798
ANALYTICAL CHEMISTRY EVALUATION OF METHOD
Table I.
Determination of Free Maleic and Phthalic Acids in Their Anhydrides % Acid
System Maleic acid-maleic anhydride
Theoretical (remainder of sample is anhydride) 100.0 100.0
1on.o
100.0
71.43 54,72 37.67 10.78 1.19
0.12
Found 99.8 99 5 99 4 100 0
71.36
54 7-1
37 53
10 81 1.12 0 11
Reagent Used TPA TPA EP EP TPA TPA TPA TPA EP
EP
Table I illustrates the determination of free maleic and phthalic acids in their anhydrides. using both the tripropylamine and the ethylpiperidine reagents. The theoretical % acid of the samples was determined by titration with sodium hydroxide, and samples Twre tested for any anhydride by the method of Siggia and Hanna ( 1 ) . The anhydrides were recrystallized from benzene in which the acids are only very sparingly soluble, whereas the anhydrides are very soluble. The crystals were dried in a vacuum desiccator, and a blank titration was run by the abovementioned method. Both anhydrides assayed about 0.03% free arid which was accounted for in the theoretical values quoted. ACKNOWLEDGMENT
Acknowledgment is made of the preliminary work done by John Garis, Jr.. lyho left before a workable system was devised. Acknowledgment is also made to Richard Stahl who made some of the check analyses. ples are taken, and smaller capacity burets are used for the titration. For the samples containing 0.1% maleic acid (shown in Table I), a 10-gram sample was taken which gave approximately a 1-ml. titration with the 0.1 N reagents. It is well to indicate for the calculation that the reagents are titrating only one carboxyl group of the acids. The sample is then titrated potentiometrically XTith the tripropylamine reagent or the S-ethylpiperidine reagent. 4 model H2 Beckman pH meter equipped with glass and calomel electrodes was used for the above work.
LITERATURE CITED
(1) Siggia. Sidney, and Hanna, J. G., - ~ N A L CHEM., . 23, 1717 (1951). (2) Smith, D. RI., and Bryant, IT-. AI. D., J . Am. Chem. SOC.,58, 2452 (1936). RECEIVED for review October 15, 1952.
Accepted December 26, 1952.
Polarographic Determination of Anthraquinone R. L. EDSBERG‘, DALE EICHLIN, AND J. J. GARIS Central Research Laboratory, General Aniline & F i l m Corp., Easton, Pa. POLAROGRAPHIC
method of analysis is described for the
A quantitative determination of anthraquinone in the presence of anthracene, phenanthrene, carbazole, maleic anhydride, and
phthalic anhydride. Polarograms are obtained in solutions of N,AV’-dimethylformamide0.1 A’ in lithium chloride, containing 0.2 ml. of 0.5 Ji aqueous lithium hydroxide to eliminate the anhydride interferences. Anthraquinone exhibits waves a t El/* = -0.83 v. and E1/g = -1.17 v. 2’s. the saturated calomel electrode, representing a reduction through the semiquinone to anthrahydroquinone. The quantitative analysis of anthraquinone by volumetric (8) or gravimetric (9, 10) chemical methods is time-consuming and involves a number of manipulations. Recently a number of polarographic investigations of anthraquinone and substituted anthraquinones indicated definite possibilities for quantitative analysis (1, 2, 4, 11, 12). The anthraquinones are reducible a t the dropping mercury electrode, but their insolubility has made analyses of unsubstituted anthraquinones rather difficult. In most cases polarograms were obtained in solvents saturated with anthraquinone. l u . I. Vainshtein has published a polarographic method for the quantitative determination of anthraquinone in the presence of benzanthrone using a solvent of 80% methyl I sulfuric ’ acid or acetic acid (11). I n this alcohol containing 0 1 . laboratory S,S’-dimethplformamide is used as a solvent for the polarographic determination of anthraquinone in the presence of anthracene, phenanthrene, carbazole, phthalic anhydride, and maleic anhydride.
this laboratory. This instrument is so constructed that a complete polarogram can be obtained in 10 minutes, startingfrom any potential between +3.0 v. and -3.0 v., covering the span from 0.5 v. to 3.0 v. The voltage changes through zero, approaching either more positive or more negative potentials. The glass polarographic cell used in this work is jacketed to provide temperature control as illustrated in Figure 1. Cells of several volumes were made to fit the water jacket, permitting determinations on voIumes from 2 to 100 ml. This type of cell is easily removed for cleaning by simply lifting the electrode assembly out of the way. A saturated calomel half cell, illustrated in Figure 2, was constructed with a removable bridge to fit the polarographic cells and to allow easy bridge replacement. This saturated calomel electrode of all glass construction using standard taper groundglass joints is similar to the one described by Brunner and
APP4RATUS
The polarograph used in this work is an automatic and recording (Brown Electronic Recorder) instrument constructed in 1 Present address, Research Division. Burroughs Adding Machine Co.. 511 North Broad St., Philadelphia, Pa.
FVLL
S C I L E
Figure 1. Polarographic Cell Assembly
V O L U M E 25, NO. 5, M A Y 1 9 5 3
799
hfeans (3). The cup of the calomel cell as shown has a hole in the side to allow the saturated potassium chloride solution over the calomel and mercury to make contact with the solution in the potassium chloride bridge. A suspension of finely divided filter paper in a saturated potassium chloride solution is placed in the potassium chloride bridge, and the filter paper pulp is firmly tamped into a plug for the lower end of the bridge. Another bridge, shown in Figure 2, provides a means of connecting the calomel half cell to the polarographic cell. This connecting bridge fitted with a filter paper plug ib filled with any desired electrolyte solution and may easily be replaced when contaminated without replacing the entire half cell. The dropping mercury electrode was constructed of marine-barometer tubing obtained from Corning Glass Works. In a cell containing 25 ml. of S,N’-dimethylformamide, 0.1 S in lithium chloride, and 0.2 ml. of 0.5 M aqueous lithium hydroxide plus 1 ml. of standard anthraquinone solution (0.924 mg. per ml. of dimethylformamide), the drop rate a t an applied potential of -1.35 v. us. the S.C.E. was measured a t T = 5.84 seconds. The weight of mercury delivered by this electrode under these conditions is m = 0.974 mg. per second. The capillary constants as expressed in the IlkoviE equation are m2/3T1/6 = 1.318 mg. seconds per second. The height of the mercury column is 46.4 em.
Figure 2. Calomel Electrode Assembly
REAGENTS
A. Platinum electrode; C,
results on these samples were found to be within 2 to 3% of t h e theoretical value or within the limits of polarographic precision. No difficulties were encountered in the analyses of the sample mixtures, and quantitative results are now being obtained by calculating directly from the IlkoviE equation.
id
=
605 12
D1lZ
C m2 /3T1/6
By keeping the temperature and capillary characteristics constant, the diffusion current can he expressed id = KC. DISCUSSION
calomel cell; N,N’-Dimethylformamide. Commercial E, KCI bridge; grade S,S’-dimethylformamide was obtained and 2. Conneeting bridge from the Du Pont Co. This solvent is suitable without any distillation or purification treatment. Anthraquinone. Anthraquinone with an elementary analysis of carbon = 80.81% (theory, 80.75%) and hydrogen = 4.02% (theory, 3.8TC0) was used in this work. Lithium Chloride. C.P. Baker’s. Lithium Hydroxide. A monohydrate of lithium hydroxide was obtained from Metalloy Corp., 2560 Rand Tower, BIinneapolis, llinn. PROCEDURE
About 25 mg. of sample are accurately weighed directly into a 25-ml. volumetric flask and dissolved in about 20 ml. of N,N’dimethylformamide. When the solution is complete, Ar,5‘dimethylformamide is added to make the volume 25 ml. To a clean, drv polarographic cell, 25 ml. of AV,N‘-dimethylformamide, 0.1 S in lithium chloride, and 0.2 ml. of a 0.5 A1 aqueous solution of lithium hydroxide are added by pipet. The dropping mercury and saturated calomel electrode assembly is then put in position, and the dissolved oxygen is removed by bubbling dry nitrogen through the solution for 10 to 15 minutes. The nitrogen bubbler is raised so that a stream of nitrogen is allowed to flow over the solution. A blank polarogram run on this cell a t a high sensitivity (0.005 microamperes per mm.) over the range of -0.5 v. to - 1.5 v. furnishes a means of calculating the residual or background current correction. Depending on the anthraquinone content, a 1-to-2-ml. aliquot of the sample solution is added to the above cell and purged for about 5 minutes. -4polarogram is run on the sample over the same voltage range. -4sensitivity was selected to allow the anthraquinone double wave to extend almost full scale on the recorder. The samples are compared with a standard anthraquinone solution for quantitative measurements. Such a comparison is made by adding a 1-ml. aliquot of standard anthraquinone solution (0.924 mg. C.P. anthraquinone per ml. S,?;’-dimethylformamide) to the same cell and repeating the polarogram. The total or limiting current is measured between -0.5 and -1.35 v. on all polarograms. On the blank polarogram this current corresponds to the residual or background current that must he subtracted from the anthraquinone waves to determine the true diffusion current. The limiting currents measured from the polarograms of the sample and sample plus standard anthraquinone are corrected for the residual current and then substituted in the equation described by Kolthoff and Lingane ( 7 ) . The first qamples analyzed were synthetic mixtures made up to contain varying amounts of anthraquinone. The quantitative
N,S’-Dimethylformamide is a good solvent for the mixture of anthraquinone, anthracene, phcnanthrene, carbazole, phthalic anhydride, and maleic anhydride and has the added advantage of being high boiling (153’ C,), which allows the easy removal of ovygen without a large evaporation loss during the nitrogen purge. Polarograms are obtained on solutions of anthraquinone in lithium chloride in .\’,.V’-dimethvlfornianiide that are 0.1 and contain 0.2 nil. of a 0.5 AVaqueous solution of lithium hg” droside. The addition of lithium hydroxide is necessary to hydrolyze the anhydrides to eliminate their interfering polarographic waves. The other constituents produce polarographic waves in S,.Y’-dimethylformamidr hut do not interfere with the anthraquinone determination. Anthraquinone produces two well defined polarographic waves at El/* = -0.83 v. and E’/z = - 1.17 v. (Figure 3).
2
f
.6..
3.. 0
e
2
E
.4..
3..
.. I ..
1
.O
-
I
J::
-3 z b
-.I
;8
-.9 VOLTS -1.0
-1.1
-12
-1.3
-/4
Figure 3. Polarogram of Anthraquinone in ,1;4’-Dimethylformamide
Both waves are well defined and exhibit half wave potentials that are constant with concentration changes. The double wave suggests a reduction reaction of the anthraquinone through the semiquinone to the anthrahydroquinone. Anthrahydroquinone as an end product is further suggested by the characteristic pink color formed in the alkaline solution after several polarograms have been run. It is interesting to note that enough anthrahydroquinone is furnished in a matter of perhaps 20 minutes running time a t a current of only 1 to 2 microamperes to produce a definite pink color. Further confirmation of this reaction was obtained by reducing some anthraquinone in an alkaline solution with sodium bisulfite to a dark red color, then polarographing this solution as described above. In this case two waves appear a t the same potentials, only this time the waves shifted to the anodic side of zero current, indicating an oxidation reaction. Blowing air through this cell for 10 minutes oxidizes the anthrahydroquinone t o a colorless solution of anthraquinone that exhibits the original two cathodic polarographic waves. indicating a
800
ANALYTICAL CHEMISTRY
reduction reaction. This evidence indicates a reversible oxidation-reduction reaction at the dropping mercury electrode. Further confirmation of the reaction and its reversibility vas obtained by calculating the electron change involved for each wave.
CONCENTRATION X IO’*
MOLAR
Figure 5. Anthraquinone Diffusion Current as a Function of Concentration
quinone concentration to diffusion current is shown in Figure 5 . These resuIts indicate that a measure of the diffusion current is easily expressed quantitatively in terms of anthraquinone. ACKNOWLEDGMEYT
The authors gratefully ackno~vledgethe help and advice of S. Siggia, H. J. Stolten, E. W. Bell, R. Hill, D. R. Hindmarch, and L. F. Frauenfelder. Thanks are also expressed to L. T. Hallett under lvhose direction this work was performed. VOLTS
Figure 4.
Anthraquinone Heduction Electron Change
The electron change was calculated by the method described by
i
Kolthoff and Lingane (?). By plotting the l o g c i against Ed a t various potentials over the wave, a straight line results having a slope of 0.06 for a one-electron-change reaction that is reversible. This was done for both waves in Figure 3, and the results are given in Figure 4. Although a linear relationship is found, the slopes indicate electron changes of 0.72 and 0.T9. This is a bit low for a clear cut one-electron-change reaction, but, in view of the other evidence already presented, i t is quite clearly a reversible reaction involving two one-electron-change reactions. Evidence for the semiquinone formation has also been given by Geake and Lemon ( 6 , 6 ) , and polarographically by Furman and Stone (4). 4 linearity check illustrating the linear relationship of anthra-
LITERATURE CITED
(1) Adkins, H., and Cox, F. IT., J . ,4m.Chem. Soc., 60, 1151 (1935). (2) Baker, R. H., and Adkins, N., Ibid., 62, 3305 (1940). (3) Brunner, 9.H., and Means, P. G., ANAL. CHEM.,23, 1525 (1951). (4) Furman, S . H., and Stone, K. G., J . Am. Chem., Soc., 70,305561 (1948). ( 5 ) Geake, A., Trans. Faraday Soc., 34, 1395-1409 (1938). (6) Geake, A., and Lemon, J. T., Ibid., 34, 1409-27 (1938). (7) Kolthoff, I. M., and Lingane, J. J.,“Polarography,” pp. 144-6,
New Tork, Interscience Publishers, Inc., 1946. (8) Xelson, 0. 4., and Senseman, C. E., J . I n d . Eng. Chem., 14, 956-7 (1922). (9) Pirak, H., 2. ungew. Chem., 41, 231-3 (1928). (10) Sokolor, P. I., and Gurevich, L., J . Chem. Ind. ( M o s c o ~ )5, ,
308-9 (1928).
(11) T’ainshtein, Yu. I., Znwdsknya Lob., 15, 411-13 (1949).
(12) Wawzonek, S., Laitinen, H. .4.,and Kwiatkowski, S. J., J . Am. Chem. Soc., 66, 827-30 (1944). RECEIVED for review October 17, 1932. Accepted January 14, 1953
Microdetermination of 3-(p=Chlorophenyl) -1,l-dimethylurea in Plant Tissue H. Y. YOUNG AND W. A. GORTNER Pineapple Research Institute of Hawaii, P.O. Box 3166, Honolulu 2, Hawaii INCE
the introduction of the potent herbicide, 3-(p-chloro-
S phenyl)-1,l-dimethylurea(CMU), by Bucha and Todd ( 2 ) ,the
need has arisen for a method for its microdetermination in plants and soils. The comprehensive paper of Lon-en and Baker ( 4 ) EhoMed that CMU can be hydrolyzed either by acid or alkali into p-chloroaniline and dimethylamine; the determination of either of thesewould serve as a means of indirectly estimating CMU. Lowen and Baker also indicated that either acetonitrile extraction of CMU in soils followed by acid hydrolysis and colorimetric determination of p-chloroaniline, or basic hydrolysis follon ed by hexane extraction and a similar colorimetric determination might be feasible. The first method, hoxvever, appeared time-consuming, and the second involved extraction difficulties. Basic hydrolysis with subsequent colorimetric determination of dimethylamine after distillation was not recommended OTT ing to the high blanks obtained on soils. This wa9 found to be true on pineapple fruit tissue also. Inasmuch as p-chloroaniline has a vapor pressure of 8.03
mm. a t 100” C. ( S ) , and its solubility in boiling 157, sodium hydroxide appeared to be slight (bv visual test), it would seem that steam distillation or direct distillation of an aqueous alkaline solution should be effective in recovering p-chloroaniline after basic hydrolysis of CMU. Estimation of p-chloroaniline in the distillate could then be made colorimetrically. This is the basis of the method described herewith, which mas employed on pineapple fruit tissue. Extraction and subsequent evaporation of organic solvents are avoided. Eighteen samples may be analyzed per day with a battery of six refluxing and distilling units. The method is highly accurate and sensitive to concentrations of 0.01 p.p.m., using 3OO-gram samples of fruit tissue. K i t h slight modification, it should Le applicable to other plant tissue and to soils. APP4R4TU.S
The all-glass refluxing and distilling apparatus consisted of a 1-liter round-bottom, short-neck boiling flask connected to a
