Short Path Distillation

A solution of 0.10 mol of freshly distilled diethylaminopropyne in 80 ml of dry (distilled from phosphorus pentoxide) acetonitrile was cooled to 5°C and dry carbon dioxide was introduced into the vigorously agitated solution at a rate of about 0.3 1/min. The temperature rose above 20°C within a few minutes, but was kept at about 30°C by occasionally immersing the flask in a bath of ice-water. The introduction of CO2 was continued until the temperature had dropped to 25°C and the typical odour of the yneamine had disappeared completely. The yellow solution was concentrated in a water-pump vacuum. The residue, a sirupy liquid, had the theoretically required weight and consisted of reasonably pure (about 955 ) allenyl-diamide. If desired the product car be distilled (short-path distillation) in a high vacuum. It solidified upon standing at -25 C. 

Short-path Molecular Distillation. Short-path molecular distillation offered great promise for the selective removal of cholesterol from milkfat. The process achieves the simplest separation of desired substance from a mixture of components of high molecular weight. 

The submitters used a short path simple distillation apparatus bp aS-ST-C (0.2 mm). 

A short-path distillation apparatus is used, the distillate (oxa-spiropentane plus dichloromethane) being trapped in a reeeiver placed in a methanol-dry ice bath cooled to — 80°. The checkers found it useful to drive out last traces of product by adding several milliliters of dichloromethane to the residual thick paste and distilling. The proton magnetic resonance spectrum (dichloromethane) shows an oetet at 8 0.85 and a singlet at S 3.00 in the ratio 4 2. 

After dilution with 200 ml. of benzene, the solution is transferred to a 2-1. separatory funnel containing 800 ml. of ice water and shaken thoroughly. The aqueous layer is separated, acidified to pH 3-4 with 2-3 ml. of concentrated hydrochloric acid, and extracted with three 100-ml. portions of benzene. All the organic layers are then combined and dried over anhydrous sodium sulfate. Filtration and concentration of the solution with a rotary evaporator, followed by exposure to high vacuum for 2-3 hours, affords 17.3-19.3 g. of the crude product (Note 3). Low-boiling impurities are removed by vacuum distillation (Note 4), the residual oil (14-15 g.) is transferred to a 50-ml. flask equipped with a short-path distillation apparatus, and vacuum distillation is continued. A forerun is taken until no rise in boiling point is observed, and then 7.2-8.6 g. (23-27%) of dimethyl nitrosuccinate is collected as a colorless oil, b.p. 85° (0.07 mm.), 1.4441 (Note 5). 

In a short path distilling apparatus is placed 3-5 g of 1,1-cyclohexanedicarboxylic acid. The flask is heated in an oil, sand, or metal bath to 160-170° until all the effervescence stops then the temperature of the bath is raised to 210°. Cyclobutanecarboxylic acid distills over at 191 -197°. It may be purified by redistillation at atmospheric pressure, bp 195-196°. 

The checkers observed that rather rapid decomposition of the product occurs unless precautions were taken. A short path distillation using a 50-ml. distilling flask equipped with a capillary nitrogen bubbler was employed. 

N.B. Short-path distillation and a high surface-to-volume ratio is necessary in order to prevent dimerization of the product. 

A solution of quinoline 1-oxide (0.29 g, 2 mmol) in cyclohexane (1 L) was dehydrated by azeotropic distillation in the reaction vessel. The solution was purged with dry N2 and irradiated with a Hanau high-pressure Hg lamp. The resulting solution was evaporated and the residue was extracted with a little cyclohexane. The insoluble part contained carbostyril (3). The cyclohexane extract was evaporated and the residue purified by short-path distillation at 50°C/0.1 Torr yield 0.174g (60%) moisture-sensitive oil. 

CHO acetone, reflux, 3 h 0 100 short-path distillation bp 70 C bath/0.2Torr 8... 

A solution of 0.96g (2.4mmol) of (4,V,5,V)-4,5-dicyclohexyl-2-[(.S )-(Z)-l-mcthyl-2-butcnyl]-l,3,2-dioxa-borolane [(S,5,S)-7] in 5 mL of petroleum ether (bp 40 - 60 C) is treated with 0.35 g (2.4 mmol) of benzaldehyde for 12 h at r.t. The solution is then concentrated and taken up in 10 mL of diethyl ether. 0.35 g (2.4 mmol) of triethanolamine is added and the mixture is heated to reflux for 4 h. The resulting boratrane is filtered and washed with three 20-mL portions of diethyl ether. The filtrate is stirred intensively with 50 mL of 20% aq NaHS03, then the aqueous phase is extracted with two 20-mL portions of diethyl ether. The combined extracts arc washed with water and brine and then dried over MgS04. Concentration of this solution ill vacuo is followed by short-path distillation at 60 X/0.1 Torr yield 0.30 g (71%) 99% ee [chiral capillary GC on a (5)-valine-(5)-a-phenylethylamide column]39. 

To a stirred solution of 2.0 mmol of LDA in 3.3 mL of a 60 40 mixture of THF/hexane at — 78 °C under a nitrogen atmosphere is added 264 mg (2.0 mmol) of tert-butyl propanoatc in 2 mL of THF. After 30 min stirring a solution of 168 mg (1.5 mmol) of ethyl (t)-2-butenoalein 1.5 mL of THE is added and the mixture is stirred for an additional hour at — 78 °C. The reaction is quenched by addition of sat. NH4C1. Extraction with diethyl ether, drying over NiiCl followed by evaporation of the solvent and short path distillation gives the adduct yield 378 mg (1.2 mmol, 84%). 

The checkers obtained an additional 2-5 g. of 2-allyl-3-methyl-cyclohexanone by redistilling the column wash and the pot residue through a short-path distillation column. This raised the total yield to 14.9-18.1 g. (54-66%). 

Distillation of the residual oil through a short-path distillation apparatus yields 9.3-9.6 g. (64-66%) (Note 7) of 2-methyl-1-hexanol, b.p. 166-167° (Notes 8 and 9). 

The flask is removed from the oil bath and cooled to room temperature. To the reaction mixture are added successively 21.4 g. (0.12 mole) of finely powdered Nduomosuccininiide (l-bromo-2,5-pyrrolidinedione) (Note 4), 50 ml. of carbon tetrachloride, and 7 drops of aqueous 48% hydrogen bromide (Note 5). The flask is heated at 70 for 10 minutes (Note 6), and the temperature of the bath is then increased to 85° until the color of the reaction becomes light yellow (ca. 1.5 hours Note 7). The reaction mixture is cooled to room temperature, and the carbon tetrachloride and excess thionyl chloride are removed under reduced pressure (Note 8). The residue is suction filtered, and the solid (Note 9) is washed several times with carbon tetrachloride (total 20 ml.) and the combined filtrate collected in a 50-rnl. flask. The solvent is removed from the solution as before, and the residue is distilled into a dry ice-cooled receiver (short-path column) to give, after a small forerun, 16.1-17.1 g. (76-80%) of 2-bromohexanoyl chloride, b.p. 44-47 (1.5 mm.) as a clear, slightly yellow oil, n12 d 1.4707. This material is of sufficient purity for most synthetic purposes (Note 10). 

The checkers found this fractional distillation to be simplified if the initial crude product was first subjected to a rapid short-path distillation under reduced pressure to remove the bulk of the dialkyl ated material and other high molecular weight components. 

Purification by short-path distillation (138-139°C/4.5 mm) resulted in a slightly diminished yield (6.25 g, 71%). 

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