VOLUME Table II.
2 3,
NO.
3,
MARCH
541
Ultraviolet Absorption Method. Ethyl alcohol was used as the solvent and absorption measurements were made with a Beckman quartz spectrophotometer. The maximum absorption for benzil in 95% ethyl alcohol occurs at a wave length of about 260 µ (6). Absorption readings were made at 260 µ and a slit width of 0.5 The Beer-Lambert law holds only approximately for benzil mm. in 95% ethyl alcohol at this wave length. For this reason it was necessary to plot a curve of log In/I versus concentration. The cloth samples were extracted with 95% ethyl alcohol and readings were made on concentrations in the range of 0.003 to 0.015 gram per liter.
Fluorometric Determination of Benzil in Cloth Containing Various Impregnating Agents
Additive Impregnated in 2.5 G. Cloth Sample Agent Weight, g. Unknown Sizing Unknown Nacconal 0.05 Nacconal 0,05 Span 80 Span 80
1951
Chlorinated paraffin Chlorinated paraffin Polyvinyl alcohol Polyvinyl alcohol
0.05 0.05
0. 125
0.125 0.013 0.013
Benzil Added
Mg. 0.025 0.025
Benzil
Mg.
0.025 0.025
0.024 0.024 0.023 0.024 0.025 0.024 0.025
0.025 0.025
0.016
0.025 0.025
0.025
0.025
0.024 0.021
DISCUSSION
Marked changes in the fluorescence of solutions containing the fluorescent compound took place with large changes of pH. Solutions made alkaline with ammonium or potassium hydroxide showed a great decrease in fluorescence. However, under the conditions of the procedure outlined above, only a slight effect due to small amounts of acidity in the alcohol was noted. Neutralization of the alcohol eliminated this difficulty. In all applications of the fluorometric method described here, a straight-line curve of Klett photofluorometer readings against milligrams of benzil in concentrations up to 0.03 mg. per ml. was obtained.
benzil concentration, using known solutions treated as described above, and make the quantitative determination of the unknown by applying the reading obtained. For best results the calibration curve and unknown samples should be run on the same day, because the aminophenols tend to darken on standing. Run a suitable blank under the same conditions with unimpregnated cloth. Tests were run using various fixatives, laundering agents, and emulsifiers which might be used in cloth impregnation studies. Of these materials, chlorinated paraffin gave the least interference and polyvinyl alcohol gave the greatest. In most cases, compensation for interferences could be made by use of suitable blanks. Results, corrected by use of blanks, of the fluorometric determination of benzil in the presence of various agents are listed in Table II. Gravimetric Method. Recoveries of 97 to 98% were obtained in the estimation of benzil by a method for the determination of water-insoluble carbonyl compounds by means of 2,4-dinitrophenylhydrazine (5). The method used was essentially the same as described by Iddles et al. with the addition of a 2-hour extraction of the cloth sample with 95% ethyl alcohol, followed by the precipitation of the benzil compound from an aliquot portion of the extract.
LITERATURE
CITED
(1) Cross, H. F., J. Econ. Entomol., 41, 731-4 (1948). (2) Cross, H. F., and Snyder, F. M., Soap Sanit. Chemicals, 25, No. 2, 135-49 (1949). (3) Farbenfabriken, formerly Friedlander, Bayer, and Co., German Patent 57,151 (1891). (4) Goldenson, J., and Sass, S., Office of Technical Services, V. S. Dept. Commerce, Kept. PB 78709 (1947). (5) Iddles, . A., Low, A. W., Rosen, B. D., and Hart, R. T., Ind. Eng. Chem., Anal. Ed., 11, 102 (1939). (6) International Critical Tables, Yol. V, p. 378, New York, McGrawHill Book Co., 1929. (7) King, W. V., Am. J. Trop. Med.. 28, 487-97 (1948). Received July
1,
1950.
Colorimetric Method for Determination of Traces of Carbonyl Compounds GERALD R. LAPPIN, University of Arizona, Tucson, Ariz., AND
LELAND
C. CLARK, Fels Research Institute for the Study of Human Development, Antioch College, Yellow Springs, Ohio
addition of a solution of sodium or potassium hydroxide to an alcoholic solution of a 2,4-dinitrophenylhydrazone produces a very intense wine-red color, presumably due to the formation of the resonating quinoidal ion I. A similar quinoidal ion
has been suggested for the colored solution formed when base is
added to the phenylhydrazone of a nitroaromatic aldehyde (7). This color reaction has been made the basis of a very sensitive method for the estimation of ketosteroids in biological extracts (3). Herein is reported the extension of the method to the quantitative determination of traces of aldehydes or ketones in water, organic solvents, or organic reaction products. The method is most useful in the range of carbonyl concentration from 10-4 to
molar, wherein few if any other methods give reliable reor are of general application. Absorption spectra were run on alkaline alcoholic solutions of a number of 2,4-dinitrophenylhydrazones. It was found that the position of the maximum as well as the value of Emax. was nearly independent of the structure of the carbonyl compound (with exceptions noted below) and were independent of the concentration of base as long as a sufficient excess was present. The colors formed were relatively stable, although slow fading over a period of several days was noted. Beer’s law was obeyed in the concentration range studied. The value of Em**, determined for a large number of compounds averaged 2.72 X 104 at 480 µ. Table I gives more exact values for a number of compounds. For actual analysis it was found unnecessary to isolate the phenylhydrazone. If it was prepared in solution, using an excess of 2,4-dinitrophenylhydrazine, the addition of base converted the excess reagent to a very light yellow substance, the absorption of which was corrected for by using a blank determination. 10_e
sults
PREPARATION
OF
REAGENTS
Carbonyl-Free Methanol. To 500 ml. of c.p. methanol were added about 5 grams of 2,4-dinitrophenylhydrazine and a few
ANALYTICAL
542
Table I.
Position and Values of Compounds
Emax.
Maximum, O cun
pound
µ
Acetaldehyde Acetone Acetophenone Anisaldehyde Aeetylacetone Acetthienone Benzaldehyde Butyraldehyde Cinnamaldehydv Cyclohexanone Cyclopentanone 3,5-Dichlorobenzaldehvd·· Furfural 9-Heptadecanone p-Hydroxyacetophenone Methyl cyclopropyl ketone Methyl ethyl ketone Methyl phenyl diketone
for Various i?raax. X 10
478 476 480 480 480 480
2.72 2.66 2.71 2.70
481
2.72
480 480 480 480 480 479 480 480 476 480 480
.5.42
2.71
2.73 2.70 2.69 2,68 2.70 2.72 2.68 2.70 2.69 2.75 5,46
drops of concentrated hydrochloric acid. After refluxing 2 hours, the methanol was distilled through a short Vigreux column. If kept tightly stoppered, the methanol remains suitable for use for several months. 2,4-Dinitrophenylhydrazine Solution. A saturated solution in carbonyl-free methanol was prepared, using 2,4-dinitrophenylhvdrazine which had been twice recrystallized from this solvent. This solution should not be used more than a week or two after
preparation. Potassium Hydroxide Solution. Ten grams of potassium hydroxide were dissolved in 20 ml. of distilled water and the solution was made up to 100 ml. with "carbonyl-free methanol. This solution will keep indefinitely. PROCEDURE
The unknown or its solution should not be more than 10 ~;i molar in carbonyl. In such dilute solutions the phenylhydrazone will not precipitate at room temperature. The solution must bo neutral or very weakly acidic to prevent precipitation of potassium salts when the base solution is added. To 1.0 ml. of the unknown or its solution in carbonyl-free methanol were added 1.0 ml. of the 2,4-dinitrophenylhydrazine reagent and 1 drop of concentrated hydrochloric acid, the tube was loosely stoppered and heated in a water bath at 50° for 30 minutes or at 100° ('. for 5 minutes. After cooling, 5.0 ml. of the potassium hydroxide solution were added. The almost black
CHEMISTRY
solution which resulted rapidly cleared to the characteristic winered color. A blank determination was made simultaneously' using 1.0 ml. of the carbonyl-free methanol in place of the sample. The optical density of the solution was determined using a Beckman Model DU spectrophotometer. The instrument was adjusted for 100% transmittance for the solution from the blank determination, no further correction for the blank being necessary. The measurement was made at 480 m/j and the calculations were made using the average value of Sm«x. In later work the instrument was standardized using acetophenone and a graph was constructed to allow direct reading of carbonyl concentration from the observed optical density. DISCUSSION
The method has been found to be applicable to a large number of aldehydes and ketones, both aliphatic and aromatic, as well as to some diketones. The only interfering structures so far encountered are nitroaromatic groups and conjugation of the chalconetype ketones. Compounds containing such groups can still be determined by using the same compound for standardization. Accuracy of the order of 2 parts per hundred was obtained in the range of 5 X 10 ~8 to 10~4 molar carbonyl. Carbonyl concentrations as low as 5 X 10-7 molar can be detected qualitatively. The authors have successfully used the method to determine carbonyl compounds in water solutions, and organic solvents such as alcohols, acetic acid, ethers, and ethyl acetate; to the detection and estimation of small quantities of carbonyl compounds formed in certain rearrangement reactions (3, 4)'· to the qualitative identification of aldehydes and ketones in an organic qualitative analysis course (for this purpose the intense color due to larger concentrations of carbonyl compounds makes it easy to distinguish visually between trace impurities and a major component); and to determine the number of carbonyl groups in a compound of known molecular weight (4). LITERATURE
CITED
(1) Chattaway, F., Ireland, S., and Walker, A., J. Chem. Soc., 1925, 1851. (2) Clark, L.. and Thompson, H., unpublished research. (3) Lappin, G., J. Am. Chem. Soc., 71, 3966 (1949). (4) Lappin, G., unpublished research. Received
May
4, 1950.
Purification of Methyl Acetate and Ethyl Acetate CHARLES D. HURD AND JAMES S. STRONG Northwestern University, Evanston, III.
)
ethyl acetate is required in some analytical operations, the separation of soluble sodium perchlorate from insoluble potassium perchlorate (5). Water and ethyl alcohol are the usual impurities to be anticipated. However, for most methods in which ethyl acetate is employed in quantitative analysis, small quantities of water and alcohol are not prohibitive. The method of purification which seems to have been generally adopted {1-5) for both methyl and ethyl acetates is the use of phosphorus pentoxide. Apparently the use of acetic anhydride for this purpose has been overlooked. The latter reagent is suitable not only for the ordinary ester of 97 to 98% purity but also for esters containing much higher amounts of alcohol. An obvious advantage is that the alcohol content becomes converted into the desired ester. This method was tested and found to be suitable. Most of the acetic acid which was formed was removable by distillation. Then, treatment with anhydrous potassium carbonate and redistillation gave essentially pure ester. One liter of ordinary methyl acetate (d|, 0.9309) was refluxed for 6 hours with 85 ml. of acetic anhydride, then was distilled such
as
(boiling point 56.0-56.5°) through a Vigreux column. The distillate was shaken with 20 grams of anhydrous potassium carbonate for about 10 minutes and redistilled. The density of this material (d7p was 0.9284, comparing with Perkin’s (3) value of 0.92825. Careful determination of the saponification equivalent of this material showed it to have a purity of 99.87 0.02%. About the same results were obtained if a few drops of sulfuric acid were added to the acetylation mixture. A mixture of 1 liter of ethyl acetate (98.01% purity, as determined by saponification equivalent), 55 ml. of acetic anhydride, and 6 drops of concentrated sulfuric acid was refluxed for 4 hours, then processed as above. After treatment with potassium carbonate and redistillation, the purity of the ethyl acetate was 99.65% as shown by saponification equivalent. =*=
LITERATURE (1) Gillo, Bull. (2) Meyer, H.,
CITED
chim. Belg., 48, 341 (1939). “Analyse und Konstitutions Ermittlung organischer Verbindungen,” p. 26, Berlin, Julius Springer, 1916. (3) Perkin, W. H., J. Chem. Soc., 45, 494 (1884). (4) Wade, Ibid., 87, 1657, 1668 (1905). (5) Willard, . H., and Smith, G. F., J. Am. Chem. Soc., 45, 286 (1923).
Received
soc.
May 31, 1950.
