Solvent tetrahydrofuran—hexane

This thinking has carried through to the present day and is reflected in our choices of mobile-phase fluids in LC water, acetonitrile, methanol, tetrahydrofuran, hexane, etc., are still among our popular choices. However, these particular materials are completely dependent on the conditions of column temperature and outlet pressure. Tswett s original conditions at his column outlet, actually the earth-bound defaults we call ambient temperature and pressure, determined his solvent choices and continue to dominate our thinking today. 

Aqueous solutions are not suitable solvents for esterifications and transesterifications, and these reactions are carried out in organic solvents of low polarity [9-12]. However, enzymes are surrounded by a hydration shell or bound water that is required for the retention of structure and catalytic activity [13]. Polar hydrophilic solvents such as DMF, DMSO, acetone, and alcohols (log P<0, where P is the partition coefficient between octanol and water) are incompatible and lead to rapid denaturation. Common solvents for esterifications and transesterifications include alkanes (hexane/log P=3.5), aromatics (toluene/2.5, benzene/2), haloalkanes (CHCI3/2, CH2CI2/I.4), and ethers (diisopropyl ether/1.9, terf-butylmethyl ether/ 0.94, diethyl ether/0.85). Exceptionally stable enzymes such as Candida antarctica lipase B (CAL-B) have been used in more polar solvents (tetrahydrofuran/0.49, acetonitrile/—0.33). Room-temperature ionic liquids [14—17] and supercritical fluids [18] are also good media for a wide range of biotransformations. 

Figure 8.14 Senipreparative class separation of a diesel engine exhaust sample. Column 25 cm x 7.9 mm, lO micrometer Porasil. Solvent gradient hexane to 5% methylene chloride over 5 min., linear gradient to 100% methylene chloride over 25 min., isocratic for 10 min., linear gradient to 100% acetonitrile over 10 min., Isocratic for 5 min., step change to tetrahydrofuran for 10 min.,...

Solvents Water (purified water or water-for-injection grade) toluene, methanol, ethanol, ether, acetate, dimethyl sulfoxide, tetrahydrofuran, hexane, cyclohexane, dichloromethane, acetonitrile, acetone Oxidizing Agents Hydrogen peroxide, chromic acid, potassium permanganate, manganese dioxide, ozone... 

DNs range from zero (solvents like hexane, tetrachloromethane), through modest donors (acetonitrile 14.1, acetone 17), to good donors like water (18), to superb donors like DMSO (29.8) and, best of all, HMPA (38.8) (see table 3.7). The DN enables us to rationalize why a solvent such as nitromethane, (6r= 35.8) is considered to be fairly nonpolar, although it has a higher dielectric constant than diethyl ether (Sr = 4.2) and tetrahydrofuran (Sr = 7.6) which are often thought to be more polar solvents than their dielectric constants would indicate. The DN of nitromethane is only 2.7, compared with that of 19.2 for diethyl ether and 20 for tetrahydrofuran. These ether solvents are much better electron-pair donors than nitromethane. 

All operations except the preparation of (t/5-C5Me5)Mo(0)2Cl should be carried out under an inert atmosphere or under vacuum employing standard Schlenk techniques. The solvents toluene, hexane, tetrahydrofuran, and dichloromethane must be completely dried and freed of oxygen by standard methods before use. 

The strong dependence of the Si/ICT lifetime on solvent polarity revealed first by transient absorption experiments in the visible region by Bautista et al. [8] was further confirmed by measurement of Si/ICT fluorescence using a streak-camera [11]. The Si/ICT state fluorescence kinetics of peridinin taken at 730 nm in solvents of different polarity are shown in Fig. 2b. The lifetime changes more than one order of magnitude, from 156 ps in n-hexane to 10.5 ps in methanol. In the middle-polarity solvents tetrahydrofuran and 2-propanol, the observed lifetimes are 77 and 54 ps, respectively. In all solvents, kinetic traces could be fitted by a single exponential decay independent of detection wavelength over nearly the entire fluorescence band (650 - 850 nm). The same decay times were also observed in transient absorption [11,12]. 

A variety of solvents including hexane, acetone, tetrahydrofuran, toluene and perchloroethylene have been used in these studies together with four analytical strategies. No sulfur has been detected. This feature is well illustrated in Figure 1, which displays the contrasting results for the pristine Wyodak sample, APCSP-2, and another exposed sample of this low sulfur coal. Elemental sulfur at the 0.002% level is easily detected in the exposed sample, none is observed in the pristine sample. 

Cannabinol, A8- and A9-tetrahydrocannabinol had the same retention volumes of 0.05 ml on a y-PorasilR column with 30% tetrahydrofuran in n-hexane and were separated from the acid degradation products with respective retention volumes of 9.5 and 11. "ml. The collection fraction containing the tetrahydrocannabinol could be purified later using the 5% tetrahydrofuran-hexane solvent system. 

The insertion of elemental tellurium into C — Li or C — Na bonds is a convenient method for the preparation of alkali metal tellurolates. Many organic lithium compounds are commercially available or can be prepared, for instance, by halogen-lithium or hydrogen-lithium exchange. The reactions of the organic lithium compounds with elemental tellurium are performed in inert organic solvents such as diethyl other, tetrahydrofuran, tetrahydrofuran/hexane, or diethyl ether/benzene at temperatures (— 196° to + 20°) compatible with the stability of the organic lithium compound. The applicability of this reaction for the synthesis of aliphatic, aromatic, and heteroaromatic lithium tellurolates is documented in Table 1 (p. 155). 

Tris(N-methylanilino)borane has previously been prepared by the reaction of boron trifluoride-ether complexes with three equivalents each of N-methylaniline and a suitable Grignard reagent,1,2 by the reaction of (N-methylanilino)potassium with boron trifluoride-ether complexes,2 and by aminolysis of boron trichloride by N-methylaniline.3 The present general procedure describes a convenient preparation of tris(N-methylanilino)-borane by the reaction of (N-methylanilino)lithium and boron trifluoride-diethyl ether in tetrahydrofuran-hexane as solvent. 

Vinyltrimethylsilane (97%), trimethylchlorosilane (98%), chlorodimethylsilane (97%), bromoform (96%), 5-bromo-l-pentene (95%), nBuLi (2.5M solution in hexanes), MeLi (1.6M solution in diethyl ether), n-decane (puriss. p.a., standard for GC, > 99.8%) and hexachloroplatinic(lV) acid hydrate were purchased from Aldrich. Platinum divinyltetramethyldisiloxane complex (Karstedt s catalyst, 3% solution in xylenes), hexamethyl-cyclotrisiloxane (95%), vinylmethyldichlorosilane (97%) and 1,1,3,3-tetramethyldisiloxane (97%) were bought from ABCR. Bromine (puriss) was bought from Eluka. Triethylamine (pure for analysis) and zinc oxide (pure) was purchased from Chempur. Solvents (tetrahydrofurane, diethyl ether, methylene chloride, pentane, ethyl acetate) were supplied by POCh (Polish Chemical Reagents). 

Solvents which are fully miscible with all other solvents (from hexane to water) are acetone, glacial acetic acid, dioxane, absolute ethanol, isopropanol, and tetrahydrofuran. 

Sections 9.4 and 10.3 have already provided the basis for optimization by attempting to work with three different solvent mixtures hexane-ether, hexane-dichloromethane and hexane-ethyl acatate for adsorption chromatography and water-methanol, water-acetonitrile, water-tetrahydrofuran for reversed-phase systems. However, this concept is not restricted to binary mixtures but a third or even a fourth component may be added in an attempt to improve the separation. An arrangement of seven different mixtures (Figure 18.11) provides the best basis for systematic evaluation. An example is outlined below. 

Complex multiphase process waste streams are generated in the production of active substances in the chemical industry. A number of standard types of chemistry reactions currently carried out in the pharmaceutical industry would generate complex waste solvent mixtures containing tetrahydrofuran, hexane, alcohols and water. 

Solvents. Tetrahydrofuran (THF). THF (Dupont) was distilled in a simple distillation setup, which had been flamed out under argon. To 1500 ml of the THF, which was passed through molecular sieves, we added 20 ml. styrene and enough 1.5N butyllithium solution in hexane to give a permanent yellow collor. A small forerun was discarded, and the THF distilled directly into 28-oz bottles, which were capped and pressured with argon. 

Styrene and a-Methylstyrene in Organic Solvents. Pulse radiolysis studies have been made on styrene and a-methylstyrene dissolved in methanol, benzene, carbon tetrachloride, dioxane, tetrahydrofuran, hexane, and cyclohexane (9, 24, 29, 30, 31). The results are easiest to understand for the aliphatic hydrocarbons and especially for the styrene in cyclohexane, which has been studied the most (31). For such solutions, two absorption bands were seen after the pulse by Keene, Land, and Swallow (24) and Schneider and Swallow (30) with peaks at 320 and 390 m/. The absorption at 320 m/u disappeared slowly by complex kinetics, and the 390-m/x absorption was very short lived, decaying by second-order kinetics with k/c = 4-7 X 10 cm. sec.-1. The relative intensities of the two peaks were quite variable. Chambers et al. saw the long lived absorption at 320 m/, but did not see a separate peak at 390 m/a, although it was observed that the absorption at 375 mfi decayed rapidly with k/e = 2.6 X 106 cm. sec.-1. 

Organolithium reagents (Section 14.3) Lithium metal reacts with organic halides to produce organolithium compounds. The organic halide may be alkyl, alkenyl, or aryl. Iodides react most and fluorides least readily bromides are used most often. Suitable solvents include hexane, diethyl ether, and tetrahydrofuran. 

The OH group was protected by reaction with tert-butyldimethylsilyl chloride (TBDMS) in order to obtain the living anionic polymerisation. Diphenylethylene (DPE) was used to lower the living chain reactivity. The monomers were added in order styrene, styrene-o-TBDMS, DPE, MMA to the solvent tetrahydrofuran (THF) at 78°C in nitrogen with stirring. The reaction was terminated with methanol and precipitated by hexane to give the product PS-b-poly(styrene-o-TBDMS)-b-PMMA which was dried in vacuum at 130°C then... 

Obtain a 50 50 mixture of two unknown solvents from your instructor. These solvents will differ in boiling point by more than 20 °C. Possible solvents include hexane, cyclohexane, heptane, octane, toluene, ethyl benzene, acetone, methanol. 1-butanol, tetrahydrofuran. 1.4-dioxane. ethyl acetate, and others listed by your... 

N,N-Dimethylthioformamide in tetrahydrofuran added at -100° during 1 min. to a stirred soln. of Li-diisopropylamide in tetrahydrofuran-hexane, after 3 min. treated with benzophenone in the same solvent, and the temp, allowed to rise to -70° during 1 hr. -> N,N-dimethyl-2-hydroxy-2,2-diphenylthioacetamide. Y 85%. F. e. s. D. Enders and D. Seebach, Ang. Ch. 85, 1104 (1973). 

Many organic syntheses requHe the use of stericaHy hindered and less nucleophilic bases than //-butyUithium. Lithium diisopropylamide (LDA) and lithium hexamethyldisilazide (LHS) are often used (140—142). Both compounds are soluble in a wide variety of aprotic solvents. Presence of a Lewis base, most commonly tetrahydrofuran, is requHed for LDA solubdity in hydrocarbons. A 30% solution of LHS can be prepared in hexane. Although these compounds may be prepared by reaction of the amine with //-butyUithium in the approprite medium just prior to use, they are also available commercially in hydrocarbon or mixed hydrocarbon—THF solvents as 1.0—2.0 M solutions. 

A number of techniques have been developed for the trace analysis of siUcones in environmental samples. In these analyses, care must be taken to avoid contamination of the samples because of the ubiquitous presence of siUcones, particularly in a laboratory environment. Depending on the method of detection, interference from inorganic siUcate can also be problematic, hence nonsiUca-based vessels are often used in these deterrninations. SiUcones have been extracted from environmental samples with solvents such as hexane, diethyl ether, methyl isobutylketone, ethyl acetate, and tetrahydrofuran (THF)... 

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