Tetrahydrofuran hexane solvent system

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 submitters have found that the hexane-tetramethylethylenediamine solvent system described above, which is required for toluenesulfonyl-hydrazones, may be replaced with tetrahydrofuran when triisopro-pylbenzenesulfonylhydrazones are used, provided that the electrophilic reagent is added to the vinyllithium species as soon as it is formed (as indicated by cessation of nitrogen evolution). 

Szepesi et al. reported an ion-pair separation of eburnane alkaloids on a chemically bonded cyanopropyl stationary phase. As counter-ion, di-(2-ethyl hexyl)phosphoric acid or (+)-10-camphorsulfonic acid were used in a mobile phase consisting of hexane - chloroform -acetonitrile mixtures (Table 8.8, 8.9). Because of the poor solubility of the latter pairing ion, diethylamine (Table 8.9) was added to the mobile phase. Addition of diethylamine considerably reduced the k1 of the alkaloids, due to suppression of the ionization of the alkaloids. However, due to the strong acidic character of the pairing ion, ion-pairs were still formed under these conditions. The camphorsulfonic acid containing mobile phases were found to be very useful for the separation of optical isomers (Table 8.10, 8.11, Fig.8.8) 6. It was also found that the selectivity of the system could be altered by choosing different medium-polarity solvents (moderator solvents) as dioxane, chloroform or tetrahydrofuran. The polar component of the solvent system affected peak shape. Based on these observations, a method was developed to analyze the optical purity of vincamine and vinpocetine. For the ana-... 

For these reactions, a large variety of base-solvent systems have been used, including sodium hydride in 1,2-dimethoxyethane or dimethylformamide, aqueous sodium hydroxide, butyl-lithium or phenyllithium in hexanes, potassium hydride in tetrahydrofuran, and sodium ethox-ide in ethanol. 

Stationary phase Polyacrylonitrile on microscope slides. Mobile phase A/, = H20-tetrahydrofuran (30 70) M2 = H20-acetone (20 80) Af, = n-hexane-benzene (90 10) M = n-hexane-CCU (90 10) A/3 = n-nonane Mf, = -hexane. Detection Self visible colored spots of the complexes. Conditions Ascending technique layer thickness 0.25 mm run 5 cm development time 100 min with A/j, 60 min with A/2 and 25 min with My-Mf, mobile phases sample loading 0.2 /ttl of freshly prepared solutions (2 mg/cm ) of complexes in acetone. Remarks With nonaqueous solvent systems, mobility of complexes increased with increasing size of the n-alkyl chain of the ligands whereas the reverse sequence prevailed with aqueous mobile phases. A linear dependence between the number of carbon atoms in the alkyl chain of the ligands and the corresponding R values of a homologous series of Co(III) complexes was found valid in both normal and reversed phase TLC. 

General Considerations. The following chemicals were commercially available and used as received 3,3,3-Triphenylpropionic acid (Acros), 1.0 M LiAlH4 in tetrahydrofuran (THF) (Aldrich), pyridinium dichromate (Acros), 2,6 di-tert-butylpyridine (Acros), dichlorodimethylsilane (Acros), tetraethyl orthosilicate (Aldrich), 3-aminopropyltrimethoxy silane (Aldrich), hexamethyldisilazane (Aldrich), tetrakis (diethylamino) titanium (Aldrich), trimethyl silyl chloride (Aldrich), terephthaloyl chloride (Acros), anhydrous toluene (Acros), and n-butyllithium in hexanes (Aldrich). Anhydrous ether, anhydrous THF, anhydrous dichloromethane, and anhydrous hexanes were obtained from a packed bed solvent purification system utilizing columns of copper oxide catalyst and alumina (ether, hexanes) or dual alumina columns (tetrahydrofuran, dichloromethane) (9). Tetramethylcyclopentadiene (Aldrich) was distilled over sodium metal prior to use. p-Aminophenyltrimethoxysilane (Gelest) was purified by recrystallization from methanol. Anhydrous methanol (Acros) was... 

A new system for grafting copolymerization was described by Kojima and collaborators (126), in 1971, involving tri-n-butyl borane and water, at 37° C, for 2 hrs, in a taper joint glass tube. This system was inefficient when organic solvents like cyclohexanone, n-hexane, tetrahydrofurane, and toluene were used instead of water. 

Very detailed separations have been obtained by numerous authors (61-66) based upon the method originally developed by Christie (67). This method is based mainly on iso-octane (similar to hexane), 2-P, water containing 500 /jlM serine adjusted to pH 7.5 with ethylamine, and trace amounts of tetrahydrofuran (THF) as a mobile-phase modifier. Lutzke and Braughler modified slightly the mobile-phase system proposed by Christie by including a flow rate gradient to maintain low column backpressure (62). According to the authors, this positively affected detector response to PLs. Markello et al. used the procedure described by Christie, albeit without the addition of serine or ethylamine (65). Melton proposed the use of two solvent mixtures only, but they included exactly the same solvents as proposed by Christie (66). However, PI and PA were not resolved. 

Various organic solvents were tested for the PLE-catalyzed asymmetric hydrolysis of diester (12) in a biphasic system. The results (Table 5) indicate that the reaction yields and e.e. of monoester (13) were dependent on the solvent used in the asymmetric hydrolysis. Tetrahydrofuran (THF), methyl isobutyl ketone (MIBK), hexane, and dichloromethane inhibited PLE. Lower reaction yields (28-56 M%) and lower e.e. (59-72%) were obtained using f-butyl methyl ether, dimethylformamide (DMF), and dimethylsulfoxide (DMSO) as cosolvent. Higher e.e. (>91%) was obtained using methanol, ethanol, and toluene as cosolvent. Ethanol gave highest reaction yield (96.7%) and e.e. (96%) for monoester (13). 

High-performance liquid chromatography is performed using a Hewlett-Packard 1090 chromatograph equipped with a ternary-solvent delivery system, an autoinjector with a 0 -20- u.L injection loop, an oven compartment, and a diode-array UV detector. An ELS detector (Alltech Associates, Deerfield, IL) is connected in series to the UV detector. Hexane, 2-propanol, and water were used for the analysis of nonionic surfactants. Water and tetrahydrofuran (THF) are used for the analysis of anionic surfactants. No preliminary sample preparation is used other than dilution. The nonionic surfactants are diluted 1 40 (v/v) with hexane. The anionic surfactants (alkyl ether sulfates and synthetic and petroleum sulfonates) are diluted 1 20 (v/v) with water-THF (50 50). The calcium sulfonate surfactants were diluted 1 20 (v/v) with a THF-38% hydrochloric acid solution of pH 1. Hydrochloric add is required to prevent salt precipitation by converting any excess water-insoluble caldum carbonate into water-soluble calcium chloride. All diluted samples are... 

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. 

Solution Polymerization. Solution polymerization is over 45 years old, but only about 3% of the PVC produced in the United States is made this way. The solution process differs from the other processes already discussed in that a solvent is added to the polymerization system. The system may be heterogeneous, in which case the monomer is soluble but the polymer is insoluble. Examples are the use of hexane, butane, ethyl acetate, or cyclohexane as solvents. After addition of a peroxide initiator and heating to 40 C, the polymerization starts and polymer precipitates out of solution as formed. In homogeneous reactions, both monomer and polymer are soluble therein. Examples are the use of dibutyl phthalate and tetrahydrofuran as solvents. 

Normal phase liquid partition. The polar characteristics of the stationary phase can be modified by incorporating ether, nitrile, nitro, diol and/or amino substituents normally at the end of a hydrocarbon chain or, on an aromatic ring, both of which are chemically bonded to the support material. The major advantage of these materials compared to the liquid-solid systems described above is the facility to undertake gradient elution. Elution is normally carried out with relatively non-polar solvents such as tetrahydrofuran, diethyl ether, chloroform and hexane. 

A. Tributylethynylatannane, An oven-dried, 2-L, three-necked, round-bottomed flask equipped with a mechanical stirrer, 100-mL addition funnel, and a nitrogen inlet is charged with 24.0 g (0.26 mol) of lithium acetylide, ethylenediamine complex (Note 1). The system is evacuated, placed under nitrogen, and 800 mL of tetrahydrofuran (Note 2) is added to the system via a cannula. The flask is cooled in an ice water bath and 70.7 g (0.22 mol) of tributyltin chloride (Note 3) is added dropwise over 45 min. The ice bath is removed and the mixture is stirred for 18 hr at room temperature. The flask is placed in an ice water bath and excess lithium acetylide is hydrolyzed with 20 mL of water. The reaction mixture is concentrated under reduced pressure and washed with hexane (3 x 50 mL). The organic layers are combined and dried over anhydrous magnesium sulfate. Filtration and evaporation of the solvent at reduced pressure gives a colorless oil. Distillation yields 21.4-24.3 g (31-35%) of tributylethynylstannane, bp 90-94 C (0.5 mm) as a water-white liquid (Notes 4-6). 

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