Water tetrahydrofuran mixture

Table II. Characteristic Parameters for Vapor—Liquid Equilibrium n-Bu4NBr in Water—Tetrahydrofuran Mixtures at 298.15°K...

The synthesis of N-(2-mercaptoethyl)-3,5-dimethylpyrazole and the workup procedure are performed in air, but the resultant thiol can best be stored under a nitrogen atmosphere. In air, the thiol is resistant to oxidation for several weeks, but the disulfide slowly crystallizes from the oil. According to the NMR spectra, the product is quite pure, but may still contain a small amount of 1,1,3,3-tetramethylurea (up to 5%). The reaction with 1,3-dichloro-2-propanol was carried out in a water/tetrahydrofuran mixture with sodium hydroxide, and appeared to proceed smoothly and in almost quantitative yields.2 This new reaction path to pyrazole-thioether ligands opens the road to the development of new chelating ligands. 

The use of nonpolar chemically bonded stationary phases with a polar mobile phase is referred to as reverse-phase HPLG This technique separates sample components according to hydrophobicity. It is widely used for the separation of all types of biomolecules, including peptides, nucleotides, carbohydrates, and derivatives of amino acids. Typical solvent systems are water-methanol, water-acetonitrile, and water-tetrahydrofuran mixtures. Figure 3.15 shows the results of protein separation on a silica-based reverse-phase column. 

IONIC ASSOCIATION AND CONDUCTIBILITY OF BROMIDES AND TETRABUTYLAMMONIUM PERCHLORATES IN WATER-TETRAHYDROFURAN MIXTURES OF LOW DIELECTRIC CONSTANT. 

Consider the following reaction of NBS, carried out in a water/tetrahydrofuran mixture, a polar opposite of carbon tetrachloride, which is the standard solvent for allylic brominations ... 

The concentration dependence of /hc in NMR and Vch in IR for binary water-tetrahydrofuran mixtures has been studied by Mizuno et who... 

The same order of reactivity observed for the hydrolysis of A-acetylazoles (Table 1-1) is also found for azolides with other N-acyl groups. Exceptional, however, are the Af-formylazoles A-formylimidazole in neutral water is hydrolyzed immeasurably rapidly even in a 1 1 mixture of water/tetrahydrofuran at 20.6 °C the half-life is in the order of only 3.7 min, approximately a factor of 100 faster than that for A-acetylimidazole under the same conditions. 131... 

The step 3 product (1.81 mmol) was dissolved in 20 ml tetrahydrofuran (THF) and then treated with triethylamine (2.17 mmol) and acetyl chloride (2.17 mmol) at 10°C and then stirred at ambient temperature and poured into water. The mixture was extracted with ethyl acetate, and then washed with saturated NaHCO and brine and then dried with MgS04 and concentrated. The residue was washed with CH2CI2 and then methyl-f-butylether and 0.70 g of product isolated. 

It has been shown recently (1) that the transfer of urea from water to water-rich water-tetrahydrofuran (THF) mixtures is an entropy-controlled phenomenon (T AS°t > AH°t ), but from water to water-THF mixtures of mole fraction Z2 > 0.20 it is an enthalpy-controlled phenomenon ( AH°t > T AS°t ) moreover, the transfer is energetically favorable in the former case and unfavorable in the latter. A minimum in the standard free energy transfer... 

When HPLC is used as part of the analysis, the mobile phase is typically a mixture of methanol and methyl-tert-butyl ether (i.e., 50 50, v/v), although other HPLC solvents for LC/MS using APCI (e.g., water, tetrahydrofuran) can be used. It is important to note that if combustible nonaqueous solvent systems are used, water or a halogenated solvent such as methylene chloride or chloroform should be added to the mobile phase postcolumn to suppress ignition in the ion source. In addition, the APCI source must be vented outside the laboratory and should not allow air into the ionization chamber. A scan range of m/z 300 to 1000 will include the known carotenoids and their most common esters. 

A solution of 24 g of 4-(N,N-dimethylaminoethoxy)bromobenzene was added dropwise over 45 min to magnesium in 90 ml of anhydrous tetrahydrofuran. 2 ml of 1,2-dibromoethane were added as catalyst. After the addition, the mixture was stirred at 25°C for one hour to obtain a solution of 0.7 M of 4-(N,N-dimethylaminoethoxy)-benzene magnesium bromide which was then added to a solution of 6.16 g of dimethylsulfide-cuprous bromide complex in 20 ml of tetrahydrofuran. The mixture was stirred at room temperature for 20 min and a solution of 3.7 g of 3,3-[l,2-(ethanediyl-bisoxy)]-5a,10a-epoxy-17a-prop-l-ynyl-8(9(1 L))-estrene-17p-ol in 50 ml of tetrahydrofuran was added thereto dropwise over a few minutes. The mixture was stirred under an inert atmosphere for one hour and was then poured into a solution of 15 g of ammonium chloride in 20 ml of iced water. The mixture was extracted with ether and the organic phase was washed with aqueous saturated sodium chloride solution, was dried and evaporated to dryness under reduced pressure. The 18.3 g of oil were chromatographed over silica gel and eluted with chloroform to obtain 4.5 g of 3,3-[l,2-ethanediyl-bisoxy]-lip-[4-(N,N-dimethylaminoethoxy)phenyl]-17a-(prop-l-ynyl)-89-estrene-5a,17p-diol with a specific rotation of [a]D20 =-44(+/-)1.5° (c = 1% in chloroform). 

To a solution of 34.6 g of 2-(pyrrol-l-yl)benzyl alcohol in 300 ml of anhydrous tetrahydrofuran and 32 ml of tetramethylethylene diamine is added 183 ml of a 2.4 molar solution of n-butyl lithium in such a manner that the internal temperature of the reaction is maintained below 30°C. On completion of the addition, the reaction mixture is stirred at room temperature for 3 hours. The reaction mixture is then cooled to -70°C by means of a dry-ice/acetone bath, and 24 ml of ethyl pyruvate is added to the mixture over 1 minute. The reaction is then allowed to warm to room temperature and stirred overnight (18 hours). The reaction is then poured into an ice-water/ether mixture and the organic phase separated, dried over magnesium sulfate and the solvent evaporated under reduced pressure to yield ethyl-4-methyl-4H,6H-pyrrolo[l,2-a][4,l]benzoxazepine-4-carboxylate, MP 94°-96°C, which may be recrystallized from a mixture of ether-hexane (1 1). 

Polar group selectivity also occurs in ternary solvent systems (5.10). For example, the addition of 5% to 25% of a third solvent to a water-acetonitrile mixture can alter the relative retention of peaks, and often resolve overlapping peaks. Dolan et al (11) have employed ternary mobile phases of water, methanol and tetrahydrofuran to analyze vitamin tablets where interfering peaks could not be resolved with binary mixtures. See Figure 4. 

More recently, this method has been successfully extended by us18 to form the inverse systems, i.e. water core/polymer shell particles dispersed, initially in oil, but then transferred to an aqueous continuous phase. Clearly, whether one needs an oil or a water core depends on the nature of the active material to be released. Now one starts with a water/oil emulsion, rather than an oil/water emulsion, but the basic principles are very similar. A variety of shell polymer systems were prepared, including PMMA and poly(tetrahydrofuran) [PTHF]. The high vapor pressure liquid used in this case was in general, acetone. It turned out, however, that these water core systems are intrinsically more difficult to make than the equivalent oil core systems, because large amounts of acetone were required to dissolve the polymers initially in the water-acetone mixtures. An oil was then required which did not mix too well with acetone. In general, mineral oil worked reasonably well. In order to transfer the water core capsules into an aqueous continuous phase, the particles were centrifuged in... 

The Step 2 product (2.3 mmol) dissolved in 30 ml of THE was treated with a borane-tetrahydrofuran complex (23 mmol) and then refluxed for 18 hours and quenched with water. The mixture was concentrated and treated with 6M hydrochloric acid and... 

Separation of Water, Methyl Ethyl Ketone, and Tetrahydrofuran Mixtures... 

Mercuriocyclization has also been utilized in order to obtain spiroketals from hemiketals. Thus, treatment of l,10-undecadien-6-one (11) with mercury(II) acetate in water/tetrahydrofuran affords, with total regioselectivity, 2,8-bis[(chloromercurio)mcthyl]-l,7-dioxaspiro[5.5]undccanc as a diastereomeric mixture. The diastereomeric ratio was not reported but depends on the reaction time, owing to the reversibility of oxymercuration-cyclization steps. Reductive removal of mercury by sodium borohydride under phase-transfer conditions gives a good yield of 2,8-dimethyl-l,7-dioxaspiro[5.5]undecane (12) as a diastereomeric mixture101,102. 

---