Boiling points of the alcohols

The 42.3 g of the bis-compound are heated under reflux in 210 cc of 96% ethanol containing 10% of hydrogen chloride, to the boiling point of the alcohol. After dissolution, the substance is boiled for 20 minutes under reflux. It is cooled, filtered and washed with alcohol. By concentrating the mother liquor and the washing liquid by evaporation, further amounts of substance are obtained. 

Saponification of the product with standard potassium hydroxide shows 93-94 per cent ester. It contains some fur-furyl alcohol, the removal of which by fractional distillation is difficult, because the boiling points of the alcohol (i6g°/752 mm.) and the ester (175°/764 mm.) are so close together. Furfuryl acetate darkens on standing. It may be redistilled with little loss to give an almost colorless product. 

Generally, alkali-catalyzed transesterification is performed near the boiling point of the alcohol, but several researchers have reported high conversion yield at room temperature (8,14). Low reaction temperature was desirable, since reaction temperature was closely related to the energy cost of the biodiesel production process. 

On the other hand, raising the temperature causes a striking increase in the rate of isomerization and since alcohol deaminations almost invariably involve reflux conditions, or temperatures close to the boiling point of the alcohol, the diazonium chloride of a polybromoamine should not be used in this reaction. 

Very often reduction of diazonium salts by ethanol requires tempera tures in the neighborhood of the boiling point of the alcohol. The reaction may take place with violence so that, once it is started, moderation by external cooling may be necessary.14 28 84... 

The literature procedure for condensation of benzil with 1,3-diphenyl-acetone in ethanol with potassium hydroxide as basic catalyst suffers from the low boiling point of the alcohol and the limited solubility of both potassium hydroxide and the reaction product in this solvent. Triethylene glycol is a better solvent and permits operation at a higher temperature. In the procedure that follows, the glycol is used with benzyl-trimethylammonium hydroxide, a strong base readily soluble in organic solvents, which serves as catalyst. 

In contrast to benzene, naphthalene can be reduced by chemical reducing agents. It is converted by sodium and ethanol into 1,4-dihydronaphthalenc, and by sodium and isopentyl alcohol into 1,2,3,4-tetrahydronaphthalene (tetralin). The temperature at which each of these sodium reductions is carried out is the boiling point of the alcohol used at the higher temperature permitted by isopentyl alcohol (b.p. 132°), reduction proceeds further than with the lower boiling ethyl alcohol (b.p. 78°). 

Reaction (1) is easily applicable to the preparation of the lower simple alkyl ethers which boil below the boiling point of the alcohol. For example, when ethyl alcohol is mixed with sulfuric acid in the cold, ethyl sulfuric acid is formed. When more alcohol is allowed to flow into such a mixture at 140-150°, ether, water, and some unchanged alcohol distill over. The mechanism of the reaction is assmned to involve, first the formation of ethyl sulfuric acid, and then the reaction of this with alcohol to form ether and regenerate the sulfuric acid. The regenerated acid combines with fresh alcohol and repeats the cycle until the water produced in the reaction by dilution diminishes its catalytic activity. Olefin formation takes place even at this temperature and decreases the yield. Further decrease in the yield results from the oxidizing action of sulfuric acid. 

For ethers which boil above the boiling point of the alcohol the procedure is modified. For example, isoamyl alcohol, boiling at 130°, is mixed with sulfuric acid and distilled slowly. Water and xmchanged alcohol pass over as distillate. The water is separated, and the alcohol is returned to the reaction mixture. When very little comes over in the distillate the ether formation is regarded as complete and the ether which boils at 172° may be removed by steam distillation. 

Observation (2) indicates that the compound contains oxygen and that it may be an ester, ether, or an anhydride. The conclusion is drawn from (3) and (4) that it was an ester. The boiling point of the compound was found to be 102°. As a number of esters boil at temperatures near 102°, the compound was identified by determining the boiling point of the alcohol formed when it was saponified. This was found to be 97°, which is the boiling point of propyl alcohol. As propyl acetate boils at 102°, the identification of the compound as this substance may be considered as satisfactory. 

If an NMR spectrometer is available, your instructor may wish to give you one of these alcohols as an unknown, leaving it to you to determine which alcohol was issued. For this purpose, you could use the infrared and NMR spectra, as well as the boiling points of the alcohol and its ester. 

The nineteenth century was a time when chemists were exploring chemical reactivity with no knowledge of mechanism and with a limited ability to identify products when compared to today s methodology (see Chapter 1, Section 1.1). Nonetheless, many reactions were discovered that are used today, and the structures of the products were accurately determined. L. Chiozza in 1856 (Italy) and Adolphe Wurtz (France 1817-1884) in 1872 reported independent experiments in which an aldehyde was treated with an alkoxide base in an alcohol solvent heated to reflux (heated at the boiling point of the alcohol). When this reaction was cooled to room temperature and treated with dilute aqueous acid at low temperatures, a P-hydroxy aldehyde (known generically as an aldol) was isolated. Because of the type of product formed, this reaction has come to be called the aldol condensation. 

Vapour Pressures.—The lowest member of the series, methyl alcohol, bears the closest resemblance to water, and, as Konowaloff has shown, the vapour pressures of mixtures of these substances are in all cases intermediate between those of the pure components, and the curve representing the relation between vapour pressure and molecular composition does not deviate very greatly from a straight line, as will be seen from Fig. 14, in which the vapour pressures of mixtures of four alcohols with water are given, at the boiling points of the alcohols under a pressure of 400 mm. 

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