G. W . Fe r n e r a n d M . G. Me l l o n, Purdue U n iversity, L afayette, Ind.
I n considering 2-propanol as a substitute fo r ethanol in analytical procedures there are relatively fe w unfavorable factors. There is very little differ
ence in the ph ysical properties of the two alcohols.
/I s a solvent fo r analytical reagents, particu larly organic reagents, 2-propanol is a satisfactory sub
stitute fo r ethanol. For inorganic reagen's in rather high concentrations the absolute alcohol must be used, since two liqu id phases are form ed with the constant- boiling mixture.
A s a reagent fo r the qualitative detection o f certain elem en’s or radicals 2-propanol is not effective,
especially where the chemicdl properties o f the alcohol are significant. Thus the flam e lest fo r boron and the ester lest fo r acetates f a il to work with 2-propanol.
Certain inorganic compounds can be separated with 2-propanol. The advantage o f the lower solubili'y o f salts in 2-propanol is canceled by the decreased solubility o f the soluble as well as the insoluble salt. However, 2-propanol is a satis
factory substitute fo r ethanol in this type o f separa
tion, and can be used in determ inations to decrease the solu bility of precipitates, an d as a washing m edium fo r precipitates.
T
H E 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 determ ination 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 th e cost of ethanol (including tax) and of the inconvenience of the precautions necessary to prevent its diversion, it w'ould be of advantage to find a suitable substi
tu te . The selection of such a substitute should be made on th e basis of low cost and of sim ilarity 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. I t is completely mis
cible with water and recent commercial production has brought th e price considerably lower than th a t of taxed ethanol. The d ata in Table I, obtained from International Critical Tables, indicate the great sim ilarity in the properties of these two compounds.
T a b l e I. P h y s i c a l P r o p e r t i e s o f E t h a n o l a n d 2 - P r o p a n o l
PbO P E R T T
Boiling p o ints, a t 760 mm.
H e at of com bustion H eat of v ap orization a t
boiling point Vapor pressure a t 20° C.
R etractiv e index. N a D line
Surface tension a t 20° C.
Viscosity
E t h a n o l
100% C tH iO H , 7 8 .4 ° C. B. CjHlOH, 7 8 .1 5 ° 328 kg.-cal./m ole 7 .1 3 kg.-cal./gram 855 jo u les/g ram 4 3 .9 m m . Hg 1.36242 a t 18.35' 2 2 .2 7 ± 0 . 1 1.716 X IO " 1
C.
2 - P r o p a n o l
100% CiHtOH , 82.26°
C. B. CjHjOH, 80.37°
47 4 .8 kg.-cal./m ole 7 .9 1 k g.-cal./gram 667 ± 2 % joules/gram 3 2 .4 mm. Hg 1.37757 a t 20° C.
2 1 .7 db 0 .3 2.1 0 1 X 10-*
■ As a laboratory reagent 2-propanol has had some applica
tion. 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
biochemical research the writer has found m any instances where isopropanol could be substituted for ethanol in labora
tory work. It is cheap and there are no restrictions govern
ing its use, nor is it likely to be an object of th e ft." Schuette and Smith (IS), using 2-propanol in th e determ ination of acid numbers, obtained more satisfactory results th a n with ethanol. Schuette and H arris (17) made the same substitu
tion in the determ ination of saponification numbers, using 2- propanol in the preparation of solutions of potassium hy
droxide.
In references to the use of 2-propanol as a su bstitute for ethanol, there are few d a ta of value in predicting its applica
bility as an analytical reagent. N either International Critical Tables nor Seidell’s “ Solubilities of Inorganic Com
pounds” contains any appreciable am ount of inform ation regarding the solubility of inorganic salts in isopropyl alcohol, d ata which would be of importance in predicting th e behavior of the reagent in inorganic analysis.
Four articles have recently been published regarding the solubility of compounds in 2-propanol. K im and D unlap (13) studied the solubilities of th e alkali chlorides and sulfates in anhydrous alcohols, including isopropyl alcohol. These salts are slightly more soluble in ethanol th a n in 2-propanol.
Ginnings and Chen (9) investigated th e 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 (12), in a stu d y of the use of nonaqueous solvents in th e rare earth group, stated th a t isopropyl alcohol is a very poor solvent for the rare earth chlorides. In determining the solubility of silver brom ate in mixtures of alcohols and w ater N eum an (15) found th a t the values in mixtures of isopropyl alcohol and w ater fall between those in ethanol-water mixtures and those in n-propanol-water mixtures.
346 A N A L Y T I C A L E D I T I O N Vol. 6, No. 5 cent commercial alcohols were dehydrated by refluxing for 24 hours over calcium oxide. A t the end of this period they were distilled through the 40-cm. column. T he density (d j5) of the 2-propanol was 0.7807 and th a t of the ethanol 0.7846.
The salts used for the determ ination of solubilities were purified by double recrystallization. The reagents used were prepared from the usual reagent quality chemicals.
G e n e r a l U s e . The use of alcohol in the preparation of analytical devices depends almost entirely upon its physical properties. No experimental work was done w ith 2-propanol in this connection; however, there seems to be no reason why it should not be used in cleaning apparatus, in washing cru
cibles, and in similar ways, since its physical properties are much like those of ethanol.
U se a s a S o l v e n t . Quite frequently the organic reagents used in analytical work are insoluble in water. In such cases the m ost common solvent is ethyl alcohol. Unless the pres
ence of 2-propanol has a detrim ental effect in determinations where alcoholic solutions of reagents are used, the only ques
tion as to its applicability is its ability to dissolve the reagents.
Solutions of dimethylglyoxime, 8-hydroxyquinoline, and
alpha-benzoinoxime were prepared in 91 per cent 2-propanol and 95 per cent ethanol. The dimethylglyoxime was pre
pared as a 1 per cent solution and the other two reagents as 2 per cent solutions. No difficulty was encountered in prepar
ing solutions of this concentration, although th e reagents dis
solved more slowly in the 2-propanol than in ethanol.
In order to determine whether there m ight be any difference in the effect of 2-propanol and ethanol on the actual determ i
nations, the solutions of dimethylglyoxime were used for the precipitation of nickel and those of 8-hydroxyquinoline for the precipitation of copper, with the results shown in Table II.
In the case of inorganic reagents the application of 2- propanol as a solvent is somewhat lim ited by the fact th a t it is salted out by m any inorganic compounds. This eliminated yellow color can be avoided by allowing solution to take place w ithout the application of heat. In the present work a yellow color appeared w ith 2-propanol after a relatively short tim e in a 0.5 N solution of this base, although no heat was applied to hasten solution. The color developed when the solution was stored in the dark as well as in the light. How
ever, a 0.1 N solution prepared in a similar m anner remained colorless. T he hydroxide dissolves more slowly in 2-propanol th a n in ethanol.
T he te st for chromates depends upon the reducing action of alcohol on sexivalent chromium to form green tervalent chromium. F or this te st 2-propanol was as satisfactory as ethanol, using the procedure recommended by C urtm an (3).
Two tests for borates are given by C urtm an. One is th e common flame te st which indicates the presence of borates by a green coloration im parted to the burning alcohol. When 2- propanol is used, a satisfactory coloration is n o t obtained the la tte r alcohol, no color being produced w ith a 0.01 per cent solution of borax, while ethanolic solutions of turm eric did produce a color a t this concentration.
T he acetate te st as given by the U. S. Pharm acopeia (22) depends upon the form ation of the acetic acid ester of the alcohol used. This test is not successful w ith 2-propanol, presumably because the alcohol is unstable in the presence of concentrated sulfuric acid (20).
Qu a n t i t a t i v e Us e s
In th e presentation of th e experimental results for the q uantitative determ inations employing 2-propanol as a re
agent the details of the procedures used are not included, because in m ost cases they are readily available in the litera
ture. In general, the determ inations were run in triplicate with each alcohol, six aliquot portions being taken from a solution of a salt of the constituent to be determined. In some cases the strength of th e stock solution was determined- by an analysis of a third set of triplicates, and in other cases the solution was prepared by direct weighing and dilution to definite volume of a twice recrystallized salt.
September 15, 1934 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 347 in th e separation of two or more constituents of a mixture the deciding factor in its application is the solubility of the ma num ber of solubility determ inations were made.
Duplicate determinations were made by placing an excess of the dried salt in each of two glass tubes with a capacity of about 100 ml. The tubes were then nearly filled with alcohol and sealed. One of the tubes was placed in the thermostat immedi
ately after being sealed off and the other was held at a tempera
ture about 10° above th at of the thermostat for about an hour and then transferred to the thermostat. The tubes were held in a rack which was arranged in such a manner th at it could be ro
tated, turning the tubes end over end. The tubes were rotated for a period of 12 hours.
At the end of 12 hours the rotation was stopped and the excess salt was allowed to settle to the bottom. The tip of the tube was then broken off and the solution drawn off into a weighing bottle through a tube containing a sintered class filtering disk. The weighing bottle was stoppered and weighed after standing in the balance case for 15 minutes. The alcohol was then evaporated and the residue dried a t 110° C., cooled, and weighed. The results for sodium and potassium chlorides are shown in Tables I II and IV.
The solubilities of calcium, barium, and strontium nitrates are shown in Table V. The procedure used for these salts was the same as th a t for th e sodium and potassium chlorides.
T o M a k e S e p a r a t i o n s . In making separations of metallic ions the samples were prepared by making a stock solution of each of the constituents, standardizing each solution, and taking 25 ml. of each solution for a sample.
The separation of calcium from barium by extraction of the calcium nitrate with a mixture of absolute alcohol and ether was carried out according to the procedure given by Hillebrand and Lundell (11). The mixture of nitrates' used contained 0.05018 gram of calcium oxide and 0.5015 gram of barium oxide. The calcium was not determined after the extraction.
Separation w ith ethanol:
Calcium was separated from magnesium by precipitation according to the method given by Hillebrand and Lundell (11).
Potassium and sodium chlorides were separated from mag
nesium chloride according to the procedure given by the same
348 A N A L Y T I C A L E D I T I O N Vol. 6, No. 5 i A repetition of this procedure with 0.1129 gram of magnesium
oxide in the presence of 0.0843 gram of sodium and potassium chlorides (7 to 10) gave the following results:
S e p a ra tio n w ith e th a n o l:
M gO : 0 .1 0 9 8 ; 0 .1 1 0 7 ; 0 .1 1 1 5 ; A v . 0.1107 S e p a ra tio n w ith 2 -p ro p a n o l:
M g O : 0 .1 1 2 1 ; 0 .1 1 2 5 ; 0 .1 1 3 1 ; A v . 0.1126
In a separation of the same elements according to the Palkin method (16) using 0.0843 gram of sodium and potassium chlo
rides (7 to 10) in the presence of 0.1129 gram of magnesium oxide the following results were obtained:
S e p a ra tio n w ith e th a n o l:
N a C l a n d KC1: 0 .0 8 8 4 ; 0 .0 8 8 1 ; 0 .0 8 8 6 ; Av. 0.0884 S e p a ra tio n w’ith 2 -p ro p a n o l:
N a C l a n d KC1: 0 .0 8 4 6 ; 0 .0 8 4 3 ; A v . 0.0844
The magnesium was not determined in this separation. The alkali chlorides are precipitated in this determination by the addition of absolute alcohol and ether. A double precipitation is necessary with ethanol, but with 2-propanol a single precipitation completely separated the sodium and potassium chlorides.
To D e c r e a s e S o l u b i l i t i e s . In some instances ethanol is used to decrease the solubility of precipitates which are too soluble to be precipitated from aqueous solution. Examples of this use are the determinations of strontium and calcium as sulfates. The procedure for calcium is given by Treadwell and Hall (21) and th a t for strontium by M ahin (
14
). Typical results are shown in Table VI.To Wa shP r e c i p i t a t e s . Alcohol is used quite frequently for washing precipitates, generally for one of two reasons: the precipitate is less soluble in alcohol than in some other medium; or, there is some advantage in using a low-boiling washing medium either to obtain more rapid drying or to make it possible to dry a t relatively low tem peratures those precipitates which decompose a t the ordinary drying tem pera
tures.
Table V II contains th e results of experiments to compare the suitability of ethanol and 2-propanol as washing media.
Li t e r a t u r e Ci t e d
(1) B a rb er a n d K olthoff, J. A m . Chem. Soc., 50, 1625 (1928).
(2) C aley a n d F o u lk , Ibid., 51, 1664 (1929).
(3) C u rtm a n , L. J ., ‘‘Q u a lita tiv e C hem ical A n aly sis,” 1st cd., M a cm illan C o., N . Y ., 1931.
(4) D ick, Z . anal. Chem., 82, 4 01-15 (1930).
(5) Ibid., 77, 352 (1929).
(6) Fales, H . A ., “ In o rg a n ic Q u a n tita tiv e A n aly sis,” 1st ed., C en
tu r y C o., N . Y ., 1925.
(7) F e rn e r an d M ellon, J . Chem. E ducation, 10, 243 (1933).
(S) G ilson, J . A;«. Chem. Soc., 54, 1445 (1932).
(9) G innings a n d C h e n , Ibid., 53, 3765 (1931).
(10) Griffin, Science, 55, 262 (1922).
(11) H illeb ran d , W . F ., a n d L undell, G . E . F ., “ A pplied In o rg a n ic A n aly sis," 1st ed., J o h n W iley & Sons, N . Y ., 1929.
(12) H o p k in s a n d Q uill, Proc. N a t. A cad. S ei., 19, 64 (1933).
(13) K irn a n d D u n lap , J . A m . Chem. Soc., 53, 391 (1931).
(14) M a h in , E . G ., “ Q u a n tita tiv e A n aly sis,” 4 th ed., M cG raw -H ill B ook C o., N . Y ., 1932.
(15) N eu m an , J . A m . Chem. Soc., 56, 28 (1934).
(16) P a lk in , Ibid., 42, 1618 (1920).
(17) S c h u e tte a n d H a rris, J . A m . P harm . Assoc., 15, 166 (1926).
(18) S c h u e tte a n d S m ith , In d. En o. C h e m ., 18, 1242 (1926).
(19) S p acu a n d D ick, Z . anal. Chem ., 71, 1S5 (1927).
(20) S tan co D istrib u to rs , In c ., “ P ro p e rtie s a n d U ses of P e tro h o l,”
N . Y ., 1932.
(21) T read w ell, W . D ., a n d H all, W . T ., " A n a ly tic a l C h e m istry ,”
Vol. I I , 7 th ed ., J o h n W iley & S ons, N . Y ., 192S.
(22) U . S. P h arm aco p eia, 10th ed., J. B. L ip p in c o tt C o., P h ila d e l
p h ia, 1926.
Re c e i v e d M ay 11, 1934. B ased upon a thesis s u b m itte d by O. W . F e rn e r (holder of th e J . T . B ak er Chem ical C om pany Fellow ship in A nalytical C hem istry, M idw est D ivision, for the y e ar 1933-1934) to th e F a c u lty of P u rd u e U niversity in p a rtia l fulfilm ent of th e req u irem en ts for th e degree of do cto r of philosophy, 1934