reduction of 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) with thiopropyl sepharose, which is then separated from NTB by filtration. Two molecules of NTB can be generated from each molecule of DTNB when a large excess of thiopropyl sepharose is used. Thiopropyl sepharose is commercially available and can be readily regenerated for repeated use in the preparation of NTB. This method is simple and more effective than any other reported methods of NTB preparation.     

Selective bromination of dihydroquinopimaric acid

The reaction of dihydroquinopimaric acid methyl ester with bromine was found to be chemo- and stereoselective. Regardless of the solvent (acetic acid, methanol, dioxane), bromination of the title compound with an equimolar amount of bromine occurs as electrophilic addition at the double C¹⁹=C²⁰ bond with formation of 14α-hydroxy- or 14α-methoxy-19R-bromo derivatives. The reaction with excess bromine (3 equiv) leads to the formation of 16S-bromo derivatives. The bromination process is accompanied by formation of epoxy bridge between the C¹⁴ and C²⁰ atoms. X-Ray analysis revealed two polymorphic modifications of (16S,19R)-16,19-dibromo-14β,20-epoxydihydroquinopimaric acid methyl ester.     

Preparation of chitosan‐based molecularly imprinted material for enantioseparation of racemic mandelic acid in aqueous medium by solid phase extraction

An S‐mandelic acid imprinted chitosan resin was synthesized by cross‐linking chitosan with glutaraldehyde in 2% acetic acid solution. S‐Mandelic acid imprinted chitosan resin was used to enantioselectively separate racemic mandelic acid in aqueous medium. When keeping the pH of sample solution (100 mM Tris‐H₃PO₄) at 3.5 and adsorption time at 40 min, the enantiomer excess of mandelic acid in supernatant was 78.8%. The adsorption capacities of S‐mandelic acid imprinted chitosan resin for S‐ and R‐mandelic acid were determined to be 29.5 and 2.03 mg/g, respectively. While the adsorption capacities of non‐imprinted cross‐linked chitosan for S‐ and R‐mandelic acid were 2.10 and 2.08 mg/g, respectively. The result suggests that the imprinted caves in S‐mandelic acid imprinted chitosan resin are highly matched with S‐mandelic acid molecule in space structure and spatial arrangement of action sites. Interestingly, the enantiomer excess value of mandelic acid in supernatant after adsorption of racemic mandelic acid by R‐mandelic acid imprinted cross‐linked chitosan was 25.4%. The higher enantiomer excess value by S‐mandelic acid imprinted chitosan resin suggests that the chiral carbons in chitosan and the imprinted caves in S‐mandelic acid imprinted chitosan resin combine to play roles for the enantioselectivity of S‐mandelic acid imprinted chitosan resin toward S‐mandelic acid. Furthermore, the excellent enantioselectivity of S‐mandelic acid imprinted chitosan resin toward S‐mandelic acid demonstrates that using chiral chitosan as functional monomer to prepare molecularly imprinted polymers has great potential in enantioseparation of chiral pharmaceuticals.     

Protic ionic liquids as recyclable solvents for the acid catalysed synthesis of diphenylmethyl thioethers

The acid catalysed formation of diphenylmethyl (DPM) thioethers was successfully achieved using the protic ionic liquid (pIL) triethylamine:methanesulfonic acid (TeaMs) as the reaction solvent under microwave irradiation. A slight excess of methanesulfonic acid (10% v/v) was required to facilitate the reaction, which was applied to a variety of thiols. Aliphatic, aromatic and heterocyclic aromatic thiols were converted to their corresponding DPM thioethers in high yields (63–99%), in short reaction times (5–20 min) and using mild temperatures (80–100 °C). Finally, the pIL (TeaMS) was recycled five times without loss of yield.     

Conversion of solid amorphous mixed zirconium-titanium phosphates into crystalline from by molten oxalic acid

Solid amorphous mixed zirconium-titanium phosphates, with general formula Zr_xTi_/1–x//HPO₄/₂.n H₂O/ where x=0.1–1, and n=3–5/, are mixed with an excess of solid oxalic acid dihydrate and digested in molten oxalic acid. Then oxalic acid is removed by extraction and the residue washed with dilute /O.OlM/ HCl solution and bidistilled water. As a result of this method, crystalline mixed zirconium-titanium phosphate is formed.