Tetrahydrofuran, ethylation

Another important issue that must be considered in the development of CSPs for preparative separations is the solubility of enantiomers in the mobile phase. For example, the mixtures of hexane and polar solvents such as tetrahydrofuran, ethyl acetate, and 2-propanol typically used for normal-phase HPLC may not dissolve enough compound to overload the column. Since the selectivity of chiral recognition is strongly mobile phase-dependent, the development and optimization of the selector must be carried out in such a solvent that is well suited for the analytes. In contrast to analytical separations, separations on process scale do not require selectivity for a broad variety of racemates, since the unit often separates only a unique mixture of enantiomers. Therefore, a very high key-and-lock type selectivity, well known in the recognition of biosystems, would be most advantageous for the separation of a specific pair of enantiomers in large-scale production. 

System (4) has been reported for the quantitative determination of steroids in health and disease [143], Prior to analysis, free steroids were removed from the sample. Conjugated steroids were enzymatically hydrolyzed, and the liberated products extracted into 1 3 tetrahydrofuran-ethyl ether. The extract was evaporated, the residue dissolved in acetic acid, and then oxidized with sodium bismuthate. The final product was acetylated or formulated, and subjected to GC analysis along with the standard. A stabilized column of 4% LAC-2R-446 and 1% 85% phosphoric acid on... 

The high reactivity of TFAT limits the number of solvents that can be used for its reactions. We have found that TFAT is unreactive towards saturated hydocarbons, benzene, and common halogenated solvents. It reacts only very slowly with nitromethane, but reacts relatively rapidly with ether, tetrahydrofuran, ethyl acetate, and acetonitrile. 

Chemicals and Standard Solutions. Cyclohexanone, cyclohexanol, 1,3,5-trichlorobenzene, 1,2,4-trichlorobenzene, phenol, 4-methylphenol, 4-chloro-phenol, 1,2,3,4-tetrahydroisoquinoline, 1-chlorohexane, 1-chlorododecane, and 1-chlorooctadecane were obtained from Aldrich. Acetone, tetrahydrofuran, ethyl acetate, toluene, dimethyl sulfoxide, and methanol were obtained from J. T. Baker. Distilled-in-glass isooctane, methylene chloride, ethyl ether, and pentane were obtained from Burdick and Jackson. Analytical standard kits from Analabs provided methyl ethyl ketone, isopropyl alcohol, ethanol, methyl isobutyl ketone, tetrachloroethylene, dodecane, dimethylformamide, 1,2-dichlorobenzene, 1-octanol, nitrobenzene, 2,4-dichlorophenol, and 2,5-dichlorophenol. All chemicals obtained from the vendors were of the highest purity available and were used without further purification. High-purity water... 

Methylene Chloride Tetrahydrofuran Ethyl Ether Ethyl Acetate Acetone Acetonitrile Isopropanol Methanol Water... 

Figure 9.4 Elution strength of binary mixtures as used for adsorption chromatography on silica [reproduced with permission from M.D. Palamareva and V.R. Meyer, J. Chromatogr., 641, 391 (1993)]. The graph covers the 12 possible mixtures of hexane, dichloromethane, te/T-butylmethyl ether, tetrahydrofuran, ethyl acetate and isopropanol.

Isooctane Toluene Chloroform Dichloromethane Tetrahydrofuran Ethyl ether Ethyl acetate Acetone Acetonitrile Isopropyl alcohol Methanol... 

C under argon. Methanol was removed azeotropically at 56 °C at a fast rate and as the boiling point began to rise, the distillation rate was reduced to 4 drops/min. and heating continued for 15h. The polymer thus prepared precipitated out of cyclohexane. The powdery polymer was crystalline with a melting point (DSC) of 212 °C. It was insoluble in the usual organic solvents such as methylene chloride, chloroform, ether, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, and dimethylsulfoxide. 

Kling test A method for determining the degree of fusion between flexible vinyl sheets, coated fabrics, and thin sections of cast or molded parts, by immersing the folded specimen in a solvent and observing the elapsed time at which disintegration commences. Useful solvent systems comprise methyl ethyl ketone, tetrahydrofuran, ethyl acetate, and carbon tetrachloride. The preferred solvent system is one that will initiate degradation within 5-10 min in a fully fused specimen. Wickson EJ (ed)... 

AI2O3, CS2, EDTA, acetone, heptane, sodium carbonate, tetrahydrofuran, ethyl acetate, isopropanol Formaldehyde, toluene diisocyanate,... 

Gurana Scarpi et al. in 2000 introduced a modification to this variant which steers away from the use of the diazomethane addition step as shown in the synthesis of 38. Thiolactam 35 is alkylated with ethyl vinyl ketone in the presence of potassium carbonate and 18-crown-6 in tetrahydrofuran (ethyl vinyl ketone is introduced in excess by slow addition over a 2 h period to prevent S-alkylation) to give the AT-alkylated ketone 36 in 97% yield. A thioiminium ion was formed with Me2S04 followed by cyclization with DBU under reflux to give 38 in a good 67% yield. ... 

Lactide is miscible with benzene, toluene, xylene, methylene chloride, chloroform, tetrahydrofuran, ethyl acetate, methanol, isopropanol, acetone, and butanone. The solubility increases with increasing temperature [25]. Lactide will hydrolyze to lactic acid in water at room temperature, and the rate of hydrolysis of we50-lactide is much higher than that of D,L-lactide [26]. 

Dicyclohexylcarbodiimide added at —25° to N-carbobenzoxy-L-alanylglycyl-glycine and thiophenol in tetrahydrofuran, ethyl acetate, and dimethylform-amide, kept several hrs. in the refrigerator -> N-carbobenzoxy-L-alanylglycyl-glycine thiophenyl ester. Y 97%. F. e. s. F. Weygand and W. Steglich, B. 93, 2983 (1960). 

Influence of Polar Functional Groups and Acyclic Double Bond on Polymerization. The polymerization can be carried out in aprotic polar solvents such as ether, tetrahydrofuran, ethyl acetate, acetonitrile and di-methylformamide as well as in hydrocarbons and haloge-nated hydrocarbons. Alcohols, ketones and sulfoxides strongly inhibited the reaction. 

Retention of geometry. Ethyl (E)-3-phenylthio-2-butanoate allowed to react 4 hrs. at -78° with n-butylmagnesium bromide and cuprous iodide in tetrahydrofuran -> ethyl (E)-3-methyl"2"heptenoate. Y 94%. Also (Z)-isomers and f. e. s. S. Kobayashi, H. Takei and T. Mukaiyama, Chem. Lett. 1973, 1097 with Li-dialkylcuprates, also with simultaneous 1,4-addition (cf. Synth. Meth. 25, 693), s. G. H. Posner and D. J. Brunelle, Chem. Commun. 1973, 907. 

Peptides. A mixture of N-benzyloxycarbonyl-L-phenylalanine, ethyl glycinate hydrochloride, triphenylphosphine, bromotridiloromethane, and ethyldiisopropyl-amine refluxed 3 hrs. in tetrahydrofuran ethyl N-benzyloxycarbonyl-L-phenyl-alanylglycinate. Y 85%. F. e. and procedure, also with CCI4 instead of CBrClg, s. L. E. Barstow and V. J. Hruby, J. Org. Chem. 36, 1305 (1971). 

Also obtained by reaction of sec-butyllithium (1.1 equiv) with 2-bromo-4,6-dimethylphenyl propionate in tetrahydrofuran/ethyl ether/hexane at -95° for 30 min and -78° for 30 min, then hydrolysis with saturated ammonium chloride (31%) (Metal-promoted Fries rearrangement) [6590]. 

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