High-vacuum distillations

Some simple apparatus, suitable for high vacuum distillation, are collected in Figs. 11, 26, 1-4. Fig. 11, 26, 1 represents an apparatus, which is particularly well adapted for solids the ground glass joint must be lubricated with a grease of negligible vapour pressure. Hickman s vacuum still is shown in Fig. 11, 26, 2 it is about 60 mm. in diameter. 

High vacuum distillation gave a crystalline product, containing small amounts of impurities, inter alia some 2-butynoic acid. Crystallization from a 3 1 mixture of pentane and diethyl ether at low temperature gave the pure acid, m.p. 77°C, in 38-45 yields. 

Hove 1. The procedure described in Ref. 1 was modified. To a solution of 2.0 mol of lithium acetylide in 1.2 1 of liquid ammonia in a 4-1 round-bottomed, three-necked flask (see Fig. 2) was added 1.5 mol of freshly distilled benzaldehyde with cooling at about -45°C. After an additional 30 min finely powdered ammonium chloride (2 mol) was introduced in 15 min. The ammonia was allowed to evaporate, then water (1.1 1) was added and the product was extracted with diethyl ether. After drying over magnesium sulfate the extract was concentrated in a water-pump vacuum. High-vacuum distillation,... 

A solution of gramine methosulfate (30.0 g, 0.10 mol) and NaCN (15,0 g, 0.30mol) in water (300 ml) was heated to 65-70°C for 1 h. A colourless oil separated as the reaction proceeded. The solution was cooled and saturated with Na2S04 and extracted with ether (400 ml). The ether was removed in vacuo and the residue purified by high vacuum distillation to give the product in 94% yield. 

Consider high vacuum distillation when material is temperature-sensitive at normal pressure ranges. 

Soianone [5( + )-/rn s-2-methyi-5-isopropyi-l,3-nonan-8-one] [1937-54-8] M 194.3, b 60< /lmni, [alp +14" (neat). Purified by high vacuum distillation and stored in sealed ampules [Kohda and Sato J Chem Soc, Chem Commun 951 7957]. It has UV (hexane) at Xmax 230nm (e 11,800). 

In this synthesis, the cationic resin Amberlite IR 122 was used as catalyst. The product was isolated by high vacuum distillation at 175°, a temperature which may have also depolymerized some of the open-chained oligomers present. ... 

For high vacuum distillation, Eckles et al. [150] suggest using a thin film or conventional batch process for industrial type installations however, there are many tray and packed colunms operating as low as 4 mm Hg, abs Eckles... 

Presence of traces of sodium hydroxide probably caused formation of the acetylenic sodium salt, which exploded dining high-vacuum distillation in a metal still [1], A laboratory investigation which duplicated the explosion, without revealing the precise cause, was also reported [2],... 

Though the ozonide appeared stable to small-scale high-vacuum distillation, the residue exploded violently at 130°C. 

Alkali-washed material, stabilised with 0.25% of pyrogallol, was distilled at 103°C/4 mbar until slight decomposition began. The heating mantle was then removed and the still-pot temperature had fallen below its maximum value of 135°C when the residue exploded violently [1], The presence of solid alkali [2] or 5% of phenolic inhibitor is recommended, together with low-temperature high-vacuum distillation, to avoid formation of acidic decomposition products, which catalyse rapid exothermic polymerisation. 

The silane, prepared by reduction of tris(2-propylthio)silylenium perchlorate with diisobutylaluminium hydride at —78°C, is subsequently isolated by high-vacuum distillation from the mixture. Heating must be very mild to prevent explosion. 

Explosion and charring of the ester dining high-vacuum distillation from an oil-bath at 110°C was ascribed to exothermic polymerisation, (probably catalysed by acidic decomposition products). 

Cupery, M. E. et al., J. Amer. Chem. Soc., 1934, 56, 1167 During isolation of the title product from polymerised l,5-hexadiene-3-yne, high vacuum distillation must be carried only to a limited extent to prevent sudden explosive decomposition of the more highly polymerised residue. 

The cyclics could be removed by high-vacuum distillation, but this was not done regularly. Two networks synthesized using a purified and unpurified crosslinker, had the same modulus within5%.Hence we concluded that the cyclics do not affect the crosslinking reaction. 

To 2,3-dioleoyloxy-l-iodopropane (3.65 g, 5 mmol) was added tris(tri-methylsilyl) phosphite (15.05 g, 50 mmol), along with a trace of butyl hydrogen phthalate. The reaction mixture was stirred under a static nitrogen atmosphere with heating at 125°C for 16 h. After this time, excess tris(trimethylsilyl) phosphite and iodotrimethylsilane were removed by high vacuum distillation (bath 100°C) to leave a colorless oil. The residue was dissolved in THF water (9 1, 50 ml) and allowed to stand in the dark at room temperature for 12 h. The solvent was... 

The main disadvantages of Evans auxiliaries 22 and 23 are that they are expensive to purchase and inconvenient to prepare, as the preparation involves the reduction of (5 )-valine 24 to water-soluble (b )-valinol, which cannot be readily extracted to the organic phase. The isolation of this water-soluble vali-nol is difficult and requires a high vacuum distillation, which is not always practical, especially on an industrial scale. Therefore, an efficient synthesis of Evans chiral auxiliary 25 has been developed, as depicted in Scheme 2-1930 ... 

NG has an apparent bp of 145°, which is merely the temp at which non-expl decompn becomes vigorous enough to resemble boiling. Apparently some decompn occurs even during high vacuum distillation, but some reported values are 125°... 

Fig. 18.2 Aroma-isolation techniques based on distillation. Left simultaneous distillation/extrac-tion right high-vacuum distillation with cryotrapping. (Reprinted with permission from [15]. Copyright 1998 American Chemical Society)...

It is very common to combine methods in obtaining aroma isolates. The simultaneous distillation/extraction method previously described is an example. Another popular combination method initially involves the solvent extraction of volatiles from a food and then high-vacuum distillation of the solvent/aroma extract to provide a fat-free aroma isolate. This technique is broadly used today to provide high-quality aroma extracts for numerous purposes. The apparatus used in solvent removal has been improved upon to reduce analysis time and efficiency the modified method is termed solvent-assisted flavour extraction (SAFE) [16]. 

IEC 40, 16—18(1948 (High-vacuum distillation), and succeeding years in January numbers under " Unit Operations ) 9) T.P. 

Checkers comment Since our rotovaps are incapable of removing DMF, high-vacuum distillation is utilized. During reduction of the volume of the solvent, all the solvent is removed and then 40 mL of DMF is added. The solid is scraped from the walls of the flask and vigorously stirred for 2 h to homogenize the solid in the DMF. The solid filtered washed 4 x 10-15 mL DMF and 2x4 mL diethyl ether to remove trapped DMF. 

Phosphorus oxybromide reacts slowly with water to yield orthophosphoric and hydrobromic acids. It dissolves readily in many organic solvents such as ether, benzene, and carbon tetrachloride. Because the bromide decomposes readily at high temperatures, it should always be melted in a hot water bath (m.p. 55 56°C), never with a flame. Prepared as described, the product contains traces of phosphorus tribromide which can be removed only by 6-fold high-vacuum distillation. 

---