Distillation bumping, prevention

These latter pieces of equipment may be called bulb-to-bulb distillation units. A commercial form is the Kugelrohr apparatus (Aldrich). The material to be distilled is placed in a suitably sized round-bottomed flask (one-third full) and attached to the receiver flask train (Fig. 2.120). This arrangement is connected to a horizontal drive shaft which enables the bulbs to be gently rocked by a safe air-or vacuum-operated oscillating motor, which speeds distillation and prevents bumping. The distillation flask may be heated up to 225 °C in an i.r.-radiant heater. The hollow drive shaft may be connected to a vacuum pumping system and the apparatus operates down to 1 x 10 5mmHg. 

When a more delicate fractional vacuum-distillation is required, the flask and column shown in Fig. ii(b), p. 26, may be used, the side-arm of the column being fitted directly into receiver C (Fig. 14). A rubber stopper must then be used to fit the flask on to the fractionating column, and it should also carry a capillary tube leading to the bottom of the flask, to provide the usual fine stream of bubbles to prevent bumping. 

I) When working with larger quantities of material, it is more convenient (and a better yield is obtained) to purify the air-dried product by distillation under diminished pressure. Use the apparatus pictured in Fig. II, 19, 4, and add a few fragments of porous porcelain to the solid. No air inlet can be employed to prevent bumping since this may lead to explosive decomposition. Collect the pure m-nitrophenol at I60-I65°/I2 mm. always allow the flask to cool before admitting air otherwise the residue may decompose with explosive violence. The recovery is over 90 per cent, of the pure m-nitroplienol. 

The distilling flask. To minimise superheating of the liquid (due to the absence of minute air bubbles or other suitable nuclei for forming bubbles of vapour), and to prevent bumping, one or more of the following precautions should be taken ... 

Alternatively, rapid magnetic stirring will prevent bumping and allow distillation without using a gas bleed. 

It may be purified by recrystallization from hot hydrochloric add, as recommended in Org. Syn. 3, 87, but on account of the difficulty of filtration this procedure is satisfactory on a small scale only. It is preferably distilled in 200-g. lots from a 500-cc. Claisen flask under 10-15 mm. pressure, b.p. 160-165V12 mm. It is important that no air inlet be used to prevent bumping, since under these conditions it partly sublimes and causes trouble by stopping up the connections. A filter or distilling flask is used as a receiver and only a short but wide bore (10 mm.) air condenser is necessary. This product is pale yellow and melts at 95-96°. The yield from 200 g. of crude product is 180-185 g-... 

Tetrahydrofuran from E. I. du Pont de Nemours and Company can be dried conveniently by adding to it lithium aluminum hydride in small portions until no further reaction (evolution of hydrogen) ensues. After the mixture has been stirred for a few minutes, most of the tetrahydrofuran is distilled from it with stirring (to prevent bumping) (Note 3), and collected in a receiver protected from moisture by a calcium chloride tube. 

For the distillation, the still head consisted of a Claisen-type adapter with a parallel side arm (24/40 standard taper joints), 21 cm. high and 10.5 cm. wide. An ordinary straight still head is attached to the parallel side arm. This large still head prevents any bumping solid from entering the condenser. 

Triethylenetetramine (redistilled, Eastman Organic Chemicals) prevents bumping and foaming and acts as a chaser for the distillation. 

The thermometer can be replaced with an inlet tube. If your flask has the provisions for both a thermometer and an inlet tube, then by all means also leave the thermometer in the reaction. The inlet tube should always be used to prevent the bad bumping that goes along with vacuum distillations. Boiling stones are useless. 

To prevent any undesirable distillation and/or bumping which would cause concentration fluctuations, the procedures outlined by Juliano (19) were carefully followed. Next, each detached dilatometer was securely clamped in a constant temperature bath which was maintained at 20, 30, or 40°C as desired. Readings were taken with a cathetometer after the initial thermal expansion to the bath temperature. The data were treated as described by Pett. (20) The dilatometric treatment was also used for those reactions where a conversion versus time curve was required for later estimation of extent of conversion. 

After about 3 hours or after analysis has indicated that the peroxide has been consumed (Note 5), the formic acid is removed by distillation under reduced pressure (b.p. 50°/125 mm.) in a stream of gas (carbon dioxide or nitrogen) to prevent bumping (Note 6). The residue in the flask, which consists of hydroxy-formoxystearic acids, is heated for 1 hour at 100° with an excess of 3N aqueous sodium hydroxide, and the hot, amber-colored soap solution is cautiously poured into an excess of 3N hydrochloric acid with stirring. The oil which separates is allowed to solidify, and the aqueous layer is discarded. The tan-colored solid is remelted on the steam bath by addition of hot water and stirred well to remove residual salts and water-soluble acids (Note 7). When the oil has solidified, the aqueous layer is discarded, and the solid is broken into small pieces and dissolved in 400 ml. of 95% ethanol by heating on the steam bath. After crystallization at 0° for several hours, the product is collected on a filter and dried under vacuum. The yield of crude 9,10-dihy-droxystearic acid is 75-80 g., m.p. 85-90°. After a second recrystallization from 250 ml. of 95% ethanol, the product weighs about 60-65 g. and melts at about 90-92°. A third recrystallization may be necessary to produce a pure product melting at 94-95°. The over-all yield is 55-60 g. (50-55%, based on the available oleic acid) (Note 8). 

Initially to prevent bumping. Final rotary evaporation to remove residual ether prior to distillation was done at 40-50 mbar (30-38 mm). 

The flask is equipped with a short column, attached to which is a condenser set for distillation. A capillary is provided to prevent bumping. The water is then distilled at a pressure of 30-40 mm. by heating the flask in a water bath which is raised to the boiling point as rapidly as is consistent with smooth... 

The column is substituted for the reflux condenser in the same set-up. Stirring during distillation prevents serious bumping. 

---