However, the conditions as described provide the most practical differentiation of the two classes of ketosteroids involved. Calibration curves prepared as described above are strictly linear. Dayto-day variations in the slope and intercept of such curves necessitate the inclusion of standard mixtures in parallel with unknowns for maximum accuracy. These variations appear to reflect the effect of minor temperature differences on the reaction rate of the A1e4-3-ketosteroid involved. Results from the application of the method to known mixtures of typical steroid pairs are given in Table I. A mean deviation for per cent A4-3-ketosteroid of =t 0.04 is obtained over the range 0 to 6%. Similar results have been obtained with steroid intermediates. Analysis of a group of typical 6a-methylprednisolone samples for per cent 6~~-methylhydrocortisone has given a mean deviation from the average of duplicates of i.0.05 (Table 11). The method is based on the assumption of a two-component system. Son-
steroidal material will therefore act as a negative interference and give a low value for A4-3-ketosteroid. A determinationof total steroid by ultraviolet spectroscopy or other applicable methods corrects for such interference. The procedure appears to be general for A4-3ketosteroids ( 2 , 10) and consequently will not differentiate mixtures of such steroids. The A4-3-ketosteroid range of 0 to 6% has been useful for the analysis of bulk preparations. Other ranges may by accommodated by suitable adjustment of sample sizes and appropriate calibration. If reaction mixtures are prepared in groups of three a t approximately 10minute intervals, 15 samples may be run by a single operator in about 3 hours, exclusive oi the time required for sample preparation. This procedure, therefore, provides a rapid, sensitive, and precise measure of small amounts of A4-3ketosteroids in bulk A1~4-3-ketosteroids. LITERATURE CITED
(1) Bunim, J. J., Pechet, M.
A. J., J . ilm. M e d . Assoc. 157, 311-18 (1955). (2) Bush, I. E., Federation Proc. 12, 186 (1953). (3) Conant, J. B., Bartlett, P. D., J . Am. Ch,em. SOC.54, 2881-99 (1932). (4) Evans, L. K., Gillam, A. E., J . Chem. SOC.1943, p 065-71. (5) Hogg, J . Lincoln, F. H., Nathan, A. H., Hanze, A. R., Schneider, W. P., Beal, P. F., Korman, Jerome, J . Am. Chem. SOC.77, 4438-9 (1955). (6) Lyster, S. C., Barnes, L. E., Lund, G. H., Meinzinger, M. M., Byrnes, TV. W., Proc. SOC.Exptl. Biol. Med. 94, 159-62 (1957). ( 7 ) Spero, G. B., Thompson, J. L., Magerlein, B. J., Hanze, A. R. hlurray, H. C., Sebek. 0. K.. hoe^ J. J . Am. Chem. SOC.78, 6213-14-fl956). ' (8) Spies, T. D., Stone, R. E., Lopez, G. G., Tellechea, C. M. D., Toca, R. L., Reboredo, Alfredo, Suarez, R. hI., J. Am. Med. Assoc. 159, 645-52 (1955). (9) Stempel, G. H., Jr., Schaffel, G. S., J . Am. Chew SOC.66, 1158-61 (1944). (10).Talbot, N.B., Ulick, Stanley, Koupreianow, Anna, Zygmuntowica, Aniela, J . Clin. Endocrinol. and Metabolism 15, 301-16 (1955). (11) Thorn, G. IT., Renold, A. E., Morse, TV. I., Goldfien, Alan, Reddg, W. J., Bnn. Internal M e d . 43.979-1000 (1955). RECEIVED for review July 23, 1958. Accepted December 11, 1958.
k?,
A..
~I
M.,Bollett,
Determination of Bound Styrene in Raw and Cured Polymers by Nitration C. L. HILTON, J. E. NEWELL,' and JACOB TOLSMA U. S. Rubber Co. Research Center, Wayne, N. J. ,Although existing methods for the determination of styrene content of polymers yielded excellent results with pure raw polymers, no satisfactory method was available for cured stocks or carbon black masterbatches. A spectrophotometric method has been developed which is applicable to raw and cured stocks without modification, is comparatively simple, requires about 3 man-hours per determination, and yields excellent results in the hands of a laboratory technician. The polymer is nitrated with concentrated nitric acid to yield pnitrobenzoic acid as the main product. Results with more than 2000 samples indicate accuracy and precision to about 3 ~ 1 % relative.
T
three most widely used methods for the determination of bound styrene are index of refraction (2, 4, I O ) , infrared absorption (3, 7, Q), and HE
Present address, Naugatuck Chemical Division of United States Rubber Co., Naugatuck, Conn.
ultraviolet absorption (6, 12, 13). For accurate results raly polymers undergoing analysis must be free from carbon black, fillers, antioxidants, soap, fatty acids, and gel. K h e n cured stocks are being analyzed, the cured polymer must be separated in a soluble form from all other ingredients in the stock. Losses of polymer may result from degradation of the polymer by the solvent or from adsorption of the polymer on the filter aids used to remove carbon blacks and fillers. Among the other methods reported in the literature are x-ray diffraction (8), mass spectrometry (11), reaction rates with nitric-sulfuric acid mixture (14), and density measurements (16). The nitration procedure described was suggested by the qualitative method in the British User's Memorandum (6) and by the A S T X method ( 1 ) . Materials most likely to cause erroneous results may be removed by extraction, and those that remain uneatracted (carbon black, fillers, and other polymers) interfere slightly, if a t all. When polymers containing bound styrene react with a n excess of nitric
acid, the polymer is first nitrated and then oxidized. The main product is p-nitrobenzoic acid as shown by the ultraviolet absorption spectrum, the melting point, and the neutral equivalent. The accuracy and precision are very satisfactory, especially for raw polymers. Calibration by a series of standard polymers, provided by the National Bureau of Standards, shows average agreement for styrene content of 0.2%. The precision is of the same order of magnitude. APPARATUS AND MATERIALS
The instrument was a Beckman Model D U spectrophotometer, with silica cells having an optical path of 1.000 cm. The slit widths for the wave lengths concerned were 285 mp, 0.720 mm.; 273.75 mp, 0.813 mm.; and 265 mp, 0.878 mm. The method was calibrated using samples of styrene-butadiene copolymers accurately analyzed by the Kational Bureau of Standards for carbon and hydrogen. The styrene contents as derived from these values ranged from 0 to 53%. Later work with mixtures of VOL. 31, NO. 5, MAY 1959
915
WAVE
L E N Q T H IN
I
Mp
300
350
j
Figure 1. Spectra of material extractable from reaction of styrene-butadiene copolymers and nitric acid
@
polystyrene and polybutadiene show that calibration using such mixtures would be just as satisfactory. The ultraviolet absorption spectra of material extracted from the reaction of styrene-butadiene copolymers and nitric acid are given in Figure 1. Reagents. Concentrated nitric acid, Baker’s analyzed reagent grade, 69.9%, specific gravity 1.420. Sodium hydroxide pellets, reagent grade, 5N, 200 grams of sodium hydroxide per liter (distilled water); O.lN, 4 grams of sodium hydroxide per liter (distilled water). Anhydrous diethyl ether, analytical reagent grade. PROCEDURE
Weigh a sample of chloroformextracted cured stock, or alcoholextracted ram stock, not exceeding 0.25 gram. Put the weighed sample in a 125-ml. standard-taper flask and add 20 ml. of concentrated (69 to 71%) nitric acid. Add a few boiling chips, and insert a water-cooled Graham condenser. Graham Ful-Jak condensers (Scientific Glass Apparatus Co., Catalog No. 5932-4) are better than Allihn condensers in the digestion apparatus. They reduce the loss of nitric acid and the air oxidation of p-nitrobenzoic acid during digestion. Place on a cold electric hot plate. Turn on the heat and allow the sample to reflux fairly vigorously for at least 16 hours (see Figure 2). After the first hour the space in the flask above the boiling acid should contain only slight brown fumes, most of the brown fumes being well up in the condenser.
916
ANALYTICAL CHEMISTRY
280
HOURS 3*Si
8
I~
250
LENGTH IN
I
350
300 WAVE
300
1 320
10
Figure 3. Ultraviolet absorption spectrum of sodium nitrate from nitric acid and sodium hydroxide
ly L
WAVE LENGTH (MILLIMICRONS)
260
Mp
Figure 2. Ultraviolet absorption spectra of material extractable from reaction of SBR rubber and nitric acid
Pour 10 to 20 ml. of distilled water into the top of the condenser and turn off the heat. The water will be slowly drawn down into the flask, washing the condenser. Allow the reaction mixture to cool enough to permit handling the flask. Disconnect the condenser and rinse the standard-taper joint with distilled water. Transfer the contents into a 400-ml. beaker and chill to below room temperature. With stirring, add 50 nil. of 5N sodium hydroxide solution (20 grams of sodium hydroxide pellets in 100 ml. of water). Because this amount is insufficient for neutralization, the solution should be still “very strongly acid” to Eimer & Amend’s Alkacid test paper or similar indicator paper. Chill the
beaker and contents to below room temperature and transfer the contents, with appropriate washing, to a 500-ml. separatory funnel. Extract the solution three times with separate 50-ml. portions of ether. Combine the ether extracts in a 500-ml. separatory funnel and wash with a 50-ml. portion of distilled water to remove any interference from nitric acid (see Figure 3). Transfer the combined ether extracts to a 400-ml. beaker containing a few grams of anhydrous sodium sulfate. Transfer the ether extract to a second separatory funnel. Extract the accumulated ether extracts with three or more portions of approximately 0.1N sodium hydroxide solution, collecting the aqueous extracts in a 250-ml. volumetric flask. Fill the volumetric flask to the line, and mix well. \17ith a 25-ml. pipet and a 250-ml. volumetric flask, dilute the alkali extract 1 to 10, using 0.1N sodium hydroxide as diluent. With 0.1N alkali in the blank cell, and the diluted alkali extract in the sample cell, measure the absorbances a t 265, 273.75, and 285 mp, with a Beckman Model DU spectrophotometer. From the absorbance values and sample weight calculate the styrene content. THEORY
It is assumed that when a butadienestyrene polymer is nitrated, and the nitration products are examined for ultraviolet absorption, the absorption due to the styrene nitration products is proportional to the styrene content of the polymer; the absorption due to the butadiene nitration products is proportional to the butadiene content.
For a pure raw polymer: a. (polymer) = Xa,(styrene)
(1
+
- X)a, (butadiene)
Table 1. (1)
where X and (1 - X) are the fractions of styrene and butadiene, respectively, and a, is the absorptivity for the material concerned. Absorptivity equals A,/bc, where A . is the absorbance of the solution, b is the optical path in centimeters, and c is the concentration in grams per liter.
Absorptivity Values for Styrene
Styrene Content, % 8.58
Sample x-454 X-478
22.61
MS660
36.26
MS662
42.98
MS661
53.09
RESULTS
a. (butadiene) was determined by the nitration and extraction of polybutadiene. The values at 265, 273.75, and 285 mp were 0.373, 0.310, and 0.265, respectively. a, (styrene) was determined by nitration and extraction of a series of samples accurately analyzed b y the Kational Bureau of Standards for carbon and hydrogen content. The styrene contents derived from these values ranged from 0 to 53%. Although these samples were prepared by a commerical company, they were available to participating members in the government synthetic rubber program carried on during the World War 11. These values should be determined for each instrument used because of differences in slit 6-idths. Three wave lengths were used in developing the present method because interfering materials might be present. Lack of agreement a t the three wave lengths indicates the presence of interferences. If interferences are present, the method cannot be considered to be accurate for that particular sample. Although p-nitrobenzoic acid is the major nitration product, i t is not the only material present. Consequently, the absorptivity for p-nitrobenzoic acid could not be uti1izc.d. When the absorptivities are inserted in Equation 1, Equations 2, 3, and 4 result.
% styrene = 1.52 a8265 - 0.56 (2) % styrene = 1.44 ae2j3.7S - 0.45 (3) % styrene = 1.60 ae285- 0.42 (4) Table IT shon s the results when Equa-
Polystyrene
100.00
Weighted av.
a,
265 mp 5.85 5.88 15.14 15.14 23.87 23.87 28.60 28.63 35.00 35.38 67.00 67.43 66.27
273.75 mp 6.14 6.23 16.11 16.11 25.20 25.46 30.16 30.32 36.78 37.04 70.84 71.12 69,71
285 m p 5.67 5.76 14.62 14.68 22.61 23.01 26.85 27.29 33.40 33.62 62.10 62.16 62.63
LITERATURE CITED
Table II. Apparent Styrene Content of Raw Polymers
Sample NE-1 X-454 X-478 MS-660 MS-662 MS-66 1
Styrene, % Present Found 0.00 0.01 0.01 8.58 8.46 8.57 22.61 22.72 22.76 36.26 35.78 36.11 42.98 42.81 43.14 53.09 52.72 53.16
Polystyrene 100.0
Error, 7* Abso- Relalute tive 0 01 .. 0.01 .. 0.12 1.40 0.01 0.12 0.11 0.49 0.15 0.66 0.48 1.32 0.15 0.41 0.17 0.40 0.16 0.37 0.37 0.70 0.07 0.13
100.59 0.59 101.01 1.01 hv. 0.24
0.59 1.01 0.63 _ 1
Table 111.
Sample JEN-1 JEN-2 JEN-3 JEN-4 JEN-5
(1) Am. Soc. Testing Materials, Philadelphia, Pa., “ASTM Standards on Rubber Products,” D-11, pp. 1004-5, 1955. (2) Arnold, A., Madorsky, I., Wood, L. A., ANAL.CHEM.23, 1656-9 (1951). (3) Binder, J. L., Ibid., 26, 1877-82 (1954). (4) Boelhoumer, C., Tjoan, T. S., Waterman, H. I., Anal. Chim. Acta 11, 74-8 (1954).
(7) Dinsmore, H: L., 20, 11 (1948). (8) Gehman, S. D., Tanderbilt Rubber Handbook,” 9th ed., . 577, 1948. (9) Hampton, R. R., CHEM.21, 923 (19‘49). . (10) Hart. E. J.. Mever. A. W..J. Am. ‘ &em. Soc. 71’(1949).‘ (11) Madorsky, S. L., et al., J . Polymer Sci. 4, 639-64 (1949).
XNAL.
’
Apparent Styrene Content of Cured Stocks
Styrene, yo Present Found 0.00 0.65 0.55 3.34 3.15 3.61 6.68 6.81 6.61 10.01 10.40 10.20 13.35 13.65 12.95
Error, % Absolute 0.65 0.55 0.19 0.27
0.13 0.07 0.39 0.19 0.30 0.40 0 31
Relative
.. 5:68 8.08 1.95 1.05 3.90 1.90 2.55 3.00 3.48
tions 2, 3, and 4 ryere applied. INTERFERENCES
The folloiving materials interfere slightly or not a t all: smoked sheet, natural rubber reclaim, Paracri! B, poly(methy1 methacrylate), polyisoprene, polyethylene, polypropylene, neoprene, and carbon black. Interferences include accelerators, antioxidants, aromatic compounds, and certain heterocyclics. The compounding ingredients including oils would be readily removed by extraction.
Such materials as a-methylstyrene, vinyl toluenes, ethylstyrenesj and divinylbenzenes will yield similar nitration Droducts and cannot be distinguished from styrene by this method. APPLICABILITY
Although the method mas developed
(12) _Meehan, E. J., Ibid., 1, 175-82 (1946).
(13) Melville, H. W., Valentine, L., Trans. Faraday Soe, 5 1 ( l l ) , 1474 ll955l \----/-
(14) Parker, L. F., Rubber Chem. & Technol. 18, 659 (1945). (15) Wood, L. A., Bekkedahl, Norman, Roth, F. L., Ind. Eno. Chem. 34. 1291 (1942).
VOL. 31, NO. 5, M A Y 1959
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