V O L U M E 2 3 , NO. 10, O C T O B E R 1 9 5 1 of rare earth was confirmed with additional stripping solution :md hydrochloric acid (1 to 3). The rare earth was precipitated \vith oxalic acid and it was found necessary to examine, as described, the filtrates from these complexing solutions for small quantities of unprecipitated earth. Interference from traces of inorganic cations in the reagents and solutions employed and the quantitative recovery of the earth appeared to present the greater difficulties in obtaining quantitative values for the rare earth mixtures. I n Table I1 are shown typical valuesobtained in the separationof lanthanum from several ixre earth mixtures. Because the presence of cerium in samples required some addit,ional elut,ion, its removal by chemical means is recommended twfore this procedure is used for the separation of lanthanum. LITERATURE CITED t
1I
Bailey, J . R., and Read. IV. T., J . A m . Chcm. SOC.,36, 1747 (1914).
1473 ( 2 ) Beck, G., Helv. Chirn. I c t a , 29,357 (1946). (3) Fitch, F. T., and Russell, D. S.,Can. J . Research, 29,363 (1951). (4) Johnson, W.C., Quill, L. L., and Daniels, F., Chem. E u y . S r t c s , 25, 2494 (1947). ( 5 ) Ketelle, B. H., and Boyd, G. E.. J . A m . Chtm. SOC., 69,2800 (1947).
Elmouist. It.. Ibid.. 53. 1217 119311. (7) hIaish, J K., J . Chem Sic., 1950,1819. (8) Moeller, T., and Brantley, J C , A V ~ L CHEW,22,433 (1950). (9) Rodden, C. J., J . Research .Vat[ Bvr Standards, 26,557 (1941) (10) Schwarzenbach, G., and Biederniann, IT., HeZv. Chtm. Acta, 31, 331 (1948). (11) Schwarsenbach, G.. Kampitsch, E.. and Steiner, R., Zhid.. 28, 828. 1133 (1945). (12) Tompkins, E'. R., Khym, J. X , and Cohn. W. E., J . A m . Chem. SOC.,69, 2769 (1947). (13) Vickery, R. C., J. Chem. SOC.,1950, 2088. (14) 1-ost, D. M.. Russell, H., and Garner, C. S., "Rare Earth Elements and Their Compounds." p. 59, S e w York. John Wiley & Sons, 1947. 161 Knlthoff. I. hI.. and
RLC>.ITLD December 4, 1950
Determination of Acetaldehyde and Acetone by the Iodoform Reaction Determination of 1,Z-Propylene Glycol STEPHEX DAL NOGARE, T. 0. NORRIS, AND JOHN MITCHELL, .JR. I'olychemirals Department, Chemical Dixision, E. I . du Pont de Nemours & Co., Inr., Wilmington, Del. The procedure described was developed to fill the need for a method applicable to the determination of very low concentrations of acetaldehyde or acetone in solution. The method is based on the reaction of these carbonyl compounds with hypoiodite to give iodoform which is measured spectrophotometrically at 347 mp. Under controlled conditions acetaldehyde and acetone give reproducibleiodoform yields of 58 and l08%, respectively, on a mole per mole basis. By means of this procedure 0 to 0.4 mg. of these compounds may be determined. In the development of the iodoform method a study was made of the reaction conditions necessary for reproducible results. The observation that iodoform in solution can be measured spectrophotometrically is a marked improvement over gravimetric and titrimetric means previously used. Specific applications of the method are reported for acetone in cyclohexanol and 1,2-propylene glycol in ethylene glycol.
0
NE of the oldest and best known qualitative tests for organic
compounds containing the aceto group, or a group capable of easy oxidation or hydrolysis bJ- alkaline hypoiodite to the ucaeto group, is the iodoform reaction. The specificity of this iraction and the low solubility of iodoform in water were properties early utilized for the determination of ethyl alcohol in water ( I f , 1 2 ) and acetone in methanol (9). The most widely used adaptation of the iodoform reaction, however, was that made bv JIessinger ( I S ) to the iodometrlc determination of acetonr. Some of the reported modifications of hleseinger's technique (1-3, 7') indicate the widespread utility of this procedure. In the course of research on the determination of small quantities of acetaldehyde and acetone in various solvents the authors btudied the iodoform reaction. I t was found that iodoform ab-
wrbs in the ultraviolet region from 400 to 260 m p . This absorption is characterized by three well defined maxima occurring a t 347, 307, and 274 mp, as shown in Figure 1. The absorption peak a t 347 mp is the most sensitive to changes in iodoform concentration and shows good agreement with Beer's law for amounts of iodoform from 0 to 3 mg. Ultraviolet absorption by iodoform thus gives a sensitive and accurate means for determining acetaldehyde and acetone in very l o a concentrations. This observation has made it possible to study the reaction variables, in order to obtain the optimum conditions for the conversion of acetaldehvde and acetone to iodoform. €3evious studies of iodoform reaction conditions include the u-ork of Hatcher and Mueller ( 5 ) , Iiolthoff ( 8 ) ,and van der Lee (IO). I n general, the observations of these n orkcis indicated that the ieaction as written CH3CH0 4NaOH JIi --+ CHI3 3 S a I HCOOXa 3HaO
+
+
+
+
+
does not reveal the critical role played by excess alkali and iodine in determining the yield of iodoform. Their work also showed that acetaldehyde and ethyl alcohol gave low yield.5 of iodoform, possibly due to side reactions involving the formation of aldol and resins. The observations of Houghton ( 7 ) indicated that yields of iodoform in excess of theory are obtained with acetone, presumably through partial conversion of acetic acid t o iodoform. However, acetic acid alone did not react (see Table I). Quantitative observations in the authors' laboratory which utilized ultraviolet absorption for the study of iodoform reaction conditions led to the development of a method capable of determining 0 to 0.4 mg. of acetaldehyde or acetone. AN4LYTICALPROCEDURE FORACETALDEHYDEANDACETONE
Apparatus. A Beckman Xodel DU spectrophotometer or other equivalent instrument may be used for absorbancy measurements. Either the hydrogen discharge or the tungsten lamp can be used to make measurements a t 347 mp.
ANALYTICAL CHEMISTRY
1474 -~ ~
~
Table I.
~
~~~
Compounds Subjected to Iodoform Procedure
Compound Methyl isopropyl ketone Mesityl oxide Formaldehyde Propionaldehyde n-Butyraldehyde Isobutyraldehyde Aldol Methanol E t h y l alcohol n-Propyl alcohol Isopropyl alcohol n-Butyl alcohol Isobutyl alcohol see-Butyl alcohol tert-Butyl alcohol Cyclohexanol
0.02 0 0
S o interferenre
0.0
1.1 0.3 3
14
0.0 0.3 0.1
0.9 0.0 0.0
0.9 0.0
CHsCOOIl
A ~ r b i cacid
Amount Giving Optical Density of 0.05, 11g 0.01 0.01 K O interference 2 3 0.3 0.02 No interference 3 20 0.7 No interference No interference 0.8 No interference 370
Conversion t o Iodoform, ?& 55 70
Formula,
the phases to separate and transfer the chloroform layer to a second 125-ml. separatory funnel containing approximately an equal volume of water. Shake vigorously. Transfer the washed chloroform layer to a 25-ml. volumetric flask, passing it first through a funnel containing a thin bed of anhydrous sodium sulfate supported on a glass wool plug. This operation is designed to remove water droplets from the extract. Make the extract to volume by adding chloroform from a dropper passing it first through the sodium sulfate to wash down retained extract Measure the absorbancy, A , a t 347 mfi of the chloroform extract against chloroform in 2.5-cm. silica cells. Determine the absorbancy of a blank and subtract this value from all sample readings. Calculations
%acetone where
1.4
1.2
a-
A X 0.284 X 100 nig. of sample
A = absorbancy corrected for blank a t 347 mp 0.421 = reciprocal of slope of acetaldehyde calibratioir curve ( B ,Fi re 4) 0.284 = reciprocal of x p e of acetone calibration curve ( A ,Figure 4) NOTES ON ANALYTICAL PROCEDURE
1.0
0
z a
=
0.8
0 v)
m
a 0.6 0.4
0.2
400
375
350
WAVELENGTH
325
300
275
250
IN MILLIMICRONS
Figure 1. Ultraviolet Spectrum of Iodoform A . Iodoform in chloroform
B . Chloroform extract of blank
Reagents. Sodium hydroxide, 20% aqueous solution. Iodine solution, about 2070. Dissolve 400 grams of potassium iodide in 800 ml. of water, then add 200 grams of iodine and mix until dissolved. Sodium thiosulfate, 5% solution. Chloroform, C.P. reagent grade. Sodium sulfate, anhydrous C.P. reagent grade. Procedure. Pipet 10 ml. of 20% iodine solution into a 125-ml. se aratory funnel and add 3.3 ml. of 20% sodium hydroxide. i d x by swirling. If the resulting solution is not distinctly orangeyellow, adjust it to this end point by dropwise addition of iodine solution. To this hy oiodite solution, add from a pipet 1 to 5 ml. of the sample sorution containing no more than 0.4 mg. of acetone or acetaldehyde, and mix immediately. Stopper the funnel and allow the mixture to stand for 5 minutes a t room temperature. If the orange-yellow color is gradually diecharged during the 5-minute reaction time, add iodine solution dropwise until the color is restored. After reaction, discharge the iodine color with a fen- drops of 5y0 sodium thiosulfate. Add 22 to 24 ml. of chloroform from a graduated cylinder and extract the iodoform by shaking .4llow
An instantaneous decolorization of the hypoiodite solution on addition of the sample indicates that dilution of the sample solution is necessary. This dilution can be made with water or methanol. The largest sample volume employed in this study was 5 ml. Dilution of the hypoiodite reagent with this volume did not affect the accuracy of the method. However, if the sample is in methanol or other nonaqueous but water-soluble solvent, the maximum volume which can be used is fixed at that which will just cause salts to precipitate from the concentrated hypoiodite reagent. A 5-minute reaction period is recommended aa the minimum convenient time. However, it waa observed that a 2-minute reaction time could be used in the case of acetone. The minimum reaction time required can be estimated by observing the point after addition of sample a t which no further addition of iodine solution is required to restore the end-point color. The significance of this end point is given in the discussion below. A single chloroform extraction will remove iodoform completely from the aqueous reaction mixture. The solubility of iodoform in water is too low to be measured even by ultraviolet absorption. In experiments in which multiple extractions were performed, no additional iodoform was detected other than that present in the initial chloroform extract. No visible iodoform precipitate results from the recommended quantities of acetaldehyde or acetone. Washing the chloroform extract with water is important. This operation markedly reduces background absorption to optical densities in the range 0.03 to 0.005. Apparently this absorption results from the extraction of some undissociated hypoiodous acid, as this compound is known to be a very weak acid (17) and its aqueous alkaline solutions show an absorption in this region of the spectrum. The drying step was introduced to eliminate troublesome water droplets on the absorption cell walls. Because of the slow decomposition of iodoform in solution, optical measurements should be made &s soon a8 possible after extraction. INTERFERINGSUBSTANCES
Interferences will be encountered from compounds which give iodoform by reaction with hypoiodite. Possible interfering compounds studied by the authors were condensation products of
V O L U M E 23, N O . 10, O C T O B E R 1 9 5 1
1475
acetone and acetaldehyde, ketones, aldehydes, and alcohols. Aqueous solutions were used which contained from 1 t o 100 m g . of the compound per milliliter of solution. Analytical data are given in Table I, which lists the per cent conversion to iodoforin under the conditions of the standard procedure. Also included ie the weight of the compound which gives an optical density of 0.05 a t 347 mp. This value is equivalent to 0.021 mg. of acetaldehyde and 0.014 mg. of acetone. The compounds listed in Table I were of C.P. quality. All alcohols reported gave negative tests for the carbonyl group.
Table 11. Decomposition of Iodoform in Chloroform ..\bsorbanc y
Li
(2.775 mg. of CHIi in 2 5 nil.) Time, hlin. Decomposed 'b
Visible pink color.
distillation of the sample often will separate interfering compounds.
-
1.4
DISCUSSION
Optical Studies on Iodoform. During this investigation optical measurements were obtained with a Cary recording spectrophotometer and a Beckman Model DU spectrophotometer. Absorbancy of the solutions was measured in 2.5-cm. silica cells. The wave lengths of the iodoform absorption maxima a t 347, 307, and 274 mp (curve A , Figure 1) were identical for solutiom in n-heptane, iso-octane, ethylene dichloride, and chloroform. Intensity of absorption in chloroform was not affected by temperatures from 28" to 50' C. Chloroform which wa3 used in this work contained 1% ethyl alcohol as preservative which reacted to give a slight absorption a t 317 mp (curve B, Figure 1).
1.2 -
>.
1.0
-
0.8
-
0
z
a
2 0
m
m
a
0.6
-
0.4 -
.,
0
1.0
2 .o
3.0
MILLIGRAMS IODOFORM IN 25 mi CHLOROFORM Figure 2.
Standard Iodoform Curve
Measured in 2.5-em. silica cells a t 347 m u
The high conversions of methyl isopropyl ketone arid rnesit) 1 oxide to iodoform indicate that the present analytical procedure, could be applied to the determination of these compounds and probably to other methyl ketones. Materials which absorb in the same region of the spectrum ab iodoform and which are chloroform-soluble will interfere in the present procedure. Many carbonyl compounds rvhich do not give iodoform will have background absorptions in this region ot the spectrum. If cyclohexanol is subjected to the analytical procedure, 0.02% iodoform is obtained assuming 1 mole of iodoform for each mole of cyclohexanol. However, as cyclohexanone exhibits absorption in this region, it appears that a large amount of the observed absorption is due to this ketone resulting from hypoiodite oxidation of cyclohexanol. As the absorption a t 347 mp is very time-dependent in this case, the interference can be reduced by employing a shorter reaction period in the analytical procedure. Two minutes were sufficient for the determination of acetone in cyclohexanol. Measurement of iodoform concentration a t another wave length might be feasible a3 a method of eliminating some interferences. In many cases carbonyl compounds which interfere by absorption a t 347 mp can be washed from the chloroform extract with aqueous hydroxylamine hydrochloride. Simple
.
Iodoform slowly decomposes to liberate iodine. Table I1 shows the extent of this decomposition with time for a chloroform solution of iodoform. This solution was kept in the optical cell and exposed to average laboratory lighting between readings. Iodine resulting from this decomposition is transparent to ultraviolet light in this region of the spectrum. Reaction Conditions. The critical study made by Hatcher and Ilueller (6) of the iodometric procedures for acetone and acetnldehyde showed that both the concentrations and the order of addition of reagents determined the yield of iodoform obtaintd 9 series of experiments was made to determine the importance of these variables as applied to small quantities of acetaldehyde and acetone. Variations in the order of addition were made a8 shown i n Table 111. In each case the reagents were added to a 125-ml. separatorv funnel with mixing after each addition. The funnel was s t o p pered and the mixture allowed to stand for 5 minutes. Dropwise addition of 20% iodine solution was made as needed to maintain an orange-yellow color, indicating a slight exc(w of iodine. In all cases 1 ml. of aqueous sample containing 0.287 mg. of acetaldehyde was added. At the end of the reaction
Table 111.
Effect of Concentration and Order of Addition of Reagents Concn. of Alkali Added,
Order of Addition Acetaldehyde Rase, iodine, sample
'5 1 1 1
10
10
20
Sample, iodine, base
10 10
.a
3 0 3 3
1 .o
20 20 20 20
3.3 3.3 3.3
! 1 10
Acetone Base iodine, sample SsmAle, iodine, base Sample, base, iodine
1 2 3 2 3 3
2.0 3.3 1.0 2.0 2.0 3.3
20
Sample, base, iodine
Volume of Alkali S o h a , MI.
Iodine added t o slight excea! in all cases.
Iodoform Yield,
%
2.0 7.4 13.0 36.1 52.1 58.0
1.8 1.8 0.5 4.0 12.5 10.0 0.7 108.6 106.0 99.5
1476
ANALYTICAL CHEMISTRY
period, excess iodine was removed by the addition of a few drops
of 5% sodium thiosulfate and the iodoform was extracted with
about 22 ml. of chloroform. Drying of the extract and measurement of the iodoform were carried out as given in the analytical procedure. The yield was calculated from the standard iodoform curve in Figure 2.
r K
B0 a
0 LL
0
a
-1
w> I-
z W
0
K
W
a
iodofoim from these experiments varied from 1.1% for 15 ml of 20% iodine to a maximum of 58.8% for 10 ml. The latter volume of iodine was just sufficient to indicate a slight excws of iodine (orange-yellow color). Data from these experiments are plotted as curve B , Figure 3. Data obtained in the same manner for acetone are given as curve D,Figure 3. I t appears from Figure 3 that the concentrations of both iodine :md alkali are critical and that optimum yields are obtained in only a relatively narron range. From 1500 to 2100 equivalents of iodine may be used per mole of acetaldehyde or acetone, so long as equivalent alkali is present as calculated from the stoichiometry of the iodoform reaction. I n this range of iodine concentrations the yield of iodoform is a t a maximum and relatively c-onstant, as seen from curves A and C, Figure 3. The j-ield icduction in this region is approximately 1 to 2% absolute as coompared to 6% in the ranges 2100 to 2500 and 1100 to 1.500 clquivalents. For acetone, these variations are not as great. Curves B and D in Figure 3 show the importance of maintaining .ufficient iodine in excess of alkali to give the orange-yellow color. The maxima for curves B and D represent quantities of sodium hydroxide and iodine which are nearly stoichiometric for the formation of sodium hypoiodite, so that the orange-yellow color may be regarded as an end point. Insufficient or excess iodine I elative to alkali results in greatly lowered iodoform yield. This visual indication of a slight iodine excess is important and should be carefully observed to obtain consistent results. Since this work was completed the acetone-iodoform macroscale reaction study of Morgan, Bardwell, and Cullis (15) has come to the authors' attention. The importance of order of addition and concentration of reagent.- ako is btrwsed by these workers.
Table I V . 600
0
I200
EQUIVALENTS Figure 3. A. B. C. D.
1800
2400
3000
OF IODINE
Effect of Excess Iodine on Iodoform Yield
Acetaldehyde, NaOH equivalent t o iodine present NaOH held eonstant, 2100 equivalents Acetone. NaOH equivalent t o iodine present NaOH hold oonstant, 2100 equivalents
The data in Table I11 illustrate the importance of order of addition of reagents, in agreement with the observations of Hatcher and Mueller ( 5 ) . However, the findings of these authors indicate that for acetaldehyde the order aldehyde, sodium hydroxide, iodine gives optimum yields of iodoform. The data of Table I11 indicate that highest conversion to iodoform results 110in the order sodium hydroxide, iodine, aldehyde. This contradiction is striking in view of the fact that the highest yield in Table I11 is in good agreement with Hatcher and Mueller's best value of 60.4%. Corresponding data for acetone, as shown in Table 111, are in good agreement although the effect of reagent order is not as great. The effect of alkali and iodine concentrations given in Tablr I11 was further investigated employing the order sodium hydro\ide, iodine, aldehyde. To 3.3 ml. of 1 to 207, sodium hydroxide solutions was added sufficient 20% iodine solution to give a slight excess. To each of these hypoiodite solutions was added 1 ml. of aqueous solution containing 0.339 mg. of acetaldehyde. After 5 minutes, the resulting iodoform was extracted with about 22 m]. of chloroform and measured as previously given. Per cent yield is plotted against equivalents of iodine in Figure 3, curve A . Similar data for acetone are plotted as curve C, Figure 3. The effect of varying the iodine concentration relative to a constant excess of alkali was similarly studied. T o separate volumes of 2 to 15 ml. of 2070 iodine solutions w'ere added with mixing 3.3 ml. of 20% sodium hydroxide followed by I nil. of aqueous acetaldehyde sample (0.339 mg.). Per cent
EEect of Time on Iodoform Reaction
Auetaldehyde, M g
Reaction Time, N n .
0.368 0.368 0.368
15
0.258
5
0.258
0.258 0.184 0.184 0.184 0,074 0.074 0 074
J
10
10 15 5 10 15 5 10 15
Absorbancy
0.875 0.875 0.851
0.574 0.569 0.592 0.430 0.424 0.430 0.183 0.168 0.187
Yield,
b
58.2 58.2 56.7 54.5 54.0 56.3 57.3 56.6 57.3 60.8 55.9 62.2
The effect of time on the yield of iodoform employing optimum Concentration of hypoiodite is shown in Table IV. Data for this table were obtained using 1-ml. aqueous samples containing the indicated amounts of acetaldehyde added to a mixture of 3.3 ml. of 20% sodium hydroxide and 10 ml. of 20% iodine solution. No marked trend with increaqing reaction time up to 15 minutes is evident. No significant difference in yield was observed in several experiments in which the temperature of the hypoiodite solution was varied from 25' to 60" C. Prior to chloroform extractions of iodoform it is recommended that excess iodine be removed from the reaction mixture. While this is not necessary, it is desirable as free iodine extracted from the hypoiodite solution masks any iodine resulting from the decomposition of iodoform. -4ppearance of a pink color in the chloroform extract is taken as an indication that the iodoform has decomposed to such an extent that the extract should be discarded, since the subsequent iodoform measurement Will be significantly low (Table 11). Excess iodine in the hypoiodite mixture can be removed with aqueous sodium thiosulfate, sodium sulfite, or additional sodium hydroxide. I n no case was the yield of iodoform altered when any of these agents was used. Preference is given to sodium thiosulfate. From the foregoing o h e i vations the analytical procedure de-
1477
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 Table V.
Analytiaal Data f o r tcetone in Cyclohexanol
Acetone i n
C yclohexanol,
Weight yo 0.480 0.384 0.288 0.192 0.096 0.038
Table VI.
Calcd. 0.453 0.368 0,277 0.185 0.092 0.037
Analysis of Samples Containing 1,2-1’rop>-lene Glycol
Composition of Sample, Weight % IGpylene Ethylrnc glycol glyroi Y5,3“ 0.0
‘1
Acetone, hlg. Found D;Herences 4 0 005 0.458 i-0 005 0.374 - 0 004 0.273 t O 004 0.189 -co 002 0.094 -0 003 0.040 ~
Absorbancy 1.545 1.260 0.919 0.637 0.317 0.135
_ _ ~ Acetaldehyde Calcd.
Found,
Ma.
mg. 0.494 0.467
‘7c
0.248 0.261
94.8 98.3 105.6 97.1
0.103 0.127
0.097 0.127
94.2 100.0
0 . 155 0.153
0.125 0.131
80.7 84.5
0.078 0.074 0.078 0.072 Rrniainder principallj- a-atpr and nonricinal glycols.
94.9 92.4
18 1
74.3
7 0
83.7
1 0
97.0
0 . :,,I
97.5“
0.321 0.475 0,232 0.269
~-
Recovery,
thr 1:ittt.r with a slight excem of glycine. Similarly, Hoepe and Treadwell (6) utilized the periodate reaction for the analysis of 1,2-propylene glycol-ethylene glycol-glycerol mixtures. The following procedure was used to obtain the data in Table VI. Synthetic mixtures of 1,2-propylene and ethylene glycols ot known purity were prepared. A sample of the neutral glycol mixture weighing 2 to 4 grams was placed in a 250-ml. volumetric flask and diluted to volume with distilled water. After mixing, a 5-ml. portion of the sample solution was transferred to a 100-ml. distilling flask fitted with an efficient condenser and 45 ml. of water were added. Just prior to distillation 0.5 gram of periodic acid was added. Distillation was started immediately and continued a t the rate of 3 to 5 ml. per minute until only about 1 nil. of solution remained in the flask. Care waa taken to aroid evaporation to dryness. The distillate was collected in a 50-1111. volumetric flask submerged in an ice bath. To minimize losses further, the tip of the condenser was modified to extend into the body of the receiver flask. When the distillation was complete, the distillate was warmed to room temperature and adjusted to volume. Aliquots containing 0.1 to 0.5 mg. of aceta1deh)tie were analyzed. I
I
I
I
1.2
1.0
~ ~ b ewas d devised for the determination of small quantitirs of acetaldehyde and acetone. The calibration curves shown in Figure 4 were obtained einploying the analytical procedure, and were used to obtain calculation factors. The acetone used as standard was at least 99% pure and contained water as the principal impurity. Freshly distilled acetaldehyde, analyzing 97% pure by a hydioxj lnmine method ( 1 8 ) , nas used to obtain the acetaldehyde standard curve. i i
>-
0.0
0
z a
m
8 0.6 u)
m DETERMINATION OF 4CETOhE IN CYCLOHEXANOL
a
The determination of ac’etone 111 cyclohexanol i l l u s t ~ ~ t can s application of the new iodoform method.
0.4
A series of six samples was prepared by adding weighed amounts of acetone to cyclohexanol and diluting with additional cycloheranol to concentrations of 0.04 to 0.5%. Then 0.1-nil. aliquots of these solutions were delivered from micropipets and subjected to the standard procedure. This sample volume was used because of the limited solubility of cyclohexanol in the reaction medium. A phase separation w a b noted if more than 0.2 nil. of sample wm taken. A reaction time of 2 minutes was used to avoid too large a background absorption due to oxidation of cyclohevanol to cyclohexanone (see interferences). The results of these aiialyses, given in Table V, indicate the accuracy of the method in this application. Acetone in these samples w m calculated from the standard acetone curve in Figure 4.
0.2
0 MILLIGRAMS ACETONE OR ACETALDEHYDE Figure 4. A. E.
Standard Curves for Iodoform from Acetone and Acetaldehyde
Acetone Acetaldehyde, chloroform solvent, measured i n 2.5-em. silica cells at 347 mp
DETERMINATIOY OF 1.2-PROPYLENE GLYCOL
The determination of 1,2-propylene glycol alone or in the presence of ethylene glycol represents another application of the iodoform procedure. The glycols firFit were oxidized with periodate in order to convert the glycols quantitatively to acetaldehyde and formaldehyde. Acetaldehyde was then determined by the iodoform method. A number of other methods utilize periodate splitting of vicinal glycols. The procedure of Warshowsky and Elving (19) is hased upon the polarographic analysis of the aldehydes which were distilled from the periodate reaction mixture. Mitchell ( 1 4 ) described an optical crystallographic method for measuring the acetaldehyde obtained in a similar manner. Reinke and Luce ( 1 6 ) reported a method based on the measurement of periodate consumed and the determination of acetaldehyde in the presence of the formaldehyde after reaction of
These data demonstrate the high sensitivity of the present method for low concentrations of 1,2-propylene glycol. APPLIC4TIONS OF METHOD
The relative specificity of the iodoform procedure given in thi5 report indicates a rather wide field of application not only to acetaldehyde and acetone but to the analysis of other compounds capable of reacting with hypoiodite to give iodoform. Potential applications of the method now being investigated include thc determination of ethyl alcohol in methanol, and 2,3-butylene glycol in ethylene glycol. In the case of ethyl alcohol in methanol the recent procedure of Williams and Reese (20)cannot be applied because of the ready oxidation of methanol by chromic acid. I t also appears possible, by means of the ultraviolet absorption
ANALYTICAL CHEMISTRY
1478
of iodoform, to investigate some aspects of the iodoform reaction mechanism. Any number of compounds may be utilized for this purpose, as indicated in the escellent review by Fuson and Bull
(4). ACKNOWLEDGMENT
The authors wish to ackno~vledgethe valuable assistance of H. D. Deveraux in obtaining some of the data in this report. LITERATURE CITED
(1) Bates, H. H., Mullaly, J. M., and Hartley, H., J . Chem. SOC., 123,401 (1923). (2) Benesch, E., Chem.-Ztg., 50,98 (1926). (3) Cassar, H. A., Ind. Eng. Chem., 19, 1061 (1927). (4) Fuson, R. C., and Bull, B. A., Chem. Reu., 15, 275 (1934). (5) Hatcher, W. H., and hfueller, W. H., Trans. Roy. Soc. Can., (3) 23, Sect. 3, 35-44 (1929).
(6) Hoepe, G., and Treadwell, JV. D., Helu. China. Acta, 25, 363 (1942). o., IND.ENG.C H E L f . , A N A L .ED.,9, 167 (1937). (7) Houghton, (8) Kolthoff, I. M., Pharm. Weekblad,62, 652 (1925). (9) Kramer, G., Ber., 13, 1000 (1880). (10) Lee, J. van der, Chem. Weekblad, 23, 444 (1926). (11) Liehn, A., Ann., SpeciaZBinding, 7, 218 (1870). (12) Ibid., p. 377. (13) Messinger. J., Ber., 21, 3366 (1SS8). . 21,448 (1949). (14) Mitchell, J., Jr., k i . 4 ~ CHEM., (15) Morgan, I
