aldehyde to determine the effect of fatty acids and ketones (Table 11). Of the ketones tested, diheptyl, dinonyl, and diundecyl showed no interference in concentrations up to 20%. Diheptadecyl ketone began to show some effect a t 10.5%. I n practice, the crude samples analyzed by the method rarely contained more than 10% by weight of ketone. Several reaction studies were made (Table 111) to determine the effect of time of the aldehyde determination. Thirty minutes is adequate for aldehydes up through dodecanal, but 60 minutes is needed for higher aldehydes. The end point is sharpened considerably by adding enough Formula 3 4 alcohol just before titrating to make the initial solvent a 1 to 1 alcohol-water miuture. The tendency of the reaction mixture to foam m-as effectively controlled by addition of Dow-Corning Antifoam A. Even jTith this addition, Cla and C18 aldehydes of high purity must be swirled for at least 5 minutes to control the violent foaming. The method has been used for routine control of aldehydes made from fatty acids. It is conceivable that some samples to which the method may be applied may contain esters. Under the alkaline conditions of the oxidation, esters would hydrolyze and consume
Table 111.
Aldehyde
Effect of Reaction Time
Reaction Time, Minutes
yo Aldehyde Found
(6) Fowler, Lewis, Kline, H. R., Mitchell, R. S., Ibid., 27, 1688 (1955).
(7) Frankfurter, G. B., West, R. J., J . Am. Chem. SOC. 27, 714-9 11905). Guenther, Ernest, Langenau, E. E., ANAL.CHEM.25, 12 (1953). Ihid., 27, 672 (1955). Hawthorne. M. F., Ibid., 28. 540 (1956). ' Homer, H. W.,J . SOC.Chem. I n d . 60,213-18 (1941). MacCormac, R.I.,Toxvnsend, D. T. A,, J . Chem. SOC.1940, 151-6;< Mitchell, J., Jr., ed., Organic ilnalysis," Vol. I, Interscience, Kew York, 1953. Mitchell, J., Jr., Smith, D. bl., !LNAL. CHEM. 22, 746-50 (1950). Ponndorf, W.,Ber. 64, 1913 (1931). Ruch, J. E., Johnson, J. B., ANAL. CHEhf. 28, 69 (1956). Satterfield, C. N., Wilson, R. E., LeClair R.M., Reid, R. C., Ibid.. 26. 1792 11954). (18) Schuite, K. E . , Storp, C. B., Fette u . Seifen 57, 36-42 (1955). (19) Ibid., 57, 600-4 (1985). (20) Siegel, H., Weiss, F. T., ANAL CHEM. 26, 917 (1954). (21) Siggia, S., Maxcy, W.,Ibid., 19, 1023-4 (1947). (22) Siggia, S., Segal, E., Ibid., 25, 640 (1953). (23) Siggia, S., Stahl, C. R., Ibid., 27, 1975 (1955). (24) Smith, W, T., Jr., Wagner, E. F., Patterson. J. 11.. Ibid.. 26. 155 (1954). \ - -
~
- 1
I
Dodecanal
5 1.i
30 60 Hexadecanal Octadecanal
D
30 GO 5
15
30 45 BO
120
97.3 98 .. 2 98.2 98.3 95 6 97.7 100.5 ~
82 8 89 0 91 4 92 2
96 3 96.3 96.5 96 5
caustic. A correction for esters could be obtained by running a saponification value. LITERATURE CITED
(1) Bailey, H. C., Xnox, J. H., J . Chem. SOC.1951, 2741-2. (2) Blank, O., Finkelbeiner, H., Ber. 31, 2979-81 (1898). (3) Ihid., 32, 2141 (1899). (4)Biichi, J., Pharm. Acta Helu. 6, 1-54 (19311. (5) Fdwler,Lewis, .ANAL. CHEM. 27, 1686 (1965).
.
RECEIVEDfor review March 19, 1957. Accepted June 24, 1957.
Densities and Refractive Indices for Glycol-Water Solutions Triethylene Glycol, Dipropylene Glycol, and Hexylene Glycol TSU-TAO CHIAO and A. RALPH THOMPSON Department of Chemical Engineering, University of Rhode Island, Kingston, R. 1.
b Analytical data which may b e used for determining compositions of aqueous solutions of three new glycols now available commercially-triethylene glycol, dipropylene glycol, and hexylene glycol-are presented. Densities a t 25" C. and refractive indices a t 20" and 25' C. were determined for mixtures of the highly purified glycols and water. Because of the points of inflection in two of the density-composition curves, usefulness of the density data for analytical purposes varies considerably with composition. The refractive index determinations give analyses accurate to within *O.l weight % in the case of all three glycols except for hexylene 1678 *
ANALYTICAL CHEMISTRY
glycol, for which the value is *0.4% above 95% glycol. Applicability of the Eykman equation was tested for the pure compounds a t 20' and 25' C. and found very satisfactory.
I
CONNECTION with a distillation project involving some of the newer glycols now available in commercial quantities, it was necessary to provide a simple but precise method for analyzing glycol-water mixtures. The glycols used were triethylene glycol, HOCzH40C2H40CzH40H; dipropylene glycol, O(CHaCHOHCHJ2; and hexylene glycol, also named 2-methyl-2,4-pentanediol or methyl amylene glycol, N
CHsCHOHCHzC(CH8)0HCH3. It was decided that both densities and refractive indices would be determined a t 25" C. over the entire composition range and that refractive index data at 20' C. would also be obtained. Although values of these properties have been reported in the literature (1) for the pure glycols, no data have been given for aqueous solutions. PURIFICATION
OF
MATERIALS
Pure grade triethylene glycol (99.7
+ %), dipropylene glycol (99.8 -t %),
+
and hexylene glycol (99.9 %) were fractionated at 10 to 15 mm. of mer-
~
cury absolute pressure and with a reflux ratio of 25 to 1 in an adiabatically operated packed column (1 inch in diameter and packed to a depth of 36 inches with 3/16-inchglass helices). As these materials are highly hygroscopic, it was necessary to take precautions to avoid the absorption of water (2, 5 , 6). The distillations were carried out in an entirely closed system and the distillate receivers were vented through drying tubes containing anhydrous activated alumina. Only the middle third of the constant boiling distillate was collected for making up the solutions. Reproducibility of the products was adequate, as evidenced by constancy of the physical properties. Despite precautions to prevent water contamination, the purified glycols contained small amounts of water as determined by means of the Karl Fischer reagent. The water contents, by weight, of the three purified products were as follows: triethylene glycol 0.02%, dipropylene glycol 0.03%, and hexylene glycol 0.04'%. Within the experimental limits, the values of density and refractive index reported for purified material are the same as for 100% pure glycols obtained by extrapolating to zero water content. The data obtained for these purified glycols may be compared with those previously reported as shown in Table I. Because of the purification procedure followed in this work, it is thought that the present values are to be preferred. The reason for wider variance in the case of dipropylene glycol is that three structural isomers are possible and no information is available on the ratio of isomers contained in the commercial products. PREPARATION OF SOLUTIONS
For each of the glycols, the purified material together with freshly boiled demineralized water (with a specific conductivity of approximately ohm-' cm.-I) was used to prepare nine solutions of various glycol concentrations from 10 to 90 weight %. These solutions of known composition were prepared by injecting approximate amounts of purified glycol and water into dried, stoppered, tared, 60-ml. vaccine bottles. The exact compositions were determined by weighing to 0.1 mg. Hypodermic syringes used to transfer the glycol were dried a t 110' C. and then allowed to cool in a desiccator until used. All solution compositions, based on amounts of material weighed and accuracy of the weighings, were known to a t least 1 part in 50,000 or 0.002 weight
~~
Table I.
Properties of Pure Compounds
Triethylene glycol Dipropylene glycol Hexylene glycol
Table
K t . 7c
Refractive Index, n~ A t 20°
.Authors 1 4558 1.4407 1.4275
II. Experimental Data Abs. Density, G./Ml. at 25' C.
At 20" C.
c.
Earlier' At 25' C..
data ( 1 ) 1.4559 1.4440 1.4263
authors ' 1.4541 1.4389 1.4257
R.I., n D At 25" C.
Triethylene Glycol Pure water 1
2 3 4 5 6 7
8
9 Purified T-glycol (0.02% H2O)
0
10.05 20.02 29.68 40.10 49.69 59.97 69.85 79.76 90.00
1.0117 1.0272 1.0426 1.0592 1.0740 1.0883 1.1000 1,1091 1.1155 1.1195
1 ,3330
1.3450 1.3573 1.3699 1.3835 1.3965 1.4102 1.4225 1.4343 1.4453 1.4558
1.3326 1.3444 I.3565 1.3689 1.3824 1.3952 1.4086 1.4208 1,4327 1.4437 1.4541
1.3330 1.3452 1.3578 1.3709 1 3836 1 3958 1.4071 1.4171 1.4261 1.4339 1,4407
1,3325 1.3446 1.3569 1.3698 1.3822 1.3940 1.4054 1.4154 I . 4244 1,4322 1.4389
1,3330
1.3325 1.3450 1.3580 1.3705 1.3819 1.3921 1.4014 1.4099 1.4172 1.4228 1 ,4257
Dipropylene Glycol Pure water 1
2 3 4 5 6 7 8 9 Purified D-glycol (0.03% H20)
0 10.00
20.00 29.97 39.99 49.69 60.07 69.94 79.76 89.47
1.0046 1.0131 1.0215 1.0288 1.0337 1.0359 1.0354 1.0323 1.0273 1.0165 Hexylene Glycol
Pure water 1
2 3 4
5 6 7 8 9 Purified H-glycol (0.0470 HZO)
0
9.98 19.95 30.00 40.01 49.92 60.04 69.89 80.02 89.89
0.9967 0.9972 0.9962 0.9918 0.9851 0.9764 0.9662 0.9538 0.9390 0.9181
DENSITY MEASUREMENTS
ity bottles which had been calibrated using boiled demineralized water. Temperature control was obtained by submerging the bottles to near the top of the stem in a Fisher Isotemp constant temperature bath maintained a t 25.00' f 0.01" C., as determined by a calibrated thermometer. Duplicate determinations were made on each solution. All m-eighings were reduced to values in vacuo and the absolute densities a t 25' C. were calculated as grams per milliliter. Expressed in these units, the density is numerically equal to the specific gravity a t 2.5' C. compared t o m-ater a t its maximum density (3.98' C.).
Density measurements were made in 10-ml. Weld-type capped, specific grav-
The experimental results for solutions of all three glycols with water are listed
%.
Density at 25O c., G./M.. Authors 1.1195 1,0165 0.9181
Specific Gravity, 20/20" c. Earlier duthors data (1) 1.1254 1.1254 1.0232 1.0252 0.9240 0.9234
1.3457 1.3588 1.3717 1,3833 1.3936 1.4032 1.4117 1.4190 1.4247 1.4275
in Table 11. Smoothed values, a t even composition increments, obtained from a large scale plot similar to Figure 1 are presented in Table 111. The maximum error resulting from uncertainties in the volume calibration of the specific gravity bottles was =kO.OOOl gram per ml. Because of the shape of the density-composition curves, the value of the density measurements for analytical purposes varies with the glycol concentration. The curve for triethylene glycol is similar to that found for diethylene glycol-water solutions by MacBeth and Thompson (6). Density measurements on solutions of this compound allow analysis to within 0.1 weight % in the composiVOL. 29, NO. 1 1 , NOVFMBER 1957
1679
tion range from 0 to 70 Iveight yo triethylene glycol. The curve for dipropylene glyco1,which shows a pronounced maximum, resembles the propylene glycol-water curve presented in another paper ( 5 ) . In the vicinity of the maximum in the density curve, the change in density with composition is relatively slight; hence, analysis by density is not satisfactory. Below approximately 25 weight % dipropylene glycol, density may be used in determining the glycol content to within *0.15 weight %. Hexylene glycol above 30% by weight exhibits a steady decrease in density as the glycol concentration is increased and density provides a basis for analysis to within 1 0 . 3 weight %. REFRACTIVE INDEX MEASUREMENTS
Refractive indices were measured by means of an improved precision Valentine refractometer, with compensating prism, and an incandescent light source. Values were readily determined to 0.0001 (Figure 2 and Table 11). By using a circulation pump connected from the constant temperature bath to the prisms of the refractometer, it was possible to maintain the desired temperature (either 20" or 25' C.) to =kO.Ol' C. For solutions of all three glycols, refractive index provides an analytical method which gives the glycol content to within approximately *O.l weight yo,except for hexylene glycol, for which the value is *0.4"/, above 95% glycol. The effect of temperature on the refractive index of these compounds is shown in Figure 3 . Within the limits of the measurements, all three purified glycols show a linear variation in refractive index with temperature over the range from 20" to 40" C. On checking the applicability of the Eykman equation, as recommended by Kurtz, Amon, and Sankin (S), it was found to give excellent checks for 20" and 25" C. for the three glycols. The Eykman equation is given by n2-1 n 0.4
+
0.9
20
0
40
100
Figure 1 . Absolute densities of aqueous glycol tions at 25' C.
0
TRIETHYLENE
solu-
GLYCOL
o DIPROPYLENE GLYCOL I I
I
1.32
40 WEIGHT % GLYCOL
20
0 Figure 2.
BO
100
Refractive indices of aqueous glycol solutions at 25'
a1 = c1
where n is the refractive index d is the density C1is a constant
J 1.450O-
Values of C, were calculated a t 20" and 25" C. and are given in Table IV. A simple empirical approximation suggested by Ward and Kurtz (7) for correcting the refractive index of hydrocarbons for small changes in temperature, An = 0.6 d, was found not to apply to the compounds used in the present investigation.
X
w
9- 1.440 W
>
1.430
a
E 1.420 I
1.410 20
ACKNOWLEDGMENT
The authors wish to express their appreciation to the Union Carbide Chem'j 680
80
60
WEIGHT % GLYCOL
ANALYTICAL CHEMISTRY
Figure 3. glycols
I 25
30 TEMPERATURE, 'C.
35
40
Effect of temperature on refractive index of pure
C.
Table 111.
Wt. % Glycol 0
10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 pure 0
10.00 20.00 30.00 40.00 50.00 60,OO 70.00 80.00 90.00 pure 0
10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 Pure
Table IV.
Smoothed Data
Abs. Density, G./MI. R.I., nn at 25" C. At 20" C. -4t 25" C. Triethylene Glycol 0.99707( 4 ) 1.3330 1.0117 1.3449 I.0271 1.3572 1.0431 1.3705 1,0591 1.3834 1.0745 1.3970 1.3956 1 ,0884 1.4103 1.4086 1.4226 1.4210 1.1001 1.4345 1.1092 1.4330 1.4453 1,1158 I.4437 1.4558 1,4541 1.1196 Dipropylene Glycol 0.99707( 4 ) 1.3330 1.0046 1.3452 1.0131 1.3578 1.0216 1.3709 1.0288 1 3836 1.0338 1.3962 1.0359 1.4071 1.0354 1.4171 1.0322 1.4263 1 ,0269 1.4343 1.0165 1.4407
1,3325 1.3446 1.3569 1.3698 1.3822 1,3944 I ,4054 1.4155 1.4246 1,4326 1.4389
Hexylene Glycol 0.99707( 4 ) 1.3330 0.9967 1 ,3458 0.9972 1 ,3589 0.9962 1.3717 0.9918 1.3833 0.9851 1.3937 0.9764 1.4032 0.9660 1.4118 1.4190 0,9539 1.4248 0.9389 1.4275 0.9181
1.4013 1.4100 1.4171 1.4228 1.4257
Applicability of Eykman Equation
Triethylene glycol Dipropylene glycol Hexylene glycol
Value At 20"C. 0,5369 0.5728 0.6156
of C,
At 25OC. 0.5369 0.5727 0.6160
icals Co., a division of Union Carbide Gorp., for contributing the samples of glycols used in this work. This project was supported by a grant from the Engineering Experiment Station of the University of Rhode Island. LITERATURE CITED
Curme, G. O., Johnston, F., "Glycols," ACS Monograph 114, Reinhold, Sew Tork, 1953. Fogg, E. T., Hixson, il. I., Thompson, A. R., ANAL. CHEM. 27, 1609 (1955). (3) Kurtz, S. S., Jr., Amon, S., Sankin, h., Znd. Eng. Chem. 42, 174 (1950). (4) Lange, K.A, "Handbook of Chemistry," 9th ed., Handbook Publ., Sandusky, Ohio, 1956. MacBeth, G., Thompson, A. R., ANAL.CHEM.23, 618 (1951). Zbid., 24, 1066 (1952). Kard, A. L.,Kurtz, S. S., Jr., IND. ENG.CHEM.,AXAL. ED. 1 0 , 573 (1938). RECEIVEDfor review April 18, 1957. Accepted June 15, 1957.
Chloric Acid Method for Determining Protein-Bound Iodine by Use of Iodine-131 JESSE F. GOODWIN, RICHARD B. HAHN, and A. J. BOYLE Department of Chemistry, Wayne State University, Detroit 2, Mich.
b A study of the loss of iodine-1 31 during the digestion of samples with chloric acid has shown that addition of chromate to the sample is unnecessary. Protein-bound iodine can b e separated from inorganic iodide by using either perchloric or trichloroacetic acid as a protein precipitant.
for the quantitative determination of protein-bound iodine have been reviewed by several workers ( 2 , 4,6). This study is concerned with losses of iodine related to modifications of the chloric acid method (1, 3, 5 ) for digesting samples. Chloric acid digestion makes it possible t o prepare a sample for analysis in a ETHODS
single container; this obviates losses of iodine during transfer. It has been reported that chloric acid mixed with small amounts of sodium chromate is the most satisfactory reagent for sample digestion because of its powerful oxidizing action a t relatively low temperatures. The effect of chromate in this digestion mixture has not been sufficiently investigated. Iodine-131 has been used in this study t o determine the usefulness of chromate in preventing iodine losses during chloric acid digestion. STANDARDIZATIONS OF TRACER SOLUTIONS
A tracer solution of iodine-131 was oxidized from sodium iodide to iodat,e
by boiling it nearly to dryness with 5 ml. of chloric acid and 10 mg. of sodium chromate. This preparation was cooled, the residue mas dissolved in 5 to 10 nil. of distilled water, and the solution volume was adjusted t o 25 ml. A welltype scintillation counter was used t o obtain 5-minute counts on 2-ml. aliquots of this solution. An average of 4900 counts per minute with a probable error of 1 8 8 counts per minute (1 I .76%) for the individual samples was found by counting six aliquots (Table I). Corrections were made for background count.
A more concentrated solution of iodine-131 iodate prepared and standardized. Six aliquots of this s o h tion gave an average of 21,878 counts VOL. 29, NO. 1 1 , NOVEMBER 1957
1681
