tion media, presumably because of gradual precipitation.
Institute of Neurological Diseases and Blindness, Public Health Service. LITERATURE CITED
ACKNOWLEDGMENT
(1) Agranoff, B., Northwestern Univer-
The authors wish to express their appreciation to Beverly Brown and Barbara Roecker for carrying out preliminary experiments on this problem, and to the Rohm & Haas Co. for gifts of their high molecular m-eight amines. The work was supported in part by grant No. B-1179, from the National
sity Liquid Scintillation Counting Symosium, August 22, 1957, Evanston, Ill. (2p Davidson, J. D., Feigelson, P., Intern. J . A p p l . Radiation and Isotopes 2, l(1957). (3) Hayes, F. N., Hiebert, R. D., Schuch, R. L., Science 116,140 (1952). Ott, D. G., Kerr, V. K., (4) Hayes, F. N., Nucleonics 14, No. 1, 42 (1956). (5) Helf, S., Castorina, T. C., White,
c. G., Graybush, R. J., ANAL. Cmar. 28, 1465 (1956). (6) Markovitz, A., University of Chicago,
personal communication. (7) Passmann, J. M., Radin, N. S., CooDer. J. A. D.. ANAL.CHEM.28, 484 (1956).' (8) Radin, N. S., Sorthwestern University Liquid Scintillation Counting Symposium, August 21, 1957, Evanston, Ill. (9) Radin, N. S., Martin, F. B., Brown, J. R., J . Bwl. Chem. 224,499 (1957). (10) Vaughan, M., Steinberg, D., Logan, J., Science 126,446 (1957). RECEIVED for review February 7, 1958. Accepted July 28, 1958.
Spectrophotometric Determination of p -tert- Buty Icatec hol a nd 0-Amino p he no1 in 2-Methyl-5-vinylpyridine KURT H. NELSON and M.
D. GRIMES
Phillips Petroleum Co., Bartlesville, Okla. p-tert-Butylcatechol in 2-methyl-5vinylpyridine can be determined b y dissolving the sample in 1.ON hydrochloric acid and extracting the p-fertbutylcatechol with diethyl ether. The p-tert-butylcatechol i s then extracted from the ether with 1.ON sodium hydroxide and i s air oxidized to the colored quinoid form for spectrophotometric measurement at 485 mp. oAminophenol is determined by dissolving the 2-methyl-5-vinylpyridine in n-heptane and extracting the oaminophenol with 0.1 N hydrochloric acid, The acid phase i s buffered with ammonium acetate-acetic acid and the o-aminophenol i s oxidized with hydrogen peroxide, after which its absorbance i s measured at 435 mp. About 40 mFutes is required to analyze a sample for both inhibitors.
I
N THE MANUFACTURE of 2-methyl-5-
vinylpyridine, inhibitors are added to prevent polymerization and other undesirable reactions during shipment and storage. Usually, p-tert-butylcatechol is added as the inhibitor, but oaminophenol may also be added for this purpose. Enough of these inhibitors is added to give an initial concentration in the range of 0.0 to O.3y0p-tert-butylcatechol and 0.0 to 0.1% o-aminophenol. Because the concentrations of the inhibitors decrease with time, a method for the determination of the concentration level of either inhibitor is necessary to assure continued effectiveness. The direct application of ultraviolet spectrophotometry to the determination of the inhibitors did not appear feasible because the 2-methyl-5-vinylpgridine 1928
ANALYTICAL CHEMISTRY
is a very strong absorber in the spectral region around 280 to 286 mp and would mask the bands arising from the p-tertbutylcatechol and o-aminophenol. p-tert-Butylcatechol in butadiene has been measured by a ferric chloride colorimetric procedure (6), by a ceric sulfate titration method (?'), and by ultraviolet measurements after removal of the butadiene by evaporation (1). It has also been determined colorimetrically in 2-methyl-5-vinylpyridine after extraction into sodium hydroxide solution, During the extraction, the p-tertbutylcatechol is air oxidized to a colored quinoid form ( 3 ) . No method for determining o-aminophenol in 2-methyl-5-vinylpyridine was found in the literature. o-Aminophenol in other materials has been determined by titration with standard perchloric or hydrochloric acid in glycol-hydrocarbon solvents, using potentiometric or thymol blue end points ( 2 ) . Another procedure describes the oxidation of o-aminophenol with an excess of standard ceric sulfate, followed b y back titration of the remaining ceric sulfate with ferrous sulfate (8). o-Aminophenol has also been determined by fluorescence measurements after reaction with benzoyl chloride (6). None of these existing methods, except the procedure for p-tert-butylcatechol in 2-niethyl-5-vinylpyridineI appeared applicable to the present case. Preliminary experiments, however, showed that the procedure for p-tertbutylcatechol gave erroneous results when o-aminophenol was also present. Therefore, the procedures described below were developed.
REAGENTS
BUFFER SOLUTIOS. Dissolve 200 grams of reagent grade ammonium acetate in 500 ml. of distilled water, add 10.0 ml. of glacial acetic acid, and dilute with distilled mater to 2000 ml. in a volumetric flask. 2-1\kTHYI&VINSLPYRIDINE. Distill 1000 ml. of 2-methyl-5-vinylpyridine a t 10 nim. pressure and 64' C. Collect approximately 800 ml. of distillate after discarding the first 20 ml. p-teTt-BUTYLCATECHOL. Purify by distillation a t 4 mm. pressure and 140' C. Prepare a stock solution by dissolving 1.000 gram of purified material in 2methyl-5-vinylpyridine and diluting t o 100 ml. with 2-methyl-5-vinylpyridine. To prepare standard solutions, transfer 0.0, 5.0, 10.0, 15.0, and 20.0 ml. of the stock solution to 50-ml. volumetric flasks and dilute to volume with 2methyl-5-vinylpyridine. 0-AMINOPHENOL. Recrystallize from ethyl alcohol. Prepare a stock solution by dissolving 0.2500 gram of purified material in 2-methyl-5-vinylpyridine and diluting to 50 ml. with 2-methyl-5vinylpyridine. To prepare standard solutions, transfer 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 ml. of the stock solution to 50-ml. volumetric flasks and dilute to volume with 2-methyl-6-vinylpyridine. APPARATUS
SPECTROPHOTOMETER. A spectrophotometer capable of recording the spectrum in the 300- t o 700-mp wave length region is preferable. A Cary Model 11 recording spectrophotometer was used in this investigation. A Beckman Model DLT or B spectrophotometer may be used by measuring absorbances at three wave lengths. Quartz or Corex cells with a 1-em. light path are also used.
0 7755
1
-
--
0.00 300
400
500
600
0.00
I
WAVE LENGTH, my
PROCEDURE
p - terf - Butylcatechol Calibration Curve. Place 10.0 ml. of 1.ON hydrochloric acid in a 60-ml. separatory funnel. Add 1.0 ml. of a standard p-tert-butylcatechol solution and 5.0 ml. of diethyl ether. Shake the funnel for 2 minutes and drain t h e acid phase into another 6O-ml. separatory funnel. Add 5.0 ml. of diethyl ether t o the second funnel and shake for 2 minutes. Discard the acid phase and transfer the ether phase to the first separatory funnel. Add 5.0 ml. of 1.ON sodium hydroxide to the ether phase and shake for 2 minutes. Drain the sodium hydroxide layer into a 50-ml. volumetric flask, dilute to volume with distilled water, and immediately record the spectrum from 300 to 700 mp, with distilled water in the reference cell. Calculate the absorbance a t 485 mp as outlined below. Repeat the procedure for the other standard solutions and plot the calibration curve. odminophenol Calibration Curve. Place 10.0 ml. of n-heptane in a 60nil. separatory funnel, and add 1.0 ml. of a standard o-aminophenol solution and 8.0 ml. of 0.1N hydrochloric acid. Shake the funnel for 5 minutes and drain the acid phase into a 50-mi. volumetric flask. Add 8.0 ml. of 0.1N hydrochloric acid to the separatory funnel and again shake for 5 minutes. Then drain the acid phase into the same volumetric flask. Add approximately 30 ml. of buffer solution and 1.0 ml. of 30% hydrogen peroxide, then dilute t o the mark with buffer solution. T r e n t y minutes after the addition of the hydrogen peroxide, record the spectrum of the solution from 300 to 700 mp, using buffer solution in the reference cell. Calculate the absorbance a t 435 mp as outlined below. Repeat the Frocedure for the other standard solutions and plot the calibration curve. Determination of P-fert-Butylcatechol. Place 10.0 ml. of 1 . O N hydrochloric acid, 1.0 ml. of 2-methyl5-vinylpyridine sample, and 5.0 ml. of diethyl ether in a 60-ml. separatory
'
'
'
'
'
600
500
400
700
WAVE LENGTH, my
Figure 2. Spectrum of oxidized o-aminophenol showing calculation of absorbance a t 435 mp
Figure 1 . Spectrum of oxidized p-fert-butylcatechol showing calculation of absorbance a t 485 mp Hypodermic syringes, 1, 5, 10, and 20 ml., fitted with 18- and 20-gage, &inch hypodermic needles.
'
700 -..
funnel. Extract the p-tert-butylcatechol twice with ether, as described above. T o the combined extracts in t h e first separatory funnel, add 5.0 ml. of 1 . O N hydrochloric acid and shake for 2 minutes. Discard the acid phase, add 5.0 ml. of 1.ON sodium hydroxide to the ether layer, and continue the determination as described for the calibration curve. Use distilled water in the reference cell. Determination of o-Aminophenol. Add 10.0 ml. of n-heptane, 1.0 ml. of 2-methyl-5-vinylpyridine sample, and 8.0 ml. of 0 1N hydrochloric acid to a 60-ml. separatory funnel. Carry out the extraction as described for the calibration curve. Twenty minutes after adding the hydrogen peroxide, record t h e spectrum of t h e solution from 300 to 700 mp, with buffer solution in the reference cell. CALCULATIONS
The calculation of the absorbance for the p-tert-butylcatechol determination is illustrated in Figure 1. First, draw a line, AB, from 350 to 650 m p . Then draw another straight line, CDE, perpendicular to the zero absorbance line a t 485 mp. Measure the absorbance along CD. Using this absorbance, read the milligrams of p-tert-butylcatechol from the calibration curve. Calculate the weight per cent p-tert-butylcatechol by means of the equation: p-tert-Butylcatechol, 7, = B
ill X D X 10 ( I )
n-here
B
M
=
weight of p-tert-butylcatechol, mg.
= volume of 2-methyl-5-vinylpyri-
dine, ml.
Table I. Temp., ' C. 15.0 20.0 25.0 30.0
95 0.9606 0.9563 0.9520 0.9478
D
density of 2-methyl-5-vinylpyridine, grams per ml. (Table I)
=
The calculation of the absorbance fqr the o-aminophenol determination IS similar to that for p-tert-butylcatechol. On the spectrum (Figure 2) for oaminophenol, draw the line, AB, from 350 to 585 mp. Draw a second line, CDE, a t 435 mp and measure the absorbance along CD. Read the milligrams of o-aminophenol from the calibration curve and calibrate the weight per cent o-aminophenol using the equation : o-Aminophenol, weight yo =
where
A
=
weight of o-aminophenol, mg., and the other terms ale the same as for Equation 1. DISCUSSION
I n plant operations, p-tertbutylcatechol is determined by dissolving the 2methyl-5vinylpyridine sample in carbon tetrachloride and extracting the p-tertbutylcatechol into sodium hydroxide solution. During the extraction the p-tert-butglcatechol is air oxidized to a colored quinoid form, which is nieasured a t a wave length of 485 my. This method is excellent in the absence of o-aminophenol, but inapplicable when both inhibitors are present. Some preliminary experiments with this type of sample showed that both inhibitors were extracted into the sodium hydroxide solution. The spectrum of this solu-
Density of 2-Methyl-5-vinylpyridine (Grams per milliliter) Purity, 97 0.9614 0.9571 0.9528 0.9485
yo 99 0.9622 0.9579 0.9536 0.9493
100 0.9626 0.9583 0.9540 0.9497
VOL. 30, N O . 12, DECEMBER 1958
1929
tion then had a peak a t 410 nip, but no peak at 485 mp. A spectrum of the sodium hydroxide solution from the extraction of 2-methyl-5-vinylpyridine containing only o-aminophenol did not show any peaks in the wave length region from 350 to 700 mp. Although few solubility data for the three components exist, the solubility behavior of the p-tert-butylcatechol should be similar to that of catechol. The distribution coefficient for catechol between diethyl ether and water is 11 a t 20' C. ( 5 ) . Therefore with the 2-methyl-5-vinylpj-ridine sample dissolved in 1.ON hydrochloric acid, it should be possible to extract the p-tert-butylcatechol quantitatively into diethyl ether while the o-aminophenol and 2-methyl-5-vinylpyridine would be retained in the acid phase. After n-ashing the ether phase with 1.ON hydrochloric acid to remove any trace of o-aminophenol, the p-tert-butylcatechol could then be extracted into sodium hydroxide solution and air oxidized to the colored quinoid form for measurement. Preliminary experiments indicated that only a small amount of o-aminophenol was extracted into the ether along with the p-tert-butvlcatechol. The spectrum of the sodium hydroxide extract had a peak a t 485 mp but no appreciable peak at 410 mp. The proposed procedure was then investigated to determine the optimum analytical conditions. Two extractions with diethyl ether were found necessary to remove all the p-tert-butylcatechol from the acid phase. A single washing of the combined ether extracts with acid removed the small amount of o-aminophenol present. A single extraction with 1N sodium hydroxide was sufficient to remove the p-tert-butylcatechol from the ether phase. I n the initial determinations of oaminophenol in 2-methyl-5-vinylpyridine, the sample was dissolved in carbon tetrachloride or benzene and the oaminophenol was extracted into 0.lN hydrochloric acid. This extract was buffered with an ammonium acetateacetic acid buffer solution before oxidizing the o-aminophenol with hydrogen perouide for colorimetric measurement
Figure 3. Absorbance of oxidized o-aminophenol solution vs. time
y
0.00 0
I
5
I
1
IO
I5
1
20 25 TIME, MINUTES
a t 435 mp. The extraction of the o-aminophenol from the 2-methyl-5vinylpyridine proved necessary because of the low solubility of 2-methyl-5-vinylpyridine in the buffered solution. This procedure gave low results because of incomplete extraction; consequently, several extractions were used to recover the o-aminophenol. The results were not significantly better when higher acid concentrations were used because the background spectrum increased rapidly as the concentration of acid increased. However, this procedure for o-aminophenol was markedly improved by substituting a paraffinic hydrocarbon, such as n-heptane or 2,2,4-triniethylpentane, for the carbon tetrachloride or benzene. With n-heptane as the solvent for the sample, the o-aminophenol was almost completely recovered in a single estraction with 0.1N hydrochloric acid. I n the final analytical procedure, the sample was dissolved in n-heptane and the o-aminophenol was separated by two extractions with 0.1N hydrochloric acid. Shaking for 5 minutes during each extraction was necessary because shorter shaking timps gave low results. The combined acid extracts were buffered and the color was developed in the same manner as before. The color required 20 minutes to reach a maximum (Figure 3). Keither p-tertbutylcatechol nor 2-methyl-5-vinylpyridine interfered in the determination of o-aminophenol by this procedure. The
~~
Table
Sample 1 2 3 4 5
6 7 8 9
1930
II. Analysis of Synthetic
2-Methyl-5-vinylpyridine Samples Containing Both p-terf-Butylcatechol and o-Aminophenol
p-tert-Butylcatechol, Wt. yo Added Found 0.000 0.421 0.315 0.262 0,210 0.157 0.105 0.053 0.000
0.000 0.418 0.305 0.263 0.185
0.000 0.434 0.295 0,257 0.209
0.139
0.140 0.096 0.048
0,097 0.048 0.000
ANALYTICAL CHEMISTRY
0.000
o-Aminophenol, Wt . yo Added Found
0.000 0.000 0.0216 0,0324 0.0132 0.0541 0.0649 0.0865 0.1057
0.000 0.000 0.0219 0.0328 0.0433 0.0543 0.0656 0.0886 0.1065
0,000 0.000 0.0214 0.0310 0,0410 0,0547
0.0673 0.0863 0,1040
I
I
30
35
40
spectra of the final solutions obtained from analyzing 2-methyl-5-vinylpyridine containing only p-tert-butylcatechol did not show any peaks in the wave length region from 350 to 700 mp. Data on the relative error and precision of the determinations were obtained by analyzing a series of synthetic samples. I n preparing these, the amounts of p-tert-butylcatechol and o-aminophenol added to 2-methyl-5vinylpyridine were varied to cover the concentration ranges expected for these inhibitors in actual samples. The compositions of these synthetic samples and the results obtained by the analytical procedures outlined above are tabulated in Table 11. According to these data, the relative error is 4.5% and the precision is 1.4% for the p-tert-butylcatechol analyses. The relative error and precision are 1.1 and 1.3%, respectively, for the o-aminophenol analyses. If a recording spectrophotometer is not available, a manually operated spectrophotometer can be substituted in the analyses. For ptert-butylcatechol, the absorbance of the solution is measured at 350, 485, and 650 mp, and these values are plotted us. wave length on a graph. A straight line is drawn between the absorbance values a t 350 and 650 mp, and a line perpendicular to the base is drawn from the value a t 485 m p . The portion of the line that corresponds to CD, Figure 1, is used for measuring the absorbance. The weight per cent of p-tert-butylcatechol is calculated using the calibration curve and equation as before. I n a similar manner the weight per cent of o-aminophenol is calculated from absorbance measurements a t 350, 435, and 585 t n p . ACKNOWLEDGMENT
The authors wish to express their appreciation to A. M. Schnitzer for supplying the two inhibitors and 2methyl-5-vinylpyridine used in this work.
LITERATURE CITED
(1) Campbell, G. G., Tacker, S 8.,AXAL. CHEX 24, 1090-2 (1952). (2) Das, 31. X., Palit, S. R., J. Indian Chem. SOC.31, 34-8 (1954). (3) Phillips Chemical Co., Method VIA-5, Adams Terminal Vinylpyridine Plant Laboratory Rlanual, 1952. (4) Seaman, IT.,Sorton, A. R., Sund-
berg, 0. E., IND. EXG.CHEJI., . ~ X A L . ED. 12, 403-5 (1940). (5) Seidell, A,, Linke, IT.F., “Solubilities of Inorganic and Organic Compounds,” Suppl. to 3rd ed., p. 659, Van Sostrand, New York, 1952. (6) Synthetic Rubber Division, Reconstruction Finance Corp., “Butadiene Laboratory Manual,” Method L. M. 2 . 1 . 9 . 3 (Sept. 25, 1951).
( 7 ) Ibid., Method L. M. 2 . 1 . 9 . 2 (Feb. 2, 1944).
(8)7Takahashi, T., Kimoto, K., Takano, I.,J . Chem. SOC.Japan, Ind. Chem. Sect. 56, 591-3 (1953).
RECEIYED for review February 15, 1958. accepted July 16, 1958. Division of -4nalytical Chemistry, 133rd Meeting, .4CS, San Francisco, Calif., April 1958.
Potassium Bromide Method of Infrared Sampling ROBERT G. MllKEY U. S. Geological Survey, Washington 25, D. C.
b In the preparation of potassium bromide pressed windows for use in the infrared analysis of solids, severe grinding of the potassium bromide powder may produce strong absorption bands that could interfere seriously with the spectra of the sample. These absorption bands appear to be due to some crystal alteration of the potassium bromide as a result of the grinding process. They were less apt to occur when the coarser powder, which had received a relatively gentle grinding, was used. Window blanks prepared from the coarser powders showed smaller adsorbed water peaks and generally higher over-all transmittance readings than windows pressed from the very fine powders.
M
has been derived from the pressed-window method of infrared sampling (3, 7 4 , in which a finely divided solid, a solution, or a n oil is mixed thoroughly with a finely ground alkali halide matrix (usually potassium bromide) , and pressed under high pressure into the form of a transparent circular disk or rectangular prism. The amount of sample in the pressed disk can be controlled for application to quantitative analysis; the spectra contain no interfering absorption peaks, which n-ould appear if the sample were analyzed in a mull, and the windows can be stored for an indefinite time. This method, however, must be used ith caution, because of possible ehemical and structural changes in the sample. Rfwarchers have reported that the preparation of pressed disk n indows has altered the spectra of samples. When benzoic acid was pressed in a potassium bromide. window, its spectra exhibited a general deterioration of the spectral peaks (4). When steroids were agitated vigorously with potassium bromide in a ball mill, the -harp absorption peaks obtained when the sample had been hand-ground in a mortar, became altered to rounded and indefinite absorption bands (6). IrUCH USE
reversible changes took place in certain carbohydrates as a result of the pressedwindow procedure of sampling, and particularly, p-D-glucose changed to a - ~ glucose monohydrate ( 2 ) . When the potassium bromide disk method mas used to obtain the spectrum of ehemisorbed ammonia, ion exchange took place between potassium and ammonia, so that the spectrum obtained was actually that of ammonium bromide, rather than of XH4+( 5 ) . Various polymorphic changes occurred in the structures of succinimide and napthalene acetamide when they were pressed into n indows (1). Csually, the changes in sample spectra appear to be due to the grinding action during the mixing of sample and matrix, preparatory to pressing. It is possible that vigorous or prolonged grinding of the sample and matrix can change the crystalline structure of the sample, producing new sets of discrete absorption bands; or, a material may be rendered amorphous, I\ ith resulting broadcning or elimination of absorption peaks. .4 parallel source of potential error lies in the effect of the grinding on the potassium bromide matrix. In the spectra of the potassium bromide pressed disk, a minor absorption band a t lyave lengths betvieen 9 and 10 microns is often considered to be due to impurities in the potassium bromide. While not generally considered an interference to sample spectra, this absorption may, in fact, be greatly augmented under certain condition. of grinding. increasing in intensity as the intensity of grinding is increased. Spectra of prepared potassium bromide blank disks indicate that this absorption could interfere seriously with the spectra of a sample. APPARATUS
Spectrophotometer, Perkin-Elmer Xodel21, with the following instrument settings: slit schedule 927, gain 5 , response 1, source amperes 0.3, speed 2. and suppression 2. Pellet die, made of hardened tool steel, with a 0.50-inch bore, and facili-
I
3 0 1 ’ ” ’ ’ 1 ’1
*
9
’
’
1
1
’
’
’
IO II WAVE LENGTH MlCRONS
-
I
Figure 1. Absorption band shown b y potassium bromide window blank KBr ground gently in mullite mortar KBr ground strongly in mullite mortar and sieved through 400-mesh screen 3. KBr in Bakelite capsule pulverized b y mechanical vibrator 4, 5. KBr in steel capsule pulverized b y mechanical vibrator
1. 2.
ties for air-evacuation of pressing chamber (Hilger and Watts, Ltd., London). Vacuum pump, 2-stageJ Welch Duoseal, Model 1400, providing a vacuum of 0.1 micron or better. Grinding vessels, mullite mortar and pestle, and mechanical dental amalgamator (Crescent Manufacturing Co., Chicago, Ill.), equipped with Bakelite capsule and pestle, and stainless steel capsule and pestle. Hydraulic press, Carver hydraulic laboratory press, 10-ton capacity (Fred 8.Carver, Inc., Summit, K. J.). PREPARATION
OF
DISKS
One hundred milligrams of reagent grade potassium bromide was ground, by hand with mortar and pestle, or alternatively ground mechanically in the dental amalgamator, then pressed under vacuum a t barely compacting pressure for 1 minute, followed by a niaximum of 20,000 p s i . for 2 minutes to form a disk with a diameter of 0.50 inch and a thickness of about 0.03 inch. RESULTS AND DISCUSSION
Figure 1 presents the spectra of several potassium bromide disks, prepared VOL. 30, NO. 12, DECEMBER 1958
1931
