Nitrobenzoic Acid Isomers Research Articles

INTERRELATION BETWEEN CATALYTIC REDUCTION RATE AND SOLUBILITY OF NITROBENZOIC ACID ISOMERS

The solubility of nitrobenzoic acid isomers is determined from the concentration of solution in equilibrium with the solid phase at a temperature of 303 K in an azeotropic aqueous solution of 2-propanol, including additives of acetic acid and sodium hydroxide, with an error of no more than 5%. It is shown that the lowest solubility in all these media is observed for para-nitrobenzoic acid, and the maximum for the meta-isomer. The addition of acid or base to the liquid phase assists an increase in solubility for all isomers of nitrobenzoic acid. The most significant changes in solubility occur in the presence of sodium hydroxide in the water-alcohol solvent. The shift of the maxima in the absorption spectra was compared with the change in the solubility value. It has been established that with increasing solubility, the rate of liquid phase catalytic hydrogenation of nitrobenzoic acid isomers on the skeletal nickel catalyst decreases. А linear correlation between the solubility of reagents and the rate of their reduction is revealed. The observed interrelation for para- and meta-isomers in neutral and acidic aqueous-alcoholic media is mostly caused by the influence of solubility on the adsorption ability of the hydrogenated compound on the surface of the nickel catalyst. Deviations from this dependence in the presence of sodium hydroxide can be explained by ionization of the of nitrobenzoic acid isomers molecules and by redistribution of the forms of hydrogen adsorbed on the surface of the nickel catalyst. The reason of the distinction in a similar correlation for isomers with a substituent in the ortho-position relative to the nitrogroup is the possibility for forming an intramolecular hydrogen bond in all used media.

Durability and mechanical properties of C–S–H/nitrobenzoic acid composite systems

The influence of nitrobenzoic acid on the nanostructure of calcium-silicate-hydrate (C–S–H) systems has been recently investigated by the authors. This study focuses on the assessment of durability and mechanical performance of the C–S–H/nitrobenzoic acid composite systems. In this context different nitrobenzoic acid isomers in various concentrations were studied. The C–S–H-based preparations were compacted into porous bodies. Their dimensional stability and the leaching of calcium ions in aqueous salt solutions containing Mg2+, Li+, Cl− or SO42− ions were evaluated. The resistance of the compacted samples to the diffusion of isopropyl alcohol was also obtained by the mass-change measurements. The microindentation technique was used to measure the creep modulus and the hardness of the samples. Evidence was obtained that nitrobenzoic acid has the potential to significantly improve the durability and mechanical properties of the C–S–H systems. This improvement, however, only occurred in the systems with the lower concentration of nitrobenzoic acid. The systems with higher concentration of nitrobenzoic acid had reduced durability and mechanical performance due to the limited interaction of the organic and inorganic phases in these systems.

Interaction of 2-, 3- and 4-nitrobenzoic acid with the structure of calcium–silicate–hydrate

Interaction of nitrobenzoic acid (NBA) with the structure of calcium–silicate–hydrate (C–S–H) was investigated. Phase pure C–S–H and C–S–H with 2-, 3- or 4NBA (0.01 and 0.02 mol/mol of Ca) were synthesized, and characterized by the X-ray diffraction, thermal analysis, Fourier transform infrared spectroscopy and scanning electron microscope techniques. Nitrogen adsorption measurements were also performed to estimate the surface area of the samples. It is suggested that all NBA isomers with the concentration of 0.01 mol/mol of Ca were able to fill the defects on the surface of the C–S–H layers, block access to the space between the stacked C–S–H layers, and possibly partially intercalate the layered structure. The C–S–H-based samples prepared with different types of NBA compounds, however, had different characteristics. The interaction of organic and inorganic phases was limited in the samples incorporating higher concentration of NBA. Traces of unreacted NBA were detected in a few samples with 0.02 mol of NBA/mol of Ca.

Mixture solubilities of nitrobenzoic acid isomers in supercritical carbon dioxide

The ternary solubilities of solid isomers of nitrobenzoic acid (NBA) were experimentally determined at 308, 318 and 328K over a pressure range of 12–18MPa in supercritical carbon dioxide (SCCO2). Compared to its binary solubility, the ternary solubilities of m-NBA increased at 308K while it decreased at 328K. However, the ternary solubilities of p-NBA increased at all temperatures and pressures except at 13MPa and 328K. A new model was developed by applying solution model and activity coefficient model for the ternary solubilities of pharmaceutical and non-pharmaceutical solid mixtures in terms of temperature, density and cosolute composition. The model equation involves four temperature independent constraint-free parameters. The model equation correlates the ternary solubilities of seven pharmaceutical solid mixtures along with current data with an average AARD around 9.5% and sixteen non-pharmaceutical solid mixtures with 9% AARD.

Thermodynamic and kinetic characteristics of liquid phase hydrogenation of substituted nitrobenzenes

Quantum-chemical calculations of the thermodynamic characteristics of hydrogenation of nitrobenzoic acid isomers and nitrophenol in the gas phase and also in aqueous and alcoholic media were performed. Correlation dependences between the calculated ΔrG298○ values and rate constants for the reaction in various media were obtained.

Microwave-assisted digestion procedures for biological samples with diluted nitric acid: Identification of reaction products

Microwave-assisted sample preparation using diluted nitric acid solutions is an alternative procedure for digesting organic samples. The efficiency of this procedure depends on the chemical properties of the samples and in this work it was evaluated by the determination of crude protein amount, fat and original carbon. Soybeans grains, bovine blood, bovine muscle and bovine viscera were digested in a cavity-microwave oven using oxidant mixtures in different acid concentrations. The digestion efficiency was evaluated based on the determination of residual carbon content and element recoveries using inductively coupled plasma optical emission spectrometry (ICP OES). In order to determine the main residual organic compounds, the digests were characterized by nuclear magnetic resonance ( 1H NMR). Subsequently, studies concerning separation of nitrobenzoic acid isomers were performed by ion pair reversed phase liquid chromatography using a C18 stationary phase, water:acetonitrile:methanol (75:20:5, v/v/v) + 0.05% (v/v) TFA as mobile phase and ultraviolet detection at 254 nm. Sample preparation based on diluted acids proved to be feasible and a recommendable alternative for organic sample digestion, reducing both the reagent volumes and the variability of the residues as a result of the process of decomposition. It was shown that biological matrices containing amino acids, proteins and lipids in their composition produced nitrobenzoic acid isomers and other organic compounds after cleavage of chemical bonds.

Separation and Retention Behavior of Aromatic Carboxylic Acid Isomers by High‐Performance‐Liquid‐Chromatography Using β‐Cyclodextrin Bonded Phase with Diamine‐s‐Triazine Moiety

AbstractA β‐cyclodextrin (β‐CD) bonded phase with diamine‐s‐triazine moiety was prepared. The separation and retention behavior of the isomers of five aromatic carboxylic acids, including toluic acid, aminobenzoic acid, nitrobenzoic acid, hydroxybenzoic acid, and naphthoic acid were investigated by a high‐performance liquid chromatography (HPLC) using the β‐CD bonded phase prepared. The influence of mobile phase pH in the range of 2.7‐3.6 on the retention of these analytes was examined. The isomers of the aromatic carboxylic acids, with the exception of nitrobenzoic acid, were optimally and effectively separated at pH 2.7, while the three isomers of nitrobenzoic acid could be well separated at pH 3.3. Compared with the chromatographic results obtained previously on the amine‐s‐triazine‐β‐CD bonded phase, the retention factors of the isomers of aromatic carboxylic acid on the diamine‐s‐triazine‐β‐CD bonded phase increase to a relatively much greater extent. Thus, the functionality of the spacer arm of the bonded phase playing an important role in the retention of aromatic carboxylic acid isomers is demonstrated. The results also imply that the hydrogen‐bonding interaction and the mechanism of anion exchange sorption as well may contribute significantly to the retention mechanisms.

Separation of positional isomers of nitrobenzoic acid by reversed-phase liquid chromatography with 2-propanol–water–acetic acid as eluent

A method for the separation of o-, m- and p-nitrobenzoic acid was developed using reversed-phase liquid chromatography. A C18 bonded column (150 mm×4.6 mm I.D.) was used as stationary phase and 2-propanol–water–acetic acid (20:80:0.4, v/v/v, pH 2.99) at a flow-rate of 1.2 ml/min as eluent; the detection wavelength was 254 nm. The nitrobenzoic acid isomers are separated with Rs≥1.5, the detection limits (at 254 nm) of the o-, m- and p-isomers are 4, 7 and 5 μg/ml, respectively. This method is very simple and reproducible.

Methylated cyclodextrins as mobile phase additives in liquid chromatography

Both 2,3,6- and 2,6-methylated derivatives of α and β cyclodextrins were added to the mobile phases in liquid chromatography using an octadecylsilyl stationary phase. The 2,3,6-methyl-substituted derivative of α-cyclodextrin improves the separation of the ortho, meta and para isomers of disubstituted benzenes and also decreases their retention compared with the unmodified α-cyclodextrin. By the addition of 2,3,6-methylated β-cyclodextrin, the three isomers of nitrobenzoic acid can be completely separated, and the separation of trans-nitrocinnamic acid is greatly improved. In contrast, 2,6-dimethylation of both α- and β-cyclodextrins did not bring about such significant improvements in the retention of the solutes investigated.

Analysis of nitrobenzoic acid isomers by high-performance liquid chromatography

Analysis of nitrobenzoic acid isomers by high-performance liquid chromatography

Gas chromatographic analysis of nitrobenzoic acid isomers

Gas chromatographic analysis of nitrobenzoic acid isomers

1365. Nitrobenzoic acid isomers compared

1365. Nitrobenzoic acid isomers compared