Dehydration by azeotropic distillation

Anhydrous Acetic Acid. In the manufacture of acetic acid by direct oxidation of a petroleum-based feedstock, solvent extraction has been used to separate acetic acid [64-19-7] from the aqueous reaction Hquor containing significant quantities of formic and propionic acids. Isoamyl acetate [123-92-2] is used as solvent to extract nearly all the acetic acid, and some water, from the aqueous feed (236). The extract is then dehydrated by azeotropic distillation using isoamyl acetate as water entrainer (see DISTILLATION, AZEOTROPIC AND EXTRACTIVE). It is claimed that the extraction step in this process affords substantial savings in plant capital investment and operating cost (see Acetic acid and derivatives). A detailed description of various extraction processes is available (237). 

Ethanol [64-17-5] M 46.1, b 78.3 , d 0.79360, d 0.78506, n 1.36139, pK 15.93. Usual impurities of fermentation alcohol are fusel oils (mainly higher alcohols, especially pentanols), aldehydes, esters, ketones and water. With synthetic alcohol, likely impurities are water, aldehydes, aliphatic esters, acetone and diethyl ether. Traces of benzene are present in ethanol that has been dehydrated by azeotropic distillation with benzene. Anhydrous ethanol is very hygroscopic. Water (down to 0.05%) can be detected by formation of a voluminous ppte when aluminium ethoxide in benzene is added to a test portion. Rectified... 

A solution of quinoline 1-oxide (0.29 g, 2 mmol) in cyclohexane (1 L) was dehydrated by azeotropic distillation in the reaction vessel. The solution was purged with dry N2 and irradiated with a Hanau high-pressure Hg lamp. The resulting solution was evaporated and the residue was extracted with a little cyclohexane. The insoluble part contained carbostyril (3). The cyclohexane extract was evaporated and the residue purified by short-path distillation at 50°C/0.1 Torr yield 0.174g (60%) moisture-sensitive oil. 

Chromenes are easily obtained by dehydration of 4-chromanols (24), in their turn readily available by reduction of 4-chromanones (23). The parent compound chrom-3-ene has been prepared by this method92 in 75-80% yield, via Meerwein-Ponndorf reduction and dehydration by azeotropic distillation over CuS04. Other reducing agents are metal... 

Toluenesulfonic acid can be dehydrated by azeotropic distillation with benzene or by heating at 100° for 4hours under water-pump vacuum. The anhydrous acid can be crystallised from benzene, CHCI3, ethyl acetate, anhydrous MeOH, or from acetone by adding a large excess of benzene. It can also be dried under vacuum at 50°. The S-benzylisothiuronium salt has m 182° (from aqueous EtOH). [Beilstein 11 IV 241.]... 

Nickel (II) acetylacetonate [3264-82-2] M 256.9, m 229-230°, b 220-235°/ 1mm, d 1.455. Wash the green solid with H2O, dry it in a vacuum desiccator and recrystallise it from MeOH. [Charles Pawlikowski J Phys Chem 62 440 1958] The complex can be conveniently dehydrated by azeotropic distillation with toluene, and the crystals may be isolated by concentrating the toluene solution. [Wilkinson et al. J Am Chem Soc 76 1970 1954, Beilstein 1 IV 3677.]... 

Aureomycin (7-chIorotetracycIine) [57-62-5] M 478.5, m 172-174 (dec), [a] -275 (MeOH), pKi 3.3, pK2 7.44, pKs 9.27. Aureomycin is dehydrated by azeotropic distillation of its solution with toluene. On cooling, the anhydrous material crystallises out and is recrystallised from C(5H6, then dried under vacuum at 100° over paraffin wax. (If it is crystallised from MeOH, it contains MeOH which is not removed on drying.) [Stephens et al. J Am Chem Soc 76 3568 1954, Laskin Chan Biochem Biophys Res Commun 14 137 7964]. [Beilstein 14 IV 2631.]... 

This process uses a multi-tube reactor containing a supported platinum-based catalyst Heat is removed by a coolant which vaporizes the benzene feed, previously dehydrated by azeotropic distillation, and also produces steam at 1.10 Pa absolute. 

Bromo-4-methylbutyric acid 556 Isovaleric acid (8.6 moles dehydrated by azeotropic distillation with benzene), bromine (1500 g dried by shaking with 11 of concentrated H2S04), and PC13 (15 ml) are heated at 70-80° until the deep red color of bromine has disappeared from the condenser (10-20 h). More bromine (25 ml) is added and heating continued to disappearance of the red color, the oil bath temperature is raised slowly to 100-105° and kept there for 1.5-2 h, and the mixture is distilled in a vacuum. The fraction of b.p. 110-125°/ 15 mm (87.5-88.6%) is used for preparation of DL-valine. 

Methoxyethylamine [109-85-3] M 75.1, b 94°, d 4 0.874, np 1.407, pl 9.40. An aqueous 70% solution of the amine is dehydrated by azeotropic distillation with benzene or methylene chloride and the amine is distilled twice from zinc dust. Store it in a tight container as it absorbs CO2 from the atmosphere. [Beilstein 4 IV 1411.1... 

The reaction is carried out in the vapour phase by passing a mixture of benzene and excess of air over a catalyst of vanadium pentoxide deposited on alumina at 350-450°C. The effluent is cooled and the condensate of maleic anhydride and acid is dehydrated by azeotropic distillation. High-purity anhydride is obtained by distillation under reduced pressure. Maleic anhydride is a white crystalline solid, m.p. 52-53°C. Maleic anhydride is preferred to maleic acid since it is more reactive and gives rise to less water on esterification. 

This process is a modification of the basic Ruhrol process. The recovery system is similar to SD, i.e., part of the effluent is recovered as molten MA and part as an aqueous maleic acid solution. The latter is dehydrated by azeotropic distillation with xylenes (Fig. 2-3). Benzene in the exhaust gases is removed in absorbers, making it odor free. 

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