Distillation under vacuum

Separation of high-molecular-weight heat-sensitive materials. High-molecular-weight materials are often heat sensitive and as such are usually distilled under vacuum to reduce their boiling temperature. 

Separation of Fatty Acids. Tall oil is a by-product of the pulp and paper manufacturiag process and contains a spectmm of fatty acids, such as palmitic, stearic, oleic, and linoleic acids, and rosia acids, such as abietic acid. The conventional refining process to recover these fatty acids iavolves iatensive distillation under vacuum. This process does not yield high purity fatty acids, and moreover, a significant degradation of fatty acids occurs because of the high process temperatures. These fatty and rosia acids can be separated usiag a UOP Sorbex process (93—99) (Tables 8 and 9). 

Considering their heat sensitivity, the separation of fatty acids and rosin with minimal degradation by fractional distillation under vacuum and/or in the presence of steam is surprisingly good (3). Tad od rosin (TOR) contains about 2% fatty acid and smad amounts of neutrals. Tad od fatty acid (TOFA) contains as Htde as 1.2% rosin and 1.7% neutrals. In typical U.S. TOFA, 49% of the fatty acids is oleic, 45% linoleic, and 3% palmitic, stearic, and eicosatrienoic acid. TOR and TOFA are upgraded to resins and chemicals for the manufacture of inks (qv), adhesives (qv), coatings (qv), and lubricants (see Lubrication AND lubricants). 

Hexaorganoditins with short-chain ahphatic groups are colorless Hquids, distillable under vacuum, soluble in organic solvents other than the lower alcohols, and insoluble in water. They are generally unstable in ak, undergoing ready oxidation to a mixture of organotin compounds. Hexaarylditins are usually crystalline soHds and are much more stable towards oxidation. 

Heat Sensitivity. The heat sensitivity or polymerization tendencies of the materials being distilled influence the economics of distillation. Many materials caimot be distilled at their atmospheric boiling points because of high thermal degradation, polymerization, or other unfavorable reaction effects that are functions of temperature. These systems are distilled under vacuum in order to lower operating temperatures. For such systems, the pressure drop per theoretical stage is frequently the controlling factor in contactor selection. An exceUent discussion of equipment requirements and characteristics of vacuum distillation may be found in Reference 90. 

These can be purified by extracting acidic and basic impurities with aqueous base or acid, respectively. However, they are somewhat sensitive to strong alkali which slowly cleaves the disulfide bond. TTie lower-melting members can be fractionally distilled under vacuum. The high members can be recrystallised from alcohol, toluene or glacial acetic acid. 

These compounds are odourless, rather unstable compounds, and should be distilled under vacuum in an inert atmosphere. They are water-soluble but can be extracted from aqueous solution with a solvent such as diethyl ether. 

Carbon tetrafluoride [75-73-0] M 88.0, b -15 . Purified by repeated passage over activated charcoal at solid-C02 temperatures. Traces of air were removed by evacuating while alternately freezing and melting. Alternatively, liquefied by cooling in liquid air and then fractionally distilled under vacuum. (The chief impurity originally present was probably CF3CI). 

Diniethylannine [95-64-7] M 121.2, m 51 , 5.17. Crystd from ligroin and distilled under vacuum. 

Nitrobenzoyl chloride [122-04-3] M 185.6, m 75 , b 155 /20mm. Crystd from dry pet ether (b 60-80°) or CCI4. Distilled under vacuum. Irritant. 

Phosgene [75-44-5] M 98.9, b 8.2 /756mm. Dried with Linde 4A molecular sieves, degassed and distilled under vacuum. This should be done in a closed system such as a vacuum line. HIGHLY TOXIC, should not be inhaled. If it is inhaled operator should lie still and made to breath ammonia vapour which reacts with phosgene to give urea. 

Phosphorus (white) [7723-14-0] M 31.0, m 590, d 1.82. Purified by melting under dilute H2S04" dichromate (possible carcinogen) mixture and allowed to stand for several days in the dark at room temperature. It remains liquid, and the initial milky appearance due to insoluble, oxidisable material gradually disappears. The phosporus can then be distilled under vacuum in the dark [Holmes Trans Faraday Soc 58 1916... 

Potassium (metal) [7440-09-7] M 39.1, m 62.3 , d 0.89. Oil was removed from the surface of the metal by immersion in n-hexane and pure Et20 for long periods. The surface oxide was next removed by scraping under ether, and the potassium was melted under vacuum. It was then allowed to flow through metal constrictions into tubes that could be sealed, followed by distillation under vacuum in the absence of mercury vapour (see Sodium). EXPLOSIVE IN WATER. 

Sodium methoxide [124-41-4] M 54.0. It behaves the same as sodium ethoxide. It is hygroscopic and is hydrolysed by moist air to NaOH and EtOH. Material that has been kept under N2 should be used. If erratic results are obtained, even with recently purchased NaOMe it should be freshly prepared thus Clean Na (37g) cut in l-3g pieces is added in small portions to stirred MeOH (800mL) in a 2L three necked flask equipped with a stirrer and a condenser with a drying tube. After all the Na has dissolved the MeOH is removed by distillation under vacuum and the residual NaOMe is dried by heating at 150° under vacuum and kept under dry N2 [Org Synth 39 51 1959]. 

Triphenyl phosphite [101-02-0] M 310.3, b 181-189 /lmni, d 1.183. Its ethereal soln was washed succesively with aqueous 5% NaOH, distilled water and saturated aqueous NaCl, then dried with Na2S04 and distilled under vacuum after evaporadng the diethyl ether. 

Consider the oil-recycling plant shown in Fig. 3.16. In this plant, two types of waste oil are handled gas oil and lube oil. The two streams are first deashed and demetallized. Next, atmospheric distillation is used to obtain light gases, gas oil, and a heavy product. The heavy product is distilled under vacuum to yield lube oil. Both the gas oil and the lube oil should be further processed to attain desired properties. The gas oil is steam stripped to remove light and sulfur impurities, then hydrotreated. The lube oil is dewaxed/deasphalted using solvent extraction followed by steam stripping. 

A 17a-hydroxyl group reduces the reactivity of the 20-ketone but direct ketalization with ethylene glycol is not impeded, Ketalization can also be effected in the presence of 17a- and/or 21-hydroxy substituents. Thus the 3,20-biscycloethyleneketal (88) is obtained from (87) in high yield by the direct procedure, or better by distillation under vacuum without a diluent. A bromine atom at C-17 and a 21-acetoxy group even in the absence of a 17a-hydroxyl group strongly hinder ketalization at C-20. ... 

Stirring. The succinimide is removed by suction filtration and washed twice with 10-mI portions of carbon tetrachloride. The combined filtrate and washings are fractionally distilled at atmospheric pressure to remove the carbon tetrachloride and excess olefin (steam bath). The residue is distilled under vacuum, giving about 60 % yield of 3-bromo-cyclohexene, bp 68715 mm or 4472 mm. 

The mixture is filtered into a 500-ml round-bottom flask, and methanol and water are removed by distillation under vacuum (bath temperature 50-60°) until the residual amine oxide hydrate solidifies. The flask is fitted with a magnetic stirrer and a short Vigreux column, and the receiving flask is cooled in a Dry Ice-acetone bath. The flask... 

To the cooled (room temperature) reaction mixture, glacial acetic acid (15 ml) is added dropwise with stirring (formation of pasty solid), followed by 50 ml of ice-cold water (dissolution of the solid). The benzene layer is separated, the aqueous layer is extracted three times with 25-ml portions of benzene, and the combined benzene extracts are washed three times with 25-ml portions of cold water. Benzene is removed by distillation at atmospheric pressure, and excess diethyl carbonate is removed by distillation under aspirator pressure. The residue is distilled under vacuum, affording 2-carbethoxycyclooctanone, bp 85-8770.1 mm, 1.4795-1,4800, about 14 g (94%). 

A 500-ml, three-necked, round-bottom flask is equipped with a condenser, a dropping funnel, and a thermometer in the reaction mixture. In the flask is placed a mixture of 85% hydrazine (115 ml, 118 g) and 225 ml of 95% ethanol with a few boiling chips. The solution is brought to reflux (mantle) and cinnamaldehyde (100 g, 0.76 mole) is added dropwise over about 30 minutes followed by an additional 30 minutes of refluxing. A still head is attached to the flask and volatiles (ethanol, water, hydrazine hydrate) are slowly distilled at atmospheric pressure until the pot temperature reaches 200° (about 3 hours). Hereafter, phenylcyclopropane is collected over the range 170-180°. When the pot temperature exceeds 250°, the recovery is complete. The crude product (55-65 g) is washed twice with 50-ml portions of water and dried (anhydrous potassium carbonate). Distillation under vacuum through a short column affords the product, bp 60°/13 mm, 79-80°/37 mm, n f 1.5309, about 40 g (45%). 

Formamide is distilled under vacuum before use. /-Butyl alcohol may be dried by distillation from sodium or calcium hydride (3 g/100 ml). All other reagents should be dry. 

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