rate of this reaction in 3F hydrochloric acid
where the quasi-second-order rate constant, k, is 20.6 i. 0.8 1. per mole per minute a t 25.00° C. This information is of value in choosing a ferrous ion concentration for use in the determination of chlorate; with less than about 0.01;11ferrous ion the reaction is too slow for convenience. On the other hand, high concentrations of ferrous ion lead to undesirably large corrections for the ferric ion present in the reagent as a n impurity. A ferrous concentration of 50mU, which permits the accurate determination of chlorate concentrations from 0.005 to 7 m X (Table I), seems to represent a reasonable compromise between these factors.
Perchlorate and chloride will not interfere in the determination of chlorate b y this method. Such strong oxidizing agents as hypochlorite, chlorine, ferric, pervanadyl, chromate, and bromate could be removed by a controlled-potential electrolysis of a weakly acidic solution prior to the determination of chlorate. Hence this information should make possible the polarographic determination of chlorate in a wide variety of materials. LITERATURE CITED
(1) Hofmann, K. A., Bel. 45, 3329 (1912). (2) Kolthoff, I. M., Lingane, J. J., “Polarography,” 2nd ed., p. 576, Interscience, hew l o r k . 1952. (3) Koryta, J., Tanygl, J., Chem. listy 48, 467 (1954). (4) Latimer, W. M., “Oxidation States of
the Elements and Their Potentials in Aqueous Solutions,” p. 56, 2nd ed., Prentice-Hall, New York, 1952.
( 5 ) Lingane, J. J., J . Ani. Chem. SOC.67, 919 (1943).
( 6 ) Luther, R., MacDougall, F. H., 2. phusik. Chenz. 5 5 , 477 (1906). ( 7 j &Teites, L., J . . Am. Chem. SOC.76, ’
5927 ( 1954).
(8) Meites, L., Ibid., 79, 4631 (195i). (9) .Meites,
L., “Polarographic Techniques,” p. 73, Interscience, NeTv Tork, 1955.
(10) Meites, L., illeitea, T., A N A L . CHEM. 23,1194(1951). (11) Meites, L., BIeites, T., unpublished experiments cited in (9). (12) Mjlner, G. W. C., “Principles and
Applications of Polarography and Other Electroanalytical Processes,” p. 289, Longmans, Green, Nen- York, 1957. (13) Taube, H., Dodgen, H., J . Bin. Chem. SOC.71, 3330 (1949).
RECEIVEDfor review June 19, 1958. Accepted August 8, 1958. Based in part on thesis submitted by H. Hofsass to the faculty of Polytechnic Institute of Brooklyn in partial fulfillment of requirements for the B.S. in chemistry degree, June 1958.
.
A Simple Sensitive Test for AI I phatic Ketones EUGENE SAWlCKl and THOMAS
W. STANLEY
Community Air Pollution Program, Robert A. Tuft Sanitary Engineering Center, U. S. Public Health Service, Department of Health, Education, and Welfare, Cincinnati 26, Ohio
F A simple, sensitive color test for acetone and other aliphatic ketones containing the structure, RCH2COCHzR’ , is based on a condensation of the ketones with 2-hydroxy-1 -naphthaldehyde under special conditions. Limits of iden’ification are about 1 to 5 y, the colors are stable, and a blue color, A,, 598 mp, is usually obtained. The procedure consists of the addition of 0.5 ml. of a 2-methoxyethanol test solution to approximately 75 mg. of the test powder, which is made of 1 part of 2-hydroxy- 1 -naphthaIdehyde and 3 parts of anhydrous aluminum chloride. The color is read in 3 minutes. The exothermic reaction of the reagent powder with 2-methoxyethanol furnishes the heat necessary for the development of the color. This test is superior in simplicity of operation, color differential between blank and test solution, color stability, and sensitivity to previous procedures.
N
for a simple, specific, and reliable test for aliphatic ketones has been shown by the numerous publications on this subject which have appeared during the last century (2, S, 7 , 8, 14, 17, 19, 20). There are four main colorimetric methods for the detection of ketones containing the struc122
EED
ANALYTICAL CHEMISTRY
ture RCH,COCH,R’. Many of these color tests involve the condensation of the ketone with an aromatic aldehyde in alkaline (1) or acid (23) media to give a colored diarylidene acetone (17). Some of the other aromatic aldehydes which have been used are furfural ( I @ , p-hydroxybenzaldehyde (WS), salicylaldehyde ( I I ) , and vanillin (18, 23). The disadvantages of the furfural test are its 24-hour duration (92) and the reportedly negative results for methyl ethyl ketone (27). The salicylaldehyde test requires 20 minutes of heating and is relatively insensitive for diethyl ketone (26). I n all these tests the blank is yellow, vihile the positive color is orange to violet. This is not a very sharp distinction because compounds such as acetophenone also react to give orange to red chalcone derivatives. A second color test is based on the formation of the blue dye, indigo, in the reaction between o-nitrobenaaldehyde and an aliphatic ketone. Acetyl derivatives, like acetophenone, acetaldehyde, and biacetyl, give positive results. The test is not very sensitivea n identification limit of 100 y being reported for acetone (9). A third color test uses sodium nitroferricyanide as the reagent (3, 9, 10, 24, 26, 28). The basis of the color reaction is stated to be the reaction of
sodium nitroprusside with the acetone anion to produce the unstable highly colored anion, [Fe(CN),(O?r’= CHCOCH3)]-4 (4). A satisfactory modification of this test has been used in clinical chemistry to test for the presence of acetone and acetoacetic acid in urine, spinal fluid, or blood serum ( I , I d , 14, 21). Ten micrograms of acetone can be detected b y the method. This test is not specific because acetophenone ( 9 ) , pyruvic acid (9), aliphatic aldehydes (S), pyrrole (g), and mercaptans give positive reactions. I n addition, aliphatic ketones, such as methyl ethyl ketone, give a fairly insensitive light orange color with the reagent. A fourth method for the detection of aliphatic ketones is based on the formation of a red-violet complex between m-dinitrobenzene and the aliphatic ketone anion in alkaline solution (5, 15). This reaction has been successful in the detection and determination of ketonic steroids. It forms the basis of all reliable methods for the determination of 17-oxo steroids (16, 29). The main disadvantages are that i t is not too sensitive for aliphatic ketones, the color is not stable, and compounds such as acetophenone and acetaldehyde give positive results ( 3 ) . The new color test for aliphatic ketones probably involves the reactions
CH30CH&H?OH
+ AICIZ
-+
[CH30CH&H20AlC12]
R I
+ HC1 + heat
R' I
80 120 SEUSITI?/ITY, Y
40
I60
Figure 1 , Effect of water in 2-methoxyethanol on sensitivity of test for acetone Total volume, 0.6 ml.
I
The purpose of the aluminum chloride is threefold. I t s exothermic reaction with 2-rnethoxyethanol is necessary to initiate the reaction because without heat the condensation vould be negligible, and a strong acid medium is necessary for this reaction, and also for the formation of the blue cationic resonance salt. Dyes such as Ia, and their postulated spiro intermediates, have been synthesized (6, I S ) b y methods roughly similar to the color test procedure. The known dyes, prepared from acetone, cyclopentanone, cyclohexanone, etc., and 2-hydroxy-1-naphthaldehyde, have the same colors in solution as the analogous test colors from acetone, etc. The color test for 2-octanone was repeated on a large scale. Following neutralization with ammonia, extraction with ether, and crptallization from aqueous pyridine, pale yellow crystals were obtained with a niclting point and mixed melting point of 185-186" C. (cor.) (to a dark blue liquid) comparing favorably lyith a n authentic sample of I, R = (CH2)dCH3 and R' = H, melting point 185.5186.0" C. (cor.) (to a dark blue liquid) (6). This fact lends credence to the postulated mechanism. EXPERIMENTAL
Reagents and Equipment. 2-Hydroxy - 1 - naphthaldehyde, obtained from Aldrich Chemical Co., Milwaukee, K i s . , ivas satisfactory without further purification. T h e reagent poii-der is made by quickly grinding i n a mortar 1 part of t h e naphthaldehyde with 3 parts of anhydrdus aluminum chloride. T h e yello^ homogeneous powder is then quickly bottled. It is stable for a t least 1 m o n t h in a tightly stoppered bottle. Although many samples of Z-methoxyethanol give negative blanks with the reagent powder, a surprising number give a positive blue color. The
following treatment iemoves the aliphatic ketones and the water present in the solvent. A solution of 0.1% 2,4dinitrophenylhydrazine in 2-methoxyethanol is allowed t o stand overnight over silica gel. Distillation gives a fraction boiling at 122-123' C. at 750mm. pressure which is satisfactory for use in the test procedure. A Cary Model 11 recording spectrophotometer was used for the determination of the wave length maxima. Procedure. One-half milliliter of a 2-methoxyethanol test solution is placed in a 15-ml. centrifuge t u b e containing 0.1 ml. (60 t o 85 mg.) of t h e reagent powder. A vigorous exothermic reaction takes place. A bright blue color appears within 3 minutes in t h e presence of aliphatic ketones containing t h e structure RCH2COCH2R'. -4 blank test is advisable for comparison, and with a good grade of anhydrous 2-methoxyethanol a light green-yellow to yellolv
Table
I.
500
550
600
,y Figure 2.
Visible absorption spectra
- - - Acetone -Ethyl acetoacetate
Color, W a v e Length Maximum, and Limit of Identification of Aliphatic Ketones in Test Identification
Compound Acetone 2-Butanone 2-Pentanone 3-Pen tanone 5-Hexen-2-one 2-Heptanone 3-Heptanone 2-Octanone 2-Xonanone 2-Undecanone 2-Tridecanone 2-Heptadecanone 2-Nonadecanone Cyclobutanone Cyclopentanone Cyclohexanone Cycloheptanone Cyclooctanone Cyclononanone Cyclopentadecanone Ethyl acetoacetate 2,CPentanedione a B = blue; R = red; V
Color. B B B B B B
msx,
584 598 597 598 598 598 590 598 598 598 598 598 598 585 579 556 1000 500 5 10
orange. VOL. 31, NO. 1, JANUARY 1959
123
color is obtained. The limits of identification and wave length maxima are reported in Table I. Although the use of 2 - methoxyethanol, containing 1% water as a solvent, gives decreased sensitivities (Figure l ) , the blank is yellow and its use might be preferred by some analysts. The results in this paper are based on the anhydrous solvent. The wave length maxima were determined by briefly heating the qualitative mixture to the boiling point, waiting 5 minutes for full color development, and then diluting to 3 ml. with 2-methoxyethanol. A blank was prepared in the same manner. DISCUSSION
Because of the sensitivity of the test for acetone, all glassware must be scrupulously cleaned and thoroughly dried (especially if acetone is used in washing the glassn-are). The limit of identification of the test for the ketones in the anhydrous solvent is in the order of 1 to 5 y. As discussed, many of these ketones give negative to weak color reactions by the four standard colorimetric methods. For acetone, the limit of identification was 0.5 y, or a concentration limit of 1 to 1~000,000a considerable improvement over the old methods. I n most cases the dye that is formed from the aliphatic ke598 mp. tones has a blue color with, , ,A Because the blank in the spectral procedure is yellow, the color differential is much greater than that found in the earlier procedures, where yellow blanks are, at times, compared to orange test solutions. An example of the type of spectral curve obtained with two different types of aliphatic ketones is shown in Figure 2. I n a few cases, red to violet colors are obtained. The dye obtained from cyclohexanone is
sterically strained and consequently absorbs a t shorter wave lengths. I n the determination of the wave length maxima, the colors were found to be stable even after several days’ standing. Proportions of 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, and 1:lO of the aldehyde and aluminum chloride were tried. The 2:1, 1:1, and 1:2 mixtures did not generate enough heat in the reaction and the sensitivity suffered. The 1:3 mixture was better than the 1 : l O and appeared to be somewhat superior to the 1:4 and 1: 5 mixtures. Other carbonyl compounds such as acetophenone, benzaldehyde, n-undecyclic aldehyde, fluorenone, anthraquinone, salicylaldehyde, 3 - methyl - 3hydroxy - 2 - butanone, 9 - acetylanthracene, 1 - phenyl - 1,3- butanedione, and 1,l - dimethyl - 3,5 - cyclohexanedione give negative results. The results for the last two compounds are apparently due to the large amount of steric strain which would be present in the dyes if they were formed. The effect of this phenomenon on the wave length maxima and the limits of identification is illustrated in the cycloalkanones, Table I. Similarly, in dimethyl 3-oxoglutarateJ steric strain in the dye, as well as the presence of electronegative groups, probably accounts for the high identification limit, 400 y, and the red color obtained in the test. Phloroglucinol gave a red color in the test, limit of identification, 5 y. This may be due to the presence of the diketonic tautomer in the compound. LITERATURE CITED
(1) Bacon, Melvin, J . Maine Med. Assoc. 38, 167, 185 (1947). (2) Bionda, Giacomo, Chim. eind. (Milan) 36, 110 (1954). (3) Bitto, B. von, Ann. 267, 372 (1892); 269, 377 (1892).
(4) Cambi, Livio, Chem. Zentr. I, 1756 (1913); 11, 1100 (1914). (5) Canback, Theodor, Scensk. Farm. Tidskr.54, l(1950). (6) Dilthey, W.,Berres, C., Holterhoff, E.. Wubken, H.. J . prakt. Chem. 114. 179 (1926). ( 7 ) Dikhey,’ W.,Wubken, H., Ber. 6lB, 963 (1928). (8) Etienne, H., Ind. chim. belge 17, 455 (1955). (9) Feigl, Fritz, “Spot Tests in Organic Analysis,” pp. 223, 225, Elsevier, New York. 1956. (10) Free, A‘. H., U. S. Patent 2,509,140 (May 23, 1950). (11) Frommer, V., Berlin klin. Wochschr. 42, 1008 (1905). (12) Galat, Alexander, U. S. Patent . 2,362,478 (Nov. 14, 1944). (131, Heilbron. I. M.. Heslou. R. N..’ Irving, F . , J . Chem. hoc. 1933; 430. (14) Ingram, J., Brit. ,Xed. J . 1944, 512; Analyst 69, 220 (1944). (15) Janovsky, J., Ber. 24, 971 (1893). (16) Kellie. 4 . . Analust 82. 722 (1957). i17/ Klendshoi. 3. C.. Feidstein: Milton. Can. J . ~$feci.’ l’echnbl. 17, 74 (1955). ’ (18) Levine, V. E., Taterka, Michael, Clin. Chem. 3 , 646 (1957). (19) Lur’e. Y . T.,Nikolaeva, Z. U., Zavodskaya Lab. 21, 410 (1055). (20) Mentzer, C., PIIolho, D., MolhoLacrois, L., Bttll. soc. chim. France 636 (1953). (21) Rabinowitch, I. N., Can. Xed. Assoc. J . 5 2 , 602 (1945). (22) Rosenthaler, L., Mikrochemie cer. Mikrochim. Acta 39, 360 (1952). (23) Rosenthaler, L.,Vegezzi, G., Mitt. Lebensm. u . Hyg. 44, 475 (1953). (24) Rothera, A . C. H., J . Physiol. 37,491 (1908). (25) Szilas, Jeno, Kisdrlctes Orvostudomhny 125 (1949). (26) Thomson, T., J . SOC.Chem. Ind. (London) 65, 121 (1946). (27) Tikhonova, V. I., Zhur. Priklad. Khim. 26, 662 (1953). (28) Wenke, M., fasopis ldkdru EeskSch 93, 183 (1954). (29) Zimmerman, TT’illiam, Vitamine u . Hormone 5 , 1 (1944). I
\ -
,
.
~
\ -
RECEIVEDfor review April 22, 1958. Accepted August 6, 1958.
Development of a Commercial Automatic Colorimetric Titrator JAMES M. THOBURN, CONRAD M. JANKOWSKI‘, and MANNING S. REYNOLDSZ Research laboratories, Central Scientific Co., 7 700 Irving Park Rd., Chicago 7 3,111. ,An automatic titrator is described, which can b e used for many routine colorimetric determinations. The titration is monitored by a light beam passing through the titration beaker; a t the end point the change in transmittance causes a meter relay to close, which in turn stops delivery of reagent. Titrations are most conveniently carried out using a motordriven syringe to deliver the titrant,
124
ANALYTICAL CHEMISTRY
although both solenoid burets and coulometric generation can b e used. Results on most titrations have standard deviations of 3 parts per thousand or better for delivery of 3.5 rnl. of titrant.
approach t o the automatic laboratory must begin with automatic titrations-probably the one operation common t o all laboratories, and the one
A
NY
that consumes the most time and is usually routine and tedious. The purpose of this research was t o devise an automatic titrator which could do some of the more common titrations 1 Present address, Department of Chemistry, State University of Iowa, Iowa c i address, Department ~ ~of Chem- ~ istry, University of New hfexico, .41buquerque, N. M.
~
