Low boiling impurities

Refractionation of the low-boiling impurities gives a further quantity of the acetoacetate, but if the initial distillation has been carefully conducted, the amount recovered is less than i g., and the refractionation is not worth while. If possible, complete the preparation in one day. If this is not possible, it is best to allow the cold crude sodium derivative (before acidification) to stand overnight, the flask being closed by a cork carrying a calcium chloride tube the yield will now fall to about 38 g. Alternatively, the crude ester may be allowed to remain overnight in contact with the sodium sulphate, but in this case the yield will fall to about 30 g. 

The purification of Hquid nitro alcohols by distillation should be avoided because violent decompositions and detonation have occurred when distillation was attempted. However, if the distillation of a nitro alcohol cannot be avoided, the utmost caution should be exercised. Reduced pressure should be utilised, ie, ca 0.1 kPa (<1 mm Hg). The temperature of the Hquid should not exceed 100°C hot water should be used as the heating bath. A suitable explosion-proof shield should be placed in front of the apparatus. At any rise in pressure, the distillation should be stopped immediately. The only commercially produced Hquid nitro alcohol, 2-nitro-1-butanol, is not distilled because of the danger of decomposition. Instead, it is isolated as a residue after the low boiling impurities have been removed by vacuum treatment at a relatively low temperature. 

After flashing the propylene, the aqueous solution from the separator is sent to the purification section where the catalyst is separated by a2eotropic distillation 88 wt % isopropyl alcohol is obtained overhead. The bottoms containing aqueous catalyst solution are recycled to the reactor, and the light ends are stripped of low boiling impurities, eg, diisopropyl ether and acetone. A2eotropic distillation yields dry isopropyl alcohol, and the final distillation column yields a product of more than 99.99% purity. 

EDC from the oxychlorination process is less pure than EDC from direct chlorination and requires purification by distillation. It is usually first washed with water and then with caustic solution to remove chloral and other water-extractable impurities (103). Subsequently, water and low boiling impurities are taken overhead in a first (light ends or heads) distillation column, and finally, pure, dry EDC is taken overhead in a second (heavy ends or product) column (see Fig. 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 typical process, potassium permanganate is used to treat the cracked liquor exiting the depolymerization plant without any pH adjustment. The liquor is usually acidic because it contains some of the phosphoric acid depolymerization catalyst. The KM11O4 treatment is followed by treatment of the CL aqueous solution with carbon followed by filtration. Next the filtered 20-30% CL aqueous solution is concentrated to 70% and the pH is adjusted to 9-10 by addition of sodium hydroxide. The caprolactam alkaline concentrate is treated widi KMn04 followed by distillation under reduced pressure to remove water and low-boiling impurities. 

Through this treatment, most of the low-boiling impurity can be removed. 

The free base is liberated by adding to the phenylhydrazine hydrochloride 1 1. of a 25 per cent solution of sodium hydroxide. The phenylhydrazine separates and is taken up with benzene (two 300-cc. portions). The combined extractions are well dried with 200 g. of solid sodium hydroxide, poured off, and distilled. Most of the benzene may be distilled under ordinary pressure, and the remainder, and any low-boiling impurities, under diminished pressure. The pure phenylhydrazine boils at 137-138°/18 mm., and is obtained as a pale-yellow liquid. It can be crystallized on cooling in an ice bath the crystals melt at 23°. The crude phenylhydrazine from two lots of aniline... 

The benzene solution of phenylhydrazine should be well dried before distilling, since the presence of moisture causes an increased amount of foaming to take place just after the benzene has distilled off. When the distillation is carried out carefully, practically no phenylhydrazine distils with the benzene or other low-boiling impurities. 

Ethyl acetate is the major low-boiling impurity of heads fractions from continuous columns if bisulfites are absent in the distilling material. A heads fraction from a typical brandy column usually contains less than 1% of these volatile impurities, although the concentrated heads from an aldehyde-concentrating column may contain as much as 10-15% aldehydes. In either case, ethyl alcohol is the major component of the heads cut, and its recovery in usable form has been a troublesome processing problem. 

The malonic ester used should be redistilled, preferably under diminished pressure, and a 2-degree fraction used in the preparation. Ordinary commercial malonic ester contains up to 15 per cent of low-boiling impurities. 

Tests in laboratory columns have indicated that to ensure adequate removal of the low-boiling impurities, 500 lb (227 kg) of the dye intermediate is lost in the low boiler s cut. Similarly, high boilers remaining in the kettle at the end of the distillation will retain 500 lb (227 kg) of the coproduct. This leaves 9500 lb (4320 kg) of the two recoverable products. The specification for the dye intermediate... 

Materials. The UFe used in this work was a portion of a larger batch originally obtained from Oak Ridge National Laboratory. Almost two-thirds of the original batch had been distilled away in previous experimental work, presumably contributing to the purification of the UFe from low boiling impurities e.g., HF, CF4, F2). Emission-spectrographic analysis of the material indicated that the predominant impurities were P, at a concentration of <400 p.p.m., and As, B, Cs, Pd, Re, Sb, Sn, and Th, each present at concentrations of <100 p.p.m. Two determinations of the triple point of a sample of the UFe yielded values of 64.1 °C. and 64.2°C. The best literature value 19) for this is 64.05°C. 

Liquid formaldehyde is not available commercially, and exists only at low temperatures. Our chemical procedure for producing liquid formaldehyde was as follows Into a dried 500 mL 3-necked round-bottomed fitted with a N2 inlet and outlet, thermocouple, and surrounded by a heating mantle was placed approximately 80g of paraformaldehyde (fills flask 2/3 full). The mixture was heated to decompose the paraformaldehyde with the internal temperature controlled with a thermocouple connected to a temperature controller set at 150 C. The formaldehyde was initially collected (under a slow N2 flow) in a small condensing trap cooled at CO2/ acetone temperature to insure removal of residual water and any low boiling impurities. After about 5 mL of formaldehyde was collected in the trap the outlet tube was coimected to the diamond anvil apparatus, which was kept under a N2 atmosphere and cooled to dry ice/ acetone temperatures. Enough formaldehyde was collected to completely cover the diamond anvil cell ( 20 mL). The cell was opened and then closed to encapsulate the sample. A rhenium gasket was used to radially confine the diamond anvil cell samples. 

Because UF has a vapor pressure of 1 atm at 56°C, it is necessary to use two columns to purify it, one to remove low-boiling impurities and the other, high-boiling. Because the triple point of UFfi is 64 C and 1140 Torr, to prevent freeze-up it is necessary to operate both columns at a pressure over 1140 Torr with condenser cooUng at a temperature over 64°C. 

The purification of DMSO for electrochemical studies has been surveyed by Reddy on behalf of a lUPAC Commission. Water is the principal impurity and the purified solvent readily absorbs moisture from the atmosphere. The recommended procedure is to remove water and low boiling impurities with molecular sieve type 5A, followed by vacuum distillation. Water may be detected by its n.m.r. signal at 3.25 ppm downfield of TMS. 

While fractionation allows high boilers such as NCI3 to accumulate, it also allows selective removal of low-boiling impurities such as oxygen. A small amount of vaporization can reduce the concentration significantly. Flashing back to lower pressures in liquefaction systems is a convenient technique [31]. 

Vanadium trichloride is a purple solid, made by thermal decomposition or reduction of the tetrachloride, the latter, in turn, being produced by chlorination of ferrovanadium as described in Chapter 2. Before use, the trichloride can be freed from the oxytrichloride, and other low boiling impurities, by simple distillation. The solid is then cooled, crushed and screened ready for use. 

Purity of the investigated Freon-23, according to chromatography, amounted to 99.98% (moisture, 0.0042%, low-boiling substances, 0.01). Prior to commencement of experiments, the freon was additionally purified to remove low-boiling impurities. 

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