Search Results
Abstract
O-Alkylation of phenol compounds was performed in a continuous flow apparatus under biphasic liquid/liquid conditions and promoted by tetrabutylammonium bromide (TBAB) as a phase-transfer catalyst. The segmented flow that is generated within the flow system is able to afford the desired ethers in high yield and in very short times.
Introduction The dimethyl ether (DME) + carbon dioxide (CO 2 ) mixture can be an attractive option for different applications. In a recent article, the present system was proposed as a solvent [ 1 ], and its solvent properties
Abstract
Unsolvated methyl cations, generated by spontaneous 
-decay of multitritiated methane, have been allowed to react with some aliphatic ethers. The reaction mixtures contain various products, mainly aliphatic ethers, that have been separated by gaschromatography and continuously counted in an ionization chamber. A mechanism involving different reaction channels can provide an explanation of the results.
, the cement has no longer enough water to hydrate and the final properties of the mortar are altered [ 3 ]. Thus, cellulose ethers are additives commonly used in mortars as water retention agents, as thickeners and film formers [ 4 ] to prevent water
Abstract
Ethers are widely used as a solvent for synthesis reactions, however, they are known as hazardous chemicals as they have low flash points and form peroxides under oxidative conditions. In this study, the oxidative reactivity of cyclic ethers was evaluated by thermal analysis. The accelerated test was performed in a pressure vessel under a high oxygen pressure (2 MPa), and DSC was used to detect the products of the reaction. Tetrahydrofuran (THF) and 1,3-dioxolane were used as a sample. The result of the DSC measurement of THF without any antioxidant showed that the DSC curve depended on the exposure time. It was found that this method can be used for the oxidation evaluation. The DSC measurement was also used for the detection of ether peroxides, and this method was faster and simpler than the potassium iodine titration.
Abstract
The yields of hydrogen and ethylene from the radiolysis of 15-crown-5, 18-crown-6, dibenzo-18-crown-6, and dicyclohexyl-18-crown-6 ethers have been measured. The quantities obtained are compared with the ones for PEG-300, PEG-600 and 1,4-dioxane measured under the same conditions. The hydrogen yields range from about 1 to nearly 2 molecules per 100 eV and these of ethylene range from 0.02 to 0.15 depending on the irradiation conditions. From the viewpoint of the rate of radiation decomposition, there is no much difference between crown ethers and their analogues including 1,4-dioxane, the simplest molecule in the series.
Abstract
A new group of poly(ester-ether) glycols was obtained by polycondensation of adipic acid with poly(alkylene glycol) or of adipic acid with mixture of poly(alkylene glycol) and ethylene glycol. Poly(ester-ether) glycols were synthesised in a two-step method at comparable laboratory conditions. We prepared series of poly(ester-ether) glycols where molar ratios [COOH]:[OH] were changed in the range from 1:1.20 to 1:2.10. The molecular mass of synthesized substances was in the range from 850 to 2500 g mol-1. Thermal stability of poly(ester-ether) glycols and obtained polyurethanes was investigated by thermogravimetric analysis and DSC method. We have found that obtained oligomerols obtained from adipic acid and poly(tetramethylene glycol) have the highest thermal stability. The differential scanning calorimetry shown occurrence of two-phase transitions for examined polyurethanes, which are described by glass transition temperature T g and the melting temperature T t.
(EtOH) [ 4 ], dimethyl ether (DME) [ 5 ] and hydrocarbons obtained by Fischer–Tropsch synthesis [ 6 ], will also be widely distributed and can be transformed in hydrogen by the aforementioned inverse processes (SR, POX and ATR). In particular, ethanol
Abstract
Crown-ethers extract uranium/VI/, neptunium/IV/ and americium/III/ into MIBK from aqueous thiocyanate solutions. The synergic extraction of U/VI/with crown-ethers and HTTA is also possible.
Abstract
New special engineering thermoplastics, poly(phthalazinone ether sulfone) (PPES) and poly(phthalazinone ether sulfone ketone) (PPESK), containing phthalazinone are synthesized through step-polymerization. The kinetics of thermal degradation of PPES and PPESK (1/1) in nitrogen is investigated at several heating rates by thermogravimetry (TG). It is concluded that, based on using Satava’s theory, the thermal degradation mechanism of PPESK (1/1) is nucleation and growth, the order of reaction of the degradation process is one (n = 1). In contrast, the thermal degradation mechanism of PPES is a phase boundary controlled reaction and the order of the reaction is two (n = 2). The kinetic parameters, including reaction energy and frequency factor of thermal degradation reaction for PPES and PPESK (1/1) are analyzed using isoconversional Friedman, Kissinger–Akahira–Sunose (K–A–S) and Ozawa method. In addition, the study focus on the influence of heating rate and ratio of ketone/sulfone on thermal stability and the life estimation are described.
