Amyl Nitrite J
A Method for Its Quantitative Determination and Some Observations on Its Decomposition R. G. HORSWELL' AND LESLIE SILVERMAIN AIedical Clinic, Peter Bent Brigham Hospital, Harvard Medical School, and Department of Industrial Hygiene, Harvard School of Public Health, Boston, 3Iass.
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at 80" C. in a water bath only 5 minutes are necessary. The color remains stable for at least 24 hours. The proportions of the solution aere modified for the quantitative method in one respect. Since as much as 1 ml. of glacial acetic acid was found not to interfere Lvith the development of the color, that quantity was used principally as a solvent for amyl nitrite. -4stock reagent was prepared for use in the subsequent quantitative determinations by mixing phenol solution 24 parts, copper sulfate solution 1 part, and glacial acetic acids 5 parts. This reagent remained stable for at least 2 months.
ITTLE information ib available in the literature in re-
gard to the stability of amyl nitrite in the presence of light and air. The only authors n h o mentioned this specific property agreed that amyl nitrite was probably unstable in light and air. Tyndall (14) in 1869 used saturated amyl nitrite vapor to demonstrate a band of light now known as the "Tyndall beam", and concluded that amyl nitrite was rapidly decomposed by strong rays of light. Spiegel (11) added t h a t amyl nitrite is also unstable in air. Leffniann ( 6 ) stated t h a t amyl nitrite in air, probably influenced by light, decomposes, While investigating certain toxic factors of amyl nitrite, it was observed that the compound did not decompose in the presence of light and air as rapidly as reported in the above references. I n order to obtain further information, the following work was undertaken. For this study, a method suitable for detecting amyl nitrite in the vapor state waq necessary. Since the authors were concerned primarily with its stability a t low concentrations in air, a method that employed a less sensitive reagent with more color stability than those previously described (1,?',IS) would permit sampling gas continuously over a long period of time. This eliminated the necessity of taking frequent readings or making dilutions. A reagent n-hich was unaffected b y light and heat was also desired. Because amyl nitrite is readily destroyed by strong acids ( 5 ) ,all methods employing such acids were unsatisfactory. Likewise, liquids in which amyl nitrite is freely miscible (5) could not be utilized for gas sampling because they decomposed the amyl nitrite, were too easily vaporized, or tended to interfere in the subsequent color reaction. Liebermann (6) found that characteristic colors were produced when sodium nitrite was mixed with phenol and sulfuric acid. Later, Feigl (4) adopted this reaction for detecting qualitatively a number of organic nitrites. Ware (17) in a method which he considered specific for distinguishing phenol, the cresols, and certain other related phenolic compounds, utilized copper sulfate, acetic acid, and a minute quantity of sodium nitrite to produce a color. I n following Ware's method, the authors found that when amyl nitrite was substituted for sodium nitrite, a similar color was produced. They subsequently adapted the method to the quantitative detection of amyl nitrite.
Using a color of medium intensity, the spectral transmittance with a Coleman double monochromator spectrophotometer through a 5 m p slit was determined, and the resulting curve is shown in Figure 1. Maximum absorption was obtained a t 515 millimicrons. The shaded area indicates the range of a 520 m p filter. The test n a s performed with amyl nitiite, amyl alcohol, valeraldehyde, ethyl alcohol, oxalic acid, and crystals (probably ammonium tetraoxalate, 12) formed by evaporating amyl nitrite, to determine whether or not impurities and decomposition products of amyl nitrite entered into the reaction. S o colors nere produced. In preparing the calibration curve (Figure 2), standards were made b) mixing 4.8 ml. of phenol solution, 0.2 ml. of copper sulfate solution, and 0.025 to 1.0 ml. of an accurately weighed quantity of amyl nitrite diluted with glacial acetic acid. Of the diluents available for amyl nitrite, glacial acetic acid was chosen because it does not interfere with the color reaction, whereas ethyl alcohol in amounts above 0.5 ml. reduces the color intensity and amyl alcohol is not miscible with the other reagents a t room temperature. At no time was more than 1 ml. of glacial acetic
Method The chemicals used were 5 per cent phenol solution made with rea ent grade white phenol crystals, 2 per cent hydrated copper sulfate solution, and c. P. glacial acetic acid. The isoamyl nitrite, havin a boiling point of 95-98' C. and an index of refraction at the% line and 20" C. of 1.3867, was prepared by C. S. Marvel (University of Illinois), following the method of Koyes (9) for preparing n-butyl nitrite. When a minute amount of amyl nitrite, or any other nitrite, is added to a mixture consistin5 of phenol solution, copper sulfate solution, and lacial acetic acid, the color of the mixture changes from a faint b k e to a deep red. This color reaches its maximum intensity within 15 minutes at 25" C., and if the solution is heated 1 Present
FIGURE1.
address, Bristol, Ind.
SPECTR.4L OF
WAVELENGTH IN M/U/MICRONS TRANSMITTANCE CURVE FOR A COLOR MEDIUM INTENSITY
Shaded area indicates range of a 520 rn# filter.
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ured into each of three sintered-glass absorbers (G-1 porosity), connected in series. These absorbers were of the type shown in ( 2 ) . The absorber system was connected to the chamber, the
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ANALYTICAL EDITION
TABLE 11. ABSORPTIONRATESAND EFFICIENCIES~ Rate
Cc./min.
No. of Samples
Concentration
R. p. m.
Retained pef Absorber, 30 Cc. of Reagent in E a c h Absorber 1 2 3
%
%
%
0 Based on known concentration and obtained with sintered absorbers of 40-50 micron porosity.
TABLE111. DECOMPOSITION RATESOF AIR-VAPORMIXTURES ( I n unlighted t a n k samples taken b y both grab a n d continuous methods) Time of Initial Final Exposure Concentration Concentration Remaining Hours P. p . m. P . p . m. 70
a
Grab sample taken from t a n k on third d a y a n d kept in dark room
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again when the sky was overcast (1000 to 2000 foot-candles). Several brown bottles were included as controls. Every 30 minutes a set of four was removed for analysis. After exposure to sunlight, only 20 per cent was recovered a t the end of 1 hour. Within 2 hours, decomposition was complete (Table 111). On a cloudy day, complete decomposition was obtained in 3 hours of exposure (Table 111). It has been intimated that decomposition in light is lessened if amyl nitrite is in a liquid state (11, 14). To study the effect of such a condition, 30 drops of isoamyl nitrite were diluted with 100 ml. of isoamyl alcohol in a brown glass-stoppered bottle and the amount of amyl nitrite per milliliter was determined. A 25-ml. glass-stoppered Pyrex flask was filled with this solution and placed in the direct sunlight. At half-hour intervals, 0.2 ml. was removed and mixed with 6 ml. of reagent. Amyl alcohol was not soluble in the reagent at room temperature, but when the mixture was heated in a water bath at 80" C. a clear solution was obtained. The colorimetric reading was made before the liquid cooled. Samples were taken and analyzed as long as significant change took place in the concentration. I t was found that decomposition of liquid took place at almost the same rate as the vapor (Table IV). A Pyrex flask, similarly filled, was placed in a photographic darkroom and exposed to illumination placed 30 cm. (12 inches) away (approximately 70 foot-candles). Samples were taken at half-hour intervals for the first 3 hours, and then again after 26 hours of continuous exposure to the light. At that time, it was found that there mas a 15 per cent decrease in the concentration (Table IV).
Discussion GRABSAMPLES. The vessels used were Pyrex gas burets with a capacity of about 300 ml., having ground-glass stopcocks at each end. The sampling tubes were evacuated before sampling and when taking the gas specimen were also flushed by means of a hand-aspirating bulb. To the amyl nitrite in the grab-sample tube, 6 ml. of reagent were pipetted in through one of the stopcocks by means of a capillary funnel which extended well down into the flask (16). After the closed vessel had been shaken for 15 minutes, the solution was drained into a colorimeter tube and read.
Decomposition of Amyl Nitrite STABILITYOF AMYLNITRITEIN AIR. From the large tank, sealed and dark, containing amyl nitrite vapor at a concentration of 1165 p. p. m., gas samples were taken with the bubbler system, first a t half-hour intervals, then hourly, and finally only occasionally, for a period totaling 48 hours. Grab samples were also obtained, stored in a dark cool place, and analyzed 3 weeks later. Amyl nitrite in a sealed dark tank showed no decomposition in 48 hours (Table 111). The concentration in grabsample bottles stored in a dark cool place did not decrease significantly in 21 days. The effect of artificial light on amyl nitrite vapor was observed by the same procedure. (Light measurements were made with a General Electric foot-candle meter.) In the large chamber, a concentration of 506 p. p. m. of amyl nitrite vapor was prepared. After control samples were taken, the inside of the tank was illuminated (average illumination 25 foot-candles), and the concentration was measured every half hour for 3 hours. There was little or no decomposition at the end of that time. To observe the effect of artificial light which he reported, the experiment described by Tyndall (14) was reproduced as closely as possible. (Illumination used was approximately 200 foot-candles.) His statement was unconfirmed, since the amyl nitrite remained unaffected even after the appearance of a Tyndall beam, which did not develop in the saturated vapor at room temperature and pressure until after 7 minutes' continuous exposure. INFLUENCE OF DIFFUSE DAYLIGHT ON VAPOR. Ground-glass stoppered bottles having capacities of from 250 to 600 ml. and 300-ml. gas-sampling tubes were filled with amyl nitrite vapor obtained from the large tank containing a concentration of 506 p. p. m. The bottles were filled in the manner described by Viles (16) and were placed where they would be exposed to the average daylight of a room (6 to 8 foot-candles). (The direct rays of th? sun never entered the room because its only window faced directly north.) For controls, brown bottles were filled at the same time and placed beside the other bottles. A bottle was withdrawn at 2 C to 48-hour intervals and the amyl nitrite content determined. The rate of decomposition when exposed to average daylight indoors is given in Table 111. Amyl nitrite was still found in the clear bottles up to 12 days; in the brown bottles there was no decrease from the original concentration. The experiment was repeated by placing bottles filled with vapor out of doors on a clear day (7000 to 10,000 foot-candles) and
The mechanism of the reaction is not known. Liebermann (6) and Feigl (4) state that they can offer no explanation. Manchot ( 8 ) suggests that the violet coloration produced by nitric oxide in solutions of copper sulfate in concentrated sulfuric acid is due to the formation of an easily dissociated compound, CuS04N0. It may be that copper sulfate acts as a catalyst in producing a diazo compound. Ethyl alcohol is used as the diluent in the method for assaying amyl nitrite described in the 11th revision of the U.
s.
T.4BLE
OF AMYLKITRITE DILUTEDWITH Iv. DECOMPOSITION AMYLALCOHOL
Time of Exposure Hours
Initial Concentration Mg./Ziter
Final Concentration Mg./Ziter
Remaining
%
Exposed to direct sunlight in Pyrex flasks (7000 t o 10,000 foot-candles) 0 1740 1740 100 0.5 1740 1260 72.4 1 1740 750 43.1 1.5 1740 525 30.2 2 1740 215 12.3 2.5 1740 185 10.6 3 1740 125 7.2 Exposed t o 50-watt light in reflector a t 30-cm. distance (70 foot-candles) 0 1740 1740 100 0.5 1740 1700 97.7 1 1740 1650 94.8 2 1740 1640 94.2 3 1740 1625 93.4 26.5 1740 1500 85.2 I n animal exposure room (6 t o 8 foot-candles), soft-glass bottle samples 102.5 519 506 0 95.1 481 506 17.75 104.5 529 50G 41.75 79.0 400 506 90 31.2 158 506 138 12.3 62.3 506 234.5 4.9 25 506 282 0 0 506 330
In outside daylight (1000 t o 2000 foot-candles), Pyrex, sampling bottles
0 1 2
I n direct sunlight (7000 t o 10,000 foot-candles) 1138 1165 1165 195 0 1165
97.7 16.7 0
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Pharmacopoeia (15) and i t is recommended that the prepared solution be used within 0.5 hour. Amyl nitrite dissolved in amyl alcohol or ethyl alcohol was found to remain stable for at least a week when the solution was prepared under artificial light and stored in a brown bottle. It is possible that amyl nitrite is decomposed by light of a specific wave length. Preliminary observations with ultraviolet and infrared light were made, but further investigation is necessary.
Conclusions A method for the quantitative determination of amyl nitrite, adaptable for vapor-air and liquid analysis, is based on the fact that a color is produced when a compound containing an -ON0 radical is combined with phenol and copper sulfate in acid solution. The method will detect amyl nitrite in air within an average deviation of 10 per cent. The advantage of this method is that the amyl nitrite vapor can be absorbed directly in the color-producing reagent. This eliminates the need for a separate solvent for amyl nitrite and simplifies the procedure because the reagent from the sampling vessel can be poured directly into a colorimeter tube and read; when determining unknown concentrations, the development of a color in the sampling tube indicates that nitrite is present and gages the length of time required to collect an adequate sample; and although the test does not compare in sensitivity with many of those already described (1, 5 , 7 , IO, I S ) , it has certain advantages for sampling a large volume of vapor a t a low concentration for long periods. Amyl nitrite has been determined a t concentrations of 5, 10, 20, and 100 p. p. m . Amyl nitrite is stable in air and relatively stable when ex-
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posed to.artificia1 light, but decomposes within 2 hours when exposed to direct sunlight.
Acknowledgment The authors wish to express their appreciation to Otto Schales for determining the spectral transmittance of the color and for his many helpful suggestions.
Literature Cited Dennis, L. M., and Nichols, M. L., “Gas Analysis”, p. 220, New York, Macmillan Co., 1929. Drinker, P., and Snell, J. R., J . Ind. Hug. Tozicol., 20, 321 (1938). Evelyn, K. A., J . Biol. Chem., 115, 63 (1936). Feigl, F., “Qualitative Analyse mit Hilfe von Tupfelreaktionen”, 3rd ed., p. 379, Leipaig, Akademische Verlagsgesellschaft. 1938. Leffmann, H.. “bllen’s Conlmercial Organic Analysis”, 5th ed., Vol. I. p. 318, Philadelphia, P. Blakiston’s Son & Co., 1923. Liebermann, C., Ber., 7, 247 (1874). Liebhafsky, H. A,, and Winslow, E. H., ISD. ESG. CHEM.,ilnal. Ed., 11, 189 (1939). Manchot, W , Ann., 375, 308 (1910). Noyes, W.A , , “Organic Syntheses”, Vol. XVI, p. 7, New York, John Wiley Bi Sons, 1936. Snell, F. D., and C. T., “Colorimetric Methods of Analysis”, Vol. I , p. 644, New York, D. Van Nostrand Co., 1936. Spiegel, L., “Der Stickstoff”, p. 154, Braunschweig, Friedrich Vieweg & Sohn, 1903. Sundquist, H., and Mohlin, E., Svensk Farm. Tid., 23, 626 (1916). Treadwell, F. P., tr. and rev. by W. T. Hall, “Analytical Chemistry”, 7th ed., Vol. 11, p. 306, New York, John Wiley & Sons, 1928. Tyndall, J., Proc. Rou. Inst. Grt. &it., 5, 429 (1869). U. S. Pharmacopoeia, 11th revision, pp. 56, 458, Easton, Penna., Mack Printing Co., 1935. Viles, F. J., J . Ind. Hug. Toricol., 22, 188 (1940). Ware, -A. H., AnaZUst, 52, 335 (1927).
Cerate Oxidimetry Determination of Glycerol G. FREDERICK SMITH AND F. R. DUKE, University of Illinois, Urbana, Ill.
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LYCEROL is ordinarily determined by oxidation, using a n excess of standard potassium dichromate in sulfuric acid solution. The reaction, 3C3Hs03 7KzCr20, 28HzS04= 9C02 7Cr2(SO& 7K2SO4 40Hz0, requires an excess of dichromate and heating for 2 hours a t 90” to 100” C. to complete the oxidation. The dichromate required for oxidation of the glycerol is determined by titrating the excess, using ferrous sulfate solution. For the backtitration the sulfuric acid concentration must be approximately 4 formal. The green color of the solution during the titration of excess dichromate makes necessary either an outside indicator “spot plate” ferricyanide estimation of the equivalence point or a potentiometric titration. The chief objection to the determination of glycerol by such procedure is the time required for the oxidation. The present work describes a procedure by means of which this required time is reduced from 2 hours to only 15 minutes and the temperature from 90-100” to 50” C. The reaction upon which the method depends is C3Hs03 8H2Ce(C104)s 3H20 = 3HCOOH 8Ce(C104)3 24HC1O4. The excess of perchlorato ceric acid is then determined by titration, using standard sodium oxalate with nitro-ferroin (nitro-ophenanthroline ferrous complex) as internal indicator. For this titration a 2 formal perchloric acid concentration is pre-
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ferred. Oxidation b y dichromate requires 14 equivalents per gram molecule of glycerol and by perchlorate cerate ion 8 equivalents.
Previous Work The determination of glycerol by the dichromate procedure, using a potentiometric end point and the platinum-tungsten bimetallic electrode pair, has been described by the Chemical Division, Procter and Gamble Company (6). The same reaction using the same electrode system and an electronically operated automatic buret sto ping device, mas used by Shenk and Fenwick (’7). Stamm 8 3 ) determined glycerol, using excess permanganate in strongly alkaline solution with titration of excess permanganate after acidification by use of oxalic acid. Glycerol was determined by Malaprade (c), using periodic acid in excess, followed by titration of the excess oxidant by one of several methods. By this procedure glycerol is oxidized to two molecules of formic acid and one molecule of formaldehyde. This oxidation of glycerol differs from the perchlorato cerate oxidation in that the formation of formaldehyde as an end product is eliminated in the latter case. The Malaprade reaction has been further studied by Allen, Charbonnier, and Coleman (1). Using the sulfato cerate ion, the oxidation of organic compounds in general results in the formation of formic acid as shown by Willard and Young (14), Cuthill and Atkins (9), and Fulmer, Hickey, and Underkofler (4). The previous papers on cerate oxidimetry by Smith and coworkers (3, 8-19) should be consulted for information con-
