tures containing from 10 to 30% weight o,p’-BPA. Similar results were obtained with three- and four-component mixtures, although practical analyses were always based on standard samples run along with the unknown mixtures, rather than on previously prepared calibration curves. An important facet of each of the procedures was the use of reference mixtures containing all the compounds in concentrations chosen to bracket the
concentrations w-hich were expected in unknowns. This practice was adopted after it was found that over-all sample composition exerted a small but signjficant effect on the various R , values and quantitative relationships.
Purity,” D 1015-55, and “Tentative Purity Methodfrom of Test Freezing for Determination Points,,, 1016of
,
KAT
“LA.
(2) Bruss, D. B., Wyld, G. E. A., ANAL. CHEM.29, 232 (1957). ( 3 ) Deal, V. Z., Wyld, G. E. A., Ibid., 27, 47 (1955). ( 4 ) Freeman. J. H.. Ibid.., 24., 955 (1952). (5) Ibid., p. 2001. ’ ((6) 6 ) Harlow, G. A., Noble, C. M., Wyld, G. E. A . , Ibid., 28, 787 (1956). \
LITERATURE CITED
(1) Am. Soc. Testing Materials, Philadelohia. Pa.. “Standard Method of Test for Measurement of Freezing Points of HighPurity Compounds for Evaluation of
I
RECEIVEDfor review October 16, 1958. Accepted March 18, 1959.
Polarographic Determination of Acetone R. E. VAN ATTA and D.
R.
JAMIESON’
Department of Chemistry, Southern lllinois University, Carbondale, 111.
b The imine produced b y reaction of acetone with n-butylamine yields a sharply defined polarographic wave ideally suited for the determination of the acetone concentration of a solution. Solutions in the range of concentrations from 0.05 to 100 volume % acetone can b e analyzed with an average accuracy to 3 ~ 1 % . The method is rapid. The determination i s made without prior nitrogen purging; currents are measured a t two potentials, followed b y reference to a suitable calibration curve.
A
may be determined polarographically by direct reduction of the carbonyl group or reduction of the species produced by the reaction of some reagent with the ketone. Because acetone is reduced a t a potential much more negative than that attainable with the usu:il supporting electrolytes, the first method requires a specially prepared quaternary ammonium salt ( 6 ) . The second involves the reaction of acetone with a reagent forming a product which is polarographically reducible within the range of potentials available with ordinary electrolyte systems. The bisulfite method (4) is based on the extent to which the presence of acetone decreases the bisulfite wave as a result of the reaction of the ketone with the reagent. Another method (3) deals with the polarographic measurement of acetone after condensation with semicarbazide. A more direct application is measurement of the wave resulting from the reducible product fornied when acetone reacts nith ammonia or an amine. CETONE
Present address, Department of Chemistry, University of Michigan, Ann Arbor, Mich.
Zuman reported the interaction of acetone with an amine ( 7 ) when the ketone was treated with 2.5M ammonia in a 2.5M ammonium sulfate solution and a well-defined wave was observed a t - 1.6 volts us. S. C. E. The equilibrium constant reported for the imine formation is 4 X 10-3 (8) which indicates that very low concentrations of reducible species are formed. This probably accounts for the low ratio of current to concentration of acetone reported. Because of the volatility effect which decreased ammonia concentration during degassing operations, the conditions of the measurement had to be rigidly controlled. The volatility effect was partially overcome by the use of methylamine ( I ) , and completely eliminated when glycine was used as the reagent (6, 8). The equilibrium constant for the imine formed with glycine was reported as 6.8 X indicating the formation of larger concentrations of reducible species. The previous studies have been mainly theoretical and the methods were not readily adapted to routine analysis. To overcome the difficulties encountered with ammonia, as n-ell as for operational convenience, n-butylamine was used as the imine-forming reagent in this investigation. This amine, which is relatively nonvolatile, is commercially available in adequate purity. A preliminary study indicated that the tendency toward volatilization had been practically eliminated and that the ratio of current to unit concentration of acetone substantially increased. This increase, with the other factors involved, was favorable for the development of an analytical method. APPARATUS
Polarograms were recorded with a Leeds & Korthrup Electrochemograph,
Type E: Manual measurements were made d h a Sargent Model I11 polarograph. -411 p H measurements were made with a Coleman Model 18-A p H meter using a Hy-alk electrode. The polarographic cell consisted of a waterjacketed H-cell (0,containing a saturated calomel electrode. The capillary used as dropping mercury electrode was constructed from Corning marine barometer tubing and had an rn value of 1.812 mg. of mercury per second and a drop time of 3.6 seconds a t a head of 60 cm., measured a t open circuit in distilled water. The temperature of the cooling water circulated through the 0.1’ C. cell was maintained a t 25.0” REAGENTS
Acetone stock solutions were prepared by measuring (microburet) the desired volume of previously dried acetone (Mallinckrodt analytical reagent grade) and diluting to volume with distilled water. The supporting electrolyte was prepared by dissolving the requisite weight of ammonium chloride (Mallinckrodt analytical reagent grade) in distilled water. n-Butylamine (Eastman Kodak 1261) and distilled water were added until the desired volume or p H was obtained. The added amine was accurately measured, so that its exact concentration in the final solution could be calculated. The weight of ammonium chloride taken was such that when one part of the acetone stock solution was diluted with four parts of electrolyte, the ionic strength of the final solution was 1.OM. The resulting solutions were then transferred to the polarographic cell, purged with nitrogen, if necessary, and polarographed, using suitable apparatus settings. EXPERIMENTAL
Initial studies of the polarographic behavior of acetone in an n-butylamineammonium chloride electrolyte medium showed a sharply defined TT ave a t - 1.58 VOL. 31, NO. 7, JULY 1959
0
1217
volts vs. S. C. E. (Figure 1). The reactions producing such behavior are presumably similar to those proposed by Zuman ( 7 ) . Further studies showed that a variation in degassing time did not affect the magnitude of the observed diffusion current, in direct contrast to results observed with an ammonia buffer. Consequently, the contribution of volatility effects to reproducibility was negligible. For practical reasons, the minimum time (5 minutes) required for oxygen removal was employed in measurements involving nitrogen purging. The very small wave appearing a t about -1.4 volts (Figure 1) resulted from the presence of an impurity in the amine reagent. This impurity can be removed by careful fractionation. but its presence does not affect analytical measurements. Because an equilibrium reaction is involved in the polarographic measurement of the acetone-imine system, it was necessary to determine whether rigid time control was required for the preparation, dilution, and measiwement of test solutions. Polarograms were recorded on test solutions a t a fixed potential, located on the limiting current portion of the wave. Stock solutions and electrolyte solutions were degassed separately. Proper instrument settings ivere made and then the requisite amounts of oxygen-free stock and electrolyte solutions were mixed in the polarographic cell. The resulting solution, with a nitrogen atniosphcre rnaintained over it, was polarographed no more than 20 seconds after mixing. The current-electromotive force curve was recorded a t constant potential (- 1.75 volts us. S. C. E.) for approximately 10 minutes, with no significant change occurring in the measured current height. Because a minimum of 20 seconds was required to prepare the test solution and the polarographic cell for measurement, it was concluded that the time required for the establishment of equilibrium is less than that necessary to initiate the polarographic measurement. The equilibrium constant for the reaction was estimated as 8.4 X 10-2, in comparison with the value of 6.8 X 10-2 for the corresponding reaction involving glycine (6, 8). To obtain optimum conditions for the polarographic measurement, the concentration of the amine must be large enough so that reasonable diffusion currents are produced and the ratio of amine to ammonium chloride concentration must be such that an adequate buffering capacity is available. Solutions which were 2.V in amine and lilf in ammonium chloride (pH approximately 10.5) gave substantial diffusion currents (about 1 pa. per mniole of acetone), but poor reproducibility. Reducing the amine concentration to 1 2 18
ANALYTICAL CHEMISTRY
I
I
I
1
I
I
Figure 1. Typical polarogram for the a cetone-n-butylamine system
T
1.3
1.4
1.5 1.6 - E v s . S.G.E.
about 1.7M (pH approximately 10) resulted in satisfactory reproducibility, while maintaining approximately the same current relations. Variation in amine concentration by a factor of *5% docs not affect the measurement of a single sample, but for adequate reproducibility on replicate determinations, exactly the same volume of amine must be used. The fact that the wave obtained, under optimum conditions, with the acetone-imine system was well-defined rendered a two-point method possibleLe., a measurement, with a manual instrument, of currents a t two potentials, one preceding (-1.45 volts) and one following (- 1.75 volts) the rising portion of the wave (Figure 1). The difference in the two currents thus obtained was proportional to the concentration of acetone in the test solution. The half-wave potential of the imine wave is about 0.6 volt more negative than that of the peroxide wave due to dissolved oxygen. I n contradistinction to the use of ammonia buffer (71, the curves in n-butylamine-ammonium chloride supporting electrolyte can be registered in the presence of oxygen, even in solutions containing much lower acetone concentrations. Using the twopoint method, linear calibration curves nere obtained, both in the presence and absence of oxygen. The lines were parallel, with that in the presence of oxygen shifted by about 0.1 current scale division to lower values. This shift is due to the difficulties of measurement of the residual current, in the presence of oxygen. Because both methods produced satisfactory standard series curves, the degassing operation was omitted in further measurements in order to reduce the time required for analysis.
1.7
1.8
ANALYTICAL PROCEDURE
On conclusion of these experiments an analytical procedure was devised for the polarographic determination of acetone in aqueous solutions.
Standard Solutions. To about 25 ml. of distilled water in a 100-ml. volumetric flask, add 1.00 ml. of dry, reagent grade acetone. Add 20 ml. of 5 M ammonium chloride solution and 17.0 ml. of reagent grade nbutylamine. Dilute to volume with distilled water. The concentration of acetone in the resulting solution is 1.0 volume %. Prepare other concentration standard solutions in like manner by varying the volume of acetone taken. Transfer the resulting solution to the polarographic cell, make the proper instrument settings and measure the current a t -1.45 and -1.75 volts us. S. C. E. Plot the difference between the two current readings as a function of the acetone concentration of the solutions. A typical linear working curve is obtained. Test Solutions. Measure 1.00-ml. samples, treat, and dilute as for standard solutions. If, upon measurement, the current exceeds or is smaller than the range of values covered by the calibration curve, dilute or increase the sample, up to a maxiniuni of 50 ml. As long as the volume of sample taken is accurately known, the concentration of acetone in the test solution may be determined. Results obtained in the analysis of a series of aqueous acetone solutions are shown in Table I. DISCUSSION
The practical minimum concentration of acetone, for measurement by this method, was found to be approximately 0.05 volume %, although measurements down to 0.0005 volume % have been made with appropriate cali-
bratiori data. More concentrated solutions, up to and including pure acetone, n q -be analyzed by proper preliminary dilution of the sample. The average accuracy attainable is to about =kl% of the acetone concentration present (Table I). The method may be subject to interference due to the presence of any compound which is polarographically reducible in the potential region of the imine wave or which reacts with the reagent amine. The first may be corrected for by preliminary polarographic measurement in the absence of the rcagent amine. The second may require preliminary chfmical treatment, such as oxidation in the case of an aldehyde. The method is particularly well suited for the determination of acetone in various mixtures. For example, the authors have determined acetone successfully in the presence of large amounts of benzophenone, benzhydrol, iwpropyl alcohol, and aluminum isopropoxide in a single solution. Some
exploratory work would have to be carried out to determine the possibility and extent of interferences in specific instances. A major advantage is that it may eliminate the necessity for separations in the case of analysis of ketone mixtures, or of mixtures containing ketones. ACKNOWLEDGMENT
The authors express their appreciation to the Research Corp. for a Frederick Gnrdner Cottrell grant which supported the investigation described. LITERATURE CITED
Brezina, M.,Zuman, P., Chem. list71 47.975 (1953). (2) Komyathy,’J. C., Malloy, F., Elving, P. J., A N A L . CHEM.24, 431 (1952). (3) Souchay, P., Graizon, M., Chirn. anal. 36,85 (1954). (4) Strnad, F., Chem. Zisty 43, 16 (1949). (5) Von Stackelberg, M., Stracke, W., 2. Elektrochem. 53. 118 11949). (6) Zuman, P., Colle~tio~dzechdsloz.. Chem. Communs. 15, 839 (1951). (7) Zuman, P., Nature 165, 485 (1950).
Analysis of Acetone Solutions Volume % Relative Error, Acetone Acetone taken found Error 7c
Table 1.
I
0.0100 0,250
0.500 10.0 25 0 75.0
0.0099 0.0101 0.248 0.254 0.508 0.501 9.94 10.1 24.7 25.2 74.5 i5.3
”
-0.0001 $0.0001 -0.002 $0.004 +0.005 +0.001 -0.06 +0.1 -0.3 +0.2 -0.5 +0.3
-1 0 +1.0
-0 8 $1 6 +l.O +o 2
-0.6 +1.0 -1.2 f0.8 -0.7 +0.4
(1)
(8) Zuman, P., Brezina, M.,Chenz. listy 46, 599 (1952).
RECEIVED for review September 26, 1958. Accepted January 26, 1959. Abstracted in part from a thesis submitted by D. R. Jamieson for the RZ. A. degree in chemietry, Southern Illinois University.
Polarographic Determination of 1, 2-DiaminocycIohexa ne in Hexamet hy lenedia mine MAYNARD E. HALL The Chemsfrand Corp., Decatur, Ala.
b A method has been developed for the determination of 1,2-diaminocyclohexane (DCH) in hexamethylenediamine (HMD). The DCH forms a complex with nickel ions and is determined indirectly from polarograms of the nickel-DCH complex. The standard deviation of the method is *5% of the amount of DCH present in HMD at concentration levels above 100 p.p.m. At pH values above 1 1.7, no interference from other impurities in HMD is encountered. The effect of pH on diffusion current, half-wave potentials, and other impurities is presented. The time required for a single analysis is approximately 25 minutes.
I
preparation of intermediates for the manufacture of Xylon 66 1,2-diaminocyclohexane (DCH) appears as an impurity in low concentrations in hexamethylenediamine (HMD), It is believed to be a source of the color which develops in the nylon polymer process. Any such color will carry through into the nylon fiber. For this reason, it is important to know the N THE
concentration of this contaminant in the HhlD and to keep it as low as possible. A literature survey revealed no published methods for the determination of DCH. Obviously, it could be determined by simple acid-base titration techniques, but in the presence of other amines such as HMD, the determination can be difficult. When present in HMD a t levels as low as 200 p.p.m., the analysis becomes even more difficult, because of the inability to separate the two compounds. The method required for analysis in lorn concentrations is one that is sensitive and free of interferences from H M D and other amine-type impurities. Infrared techniques do not possess sufficient sensitivity, and direct ultraviolet methods cannot be applied, because this impurity does not absorb light in the 200- to 400-mp region. Polarography offered possibilities, because of its sensitivity, but even here it would be necessary to take an indirect approach, because any reduction due to DCH could not be detected in the presence of HMD. Horton, Thomason, and Kelley (1) described an indirect
polarographic method for the analysis of propylenediamine by making a c o p per-diamine complex which reduced a t a voltage different from that of the uncomplexed copper ions. For such a technique the metal ion must not complex with the compound used as the supporting electrolyte. This requirement was met by the development of a technique which employed nickel ions, which form a reducible complex with DCH but not with HhID, the supporting electrolyte. The time required for a single analysis is approximately 25 minutes. APPARATUS AND REAGENTS
Polarographic measurements were made with a Leeds & Northrup Type E Electrochemograph. H-type polarographic cells containing a saturated calomel reference electrode separated from the solution compartment by a I-cm. fine sintered-glass disk and a potassium chloride-agar plug were employed. The capillary and other polarographic characteristics for the nickelDCH complex are given in Table I. The mercury column height, h, was 64 cm. All experimental measurements were made in an air-conditioned room VOL. 31, NO. 7, JULY 1959
1219
