Authors:Sergei N. Shtykov, Elena G. Sumina, Varsenia Z. Uglanova, and Victor G. Berezkin
A comparison of the chromatographic behavior of benzoic acids on normal (silica gel), reversed (RP-18), and polyamide-11 plates using thin-layer chromatography (TLC) with controlled gas phase inside the chamber has been performed. This variant of TLC is based on the use of a gas phase moving over the TLC plate for regulation of the stationary and mobile phases as well as the acid—base properties of analytes during the separation process. The feasibility of such an approach is illustrated by the separation of benzoic acid derivatives using carbon dioxide, ammonia, and acetic acid vapor. It was shown that a gradual change of mobile phase acidity makes it possible to enhance separation efficiency and selectivity, this effect being dependent on the type of the stationary phase. The most considerable change in the retention of benzoic acid derivatives was observed for normal-phase plates with silica gel or silica sol, or starch binders used as the stationary phase. An alteration of surface acidity for polyamide and RP-18 plates is not so pronounced as for silica gel ones so that a smaller change in chromatographic parameters of benzoic acid derivatives was observed.
Authors:Manuel Monte, Luís Santos, José Fonseca, and Carlos Sousa
The vapour pressures of six para-substituted benzoic acids were measured using the Knudsen effusion method within the pressure range (0.1–1 Pa) in the following
temperature intervals: 4-hydroxybenzoic acid (365.09–387.28) K; 4-cyanobenzoic acid (355.14–373.28) K; 4-(methylamino)benzoic
acid (359.12–381.29) K; 4-(dimethylamino)benzoic acid (369.29–391.01) K; 4-(acetylamino)benzoic acid (423.10–443.12) K; 4-acetoxybenzoic
acid (351.28–373.27) K. From the temperature dependence of the vapour pressure, the standard molar enthalpy, entropy and Gibbs
energy of sublimation, at the temperature 298.15 K, were derived for each of the studied compounds using estimated values
of the heat capacity differences between the gaseous and the crystalline phases. Equations for estimating the vapour pressure
of para substituted benzoic acids at the temperature of 298.15 K are proposed.
Benzoic acid, lithium benzoate, and sodium benzoate were tritiated with virtually 100% regioselectivity in the ortho-positions by the T-for-H exchange reaction with HTO in the presence of RhCl3.3H2O. The labeling of both alkali metal salts was favored by a factor of about 3 over that of benzoic acid. Methyl benzoate was essentially inactive in the present reaction.
The physical state of benzoic acid (BA) and its interaction with ethyl cellulose (EC) were examined in ethyl cellulose—benzoic acid matrices by Differential Scanning Calorimetry (DSC). The glass transition temperature (Tg) of EC of various matrices having BA in solid solution form (upto 27.7%) was reduced. The BA in matrices containing more than 38.9% drug exhibited distinct melting endotherms due to crystalline form. The peak temperatures of these endotherms were lowered and they broadened as the concentration was lowered. The solubility of BA increased at its melting point as compared to ambient temperature. The melting enthalpy of BA, when plotted as a function of its concentration yielded a straight line with intercept of 330 mg g–1 of matrix. This is the solubility of BA in EC at its melting temperature. Fourier Transform Infra Red Spectroscopy (FTIR) investigations confirmed that hydrogen bonding occurred between EC and BA through hydroxyl groups.
The kinetic behavior of deuteriation of benzoic acid with D2O acidified with HCl in the presence of homogeneous K2PtCl4 catalyst has been investigated in the 100–130°C temperature interval. The quasiunimolecular H/D rate constants at 100 and 130°C corresponding to an exchange process in ortho positions of the substituted benzene ring hydrogens were determined by1H NMR integration signal. These same constants for meta and para positions have been deduced by analysis of the composite1H NMR signal, and the Arrhenius activation energies for these exchange reactions were estimated.
The thermal decomposition of benzoic acid and its derivatives containing —OH, —NH2, —COOH and —SO3H functional groups as substituents in ortho, meta and (or) para position together with sulphanilic acid was investigated.
The analyses were performed using derivatograph, sample mass ranged from 50 to 200 mg, heating rates from 3 to 15 K min−1 and static air atmosphere. It has been established that thermal decomposition of these aromatic acids proceeds through three
common stages. In the first stage the phase transformations occur. The following two stages are due to the formation of intermediate
products of the thermal decomposition and their combustion. Principal component analysis (PCA) was applied for evaluation
of the results. Thanks to this method the influence of specific functional groups and their positions on the benzene ring
on the thermal decomposition of the compounds under investigation was determined.
Authors:M. Glorius, H. Moll, G. Geipel, and G. Bernhard
The complex formation of uranium(VI) with salicylhydroxamic, benzohydroxamic, and benzoic acid was investigated by time-resolved
laser-induced fluorescence spectroscopy (TRLFS). We observed in all three systems a decrease in the fluorescence intensity
with increasing ligand concentration. All identified complexed uranyl species are of the type MpLqHr. In the uranium(VI)-salicylhydroxamate system a 1: 1 complex with a stability constant of log β111 = 17.34±0.06 and a 1: 2 complex with a stability constant of log β122 = 35.0±0.11 was identified. Also in the uranium(VI)-benzohydroxamate system the stability constants are determined to be
log β110 = 7.92±0.11 and log β120 = 16.88±0.49. In the uranium(VI)-benzoate system only a 1: 1 complex is existent with a stability constant of log β110 = 3.56±0.05.
Authors:K. Chatterjee, D. Dollimore, and K. Alexander
Hydroxy benzoic acids were subjected to rising temperature thermogravimetric analysis. After optimizing the procedural variables,
the kinetics of decomposition was determined and methyl paraben was taken as the calibration compound to characterize the
evaporation patterns for the ortho and meta derivatives. The Eact values for ortho, meta and para derivatives were 64.8, 78.2, and 119.1 kJ mol–1, respectively. The Antoine and Langmuir equations were utilized to determine the coefficient of evaporation k, which was 1245250.8, units being in the SI system. The vapor pressure plots were generated for the ortho and meta derivatives; ΔHvap for these two compounds were obtained as 66.7 and 80.4 kJ mol–1, respectively.
Authors:J. Raj, N. Singh, S. Prasad, A. Seth, and T. Bhalla
The free and agar immobilized cells of
NHB-2 having nitrilase (EC 22.214.171.124) activity were used to catalyse the transformation of benzonitrile to benzoic acid. The whole cells of
NHB-2 were immobilized in agar which exhibited maximum conversion of benzonitrile to benzoic acid in 0.1 M potassium phosphate buffer pH 7.5 (free cells) 8.0 (immobilized cells), temperature 40 °C, cells 2 mg dcm ml
reaction mixture and benzonitrile (4% v/v) in 4 h (free cells). The effect of temperature on the stability of nitrilase was studied and cells retained 100% activity at 30 °C and lost 50% activity at 40 °C. In a fed batch mode of reaction 108 and 84 gl
benzoic acid was produced using free and agar entrapped cells (2 g dcm). The agar immobilized cells were recycled up to three times and 80, 62, 20 gl
benzoic acid was again produced respectively in each of three cycles and a total 244 g benzoic acid was produced by recycling the same mass of immobilized biocatalyst.
Authors:G. P. Bettinetti, C. Caramella, F. Giordano, A. La Manna, C. Margheritis, and C. Sinistri
Thermal analysis of the binary system benzoic acid (BA) and trimethoprim (TMP) provided evidence of the formation of two molecular compounds. BA-TMP and two crystalline forms of (BA)2-TMP were characterized on the basis of their thermodynamic parameters as well as of crystallographic and spectroscopic properties. The availability of these compounds (by recrystallization) allowed interpretation of thermal effects in the DSC curves of the mixtures and the theoretical phase diagrams could be drawn. The results are consistent with the model of a very slight dissociation of the molecular compounds in the melt.