Solubility and decomposition of organic compounds in subcritical water

In this article, studies on organic solubility and stability in subcritical water reported during the past 25 years have been reviewed. Data on the solubility and decomposition of organic compounds in subcritical water, a green solvent, are needed in environmental remediation, chemistry, chemical engineering, medicine, polymer, food, agriculture, and many other fields. For solubility studies, the experimental systems used to measure solubility, mathematical equations derived and applied for the modeling of the experimentally determined solubility data, and the correlation between the predicated and experimental data have been summarized and discussed. This paper also reviewed organic decomposition under subcritical water conditions. In general, the solubility of organics is significantly enhanced with increasing water temperature. Likewise, the percentage of organic decomposition also increases with higher temperature

Simultaneous determination of citalopram, paroxetine, fluoxetine, and sertraline by high-temperature liquid chromatography

A lack of serotonin in the brain is associated with depression. Selective serotonin reuptake inhibitors (SSRIs) are widely used to help treat depression and associated symptoms. A method has been developed for the simultaneous determination of SSRIs by high-temperature liquid chromatography (HTLC). Citalopram, paroxetine, fluoxetine, and sertraline compounds, which are widely used as antidepressant active agents, have been chosen as SSRIs. The separation of the SSRIs have been carried out by using four different column types, including XTerra MS C18, Zorbax SB-Phenyl, Alltima C18 and Phenyl Hypersil columns, and their chromatographic performances have been evaluated. The best separation has been obtained on the Zorbax SB-Phenyl column (150 mm × 4.6 mm, 5 μm) among the four different columns studied. The separation temperature and the composition of mobile phase were examined for the optimization of chromatographic separation. Chromatographic separation of SSRIs has been carried out at temperatures ranging from 100 to 200 °C with variable flow rates (0.5-1.5 mL/min). Water:acetonitrile:acetic acid mixtures containing with 10 or 20% acetonitrile and 2% acetic acid have been used as mobile phase. The best separation was observed at volume ratio of 78:20:2 (water:acetonitrile:acetic acid) at elevated temperature on the Zorbax SB-Phenyl column. The wavelength of UV detector was set at 254 nm. All four analytes were eluted within 8 min at 200 °C. At the end of working, it was observed that the retention times of all four analytes decreased with increasing temperature and was stated that the temperature was an effective parameter for chromatographic separation. Furthermore, the relationship between retention factor and separation temperature was examined using Van’t Hoff plots and the results demonstrated with correlation coefficient greater than 0.91 on Zorbax SB Phenyl column. Consequently, the proposed HTLC method for separation and analysis of SSRIs may be used as a green alternative technique

Application of response surface methodology and central composite design for the optimization of textile dye degradation by wet air oxidation

Background: The present study is aimed at investigating the degradation of azo dye solution of AR 274 by wet air oxidation conditions. The central composite design matrix and response surface methodology were applied in designing the experiments to evaluate the interactive effects of the three most important operating variables. Thus, the interactive effects of oxygen pressure (3.0 to 5.0 MPa), temperature (100°C to 250°C), and time (30 to 90 min) on the degradation of dye were investigated. Results: The predicted values were found to be in good agreement with the experimental values (R2 = 0.9981 and Adj-R2 = 0.9965), which define the propriety of the model and the achievement of CCD in the optimization of WAO process. Conclusions: Intermediates of dye degradation were detected by GC-MS, the possible degradation mechanism for the WAO of dye was discussed, and the probable degradation pathway was deduced. © 2012, Demirel and Kayan; licensee Springer

Degradation of Acid Red 274 using H2O2 in subcritical water: Application of response surface methodology

WOS: 000300262400013PubMed: 22169144In this research, the degradation of Acid Red 274 (AR 274) was investigated under subcritical water conditions using H2O2, which led to the oxidative degradation of Acid Red 274 up to its 80% of mineralization. The Box-Behnken design matrix and response surface methodology (RSM) were applied in designing the experiments for evaluating the interactive effects of the three most important operating variables. Thus, the interactive effects of temperature (100-250 degrees C), oxidant (H2O2) concentration (50-250 mM), and time (30-60 min.) on the degradation of AR 274 were investigated. A total of 17 experiments were conducted in this research, and the analysis of variance (ANOVA) indicated that the proposed quadratic model could be used for navigating the design space. The proposed model was essentially in accordance with the experimental case with correlation coefficient R-2 = 0.9930 and Adj-R-2 = 0.9839, respectively. The results confirmed that RSM based on the Box-Behnken design was a compatible method for optimizing the operating conditions of AR 274 degradation. (C) 2011 Elsevier B.V. All rights reserved

Aqueous solubility and chromatographic studies of antifungal drug-fluconazole at high temperature conditions

Fluconazole is a novel triazole antifungistatic drug, which can be administered both orally and intravenously and is currently used for the treatment of systemic and superficial fungal infections. In this study, the solubility of fluconazole in water at elevated temperature and pressure was investigated at temperatures in the range of 298 to 473 K under autogenous- 5.0 MPa pressure. The results showed that the solubility of fluconazole was increased 146-fold at the highest experimental temperature of 473 K. Based on the experimental data, a mathematical model was developed to predict the solubility of fluconazole in subcritical water. The model was validated successfully and the theoretical solubility values matched well with the experimental data. Furthermore, a modified Apelblat equation provided a good fit to the experimental values except at low temperature. The molar enthalpy and the molar entropy of dissolution of fluconazole in subcritical water at temperatures ranging from 298 to 473 K were calculated. The good solubility of fluconazole in subcritical water allowed us to perform high temperature liquid chromatography (HTLC) for the determination of this agent. Moreover, thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis confirmed that fluconazole had excellent thermal stability under subcritical conditions

Green chromatographic separation of coumarin and vanillins using subcritical water as the mobile phase

WOS: 000389138700017PubMed: 27060112Pure water was used as the eluent for separation of coumarin, vanillin and ethyl vanillin at temperatures ranging from 100 to 200 degrees C using a homemade subcritical water chromatography (SBWC) system. Chromatographic separations were performed on five commercial columns including XTerra MS C18, XBridge C18, Zorbax RRHD Eclipse Plus, Zorbax SB-Phenyl and Zorbax SB-C18 columns. The retention time of all three solutes decreased with increasing water temperature. The shortest retention time among all acceptable separations, less than 4 min, was achieved on the Zorbax SB-C18 column at 200 degrees C. While separations on the XTerra MS C18 column resulted in fronting peaks and a degradation peak from ethyl vanillin on the Zorbax RRHD Eclipse Plus column was observed, all three other columns yielded reasonable separations under SBWC conditions. In addition to separation of the standard test mixture, separation of coumarin contained in a skincare cream sample was also carried out using SBWC.Scientific and Technological Research Council of Turkey (TUBITAK) [KBAG-112T336]This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK, grant number: KBAG-112T336)

Solubility of fluconazole in (ethanol + water) mixtures: Determination, correlation, dissolution thermodynamics and preferential solvation

In this research, the equilibrium mole fraction solubility of fluconazole (FLC) in some aqueous-ethanolic mixtures was determined at seven temperatures from (293.15 to 323.15) K. The respective apparent thermodynamic functions (Gibbs energy, enthalpy, and entropy) for the dissolution, mixing and solvation processes were computed using the van't Hoff and Gibbs equations. The enthalpy–entropy relationship for FLC was non-linear in the plot of enthalpy vs. Gibbs energy of solution with negative slope in the composition regions of 0.00 ≤ w1 ≤ 0.40 and 0.70 ≤ w1 ≤ 1.00. Thus, the driving mechanism for FLC transfer processes in water-rich mixtures is the entropy. In addition, by means of the inverse Kirkwood-Buff integrals is observed that FLC is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in the mixtures of 0.23 < x1 < 1.00

Solubility and chromatographic separation of 5-fluorouracil under subcritical water conditions

WOS: 000399436000048The drug 5-fluorouracil is used to treat several cancers including colon, esophageal, stomach, pancreatic, breast, and cervical cancer. In this study, the solubility of 5-fluorouracil in subcritical water was determined at temperatures ranging from 298 to 473 K under a constant pressure of 5.1 MPa. Our results show that the solubility of 5-fluorouracil is enhanced more than 12 -fold by increasing the temperature from 298 to 473 K. A new approximation model was developed to predict the solubility of 5-fluorouracil in subcritical water. Our predicted solubility values are comparable with the experimental ones. The modified Apelblat equation also yields good agreement with experimental values. Since our solubility study reveals that 5-fluorouracil has adequate solubility in subcritical water, the separation of 5-fluorouradl was conducted using subcritical water chromatography (SBWC) with water only mobile phase. Good chromatographic separation of 5-fluorouracil was achieved at temperatures of 348 to 473 K.Scientific Research Project Unit (BAP) of Aksaray University [2016/038]The authors gratefully thank the Scientific Research Project Unit (BAP) of Aksaray University (2016/038) for the financial support of this work

Assessment of Orange Peel Hydrochar as a Soil Amendment: Impact on Clay Soil Physical Properties and Potential Phytotoxicity

Purpose: The main objectives of this work were the following: (1) to investigate the applicability of orange peel hydrochar as a soil amendment for improving the physical properties of a compacted, clay soil and (2) to study the growth of maize on substrates composed of clay soil and hydrochar and determine any potential phytotoxic effects. Methods: The effect on soil’s bulk density (BD), aeration, water holding capacity (WHC), and hydraulic conductivity were examined with hydrochar additions of 5, 10 and 15% (w/w) and determined by conventional laboratory methods. Potential phytotoxic effects were determined through the Zucconi germination index on fresh, diluted and 4-week old undiluted hydrochar extracts. The effect of hydrochar on maize growth was studied in clay soil (as reference), clay soil with 5% (w/w) fresh hydrochar, clay soil with 5% (w/w) of 4-week-old hydrochar and clay soil with 5% (w/w) biochar (for comparison). Results: At an application rate of 5% (w/w) hydrochar, the bulk density was reduced from 1.35 to 1.22 g/cm3, the air-filled porosity was increased from 33 to 37% and the saturated hydraulic conductivity from 0.96 to 1.01 cm/h. The water holding capacity remained practically unchanged, however it was considerably reduced at higher application rates. The seed germination test indicated strong phytotoxicity of the fresh, undiluted hydrochar extract, which was reduced when the extract was diluted or the hydrochar allowed to mature for 4 weeks. The pot tests indicated that hydrochar did not improve the yield of maize, probably due to the presence of phytotoxic substances. Conclusions: This study demonstrated a new valorization pathway for a significant agricultural waste. Additionally, it proved the applicability of orange peel hydrochar for improving the physical properties of clay soil. However, due to phytotoxic effects, further work is required before a field application is considered. © 2018 Springer Nature B.V

Fabrication of palladium nanoparticles supported on natural volcanic tuff/Fe3O4 and Its catalytic role in microwave-assisted suzuki-miyaura coupling reactions

Natural minerals have a huge potential as stabilizers in the catalytic systems due to their high mechanical durability, porous surface, non-toxicity and abundance in nature. This study aims to the development of a magnetically retrievable, heterogeneous palladium catalytic system derived from volcanic tuff (VT), an abundant form of zeolite, for Suzuki-Miyaura coupling (SMC) reactions. For this purpose, a new catalyst support was designed by loading volcanic tuff with Fe3O4(VT/Fe3O4) and palladium nanoparticles were prepared on VT/Fe3O4 via wet chemical reduction method (Pd NPs@VT/Fe3O4). Then, Pd NPs@VT/Fe3O4 was evaluated as a heterogeneous catalyst in the microwave-assisted production of biaryl via SMC reactions. Pd NPs@VT/Fe3O4 efficiently coupled various substituted aryl iodides, bromides and chlorides in a very short reaction time, solvent-free media and in an air environment. Catalytic tests indicated that Pd NPs@VT/Fe3O4 converted aryl halides into desired biaryls with a high yield up to 99%. Moreover, it was showed that Pd NPs@VT/Fe3O4 retained its stability and catalytic performance by producing 92% yield after eight successive cycles. This study demonstrated that VT can be a good alternative support alongside other known supports such as biopolymers, carbon and silica based materials and it can be utilized for the synthesis of different catalysts. Graphic