Azeotropes of Methanol

METHANOL FORMS BINARY AZEOTROPES WITH °h- B.P. of Azeotrope °c. °Jo B.P. of Azeotrope °c. 5 I- 

85 trans -1 -Bromopropene 50. 8 84 Ethyl formate 51.0 62 T richlo roe thy lene 59. 3  

5 3 - Bromopropene 54,0 76 Ethyl propyl ether 55.5 METHANOL FORMS TERNARY AZEOTROPES WITH  

65 Chloromethyl methyl ether 56.0 60 Is obutyr aldehyde 62. 7 55 Carbon disulfide  

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Binary mixtures of THF and methanol are often required to be separated and the azeotrope of methanol/pentane can be used to do this followed by a water wash to remove the methanol from pentane that will be effectively dry. 

Table 2 Azeotropes of Methanol-Containing Binary Systems ...

Dimethylamine also reacts with the azeotrope of methyl acetate and methanol to give DMAC in 45% yield (5). 

Methyl borate is beheved to be the boric acid ester produced in the largest quantity, approximately 8600 metric tons per year (28). Most methyl borate is produced by Morton International and used captively to manufacture sodium borohydride [16940-66-2]. Methyl borate production was studied in detail during the 1950s and 1960s when this compound was proposed as a key intermediate for production of high energy fuels. Methyl borate is sold as either the pure compound or as the methanol azeotrope that consists of approximately a 1 1 molar ratio of methanol to methyl borate. 

To a stirred and refluxing solution of 40 parts of benzene and 35 parts of dimethylformamide (both solvents previously dried azeotropically) are added successively 1.6 parts of sodium hydride and 7.7 parts of Ct-(2,4-dichlorophenyl)imidazole-1-ethanol, (coolingon ice is necessary). After the addition is complete, stirring and refluxing is continued for 30 minutes. Then there are added 7.8 parts of 2,6-dichlorobenzyl chloride and the whole is stirred at reflux for another 3 hours. The reaction mixture is poured onto water and the product 1-[2,4-dichloro-/3 (2,6-dichlorobenzyloxy)phenethyl] imidazole, is extracted with benzene. The extract is washed twice with water, dried, filtered and evaporated in vacuo. The bese residue is dissolved in a mixture of acetone and diisopropyl ether and to this solution is added an excess of concentrated nitric acid solution. The precipitated nitrate salt is filtered off and recrystallized from a mixture of methanol and diisopropyl ether, yielding 1-[2,4-dichloro- (2,6-dichlorobenzyl-oxv)phenethyl] imidazole nitrate melting point 179°C. 

Inasmuch as methyl nitrate is very sensitive to mechanical action, it was found much safer to use it in methanol soln. Such solns, called Myrol, may be obtained directly in the methyl nitrate manufg process, since all that is necessary is to use an excess of methanol. One of the most suitable solns proved to be an azeotropic mixt consisting of about 75% methyl nitrate and 25% methanol. This mixt has a bp of 57.5°. Myrols contg at least 25% methanol will not evaporate to leave 100% methyl nitrate... 

To a flask containing 34.5 gm (0.53 mole) of sodium azide in 70 ml of water and 25 ml of methanol is added 68.5 gm (0.50 mole) of n-butyl bromide while stirring at room temperature. The resulting mixture is heated and stirred on a steam bath for 24 hr. The bottom layer of n-butyl bromide disappears after this time and a top layer of crude n-butyl azide forms. The crude azide is separated and then treated overnight with alcoholic silver nitrate to remove traces of butyl chloride. The mixture is then filtered, washed with water, and distilled behind a safety barricade to yield 40.0 gm (90 %) of n-butyl azide, b.p. 106.5°C (760 mm), n 9 5 1.4152, d29-5 0.8649. (NOTE n-Butyl azide and methanol form an azeotrope (b.p. 60°C) from which the azide is liberated by the addition of a saturated solution of calcium chloride.)... 

Azeotrope formers, generally polar compounds, have the ability to form, with hydrocarbons, nonideal mixtures having vapor pressures higher than either component in the mixture and therefore lower boiling points. Fortunately, different types of hydrocarbons show different degrees of nonideality with a given azeotrope former. For example, benzene and cyclohexane boil at about 176° F., while the methanol-cyclohexane azeotrope boils at 130° F., and the methanol-benzene azeotrope boils at 137° F., a difference of 7° F. Hence, fractionation of a mixture of benzene and cyclohexane in the presence of methanol effectively separates the two hydrocarbons. 

Benzene is added to facilitate the removal of methanol. Although an aqueous wash will remove the methanol, azeotropic removal with benzene is simpler and provides a slightly higher yield. 

Methyl borate (b.p. 68°) forms a 1 1 azeotrope (b.p. 54.6°) with methanol (b.p. 64°).5 Since the presence of even a small amount of methanol reduces the yield considerably more than would be expected from the stoichiometry,4 6 methyl borate stocks should be freshly distilled through a good column to remove as fore-run any methyl borate-methanol azeotrope which may have been formed by hydrolysis during storage. 

If pigment isolate is to be analyzed in an aqueous system, the extract should not be taken to dryness. For some analytical applications, the sample should be taken to dryness and then dissolved in methanol or other appropriate solvent. In the latter concentration stages, azeotropic removal of water can be facilitated by addition of methanol. 

Another use for this set of curves is for estimating the azeotropic boiling point and composition at pressures other than atmospheric. Consider the azeotrope methanol-benzene. Since the vapor pressure curves of methanol and benzene are known, the difference in boiling point, A, can be obtained at any pressure. From this value of A and the C-A curve for methanol-hydrocarbons the azeotropic concentration C at that pressure can be determined. For example, the effect of pressure on the methanol-benzene azeotrope is shown in Table I. 

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