Polarographic Analysis of Solutions of Alkyl Aryl Ketones and Benzaldehyde ROBERT H. BOYD' and ALEXANDER R. AMELL* Department o f Chemistry, Lebanon Valley College, Annville, Pa.
The polarographic characteristics of tert-butyl phenyl ketone, isopropyl phenyl ketone, n-propyl phenyl ketone, and benzaldehyde, and mixtures of the ketones with benzaldehyde are given. The half-wave potential of each is independent of the other carbonyl, and sufficiently separated so that mixtures can be analyzed with errors of less than 3% in the concentration of Letone. The diffusion currents are linear with concentration and independent of the presence of the other carbonyls. The errors for benzaldehyde are less than for ketone.
The oxidation mixture to be analyzed is a result of the normal oxidation of an alkylarylcarbinol (4,7 )
n-ith simultaneous anomalous oxidation:
A
SERIOUS difficulty in the study of osidations of alkylarylcarbinols is the lack of a suitable method of analyzing the resulting oxidation misture. If some of the constituents of this misture are reducible a t the dropping mercury electrode, there exists the possibility of analyzing the miyture polarographicallv.
O r
OH The cleavage products may undergo further oxidation to givc ArCOOH and R'CHO, if ROH is a primary alcohol. These secondary oxidations are minimized by properly choosing the conditions of the reaction (4). The carbinols oxidized viere tert-butylphenylcarbinol, isopropylphenylcarbinol, and n-propylphenylcarbinol, each of which gave the corresponding ketone and benzaldehyde as products. The information obtained by determination of the concentration of the ketone and the benzaldehyde mill add considerably to the knon ledge of the mechanism of normal and anomalous oxidations. Iiolthoff and Lingane ( 5 ) give polarographic characteristics of n-propyl phenyl ketone, isopropyl phenyl ketone, and benzaldehyde. This paper is concerned mainly with the determination of the characteristics of tert-butyl phenyl ketone, and the relationship of the diffusion current to the concentration of the ketones in solution iT-ith benzaldehyde.
Table I. 0 1 0 2
0 5
10
CARBONYL C O N C E N T R A T I O N , M H O L E S ,
,
Tsonronvl Isopropyl . . .=.. ~ alcohol - . ~~~~
50% dioxane-water 80% dioxane-water 50% ethyl alcohol-water
- D
Figure 1. Wave height as a function of concentration of carbonyl Benzaldehyde
A Isopropyl phenyl ketone
2
Supporting Electrolytes Tetraethvlammonium bromide Tetraethylammonium Lithium chloride Tetra-n-butylammonium iodide Lithium hydroxide
8 lert-Butyl n-Propyl phenyl ketone phenyl ketone
The literature of organic polarography is voluminous ( 8 ) ,but relatively little has been done on the determination of tTvo or more reducible organic compounds in the same solution. Adkins and coworkers (1, 8 ) have worked with aryl aryl and alkyl aryl ketones. In some two-ketone systems the diffusion current was quantitatively proportional to the concentration of the ketones being determined and independent of other ketones presente.g., n-propyl phenyl ketone and benzophenone, and isopropyl phenyl ketone and benzophenone-but this was not the case with other combinations-e. g., acetophenone and benzalacetone. Benzalacetone had a marked effect on the wave height of acetophenone. 1 Present
Solvents and Supporting Electrolytes Studied Solvents
2 0
5
a
1
OH
address, Pennsylvania State University, University Park, Pa. Present address, Cniversity of New Hampshire, Durham, N. H.
I n an attempt to find the best solvent and electrolyte to use in this work, the materials in Table I Jvere investigated. A combination of lithium hydroxide and 50% ethyl alcohol-Tvater gave the best results. A clearly defined wave and an electrolyte with a half-wave potential that did not interfere with the determination of the benzaldehyde or the ketones mere obtained. I n all the work reported in this paper 0.1M lithium hydroxide was used as the electrolyte and 50% ethyl alcohol-water as the solvent. EXPERIMENTAL
Materials. The tert-butyl phenyl ketone was prepared in these laboratories by the oxidation of tert-butylphenylcarbinol ( 7 ) . It had a refractive index (n*g I) of 1.5073; literature value is 1.5086 (6). The isopropyl phenyl ketone &-asEastman Kodali white label with the following constants: n*z = 1.5142, d:2" = 0.981; literature values are n'g e = 1.5192, d:$ 0.985 ( 6 ) . 1280
V O L U M E 28, NO. 8, A U G U S T 1 9 5 6
1281
The n-aroavl ohenvl ketone was also Eastman Iiodak white label: n;;.; 2 i.516g, n:01.80, 0,984; literature values: nl: = 1.5202, d:," = 0.990. Eastman Kodak chlorine-free benzaldehyde n-as distilled in a nitrogen atmosphere a t reduced pressure- before use. Experimental: n2,0 = 1.5442; literature value: 1.5456 (6). Baker's C.P. lithium hydroxide was used as the electrolyte. The ethyl alcohol was C.P. absolute alcohol. Originally it waa distilled through a fractionating column, but as no noticeable interferences appeared, if used wit,hout this purification, the purification was discontinued. Distilled wat.er was used throughout. M ) of the ketones and benzaldehyde in Stock solutions 50y0 ethyl alcohol-water solvent were prepared quantitatively. .4 lithium hydroxide stock solution, also prepared in 50% ethyl alcohol-\rater, had a strength such that upon final dilution a 0.1W solution resulted. Apparatus. A Sargent-Heyrovskp Model XI1 polarograph was used for this analysis. All polarograms were taken on photographic paper. A Beckman Model G p H meter was used for pH measurements. I n conjunction with a saturated calomel electrode, the pH meter was used to correct the cell potential to volts us. the saturated calomel electrode, by immersing the saturated calomel electrode in the solution and inserting the other lead in the form of a copper wire into the mercury arm of the cell. The correction \vas found to be -0.210 volt, which must be added to the electromotive force as calculated from the rotating potential divider. ( S o correction was made for the internal resistaiice-drop across the instrument.) The capillary \vas a Bargent dropping mercury capillary with these characteristics:- pressure, 35.9 em. of mercury, m = 1.886 mg. per second, t = i.8 seconds per drop, m ' / d Z / z = 2.150 (open circuit in distilled tvater). The drop time in solution was 3.9 seconds per drop a t 0.0 volt and 3.3 a t 1.00 volt. A conventiorisl Ileyrovsk9 polarographic cell was used in all analvses. Temaerature \vas maintained a t 25.0" k 0.5' c. bv immersing the entire cell in a water bath.
-
concentration. If the curve is extrapolated to zero benzaldehyde concentration, it does not pass through theorigin. This seems to be due to a slight prewave, a rise that immediately precedes the benzaldehyde wave. As this is constant and cannot be separated from the benzaldehyde diffusion current, its height was incorporated in the height of the benzaldehyde wave. Being a constant, it does not interfere with the analysis. The estimated half-wave potential of this prewave does not correspond to any impurity in ethyl alcohol. The lithium hydroxide, the ethyl alcohol, and the water were varied independently without producing a noticeable effect on the prewave. The intercept of Figure 1 corresponds to the height of the prewave. The primary concern of this work is the concentration determination of the species; as the prerave does not interfere, it was not studied further.
i.. .- .-. .......
60
?----A
'I______.; -,.....;---.-;.__.__
,
3..:f
10 0
04
BENZaLDEHYDE
0 8
12
16
2 0
2 4
CCNCENTSLlION,NMOLES/LlTER
Figure 3. Dependence of wave height of ketone on benzaldehyde concentration B.
2.44 m.11isopro??! pl.cny1 ketone 1.37 m.ll ferl-bu:yl phenyl ketone
E. F.
1.22 m M isopropyl phenyl ketone 0.46 m.V iert-butyl phenyl ketone
A.
C. 1.83 m.lf isopropyl phenyl ketone D. 0.91' niJ1 terf-butyl r>l.enylketone
,j 0
3 8
0 4
KETONE
1 2
I 6
2 0
2 4
z'e
CChCENTRATlON, M M C L E S / L I T E R
Figure 2. Dependence of wave height of benzaldehyde on ketone concentration A.
B.
1.83 m M in benzaldehyde 1.37 m M in benzaldehyde
C. 0.916 m M in benzaldehyde D. 0.46 m M in benzaldehyde 0 tert-Butyl phenyl ketone 9 Is opropyl phenyl ketone
Procedure. The solution to be analyzed was prepared in the cell from the stock solutions by dilution to give a ketone and benzaldehyde concentration in the neighborhood of 10-SM. The cell was placed in the constant temperature bath for about 8 minutes to allow it to reach temperature equilibrium. d photographic plate was used to record the curve of current us. voltage. After developing, this graph was analyzed to determine the diffusion current and the half-wave potential. The pH and the electromotive force correction n7eremeasured directly in the cell. RESULTS AND DISCUSSION
The results of the benzaldehyde determination are given in Figure 1. The diffusion current is directly proportional to the
Borchesdt, Meloche, and Adkins ( 2 ) report a constant correction factor which must be subtracted from the wave height to give a proportionality between wave height and concentration. S o prewave is apparent upon inspection of their published polarograms. The intercept of Figure 1 would correspond to a mathematical factor to be subtracted from the measured wave height to give proportionality. The prewave does affect the measured half-wave potential of the benzaldehyde, which was.determined to be -1.51 =k 0.02 volts us. S.C.E. a t an apparent pH of 12.8. The literature reports -1.48 volts us. S.C.E. a t pH 11.3 (6). Figure 1 also indicates the linearity of the diffusion current with the concentration of tert-butyl phenyl ketone, isopropyl phenyl ketone, and n-propyl phenyl ketone. The half-wave potentials of the ketones are -1.92 f 0.03, -1.82 =t0.02, and - 1.75 f 0 02 volts, respectively, all measured against a saturated calomel electrode a t an apparent pH of 12.8. The literature values for the reduction potentials of isopropyl phenyl ketone and n-propyl phenyl ketone are -1.TO and -1.61 volts us. N.C.E. (pH not given) ( 3 ) . Although the concentrations of the ketones and benzaldehyde are directly proportional to their diffusion current, the relationship may not hold when one of the ketones is in solution with benzaldehyde. Figure 2 gives the diffusion current of a series of benzaldehyde solutions as a function of the ketone concentration. Figure 3 gives the diffusion current of ketone solutions aa a function of the benzaldehyde concentration. The slopes of each curve are 0 within experimental error, indicating that the diffusion current of the carbonyl is independent of the other component.
1282
ANALYTICAL CHEMISTRY
The half-wave potential measured for each component was the same as in the absence of the second component. ACKNOWLEDGMENT
The authors wish to thank H. A. Neidig, Lebanon Valley College, for his encouragement and assistance on this problem. LITERATURE CITED
(1) Adkins, H., Cox, F., J . Am. Chem. SOC.60, 1151 (1938).
(2) Borchesdt, G. I., Xfeloche, V. IT., Adkins, H., Ibid., 59, 2171
(1937). (3) Davies, IT. P., Evans, D. P., J . Chem. SOC.1939, 546. (4) . , Hamoton. J . . Leo. A.. Westheimer. F. H.. J . Am. Chem. SOC.78. 306 (1956). ( 5 ) Kolthoff, I. M., Lingane, J. L., “Polarography,” 2nd ed., Interscience, New York, 1952. (6) Lange, N. A., “Handbook of Chemistry,” 7th ed., Handbook Publishers, Sandusky, Ohio, 1949. (7) Neidia, H. A,, Funck, D. L.. Ghrich, R.. Baker, R.. Kreiser. W., J . Am. Chem. SOC.72, 4617 (1950). (8) Wawaonek, s., A N A L . CHEM.26, 65 (1954). RECEIVED for review Sovember 2 5 , 1955. Accepted >lay 4 , 1956.
X-Ray Fluorescence Determination of Barium, Titanium, and Zinc in Sediments GEORGE J. LEWIS, JR., and EDWARD D. GOLDBERG Scripps lnstitution o f Oceanography, f a Jolla, Calif.
X-ray fluorescence analysis has been applied to the rapid and quantitative assay of barium, titanium, and zinc in marine sediments. Internal standards were used to minimize matrix effects in the samples, which ranged in composition from nearly pure calcium carbonate to glauconite and deep-sea clays, which have compositions similar to materials encountered in ordinary silicate analysis. Arsenic was employed as the internal standard for zinc, and lanthanum served for both barium and titanium. The barium La1 and titanium K a peaks, which had the highest usable sensitivities, overlapped and empirical corrections to compensate for this effect were ascertained. The lower limits of detectability were 0.01% for titanium and barium and 0.004% for zinc.
S
TUDIES on the geochemistry of marine sediments have necessitated the determination of such minor elements as barium, titanium, and zinc in clay and calcareous materials. Xray fluorescent techniques appeared advantageous for a number of reasons. With the selection of proper internal standards ( I ) , the methods can be applied to a large variety of mineral types.
Table I.
Composition of Typical Marine Clay and Mock Clay Used in Preparation of Standards Weight % of Constituents Marine Synthetic clay clay 59 60 17 15 8 7 3 5 4 4 4 1
INSTRUAMENTATION
-4 Norelco x-ray spectrograph with a 50-kv. tungsten tube (Machlett OEG-50), an argon-filled Geiger tube detector, and a lithium fluoride analyzing crystal were used. For the barium and titanium determinations a helium path was constructed from a polyethylene bag and attached to the apparatus in essentially the manner described by Davis and Van Nordstrand (2). Helium flow rates of a t least 700 ml. per minute were used to obtain maximum reproducibility of results. A tenfold increase in sensitivity for the barium Loll and the titanium K a radiation resulted from the substitution of a helium path for an air path. An aluminum planchet designed to hold about 1 gram of sample was machined to fit the sample holder provided with the instrument. The x-ray tube was operated a t 45 kv. and 35 ma. EXPERI3f ENTAL
Standards. Reagent grade chemicals were used throughout the investigation. Standard zinc samples were prepared by the addition of zinc acetate dihydrate to portions of a mock marine clay of the composition given in Table I, on a water-free basis. Barium and titanium primary standards were made by the addition of barium carbonate and titanium dioxide to calcium carbonate. Internal Standards. The choice of an internal standard for a given element depends not only upon the desirable characteristic of having an x-ray fluorescence peak adjacent to the peak of the element in question but also upon the following criteria: (1) ready availability in an inexpensive and stable form; (2) sufficient peak separation from the element in question to make background measurements possible; (3) absence from the matrix
Table 11. X-Ray Fluorescence Peak and Background Wave Lengths of Elements and Internal Standards
5 2
5
1
The nondestructive nature of the technique does not demand the sacrificing of the small amounts of sample available for analysis. Finally, the method is rapid and reasonably simple. This paper considers some of the problems encountered in the quantitative x-ray spectrographic assay of titanium, barium, and zinc in marine sediments of widely varying composition.
Element
(Lithium fluoride used a s analyzing crystal) Wave Length, Degrees 28 Emission .I. Peak Background
{:;:E
Zinc
Ka
1.437
41.81
Arsenic
Ka
1,177
33.98
Barium
Lai
2.776
87.16
Titanium
1; a
2,750
86.08
{gi:;! {E;:
Lanthanum
Lai
2 665
82.86
81.50 (85.00
E::{
