Distillation, fractional reduced pressure

Fractional Distillation under Reduced Pressure. One great disadvantage of the simple vacuum-distillation apparatus shown in Fig. 12(a) is that, if more than one fraction distils, the whole process has to be stopped after collecting each consecutive fraction, in order to change the receiver F. This may be overcome by replacing the simple receiving flask F by a pig (Fig. 13) which collects consecutive... 

Bromoform. Commercial bromoform should be shaken thoroughly with water, separated, dried over powdered anhydrous sodium sulphate and then fractionally distilled under reduced pressure using a water-condenser. It should be stored in a dark cupboard. It is an excellent solvent, has the advantage of a high Constant, and very seldom causes association of the solute. 

The dotted line in Fig. 11,17, 2 refers to the modification of the apparatus for use in fractional distillation under reduced pressure a Perkin triangle or equivalent receiver device ( vacuum distilling adapter ) is generally employed for collection of the various fractions. 

Pour the resulting dark reddish-brown liquid into 500 ml. of water to which 17 ml. of saturated sodium bisulphite solution has been added (the latter to remove the excess of bromine). Steam distil the resulting mixture (Fig. II, 41,1) , collect the first portion of the distillate, which contains a little unchanged nitrobenzene, separately. Collect about 4 litres of distillate. Filter the yellow crystalline solid at the pump, and press well to remove the adhering liquid. The resulting crude m-bromonitrobenzene, m.p. 51-52°, weighs 110 g. If required pure, distil under reduced pressure (Fig. II, 19, 1) and collect the fraction of b.p. 117-118°/9 mm. it then melts at 56° and the recovery is about 85 per cent. 

The iodobenzene is conveniently distilled under reduced pressure and the fraction b.p. 77- 80°/20 mm. or 63-64°/8 mm. collected. The product has a higher degree of purity than that obtained directly from benzene (Section IV,21). 

If pure 3-bromo-4-aminotoluene is required, the crude base may be purified either by steam distillation or, more satisfactorily, by distillation under reduced pressure. The oil is dried with 5 g. of sodium hydroxide pellets, and distilled under reduced pressure from a Claisen fiask with a fractionating side arm a little p-tolui-dine may be present in the low boiling point fraction, and the pure substance is collected at 92-94°/3 inin. or at 120-122°/30 mm. The purified amine solidifies on cooling and melts at 17-18°. 

Another method of purihcation consists in distillation under reduced pressure. The fraction of b.p. I40-I50°/20 mm. is collected separately, - it solidihes on standing, melts at 76-76-5°, and is practically pure-... 

Methyl 2-hydroxy-2-carbomathoxy-4-haptenoate (3), A solution of dimethyl mesoxalate 2 (1.46 g, 10 mmol] and 1-pentene 2 (0 70 g, 10 mmol) in CH2CI2 was heated at 140 C lor 16 h. The solvent was reirroved and the residue distilled under reduced pressure. The fraction collected between 90 and 105°C (0 5 torr) was diluted with Et20 (20 mL), washed with water and dned The residue after evaporation of the solvent, gave on dislillation 1 55 g of 3 (62%), bp 89-90 C (0 2 torr). 

This solution is then cooled and made slightly acid by adding about 275 cc. of 50 per cent acetic acid (Note 4). Salt is added if necessary to cause the ester to separate. The ester layer is separated, dried over calcium chloride and fractionally distilled under reduced pressure from a modified Claisen flask (Org. Syn. 1, 40). 

The solution of sodium methyl sulfide in absolute alcohol is transferred to a 3-I. three-necked flask, which is placed on a steam bath and fitted with a dropping funnel, a reflux condenser, and a mechanical stirrer. The solution is heated until the alcohol begins to boil. Heating is then discontinued and 302 g. (3.7s moles) of ethylene chlorohydrin (Note 5) is added dropwise with efficient stirring over a period of about two hours (Note 6). The reaction mixture is concentrated by distilling as much of the alcohol as possible on the steam bath. The mixture is then allowed to cool and the sodium chloride removed by filtration. The flask is rinsed, and the sodium chloride washed with three loo-cc. portions of 95 per cent alcohol. The combined filtrate and washings are concentrated on the steam bath under reduced pressure until no further distillate passes over. The residue is then transferred to a modified Claisen flask (Org. Syn. Coll. Vol. i, 125) and fractionally distilled under reduced pressure. The yield is 238-265 g. (74-82 per cent of the theoretical amount based on the sodium used) of a product boiling at 68-7o°/20 mm. 

The common methods of purification, discussed below, comprise distillation (including fractional distillation, distillation under reduced pressure, sublimation and steam distillation), crystallisation, extraction, chromatographic and other methods. In some cases, volatile and other impurities can be removed simply by heating. Impurities can also sometimes be eliminated by tbe formation of derivatives from which the purified material is regenerated (see Chapter 2). 

It is not advisable to store large quantities of picrates for long periods, particularly when they are dry due to their potential EXPLOSIVE nature. The free base should be recovered as soon as possible. The picrate is suspended in an excess of 2N aqueous NaOH and warmed a little. Because of the limited solubility of sodium picrate, excess hot water must be added. Alternatively, because of the greater solubility of lithium picrate, aqueous 10% lithium hydroxide solution can be used. The solution is cooled, the amine is extracted with a suitable solvent such as diethyl ether or toluene, washed with 5N NaOH until the alkaline solution remains colourless, then with water, and the extract is dried with anhydrous sodium carbonate. The solvent is distilled off and the amine is fractionally distilled (under reduced pressure if necessary) or recrystallised. 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

Diethyl malonate [105-53-3] M 160.2, b 92"/22mm, 198-199"/760mm, d 1.056, d s 1.0507, n 1.413. If too impure (IR, NMR) the ester (250g) has been heated on a steam bath for 36h with absolute EtOH (125mL) and cone H2SO4 (75mL), then fractionally distd under reduced pressure. Otherwise fractionally distil under reduced pressure and collect the steady boiling middle fraction. 

Ethoxy-7V,7V-diethylaniline [1846-92-2] M 193.3, b 141-142 /15mm pK st 6-l- Refluxed for 3h with acetic anhydride, then fractionally distilled under reduced pressure. 

Isoamyl ether [diisopentyl ether, di-(l-butyl-3-methyl) ether] [544-01-4] M 158.3, b 173.4 , d 0.778, n 1.40850. This is a mixture of 2- and 3-methylbutyl ether. It is purified by refluxing with sodium for 5h, then distilled under reduced pressure, to remove alcohols. Isoamyl ether can also be dried with CaCl2 and fractionally distd from P2O5. 

Tri-n-butyi borate [688-74-4] M 230.2, b 232.4 , u 1.4092, d 0.857. The chief impurities are n-butyl alcohol and boric acid (from hydrolysis). It must be handled in a dry-box, and can readily be purified by fractional distillation, under reduced pressure. 

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