Recovering tetrahydrofuran

For recovery of tetrahydrofuran, the condensate from the cooling traps and the low-boiling material from the fractionations are combined, cooled in an ice bath, and treated carefully with 15-20 cc. of 40 per cent alkali. The upper layer is separated, dried with a little calcium chloride, and distilled. The recovered tetrahydrofuran, b.p. 64-67°, weighs 20-22 g. (17-19 per cent of the original material). The residue (12-14 g-) remaining after disdllation of the tetrahydrofuran distils at 43-45°/io mm. and is tetramethylene dichloride. 

Butane-Based Transport-Bed Process Technology. Du Pont aimounced the commercialization of a moving-bed recycle-based technology for the oxidation of butane to maleic anhydride (109,149). Athough maleic anhydride is produced in the reaction section of the process and could be recovered, it is not a direct product of the process. Maleic anhydride is recovered as aqueous maleic acid for hydrogenation to tetrahydrofuran [109-99-9] (THF). 

An important future use for maleic anhydride is beUeved to be the production of products in the 1,4-butanediol—y-butyrolactone—tetrahydrofuran family. Davy Process Technology has commercialized a process (93) for producing 1,4-butanediol from maleic anhydride. This technology can be used to produce the product mix of the three molecules as needed by the producer. Another significant effort in this area is the tetrahydrofuran plant under constmction in Spain by Du Pont in which butane is oxidized and recovered as maleic acid and the maleic acid is then reduced to tetrahydrofuran (109). 

Electrolysis of dilute solutions of hydrogen cyanide in ammonium bromide to give cyanogen bromide. This is then dissolved in a solvent such as tetrahydrofuran and reacted with gaseous ammonia to produce cyanamide. The cyanamide is then heated in an autoclave at about 190-200°C in the presence of ammonia and the melamine, recovered by filtration. 

The packing wash consisted of 0.5 ml 20% of tetrahydrofuran in a 0.5% solution of acetic acid in water, followed by 2 ml of hexane. The packing was then dried in a stream of nitrogen and washed with a further 3 ml of 25% tetrahydofuran in hexane and again dried under nitrogen. The recovered aflatoxins were finally eluted with two 2 ml aliquots of 1% tetrahydrofuran in methylene dichloride into a silanized tube. 

THF Conversion. Tetrahydrofuran (THF) conversion was calculated from the difference between the initial and the final solubilities of the total coal-solvent slurry in THF. It was assumed that all of the solvent and none of the starting coal was soluble in THF. THF conversions were calculated on an MAF coal basis and adjusted for the coal not recovered from the autoclaves. The filter cake resulting from filtration of the product at 250 C was continuously extracted with THF for up to 3 days. 

The coal residue was separated into a THF-soluble fraction and a THF-insoluble residue. The wt % yields and atom % 2H compositions are given in Table I. The coal residue was 6 wt % soluble in tetrahydrofuran. The soluble fraction had 23 atom % 2H content. Evaluation of the 2H NMR data showed that 85 wt % of this fraction was derived from the coal and that its deuterium content was 10%. The chemically-bonded naphthalene-d8 content of the THF-soluble fraction, estimated from the 2H NMR data, was about 15 wt % or approximately 1 wt % of the coal. The insoluble residue had 6 atom % 2H content. This indicates that the residue contained approximately 1 wt % chemically-bonded naphthalene which was estimated from the difference in the atom % 2H content of the insoluble residue and recovered naphthalene-d8. This gives a total chemically-bonded naphthalene-d8 content of approximately 2 wt %. Similar results were obtained in extraction experiments made with phenanthrene (30), where it was found that 3-7 wt % of the phenanthrene was chemically linked to the coal product. 

Reliable mechanistic conclusions require high intrazeolite yields that account for the majority of the substrate mass balance. This can be a challenge because of the small-scale reactions often conducted for mechanistic studies. In addition, rapid removal of the products from the zeolite, and/or low conversions to decrease residence time, is occasionally necessary because of the sensitivity of the reaction products to the zeolite environment.44,45 Intrazeolite products are generally recovered by extractive techniques from either the intact zeolite, or from a mixture formed after mild digestion of the zeolite. Polar solvents such as tetrahydrofuran or acetonitrile coupled with a continuous extraction technique is in particular an effective means to remove polar products with an affinity for the interior of the zeolite.44 Zeolite digestion with mineral acids, in order to liberate the products, must be conducted with care in order to prevent acid catalyzed product decomposition or reaction.46,47... 

B. (2S, 3R)-2,4-Dimethyl-1,3-pentanediol3. To a stirred solution of (+)-2 (2.75 g, 5 mmol, 96 4 isomeric purity) in tetrahydrofuran (THF) (50 mL) is added lithium aluminum hydride (0.19 g, 5 mmol) at 0°C. The reaction mixture is stirred at room temperature for 1 hr and quenched by the careful addition of sodium sulfate decahydrate (5 g). The mixture is stirred vigorously for 30 min and filtered. The filtrate is concentrated, dissolved in 75 mL of a 1 1 mixture of hexane and dichloromethane. This solution is dried over sodium sulfate, filtered and concentrated under reduced pressure. Trituration of the resulting oil with hexane (50 ml) results in the precipitation of auxiliary alcohol 4 (1.6-1.8 g) which is recovered by filtration (Note 11). The residue is separated by chromatography over silica gel (40 g) (Note 2) with hexane and ethyl acetate (3 1-1 1) to afford additional 4 (0.2-0.4 g. Note 12) and 3 (0.60 g, 92%) (Notes 13, 14). 

Tetrahydrofuran (THF, UV grade) was used as the mobile phase throughout this work since the extent of fractionation could be demonstrated by direct analysis of the preparative fractions without the need for concentration. When samples are to be recovered by removal of solvent, other mobile phases (methylene chloride, etc.) may be preferred to avoid concentrating solvent impurities which are formed in THF on exposure to air unless additional precautions are taken. 

An interesting alternative procedure is to stir ZrCl2(r)s-C,H5)2 in tetrahydrofuran with 0.5 g-atom of magnesium turnings. A red color develops and after 3-5 days a 30% yield of ZrHCl(r)5-CsH5)2 can be recovered by filtration, t Available from Alfa Products, Ventron Corp., P.O. Box 299, Danvers, MA 01923. 

The regio- and stereoselective alkylations of a number of bicyclic racemic dioxopiperazines have been reported3. For example, dioxopiperazine 9 is deprotonated by lithium diisopropyl-amide in tetrahydrofuran at — 78 °C to yield a monoanion. Alkylation with iodomethane in the presence of hexamethylphosphoric triamide gives products 10 and 11 in a 81 19 ratio and 75 % yield based on recovered starting material3. 

High stereoselectivities (94-100 %) are attained in the reduction of aromatic ketones by use of a new chiral borane complex with (S)-2-amino-3-methyl-l,l-diphenylbutan-l-ol,(S-68) readily prepared in two steps from (S)-valine, in an experimentally convenient procedure961. (S)-Valine methyl ester hydrochloride was converted with excess of phenylmagnesium bromide into (S-68). The same treatment of (R)-valine gave (R-68). In a typical asymmetric reduction the reagent, prepared from (S-68) and borane, and the ketone (69) in tetrahydrofuran were kept at 30 °C for some hours. The corresponding alcohols were obtained in high optical purity. (S-68) could be recovered to more than 80% without racemization 96). 

Orthophosphoric acid of 95% concentration is most efficient for effecting cleavage of tetrahydrofuran. Commercial orthophosphoric acid (85%) may be used however, the yield drops to 82% and approximately 10% of the tetrahydrofuran is recovered. Anhydrous orthophosphoric acid and tetraphosphoric acid cannot be employed conveniently because of the limited solubility of hydrogen iodide in these reagents. 

Irradiation procedures. Mesophase solutions and neat solid samples of BN were prepared and sealed under N2 or vacuum in Kimax capillary tubes. Isotropic samples were either degassed (freeze-pump-thaw techniques) and sealed in pyrex tubes or saturated with N2 in pyrex tubes. Nitrogen was bubbled through the latter solutions during irradiation periods. When ther-mostatted, samples were placed in a temperature controlled ( 1°) water bath. All samples were irradiated with a 450 W Hanovia medium pressure Hg arc and were stored at -30°C until their futher use. Usually, a "dark sample was prepared and treated in an identical fashion to the irradiated samples except that it was shielded from the light. JSN from each tube was recovered by either column chromatography (silica or alumina and pentane eluant) at 4°C followed by solvent removal at 0°C and reduced pressure or by hplc (tr-hexane) at room temperature followed by solvent removal at 0°C and reduced pressure. Neat solid samples were dissolved in one of either benzene, tetrahydrofuran or toluene and were frozen until analyzed. 

Buffered Tetrahydrofuran. In 1973, Tettamanti et al. [19) described an improved procedure for the extraction, separation and purification of brain gangliosides. In this method, the brain tissue was subjected to homogenization and extraction with buffered [potassium phosphate buffer, pH 6.8) tetrahydrofuran. Following centrifugation, diethyl ether was added and the mixture separated into organic and aqueous phase. The gangliosides, recovered exclusively in the aqueous phase, were then freed of residual phospholipids and other minor contaminants [i.e. peptides)by column chromatography on silica gel.This procedure, as shown by the authors,was superior to the commonly used chloroform/methanol... 

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