Adsorption studies of acetic acid dimers on activated charcoal from organic solvents

Acetic acid exists as dimers in organic solvents like benzene, toluene and xylene. Adsorption of dimeric acetic acid on activated charcoal (AC) at various temperatures from benzene, toluene and xylene solutions have been studied. The system obeys Langmuir isotherm, thus signifying a monolayer adsorption of dimers. Corrections on AC-solvent pore volume fillings, molecular cross sectional surface area of acetic acid dimers, the adsorption equilibrium constants, the free energy change and the enthalpy change values are computed at different temperatures for the three solvents. The adsorption process has been found to be physisorption type. The FTIR measurements show that the adsorbed acetic acid dimer seems to retain the cyclic structure against the open chain non-cyclic structure.     

Adsorption of benzoic acid and hydroquinone by organically modified bentonites

Two organobentonites (ODTMA-B, HDTMA-B) were synthesized using hexadecyltrimethyle ammonium bromide (HDTMAB) and octadecyltrimethyle ammonium bromide (ODTMAB). Synthesized organobentonites were characterized by X-ray diffraction particle size, and surface area analysis. Particle size analyses of the original bentonite and organobentonites showed that the organobentonites contained a greater number of coarse particles than present in the original bentonite. While the basal spacings of the organobentonites increased organic cation, the surface area decreased.

To evaluate the potential use of two modified bentonites in removing organic pollutants such as benzoic acid and hydroquinone from water, adsorption experiments were performed under conditions of varied pH (3, 6 and 11) and temperatures(298 and 313 K). Experimental results showed that the sorption capacities increase with decreasing pH value and increasing temperature. The adsorption equilibrium of benzoic acid and hydroquinone on organobentonites was described by the Langmuir and Dubinin–Radushkevich (D–R) models. It was concluded that the isotherm shapes were not affected by pH and temperature. Adsorption capacity of ODTMA-B for benzoic acid was higher compared to that of HDTMA-B at various pH and temperatures.     

Characterization of racemization of chiral pesticides in organic solvents and water

Eight chiral pesticides, which were selected to cover different pesticide species and origins of chirality, were investigated to explore their chiral stability in organic solvents and water. Profenophos, fenamiphos, quizalofop-ethyl, dichlorprop-methyl (DCPP-methyl) and acetochlor were showed stable under all test conditions. However, significant racemization was observed for malathion, phenthoate and fenpropathrin in methanol, ethanol and water, but not in n-hexane, isopropanol, acetone or methylene chloride. The kinetic parameters (rate constant k and half-life T_1/2) of the abiotic racemization were calculated through a mathematical model of the first-order reaction. Furthermore, the extent of racemization varied among the solvents and was also affected by temperature dependence. The racemization of malathion, phenthoate and fenpropathrin in water was documented to be pH-dependent and took place more rapidly at pH 7.0 than at pH 5.8. The observed racemization was deduced to occur via a proton exchange process at the chiral center, and the relationship between the abiotic racemization and pesticide structure was further explored. Findings from this study are useful for better understanding enantioselectivity of chiral pesticides in environment and also for proper analysis, formulating or handling of enantiopure products.     

Thermodynamics of ionization of benzoic acid in water at 298°K

The standard heat of ionization of aqueous benzoic acid has been determined by solution calorimetry. The value obtained for H ^o of ionization, 0.11±0.04, is in good agreement with H ^o from other calorimetric values; 0.10±0.05 kcal-mole ^–1 is suggested to be the best value for this ionization at 298° K.     

Effect of acid on morphology of calcite during acid enhanced defluoridation

Fluoride removal from water by lime materials is a promising defluoridation process. Acid enhanced limestone defluoridation (AELD) technique involves precipitation of CaF₂ as well as adsorption of fluoride on the surface of limestone which is capable of reducing fluoride concentration to below the WHO guideline value of 1.5 mg/L. Acids such as acetic acid and citric acid are added to the fluoride water before filtration through limestone column to enhance the Ca²⁺ activity in solution for precipitation of fluoride as CaF₂. This paper describes the effects of these acids on the quality of the limestone during the AELD process, which has been studied to evaluate the reusability of the limestone. The reaction products that formed during the AELD process have also been analyzed. The detail study of the morphology of the limestone before and after use have been done using various analytical techniques, viz., X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. The study reveals that the limestone degrades to some extent in the process due to dissolution of calcium carbonate by the acids and adsorption of fluoride by the limestone. While appreciable quantity of the citrate salt of calcium was formed in the column, the acetate salt mostly remained dissolved in the water. Since mainly the surface of the limestone particles take part in the reaction, the limestone particles can be reused for the defluoridation process after cleaning the outer surface. The limestone after use remains also suitable as raw material for cement.     

食品中苯甲酸和山梨酸的气相色谱法分离分析

用毛细管气相色谱法对食品中的防腐剂苯甲酸和山梨酸进行了分离分析。样品用乙醚萃取，萃取物蒸发至干，残渣用氯仿溶解后直接进行色谱分析，FFAP石英毛细管柱，柱温220℃，邻苯二甲酸二甲酯为内标物。两种化合物在0.25mg/mL-4.00mg/mL范围内具有良好的线性关系。     

Naphthalene adsorption on activated carbons using solvents of different polarity

The hydrophobic-hydrophilic character of a series of microporous activated carbons was explored as a key factor in competitive adsorption of a non-polar compound from liquid phase. The selectivity of the carbon surface towards naphthalene was explored by performing the adsorption isotherms in water, cyclohexane and heptane. Solvent polarity and adsorbent hydrophobic character were found to strongly influence the adsorption capacity of naphthalene. In aqueous media, despite the non-polar character of the adsorbate, surface acidity lowered adsorption capacity. This is attributed to the competition of water from the adsorption sites, via H-bonding with surface functionalities and the formation of hydration clusters that reduce the accessibility and affinity of naphthalene to the inner pore structure. In organic media the uptake decreased due to competition of the hydrophobic solvent for the active sites of the carbon and to solvation effects. This competitive effect of the solvent is minimized in oxidized carbons as opposed to the trend obtained in aqueous solutions. The results confirmed that although adsorption of naphthalene strongly depends on the narrow microporosity of the adsorbent, competitive adsorption of the solvent for the active sites becomes important.     

High pressure effects on benzoic acid dimers: Vibrational spectroscopy

To understand pressure effects on dimer structure stability, Raman and FTIR spectroscopies were used to examine changes in H-bonded dimers of benzoic acid (BA). Experiments were performed on single crystals compressed to 33 GPa in a diamond anvil cell (DAC). Several changes in Raman spectra were observed in the range 6–8 GPa indicating modification in the dimer structure suggesting the lowering of molecular symmetry. Pressure increase above 15 GPa induced strong luminescence and a gradual change of the crystal color from white to yellow/brownish. FTIR measurements on the sample released from 33 GPa indicated formation of a new compound. It is proposed that molecules of this compound are composed of the hydroxyl group associated with alcohol, carbonyl group associated with ketone, and the sp³ hydrocarbon groups. This study demonstrates that sufficient high pressure compression and subsequent decompression can lead to significant changes in the H-bonded dimer structure, including the breaking of bonds and formation of new chemical compound.     

Solubility of daidzin in different organic solvents and (ethyl alcohol + water) mixed solvents

The solubility of daidzin in different organic solvents and (ethyl alcohol + water) mixed solvents was measured by high performance liquid chromatography (HPLC) analysis method from T = (283.2 to 323.2) K at atmosphere pressure. The results show that at higher temperature more daidzin dissolves, and moreover, the solubility increases with the ethyl alcohol mole fraction increase in the (ethyl alcohol + water) mixed solvents. The experimental solubility values were correlated by a simplified thermodynamic equation, λh equation and modified Apelblat equation. Based on the solubility of daidzin, the enthalpy and entropy of solution were also evaluated by van’t Hoff equation. The results illustrated that the dissolution process of daidzin is endothermic and entropy driven.     

Electrokinetic study of adsorption of ionic surfactants on titania from organic solvents

The electrokinetic potential of titania was studied as a function of concentration of SDS, DOSS and CTMABr in a series of solvents. In water and 50–50 water–methanol mixture, which are the most polar studied solvents, the organic ion is adsorbed on titania and the small inorganic ion remains in solution. In hexane the adsorption behavior is reversed, that is, the organic ion remains in solution and the small inorganic ion is adsorbed on titania. The borderline between these two types of behavior corresponds to solvent dielectric constant of about 25. In solvents, which have a dielectric constant in this range (methanol and 1-propanol) the adsorption preferences vary from one surfactant to another. The affinities of the organic ion and of the small inorganic ion to the surface are often similar, and then none of the ionic components is preferentially adsorbed, and the electrokinetic potential is not affected. In such cases, ionic surfactants are not suitable as agents for regulation of zeta potential.     

Nanoporous asymmetric polyaniline films for filtration of organic solvents

A new family of functional materials is reported for organic solvent nanofiltration, with excellent chemical stability and high retention of solute molecules. Integrally skinned asymmetric polyaniline (PANI) membranes were fabricated from concentrated solutions of doped PANI by phase inversion. Doped PANI solutions were prepared by adding organic acids directly to PANI dissolved in a mixture of NMP and 4-methyl piperidine before casting. Among the organic acids investigated, maleic acid, phthalic acid, sulfosalicylic acid and camphorsulfonic acid were able to dope PANI without causing gelation. These acids acted as soft templates, creating nanoporosity in the thin skin layer of the asymmetric PANI film. Their removal by alkaline extraction created membranes through which small solvent molecules can pass. After extracting the organic acids, the membranes were thermally crosslinked which conferred excellent solvent stability. These membranes had a molecular weight cut-off (MWCO) in the range of 150–250 g mol⁻¹ in methanol, making them the tightest OSN membranes reported to date. It was found that an increase in crosslinking temperature or time led to a decrease in solvent flux. PANI membranes were found to be resistant to a variety of organic solvents such as ethyl acetate, acetonitrile and acetone. These remarkable membranes have the potential to be used in OSN operations at high temperatures (up to 150 °C), and gave increasing fluxes with increasing temperature while maintaining a high solute rejection.     

Imidazolium ionic liquid-supported sulfonic acids: efficient and recyclable catalysts for esterification of benzoic acid

Several imidazolium ionic liquid（IL）-supported sulfonic acids with different anions,[C₃SO₃Hmim]HSO₄,[C₃SO₃Hmim]BF₄, [C₃SO₃ Hmim]PF₆,and[C₃SO₃Hmim]CF₃SO₃,were synthesized and applied as catalysts for esterification reaction of benzoic acid. The experimental results indicate that imidazolium IL-supported sulfonic acid containing anion of HSO₄^- shows the best catalytic activity.Only when less[C₃SO₃Hmim]HSO₄（0.3 equiv.） applied,was the product obtained with high yield of 97%.Furthermore, the produced esters could be separated by decantation,and the catalyst could be reused after the removal of water.     

Degradation of benzoic acid and its derivatives in subcritical water

In this research, the stability of benzoic acid and three of its derivatives (anthranilic acid, salicylic acid, and syringic acid) under subcritical water conditions was investigated. The stability studies were carried out at temperatures ranging from 50 to 350 °C with heating times of 10–630 min. The degradation of the benzoic acid derivatives increased with rising temperature and the acids became less stable with longer heating time. The three benzoic acid derivatives showed very mild degradation at 150 °C. Severe degradation of benzoic acid derivatives was observed at 200 °C while their complete degradation occurred at 250 °C. However, benzoic acid remained stable at temperatures up to 300 °C. The degradation products of benzoic acid and the three derivatives were identified and quantified by HPLC and confirmed by GC/MS. Anthranilic acid, salicylic acid, syringic acid, and benzoic acid in high-temperature water underwent decarboxylation to form aniline, phenol, syringol, and benzene, respectively.     

非线性主成分回归分光光度法同时测定复方制剂中两组分的含量

构造多组分体系的非线性模型,并用主成分回归法来解析,建立了同时测定两组分的非线性主成分回归分光光度法,方法用于复方苯甲酸制剂中苯甲酸和水杨酸含量的测定,结果优于线性主成分回归分光光度法。     

Supramolecular solvents in the extraction of organic compounds. A review

The increasing pressure to decrease organic solvent usage in laboratories is fostering the search for alternative solvents. The liquid-liquid phase separation of surfactants, induced by environmental conditions, viz. temperature, electrolytes, pH, etc., has been largely used in analytical extraction and concentration schemes. The surfactant-rich phase is a nano-structured liquid, recently named as supramolecular solvent, generated from the amphiphiles through a sequential self-assembly process occurring on two scales, molecular and nano. This review covers progress on both theoretical and practical aspects related to the use of supramolecular solvents in analytical extractions reported over the last decade. Advances allowing a better understanding of the mechanisms of solvent production and solvent structure are outlined. Emphasis is then placed on solvent composition and its consequences on extraction efficiency, concentration factors and suitability for solubilising analytes over a wide range of polarities. Recent developments in formats and strategies making supramolecular solvents compatible with chromatographic and electrophoretic techniques along with a variety of detection systems are discussed. Applications of supramolecular solvents to the extraction of organic compounds mainly in the biological, environmental and agrifood areas are critically reviewed and main future trends outlined.     

Solubility of naproxen in several organic solvents at different temperatures

By using the van’t Hoff and Gibbs equations the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, were evaluated from solubility data of naproxen (NAP) determined at several temperatures in octanol, isopropyl myristate, chloroform, and cyclohexane, as pure solvents. The water-saturated organic solvents also were studied except cyclohexane. The excess free energy and the activity coefficients of the solutes, and the mixing and solvation thermodynamic quantities were also determined. The NAP solubilities were higher in chloroform and octanol with respect to those obtained in cyclohexane. In addition, by using literature values for NAP aqueous solubility, the thermodynamic functions relative to transfer of this drug from water to organic solvents were also estimated.     

高效毛细管电泳法同时测定药品中苯甲酸和山梨酸钾

建立了毛细管电泳-紫外检测法测定硝酸咪康唑乳膏、小儿止咳糖浆及复方苦参水杨酸散中苯甲酸和山梨酸钾的方法。在230nm波长处以焦性没食子酸为内标物,分离电压为20kV,分离温度为25℃,用20mmol/L硼砂缓冲液(pH9.2)作毛细管电泳的运行液,被测组分与内标物得到快速分离。苯甲酸和山梨酸钾的进样质量浓度在1～400mg/L范围内与电泳峰面积呈良好的线性关系,相关系数r均为0.9999,检出限均为0.15mg/L。方法可用于药品中苯甲酸和山梨酸钾含量的测定。     

Solubility of benzoic acid in acetone, 2-propanol,acetic acid and cyclohexane: Experimental measurement and thermodynamic modeling

In this study the solubility of benzoic acid in acetone, 2-propanol, acetic acid and cyclohexane was experimentally determined over the temperature range of (277–346) K at around 5 K intervals by employing a gravimetric method. The experimental results showed that acetone had the best solubility for benzoic acid followed by 2-propanol, acetic acid and cyclohexane and the solubility in acetic acid had the strongest positive temperature dependency. The newly measured solubility data was also compared with the available literature data. Several commonly used thermodynamic models, including the empirical Van’t Hoff equation, the λh equation, the Wilson, NRTL and UNIQUAC equations, were applied to correlate the experimental solubility data. The adjustable parameters for each model were optimized by fitting the solubility data measured in this work. It was found that the three-parameter NRTL equation could give the best correlation results. Better predictions of the solubility of benzoic acid in acetic acid at higher temperature were observed using the Wilson and UNIQUAC equations than the other three equations which all gave underestimations.