Functions of Hydrotropes in Solutions

Hydrotropes affect a several‐fold increase of the solubility of sparingly soluble solutes under normal conditions. Their water‐solubility can significantly enhance the solubility of organic solutes such as esters, alcohols, aldehydes, ketones, hydrocarbons, and fats. While the study of hydrotropes is pioneered by a biochemist, greater appreciation of their role and applicability has happened rather in chemistry and chemical engineering than in biology. Hydrotropes are widely used in drug solubilization, as extraction agents for fragrances, as agents to increase the rate of heterogeneous reactions, and for separation of close‐boiling liquid mixtures through extractive distillation and liquid‐liquid extraction. Applications of hydrotropy and its mechanism are discussed and the scope for future work is presented in this review.     

Additive-induced association in unconventional systems: A case of the hydrotrope

It is well known that hydrotropes have a very high minimum hydrotrope concentration (MHC), posing a question on their applications. We have found that MHC (obtained by conductivity and surface tension measurements) can be reduced by the addition of foreign materials. The association tendency can be improved by the addition of salts, n-alkanols, and ureas. Urea decreases or increases the MHC depending on whether the urea content is lower or higher (e.g., the increased solubility of sparingly soluble riboflavin corroborates the increase in the hydrotropic properties of the system). In the present work, the association tendencies of sodium salicylate (a well-known hydrotrope), sodium dodecyl sulfate, and sodium bromide were compared. The results have direct implications in the mechanism of protein denaturation and may provide insight into the role of urea in supramolecular assemblies.     

Dissociation ability of humic acids: Spectroscopic determination of pKa and comparison with multi-step mechanism

Humic acids are operationally defined as the fraction of humic substances which is not soluble under acidic conditions. This, does not mean, however, that their solid particles easily dissolve in water. Experimental results suggest that the dissolving of solid humic acids in an aqueous environment is more complex than the conventional solubility behaviour of sparingly soluble solids. The multi-step mechanism of their interaction with water includes partial equilibrium dissolution as well as direct equilibrium dissociation from the solid state. In this work, the pK_a value of the dissolved humic acid fraction was determined on the basis of changes in the shape and intensity of their UV/VIS spectra measured in media with various values of pH. The shape of the spectra depends on the pH value, because acidic and alkaline media, in which these compounds are dissolved, shift their dissociation equilibrium towards non-dissociated molecules or to completely dissociated species. The aim of this work was to characterize the dissociation behaviour of selected humic samples by means of dissociation constants using this method. It was shown that the obtained values of pK_a characterize the real dissociation behaviour of humic acids in an aqueous environment and can be used as the mean or effective value of pK_a corresponding with the multi-step mechanism of dissociation of humic acids.     

Effect of hydrotropes on solubility and mass transfer coefficient of lauric acid

A comprehensive investigation on the solubility and mass transfer coefficient enhancement of lauric acid through hydrotropy has been undertaken. The solubility and mass transfer studies were carried out using hydrotropes such as sodium cumene sulfonate, sodium p-xylene sulfonate and sodium p-toluene sulfonate under a wide range of hydrotrope concentrations (0 to 3.0 mol/L) and different system temperatures (303 to 333 K). The effectiveness of hydrotropes was measured in terms of Setschnew constant K _s and reported for all hydrotropes used in this study. The solubility data are also fitted in a polynomial equation as the function of hydrotrope concentration.     

Solubility criteria for a thermally stable polymer determined by gas–solid chromatography

The Gibbs energy of adsorption, the Flory-Huggins interaction parameter χ, and a specific interaction parameter A, based on hydrogen-bonding and charge-transfer complexing properties of solvents, are obtained by gas—solid chromatography for a type of polyquinoxaline denoted as PQF. Interactions between 40 organic solvents and PQF have been determined at 176.35° and 200.85°C. PQF is an aromatic, heterocyclic polymer which is at least partially soluble in several organic solvents. The parameters χ and Λ and the solubility parameters of solvents are proposed to be the determining factors for miscibility of a PQF—solvent pair.     

Electrometric Study on Cu(II), Hg(II), and Ag(I) Complexes of Furfuryl Mercaptan and the determination of their solubility products

Furfuryl mercaptan has been found to form soluble and sparingly soluble complexes with metals. The composition and stabilities of the soluble complexes of uranyl [1], zinc [2], thorium [3], lanthanum and cerium [4] have already been reported by the authors. The present communication describes the composition of sparingly soluble complexes of Cu(II), Hg(II) and Ag with furfuryl mercaptan by amperometric, condutometric and potentiometric methods and the determination of their solubility products by polarographic technique applying RINGBOM 's method.     

The influence of molecular diffusion on mass transfer between turbulent liquids

The influence of molecular diffusion on liquid—liquid mass transfer in a stirred transfer cell has been found by measuring the rates transfer of helium and iso-butane from water to toluene and dekalin. These solutes have very different diffusion coefficients, their presence does not alter the physical properties of the liquids and, because their equilibrium distributions strongly favour the organic phases, the water phase mass transfer coefficient could be determined and was found to depend on the square root of the diffusion coefficient.The results are compared with the predictions of a model for liquid—liquid mass transfer under turbulent conditions, based on the approach of an eddy to the interface being restrained by interfacial tension and gravitational forces and taking into account eddy pressure fluctuations in both phases. This model provides a correlation for these results, as well as water phase mass transfer coefficients for the transfer of iso-butane from water to n-octanol, and previous stirred transfer cell results.     

Enhancement of oxygen mass transfer rate in the presence of nanosized particles

Absorption of gases into a liquid is essentially important for two- or three-phase reactions, because the diffusion of a sparingly soluble gas, like oxygen, across a gas-liquid interface generally limits the reaction rates. Using a third, dispersed phase, the mass transfer rate could be significantly increased. The question arises how the absorption rate can be described in the presence of very fine, nanometer size particles or droplets. Its mathematical model should take into account the specific properties of the nanoparticles, e.g. the Brownian motion of particles, its effect on the diffusion of the bulk phase molecules, the mass transfer rate into the nanoparticles, its dependency on the particle size, etc. The mass transfer rate of oxygen, in the presence of nanometer size, organic droplets, has been investigated both experimentally, using organic submicron n-hexadecane droplets, and theoretically. The effect of the Brownian motion of the nanoparticles as well as its effect on the diffusivity in the nanofluid has been discussed. Accordingly, the enhanced diffusion coefficient, due to the convective motion of the continuous liquid phase induced by the moving particles, has been predicted and its effect on the mass transfer enhancement has been calculated using both homogeneous and heterogeneous mathematical models. The predicted data were compared to the measured ones.     

Effect of Organic Additives on the Phase Separation Phenomenon of Amphiphilic Drug Solutions

The effect of various organic additives, viz. sugars, ureas, alcohols, hydrotropes and bile salts on the clouding (phase separation) phenomenon of the amphiphilic antidepressant drug amitriptyline hydrochloride was investigated in the present study. All sugars lowered the cloud point (CP) due to their water structure-making property. Urea and alkylureas were found to lower the CP. In contrast, thioureas increased the CP slightly, but the presence of methyl group(s) had a similar effect in alkylureas. Short chain alcohols affected the CP insignificantly while higher ones decreased it, and medium chain alcohols showed peak behavior. Addition of hydrotropes and bile salts increased the CP at lower concentrations, while a decrease was observed at higher concentrations (like the medium chain alcohols). In addition, thermodynamic parameters were also evaluated but only for those additives which formed mixed micelles with the drug.     

Chemical engineering aspects of precipitation from solution

Precipitation is a rapid solidification. As a rule, it applies to substances which are sparingly soluble and is coupled with a chemical reaction or with a salting out process. The chemical engineer has to ensure that the product obtained has a constant and preferably coarse size distribution. This contribution compares the literature data on crystallization of soluble and sparingly soluble substances; it can be shown that, during precipitation processes, nuclei are formed, most probably by a primary mechanism. Analysis of the processes occurring during precipitation, such as chemical reaction, mixing and crystallization, leads to recommendations for the operation of precipitation processes.     

气体在混合溶液中溶解度的分子热力学计算

开发出一个分子热力学模型来预测低压下难溶于溶剂且不与溶剂发生反应的气体在二元混合溶液的溶解度,混合物中含有缔合作用成分及溶剂化作用成分,即形成配位化合物。在该模型中,Gibbs能为三个等温混合过程的和。溶质的偏摩尔过量Gibbs能由两部分组成,即化学和物理贡献。为了验证该模型的准确性,将该模型用于计算氮气在丙酮和氯仿混合物的溶解度。考虑实验的不确定度,氮气在二元混合溶液中的溶解度与实验数据吻合良好。     

ENHANCEMENT OF SOLUBILITY AND MASS-TRANSFER COEFFICIENT OF 1,2-DIHYDROXY-9,10-ANTHRAQUINONE (ALIZARIN) THROUGH HYDROTROPY

The effect of hydrotropes potassium p-toluene sulfonate (KPTS), citric acid, and nicotinamide on the solubility and mass-transfer coefficient of 1,2-dihydroxy-9,10-anthraquinone (alizarin) was studied. Solubility studies were carried out under a wide range of hydrotrope concentrations (0 to 3.0 mol·L^?1) and different system temperatures (303 to 333 K). It was observed that the solubility and mass-transfer coefficient of alizarin increases with an increase in hydrotrope concentration and system temperature. The maximum enhancement factor, the ratio of the value of solubility in the presence and absence of a hydrotrope, was determined for all experiments under study. The effectivity of hydrotropes was measured by the determination of the Setschenow constant, K_s. The order of effectiveness of various hydrotropes based on K_s values is potassium p-toluene sulfonate > citric acid > nicotinamide.     

Generation and Deposition of Organic Nanoparticles in a Liquid Ring Pump

A new method for the production of organic nanoparticles or nanosuspensions in a liquid ring vacuum pump is presented. A hot carrier gas charged under vacuum conditions with poorly water‐soluble organic substances is compressed and simultaneously cooled by the partially evaporating sealant water of the liquid ring vacuum pump. During compression and quenching, the gas‐vapor mixture becomes highly supersaturated and aerosol formation initiated by homogeneous nucleation occurs in the compression chambers between the impeller blades of the pump. The thus generated gas‐borne droplets or solid particles are mainly trapped and enriched in the sealant ring liquid, which is discharged, separated from the carrier gas in an external separator and returned to the pump. Experiments yielded aqueous nanosuspensions of insoluble organic substances with typical particle sizes between 50 and 300 nm, as well as foam in the external gas‐liquid separator. The foam showed stable structures due to incorporated solid nanoparticles.     

Étude des conditions opératoires optimales de synthèse du 2-furyl oxirane à l'aide de modèles empiriques et mécanistiques

The operating conditions of the synthesis of 2-furyl oxirane by solid—liquid phase transfer in low hydrated organic medium in two different experimental domains (different particle size distributions of the base; different sulphonium salts) were optimized according to two different optimization approaches. The first approach is based on the use of empirical models (response surface models) and the second on the use of mechanistic models (“tendency modelling”). A comparison of the optimization results allows an assessment of relative benefits and drawbacks of the two approaches. Optimum yields in the two different experimental domains were 89 and 95.5%, respectively.     

Hydrotropic properties of some short-chain alkylbenzene- and alkylnaphthalene sulfonates

Alkylbenzene sulfonates based on toluene, xylene and cumene, and alkylnaphthalene sulfonates act as hydrotropes in surfactant systems. One measure of hydrotropicity is the amount of hydrotrope required to clear a cloudy detergent formulation; some hydrotropes are more effective than others, depending on the surfactant formulation. Another measure is the modification of the viscosity of surfactant formulations; the change in the viscosity depends on the amount and type of hydrotrope used and on the specific formulation involved. Additionally, alkylnaphthalene sulfonate hydrotropes change the solubility of nonionic surfactants in water, and both types of hydrotrope raise the cloud point of nonionic surfactant solutions; however, the naphthalene-based hydrotropes are more efficient. Ross-Miles foam test data are used to compare the foam characteristics of different alkylnaphthalene sulfonates. A critical micelle concentration (CMC) was determined for the alkylnaphthalene sulfonates, but although alkylbenzene sulfonates do show some surface activity, a CMC could not be found for these materials. Presented as a poster session at the AOCS Annual Meeting & Expo, May 1997, Seattle, Washington, and at Soaps, Detergents, and Oleochemicals: An AOCS International Conference, October 1997, Fort Lauderdale, Florida.     

Dendronized Polyimides Bearing Long-Chain Alkyl Groups and Their Application for Vertically Aligned Nematic Liquid Crystal Displays

Polyimides having dendritic side chains were investigated. The terphenylene diamine monomer having a first-generation monodendron, 3,4,5-tris(n-dodecyloxy)-benzoate and the monomer having a second-generation monodendron, 3,4,5-tris[-3’,4’,5’-tri(n-dodecyloxy)benzyloxy]benzoate were successfully synthesized and the corresponding soluble dendritic polyimides were obtained by polycondensation with conventional tetracarboxylic dianhydride monomers such as benzophenone tertracarboxylic dianhydride (BTDA). The two-step polymerizations in NMP that is a general method for the synthesis of soluble polyimides is difficult; however, the expected dendritic polyimides can be obtained in aromatic polar solvents such as m-cresol and pyridine. The solubility of these dendoronized polyimides is characteristic; soluble in common organic solvents such as dichloromethane, chloroform, toluene and THF. These dendronized polyimides exhibited high glass transition temperatures and good thermal stability in both air and under nitrogen. Their application as alignment layers for LCDs was investigated, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs).     

Ionic liquid (molten salt): Thermoregulated catalyst support for catalytic hydrosilylation process

The high melting point molten organic salts N-alkylpyridinium hexafluorophosphates have been used as thermoregulated supports. The influence of the structure of the molten organic salts on hydrosilylation reactions has been investigated and it was found that the alkyl chains attached to the pyridinium have an impact on the catalytic activities and selectivities. Additionally, by using this kind of thermoregulated catalyst support, the catalyst phase is liquid phase under the reaction conditions, whereas the catalyst supported by molten organic salt is solid phase at room temperature, therefore, it can be reused simply by decantation.     

Effect of gassing rate on solid–liquid mass transfer coefficients and particle slip velocities in stirred tank reactors

While solid–liquid dispersion in mechanically agitated vessels has been widely investigated, the suspension of particles with simultaneous gas dispersion is, however, less well understood. A consideration of the gassing rate is of particular importance when designing “dead-end” batch reactors. Solid–liquid mass transfer coefficients were determined using the technique of dissolving a sparingly soluble solid, salicylic acid loaded onto silica gel, in water. Mass transfer was found to be dependent on a variety of geometric, physical and hydrodynamic properties; with the significant exception of agitation speed the influence of the latter properties was independent of gas dispersion. Flow visualisation with positron emission particle tracking has been used alongside the mass transfer measurements to study the effects of gas injection on the liquid flow patterns and the solid–liquid slip velocities. Time-averaged relative slip velocities were determined by simple subtraction of the data obtained using a neutrally buoyant particle. Gas dispersion was found to affect the particle–liquid slip velocity, explaining the mass transfer coefficient trends observed. While only a small diameter vessel has been used it does point to considerable non-uniformity of mass transfer in larger vessels.     

Strength and morphology of solid bridges in dry granules of pharmaceutical powders

This is an experimental study of the tensile strength of solid bridges between primary particles comprising granules of lactose or mannitol. We report on two systems: granules prepared with ethanol granulating solutions, in which the base powders were at most sparingly soluble, and aqueous granulating solutions, in which the base powder solubility was large. Both systems were studied with and without hydroxypropylcellulose (HPC) or polyvinylpyrrolidone (PVP) or surfactants (Triton-X100, sodium lauryl sulfate or polysorbate 80) added to the granulating solution. The interparticle bridge strength was determined from the granule crush strength with a simple model that assumes that solid bridges form by evaporation of solvent from liquid bridges that maintain their shape during drying.Lactose granules prepared with pure ethanol are very weak, with crush strength comparable to that predicted by JKR theory, consistent with its negligible solubility. Mannitol, which is sparingly soluble, forms granules with bridge strength similar to the theoretical (Griffith) strength of a pure mannitol. Addition of HPC or PVP to the granulating solution produces bridges with strength comparable to that of pure polymer films. In comparison, the behavior of granules prepared with aqueous granulating solutions was much more complex due to the high saturation concentration of base powder. Granules produced with pure water had bridge strength approximately 20% of the theoretical strength. Addition of HPC or PVP to lactose granules increased the bridge strength modestly, but the strength was much smaller than that of the corresponding pure polymer films. Addition of HPC to mannitol granules had little effect on bridge strength, while PVP reduced bridge strength by approximately 30%. Addition of surfactants to the granulating solution also reduced dry bridge strength. These results reflect the complex microstructure and resulting mechanical properties of dry bridges produced by coprecipitation of the sugars and polymers (or surfactants).     

纯气体在非挥发性溶剂中溶解度的关联

根据汽液平衡的基本性质和气体在液体中溶解时的特殊情况,采用RK方程的维里展开式和正规溶液理论,推得了气体溶解度与温度、压力的函数关系式,并用它对不同温度下加压气体的溶解度进行了关联和外推计算.