Some Applications of the Komarowsky Reaction STEPHEN DAL KOGARE AND JOHN MITCHELL, J R . Polychenticals Department, E. Z. du Pont de Nemours & Co., Znc., Wilmington, Del.
A study of the Komarowsky reaction was undertaken initially to determine the value of this colorimetric technique for the determination of glycol impurities in ethylene glycol. The colorimetric procedure which was evolved proved suitable for the measurement of 1,2-propylene glycol in the presence of ethylene glycol. Several other glycols, monohydric alcohols, ketones, and aldehydes were tested to determine the suitability of the method for their analysis. In addition to the glycol determination, applications of the method are reported for the analysis of cyclohexanol-cyclohexanonem i x tures and for isovaleraldehyde in succinic acid. The colorimetric reaction is limited in its practical application to simple binary or ternary systems in which the measured component is present in small amounts and the major component does not react to give a colored product with the reagent.
S
EVERAL colorimetric procedures for the estimation of the hydroxyl group have been reported in the literature. Of
these, the reaction between aromatic aldehydes and alcohols, known as the Xomarowsky reaction (6), is perhaps the most widely used. Essentially all of the published procedures which employ this color reaction have dealt with the estimation of monohydric compounds by reaction with vanillin, benzaldehyde, salicylaldehyde, or p-dimethylaminobenzaldehyde. Penniman and coworkers ( 7 ) and Coles and Tournay ( 1 ) employed one of these aldehydes in a sensitive test for higher alcohols in distilled liquors. However, no reports have been published on the application of the Komarowsky reaction to the determination of glycols or other types of compounds. Initial research indicated that vanillin could be used as reagent for the colorimetric determination of some glycols and alcohols. However, studies with other aromatic aldehydes demonstrated that p-hydroxybenzaldehyde gave more stable and reproducible colors. Conditions were established in which the reaction product of ethylene glycol showed no significant color, while purplecolored solutions were obtained vithother glycols. These observations led to the development of a colorimetric procedure for the determination of I,2-propylene glvcol in ethylene glycol. The reaction also was found suitable for the analysis of many other systems. Briefly, the method consists of treating the sample at 100" C. with p-hydroxybenzaldehyde and aqueous sulfuric acid for an optimum time period. After dilution, the color of the solution is read with a spectrophotometer, and the concentration of the desired component is calculated from a calibration curve.
to room temperature, the liquid was transferred to a 25-ml. volumetric flask, and the tube was rinsed R-ith three 5-ml. portions of 1to 1 sulfuric acid. After dilution to the mark with 1 to 1 sulfuric acid, the absorbancv of the final solution was measured at 540 mu in 1-cm. Corex cell; against a blank. The blank, containing 3 ml. of water plus the reagents, was treated in the same manner as the sample. Absorbancy measurements vere made within 1 hour after dilution. The 1,2-propylene glycol content mas then determined from a reference curve plotted with data obtained from k n o m mixtures. DISCUSSION
The data obtained with 1,2-prop)-lene glycol, which gives a strong color reaction, and ethylene glycol, which gives a negligible color, illustrate the conditions necessary for maximum color development. Typical ahsorption sprctra for the purplccolored
I3
"4
1
PROCEDURE FOR 1,Z-PROPYLEKE GLYCOL IN ETHYLENE GLYCOL
Reagents. Eastman Kodak Co. No. 985 p-hydroxybenzaldehyde was twice recrystallized from hot water. The pink crystals were dried in an oven a t about 105" C., ground to a fine powder, and stored in an air-tight container. Apparatus. A Beckman Model DU spectrophotometer equipped with a tungsten light source and 1-cm. Corex cells was used in this work. Procedure. An aqueous solution of an accurately weighed quantity of the sample mas prepared so that 1 to 3 ml. contained between 0 and 0.2 mg. of 1,2 propylene glycol and no more than 10 mg. of ethylene glycol. One to 3 ml. of the solution was transferred to a 1 X 8 inch test tube containing 30 & 1 mg. of p hydroxybenzaldehyde. If necessary, additional mater was added to make a total volume of 3 ml. of water in the tube. The contents were mixed by swirling the tube, and 5 ml. of concentrated sulfuric acid was added slowly. The tube was shaken carefully until the solution cleared, then placed in a boiling water bath for 30 minutes. After the solution had cooled spontaneously
WAVE LENGTH-
mp
Figure 1. Absorption Spectra of Blanks and of 1,2Propylene Glycol-p-Hydroxybenzaldehyde Reaction Product 1 and 3. 2.0 ml.of HzO 2. 3.0 d. of H20 4. 2.25 ml. of HzO 5. 2.5 ml. of H10 6. 3.25 ml.of H20
1376
V O L U M E 2 5 , NO. 9, S E P T E M B E R 1 9 5 3
1377
reaction product of 1,2-propylene glycol and p-hydroxybenzaldehyde are shown in Figure 1. The strong maximum a t 494 mp is a function of the water content of the reaction mixture, since it occurs in both the sample (curves 3 to 6) and blank spectra (curves 1 and 2). When less than 2 ml. of water is present in the mixture, this maximum almost disappears as seen from curves 1 and 3 of Figure 1. The absorption at 540 mp is a measure of the color resulting from the reaction and is rather insensitive to variations in water content. This is more clearly shown in Figure 2. This curve was obtained by plotting total water content of the reaction mixture against the absorbancy a t 540 mp. Less than 2.5 ml. or more than 3.25 ml. of miter results in decreased absorbancy, while a relatively constant color is obtained between these limits.
-
3
2 0.4 v
0.3
-
0.P
-
0.1
1 '
2.0
Intensity No color (10mg.) h-o aolor Intense Strong Intense Strong Intense Strong Weak
linear (Figure 3), such curves must be drawn in order to calculate quantitative analytical results. The sensitivity of the color reaction can be estimated from Figure 3; as little as 0.01 mg. of propylene glycol can be detected easily. Heating Time. Further investigations proved that the time of heating also is a factor in the reproducibility of the method. The curves in Figure 4 show that the maximum color is developed only after heating for 30 minutes in a boiling water bath. Heating for a total of 45 minutcs causes no appreciable change, but longer heating causes a decrease in color intensity. Heating a reagent blank for periods up to 45 iii nutes results in no change in absorbancy, but further heating produces a significant increase. The purple dye formed in the reaction of hydroxy compounds with p-hydroxybenzaldehyde is sensitive to water. The purple compound is stable only in strong sulfuric acid. When water alone is used as a diluent after the reaction, a purple precipitate forms which, on standing, redissolves to give a colorless solution, indicating that the colored reaction product is not water-soluble and is easily hydrolyzed. In 1 to 1 aqueous sulfuric acid the color is fairly stable. Even in this solvent, however, a decrease in color of approximately 4 and 10% is observed after 5 and 24 hours, respectively.
0
t
2.5
3.0
TOTAL WATER CONTENT
Figure 2.
Color Reaction w i t h Glycols
Compound Ethylene glycol Diethylene glycol 1,2-Propylene glycol dl-Glyceraldehyde 2,3-Butylene glycol Pentamethylene glycol 2 4-Amylene glycol Hexamethylene glycol Glycerol
BLANK 0
I O
0.
Table I.
-
I
J
3.5
4.0
MILLILITERS
Effect of Water on Absorption at 540 m p
Meet of Hydrogen Ion. rlpparently the reaction is not catalyzed by hydrogen ion. KO colored product was evident from ekperiments in which various dilute acids were used to develop the color. Instead, the high concentration (about 70%) of sulfuric acid which is required suggests that the colored products arise from dehydration or condensation reactions between the hydroxy compound and the aromatic aldehyde. This observation is in agreement with the suggestions of Fellenberg (5) and of Duke (4). The former postulated the intermediate formation of olefins by dehydration of the hydroxy compounds, and the latter author proposed a condensation mechanism involving foimation of carbonium ions followed by coupling to form colored reaction products. Reagent Concentration. .hiother critical variable in the colorproducing reaction is the concentration 01 p-hydioxybenzaldehyde. Figure 3 shows the effect of increasing thic i+agent from 20 to 50 mg. in the reaction mixture With >n;ieasing concentrations the absorbancy :it 540 mp also is increased. This observation is surprising because a t the 20-mg level the molar ratio of p-hydroxybenzaldehyde to the glycol is considerably greater than 50 to 1 . This effect permits some control of the sensitivity of the analytical method. As might be expected, an increase in the amount of p-hydroxvbenzaldehyde is accompanied by an inCI pase in the blank absorption In this investigation, 30 my of p-hydroxybenzaldehyde was selected as a convenient amount which gave blank absorbancy values from 0.05 to 0.07. Because the calibration curves are non-
1.3
-
I..?
-
/ . I
-
0
ho * O MG'
0.05
0.10
0.I5
I,P- PROPYLENE GLYCOL- MILLIGRAIIS
Figure 3. Effect of Quantity of p-Hydroxybenzaldehyde on Intensity of Color
Other Compounds. I n addition to 1,2-propyIene glycol, several other glycols were studied. Results on 1-mg. samples are given in Table I. All of the glycols exhibited the same type of spectrum with only minor displacement of the absorption maximum in the 540 mp region. The maxima ranged from 540 to
ANALYTICAL CHEMISTRY
1378 565 mw. Pieither ethylene glycol nor diethylene glycol reacted to give a significant color. These results together with the observation that nearly colorless products are obtained from methanol, ethanol, and methyl Cellosolve (see Table 11) indicate that the purple dye is obtained only with hydroxy compounds containing more than two uninterrupted carbon atoms. /.I
Table 11. Color Reaction with Monohydric Compounds (1 Mg.) Methanol Methanol Ethanol Methyl Cellosolve 1-Propanol 2-Propanol 1-Butanol 2-Methyl-I-propanol 2-Methyl-2-propanol Cyclohexanol Phenol Benzyl alcohol Picric acid
_1
0.170 mg. RG. 1.0
-
0.9
-
Intensity S o color
No color No color Weak Very weak
Weak Intense Intense Strong Very weak (ppt.) N oo color
______Table 111. 1,2-Propy-lene Glycol in Ethylene Glycol
0.8
1,2-Propylene Glycol Found, 76 18.1
-
Sample Weight, h l g . 0 5@4 0 504
0.6
-
7.9 7 9
1.18 1 18
8.1 7.6
0.5
-
0.0 0.0
I 12 1 12
0.0 0.0
0.057 mg. RG.
8
52
0.113mg.RG.
1,2-Propylene Glycol, % a 18.1 18.1
0.7
L 0 p
-
0.4
a
17.4
Remainder ethylene glycol.
/------O
O------l
0.30.P
-
0.1
-
0.5
0 ' /5
Figure 4.
30 45 HEATING TIME- MINUTES
60
Effect of Heating Time on Color
Varying amount9 of 1,2-propyleneglycol
Other types of compounds also were studied. The results with several monohydric compounds are shown in Table 11. Positive reactions with p-hydroxybenzaldehyde also were obtained with the following ketones: acetone, methyl ethyl ketone, ethyl isopropyl ketone, and cyclohexanone. Formaldehyde did not produce a purple dye, but acetaldehyde and propionaldehgde gave positive reactions. Other ketones and aldehydes also probably give colored reaction products. The lower aliphatic acids did not react, nor did their methyl, ethyl, and n-propyl esters.
s
0.4
8 8 0.3 k
9
0.2
0.I
500
APPLICATIONS
Determination of 1,2-Propylene Glycol in Ethylene Glycol. Ethylene glycol failed to give a colored product (Table I). Consequently, a method became available for the direct estimation of certain other glycols in ethylene glycol. Application of the new colorimetric procedure to the determination of 1,2-propylene glycol in ethylene glycol gave the analytical results shown in Table 111. In this case, known binary solutions were prepared from the purified glycols. The ethylene glycol was 99.6% pure and the propylene glycol 96% pure as determined by the acidimetric periodate procedure (3) and by the iodoform method ( 2 ) , respectively. The large proportion of ethylene glycol present in these samples did not interfere with the analysis for l,2-propylene glycol. Determination of Cyclohexanol and Cyclohexanone in Cyclohexane. The analytical procedure used for the determination of 1,Spropylene glycol in ethylene glycol was found equally satisfactory for the simultaneous determination of concentrations (in parts per million) of cyclohexanol and cyclohexanone in cyclohexane solutions. The hydrocarbon solvent did not interfer e with color formation. Apparently cyclohexanol and cyclo-
Figure 5.
550 600 650 WAYE L Eh'GlH mp
-
700
-4bsorption Spectra of Cyclohexanol and Cyclohexanone Reaction Products 1. 2.
CycIohexanone Cyclohexanol
hexanone are extracted into the sulfuric acid-water layer where they are converted into colored products. The dye resulting from each of these compounds exhibits a characteristic absorption maximum, as shown in Figure 5. Both cyclohexanol and cyclohexanone show a maximum at 535 mp. At 625 mp, however, absorption by cyclohexanone is almost negligible. Consequently, it is possible to calculate the composition of mixtures by means of simultaneous equations. In Table IV are listed the results obtained with four synthetic mixtures of cyclohexanol and cyclohexanone in cyclohexane. This application illustrates the remarkable sensitivity of the phydroxybenzaldehyde reagent for small amounts of these compounds. I t is of interest to note that 1 ml. of cyclohexane containing about 3 p.p.m. of cyclohexanone and 3 p.p.m. of cyclohexanol will have an absorbancy of 0.6 at 535 mp and 0.4 a t 625 mp.
V O L U M E 25, NO. 9, S E P T E M B E R 1 9 5 3 Table IV. Determination of Cyclohexanol and Cyclohexanone in Cyclohexane" Cyclohexanol Cyclohexanone Added, P.P.M. Found, P.P..M. Added, P.P.M. Found, P.P.M. 1.0 1.6 4.2 3.8 2.3 2.5 3 3 3.5 3 5 2.1 1 5 3.8 4 6 4 3 14 1 3 a One milliliter of cyclohexane aolution mas taken as sample -
_____ _ ~ _ _ ~. . Analysis for Isovaleraldehyde in Succinic kcid ~
Table V.
Absorbancy at 550 nip 0.095 0.243 0.328 0.653 0.785
Isovaleraldehydr. 3Iole '7c Added Found 0.011
0.012
0.033 0.044
0.034 0.046 0.093 0.I14
0.088
0.110
1379 of relatively large quantities of pure succinic acid. Some results from this application are presented in Table V. Concentrations of 0.01 to 0.1 mole % of aldehyde in the acid were determined with good accuracy. In all cases 100-mg. samples of the succinic acid were taken. These results were obtained after reference to a calibration curve obtained with pure isovaleraldehyde. CONCLUSIONS
Although the Komaron-sky reaction is not highly specific. it provides a rapid and reasonably precise means of analysis for those cases in which it can be applied. Generally, these comprise simple binary systems in which the major component does not react. More complicated mixtures may be analyzed if the absorption maxima of the components are sufficiently separated as was shoirn for mixtures of cyclohexanol and cyclohexanone in cyclohexane. ACKNOWLEDGMENT
The data in Table IC indicate that cyclohexanol can be measured with greater accuracy than cyclohexanone, because of the correction for cyclohexanol incorporated into the calculation for cyclohexanone. The interesting observation was made that the cvclohexanol color disappeared on dilution with water, whereas the cyclohexanone color persisted. This could be incorporated into the analytical procedure with resulting simplification of the calculations. Determination of Isovaleraldehyde in Succinic Acid. The Komarowsky reaction may be used for the measurement of small amounts of various aldehydes in the presence of organic acids which do not give a positive color test. The present analytical procedure was used to determine isovaleraldehyde in the presence
The authors wish to acknowledge the valuable assistance of Ella Mae Gardner and Anne Greco in obtaining many of the data reported in this paper. LITERATURE CITED
(1) Coles, H. W., and Tournay, W. E., IND.ENG.CHEM.,ANAL.ED., 14,20-2 (1942). (2) Dal Kogare, S., Korris, T. O., and Mitchell, J., Jr., ANAL.CHEZI., 23. 1473-8 119513. (3) Dal kogare, S:, and Oemler, A. N., Ibid., 24, 902 (1952). (4) Duke, F. R., Ibid., 19,661-2 (1947). (5) Fellenberg, T. von, Mitt.Gebiete Lebensm. u. Hyg., 1, 311 (1910). (6) Komarowsky, A., Chem.-Ztg., 27,807, 1086 (1903). (7) Penniman, W. B. D.. Smith, D. C., and Lawshe, E. I., IND.ESG. CHEM.,AKAL.ED.,9,91-5 (1937). RECEIVED for review January 9, 1953. Accepted .June 18, 1953.
Experimental Ebullioscopic Constants Variation with Molecular Weight of Solztte and Type of Solvent GLIDE i. GLOVER AND CIIkRLO'I'TE: P . HILL Research Laboratories, Tennessee Eastnian Co.. Kingsport, Tenn.
Recently, techniques for measuring small temperature differences in ebullioscopy have been greatly improved. As a result, ebullioscopic molecular weight determinations have been refined to an extent which justifies a critical consideration of the ebullioscopic constant, &. The constant was measured in several of the more common solvents for molecular weight determination with a group of randomly selected solutes ranging in molecular weight from 110 to 891. Only in the case of relatively polar solvents was I
