1878
ANALYTICAL CHEMISTRY
New Brunswick Laboratory of the Atomic Energy Commission chemically analyzed the different samples. LITERATURE CITED
(1) Birks, L. S., and Brooks, E. J., ANAL.CHEM.,23, 707-9 (1951).
(2) Birks, L. S., Brooks, E. J., Friedman, H., and Roe, R. M., Ibid., 22, 1258-61 (1950). (3) Campbell, W. J., and Carl, H. F., Ibid., 26, 800-5 (1954). (4j General Electric X-ray Corp,, Milwaukee, Wis., “SPG Fluores-
cent X-ray Spectrometer, Directions No. 116938.”
(5) General Electric X-ray Corp., Milwaukee, Wis., “XRD-3 Instruotion Manual.” (6) Hevesy, G. yon, “Chemical Analysis by X-rays and Its Applications,” McGraw-Hill, New York, 1932. (7) Kokotailo, G. T., and Damon, G. F., ANAL.CHEM.,25, 1185-7 (1953). RECEIVED for review July 13, 195.5. Accepted September 16, 1955. Fourth Bnnual X-Ray Symposium, Denver Research Institute, University of Denver, Denver, Colo., August 1955. Mound Laboratory is operated by Monsanto Chemical Co. for t h e United States -4tomic Energy Commission under Contract No. ST-33-1-GES-53.
Dete rmination of Beta, Beta'-Ox y dipropionitriIe and Ethy Iene Cyanohydrin with Acrylonitrile by Infrared Absorption ELSIE
F. DUPRE, ANNE C. ARMSTRONG’, ELlAS KLEIN,
and
ROBERT T. O’CONNOR
Southern Regional Research Laboratory, N e w Orleans, La.
This paper presents an analytical method for the determination of B,P’-oxydipropionitri& and ethylene cyanohydrinin admixture with acrylonitrile. In several reactions involving acrylonitrile the efficiency is decreased by the formation of by-products, among which are @,B’-oxydipropionitrileand ethylene cyanohydrin. Studies of the effect of catalyst, temperature, etc., to reduce the formation of these undesirable by-products require a method for their analysis in admixture with acrylonitrile. A simple multicomponent analysis by means of infrared absorption spectra is described, which permits a simultaneous determination of the three compounds. This method, which is being used in connection with studies on the cyanoethylation of cotton, has been tested by the analysis of known mixtures and found to be satisfactory.
A
MOST important problem in the cyanoethylation of cotton and in other reactions involving the use of acrylonitrile is the loss of acrylonitrile through the formation of the by-products, among which p,P’-oxydipropionitrile and ethylene cyanohydrin are prominent. Because these losses are a major element in the chemical costs of the process, studies of the effects of the variations of catalyst and temperature on this reaction have been made. Before a quantitative study of the formation of P,B’-oxydipropionitrile and/or ethylene cyanohydrin could be undertaken, a satisfactory analytical method for the measurement of these three compounds in admixture was essential. No chemical methods for this analysis were available. This paper describes a method of multicomponent analysis by means of infrared absorption spectra.
chloroform solution. A detailed study was made of these spectra to select bands which would be suitable for quantitative analysis. In the 8- to 11-micron region (Figure 1)each compound exhibited a strong band a t a wave length a t which each of the other two components was very transparent. These maxima, which were used for the quantitative analyses, are: acrylonitrile, 10.36 microns ; ethylene cyanohydrin, 9.42 microns; and P,P’-oxydipropionitrile, 8.85 microns. Spectra were scanned over this 3-micron region after balancing the instrument with chloroform in the absorption cell. Thus, the effect of solvent was compensated for in making all measurements. The spectra of the pure compounds and analytical samples were then obtained by playback from the tape recorder immediately after standardization. Entrance slits a t the three selected wave lengths Rere: 10.36 microns, 0.35 mm.; 9.42microns1 0.44 mm.; and 8.85 microns, 0.28 mm. Applicability of the Beer-Lambert law was checked for each of the three compounds a t the selected wave lengths (Figure 2). From the slopes of these types of Beer-Lambert curves, the average values of absorptivities for both maxima and background for each of the three compounds at 10.36, 9.42, and 8.85 microns were obtained. Absorptivities a t the maxima of the selected absorption bands for each of the three
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EXPERIMENTAL
Infrared absorption measurements were made with a Beckman I R 3 T automatic recording infrared spectrophotometer, using a single 0.4-mm. sodium chloride cell for both standardization and “playback.” Acrylonitrile was prepared from commercial grade material by drying over sodium sulfate and filtering: $io = 1.38886. Ethylene cyanohydrin was also prepared from commercial grade material by redistillation: boiling point 82“ per 4 mm. of mercury; 7ar;0 = 1.43737. B,jY-Oxydipropionitrile was synthesized by the method described by Bruson ( 1 ) : boiling point 155” per 4 mm. of mercury; = 1.43914. INFRARED ABSORPTION SPECTRA
Complete infrared absorption spectra in the rock salt region from 2 to 12 microns were obtained for the pure compounds in I
Present address, Florida State College, Tallahassee, Fla.
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WAVE LENGTH MICRONS Infrared spectra in chloroform solution, 8 to 11 microns
Figure 1.
A.
Acrylonitrile
C.
Ethylene cyanohydrin
B. B,B’-Oxydipropionitrile
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V O L U M E 2 7 , NO. 1 2 , D E C E M B E R 1 9 5 5 Table I. blixture No. I
I1 I11 IV V VI
Acrylonitrile, % Added Found 76.60 75.08 78.71 80.38 78.92 80.68 87.00 89.06 80.97 79.36 68.13 65.89
Recovery Tests on Mixtures p,p’-O?ydipropionitrile, % Added Found 12.70 1 2 . 7 6 14.64 14.41 21.08 20.13 0.00 0.00 12.12 12.03 17.96 1 6 . 7 8
Ethylene Cyanohydrin,
%
Added 10.70 6.65 0.00 13.00 6.91 13.91
Fopnd 11161 7.40 0.00 13.45 7.52 15.84
Total. % Added Found 99.45 100.00 100.00 102.19 100.00 100.81 100.00 102 51 100.00 98.91 100.00 98.51
equations are, in the strictest quantitative sense, applicable only t o this instrument. They should, however, be expected to be reasonably satisfactory for measurements with any Beckman IR-2 or IR-2T spectrophotometer, operated under conditions which permit use of the above suggested slit widths. For analysis under other settings or with other types of instruments the absorptivities must be redetermined.
i Table 11. Analyses of Cyanoethylation Mixtures Acrylonitrile 95.54 95.58 94.59 93.43 95.34 96.65 96.47 94.88 93.86 93.60 91.82 96.31 85.55
Run
p,p’-Oxydipropionitrile
0.00 0.00 0.00 1.64 2.20 0.69 0.05 0.00 0.00 1.37 1.22 0.89 8.34
Per Cent Ethylene cyanohydrin 0.00 0.00 2.14 0.00 0.00 0.72 3.22 0.55 1.84 0.00 1.48 0.97 0.64
Water 1.5 1.6 1.5 2.4 3.5 1.6 3.0 3.4 4.3 3.5 3.9 3.1 3.5
Total 97.04 97.18 98.23 97.47 101.04 99.66 102.74 98.83 100.00 98.47 98.39 101,27 98.03
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0.3pure compounds are: acrylonitrile 10.36 microns, 2.14; ethylene cyanohydrin 9.42 microns, 2.08; and ?,?’-oxydipropionitrile 8.85 microns, 2.70. By a simultaneous solution of expressions for the total absorption contributed by each of the three compounds a t each of the three selected wave lengths, the following tricomponent equations were obtained:
- 0.0119A - 0.0199B) X (0.37158 - 0.0158B - 0.0073C) X = (0.4821B - 0.03644 - 0.0028C) X
x = (0.4671C y z
=i
100 100 100
where 2, y, and z are percentages of acrylonitrile, p,B’-oxydipropionitrile, and ethylene cyanohydrin, respectively, in an admixture, and A , B, and C are absorptivities of the sample a t 8.85, 9.42, and 10.36 microns, respectively. The equations were tested by the analysis of mixtures of known ratios of the three components. Results are shown in Table I. Mixtures from cyanoethylation of cotton in several laboratory experiments and in a single pilot plant experiment were analyzed according t o the method described. The results are reported in Table 11. DISCUSSION
In the 8- to 11-micron range, selected for the multicomponent infrared analysis, a strong maximum for each compound, at nvave lengths where the other components are almost completely transparent, permits satisfactory simultaneous tricomponent analysis. The selected maxima, completely resolved in the spectra of an admixture containing all three components, yet included in only a 3-micron range, facilitate automatic recording measurements. The method could easily be adapted t o null-type instruments using cell-in-cell-out techniques. Figure 2 illustrates that the Beer-Lambert law is followed by all three compounds if the concentration is not more than 10 grams per liter in chloroform. At higher concentrations a departure from linearity was found, increased concentration resulting in less than the expected increase in absorbance. Chloroform solutions of samples containing approximately 10 grams per liter were found t o give satisfactory absorbances for the quantitative measurements involved in studies of the kinetics of the formation of by-products from acrylonitrile. The absorptivities given above are, like all infrared quantitative measurements, strictly applicable only t o the instrument on which they were obtained. Consequently, the multicomponent
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CONCENTRATION Figure 2.
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Beer’s law in chloroform solution
A . Acrylonitrile a t 10.36 microna B. p,p‘-Oxydipropionitrile a t 8.85 microns C. Ethylene Cyanohydrin a t 9.42 microns
Absorptivities a t the three selected wave lengths for the three pure compounds have been measured on a Perkin-Elmer Model 21 split-beam spectrophotometer and multicomponent equations calculated. The instrument settings were: resolution, 915; response, 2; gain, 7; speed, 4; and suppression, 2. At these settings entrance slit widths and calculated absorptivities were found to be: Acrylonitrile Ethylene cyanohydrin @$‘-Oxydipropionitrile
10.36r,slitwidth0.11 mm.,a = 1.80 9 . 4 2 ~ , s l i t w i d t h O . O 9 2 m m . , a= 1 . 7 3 8 . 8 5 p , s l i t u.idth0.08 mm., a = 2 . 4 5
From these data the following simultaneous equations were obtained:
x y
z
(0.5565C - 0.0071A - 0.0162B) X 100 (0.40958 - 0.0173B - 0 0056C) X 100 (0.5788B - 0 03239 - 0 0065C‘) X 100
These equations should give reasonably satisfactory results from data obtained with the Perkin-Elmer RIodel21 spectrophotometer operated under the conditions and at the slit widths cited. Data in Table I illustrate that satisfactory results have been obtained by the proposed method. The method is being used t o study the effects of variation of catalyst on the formation of B,B’-oxydipropionitrile and ethylene cyanohydrin from acrylonitrile during the cyanoethylation of cotton. LITERATURE CITED
(1) Bruson, H. A,, U. S. Patent 2,382,036 (Aug. 14, 1945). RECEIVED for review J u n e 7, 1955. Accepted September 6, 1955. Mention of names of firms or t r a d e products does not imply t h a t t h e y are reoommended o r endorsed b y U.S. Department of Agriculture over other firms or similar products not mentioned.
