Modification of Ferrous Thiocyanate Colorimetric Method for Determination of Some Atmospheric Oxidants GLENN W. TODD Department of Plant Biochemistry, University of California, Riverside, Calif.
KO satisfactory method for measuring the oxidants produced by the reaction of ozone with hydrocarbons in the gas phase has been available. The ferrous thiocyanate method for the determination of peroxides was modified and used for the determination of gaseous oxidants. The reagent responds to very low concentrations of the reaction products of ozone and hexene or gasoline while being fairly insensitive to ozone alone. It is somewhat sensitive to nitrogen dioxide but not to nitrous oxide, formic acid, formaldehyde, valeric acid, or isovaleraldehyde. It appears to be useful in sampling naturally polluted atmospheres as well as atmospheres artificially polluted with various ozonated hydrocarbons.
A
TMOSPHERIC pollution (or smog) in the Los Angeles basin has become a problem of much interest in the past few years. Certain constituents in this pollution produce a type of damage to agricultural crops that appears to be unique (9). I t has been postulated that the plant damaging substances are organic peroxides produced by the reaction of ozone and volatile unsaturated hydrocarbons found in the atmosphere (6). HaagenSmit has demonstrated the presence of short-chain organic peroxides in the Pasadena atmosphere during a period of aggravated pollution, using the enzyme peroxidase ( 4 ) . However, the enzyme is unable to utilize the longer chain peroxides as a substrate. These latter peroxides have not been identified as such in the atmosphere.
ing substances present. Another reagent that is used for meaeuring atmospheric oxidants is phenolphthalin (5, 8). This reagent measures some peroxides as well as ozqne, but its greatest sensitivity seems to be to ozone. Most other reagents used for the detection of organic peroxides were found to be extremely sensitive to ozone. The ferrous thiocyanate reagent previously used to determine organic peroxides in the liquid phase (11) is not nearly so sensitive to ozone as the other reagents tested and, therefore, is useful in measuring other atmospheric oxidants which are present in only minute amounts. MATERIALS AND METHODS
The ferrous thiocyanate reagent for peroxides, which is a modification of that given by Wagner and others ( I I ) , wasprepared in the following manner: One-half gram of ammonium thiocyanate and 1.0 ml. of 6 N sulfuric acid were added to 100 ml. of water. To this 0.1 gram of ferrous ammonium sulfate was added and shaken. The rea ent was then diluted with 100 ml. of water to give a low blank coyorimetric density. The solution, which darkens upon standing, should be prepared fresh daily. The pigment formed can be removed with decolorizing carbon; thus the reagent probably could be used with an automatic recorder of the type described by Littman and others ( 7 ) . The amount of color developed was read with a Fisher Electrophotometer using a 425-mp filter (the
Table I. Response of Potassium Iodide and Thiocyanate Reagents to Ozone, Hydrocarbons Alone, and Reaction Products from Ozonated Hydrocarbons
Sample Hexene only Ozone only Ozone plus hexene Gasoline only Ozone only Ozone plus gasoline
PEP MOLE OF GAS
Figure 1. Response of potassium iodide and thiocyanate reagents to ozone alone and ozone plus hexene X.
Ferrous thiocyanate Ozone only
---
-Ozone plus hexene
0 . Potassium iodide .. - - Ozone only __ Ozone PIIE hexene
A common technique for measurement of the level of pollution is to determine the oxidant concentration with a 20% buffered potassium iodide solution, which, under the conditions used, measures atmospheric ozone (IO), nitrogen dioxide (S), and some peroxides ( 1 2 ) . Since ozone damage to plants has been observed in the area only rarely, a measure of other oxidants present might appear to give a better indication of t,he amount of plant damag-
fi eq. per 22.4 Liters Peroxides Ozone determined d t h determined with ferrous thiocyanate 1xJtaqsium iodide 0.006 0.0 0.382 0.031 0.104 0.117 1.01 0.237 0.498 6.34 1.22 1.187
Rubber Cracking NO
Yea NO
...
primary absorption band lies a t about 460 mp). A standard curve waa prepared by adding known amounts of ferric iron to the reagent. A standard curve may also be prepared using known amounts of hydrogen peroxide (1 mole releases 2 equivalents of ferric iron). The results are expressed as the number of microequivalents ( k eq.) of ferric iron produced by 22.4 liters (1 mole) of the gas. Ozone was determined by passing the gas through a 20% potassium iodide solution buffered a t pH i . 0 with O.1M phosphate. The total iodine released after acidification with sulfuric acid was titrated with 0.005N sodium thiosulfate using a starch end point. The results are expressed as the number of microequivalents of iodine released by 22.4 liters (1 mole) of the gas. I n the experiments reported in Figure 1, the ozone was produced by passing cvlinder oxygen through a corona discharge tube (manufactured by the Mueller Yeon Co., 1231 Sunset Boulevard, Los Angeles 26, Calif.). The vapor of 1-hexene (obtained from Phillips Petroleum Co.; technical grade 95 mole % minimum) was introduced into the system by passing a stream of cylinder nitrogen through the Ilquid. The rates of flow of tHe various components were measured bv passing them through small calibrated capillaries. The rate of ovvgen flow (containing the ozone) was 35 liters per hour. The stream of nitrogen was regulated to a flow of 2 liters per hour and wm bubbled through the liquid 1-hexene a t 20" C. The ozone and hexene were in contact for about 45 seconds (calculated mean residence time). The
1490
V O L U M E 2 7 , N O . 9, S E P T E M B E R 1 9 5 5 mixture was then diluted with carbon-filtered air a t the rate of 800 liters per hour. This gave a final hexene concentration of about 570 p moles per mole of gas assuming no reaction with the ozone. The final ozone concentration is presented with the data assuming no reaction with the hydrocarbons (hexene). Where gasoline was substituted for 1-hexene the amount used was much higher because a high proportion of nonreactive materials is present (only the olefinic compounds are easily ozonated). In one experiment (reported in Table I ) where ozone and hexene were used, they were mixed in a small tube and further placed into a large chamber (187 cubic feet) which gave a mean residence of about 1 minute. The final hexene concentration was 17 moles per mole and the ozone concentration was 0.2 p mole per mole. One micromole of a substance per 22.4 liters of a gas equals one part per million by volume. The final concentrations were calculated as though none of the reactants were used up. The cracking of rubber as used in one experiment is a very sensitive indicator of the presence of ozone (Z). The strips of rubber remained in the air stream for 20 minutes (a flow of 2.8 liters per minute) and were subsequently examined for cracking. When the ozone concentration exceeds about 0.16 p eq. per mole, cracking is observed in this length of time.
I - 1,' -6
dl
02
03
04
1491 cyanate reagent is not very responsive to ozone but is much more sensitive to the reaction products of ozone plus hexene. The potassium iodide reagent releases 1 equivalent of iodine for each equivalent of ozone present, whereas the thiocyanate reagent releases only 1 equivalent of ferric iron for each 30 equivalents of ozone present. Bfter the addition of hexene to the ozone, the response of the thiocyanate reagent increased to more than four times the response to ozone alone. The potassium iodide reagent gave a fairly low response to the reaction products of ozone plus hexene. There may have been some unreacted ozone remaining a t the higher concentrations accounting for the somewhat erratic experimental points with the potassium iodide reagent which is extremely sensitive to ozone. Since this reagent was modified for use in atmospheric sampling it was desirable to know what other substances might occur in thc air which would interfere with the tmt. Ozone does show a slight interference. The oxides of nitrogen are also preFent in the I m Angeles atmosphere and occur to the extent of 0.4 p.p.m. (0.4 p mole per mole of gas during a period of extended pollution) ( I 1. The results of a test of the response of ferrous thiocyanate to nitrogen dioxide in air are given in Figure 2. The high blank represents substances that color the thiocyanate present in the air used. If the curve is translated so that it passes through the origin, then 0.5 p mole of ferric iron is released for each micro mole of nitrogen dioxide present in the sample. However, according to Effenberger (S), neutral buffered potassium iodide releases 1 mole of iodine for each mole of nitrogen dioxide present. Thuq, when nitrogen dioxide occurs in the atmosphere it will cause color development of these reagents, although to a greater extent with the potassium iodide than with the thiocyanate.
05
)MOLES OF NO2 MOLE OF GAS
Figure 2. Response of ferrous thiocyanate reagent to low concentrations of nitrogen dioxide gas in air -
-.
Translation line through origin
The nitrous oxide (98%) and nitrogen dioxide (98%) were obtained in cylinders from the Matheson Chemical Co. RESULTS 4ND DISCUSSION
Preliminary studies indicated that the response of the thiocyanate reagent mas definitely marked to ozonated hexene while the response to ozone alone was low. Table I shows such an experiment where the ozone (0.4 p eq. per mole of gas) and 1hexene (17 p moles per mole of gas) were mixed in a very large rhamher (187 cubic feet) and the mean residence time was 1 minute. When ozone is present alone the amount measured by the thiocyanate reagent is less than one tenth the value of the determination of ozone with potassium iodide. The rubbercracking test indicated that the ozone concentration was less than 0.16 p eq. per mole after the addition of hexene. The thiocyanate reagent value was much higher after hexene was added indicating that ozonated intermediates were present. presumably peroxides. The results of a similar experiment where gasoline was used as the hydrocarbon, together with a ehorter reaction time, is also given in Table I. Again the thiocyanate reagent indicates the presence of ozonated intermediates when the gasoline and ozone are mixed. The high value obtained 15 ith gasoline alone with both reagents is probably due to oxidizing agents present in the gasoline. A more complete investigation was made of the sensitivity of both potassium iodide and ferrous thiocyanate to ozone alone and to ozone and hexene. Figure 1 shows that the ferrous thio-
Figure 3. Comparison of response of potassium iodide and thiocyanate reagents to contaminants present in naturally polluted air
Several other substances that occur in the Los Arigeles atmosphere during periods of smog, or might be expected as end products in the reaction of ozone and hexene, caused no color development of the thiocyanate reagent. These were: 98% nitrous oxide, 5000 p.p.m. of formaldehyde, formic acid, valeric acid, or isovaleraldehyde. The usefulness of the thiocyanate reagent for sampling naturally occurring pollution was determined on outside Riverside air (Figure 3). Five cubic feet of outside air were passed through 20 ml. of the thiocyanate reagent. It is compared to the amount of iodine released from buffered potassium iodide reagent. When the visibility decreased and the amount of iodine released from the potassium iodide solution incrensed (as measured by a continuous oxidant recorder) ( 7 ) , a parallel increase was also shown h y the ferrous thiocyanate reagent. This indicates that when the amount of oxidant present in the atmosphere increases, the amounts of substances (po%4hlyperoxides) giving a reaction with
1492
ANALYTICAL CHEMISTRY
the thiocyanate reagent also show an increase, probably being dependent on the amount of hydrocarbons present. ACKNOWLEDGMENT
The author wishes to acknowledge the technical assistance of Stanley 0. Sjursen on this project. LITERATURE CITED
(1) Air Pollution Control Distr., Co. of Los Angeles, Calif., 2nd Rept. (Tech. and Adm. Rept.) 1950-51. (2) Bradley, C. E., and Haagen-Smit, A. J., Rubber Chem. & Technol., 24, 750 (1951). (3) Effenberger, E., Z . anal. Chem., 134, 106 (1951).
Haagen-Smit, 8 . J., I n d . Eng. Chem., 44, 1342 (1952). Haagen-Smit, A. J., and Fox, AI. bI., "Determination of Total Oxidant in Air," unpublished report (March 1953). Haagen-Smit, A. J., Darley, E. F., Zaitlin, Ai., Hull, H., and Xoble, W., Plant Physiol., 27, 18 (1952). Littman, F. E., and Benoliel, R. W., ANAL.CHEM.,25, 1480 (1953).
McCabe, L. C., I n d . Eng. Chem., 45, l l l A (September 1953). Middleton, John T., Kendrick, J. B.. Jr., and Schwalm, H. W., PlantDwease Reptr., 34,245 (1950). Thorp, C. E., IND. ENG.CHEM.,ANAL.ED.,12, 209 (1940). Wagner, C. D., Clever, H. L., and Peters, E. D., ASAL CHEM., 19,980 (1947). Wagner, C. D., Smith, R. H., and Peters, E. D., Ibid., 19, 976 (1947).
RECEIVED for review
March 21, 1955.
.4ccepted May 31, 1955.
Analysis of Certain AIkylated Phenol Mixtures by Bromination WILLIAM L. SPLIETHOFF' and HAROLD HART Kedzie Chemical Laboratory, Michigan State University, East Lansing, M i c h .
By taking advantage of the different number of ortho or para positions available for bromination in non-
alkylated and alkylated phenols, it has been possible to apply the acid bromate-bromide method to the analysis of certain phenol mixtures. Attention to the percentage of excess bromine and the reaction time is necessary, the best conditions being determined by a study of known mixtures before applying the method to unlinowns.
T
cited above, it has been found that the bromate-bromide technique can give satisfactory results, provided one uses a limited excess of bromine and short bromination times. The conditions must be carefully established with known mixtures. This paper describes the application of the bromate-bromide method to mixtures of certain alkylated phenols. SOLUTIONS AND REAGENTS
Sodium Thiosulfate, O . l N , standardized against a weighed sample of potassium iodate using standard analytical procedure. Bromide-Bromate Solution, 0. lN, prepared following the directions of Ruderman (4). Hydrochloric Acid, concentrated acid, specific gravity 1.19. Potassium Iodide, 10% aqueous solution. Methanol. hferck & Co. absolute methanol, c.P.,acetone-free, was used without further purification. Phenol. C.P. grade phenol wae triply distilled, the final distillation being carried out in a nitrogen atmosohere, boiling- point _ 179" t o 18'0' C. +Cresol. Kater-white, C.P. grade o-cresol (Fisher Scientific Co.) was used without further purification. @-Cresol. Prartical grade p-cresol was triply distilled to give
HE quantitative bromination of phenols by acid bromatebromide solution has been reviewed and examined thoroughly by Ruderman (4). The effect of acid concentration, bromination time, temperature, and substituents was investigated. I n particular, Ruderman showed that an appreciable excess of bromine and long reaction times very often resulted in overbromination-Le., bromination in excess of the number of unsubstituted ortho and para positions. But in certain cases-for example, m-cresol and phenols with tert-alkyl substituentsexcellent results were obtained Table I. Analysis by Bromination of Phenol, o-(a-Phenylethyl)phenol, regardless of the percentage of p-(a-Phenylethyl)phenol, and Mixtures of These excess bromine. Others-for Millimole example, p-cresol-gave good 0ReNet (a-Phenyl- (a-P?&4action 3feq. Meq. results when a reasonable (say Phenol, % BrOa-Meq. Brz ethyl)ethyl). Time, 10 to 30%) excess of bromine Phenol phenol phenol Sec . BrS20a-.4bsorbed Ra Found Calod. was used. The most critical 2.3434 2.92 0,3726 120 2.7160 0.402 2.3585 2.93 0,3575 120 2.7160 0.402 variable with most phenols ap2.3585 2.93 0,3575 240 2.7160 0.402 2.3640 2.95 0,3520 20 2.7160 0.402 peared to be the percentage of 2.3840 2.97 2.7160 0.3320 25-30 0.402 excess bromine. 2 , 3 7 9 0 2 .96 2 . 7 1 6 0 0 . 3 3 7 0 26-30 0.402 To study the kinetics of the 1.4577 1.92 20 1.6490 0,1913 0,384 1.4577 1.92 0,1913 20 1,6490 0.384 alkylation of several phenols 1,4770 1.95 30 1,6390 0,1720 0.384 witha-phenyl ethyl chloride(d), 0.7256 2.20 0,0504 60 0,7760 0.1656 0.6803 2.06 0,0957 10-15 0,7760 0.1656 it became necessary to analyze 0.6904 2.09 0,0856 10-15 0,7760 0.1656 mixtures of phenols and their 0.6753 2.05 0.1007 0,7760 0.1656 5 1.3845 2.09 0,0705 25-30 1.4550 0.3312 alkylated homologs. One pos85.3 90.0 0.206 2.510 20 2.7160 0.0212 0.0229 0.396 sible method would take advan89.8 90.0 0.156 2,550 2.7160 0,0229 25-30 0,0212 0.396 8 9 . 8 9 0.0 0.156 2.550 25-30 2.7160 0,0212 0,0229 0.396 tage of the different number of 72.6 74.9 0.216 2.884 30-35 3.100 0,0772 0.0567 0,396 ortho or para positions avail73.9 74.9 0,201 2.899 3.100 25 0.0772 0.0557 0.396 73.0 74.9 able for bromination in thenon0,212 2.888 25 3.100 0.0557 0.0772 0.396 46.4 49.7 alkylated and alkylated phe0.236 3.935 4.171 20 0.193 0.209 0.396 48.7 49.7 0.201 3.970 4.171 25-30 0,193 0.209 0.396 nols. Despite the limitations 48.7 49.7 0,201 3.970 4.171 25-30 0.193 0,209 0.396 I
1 Present address, Pioneering Research Division, Textile Fibers Department, E. I. Du Pont de Nemours & Co., Wilmington 98. Del.
0,201 4.171 25-30 0.193 0.209 0.396 0.158 0.278 0.201 20-25 3.100 0.246 a Ndmber of reactive positions per m o l e c u l e i . e . , for phenol, R = 3.
3.970
2.854
-
I
48.7 24.0
49.7 24.8
