ANALYTICAL CHEMISTRY
1754 analyzed. In the present installation zero checking of the instrument is required about every 10 days. Typical results obtained on a refinery stream by the continuous toluene analyzer are shown in Table I and compared with laboratory measurements by specific dispersion methods. I n Table I1 analyzer results obtained prior to plant installation are compared with toluene measurements by mass spectrometer. The deviations in these data appear to be somewhat systematic and may have been caused partly by improper temperature control of the analyzer sample cell. In Figure 6 an actual analyzer record is shown for an operating period of 24 hours, during which time a check was made on a 60% toluene reference sample. Over 2 weeks of operation had elapsed since previous adjustment of the recorder. These results indicate that the present analyzer is accurate to better than &l% toluene. Credits accruing to the use of an instrument of this type on process streams depend largely upon the type of stream for which it is being used and may run into several thousand dollars per year based on increased yield and/or quality of products.
ACKNOWLEDGMENT
The authors express appreciation to the Humble Oil and Refining Co. for permission to publish this work. LITERATURE CITED
(1) Anderson, K., Bettis, E. S., and Revinson, D., ANAL. CHEM.,
22, 743 (1950). (2) Blaedel, W.J., and Malmstadt, H. V., Ibid., 22,734 (1950). (3) Blake, G. G., Australian J . Sci., 11, 59 (1948).
(4) Burrell, C. M., Majury, T. G., and Melville, H. W., Proc. Roy. Soc., A205, 309 (1951). (5) Engelder, P. O., Instruments, 24, 335 (1951). (6) Forman, J., and Crisp, D., Trans. Faraday SOC.,42A, 186 (1946). (7) Frank, F. C., Ibid., 42A, 19, 24 (1946). (8) Jensen, F. w., and Parrack, -4. L., IND.ENG. CHEM.,ANAL. ED.,18, 595 (1946). (9) Kirkwood, J. G., Trans. Faraday Soc., 42A, 7 (1946). (10) Thomas, B. W., Instruments, 23,1130 (1950). (11) West, P. W., Burkhalter, T. S., and Broussard, Leo, ANAL. CHEM.,22, 469 (1950). RECEIVED May 14, 1951.
*Analysis of Mixtures of Aldehydes and Ketones B. E. GORDON’, FRED WOPAT, JR., H. D. BURNHAM, AND L. C. JONES, JR. Research Laboratories, Shell Oil CO., Inc., Wood River, Ill.
I
N T H E course of an investigation of the applicability of
ozonolysis to the determination of the composition of complex mixtures of olefins, it was necessary to develop methods for the analysis of the mixtures of aldehydes and ketones resulting from hydrogenation of the ozonides. The similarity of the chemical reactivities of the higher members of each series seemed to preclude the use of any but physical methods for their differentiation. Infrared spectrophotometry was considered but not deemed promising because of the difficulty of preparing sufficiently pure calibration standards, and, more important, obtaining the micro quantities of aldehydes and ketones from ozonolysis free from extraneous compounds such as hydrogenation solvent and the acids, esters, etc., formed by side reactions during the ozonolysis. A4numberof investigators (.2,4,5,11,1S,I5,16)have employed chromatographic separation of the 2,4-dinitrophenylhydrazones of the aldehydes and ketones as a qualitative method. The extraneous impurities mentioned above are removed during the preparation of the derivatives. Furthermore, if the separation is quantitative, it is a very simple matter to determine the separated hydrazones spectrophotometrically by virtue of their strong visible or ultraviolet absorption ( 1 , IS). It is then possible to identify the isolated derivatives by their characteristic crystalline properties, such as melting points or mixed melting points and x-ray diffraction patterns (6, I O ) . In order to make this logical sequence of operations work, however, it was necessary to separate the hydrazones quantitatively through chromatography, to confirm published data on the extinction coefficients of the various 2,4-dinitrophenylhydrazones,and to extend somewhat the existing x-ray diffraction data on these compounds in their various polymorphic crystalline forms and geometric isomers. CHROMATOGRAPHIC SEPARATION OF 2,4-DINITROPHENY LHYDRAZONES
Strain (16), working with the 2,4-dinitrophenylh~~drazones of p-ionone and camphor, obtained satisfactory separation between these two compounds when adsorbed and developed in Tswett columns of fibrous alumina or talc. More recently Roberts and Green (I2),Rice, Keller, and Kirchner ( 1 1 ) , and Cavallini (4, 6) Present address, Research Laboratories, Shell Oil Co., Martinez, Calif.
found it possible to separate qualitatively mixtures of the 2,4dinitrophenylhydrazones of acetaldehyde, propionaldehyde, acetone, and methyl ethyl ketone when acetone and propionaldehyde were not present in the same mixture. Roberts and Green used silicic acid and SuperCel adsorbent in 2 to 1 ratio, while Rice et al. and Cavallini used the paper chromatographic technique. Since completion of the work described here, White (16) has reported the separation of a large number of the 2,4dinitrophenylhydrazones of aliphatic aldehydes and ketones on a mixture of bentonite and diatomaceous filter aid. He was unable, however, to achieve complete separation with one adsorption of the derivatives of formaldehyde and acetaldehyde or of methyl ethyl ketone from that of either propionaldehyde or n-butyraldehyde. In the present investi$551 50 gationa numberof adsorbe n t s , i n c 1u d i n g those mentioned above as well as silica gel, a c t i v a t e d alumina, calcium carbonate, and a mixture of 2 p a r t s of s i l i c i c a c i d (Merck’s p r e c i p i t a t e d silicic acid, through 100 mesh) and 1 part of Celite analytical filter aid ( J o h n s - M a n v i l l e Co.), were tested for efficiency in the separation of acetaldehyde and n-butyraldehyde. Of these the last combination w a s m o s t effective. The adsorption experiments were carried out in ALL DIMENSIONS IN MM. the apparatus shown in Figure 1. Adsorption Column Figure 1.
1755
V O L U M E 2 3 , NO. 1 2 , D E C E M B E R 1 9 5 1 The wide upper portion of the column serves as a reservoir for developing solution and the long narrow section holds the adsorbent. The base of the column is flat. This is important, because proper packing of the column requires the application of considerable pressure upon the adsorbent by means of a plunger whose diameter is about 1 mm. less than the inner diameter of the column. During this operation the flat column base is supported upon a large cork drilled to receive the delivery tube. The hose nipple on the cap of the adsorption column is connected t o a nitrogen line regulated a t about 2 t o 5 pounds per square inch gage. The procedure that was found to give most satisfactory separation of the various hydrazones is given below.
Table I. Chromatographic Separation of Binary and Ternary Mixtures of 2,4-Dinitrophenylhydrazones yo E t h y l E t h e r in
System (as Dinitrophenylhydrazones) Acetaldehyde n-Butyraldehyde Acetaldehyde Acetone Propionaldehyde Formaldehyde Acetaldehyde
Petroleum E t h e r Developing Eluting solution solution 4 8
Band N0.D
2 1
4
8
3 2 1
8
12
2 1
M.P. a.
c.
165 121 167 125 154 167b 166b 125 116 182 120 180
3 5 Acetone 2 Methyl ethyl ketone 1 Isobutyraldehyde n-Butyraldehyde 2 4 2 Isobutyraldehyde 1 Methyl ethyl ketone 2 i'iot resolved n-Butyraldehyde .. Propionaldehyde 2 4 2 153 Methyl ethyl ketone 1 116 a Bands numbered in order of elution. bottom band is number 1, etc. b Mixed melting points definitely established lower band a8 acetaldehyde.
....
....
Procedure. Mix silicic acid and Celite in a 2 to 1 weight ratio and activate a t 170' to 200' C. for 24 hours in a large evaporating dish, Add a 1-cm. plug of glass wool to the column and press down firmly with the plunger. Add the activated adsorbent in 2to 3-cm. increments and slowly press down with the plunger, using a force of 75 t o 100 pounds. Repeat additions until the column is filled t o depth of about 20 cm. Place a perforated porcelain disk on top of the adsorbent t o prevent disintegration of the column when the sample is poured in. The column is now ready for use. The technique of precipitation of the 2,4-dinitrophenylhydrazones is essentially that of Iddles and Jackson (9) and the method described below resulted in recovery of added carbonylic compounds similar to those of the earlier workers. Prepare the 2,4-dinitrophenylhydrazones as follows: Add slowly with stirring about 10 ml. of alcoholic solution containing approximately 1 me.of aldehydes and ketones t o 100 ml. of a saturated solution of 2,4-dinitrophenylhydraeinein 2 N hydrochloric acid. Digest the precipitate a t 0" C. for 1 hour and filter through an Alundum crucible using suction. Wash with 100 ml. of water and dry in vacuum over sulfuric acid. Weigh the precipitate to determine the total yield of carbonyl compounds. Dissolve a weighed portion of the dry, mixed hydrazones (35 t o 60 mg.) in 10 to 20 ml. of chloroform and carefully pour the solution onto the column. After adsorption of the chloroform add 50 ml. of petroleum ether and allow it to percolate into the adsorbent. Then pour 250 ml. of the proper developing solution (2% ethyl ether in petroleum ether is usually satisfactory a t the start) on the column, replace the cap, and apply a pressure of 2 t o 5 pounds per square inch gage of nitrogen. As separation of the bands occurs, gradually increase the ethyl ether content of the mixed developer to a maximum of about 10% by volume. Collect the solution corresponding to each eluted colored band in a separate 500-ml. Erlenmeyer flask. Remove the solvent by gentle heating in an air stream until the dry 2,4-dinitrophenylhydrazone remains in the flask. This procedure differs from that of Roberts and Green in several respects. They had recommended 25% by volyme of benzene in petroleum ether as a solvent for the 2,4-dinitrophenylhydrazones.
This work was undertaken to complete an analytical scheme for the elucidation of structure of mixtures of the products of olefinic degradation by ozonolysis. Although the requisite methods existed in other applications, this paper attempted to combine the techniques into one general method. The results were satisfactory in dealing with aldehydes and ketones from formaldehyde up to the C4 carbonyls. Above this the number of possible isomers results in a matrix too complex for complete analysis. This procedure presents in organized form a general method for thp analysis of mixtures of carbonylic compounds from C1 through C4 structure. Above this, further work is necessary to determine the degree of specificity of the method for Cs, Co, and C, isomers. Possibly the method, when applied to higher homologs, will express results as groups of carbonyls rather than individual members.
However, excessively large quantities of this mixture are required to dissolve small amounts of the sample. In order to obtain a tight, uniform band of hydrazones in the column it is desirable to use as small a volume of hydrazone solution as possible. Of the other solvents tested-ethyl ether, 2,2,4-trimethylpentane, carbon tetrachloride] n-pentane, acetone, and chloroform-the last was most satisfactory in this respect. The developing solution used was ethyl ether in petroleum ether. The concentration required depended on the hydrazones involved. To separate propionaldehyde from n-butyraldehyde a 2 to 3% solution was sufficient. To separate formaldehyde from acetaldehyde, a 6 to 10% solution was usually required. The proper technique was found to be to start with a 2% ethyl ether in petroleum ether and gradually increase the pblarity of the solution as development proceeded, thereby giving the more weakly adsorbed materials a chance to separate and resolve before being eluted. Qualitative experiments with mixtures of purified hydrazones were carried out, in which the hydrazones operated by chromatography were identified by means of melting points or mixed melting points after repeated recrystallizations. These experiments are summarized in Table I. These data established the relative strengths of adsorption of the 2,4-dinitrophenylhydrazone derivatives as follows: formaldehyde > acetaldehyde > acetone > propionaldehgde > methyl ethyl ketone = n-butyraldehyde > isobutyraldehyde. I n subsequent Fork with unknowns the 2,4-dinitrophenylhydrazone derivatives of n-valeraldehyde, methyl propyl ketone, and a few other higher homologs have occasionally been separated from reaction mixtures in fairly pure state by this procedure. Table 11. Extinction Coefficients for 2,4-Dinitrophenylhydrazones of Various Aldehydes and Ketones at 356 mp Extinction Coefficient Extinction :ram Roberts Coefficient and Green (IS), in CHCla, Liter/Cm./G. Aldehyde or Ketone Liter/Cm./hfg. Mole Formaldehyde 0,0880(18,600)@ 18,200 Acetaldehyde 0.0948 (21,500) 21,000 Propionaldehyde 0 0904 (21,500) 21,800 n-Butyraldehyde 0 0880 Isobutyraldehyde 0 0832 n-Valeraldehyde 0 0585 Isovaleraldehyde 0 0879 Acetone 0.0876 (21,100) 21:ooo Methyl ethyl ketone 0 0823 .. Methyl isopropyl ketone 0 0785 .. Diethvl ketone 0.0785 .. a Numbers in parentheses are molar extinction coefficients for comparison with values from (IS).
.. .. ..
COLORIMETRIC DETERMINATION OF 2,4-DINITROPHENYLHYDRAZONE DERIVATIVE
All the 2,4-dinitrophenylhydrazones studied here have an intense, broad absorption band near 356 mp ( 1 , 13). These bands
ANALYTICAL
1756 are sufficiently diffuse and closely spaced to be nearly useless for the qualitative or quantitative analysis of mixtures of the derivatives, especially if the qualitative composition is unknown. They are useful, however, in determining the total amount of a pure derivative of known structure. The extinction coefficients of a large number of the 2,4-dinitrophenylhydrazones a t 356 mp were determined with a Beckman quartz spectrophbtometer, Model DU (S), using a 0.20-mm. slit width. As it is probable that for absorption bands of this width the calibration of different instruments will be essentially identical (Y),these extinction coefficients may be of some value to other workers and therefore are given in Table 11. A comparison of four of these molar extinction coefficients obtained by Roberts and Green ( I S ) shows total agreement. Strict adherence to the Lambert-Beer law was noted in all cases. If the qualitative composition of the original mixture is known, the identity of each hydrazone is known from its position in the chromatogram. However, as this will not be the case in general, the most practical procedure involves obtaining the spectrophotometric data for each chromatographic fraction first and calculating the concentrations of the individual components with the appropriate extinction coefficient after they have been identified by melting points or x-ray diffraction data. For this reason extinction coefficients are given a t a single wave length, which in many cases does not correspond to that of maximum absorption. PROCEDURE FOR SPECTROPHOTOMETRIC ESTIMATION O F 2,4-DINITROPHENY LHYDRAZONE
Take up the 2,4-dinitrophenylhydrazone from the preceding operation in chloroform and dilute quantitatively t o such a volume, V (in liters), with this solvent that an optical density of 0.2 to 0.6 a t 356 mp is obtained. Measure the optical density a t 356 mp, D,with the Beckman D U spectrophotometer with a 0.20-mm. slit, a 1-em. cell, and chloroform blank. The weight of the particular hydrazone may then be computed from the equation: 100 UT' Weight of hydrazone (mg.) = __-
K
CHEMISTRY
where D and V are as defined above and K is the appropriate extinction coefficient from Table 11. IDENTIFICATION OF 2,4-DINITROPHENYLHYDRAZONES
The derivatives isolated by chromatography were never in sufficiently pure state to be identined directly by their melting points. This was probably due in part to incomplete resolution of the various components and in part to residual impurities from the solvents and eluants used in chromatography. Several recrystallizations were ordinarily necessary to reach a constant melting point which could be relied upon for identification. Inasmuch as some of the chromatographic fractions contained no more than a few milligrams of material, this a a s not in general a very satisfactory procedure. The melting point or mixed melting point techniques have other complications N hen applied to the identification of the 2,4-dinitrophenylhydrazone. Some of these may exist as two geometric isomers of different physical properties. I n addition, any of the isomers of a given 2,zl-dinitrophenylhydrazone may occur in t n o or more different polymorphic crystalline forms ( 6 ) , each of which has its characteristic melting point. Add to these factors the similarity of the melting points of many of the derivatives (cf. formaldehyde and acetaldehyde in Table I) and it is apparent that alternative methods of identification would be highly desirable. Clark ( 6 ) in his thorough study of several 2,4-dinitrophenylhydrazones has pointed out that x-ray diffraction data should be a powerful tool for such a problem. The data presented in his paper, although useful, did not cover all the derivatives encountered in this work. It was necessary, therefore, t o prepare as many of the pure derivatives as iossible and to obtain complete x-ray diffraction data for each. tandards for this purpose were prepared by the procedure given above from the purest samples of aldehydes and ketones available. The derivatives were purified by repeated crystallizations from ethyl alcohol and in some cases by chromatography. More than one form of most of the compounds has been isolated. The x-ray data for these compounds are presented in Table 111. Different polymorphic forms are indicated by Roman numerals.
Table 111. X-Ray Diffraction Data for 2,4-Dinitrophenylhydrazones "4-Dinitrophenylhydrazine Relative d . A. intensity 9.0 5.81 0,'s 4.48 .. 4.11 3.75 1'.0 3.57 3.47 0.9 3.40 3.17 0.8 3.06
..
2,4-Dinitrophenylhydrazone of n-Butyraldehyde Form I Relative d , -4. intensity 14.0 1.0 7.5 0. ki
!:$
4.7 4.08 3.76 3.63 3.44 3.27 3.21 2.91
0 .i 0.2
.. ..
0.4
..
2,4-Dinitrophenylhydrazone of Acetone Relative d . A. intensity 9.2 1.0 5.82 0.4 5.08 .. 4.92 4.63 0.6 4.39 4.29 .. 3.86 3.73 3.27 0.5 3.05
.. .. ..
of -4cetaldehyde 2 4 - ~ i ~ i t ~ ~ ~ h 2,4-Dinitrophenylhydrazones ~ ~ ~ i h ~ d ~ ~ Lone of Formaldehyde Form I Form I1 Relative Relative Relative d , 8. intensity d , A. intensity d , A. intensity 10.3 1.0 9.35 1.0 9.2 1.0 7.7 6.75 6.83 0.5 0.4 5.18 5.40 5.70 0.6 4.69 4.88 4.75 0.4 ,. 4.71 4.52 4.38 0.9 .. .. 3.95 3.95 3.66 .. .. 3.61 3.58 3.23 0.9 3.46 3.23 0,'s 0.5 .. 3.23 3.15 0.4 .. .. 3.08 3.03 .. .. .. ..
..
..
..
2.4-Dinitrophenylhydrazonesof Isobutyraldehyde Form I Form I1 Relative Relative d , A. intensity d , A. intensity ' 12.6 1 0 11.7 1.o .. 5.90 0.3 7.35 6.30 .. 4.62 .. 4.77 4.36 4.50 0.5 3.93 0:s 4.31 .. 3.26 0.2 4.02 .. .. .. 3.88 .. .. .. 3 67 3 57 3 36 0 8 3 26 0 9 2 4-Dinitrophenylhydra;one of Diethyl Ketone Relative d , A. intensity 12.0 1.0 7.06 0.7 5.47 .. 4.77 4.52 0.'6 4.17 0.9 3.40 3.13 0'. i
.. ..
..
..
.. ..
.. , .
..
2,4-Dinitrophenylhydrazonesof Isovaleraldehyde Form I Form I1 Relative Relative d , A. intensity d , A. intensity 12.7 1.0 11.8 1.0 7.5 6.47 0.8 .. 5.80 5,lS 4.28 0'. '4 4.11 0 . '5 3.24 .. 3.91 0.7 3.15
2,4-Dinitrophenylhydrazonesof Methyl Ethyl Ketone Form I n Form IIa Relative Relative d , .4. intensity d, 4 . intensity 12.5 1.0 11.9 1.0 7.15 0.9 7.78 0.9 6.64 5,52 0.8 4.11 4.92 0.5 4.23 3.94 0.6 3.88 3.58 3.39 3.71 3.35 3.27 3.17 3.05
.. ..
2,4-Dinitrophenylhydrazonesof Propionaldehyde Form I Form I1 Relative Relative d , A. intensity d , A. intensity 10.3 1.0 10.9 1.0 5.75 0.7 6.02 0.8 5.48 4.71 0.6 .6 4.83 4.58 .. .. 4.39 3.69 .. 4.13 3.35 .. 0.5 3.61 .. .. 3.52 .. 3.27 0.9 .. .. ..
..
..
5 Data for only one form of methyl ethyl ketone D S P H are listed by Clark, the characteristic long spacin for which agrees well with t h a t of form I rnethyf ethyl ketone D N P H in table. Second and third most intense lines of Clark's compound agree substantially with maxima observed for form I1 methyl ethyl ketone D N P H . I t is possible that the material listed by Clark is a mixture of the two forms of methyl ethyl ketone D N P H . These are geometric isomers.
1757
V O L U M E 2 3 , NO. 1 2 , D E C E M B E R 1 9 5 1 The data were obtained with the S o r t h American Philips Co. Geiger-counter x-ray spectrometer (8) equipped with a Brown Electronik strip chart recorder. Intensity data were estimated from the heights of the diffraction peaks above background. Differences in relative intensities reported in this investigation from those of Clark et al. are undoubtedly due to the fact that preferred orientation was encouraged in this work, as it often led to enhancement of the most characteristic eaks and thus facilitated the identification of small samples. $he diffraction peaks reported are the best average values from a large number of runs. 01ily those d values which have been observed in several preparations are reported. Derivatives from chromatography have occasionally exhibited extraneous diffraction lines not noted in the standards and in a few cases patterns have been obtained from unknowns which could not be identified a t all. Fortunately such cases have been rare. The procedure followed with fractions from chromatography was as follows: Evaporate the chloroform solution of the hydrazone to dryness.
If the sample size permits, recrystallize the hydrazone from alcohol. Transfer the crystals to the cup formed on a standard 1 X 3 inch microscope slide by cementing (with Duco household cement) a 1-cm. length of 18- to 20-mm. outside diameter glass tubing to the center of the slide. Wet the crystals with a drop or two of alcohol and allow to dry. Remove the tubing and carefully strip any residual cement from the slide. Record the diffraction pattern from 2 '6 =.5" to 2 6' = 40" using an iron anode x-ray tube and a manganese radiation filter. Identify the hydrazone by comparison with standard patterns for each of the hydrazones or form a comparison of the calculated d values for the crystals and the observed intermties with the values for the various hydrazones which appear in the tables. If the sample is too small for convenient recrystallization, dissolve the crude crystals in alcohol a t room temperature in the cup on the slide and allow to evaporate to dryness again. .Zmilligrani or less of material will usually give an adequate pattern by this technique. Identification is considered positive if six or more diffraction maxima agree with those of a standard pattern. ANALYSIS OF KNOWN MIXTURES
A number of synthetic blends of pure 2,4-dinitrophenylhydrazones have been analyzed by these procedures. Representative results are presented in Table IV. One feature of these analyses is of interest. The presence of methyl ethyl ketone often leads to serious difficulties. It has been mentioned that its 2,4-dinitro phenylhydrazone may not be resolved from that of n-butyraldehyde. The data of Table IV indicate that i t is also incompletely resolved from mixtures containing isobutyraldehyde. P a r t of the difficulty undoubtedly arises from the anomalous behavior of methyl ethyl ketone. The 2,4-dinitrophenylhydrazone of this ketone, if passed through the chromatographic column by itself, will split into two bands. This phenomenon has been observed repeatedly and occurs even when the derivative is prepared from very pure methyl ethyl ketone and is further purified by repeated recrystallizations. Readsorption of each of the bands usually results in the separation of two more bands. -1possible explanation is that this is due to the separation of the syn and anti isomers of the 2,4-dinitrophenylhydrazone.
NO2
I
Table IV.
Quantitative Analysis of Mixtures of 2,4-Dinitrophenylhydrazones
Hydrazone Hydrazone Added, Recovered, % Hydrazone System 3Ig. AIg. Deviation 29.1 29.1 Acetaldehyde 0.0 Propionaldehyde +0.5 19.8 19.9 16.2 16.6 Propionaldehyde -2.4 17.4 1 7 . 4 n-Butyraldehyde 0.0 n-Butyraldehyde 20.0 20 8 +4.0 Isobutyraldehyde 17.5 17.8 +1.8 Acetaldehyde 24.5 23 .0 -6.0 10.6 11.2 Propionaldehyde +5.7 18.1 19.4 Acetone +8.0 n-Butyraldehyde 15.4 16.3 +.i.8 Isobutyraldehyde 14.4 12.6 -12.4 Methyl ethyl ketonea 19.0 16.8 -11.4 15.7 10.8 -31.2 Isobutyraldehyde Formaldehyde 13.5 13 5 0.0 Acetaldehyde 17.0 16 6 -2.4 Propionaldehyde 22 4 22 5 f0.4 n-Butyraldehyde 12.4 12 4 0.0 Propionaldehyde 16.0 14.7 -2.0 n-Butyraldehyde 14.8 13.3 i 3 . 2 17.5 16.3 Iaobutyraldehyde -5.8 16.3 Acetaldehyde 16.5 0.0 21.4 22 5 Propionaldehyde +5.2 Methyl ethyl ketone 13.9 17.5 +10.2 21.0 Isobutyraldehyde -20.0 16.8 u This mixture resolred into three bands. Further purification of each of hydrazones did not improve quantitative analysis.
This explanation seems to be substantiated by the fact that a similar separation is observed for other unsymmetrical ketones and also to a much lesser extent with aldehydes other than formaldehyde. In the case of the 2,4-dinitrophenylhydrazonesof the aldehydes, the second band is too small to have a large effect on the accuracy. However, in the case of methyl ethyl ketone it is apparent that the overlapping of one of its chromatographic bands with those of other components leads to large errors in the determination of these compounds by this scheme of analysis. White (16) and Schroeder ( 1 4 ) seem to have experienced this same difficulty, in that a single derivative will occasionally give rise to two adjacent bands which on elution and evaporation yield apparently identical compounds. The authors' work suggests that a certain degree of racemization may occur if the separated isomers are heated, which might account for the seeming identity of White's separated fractions. The proposed analytical method is a very laborious one which could probably be tolerated only in research investigations where it is necessary to obtain complete information on samples of diverse and unknown composition. About 8 hours are required for the chromatographic separation and 8 to 12 hours more to obtain and interpret the spectrophotometric and x-ray diffraction data. The exact amount of time depends, of course, upon the complexity of the sample. Obvious simplifications might be permitted if the qualitative compositions were known with certainty, obviating the necessity for the x-ray data. A smaller sample might then be taken, a smaller column used, and the whole process speeded up considerably. Appreciable savings in man-hours may also be achieved by operating as many as four to six chromatographic columns simultaneously. The methods have been found to be of considerable value for the purpose for which they were originally devised, the investigation of the nature of the reduction products of the ozonides of complex mivtures of olefins.
I
i Y
LITERATURE CITED
/\
H
N
/I
C CH,CH, /
\CHI
syn form
C H i 'CH2CH3 anti form
(1) Braude, E. .4., and Jones, E. R. H., J . Chem. Soc., 1945,498. ( 2 ) Buchman, E. R., Schlatter, M. J., and Reims, A. O., J . Am. Chem. SOC.,64,2701 (1942). (3) Cary, H. H., and Beckman, A. O., J . Optical SOC.A m . , 31, 682 (1941). (4) Cavallini, D., Frontali, K., and Toschi, G., Nature, 163, 568 (1949).
ANALYTICAL CHEMISTRY
1758 (5) Ibid., 164, 792 (1949). 16) Clark, G. L., Kaye, W. I., and Parks, T. D., IND. ENO.CHEM.,
ANAL.ED.,18,310 (1946). (7) Ewing, G. W., and Parsons, T., ANAL.CHEM.,20,423 (1948). (8) Friedman, H., Electronics, 18, 132 (1945). (9) Iddles, € -4., I. and Jackson, C. E., IND. ENG.CHEM.,ANAL. ED., 6,454 (1934). (10) Lange, J. J. de, and Houtnian, J. P. UT., Rec. trav. chim. PaysBas, 65,891 (1916).
(11) Rice, R. G., Keller, G. L., and Kirchner, J. G., ANAL. CEEM., 23,194 (1951) (12) Roberts, J. D., and Green, IND. ENG.C H m f . , ASAL. ED., 18, 335 (1946). (13) Roberts, 6. D., and Green, C.. J . Am. Chem. Soc., 68,214 (1946). (14) Schroeder, S B., Ann. K . Y . Acad. Sei., 49,204 (1948). (15) Strain, H. H., J . Am. Chem. Soc., 57, 758 (1935). (16) T h i t o , J. V , Jr., ANAL.CREM.,20,726 11948). RECEIVED March 25, 1949.
c.,
Determination of Small Concentrations of Carbonyl Compounds by a Differential pH Method HARRY R. ROE AND JOHN MITCHELL, JR. Polychemicals Department, E. I . du Pont de Nemours & Co., Inc., Wilmington, Del.
A procedure was required for rapid determination of small concentrations of active carbonyl compounds. The method developed involves measurement of the pH of 0.5 iV aqueous hydroxylamine hydrochloride before and after addition of the sample. The decrease in pH is a direct function of the amount of carbonyl compound in the sample. Calibration by a standard working curve permits accurate quantitative analyses. This 5-minute procedure has been applied successfully to 0.0 to 0.023 millimole per milliliter of aldehydes and methyl ketones in benzene, dioxane, methanol, or water solution.
liter. The p H of this solution should be 3.05 z!= 0.05. (Both Eastman Kodak Co. 340 and Fisher Scientific Co. H330 hydroxylamine hydrochloride were found satisfactory. Undoubtedly other sources of the C.P. quality chemical are available.) APPARATUS
A Beckman pH meter, Laboratory Model G, equipped with standard glass electrode So. 290 and standard calomel electrode No. 270 was used in this work. Other pH meters of equivalent quality are satisfactory. The meter should be standardized against a known buffer solution having a pH in or near the working range of the analysis (pH 2 , 3 , or 4). PROCEDURE
A
LDEHYDES and ketones react with hydroxylamine hydrochloride, forming oximes and releasing hydrochloric acid, Under selected conditions, the decrease in pH resulting from this reaction is a direct measure of carbonyl concentration. Huckabay, Sewton, and Metler (2) employed oximation with hydroxylamine hydrochloride for the determination of traces of acetone in liquefied gases by making a direct titration of the released hydrochloric acid. Later Byrne (1) described a method for the determination of traces of acetone in aqueous solutions by measuring the resulting change in pH. Studies made by the authors have shown that, with certain modifications, the differential pH principle has a much broader application. Rapid determinations may be madeof small concentrations of many carbonyl compounds in benzene, dioxane, methanol, or water solution. The procedure involves the controlled reaction of the sample with 0.5 N hydroxylamine hydrochloride solution. I n the range 0 t o 0.023 millimole of active carbonyl per milliliter the resulting decrease in pH is sufficiently marked to permit a direct correlation with carbonyl concentration. The time required for a single analysis is about 5 minutes. Results are reproducible to &2% relative.
One milliliter of 0.5 N hydroxylaniine hydrochloride is added to 10 ml. of distilled water in a 50-ml. beaker. The pH meter is adjusted to the temperature of the resulting solution and the pH is determined. This “blank pH” should be in the range 3.65 to 3.75. Then 10 ml. of the sample, containing no more than 0.23 millimole of aldehyde or ketone, are added, and the solution is mixed thoroughly and allowed to stand for 5 minutes a t room temperature. When the carbonyl content of a xater-immiscible sample, such as benzene, is being determined, stirring should be continued for the entire 5-minute reaction period in order to assure quantitative transfer of the carbonyl to the aqueous phase. At the end of this time, the temperature of the solution is checked and, if necessary, the pH meter is again adjusted, and the p H determined. The net decrease in pH observed is referred to a standard working curve (see Figure 1 ) to give a quantitative estimation of carbonyl.
REAGENT
Hydroxylamine hydrochloride, containing no free hydrochloric acid, is used. The quality of the hydroxylamine hydrochloride may be checked in the following manner: Five grams of the reagent are dissolved in 25 ml. of water and a few drops of bromophenol blue indicator solution are added. (If no free hydrochloric acid is present, the solution will be neutral to the indicator.) If free hydrochloric acid is present, as shown by the development of a yellow color, the solution should be neutralized with standard 0.5 N sodium hydroxide solution and the titer noted. A 0.5 N hydroxylamine hydrochloride solution is used in the analysis. I t is prepared by dissolving 35 grams of C.P. hydroxylamine hydrochloride, NH,OH.HCI, in water, adding the calculated amount of 0.5 N sodium hydroxide to neutralize exactly any free hydrochloric acid, and diluting the resulting solution to 1
C)-DIOXANE OR BENZENE SOLUTION @-METHANOL OR WATER SOLUTION
0.003 o.dos
o.do9
0.012
0015
O.dl8
O.d21
CONCENTRATION ( r n M / r n l )
Figure 1. Analytical Data for Acetone or Butyraldehyde in Various Media
