Azeotropically dried

Most, if not all, of the acetonitrile that was produced commercially in the United States in 1995 was isolated as a by-product from the manufacture of acrylonitrile by propylene ammoxidation. The amount of acetonitrile produced in an acrylonitrile plant depends on the ammoxidation catalyst that is used, but the ratio of acetonitrile acrylonitrile usually is ca 2—3 100. The acetonitrile is recovered as the water azeotrope, dried, and purified by distillation (28). U.S. capacity (1994) is ca 23,000 t/yr. 

Cyclohexanol [108-93-0] M 100.2, m 25.2", b 161.1", d 0.946, n 1.466, n s 1.437, n 1.462. Refluxed with freshly ignited CaO, or dried with Na2C03, then fractionally distd. Redistd from Na. Further purified by fractional crystn from the melt in dry air. Peroxides and aldehydes can be removed by prior washing with ferrous sulfate and water, followed by distillation under nitrogen from 2,4-dinitrophenylhydrazine, using a short fractionating column water distils as the azeotrope. Dry cyclohexanol is very hygroscopic. 

Azeotropic drying of organic substances is also effective, providing the material is relatively nonvolatile. A benzene or toluene solution of the compound is distilled (in a Dean-Stark trap, if available) until the distillate is free of water droplets. The remaining solution is essentially dry. 

Scheme 12.2 shows various types of alcohols that are most susceptible to Mn02 oxidation. Entries 1 and 2 illustrate the application of MnOz to simple benzylic and allylic alcohols. In Entry 2, the Mn02 was activated by azeotropic drying. Entry 3 demonstrates the application of the reagent to cyclopropylcarbinols. Entry 4 is an application to an acyloin. Entry 5 involves oxidation of a sensitive conjugated system. 

Free amine 36 was isolated as a hygroscopic hydrate which was very difficult to dry in the solid state and required azeotropic drying using THF (expensive and time consuming). 

Solutions of the hydroperoxide in halogenated solvents, and especially dichloro-ethane are much less stable than in toluene (reference 5 above). On a large scale, the azeotropic drying of solutions of the hydroperoxide in dichloroethane may present a thermal hazard. 

A violent explosion ocurred during prolonged azeotropic drying at 105-110°C of a 75 wt% benzene solution of the salt. Traces of a nitrate ester may have been formed from a slight excess of nitrate ion. 

A dry solution of the sodium salt in n-butanol was usually prepared by azeotropic drying. Use of excessively wet recovered butanol led to complete removal of the butanol with the water and heating of the dry salt at 200°C, when rapid decomposition occurred, leaving a glowing carbonised residue. 

Octyne, cyclopentenone, and nickel acetylacetonate were purchased from the Aldrich Chemical Company, Inc. The checkers recrystallized the latter compound from anhydrous methanol followed by azeotropic drying with hot toluene. 

TBA-BH4 (Table 11.8) in CH2C12 (400 ml) is azeotropically dried by evaporation of ca. 250 ml of the CH2C12 under reduced pressure. The organic substrate (0.1 mmol) is added under argon and the mixture cooled to 0°C. The haloalkane (0.2 mol) (Table 11.8) is added dropwise and the mixture stirred for 30 min at room temperature. The excess boro-hydride is destroyed by the addition of EtOH (25 ml) and the solution is neutralized with HC1 (20%). The aqueous phase is separated and extracted with CH2C12 (2 x 20 ml). The combined organic solutions are washed with H20 (10 ml), dried (MgS04), and fractionally distilled to yield the reduced product. 

Several stages required anhydrous conditions and hence prolonged azeotropic drying of solutions. For example, the resolution required strictly anhydrous conditions to avoid decomposition of the morpholinol. 

Most, if not all, of the acetonitrile produced commercially in the United States recently was isolated as a by-product from the manufacture of acrylonitrile by propylene ammoxidation. The acetonitrile is recovered as the water azeotrope, dried, and purified by distillation. 

Table 6.2 lists the ultraviolet cutoff for a variety of solvents commonly used in UV-VIS spectroscopy. The solvent chosen must dissolve the sample, yet be relatively transparent in the spectral region of interest. Typically, very low concentrations of sample will be present in the solvent. It is therefore important to avoid solvents that have even weak absorptions near the solute s bands of interest. Methanol and ethanol are two of the most commonly used solvents. Care must be exercised when using the latter that no benzene (an azeotropic drying agent) is present as this will alter the solvent s transparency. Normally, this will not be a problem in spectral grade solvents. 

In tank 25 the products of hydrolytic condensation are distilled from toluene. Cooler 26 is filled with water, and the tank jacket is filled with water vapour. The contents of the tank are heated to 80-90 °C and held at this temperature for 1 hour. The separated water and the intermediate layer are poured off into the intermediate container (not shown in the diagram) then toluene is distilled. First, the temperature in the tank at atmospheric pressure reaches 130 °C then, the tank is cooled to 70-90 °C and a residual pressure of 0.04-0.06 MPa is created in the system. Further distillation is conducted in the tank to 150 °C. The toluene vapours condensed in cooler 26 are collected in receptacle 27 and sent by compressed nitrogen flow (0.07 MPa) into flusher 28 as they accumulate. The flusher is filled with water, and the mixture is agitated for 10 minutes after that the agitator is switched off and the mixture is settled for 2 hours. The bottom layer, aqueous-alcoholic solution, is poured into neutraliser 13, and the top layer, washed toluene, is sampled for moisture content. If moisture content does not exceed 0.06%, toluene is poured into receptacle 30, sent to azeotropic drying (until the moisture content does not exceed 0.02%) and re-used in reactive mixtures. 

The target oligomer is synthesised in reactor 10. For this purpose, Laprol is loaded from batch box 11, and toluene is loaded from batch box 12. The agitator is switched on, the temperature in the reactor is increased to 110-130 °C (to 85-110 °C in vapours) by sending vapour into the jacket and at this temperature toluene is subjected to azeotropic drying. The vapour of the azeotropic mixture (toluene + water) rises up packed tower 13 and condenses in refluxer 14. The condensate splits in Florentine flask 15. Toluene from the top part of the apparatus is sent back (through a side choke) to reflux tower 13, and toluene-containing water is collected in receptacle 16. Thus the toluene solution of Laprol is dehydrated until moisture content is not more than 0.01%. 

Crystal potassium acetate used in the synthesis of triacetoxyphenylsilane contains crystalline hydrate water. Since acetylation should be carried out in an anhydrous medium, potassium acetate is subjected to azeotropic drying by the technique described on page 177. 

The azeotropic drying of potassium acetate is carried out with toluene, fed into reactor 5 from batch box 4. The excess of toluene is sent through Florentine flask 7 into collector 9 and from there to regeneration. 

Distillation is carried out for many reasons concentration of a substrate in a solvent, removal of one solvent from a mixture and often its replacement by another, azeotropic removal of unwanted solvents (very frequently azeotropic drying), fractionation to separate a pure soivent for reuse, and removal of a low-boiling product of a reaction frequently to prevent its further reaction with the initial substrates or product (e.g., removal of water by passing a wet distillate through molecular sieves). 

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