September15,1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
methods are satisfactory for waters whose residues consist essentially of calcium and magnesium. The conditions for most accurate estimation exist when the fluorine is between 0.05 and 1.5 per cent of the residue. LITERATURE CITED (1) Churchill, H. V., IND.ENQ.CHEW, 23, 996-8 (1931). (2) Dean, J. Am. Dental Assoc., 20, 319 (1933). (3) Dean, U. S. Pub. Health Serv., Pub. Health Rept. 48, (1933). (4) Kempf, G. A., and McKay, F. S., Ibid., 45, 2923 (1930).
703
345
(5) Kolthoff, I. M., and Stansby, M. E., IND.ENG.CHEM.,Anal. Ed., 6, 118-23 (1934). (6) Papish, J., Hoag, L. E., and Snee, W. E., Ibid., 2, 2 6 3 - 4 (1930). (7) Sanehis, J, M,, Ibid., 6, 134-5 (1934). (8) Sebrell, Dean, Elvore, and Breaux, U. S. Pub. Health Serv., Pub. Health Rept. 48, 437 (1933). (9) Smith, M. C., Lana, E. M., and Smith, H. V., Univ. Aria. Coll. Agr., Tech. Bull. 32 (1931). (10) Thompson, T. G., and Taylor, H. J., IND.ENQ.CHEM,Anal. Ed., 5, 87-9 (1933). (11) Willard, H. H., and Winter, 0. B., Ibid., 5, 7-10 (1933). RFJCEIYED January 30, 1934.
Analytical Uses of %Propanol G. W. FERNER AND M. G. MELLON, Purdue University, Lafayette, Ind. I n considering 2-propanol as a substitute for ethanol in analytical procedures there are relatively few unfavorable factors. There is very little difference in the physical properties of the two alcohols. As a solvent for analytical reagents, particularly organic reagents, 2-propanol is a satisfactory substitute for ethanol. For inorganic reagen's in rather high concentrations the absolute alcohol must be used, since two liquid phases are formed with the constantboiling mixture. As a reagent for the qualitative detection o j certain elemen's or radicals 2-propanol is not effective,
T
HE extent and variety of the uses of ethanol in analytical chemistry, indicated in a preliminary paper ( 7 ) , include the preparation of materials for analytical work, such as analytical devices, reagents, and samples; and the determination of constituents, involving reactions such as the separation of materials, the reduction of the solubility of precipitates, and the removal of adhering liquids. In view of the cost of ethanol (including tax) and of the inconvenience of the precautions necessary to prevent its diversion, it would be of advantage to find a suitable substitute. The selection of such a substitute should be made on the basis of low cost and of similarity in properties. Of the lower members of the series of aliphatic alcohols having physical and chemical properties similar to those of ethanol, 2-propanol is most nearly like ethanol. It is completely mi+ cible with water and recent commercial production has brought the price considerably lower than that of taxed ethanol. The data in Table I, obtained from International Critical Tables, indicate the great similarity in the properties of these two compounds.
TABLE I.
PHYSICAL PROPERTY Boiling points, at 760 mm. Heat of combustion
Heat of vaporization at boiling point Va or gressure at 200 C. Refractive index. Na D line Surface tension at 20' C. Viscosity
PROPERTIES OF ETHANOT, AND 2-PROPANOL ETHANOL 2-PROPANOL 100% CzHsOH 78.4' 100% CaHiOH 82.26" C. B. CzHsOH,' 78.15' C. B. CSHIOH,'80.37' 328 kg.-cal./mole 474.8 kg.-cal./mole 7.13 kg.-cal./grem 7 . 9 1 kg.-cal./gram 855 joules/ ram 4 3 . 9 mm. f i g
667 i 2% joules/pram 3 2 . 4 mm. Hg
1.36242 at 18.35' C. 22.27 0.1 1.716 X 10-2
1.37757 at 20' C. 2 1 . 7 ;t 0 . 3 2.101 x 10-2
*
As a laboratory reagent 2-propanol has had some application. Griffin (10) successfully substituted it for ethyl alcohol in histological work, the preparation of reagents, and general laboratory use. Gilson (8) states, "During several years of
especially where the chemical properties of the alcohol are sign6cant. Thus the flame test f o r boron and the ester test for acetatesfail to work with 2-propanol. Certain inorganic compounds can be separated with 2-propanol. The advantage of the lower solubiliy of salts in 2-propanol is canceled by the decreased solubility of the soluble as well as fhe insoluble salt. However, 2-propanol is a satisfactory substitute for ethanol in this type of separation, and can be used in determinations to decrease the solubility of precipitates, and as a washing medium for precipitates. biochemical research the writer has found many instances where isopropanol could be substituted for ethanol in laboratory work. It is cheap and there are no restrictions governing its use, nor is it likely to be an object of theft." Schuette and Smith (18),using 2-propanol in the determination of acid numbers, obtained more satisfactory results than with ethanol. Schuette and Harris (17) made the same substitution in the determination of saponification numbers, using 2propanol in the preparation of solutions of potassium hydroxide. In references to the use of %propanol as a substitute for ethanol, there are few data of value in predicting its applicability as an analytical reagent. Neither International Critical Tables nor Seidell's "Solubilities of Inorganic Compounds" contains any appreciable amount of information regarding the solubility of inorganic salts in isopropyl alcohol, data which would be of importance in predicting the behavior of the reagent in inorganic analysis. Four articles have recently been published regarding the solubility of compounds in %propanol. Kim and Dunlap (IS) studied the solubilities of the alkali chlorides and sulfates in anhydrous alcohols, including isopropyl alcohol. These salts are slightly more soluble in ethanol than in 2-propanol. Ginnings and Chen (9) investigated the ternary systems, water, 2-propanol, and salts, obtaining qualitative results with seventy-five common inorganic salts and quantitative results with ten salts. Hopkins and Quill ( l a ) , in a study of the use of nonaqueous solvents in the rare earth group, stated that isopropyl alcohol is a very poor solvent for the rare earth chlorides. In determining the solubility of silver bromate in mixtures of alcohols and water Neuman (15) found that the values in mixtures of isopropyl alcohol and water fall between those in ethanol-water mixtures and those in n-propanol-water mixtures.
ANALYTICAL EDITION
346
TABLE11. DETERMINATION OF NICKEL AND COPPER
Vol. 6, No. 5
alpha-benzoinoxime were prepared in 91 per cent 2-propanol and 95 per cent ethanol. The dimethylglyoxime was prepared as a 1per cent solution and the other two reagents as 2 ELEMENT AMOUNT DET~RMINED PRESENT FOUND per cent solutions. No difficulty was encountered in preparNickel with 0.0564 0.0559 0.0560 ing solutions of this concentration, although the reagents disdimethyl0.0559 0.0560 glyoxime 0.0559 0.0560 solved more slowly in the 2-propanol than in ethanol, Av. 0.0559 Av. 0.0560 In order to determine whether there might be any difference Copper with 0.1052 0.1054 0.1054 8-hydroxy0.1052 0.1053 in the effect of 2-propanol and ethanol on the actual determiqmnoline 0.1053 0.1054 Av. 0.1053 Av. 0.1054 nations, the solutions of dimethylglyoxime were used for the precipitation of nickel and those of 8-hydroxyquinoline for the TABLE111. SOLUBILITY OF SODIUM AND POTASSIUM CHLORIDESprecipitation of copper, with the results shown in Table 11. IN ETHANOL In the case of inorganic reagents the application of 2(Grams of salt per 100 grams of solvent) propanol as a solvent is somewhat limited by the fact that it is P ~ CRNT R ALCOHOLBY WEIQHT salted out by many inorganic compounds. This eliminated SALT TEMP. 86.4 89.6 92.3 96.9 100 the 91 per cent alcohol from consideration except for dilute c. solutions of reagents. Absolute 2-propanol has been used 0.0432 0.0263 0.1413 0.0865 KCI 16 . . .. 0.0860 0.0431 0.0268 0.2256 0.1415 as a solvent for potassium hydroxide by Schuette and Harris 0.0502 0.0291 0.1744 0.1085 25 0.2777 KC1 (17) and Schuette and Smith (18)in the determination of acid 0.2780 0.1743 0.1082 0.0499 0.0286 35 0.3139 0.1997 0.1203 0.0599 0.0325 KCI and saponification numbers. The latter authors state that a 0.3130 0.1992 0.1212 0.0605 0.0326 yellow color can be avoided by allowing solution to take place 0.1187 0.0657 0.3712 0.2369 NaCl 16 0.5771 0.0656 0.2346 0.1179 0,5763 0.3710 without the application of heat. In the present work a 0.2671 0.1221 0.0657 NaCl 25 0.6414 0.4184 yellow color appeared with 2-propanol after a relatively short 0.2669 0.1218 0.0658 0.6420 0.4179 time in a 0.5 N solution of this base, although no heat was 0.1338 0.0667 0.4345 0.2708 35 0.6582 NaCl 0.1331 0.0666 0.4345 0.2705 0.6590 applied to hasten solution. The color developed when the solution was stored in the dark as well as in the light. HowTABLEIv. SOLUBILITY O F SODIUM AND POTASSIUM CHLORIDES ever, a 0.1 N solution prepared in a similar manner remained I N %PROPANOL colorless. The hydroxide dissolves more slowly in 2-propanol (Grams of salt per 100 grams of solvent) than in ethanol. -PER CENTALCOHOLBY WEIQHUSE IN QUALITATIVE TESTS. In certain qualitative tests SALT TEMP. 87.7 92.6 96.5 100 for chromates, borates, and acetates, ethanol is used as a 0 c. ~. 0.0023 0.0284 0.0078 16 0.1099 KC1 reagent or as a solvent for a reagent. In order to test the 0.0029 0.0289 0.0071 0.1092 suitability of 2-propanol for this purpose the tests were 0.0084 0.0026 25 0.1279 0.0300 KC1 0.0085 0.0029 0,1281 0.0296 carried out in duplicate, using ethanol in one case and 235 0.1494 0.0362 0.0102 0.0029 KC1 propanol in the other. 0.1495 0.0366 0.0107 0.0029 16 .0.2647 0.0645 0.0175 0.0040 The test for chromates depends upon the reducing action of NaCl 0.2652 0.0649 0.0164 0.0039 alcohol on sexivalent chromium to form green tervalent 25 0.2810 0.0632 0.0157 0.0041 NaCl chromium. For this test 2-propanol was as satisfactory as 0.2813 0.0629 0.0166 0.0041 NaCl 35 0.2968 0.0697 0.0183 0.0031 ethanol, using the procedure recommended by Curtman (3). 0,2967 0.0705 0.0184 0.0029 Two tests for borates are given by Curtman. One is the common flame test which indicates the presence of borates by EXPERIMENTAL WORK a green coloration imparted to the burning alcohol. When 2propanol is used, a satisfactory coloration is not obtained PREPARATION OF MATERIALS.The constant-boiling alcohols were purified by a single distillation of the commercial because of the smokiness of the flame, which obscures the product through a 40-cm. Vigreux distilling column. The 2- slight green color. The lack of color may also be due to the propanol had a density (dt6) of 0.8120, corresponding to an lower volatility of the isopropyl ester. The turmeric test 87.7 per cent solution by weight; the respective values for described by the same author is successful with both ethanol the ethanol were 0.8062, and 92.3 per cent. The 98 to 99 per and 2-propanol. However, the test is not as sensitive with cent commercial alcohols were dehydrated by refluxing for 24 the latter alcohol, no color being produced with a 0.01 per cent hours over calcium oxide. At the end of this period they solution of borax, while ethanolic solutions of turmeric did were distilled through the 40-cm. column. The density (dt6) produce a color a t this concentration. The acetate test as given by the U. S. Pharmacopeia (22) of the %propanol was 0.7807 and that of the ethanol 0.7846. The salts used for the determination of solubilities were depends upon the formation of the acetic acid ester of the purified by double recrystallization. The reagents used were alcohol used. This test is not successful with 2-propanol, presumably because the alcohol is unstable in the presence of prepared from the usual reagent quality chemicals. GENERALUSE, The use of alcohol in the preparation of concentrated sulfuric acid (20). analytical devices depends almost entirely upon its physical QUANTITATIVE USES properties. No experimental work was done with 2-propanol I n the presentation of the experimental results for the in this connection; however, there seems to be no reason why it should not be used in cleaning apparatus, in washing cru- quantitative determinations employing 2-propanol as a recibles, and in similar ways, since its physical properties are agent the details of the procedures used are not included, because in most cases they are readily available in the literamuch like those of ethanol. USE AS A SOLVENT. Quite frequently the organic reagents ture. In general, the determinations were run in triplicate used in analytical work are insoluble in water. In such cases with each alcohol, six aliquot portions being taken from a the most common solvent is ethyl alcohol. Unless the pres- solution of a salt of the constituent to be determined. In ence of Spropmol has a detrimental effect in determinations some cases the strength of the stock solution was determined where alcoholic solutions of reagents are used, the only ques- by an analysis of a third set of triplicates, and in other cases tion as to its applicability is its ability to dissolve the reagents. the solution was prepared by direct weighing and dilution t o Solutions of dimethylglyoxime, 8-hydroxyquinoline, and definite volume of a twice recrystallized salt. ETHANOL SOLUTION OB REAQENT
~
7 -
O
%PROPANOL
SOLUTION OP REAQENT FOUND
-
