The Identification of Alcohols in Aqueous Solution
BY WILLIAM N. LIPSCOMB AND ROBERT H. BAKER
The identification of an alcohol when it appears in aqueous solution as from the saponification of an ester usually involves its isolation by repeated distillation, salting out, and drying. Henstock2 was able to avoid this time-consuming procedure by the use of the Schotten-Baumann reaction of p-nitrobenzoyl chloride at —15°.
We have found that the more satisfactory 3,5-dinitrobenzoates may be formed by slight modification of the Henstock procedure. The process involves adding alkali and sodium acetate to the aqueous solution of the alcohol and shaking it at 0° with a hydrocarbon solution of 3,5-dinitroben-zoyl chloride.
The yield of ester is affected rather critically by the temperature, the nature and concentration of the alkali, and to a lesser extent by the catalytic effect of sodium acetate. Preliminary experiments showed that it was necessary to dissolve the solid dinitrobenzoyl chloride in an inert solvent so as to keep it in a liquid phase during the course of the reaction. When ether is used for this purpose the melting points of the esters, with the exception of ethyl, are consistently low. This is true even when extreme care is taken to remove all alcohol from the ether and therefore must be due to cleavage of the ether. Benzene is satisfactory except for its high melting point and this is easily lowered by the addition of dry ligroin.
Although the yield of ethyl ester is greater at 0° than at room temperature, it is not necessary to employ the difficultly-maintained lower temperatures. The yield of ethyl ester is four times as great when formed in the presence of 5% sodium hydroxide as it is when a similar concentration of sodium carbonate is used, and weaker bases such as sodium bicarbonate give negligible yields of the ester. Increasing the concentration of sodium hydroxide in the reaction mixture at 0° increased the yield of ethyl ester as shown in Fig. 1. It is impractical to use concentrations of sodium hydroxide in excess of 20% because the reaction mixture becomes semi-solid and difficult to handle.
Reagent.-To 25 g. of 3,5-dinitrobeazoyl chloride is added 50 ml. of dry sulfuric acid-washed ligroin and the resulting solution is then diluted to 250 ml. with dry ben-zene.
Procedure.-One-half grain of sodium acetate crystals is dissolved in 10 ml. of a 5% aqueous solution of the alcohol, then 10 ml. of 40% sodium hydroxide is added and the solution cooled to 0°. Five ml, of the solution of 3,5. dinitrobenzoyl chloride in benzene-ligroin is then added and the mixture alternately shaken and placed in an ice-bath for one-half hour. The mixture is then transferred to a separatory funnel and extracted with 30 ml. of ether The ether solution is washed with an equal volume of water, then 5% hydrochloric acid, and again with water. Evaporation of the solvent yields the crude derivative as recorded in Table I.
SUMMARY OF RESULTS
Alcohol crude Yield M.p. of crude M.p.in
ester,g % ester,°c lit.,α °C.
Methyl 0.09* 17
Ethyl .27 52
n-Propyl .37 67
Isopropyl .10 18
n-Butyl .37 64
s-Butyl .06 10
Isobutyl .30 52
t-Butyl .01 1
Allyl .22 42
Shriner and Fuson, "Systematic Identification of Organic Compounds," John Wiley and Sons, Inc., New York, N. Y., 2nd Ed., 1940, p. 185. * Obtained only after three successive additions and shakings with the acid chloride solution,
CONTRIBUTION FROM THE
UKIVERSITY of KENTUCKY RECEIVED OCTOBER 6, 1941
THE UNIVERSITY OF KENTUCKY JOURNAL OF UNDERGRADUATE SCHOLARSHIP