Supercritical 2-propanol Research Articles

Reactivation of Ni-TiO2 catalysts in hydrogen flow and in supercritical 2-propanol-Comparative study by electron spin resonance in situ.

Highly dispersed Ni-TiO2 catalyst has been studied in the process of preparation and under catalytic transfer hydrogenation reaction conditions in supercritical 2-propanol (250°C, 70 bar) using electron spin resonance in situ. Electron spin resonance in situ has been used to study the process of the catalyst passivation and subsequent reduction of the oxide layer in the gas flow. Reduction of the NiO layer on the surface of passivated Ni nanoparticles has been detected in supercritical 2-propanol, which is in agreement with kinetic modeling data. It has been found that the reduction of the nickel oxide layer in supercritical 2-propanol occurs at a lower temperature compared with the reduction in hydrogen flow, according to in situ electron spin resonance study.

Depolymerization of Alkaline Lignin in the Medium of Supercritical 2-Propanol

The results of optimizing the conditions of alkaline lignin depolymerization in a medium of supercritical 2-propanol in order to obtain low molecular weight aromatic compounds, which are potential renewable raw materials for organic synthesis, production of various products and materials, are presented. The designed experiment was applied, based on a central composite rotatable uniform plan design of the second-order for three variables (temperature, process time, liquid module) varied at five levels. The target parameters for optimization were the degree of conversion of lignin to soluble products and their molecular weight. Based on the obtained dependences the optimal depolymerization conditions (450°C, 8 min, liquid module 20) were determined, which ensured the degree of lignin conversion at the level of 73%. Using high-resolution mass spectrometry, it was shown that the resulting depolymerization products have an extremely complex component composition, which includes mainly monomeric and dimeric phenols.

Decrosslinking reaction kinetics of silane-crosslinked polyethylene in sub- and supercritical fluids

Supercritical methanol is a popular fluid as a supercritical medium for decrosslinking reaction of crosslinked polyethylene. However, due to its toxicity, a safe alternative medium is much to be desired. In this work, various sub- and supercritical fluids with different polarity characters were investigated to find a safe alternative medium for continuous decrosslinking of silane-crosslinked polyethylene (S-XLPE). Like methanol, all examined fluids, including ethanol, propanol, and water, exhibited first-order reaction kinetics regarding the gel content in the continuous decrosslinking process. The reaction rate constant values were observed as 2.806, 2.569, 2.383, and 2.130 min−1 in supercritical methanol, supercritical ethanol, supercritical 2-propanol, and subcritical water at 380 °C, respectively. As a non-toxic fluid with reaction kinetics very comparable to that of methanol, ethanol was found to be the best alternative medium for the continuous decrosslinking reaction of S-XLPE.

Development and Validation of Enantiomeric Purity of Montelukast by SFC Method on Amylose Based Stationary Phase

A new Supercritical fluid liquid chromatographic (SFC) method has been developed in normal-phase conditions for the determination of enantiomeric purity of Montelukast sodium (S,E)-2-(1-((1-3-(2-(7-chloroquinolin-2-yl)vinyl)phenyl)-3-(2-(2-hydroxypropan-2-yl)phenyl)propylthio)ethyl) cyclopropyl) acetic acid (R-isomer) (Anti asthmatic drug) in bulk drugs and in dosage forms. The sample was screened on the analytical SFC to determine the best column for the separation. The screening conditions are Column: Chiralpak AS-H (250 mm x 4.6 mm, 5 μm) column using a mobile phase system containing Supercritical fluid (Co2) and 2-Propanol in the ratio (85:15% v/v). The mobile-phase compositions and the differences in separation capability of the method is noted. The resolution between two enantiomers is found to be greater than 1.5. The SFC method for the separation of enantiomers of Montelukast is proved Accurate, Precise, Linear and robust. Relative standard deviation of retention times and peak areas were better than 0.2% and 0.4%, respectively, for precision.

Supercritical alcohols as solvents and reducing agents for the synthesis of reduced graphene oxide

We report on a facile, simple, and green graphene oxide (GO) reduction method based on a supercritical alcohol approach. The influence over the chemical, thermal, morphological, and textural properties of reduced graphene oxides (RGOs) of five different alcohols in their supercritical conditions – methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol – was investigated in detail. Although the thermal stabilities and Fourier-transform infrared spectra of RGOs produced using the different alcohols are very similar, a substantial difference in the carbon-to-oxygen ratios measured by X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller surface areas are observed. The RGO produced using supercritical ethanol exhibited a much higher carbon-to-oxygen ratio of 14.4 and a much larger surface area of 203m2/g compared with that produced using the other supercritical alcohols. Raman spectra showed that the RGOs produced using supercritical ethanol and supercritical 2-propanol retained more of the graphitic structure. X-ray diffraction analysis revealed that RGOs produced using supercritical 1-propanol and supercritical 1-butanol retained at least two different interlayer spacings. The deoxygenation mechanism of GO in supercritical ethanol is proposed based on gas and liquid product analysis.

Development and Validation of Enantiomeric Purity of Montelukast by SFC Method on Amylose Based Stationary Phase

A new Supercritical fluid liquid chromatographic (SFC) method has been developed in normal-phase conditions for the determination of enantiomeric purity of Montelukast sodium (S,E)-2-(1-((1-3-(2-(7-chloroquinolin-2-yl)vinyl)phenyl)-3-(2-(2-hydroxypropan-2-yl)phenyl)propylthio)ethyl) cyclopropyl) acetic acid (R-isomer) (Anti asthmatic drug) in bulk drugs and in dosage forms. The sample was screened on the analytical SFC to determine the best column for the separation. The screening conditions are Column: Chiralpak AS-H (250 mm x 4.6 mm, 5 μm) column using a mobile phase system containing Supercritical fluid (Co2) and 2-Propanol in the ratio (85:15% v/v). The mobile-phase compositions and the differences in separation capability of the method is noted. The resolution between two enantiomers is found to be greater than 1.5. The SFC method for the separation of enantiomers of Montelukast is proved Accurate, Precise, Linear and robust. Relative standard deviation of retention times and peak areas were better than 0.2% and 0.4%, respectively, for precision.

Transformation of benzonitrile into benzyl alcohol and benzoate esters in supercritical alcohols

Abstract The reactions of benzonitrile in supercritical methanol, ethanol, and 2-propanol were investigated under non-catalytic conditions. In supercritical methanol, benzonitrile was converted to methyl benzoate in high yield. The esterification reaction also occurred in supercritical ethanol to afford ethyl benzoate in moderate yield. The esterification could occur via a route analogous to the Pinner reaction. On the other hand, benzonitrile in supercritical 2-propanol yielded no ester. Benzyl alcohol was the major product in supercritical 2-propanol. We investigated the reaction of the C N bond in supercritical 2-propanol. In supercritical 2-propanol, N -benzylideneaniline was transferred to the reduction product ( N -benzylaniline) and hydrolysis products (benzyl alcohol and aniline). The hydrolysis reaction was restricted when the reaction was carried out in supercritical 2-propanol with a low water content. This indicates that the water in the 2-propanol acts as a reagent for the hydrolysis of the C N bond. These results suggested the following reaction process: C 6 H 5 C N→C 6 H 5 CH NH→C 6 H 5 CHO→C 6 H 5 CH 2 OH.

Mechanism for the reduction of ketones to the corresponding alcohols using supercritical 2-propanol

The mechanism for the reduction of ketones into the corresponding alcohols using supercritical 2-propanol under non-catalytic conditions was investigated. The studies of the kinetic-isotope effect and isotopic-labeling for the reduction of benzophenone and acetophenone were carried out using (CH 3) 2C D(OH), (CH 3) 2CH(O D), (C D 3) 2CH(OH), and (C D 3) 2C D(O D). It was clarified that the α- and hydroxyl hydrogens on 2-propanol, respectively, transfer to the carbonyl C and O in the rate-determining step. These isotope studies also suggested that this reaction proceeds via a six-membered cyclic transition state analogous to that of the Meerwein–Ponndorf–Verley reduction. The fact that Hammett's reaction constant for this reaction was low, i.e., ρ=0.33, and that the reduction of the prochiral ketones using optically active alcohols at supercritical or high temperature provided optically active products also supported the existence of a six-membered cyclic transition state.

Study on the Reactivity of Diarylmethane Derivatives in Supercritical Alcohols Media: Reduction of Diarylmethanols and Diaryl Ketones to Diarylmethanes Using Supercritical 2-Propanol

We found that diarylmethanols and diaryl ketones were smoothly reduced to the corresponding diarylalkanes using supercritical 2-propanol in good yields. Furthermore, we determined the specific reaction of fluorene using supercritical methanol at high temperature.

Selective reduction of unsaturated aldehydes to unsaturated alcohols using supercritical 2-propanol

Supercritical 2-propanol selectively reduced unsaturated aldehydes to the corresponding unsaturated alcohols at 573 K. The formation of saturated aldehydes or saturated alcohols was negligible. The reduction of unsaturated aldehydes to unsaturated alcohols using supercritical 2-propanol is useful for the industrial production of fine chemicals because it proceeds without the further addition of a catalyst and generates no by-products other than an oxidation product, acetone, from the supercritical alcohol.

Penetration of Titanium Tetraisopropoxide into Mesoporous Silica Using Supercritical Carbon Dioxide

A penetration of titanium tetraisopropoxide (TTIP) and a reaction with silanol groups to form TiO2 layers on the inner surface of mesoporous silica samples were studied. Influence of the solvent on the penetration behavior was discussed. The TTIP could penetrate into the mesopores with diameters of 2.3 and 2.7 nm and the pore size was decreased by the TTIP coating, only when supercritical CO2 were used as solvent. The pore size change was also observed for mesopores larger than 3.5 nm by using both supercritical CO2 and liquid 2-propanol. These behaviors are reasonably discussed not only by the relation between the pore diameter and the solvated TTIP molecular size, but also by the adsorption energy of the solvent molecules on the silica surface. A difference of the penetration behavior of TTIP from that of tetraethoxyorthosilane (TEOS) suggested that the reactivity with silanol groups on the silica surface also affected the penetration behavior.

Novel Direct Reduction of Diaryl Ketones to Diarylmethanes Using Supercritical 2‐Propanol.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel direct reduction of diaryl ketones to diarylmethanes using supercritical 2-propanol

We found that diaryl ketones reduce directly to diaryl alkanes under supercritical 2-propanol. This method was applied to one-pot synthesis of anthracene from anthraquinone derivatives by the addition of sulfur in excellent yields.

Reduction of acetophenone using supercritical 2-propanol: the substituent effect and the deuterium kinetic isotope effect

The reductions of several substituted acetophenones using supercritical 2-propanol were carried out to estimate the Hammett's reaction constant ( ρ=0.33). Also, the reduction of acetophenone using supercritical deuteriated 2-propanol was carried out to determine the rate-determining step. The kinetic isotope effects were observed in the reduction using 2-deuterio-2-propanol ( k H/ k D=1.6) and O-deuterio-2-propanol ( k H/ k D=2.0). These findings suggest that the reaction proceeds via a cyclic transition state between acetophenone and 2-propanol similar to that of the Meerwein–Ponndorf–Verley reduction.

Reactions of supercritical alcohols with unsaturated hydrocarbons

The reactions of some supercritical alcohols were investigated using 1,1-diphenylethylene, styrene, allylbenzene, and diphenylacetylene as the reaction partners. 1,1-Diphenylethylene in supercritical methanol was hydroxymethylated to afford 3,3-diphenyl-1-propanol as the major product. The alkenes containing a single and no conjugate phenyl group were also hydroxymethylated in supercritical methanol, but the reaction rates were significantly reduced when compared with that for 1,1-diphenylethylene. Styrene was converted to the hydroxyalkylated products in supercritical ethanol and 2-propanol as well as in supercritical methanol. The rates of the hydroxyalkylation of styrene were strongly dependent on the structures of the supercritical alcohols; the order of reactivity was 2-propanol>ethanol>methanol. The relation between the structures of the alcohols and the rates of hydroxyalkylation suggests that the reaction begins with an attack on the electrophile ( +CR 2OH or δ+CR 2OH) by the pi electrons of the styrene double bond. All the examined alkenes afforded their hydrogenated derivatives other than the hydroxyalkylated ones. In addition, supercritical alcohols acted as hydroxyalkylating or hydrogenating reagents for the triple bond in the reaction with diphenylacetylene.

An IR Study of Hydrogen Bonding in Liquid and Supercritical Alcohols

IR spectra in the region of the OH stretching band of liquid-like and supercritical methanol (Tc = 239.4 °C, Pc = 80.8 bar), ethanol (240.9 °C, 61.4 bar), 2-propanol (235.2 °C, 47.6 bar), and 1-butanol (289.9 °C, 44.1 bar) (data from ref 1, J. Chem. Eng. Data 1995, 40, 1025) have been recorded over a wide range of temperature and pressure up to 450 °C and 1000 bar. The spectra were obtained using a high-pressure, high-temperature IR cell and a specially developed measuring technique, in which the integrated intensity of the absorption band of the C−H stretching vibrations is used as an internal standard. This analysis allows the fraction of hydrogen-bonded and non-hydrogen-bonded hydroxyl groups in 2-propanol and 1-butanol to be estimated over the whole range of experimental conditions as a function of both temperature and pressure. With this approach, it is unnecessary to know the density of the sample or even the path length at which the spectra were obtained. However, the approach is less reliable in t...