Alcohol-water Solvent Research Articles

Effect of Dispersion Media Composition on the Structure and Rheology of the Short-Sidechain Perfluorosulfonic Acid Ionomer Dispersions

Perflourosulfonic acid (PFSA) ionomers are used in many applications including polymer-electrolyte membrane fuel cells and electrolysers owing to their many attractive properties such as excellent ion-conductivity, chemical resistance, mechanical properties, and thermal stability. In polymer-electrolyte membrane fuel cells and electrolysers, they are used as the membrane and as a component in the catalyst layers, to provide proton conductivity and serve as a binder for the catalyst particles, which are two key components of these devices. Understanding the structure and rheological properties of the ionomer dispersions is important for solution-processed fabrication of the membranes and the catalyst layers, and will enable better control their final structure/morphology, and improve the device performance. A water-alcohol solvent mixture is a common dispersion media for ionomer dispersions as well as the catalyst inks. While significant efforts exist on the structure of ionomer dispersions in water-alcohol solvent mixtures, their rheological properties, particularly the effect of solvent composition at non-dilute concentrations remain less explored. In this talk, the effect of water-alcohol (isopropanol) composition of the dispersion media on the rheological properties of ionomer dispersions will be presented. The results of small-angle x-ray scattering characterization of the ionomer dispersions will be also discussed. As a model ionomer, a short sidechain perfluorinated ionomer (PFSA), produced by 3M, was used. In dispersions with low ionomer concentrations, the zero-shear viscosity scaling with concentration was found to be similar for all alcohol fractions in the solvent mixture, following Fuoss’s law for polyelectrolytes. Whereas at higher concentrations, beyond the semi-dilute unentangled regime, their scaling was strongly dependent on alcohol fraction, where the scaling exponent increasing with increasing the alcohol fraction. Furthermore, the dispersions showed dramatic shear-thickening and strain-stiffening behaviors at higher alcohol fractions. The rheological observations suggest water-alcohol composition significantly alters the interactions between ionomer, and consequently their structure, and has strong implications in processing as well as on the morphology/structure of the membranes and the catalyst layers.

Solvation dynamics on the diffusion timescale elucidated using energy-represented dynamics theory.

Photoexcitation of a solute alters the solute-solvent interaction, resulting in the nonequilibrium relaxation of the solvation structure, often called a dynamic Stokes shift or solvation dynamics. Thanks to the local nature of the solute-solvent interaction, the characteristics of the local solvent environment dissolving the solute can be captured by the observation of this process. Recently, we derived the energy-represented Smoluchowski-Vlasov (ERSV) equation, a diffusion equation for molecular liquids, which can be used to analyze the solvation dynamics on the diffusion timescale. This equation expresses the time development for the solvent distribution on the solute-solvent pair interaction energy (energy coordinate). Since the energy coordinate can effectively treat the solvent flexibility in addition to the position and orientation, the ERSV equation can be utilized in various solvent systems. Here, we apply the ERSV equation to the solvation dynamics of 6-propionyl-2-dimethylamino naphthalene (Prodan) in water and different alcohol solvents (methanol, ethanol, and 1-propanol) for clarifying the differences of the relaxation processes among these solvents. Prodan is a solvent-sensitive fluorescent probe and is thus widely utilized for investigating heterogeneous environments. On the long timescale, the ERSV equation satisfactorily reproduces the relaxation time correlation functions obtained from the molecular dynamics (MD) simulations for these solvents. We reveal that the relaxation time coefficient on the diffusion timescale linearly correlates with the inverse of the translational diffusion coefficients for the alcohol solvents because of the Prodan-solvent energy distributions among the alcohols. In the case of water, the time coefficient deviates from the linear relationship for the alcohols due to the difference in the extent of importance of the collective motion between the water and alcohol solvents.

RATE AND SELECTIVITY OF HYDROGENATION OF 2-NITRO-2'-HYDROXY-5'-METHYLAZOBENZE OVER NICKEL CATALYST IN AQUEOUS SOLUTIONS OF ALIPHATIC ALCOHOLS

Elucidation of the causes and character of the composition and nature solvent influence on the kinetic regularities and selectivity of hydrogenation reactions of compounds containing several reactive groups is of theoretical and practical significance. In the present work, the process of 2-nitro-2'-hydroxy-5'-methylazobenzene catalytic hydrogenation in the liquid phase is considered in order to obtain the corresponding benzotriazole, an effective UV stabilizer of polymeric materials. The process was carried out on a skeletal nickel catalyst in aqueous solutions with different contents of aliphatic alcohols, both at atmospheric and elevated hydrogen pressures. It has been experimentally established that the shape of the hydrogenation kinetic curves is determined by the composition of the water-alcohol solvent and is transformed from the dependence with a maximum in media with low alcohol content to the stepped curve in concentrated solutions. The dependences of the reaction rate on the content of aliphatic alcohol are complex, and the maximum hydrogenation rates are observed in solvents with a content 0.6÷0.7 ppm. of alcohol. The change in the process rate is associated with a change in the solubility, value of adsorption and reactivity of the starting compound and hydrogen. These factors also determine the selectivity of the process due to their influence on the rates of individual steps in the 2-nitro-2'-hydroxy-5'-methylazobenzene conversion scheme, in particular, on the cyclization rate of the associative surface complex "nitroazobenzene∙H2". The cyclization product of the complex is an intermediate compound, benzotriazole N-oxide, the reduction of which leads to the formation of a substituted benzotriazole. It is shown that the maximum yield of the target product is 48÷3% at atmospheric hydrogen pressure, and increases to 73.5-0.5% at PН2 = 1 MPa.

Tunable UCST behaviour of a hydrophobic dialkoxynaphthalene-functionalized homopolymer based on reversible supramolecular recognition

Thermoresponsive polymers with reversible phase transition are appealing to various applications. Herein, we designed and synthesized a thermosensitive homopolymer bearing hydrophobic dialkoxynaphthalene moieties as polymer side chains that revealed UCST behaviourin pure ethanol and ethanol/water mixtures. It is reported that the complexation with the tetracationic macrocycle cyclobis(paraquat-p-phenylene) (CBPQT4+) host is strongly dependent on the degree of complexation due to steric hindrance and charge repulsion.Moreover, it was found that the cloud-point temperatures (TCP) of the homopolymer could be modulated by host–guest complexation with CBPQT4+ in alcohol-water solvent mixtures up to 6 equivalents of the host. When heated above theclearance-point temperatures, the homopolymer dissolves, but the host–guest interactions become unstable and are disrupted due to the effect of the solventand the higher temperature. Subsequent cooling led to the collapse of the homopolymer, together with the reformation of the host–guest complexes resulting in a purple opaque solution. The tunable UCST approach may enable practical applications in the biomedical field or interactive smart materials.

Viscoelasticity Enhancement and Shear Thickening of Perfluorinated Sulfonic Acid Ionomer Dispersions in Water–Alcohol Solvent Mixtures

Viscoelasticity Enhancement and Shear Thickening of Perfluorinated Sulfonic Acid Ionomer Dispersions in Water–Alcohol Solvent Mixtures

OBTAINING DRY EXTRACTS FROM LICORICE ROOTS (GLYCYRRHIZA GLABRA) AND ITS STANDARDIZATION

Licorice (Glycyrrhiza glabra) root has long been used in traditional medicine due to its various therapeutic properties. One of the main active components in licorice root is glycyrrhizin, which has been shown to possess numerous pharmacological effects. Glycyrrhizin, one of the major compounds present in licorice root, has been shown to possess anti-inflammatory, antioxidant, and anti-tumor propertiesas well as antiviral properties against influenza virus and coronavirus COVID-19. The demand for licorice root extracts is increasing, particularly for use in the food and pharmaceutical industries. However, the quality and consistency of licorice extracts can vary depending on the extraction method used. Therefore, the aim of this study was to optimise the technology for obtaining dry extracts from licorice roots and standardise the process for increased consistency and quality of the final product. In this study, two different methods for extraction were compared: ultrasound-assisted extraction using water and alcohol-water solvents. The extracted samples were then subjected to various quality control tests, including glycyrrhizin content and moisture content. The content of glycyrrhizin in the obtained dry extracts was determined using high-performance liquid chromatography (HPLC). The standardisation of the dry extract was performed according to the Pharmacopoeia of the Eurasian Economic Union. The results showed that the optimised technology for obtaining dry extracts from licorice roots was water extraction with ultrasound, as it yielded a higher content of glycyrrhizin compared to ethanol extraction with ultrasoundand the optimal conditions for ultrasound-assisted extraction were an extraction time of 60 minutes, frequency of ultrasound bath at 40 kHz, an extraction temperature of 30°C, and a solid-to-liquid ratio of 1:6. The standardisation process confirmed the presence of glycyrrhizic acid and purity of the obtained dry extract.

Effect of Water on Direct Radioiodination of Small Molecules/Peptides Using Copper-Mediated Iododeboronation in Water-Alcohol Solvent.

Direct radioiodination of peptides using copper-mediated iododeboronation is a promising radiosynthetic method for solving issues of classical direct radiolabeling, such as toxicity of the organotin precursor (iododestannylation) or formation of radio byproducts (by electrophilic iodination of a tyrosine residue). However, the parameters for optimizing the reaction conditions for various peptides are not completely understood. In particular, considering peptide solubility, the effects of water-containing solvents on labeling efficiency should be thoroughly investigated. Herein, we describe the effect of water on copper-mediated radioiododeboronation and the key factors for ensuring the successful radiolabeling of small molecules and peptides in water-organic solvents. 125I-labeled substrates containing peptides ([125I]m/p-IBTA) were obtained with high radiochemical conversions (RCCs: >95%) using an alcohol solvent, and a decrease in these RCCs was observed with increasing water content in the methanol solvent. Additionally, when using water-methanol solvents, a difference in RCC due to the substituent effect was also observed. However, the RCCs can be improved without the use of other additives by adjusting the copper catalyst and time of the labeling reaction or by utilizing substituent effects. This study contributes to the improvement of the design of boronic peptide precursors and radiolabeling protocols using copper-mediated iododeboronation.

THE OBTAINING OF WATER-ALCOHOLIC AND SUGAR EXTRACTS FROM BERRIES

It was investigated the extraction of the dry substances with a water-alcohol solvent and the subsequent preparation of sugar extract from black currant, jostaberry, and plum. The water-alcohol solvent extracts the least dry matter from currant berries. The dry substance content in the black currant extract was 1.6%, while water-alcohol extracts from jostaberry and plum contained 4.3-5.5% of dry substances. At the same time, the content of dry substances in the extract is 1.6%, while water-alcohol extracts from gooseberry and plum contain 4.3–5.5% of dry substances. A significant amount of alcohol accumulates in the berries during the water-alcohol extraction. The alcohol content in all extracts, compared to the extractant, decreases from 40.0 to 25.06–26.39 wt. %. Simultaneously the alcohol losses decrease in further obtaining sugar extract from berries. The alcohol content in berries reaches 9.79 wt.% in black currant, 14.51 wt.% in plum, and 14.92 wt. % in jostaberry extract, particularly. The obtained sugar extracts contain different amounts of dry matter depending on the type of berries. The maximum degree of sugar utilization (79.0%) was during the preparation of black currant extract, which contains the maximum amount of dry substances (43.4%). The degree of sugar utilization by the plum extract obtaining was 71.6%. That corresponds to the dry substances content in the extract at 34.5%. The minimum degree of sugar utilization (31.5%) was during the production of jostaberry extract. The degree of sugar use ensures the content of dry substances in the extract of 31.8%. It was established that water-alcohol and sugar extracts from berries have maxima of visible light absorption in the range corresponding to anthocyanins absorption. The highest optical density has a water-alcohol extract from currants. A high content of polyphenolic compounds characterizes that. We established that acids are extracted almost the same amount from the berry raw material with a water-alcohol solution and during sugar treatment. The extracts from jostaberry have the maximum acidity, and its lowest value is characteristic of extracts from plum. The degree of extraction of vitamin C from berries was approximately the same and was 59% for jostaberry and 66% for black currant and plum. The perspective of using berries after extracting them as raw materials for obtaining various confectionery products is indicated.

Solvent-dependent structural and electrochemical properties of zinc cobaltite via a self-assembled mechanism for battery-type supercapacitors

This paper reports the influence of the solvent’s properties on the growth mechanism of zinc cobaltite (ZnCo2O4) microstructures and their surface morphologies. We observed that the ZnCo2O4 microstructures (ZCO) offer a large number of interacting sites due to the solvent variation, influencing the phase purity and high crystallinity of the ZnCo2O4, which strongly affects its electrochemical conductivity. ZCO crystals were synthesized separately in water, ethanol, and isopropyl alcohol solvent at 180 °C for 12 h, governing the formation of 2D sheet-like morphology in water (ZCO-DIW), 3D flower-like and peanut-like morphologies in ethanol (ZCO-ETH), and isopropyl alcohol (ZCO-IPA), respectively. The successful formation of ZCO morphologies was confirmed through high-resolution scanning electron microscopy. Concerning the solvent variation, the specific surface area of the three ZCO electrodes varies in ascending order as ZCO-DIW (23.78 m2 g−1) < ZCO-IPA (27.19 m2 g−1) < ZCO-ETH (37.19 m2 g−1). We also proposed a model for this solvent-dependent formation mechanism of three ZCO electrodes via the self-assembly process. The electrochemical performance of the ZCO electrodes exhibits excellent battery-type behavior with a specific capacity of 98.89 mAh g−1 (for ZCO-ETH) owing to the highly porous flower-like morphology. These results revealed a simple and cost-effective synthesis strategy to fabricate micro/nano-structure with diverse morphology for a wide range of interfacial applications.

Understanding the role of saturated alcohols in transforming crystal morphology of calcium minodronate grown from aqueous solution

The influence of saturated alcohols on calcium minodronate (Ca(Min)2) crystal morphology was studied with a combination of crystal growth experiments and molecular simulations. The modified attachment energy (AE) model was used for the construction of Ca(Min)2-alcohol-water model to reveal the crystal-solvent interactions. The interfacial configuration and the mass density profile were illustrated for analysis. The results indicated that there were varied adsorption behaviors in various alcohol-water solvents. Moreover, it was noted that the (200)/(110) side ratio of crystal morphology had basiclinearity with the volume of alcohols and had a certain correlation with alcohol properties. This research would have a prospective application in predicting Ca(Min)2 crystal morphology and could offer an instruction in selecting and adding alcohols to regulate the target crystal morphology.

Feedstock-agnostic reductive catalytic fractionation in alcohol and alcohol–water mixtures

This work demonstrates that reductive catalytic fractionation can be a feedstock-agnostic process on hardwoods, softwoods, agricultural residues, and grasses, especially with water-alcohol solvent mixtures.

Tuning the Rheology of Anode Inks with Aging for Low-Temperature Polymer Electrolyte Membrane Water Electrolyzers

Low-temperature polymer electrolyte membrane water electrolyzers (PEMWE) are an attractive clean energy technology to produce hydrogen (H2), which is an energy carrier for several applications such as transportation and grid-scale energy storage and distribution (as supported by the US Department of Energy’s H2@Scale initiative). The catalyst layers -- composed of catalyst particles and ionomer, which acts as a binder for the catalyst and a proton conducting medium -- are key components of the PEMWE membrane electrode assembly (MEA). The catalyst layers are commonly fabricated by solution-processing an ink, which is a mixture of catalyst and ionomer often dispersed in a water-alcohol solvent mixture. Tuning the rheological properties of the anode inks (typically composed of iridium oxide catalyst, IrOx), particularly increasing their viscosity without significantly increasing the solids loading, to suit various scalable coating methods, is generally a challenge due to relatively low porosity and high density of the IrOx catalysts compared to the carbon-supported cathode catalysts. The typically low viscosities of the anode inks combined with high particle densities often cause stability/settling issues and challenges obtaining unform coatings, leading to inhomogeneous distribution of the catalyst that may have a negative effect on electrode performance. In this presentation we report on a dramatic enhancement in the viscoelasticity of the anode inks with aging, where the ink transitions from a liquid-like to a weak gel-like structure. The steady-shear and oscillatory shear rheology characterizations of the inks as a function of aging/time, the impact of formulation conditions (ionomer-to-catalyst ratio and dispersion media composition) on the viscoelastic enhancement with aging, and possible mechanisms for the observed behavior will be discussed. In addition to the rheological measurements, X-ray scattering characterization of the ink structure will be presented. The implications of the rheological changes on ink stability and processing will also be discussed. Additionally the impact of ink age on MEA performance will be presented.

Liquid-liquid equilibrium of water, ethyl acrylate, and alkyl alcohol solvents: Extractant screening and thermodynamic analysis

Ethyl acrylate (EA) has a wide range of uses, providing convenience for industrial production and daily life. The production process often produces water by-products, so this work selects four commonly used alcohols (1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol) as extractants to explore the liquid–liquid equilibrium (LLE) of water + EA + extractants. Through the analysis of partition coefficient (D), and separation factor (S), it is found that the data of all systems are>1. At the same time, the RMSD% and AAD% calculated by the regression of thermodynamic models (NRTL and UNIQUAC) are both less than 1, indicating that all four alkyl alcohols can separate EA from aqueous solutions well, and 1-octanol has the best effect. Furthermore, the consistency of the LLE data is demonstrated using MATLAB tools.

Novel insights into the mechanism for protic solvent promoting Pd/C-catalyzed hydrodechlorination of chlorinated organic compounds

• Protic solvents promoted catalytic HDC of 4-CBP with Et 3 N over Pd/C catalyst. • HDC rate of 4-CBP increased with increase of water content in mixed solvent systems. • Mechanism for protic solvents promoting Pd/C-catalyzed HDC reactions was elucidated. • Protic solvents participated in Pd/C-catalyzed HDC and hydrogenation reactions. Solvent effects in liquid-phase hydrodechlorination (HDC) of chlorinated organic compounds (COCs) over Pd/C catalyst were systematically studied. For the HDC of 4-chlorobiphenyl (4-CBP) with triethylamine (Et 3 N), Pd/C exhibited much higher catalytic activity in protic solvents than that in aprotic polar and non-polar solvents, and a clear correlation between the HDC rate and polarity of protic solvents was observed. Moreover, water promoted Pd/C-catalyzed HDC of 4-CBP in homogeneous alcohol-water solvents and biphasic organic-water solvents with Et 3 N, and the HDC rate of 4-CBP increased with the increase of water content in the above solvent systems. Catalyst characterization (FT-IR and XRD) combined with solvent parameters and isotope labelling analysis were introduced to explain in-depth the solvent effects in the HDC of 4-CBP with Et 3 N. It was found that protic solvents would transfer active hydrogen atom (H*) via hydrogen bonding network or exchange their hydroxyl hydrogen with H*, which was beneficial to the stabilization of H* and interface HDC reaction. Thus, the higher HDC rate was achieved in solvent systems contained protic solvents with higher hydrogen-bond donor capability ( α ) values. On the other hand, non-polar and polar aprotic solvents had a negative effect on H* and mass transfer, and thus suppressed interface HDC reaction. Similar solvent effects were observed in Pd/C-catalyzed hydrogenation of unsaturated bonds-containing groups (nitryl group, carbonyl group, and carbon-carbon double bond). The results presented here would provide vital guidance for the rational selection of solvent systems for Pd/C-catalyzed HDC of COCs and hydrogenation of unsaturated bonds-containing groups.

Carbons derived from alcohol-treated bacterial cellulose with optimal porosity for Li–O2 batteries

Porous carbons are important cathode materials for metal-air batteries, but the most usual methods to prepare these porous structures are complex and of high cost. We have prepared porous carbons from bacterial cellulose (BC) hydrogels by a simple water-alcohol solvent exchange before carbonization. Alcohol treatment facilitates looser and more open structures than untreated BC, resulting in porous carbon structures with high surface area, appropriate for electrochemical applications. Used as cathodes in lithium-oxygen batteries, the carbon derived from 1-butanol treated BC has excellent discharge capacity (5.6 mA h cm−2) and good cycle life. This work presents a sustainable, straightforward and fast way to prepare porous carbon materials from BC.

Structure-property relationships on recrystallized β-cyclodextrin solvates: A focus on X-ray diffractometry, FTIR and thermal analyses

The goal of the study was to evaluate the influence of the solvent properties on the crystal characteristics of β-cyclodextrin (β-CD) recrystallized from alcohol-water solvent mixtures, with possible applications for the preparation, purifying and complexation of β-CD. For the first time, structure-property relationships (QSPRs) between the hydrophobicity of alcohols or dielectric constant of solvents used for recrystallization of β-CD and its properties (such as crystallinity index, CI) have been obtained. Recrystallized β-CD from water and C1-C4 alcohol-water solutions provide β-CD with higher CI values of 99.4(±5.9)% for ethanol-water (1:4, v/v) as recrystallizing system. This property has a parabolic variation with the logP (octanol/water partition coefficient) of the alcohol (r2 = 0.998). Solvent parameters also influence the β-CD crystal characteristics, as was demonstrated by X-ray diffractometry refinement, infrared spectroscopy and thermal analyses.

Formation of Fe, Pt and (Pt/Fe) ultra-fine metal nanoparticles in different solution polarity prepared by Nd-YAG pulsed laser

Iron(Fe/FeO), Platium (Pt) and (Pt/Fe) ultra Fine(UF) nanoparticles (NPs) were synthesized by pulsed (Q-switched, 1064 doubled frequency-Nd: YAG). The laser ablation of Fe and Pt metal plates has been performed by immersing these metal plates in deionised water (DDW) and ethanol alcohol solvent. The pulsed laser ablation in liquids (PLAL) process preformed with 100 pulse energy of 700 mJ and liquid depth is 5 mm. The formation efficiency of PLAL process was quantified in term of the absorption spectrum peaks and TEM images anlaysis. The absorption spectra of Iron (Fe/FeO, Pt) in DDW reveal a sharp and single peak around (292/363 and 234)nm, respectively, indicates the production of pure and spherical shape of Fe/FeO, Pt UF NPs with an average size in the range of 2-5 nm. While, it was notice absorbance peaks wavelength shifted to the shorter wavelength in ethanol alcohol due to high polarity of alcohol in both bimetalic nanoparticles (Fe and Pt). By changing the solution polarty it can open an easy way to control the size and shape of Fe and Pt and Bimetals (Pt/Fe ) colloidal nanoparticles.

The microstructure and magnetic properties of yttrium iron garnet film prepared using water-alcohol solvents

This study reports on the preparation of yttrium iron garnet thin films using three different solvents via a sol-gel method, followed by a spin coating technique and an annealing process at 750 °C for 2 h in the air. The three different solvents were water-ethanol, water-methanol and water. The microstructure analysis using an X-ray diffractometer revealed that the films prepared using a water-alcohol solvent crystallized into YIG single phase at a low annealing temperature (750 °C). The film thicknesses are in the range of 200 nm to 400 nm. The film prepared using a water-ethanol solvent has the smallest crystallite size. All films are soft ferrimagnetic at room temperature and the film prepared using a water-ethanol solvent exhibits the highest saturation magnetization value (162 emu/cm3).

Preferential Ion Microsolvation in Mixed-Modifier Environments Observed Using Differential Mobility Spectrometry.

The preferential solvation behavior for eight different derivatives of protonated quinoline was measured in a tandem differential mobility spectrometer mass spectrometer (DMS-MS). Ion-solvent cluster formation was induced in the DMS by the addition of chemical modifiers (i.e., solvent vapors) to the N2 buffer gas. To determine the effect of more than one modifier in the DMS environment, we performed DMS experiments with varying mixtures of water, acetonitrile, and isopropyl alcohol solvent vapors. The results show that doping the buffer gas with a binary mixture of modifiers leads to the ions binding preferentially to one modifier over another. We used density functional theory to calculate the ion-solvent binding energies, and in all cases, calculations show that the quinolinium ions bind most strongly with acetonitrile, then isopropyl alcohol, and most weakly with water. Computational results support the hypothesis that the quinolinium ions bind exclusively to whichever solvent they have the strongest interaction with, regardless of the presence of other modifier gases.

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.