ANALYTICAL EDITION
100
centration in the air of the chamber is equal to 0.004 per cent, then the error of the result will be *d(0.003
x
x
+ (0.004 x
or in the case shown on the figure ( t "dO.09
+ (0.004 X
=
x V)z
1, L = 10 X lo3) X V)2
Vol. 5, No. 2
Curve C on Figure 1 shows the increase of the error as the volume of the chamber increases according to the assumptions made. LITERATURE CITED (1)
Kleiber, M., Pjliigers Arch. ges. Physiol., 220, 599-605 (1928).
RECEIVED October 1, 1932.
Preparation of Aldehyde-Free Ethyl Alcohol Rapid Method ALBERTW. STOUTAND H. A. SCHUETTE, Department of Chemistry, University of Wisconsin, Madison, Wis.
C
URRENT methods for the preparation of waterwhite alcoholic potassium or sodium hydroxide sohtions are far from satisfactory, being not only uneconomical of time and materials but inconstant of performance in so far as they do not lead with certainty to the desired end. There is, therefore, an obvious need for an inexpensive method which will efficiently and rapidly remove the troublesqme aldehydes, to which, in virtue of .their forming brown resinous products with alkalies, the discoloration of the so-called alcoholic potash (or soda) solution is primarily ascribed. The m e t h o d s f o r accomplishing these ends are of two kinds, preventive and r e m e d i a l . I n the former group there are several which merit m e n t i o n . First, there is the timehonored procedure, to which both the Association of Official A g r i c u l t u r a l Chemists and the American Society for Testing Materials have given approval, of letting the raw alcohol stand in contact with potassium hydroxide for several days or of hastening the reaction by digesting the mixture for hours under reflux. Doubtless many an analyst following this procedure has been annoyed by the discovery that his labors have yielded a product of unsatisfactory character, a distillate FIGURE1. COMBI- which was obtained at some sacrifice NATION REFLUX AND DISTILLATION APPA- of expensive solvent, b e c a u s e of incomplete recovery of the solvent from RATUS the alkaline reaction mixture. Then there is the procedure of Dunlap (4), who appears to have based his method upon a suggestion of Winkler (6) that the use of silver oxide under prescribed conditions leads to the preparation of an anhydrous product. The analyst, however, must anticipate his needs well in advance of use and must be satisfied with a product whose water content has been slightly increased, inasmuch as the silver oxide is formed in situ from reagents, one of which is in aqueous solution. This method for making ethyl alcohol aldehydefree, or substantially so, is not necessarily expensive, because the silver can be recovered and little alcohol is lost during purification. This procedure has received recognition in the U. S. Pharmacopeia. Finally, there is the method which is used in the purification of ethyl alcohol for determination of aldehydes in citrus flavoring extracts (2). Chace (3) seems to be responsible for this mode of procedure, which embodies the use of m-phenylenediamine hydrochloride. A 48-hour diges-
tion period of this reagent with the alcohol must precede distillation, the permissible recovery being approximately 85 per cent. I n the second group, or remedial methods, is one which to date seems to have passed unnoticed. It is suggested by Englis and Mills (6),who found that the addition of sodium hydrosulfite to a discolored alcoholic potash solution is effective, although the reaction rate is exceedingly slow. This method is, however, essentially a preventive one, in that the recommended course of procedure is to add the hydrosulfite to the alcoholic alkali solution immediately after it has been prepared. The reaction whereby discoloration is prevented is probably twofold: the inhibition of the photochemical decomposition of alcohol to aldehyde, and the reduction of any aldehyde present per se to alcohol. Fundamentally, however, the analyst does not get away from the necessity of beginning his preparation with a solvent which is substantially free of aldehydes. The method herein proposed, in part suggested by the observations of Englis and Mills, rests upon an application of the fact that nascent hydrogen reduces an aldehyde to its corresponding alcohol at moderate temperatures. This reaction, which is an exothermic one, is brought about by adding to the raw alcohol potassium hydroxide and metallic aluminum, or any metal or alloy yielding hydrogen under these conditions, and digesting the whole for a short time. Zinc may be substituted for the aluminum, but because it is slower to react with alkali than aluminum, its use in the treatment of a product relatively high in aldehyde content will require a longer digestion period. Sodium amalgam may also be used to effect the reduction, but recourse to this reagent hardly seems necessary unless one desires to prepare a product which is both water- and aldehyde-free. Since the alcohol of commerce is relatively low in aldehyde content, a satisfactory degree of reduction will be obtained without a preliminary digestion by the addition of 5 to 10 grams of the metal in granular form and 8 to 10 grams of potassium hydroxide to one liter of alcohol. Ethyl alcohol containing 0.2 per cent added acetaldehyde has been successfully treated by this method by refluxing the reaction mixture for one hour before distillation. The efficiency of the proposed procedure for removing aldehyde from ethyl alcohol was demonstrated by the following experiment, in which *conditions far more drastic than any likely to be met with in actual work were set up. Separate portions of a standard solution of acetaldehyde (17 mg. per cc.) in purified alcohol were treated, respectively, with potassium hydroxide and aluminum, and with alkali only. Both solutions were then subjected to reflux distillation, during the course of which samples were withdrawn from time to time for analysis as to aldehyde content ( I ) .
March 15, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
101
EFFICIENCIES OF Two DE-ALDEHYDINQ TABLEI. COMPARATIVE is actually a partial dehydration of the product, the moisture PROCEDURES content in this instance having been reduced from 7 to 3 OFFICIALMETHOD PROPOSED METHOD TIME per cent. This, however, is less important than that the Mg./cc. Mg./cc. Min, proposed mode of procedure is efficient, economical of time 0 10 and materials, and simple. It has been put to test with 30 good success for the past year in the student laboratory of 40 60 the Department of Chemistry and has never failed to pro90 120 duce an excellent product when the conventional methods proved wanting. It :was, of course, inevitable that resinification of some Throughout this study all distillations, both reflux and of the aldehyde should occur in that portion to which both otherwise, were made in an all-glass apparatus (Figure 1) aluminum and alkali had been added; nevertheless it is which had been constructed from a round-bottomed flask, apparent that the reducing action.of the metal is a material a straight condenser, and a ground-glass joint, the latter aid in speeding up removal of the aldehyde. The evidence being given a reverse bend. By merely turning the conappears convincing that the last traces of aldehyde bodies denser from its upright position for reflux distillation through are removed with greater dispatch and convenience than by an angle of M O O , the system becomes a distillation outfit other procedures. It is these last traces which appear to without the necessity of interrupting the heating. be the troublesome factors in purifying ethyl alcohol for alkali-solvent purposes. ACKNOWLEDGMENT As a result of a series of determinations of saponification Acknowledgment is made of the assistance given by Milford numbers of fatty oils with reagents prepared from ethyl alcohol, purified on the one hand by the silver oxide method A. Cowley, who helped design and construct the all-glass (4) and on the other by the combined action of alkali and apparatus used. metallic aluminum, it was found that the use of ethyl alcoLITERATURE CITED hol treated by the latter procedure causes no significant (1) Assoc. Official Agr. Chem., Official and Tentative Methods, p. differences. Pertinent data are recorded in Table 11. TABLE11. COMPARISON OF SAPONIFICATION NUMBERS OIL Sesame Cottonseed Rye ~
~~
ALCOHOL ALCOHOL BY SILVPR ALUMINUM AND OXIDP POTASSIUM HYDROXIDE
BY
191.8 194.9
176.5
191.6 196.0 176.8
A rough determination of the water content of a sample of alcohol before and after purification has shown that there
144 (1930). (2) Ibid.. D. 256.
(3j Chade; E. M., J. Am. Chem. Soc., 28,1472-6 (1906). (4) Dunlap, F. L., Ibid., 28,395-8 (1906). (5) Englis, D. T., and Mills, V. C., J. Assoc. Oficial Agr. Chem., 12, 248-50 (1929). (6) m'inkler, L. W., Ber., 38, 3612-16 (1905). R E C E I V ~September D 2,1932. Presented before the Division of Agricultural and Food Chemistry a t the 84th Meeting of the American Chemical Society, Denver, Colo., August 22 to 26, 1932.
A Laboratory Esterifying and Fractionating Apparatus CARROLA. DORAN, E. I. du P o n t de Nemours & Co., Inc., Research Laboratories, Parlin, N. J.
T
HE difficulty of duplicating exact plant conditions of large scale processes in smaller laboratory equipment is well known in industrial research laboratories. In plant distillation processes the equipment used is usually capable of being operated over a very wide range of conditions. These variations include rates of operation, amounts of reflux, ratios between internal and external reflux, points a t which reflux is returned to the system, points of crude feed to the system, selectivity in layer take off in the condensate, etc. Many types of laboratory columns (1, 2) and distillation set-ups (3, 4,6) have been described in the literature for bringing about careful, precise fractionations. The use of such equipment is primarily for analyses by fractionation and cannot readily be applied t o the duplication of general plant procedure The apparatus here described has been successfully used in the research laboratories of the du Pont company in connection with the manufacture of industrid solvents, plasticizers, etc., involving plant problems dealing with fractionation, vapor drying, and liquid-vapor countercurrent flow. As shown in the accompanying figure, it is fitted with a vapor line from the kettle, as well as a separate liquid reflux line
to the kettle. The fractionating portion of the column is large to give capacity to the apparatus and is fitted with side auxiliary taps to provide various feed points, thermometer wells, or reflux return points along the column. The dephlegmator is adjustable in the cooling-water height as well as rate of cooliiig-water flow. The receiver is suited to take off either layer of a two-layer condensate and to return either layer part,ially or wholly to the kettle or to various points in the fractionating column. The fractionating portion of the column is well insulated to prevent the transfer of heat from the liquid and vapors in the column to the outside wall. This minimization of heat transfer from the column is very important in duplicating plant conditions where the transfer is very small. Experience with this apparatus has shown it closely to approach plant duplication. DESCRIPTION, ASSEMBLY, AND OPERATION The over-all height of the apparatus as shown in the figure is approximately 111 cm. (44 inches) and it occupies about 0.09 square meter (1 square foot) of bench space. It is assembled from three major parts: kettle, column, and re-
