ANALYTICAL CHEMISTRY
216
In their investigations, emphasis was placed on titratioiis of systems of electrolytes with a capacitor cell. For applications of that type, changing the frequency may have marked effects on the performance of the instruments. The loading of the oscillator, however, precludes the great increases in sensitivity which may be obtained with careful L/C balance and systems of nonelectrolytes. For example, with an instrument of the type used b3 Burkhalter, Vest, and Broussard ( 4 ) , the substitution of a capacitor cell for an “inductance” cell may make sample handling more convenient but leads to no appreciable change in sensitivity for solutions of electrolytes. These observations were confirmed by the work of Blaedel and Nalmstedt ( 2 ) . Anderson and Betts have published ( I ) data o n studies of systems of electrolgtes with an instrument of the “grid-dip” type This instrument gives excellent results in the hands of the authors in comparison to other similar instruments; there is an important frequency effect. The heterodj ne instruments and, more markedly, those de-
pending primarily on the Q of the circuit are theoretically limited in titrations of electrolytes. For work with electrolytes, the best circuit should be one that does not depend on the detuning of the primary oscillator circuit. The stability required for applications outside of the research laboratory is of the order of 1 part in 107, a requirement that is very difficult to achieve even with the highest quality components. Introducing solutions of electrolytes as dielectric materials is in direct opposition to the requirements for stability. BIBLIOGRAPHY
(1) Anderaon, Kermit. and Botts. E. S.,.INAL. CHEX.,22, 743 \19601. ( 2 ) Blaedel, IT’. J., and Malrnstedt, H. V.,Ihid.,22, 734 (1950). (3) Terrnan, F. E., “Radio Engineers’ Handbook,” Yew Yolk, McGraw-Hill Book Co., 1943. (4) West, P. IT., Burkhalter, T. S., a n d Broussard, L., Ax.\L. CHI)!. 22, 469 11950). R E C E I V E DJune 28. 1950
Identification of Alcohols in Dilute Aqueous Solution i. D. IIOLLEY
AND
It. W. HOLLtiY
Vew York S t a t e Agricultural Experiment Station. Gerieuu, \. 1 .
T H E course of an investigation of the volatile constituentb Iof Nalcohols of fruits, methods were desired for the isolation of derivatives from very dilute aqueous solutions and for the fractionation of less than 1 mg. of mixtures of alcohol derivatives By the use of modified Schotten-Baumann conditions Henstock ( 1 ) prepared p-nitrobenzoatw from 0.25 t o 1.5% alcohol solutions, Lipscomb and Baker ( 3 ) prepared 3,5-dinitrobenzoate~ from 5% alcohol solutions, and White ( 7 ) prepared 3,j-dinitrobenzoates from 0.5% alcohol solutions. €Ion-ever, none of these workers extended the preparation of derivatives to lower concentrations. By using the procedure of White under controlled conditions 3,5-dinitrobenaoates were obtained from primary alcohols a t a concentration of 0.001% (100 microgram8 of ethyl 3,5-dinitrobenzoate were obtained from 10 ml of 0.001% ethyl alcohol; 20% yield) KO attempt was made to investigate lower concentrations, as the methods of detection and identification of the 3,5-dinitrobenzoate became limiting. i P< A
0
cu
60-
:b
?! >
f
i
.
€100
PREPARATION OF 3,5-DINITROBENZOATES
T o 10 ml. of the aqueous solution in a 100-ml. glass-stoppered flask are added 0.1 ml. of redistilled pyridine and 1 ml. of benzene (commercial). The mixture is cooled in an ice bath, and 11 grams of anhydrous potassium carbonate are added a t such a rate that the temperature does not exceed 25” C. A solution of 0.5 gram of 3,5dinitrobenzoyl chloride (Eastman) in 2 ml. of benzene is added in portions a t room temperature with shaking. Three minutes after the addition of the acid chloride is complete, 30 ml. of sodium-dried ether are added and the mixture is shaken. The ether is decanted into a centrifuge tube. The extraction is repeated twice. The ether solutions are centrifuged, filtered through a dry filter paper, and evaporated a t atmospheric pressure. The residue is heated at 70’ to 80’ a t 20 mm. until the odor of pyridine can no longer be detected. The residue is extracted with 10 ml. of hot petroleum ether (ligroin). After cooling, this solution is applied to the chromatographic column. CHROMATOGRAPHIC SEPARATION
The column is a 1.8 X 40 cm. borosilicate glass tube which is joined a t the top to a 100-ml. bulb that serves as a solvent reservoir. The tube is constricted a t the bottom and joined to a borosilicate glass stopcock. The adsorbent is supported on a plug of
Le O L
.60.
.40 .
< 2 IO
.zo .
-
,
100
200
a00
400
500
1
VOLUME OF EFFLUENT, ML.
Figure 1. Chromatographic Separation of Mixture of 100 Micrograms of Each of Seven 3,5-Dinitrohenzoates
The excellent chromatographic method described by White arid Dryden (8)for the separation of 3,5-dinitrobenzoates involves thc use of a fluorescent indicator on a silicic acid-diatomaceous earth column. I t requires approximately 1 mg. of a 3,s-dinitrobenzoate for detection. I n the present work the fluorescent indicator has been omitted. The eluate is collected systematically in fractions, and the concentration of 3,5-dinitrobenzoate i n each fraction is estimated spectrophotometrically. This makec possiblr the detection of as little as 30 niicrogranis of a 3.5-dinitrobenzoate
Figure 2. Chromatographic Separation of llIixture of 3,5-Dinitrobenzoates Prepared from Dilute Aqueous Solution of Alcohols A blank using 10 m l . of water showed that t h e small peak a t 200 m l . is due t o a contaminant. I t was found i n all samples of 3.5-dinitrobenzoates prepared from aqueous solution and showed a n ahsorption maximum at 255 mu
V O L U M E 24, N O
217
1, J A N U A R Y 1 9 5 2
__
~
~~
of six primary alcohols.
Table I. lllelting Points of 3,5-Dinitmbenzoates Obtained from Chromatographic Separation (Figure 2) Fraction Effluent Val.. MI 475-495
360-380 315-330 290-300
27'0-280 250-260
Melting
105-107 89-92
Point
Reported hfeltinp Point ($1, ' C . 108 (methyl) 93 (ethyl)
Xor crystalline
59 in-hexyl)
(Micro. Corr.),
C.
74 (n- rap 1) 64 (n-guty% 6 1 (isoamyl1
67.5-71 2 63-88 38-46
glass wool and a filter paper disk. T o avoid contamination, the stopcock is not lubricated. The pressure regulator is described and compressed air is used. by Xlarvel and Rands (4), The adsorbent is a 2 to 1 (by weight) mixture of silicic acid (Merck, reagent) and Celite analytical filter-aid (Johns-llanville). The petroleuni ether (ligroin) is practical grade (Eastman S o . I' 513), specially purified to remove impurities that absorb in the ultraviolet. I n a typical purification, 2 kg. of petroleum ether are first washed with 500 1111. of concentrated sulfuric acid in a separator funnel, and then stirred overnight with 3 pounds of fuming sulyuric acid. (The fuming sulfuric acid is added slowly as heat is evolved,) After washing with water and sodium carbonate, the petroleum ether is dried over calcium chloride and distilled. The fraction boiling at 65" to 85' is used. I t does not absorb light in a 1-em. cell in the ultraviolet above 228 mp. In the recovery of petroleum ether from the chromatographic separation a similar procedure is followed, but the fuming sulfuric acid treatment is omitted. Eighteen grams of the adsorbent are added all a t once to the column without suction, with the stopcock open. The column k gently shaken, and pressure is applied (40 cm. of mercury). The pressure is released gradually. The top of the column is lightly tamped. Fifty milliliters of petroleum ether are added to the column and forced through under approximately 50-cm. pressure. When solvent comes through at the bottom of the column the petroleum ether solution of 3,5-dinitrobenzoates is added. When all this solution has been forced int,o the column, the developer is added. The eluate is collected in 5-nil. fractions from this point. The developer is forced through under approsjmately 5O-cm. pressure, and flows a t the rat,e of about 1.5 ml. per minute. The following solutions are used: \'Ol.>
hll.
50 50
50 80 50 200 100
Petroleum Ether, 1;
By evapoiation of the sc lvent from the :tppropriate fractions, four of the 3,hlinitrobcnz ates were obtained with fairly sharp melting points, as shol n in Table I. Further fractionation would be necessary for the isolation of purv material in the case of the other two
i
v./\-.~#
100 99 98 97 96
95
90
Ether, %
IV.
v.8
I
;
300
400
so0
800
VOLUME OF EFFLUENT, ML.
Figure 3. Chromatographic Separation of Jlixture of 3,S-Dinitrobenmates from Grape Juice Fraction
3
! 10
Fresh developer is added when approsimately 5 ml. of the previous solution remain above the adsorbent. The use of a developer of gradually increasing ether content resulted in better sepxat,ion than use of 5% ether throughout. The optical density of the solutions is read a t 240 mp using a Beckman Model DU quartz spectrophotometer. The solutions were diluted to give optical density readings below 0.70. Ethyl 3,5-dinitrobenzoate shows increasing absorption from 300 to 228 nip. The wave length 240 mp is a compromise between convenience and high extinction coefficient ( e = 18,000). Beer's law is followed satisfactorily. RESULTS AND DISCUSSION
.ilthough the preparation of the fluorescent adsorbent and the use of ultraiiolet light (8) are obviated, by the modifications of tlic chroniatogi,aphic method, specially purified petroleuni ether is necessary, and thc collection of a large number of fractions is tedious unless :LII automatic fraction collector is available. Howver, the substitution of the spectrophotometric method of detection of 3,5-dinitrobenzoates for the visual method renders the chromatographic method more sensitive. Figure 1 shows the separation of a nlixture containing 100 micrograins of each of seven 3,5-dinitrobenzoates. By the use of this sensitive chromatographic technique in conjunctioii with the procedure for preparing 3,5-dinitrobenzoates from dilute aqueous solutions, the detection of alcohols in dilute itqueous solution is made very simple. Figure 2 shows the chromatographic separation of the mi.sture of 3,5-dinitrobenzoates -If in each obtained from 10 ml. of a solution which was 1 X
Primary alcohols react niorc readily than secondary alcohols, which react more readily than tertiary nlcohols. A primary ulcohol can be detected by this method ill solutions us dilute as I to 2 X lo-.' Ill. isopropyl :tnd sec-butyl alcohols were detectecl :it a concentration of' 1 X 10-3 Jf. -1concentration of 0.1 .I/ of tert-butyl alcohol (0.7%) was necessary lor detection. Esters do not react appreciably under these conditions. h 0.1 .If solution of absolute ethyl wetate Jielded less ethyl 3,5-dinitrobenzoate than did a 2 X l o + Jf ethyl :ilcohol solution, indicating less than 0.29r, transesterification. In their study of chromatography on silicic acid-Celite, Truetilood and lZalmberg (6') found linear adsorption isothernis for ii vuriety of compounds. They found that the behavior of mistures was the sum of the separate behaviors of the individual compounds. In the present study, over the range of 100 micrograms to 20 mg. of 3,5-dinitrobenzoute,concentratiou or the presence of other 3,5-diiiitrobenzoateu had no apparent effect on the "peak cffluent volume" (4). The position a i d shape of the peaks there(ore furnish information as to the identity and homogeneity of the fractions, and a judicious selection of material for further study is possible. The sensitivity of the spectrophotometric determination and the constancy of behavior of compounds in mixtures makes possible the detection of a trace of one 3,5-dinitrobenzoate in the presence of a large excess of another. The fractionation of such a nlisture is shown in Figure 3. Twenty-four milligramci of the mixture were subjected to the chromatographic adsorption. Fraction 350-450 ml. was ethyl 3,5-dinitrobenzoate (20 mg.); fraction 495-525 ml. was methyl
ANALYTICAL CHEMISTRY
218 3,ci-ciiiiitrobenzoate (1.2 mg. j; fmction 300-320 nil. !vas chiefly isopropyl 3,%1iinitrobcrizoate (0.1 mg.). The position of niethyl 3,5-dinitrobenxoate is different froin that in FiLmres 1 and 2, as a somewhat different solwrit pystpni \vCi5 r i w i in the tievelopment. The method of separation described here has certain advaiitages over the paper-chromatographic method of Rice, Keller. and Kirchner (6)in that complex mixtures can be separated i n :I single system, the compounds can be recovered for further stud!,, and somewhat miailer quantities of the cornpounds 3re used. LITERATLRE CITED
1 I Ilenatock 1I
J
C'lirriL
II., a n d lliilliket~,S, l'., "Identification uf 1'ut.e Organic Compounds," 1,. 644. S e w Y c J ~ .John ~ , Wilev L Sons.. 1946. ,'I I Lipsoomb. IT. >-.*and Baker. I{. FI., .I. A m . Chem. S'oc., 64, 1751 (1942). i 4 ) Marvel. C:. P.,and Rands, R. I).. .Jr.. Ibid., 72, 2642 (1950). ( 5 ) Rice, R. G . , Keller, J. G., a n d Kirchner. J. G., ~ ~ N A LCHEM., . 23, 194 (1961). ( 6 1 Trueblood, K. S . , and Maimberg, E. JT., J . A m . Chem. SOC.,72, 411' (1950). : 7 ) \ \ l i t e . J . \\-., J r . , Food Reseurch, 15, 08 (1960). $ 8 ) i\-hite, J , Ti.. ,Jr , and Dryden E. C . , - ~ X A L , CHEJII.,20, 563 (1948 I , 12) Huiitress. E.
RECEIVED Julr 19, 1951. .lpproved as Journal Paper S o . 868. S e w York State l g r i c u l t u r a l Experiiiient Station, Geneva, S T., on July 12, 1951.
S O L 1933, 21b
Estimation of Thorium by Selenious Acid THE use of selenious acid to precipitate thorium from neutral or buffered solutions was first reported by Kota ( 2 ) ; the thorium selenite was deterniined gravimetrically. Avsilnble information in the literature about the operative conditions and the accuracy and reproducibility of the above method is, however, meager. Series of esperiments were, therefore, carried out t o investigate the adaptability of selenious acid for quantitative estimation of thorium. The present paper reports a simple iodometric method for its determination in thorium selenite. EXPERIMENTAL
h i e selenious acid, d t a i n e d by recrystallizing a sample of Slerck's reagent grade several times from absolute alcohol, was dissolved in water and allowed t o stand for about 4 hours. The clear aqueous solution was used t o precipitate thorium. Preliminary experiments showed that the precipitation of thorium from its aqueous solution by selenious acid is not quantitative, presumably because of the partial dissolution or hydrolysis of thorium selenite. To a n aliquot quantity of pure thorium nitrate (or chloride) solution with a p H adjusted between 5.5 and 6.0, an equal volume of alcohol was therefore added and thorium selenite was precipitated completely by adding a slow stream of an aqueous 20% solution of selenious acid with constant stirring. The precipitate was filtered through Whatman KO.41 paper and washed with 25 t o 30 ml. of 2% selenious acid solution followed by absolute alcohol till free from excess of the precipitant. It was then dissolved in a minimum quantity of concentmted hydrochloric acid and diluted t o 250 ml. The total acidity of the made up solution was maintained between 1 and 2 N .
'lable 1 .
Estinlation of 'I'horiunl b y Selenious .\cid CeOI in CeCij or Ce(l;Oa)z
K X ~ , t .s
o.
.Added (:raiii
'I'tiOz T a k e n . 'i'liOr Obtained. C;rLll,l
Grail1
Difference, Graiu
0 . 06.10
0,0638
- 0,0002
0,1556 0.1580 0.1010 0.3155 0.2350 0,4736 0 1011 0.1008 0,155G
-o.0004 - 0.0005 - 0.0020 - 0,0004
0,0796 0.1558 4
5 13
... ...
7
8 9
10 11 12
13 11
0 .'lo48 0,122'
0.0766 0.1476
0.15138 -~
0.1580 0.1014 0.3150 0.2370 0.4740 0,1014
0.1010 0 1558 0.1664 0,2012 0.2136
0.0798
0.1663 0.2011 0.2133
_ _ _ _ _ _ _ _ _ ~ ~
- 0.0002 - 0.0002
-0.0002 -0.0002 -0.0002
staiidard thiosulfate and back-titrating it against iodine solution of h o \ v n strength ( 3 ) . .4s the addition of a large excess of thiosulfate leads t o high results in the iodometric estimation of selenium ( I ) , it was necessary to predetermine by trial experiments th(1 appropriatr quantity of thiosulfate reacting with the thorium selenite solution taken for titration. The reaction may be represented as follows:
+ 4Xa?S?O3+ 4HC1+ Sa2SeS10e+ Na&06 + 4SaCI + 3H20 (1)
H2S~r)z
hcLording to Equation 1, 1 mole of selenious acid corresponds to 4 moles of thiosulfate: it follows that a knowledge of the amount of tliiosulfnte reacting with selenious acid available from thorium seleiiitc serves :is a direct measure for the estimation of' thorium. h typical set of results obtained by the alternative method is given iri Table I. In all but one case (experiment 7) the error does not exceed 1%, an accuracy that compares favorably with the classical gravimetric procedures. Selenious acid precipitates quadrivalent cerium from neutral or slightly acid solutions. Prior reduction of cerium to the cerous condition is therefore necessary to prevent its interference in the estimation of thorium. The addition of excess alcohol to a cerous salt solution leads to the precipitation of cerous selenite. A quantitative separation of thorium from R solution containing cerous salts is therefore carried out by effecting the initial precipitation of thorium selenite in a medium containing not more than 50% alcohol and filtering the precipitate quickly through IVhatman No. 41 filter paper. Experiments 10 to 14 (Table I ) refer to such a separation of thoriuni from solutions containing varying quantities of cerous chloride (or nitrate). ACKNOWLEDGMENT
The authors \\-ish to express their sincere thanks to S. S.Joshi for facilities and keen interePt in the a o r k and to the Xational Institute of Sciences of India for :in sward of a research fellowship to one of them (G.S.D.1.
-0.0001
i o . 0002 -0.0003
__
To 10 nil. of this solution about 2 grunis of potassium iodide were added and the liberated iodine was titrated against standard thiosulfate ( 4 ) . Alternatively, the estimation was carried out b ~ adding . t o il known volume of thorium selenite solution ii slight excess of
LITERATURE CITED
( 1 ) Coleinanri and McCrosky, TND. ESG. CHEM.,. ~ A L ED., , 9,431 (1937). ( 2 ) Kota. Chem. L i s t g , 27,.79, 100, 150, 194 (1933). J . , 18, 705 (1896). (3) yorris and F ~ ~ , (4) yogel,"Text Book of Quantitative ~ ~ A ~ n a~l y spp, ~ , ~362~ 3 . London, Longmans, Green & Co.. 1945.
aem,
RECEIVED.\larch 15, 1981.
~
~
