counted. An ayerage of these two background determinations was used in correcting the sample count. To prevent cross contamination of samples, each individual sample was stored in a small, ground-glass-covered neighing pan and was exposed only during the counting. period. The countiiig reproducibility is shown in Table 11, in which are listed all the values obtained in counting the six standard plates used in the analyses of mixtures 6, 7, anti 8. All counting rates were determined for infinitely thick layers of the plated acid. Reference to Figure 2 indicates that acid layers greater than 30 mg. per sq. cm. increase in counts only slightly as the weight of the acid layer increases. In this investigation approximately 90% of the plates counted weighed between 30 and 50 mg. per sq. cm. The counting fluctuation in this area is only about 1.9%.
Table II. Reproducibility of Counting Data of Standard Radioactive p Chloropropionic Acid
Counting
Plate 1 2
3 4
5 6
Date Counted 10/12/57 iO)iZ)i7 10/17/57 10/17/57 10/23/57 10/23’/57
Time, Minutes 5
5 11 6
10 10
Corrected Counts per Minute 994n __-_
9962 9973 9990 9789 9953 Av. 9939
LITERATURE CITED
11) Andrussow. L.. Stein. G. (to General Aniline and Film Corp.), U: S. Patent 2,210,564 (Aug. 6, 1941). (2) Bass, S. L. (to Dow Chemical Co.), Zbzd., 2,010,685 (Aug. 6, 1935). (3) Bass, S. L.. Burlew. W. L.. Zbid.. ’1.993.713 (March 5. 1935). (4) ’Bauer, W., Lauth, H.’ ( t o Rohm & Haas Co.), Zbid., 2,087,466 (July 20, 19371 -I_.,.
ACKNOWLEDGMENT
The authors are indebted to the Research Corp. for the grant-in-aid to the College of St. Catherine which made this research possible.
( 5 ) Calvin, M., Heidelberger, C., Reid,
J. C., Tolbert, B., Yankwich, P., “Isotopic Carbon,” pp. 278-82, Wiley, New York, 1949. (6) Carney, T. P., “Laboratory Fractional Distillation,” pp. 175-81, Macmillan, New York, 1951.
( 7 ) Harrison, G. C., Thompson, J. M. (to Minnesota Mining & Mfg. Go.),
U.S.Patent 2,682,504 (June 24, 1954).
(8) Hevesey, G., Hofer, E., Sature 134,
879 (1934). (9) Huntress, E. H., ,‘Organic Chlorine Compounds,” Kiley, SeB- York, 1948. (10) Isherwood, F. .4.,Bzochem. J . 40, 688 (1946). (11) Jacobs,’ W. .4.,Heidelberger, M., J . Am. Chem. Soc. 39, 1465 (1917). (12) Marvel, C. S., Rands, R. D., Zbid., 72, 2642 (1950). (13) Porret, D. (to Ciba, Ltd.), U. S. Patent 2,679,530 (May 25, 1954). (14) Radin, X., A‘ucleonics 1, No. 2, 48 1‘19471 \---.,-
(15) Rittenberg, D., Foster, G., J . Biol. Chem. 133, 737 (1940). (16) Rohm ’ & Haas, German Patent 579,654 (June 29, 1933).
(17) Schenker. H. H.. Rieman., W.., ANAL. 25. i637 (1953). (19531. ’ CHEM.25, Sihmid, K., Helv. Helv. Chim. Chzm. (18) Schmid, H., Schmid, Acta 35, 1879 (1952). (19) Staudinger, H., Kohlschutter, H. W., Ber. B64, 2091 (1931). 120) Terentev. A. P . T’inoeradova. E V., J . Gen. Chem. tr.3.S.R.)’ 14, 1044 (1944). (21) Cssing, H., .Vattire 144, 977 (1939). (22) Weissberger, A , , ed., “Technique of Organic Chemistry,” Vol. IV, pp. 623-7, Interscience. Ye% York. 1991. (23) \Tieland,’ T., Feld, V.,2. angew. Chem. 63, 258 (1951).
RECEIVEDfor review Fehrunry 7 , 1958. Accepted May 22, 1958.
Improved Method for Determining Ketones in Lacquer Solvents New Direct Application to Lacquer Vehicles G. G. ESPOSITO and M. H. SWANN Coating and Chemical laborafory, Aberdeen Proving Ground,
b The cause of poor accuracy in the determination of ketones in lacquer solvents by the hydroxylamine hydrochloride method was investigated. Two outstanding sources of error were found, and ways of overcoming these were incorporated in a new modification of this method which allows precise determination of ketones in lacquers and lacquer thinners. A technique for determining ketones directly on lacquer vehicles without prior removal of solvents is included.
L
solvents and thinners are usually mixtures and may contain aromatics, alcohols, esters, and ketones. The ester and ketone content is particularly important because these are the active solvents and all lacquer specifications require analysis for these two ingredients. The solvents are usually separated from lacquers by vacuum ACQTJER
Md.
distillation and the esters determined b y saponification. This method is accurate and not subject to interference from the other constituents. Methods for determining ketones in such mixtures have not been as satisfactory; precision and repeatability by the same analyst have been fair, but reproducibility in the hands of different analysts has been poor. An attempt has been made to determine the reason for this and to develop or improve existing methods. T h e improved method has also been applied directly to lacquer vehicles to eliminate the need for prior solvent removal. There are four classical methods in the literature for determining ketones, based on their reactions with sulfites or bisulfites, iodine, phenylhydrazine, and hydroxylamine or hydroxylamine hydrochloride. Several modifications of the last method also appear. The
sulfite (3) and iodine (9) methods are limited to aqueous reaction media, and because some of the ketones used in lacquer solvents are not completely water-soluble, these methods do not possess general applicability. Some of the lacquer solvents interfere in the iodine method. One of the phenylhydrazine (1) modifications requires 15 hours to complete the analysis and the others suffer from the same weakness inherent in all the hydroxylamine methods (1)-namely, the uncertainty of the end point obtained by titration with alkali or acid to the methyl orange or bromophenol blue end point in alcohol. The color changes a t the end point are so gradual that a blank must be prepared, and the colors matched as closely as possible, allowing room for error due to differences of opinion. Relatively concentrated standard solutions ( 0 . W ) of either alkali VOL. 30, NO. 10, OCTOBER 1958
1643
Table I.
Analysis of Some Lacquer Solvents
Present, Solvent % Found, % 1. RIethj 1 isobutyl ketone 100 0 100 2,100 2 2. Methyl isobut j 1 ketonpa 28 7 28 7,28 9 3. Methj-I isobutvlketone" 11 9 11 9,12 0 4. M&hyl eth! 1 ketone 100 0 100 0,100 0 5, ?\Ieth>1 eth) 1 11 9 12 0,12 0 ketones 6. Methyl eth? I ketone 16 3 16 3 Methyl isobutrl ketonea 16 3 16 5 Also contain 10-20z esters, 10-3070 alcohols, and 40-50% aromatic solvents. (1
Table II.
Comparison of Direct and Indirect Methods
Indirect Method, on Distillate, 5
Direct Method, on Lacquer Vehicle, 7 0
38 6
38 3 42 0 38 2 37 9
42 0 38 4 38 3
or acid must be used to help offset the uncertainty of the end points; more accurate volumetric analyses could be obtained if larger volumes of weaker solution. of 0.1 or 0.2 normality could be used. For analyzing lacquer solvents, the hydroxylamine hydrochloride methods have the advantage of using alcohol as a titration medium, and these methods R-ere studied to determine the cause of the uncertainty in titration end points. It was found that the optimum ratio of alcohol to water needed for the reaction is not the same as the optimum ratio for the final titration. By preparing a highly concentrated reagent solution in water (10 times the usual concentration) it is possible to provide the best alcohol to water ratio for the reaction: then, by adding absolute alcohol. the ideal ratio is again provided for the titration. It was also found that the transition point of the two indicators used in these methods, methyl orange and bromophenol blue, is about the same as the natural acidity of hydroxylamine hydrochloride, and this tends to prevent a sharp color change as the end point is approached. Substitution of thymol blue for these indicators allon 3 color changes a t slightly lower pH, so that a blank titration is not required n i t h each analysis, there is no need for color matching, and a weaker alkali (0.2N) can be used. There is no interference from other lacquer solvents and accuracy is improved (Table I). Through a slight modification of this revised method. ketones may be 1644
ANALYTICAL CHEMISTRY
determined directly on lacquer vehicles, avoiding the time-consuming isolation of the solvents through vacuum distillation. This new technique is both rapid and accurate (less than 1% error). Results are given in Table 11. If analysis for esters is needed, distillation of the lacquer solrents will be necessary. PROCEDURES
Reagents. Hydroxylamine hydrochloride solution. Weigh 36 grams of hydroxylamine hydrochloride into a 100-ml. volumetric flask, dissolve in mater, and dilute to volume. Standard potassium hydroxide solution. Dissolve 6.5 grams of potassium hydroxide in 100 ml. of absolute methanol, filter, and dilute to 500 ml. with methyl alcohol. ANALYSISOF LACQUERSOLVENTS OR THINNERS.A glass-stoppered 100-ml. volumetric flask, containing 20 to 30 ml. of absolute ethyl alcohol is accurately weighed, and 10 ml. of the lacquer thinner are added. It is immediately stoppered, reweighed, and diluted to the mark with absolute ethyl alcohol. After thorough mixing, a n aliquot of 5, 10, or 15 ml., according to the following table, is Rithdrawn by means of a pipet. Ketone Anticipated,
Aliquot Size, RI1. 15 10
c /c
0-30
30-60
5
60-100
Ethyl Alcohol t o Be Added, hI1. 0 5
10
The sample aliquot and alcohol are transferred to a glass-stoppered 250-ml. Erlenmeyer flask containing 2.5 ml. of the hydroxylamine hydrochloride reagent and allowed to stand at room temperature. After 1 hour, 85 ml. of absolute ethyl alcohol and 1.5 ml. of 0.1% thymol blue indicator (in absolute alcohol) are added. The sample is titrated before a brightly lighted background with 0.2N potassium hydroxide until the color change is from red to vellow-, adding the alkali in 0.1-ml. portions, and agitating vigorously as the end point is approached. The buret reading is noted, and the flask restoppered, and allowed to stand for 30 minutes. If some of the pink color reappears, the titration is continued to a permanent yellow end point. The total volume of titrant is used for the calculation:
yc ketone where 17,
=
V2
=
N
=
F
=
W
= =
0.98
=
- V2) x N x P x 100 W X 0.98 X aliquot fraction
(VI
Since the two ketones most used in lacquer solvents are methyl ethyl ketone and methyl isobutyl ketone, separate determinations following fractional distillation can be made. The procedure involves preliminary determination of total ketone calculated as methyl isobutyl ketone, followed by an analysis of the distillate obtained below 93 O C. and correction of the former calculation. Example 6 of Table I \vas analyzed by this method. Into a 50-ml. distillation flask are weighed 20 nil. of the thinner. A fraetionating column (Vigreux type) with approximate dimensions 20 x 130 mm. is attached together with a short watercooled condenser. The sample is distilled a t the rate of 1 ml. per minute, and the distillate is collected in a 100-ml. volumetric flask containing 30 to 40 nil. of absolute ethyl alcohol. The distillation is stopped when the vapor temperature reaches 93" C. The distillate is diluted to the mark n ith alcohol an aliquot withdrawn, analyzed as described, and calculated as methyl ethyl ketone.
% methyl isobutyl ketone = % total ketones (as methyl isobutjl ketone) -(1.39 X % methyl ethyl ketone) DIRECTDETERMINATIOX OF KETONES ISLACQUER VEHICLES. Approximately
8 or 9 grams of lacquer vehicle are accurately weighed into a 100-nil. volumetric flask and dissolved in 5 ml. of dioxane. While the sample is swirled. 40 ml. of absolute ethyl alcohol are added slowly from a buret, followed by 12 ml. of distilled water similarly added. Finally the sample is diluted to volume with absolute ethyl alcohol, mixed thoroughly, and allowed to stand for at least 5 minutes. The sample will be cloudy but satisfactory for analysis. T o 0.9 gram of hydroxylamine hydrochloride crystals in a 250-nil. Erlenmeyer flask, 15 ml. of the prepared sample are added from a pipet. A magnetic stirring bar is used to agitate the sample until the hydroxylamine hydrochloride dissolves (about 20 minutes). The sample is allowed to stand for 45 additional minutes and titrated as outlined. Calculation is made on the volatile vehicle basis. Some results of analysis by this method are compared in Table I1 with analytical data on the same saniples after vacuum distillation of the solvents. DISCUSSION
ml. of standard potassium hydroxide required for titration of sample ml. of standard potassium hydroxide required for titration of blank normality of standard potassium hydroxide solution milliequivalent weight of ketone being analyzed weight of sample correction factor for incompleteness of reaction
Hydroxylamine hydrochloride reagent contains a small amount of free hydrochloric acid which does not change significantly in storage. It is necessary to measure the amount of acid in 2.5 ml. of reagent (or in 0.9 gram) and correct all samples accordingly, but a blank must be run only when a new supply of reagent is prepared. An excess of alcohol inhibits the first stage of the reaction and causes low
results. Because the hydrochloric acid released tends to reverse the reaction between hydroxylamine and ketones. it is necessary to neutralize most of the acid with one titration and the rest by a final titration. A 98% yield was obtained consistrntly.
ACKNOWLEDGMENT
The advisory assistance of C. F. Pickett, director of the laboratory, is acknowledged and appreciated. LITERATURE CITED
(1) Jacobs, hI. B., Scheflan, L., “Chemical
Analysis of Industrial Solvents,” x-01. VII, pp. 417, 422, Interscience, Sew York, 1953. (2) hlessinger, J , , J , sot, them. ~ ~ 18, d . 138 (1889). (3) Ripper, AT., Monatsh. 21, 1079 (1900). RECEIVEDfor review Februray G , 1958. Accepted 3Tay 27, 1958.
Voltammetric Studies with the Graphite Indicating Electrode PHILIP J. ELVING and ALAN F. KRlVlS Department of Chemistry, University o f Michigan, Ann Arbor, Mich.
In preparation for use of the graphite electrode in chronopotentiometry, automatically recorded current-potential curves obtained with it were further evaluated b y studying a variety of inorganic and organic reversible and irreversible systems. In mineral acid solutions penetration of the solution into wax-impregnated graphite resulted in poor reproducibility. Satisfactory results are obtained in slightly acidic and neutral media; alkaline media were not investigated. Experimental conditions must b e carefully controlled for good results. The reductions of silver(1) and mercury(l1) are comparable to those obtained with the platinum electrode; iron(ll1) gave poor results. Results with the quinone hydroquinone system were good, except that Eli2 for the oxidation and reduction processes did not coincide. Oxidation studies of the three isomeric phenylenediamines and the three isomeric dihydroxybenzenes a t p H 5.5 were satisfactory. The oand p-phenylenediamines undergo 2e oxidation, the latter showing semiquinone formation; the meta shows a le wave due apparently to the formation of a free radical which polymerizes. Hydroquinone and catachol show the same 2e oxidation; the meta isomer, resorcinol, apparently oxidizes to a free radical which polymerizes to a film that coats the electrode.
-
T
most Ll-idely used solid indicating microelectrodes in voltammetry have been t h e noble metals, mainly platinum (8). However, a large variety of other materials such as t h e coinage metals (11) and their amalgams ( I ) , tungsten (Z), and some alloys ( 7 ) have been investigated. T h e major defect of the solid indicating microelectrode is t h e influence of previous use upon t h e results obtained. I n some instances, HE
plating on the electrode surface during electrolysis changes its characteristics; in organic investigations. films may form on the electrode surface. T o alleviate some of the difficulties observed with platinum electrodes, the properties of t h e graphite indicating electrode have been investigated in recent years (4-6, 10). A carbon rod has a unique advantage in that the usable electrode surface is readily renewed for each run-e.g., b y simple breaking off of the end of the rod. The graphite electrode was found to be a poor substitute for either platinum or gold in t h e case of some inorganic reactions; it was excellent for some organic systems. The results obtained were critically dependent on experimental technique and electrolysis conditions-e.g., rate and direction of polarization, and pretreatnient of the electrode. The high residual current usually produced mas found to be a function of the binder, or lack of binder. used in formulating the rod. Impregnation of the carbon rod with a waxy material decreased the residual current considerably but did not affect the faradaic current-Le., the current due t o oxidation or reduction of the species under study-to the same extent; the particular wax used controlled the il:ir ratio to a large extent, and also affected Ell2 and il. Pretreatment of the electrode b y electrolysis had a large, but not completely consistent effect on the curves obtained. I n view of these difficulties n-ith the graphite electrode, it was decided to investigate the use of the graphite indicating electrode for chronopotentiometric studies and, in particular, for analysis b y the latter technique. However, further information on the graphite electrode when used under standard voltammetric conditions seemed desirable. Consequently, a variety of types of electrode reactions which it was desired to investigate chronopo-
tentiometrically, n-ere studied---e.g.. reversible reactions where both oxidized and reduced species were soluble and vihere one species T T ~ Sinsoluble, and irreversible reactions. The availability of a larger store of information about the behavior of the graphite electrode would permit more valid conclusions to be drawn concerning the results obtained with any one electrode reaction. EXPERIMENTAL
Reagents. Cupferron (‘2. F. Smith Chemical Co.) n as purified by recrystallization from ethyl alcohol and Norite and from ethyl alcohol alone. All other organic chemicals were Eastman Kodak Co. white label grade and were used without further purification. Nitrogen used to deoxygenate the test solutions n-as purified by passage through two alkaline pyrogallol scrubs. A11 other inorganic chemicals were of reagent or C.P. grade and were used without further purification. Electrodes. Exploratory espeiinients indicated t h a t exceptionally pure graphite electrodes were needed. because even minute traces of contaminants caused noticeable polarographic waves. Therefore, Kational Carbon Co. Special Spectroscopic Grade electrodes (0.25-inch diameter) mere used. The rods were either coated Kith ceresin a a x (Fisher Scientific Co.) to insulate theni, or were soaked in molten ceresin wax a t 80’ C. for 1 hour, removed from the wax, allowed to cool thoroughly, and then coated with Seal--411 cement (Allen Products Corp.). Electrical contact 11-as made via a small mercury pool held in a short piece of rubber tubing on the upper end of the rod. Three varieties of external reference electrode and salt bridge were used. Reduction of silrer(1) and mercury(I1) was studied with a potassiuni nitrate salt bridge and either a saturated mercurous sulfate or a saturated calomel half cell. The other systems n-ere investigated 11ith a potassium chloride salt bridge and a silver-silver chloride
VOL. 30, NO.
10, OCTOBER 1958
1645
