18-F), and was useful in determination of exposure t o nitro compounds during medication with aromatic amines (18-F). Differences between the two methods, less than zk5 mg. per liter, probably are not significant in view of the variability of natural occurring aromatic amines such as conjugated tryptophan degradation products (5). Recovery of known quantities of the aromatic nitro derivatives listed in Table I after addition to fresh urine fell in the range 50 t o 90%. The yield varied with individual donors, with the same donor from day t o day, and with the time elapsed between addition of the known and start of reduddn. However, the corresponding aromatic amines added t o urine under similar conditions could be recovered nearly quantitatively (95 t o 100%) even after 24 hours at room temperature. Therefore, the observed nitro compound losses were not due to interferences with the diazotization and coupling reactions, h u t may be due t o enzyme-promoted
hydroxylation reactions which are known to occur in vivo (11, 14). Observed decrease in steam volatile derivatives, as either exposure specimens or knowns aged a t room temperature, confirms the activity of a competitive reaction system. Since presentation of this paper, the presence of p-nitrophenol in the urine from workmen exposed to nitrobenzene has been confirmed b y differentially coupling the diazotized amines from reduction at 60” and 80” C., the temperature at which p-aminophenol couples. Further study to resolve this reaction system is in progress. LITERATURE CITED
Boescken, J., Rec. trav. chinz. 55, in4n iimfii. BragLH. G., Thorpe, FV. V., Kard, P. B., Biochem. J.48,394 (1951). Brown. R. R.. Price, J. M., J . Biol. Chem. 219, 985 (1956). ’ Bushby, S. R. M., Woiwod; A. J., Biochem. J. 63,406 (1956). Elvove, E., J . Ind. Eng. Chem. 11, 860 (1919). \ - - - - I .
English, F. L., -1x.k~. CHEX 19, 457 (1947). Flemine. A. J.. D’Alonzo. C. A.. ZapG’ J. A,.,’ “hlodern ’ Occupa: tional Medicine,” p. 114, Lea & Febiger, Philadelphia, 1954. Jacobs, M. B., “Analytical Chemistry of Industrial Poisons, Hazards, and Solvents,” 2nd ed., p. 722, Interscience, Kew York, 1949. Lubs, H. A,, (to E. I. du Pont de Kemours 8: Co.), U. S. Patent 2,164,930 (July 4, 1939). Pinto, S. S., Wilson, IT. L., J . Ind. Hyg. Toxicol. 25, 381 (19q3). Von Oettingen, W. F., U. S. Public Health Bull. No. 271, pp. 4, 87, 1941. (12) Kestfall, B. B., Smith, M.I., Proc. SOC. Exptl. Biol. M e d . 51, 122 (1942). (13) Killiams, “Detoxication Mechsnis%,” %ley, Kew York, 1947. (14) Wilson, K.. llader, P. P., Palmer, L., Southern California Air Pollution Foundation Doc. 00766, 1955. RECEIVED for review June 28, 1957. Accepted January 31, 1958. Ninth Delaware Chemical Symposium, University of DelaTare, Kewark, Del., February 16, 1957.
Dete rminuti o n of Iodoform by Photooxid CI ti o n SAMEER BOSEl Department of Chemistry, Mahakoshal Mahavidyalaya, Jabalpur, India
b A procedure for the determination of iodoform was developed based on the rapid decomposition of iodoform into free iodine in visible light. All three atoms of iodine are quantitatively oxidized. The maximum amount of iodoform estimated b y this method is 0.1 gram; analytical precision is to 0.5% or better. Acetone in the presence of other aldehydes has also been evaluated b y converting it to iodoform.
A
and easy method for estimating iodoform was needed in the study of a reaction where iodoform was one of the products. It has been known for some time that iodoform absorbs light in the visible region ( 1 ) . Emschwiller observed (8) that on photooxidation of iodoform, iodine pentoxide is produced, but later (3) showed that the first product of photooxidation is probably free iodine and iodine pentoxide is produced only by secondary reactions. An attempt to determine iodoform in ether by photoelectric colorimeter failed, as the faint yellow color of the solution became rapidly deeper because of iodine liberated on exposure to light. The following proPresent address, 310 Napier Town, Jabalpur, India. PRECISE
cedure is based on the quantitative decomposition of iodoform which occurs when a solution in ether-benzene mixture is exposed to bright sunlight in the presence of air. EXPERIMENTAL
All chemicals used were of analytical reagent grade except iodoform, which was C.P. Iodine solution, 0.1N and O.05N. Sodium thiosulfate solution, O.1N and 0.05N. Sodium hydroxide solution, 1. O S . Sulfuric acid solution, 1 . O N . Sodium acetate solution, 20 grams of sodium acetate dissolved in 100 ml. of water. Starch solution, 1% aqueous. Phenolphthalein solution, 1y0 stock solution prepared by dissolving 0.5 gram in 30 ml. of ethyl alcohol and diluting to 50 ml. with mater. Reagents.
Preliminary Experiments. To find a suitable solvent for iodoform, the effect of various solvents on the process of photooxidation was investigated. Iodoform solutions (0.05%) were prepared in ether, benzene, chloroform, and carbon tetrachloride, and 100 ml. of each was exposed to bright sunlight in a 250-ml. conical flask of borosilicate glass which was corked and sxirled from time to time. Benzene and carbon tetrachloride solutions developed a violet tinge and completely decomposed in 1 hour into free iodine and a n unknown gaseous product which was allowed to escape by opening the cork occasionally. The liberated iodine was titrated with 0.05X sodium thiosulfate solution after 1 gram of solid potassium iodide and starch solution had been added t o the flask. K i t h ether solution, the decomposition mas initially
Table I. Effect of Solvent on Photooxidation of iodoform (Iodine obtained from 100 ml. of 0.05% solution after 1 hour’s exposure to sunlight) Initial Rate of Iodine Obtained, RIg. S o h ent Decomposition Exptl. Theory Ether Very rapid 24.8 48 4 Benzene Rapid 48 2 48 4 48 1 48.4 Carbon tetrachloride Slow Chloroform Slow 30.0 48.4
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1137
present in about 120 ml. of air endosed in the flask was found enough for photooxidation of 0.1 gram of iodoform (Table 11).
Table II. Estimation of Iodoform Dissolved in Ethyl Alcohol
Exposure to Sun, Minutes
(Ten milliliters of solution estimated) Iodoform, Mg. Found Present
45 45 40 40 35 35
99.6 91 .o 79.8 75.2 60.0 49.9 Table 111.
100.0 91.4 80.1 75.5 60.2 50.1
Estimation of Iodoform-Water Mixture
Water, M1.
Exposure to Sun, Minutes
50 100 100 150
45 45 40 40
Iodoform, Mg. Present Found 99 8
100.4 80.1 80.4
-n
99.9 79.8 80.0
-0.5 -0.4 -0.5
very rapid and soon developed a red color, but the reaction practically stopped after only half of the iodoform had decomposed. This might be due to the red color of the solutions acting as an autofilter and preventing further action, as red light has been known to be least reactive photochemically. Chloroform solution decomposed slowly; it also developed a red color and the decomposition was carried to 60% only, The initial rate of decomposition was very rapid in ether. The second best solvent was benzene. As ether is very volatile, a mixture of ether and benzene was most suitable. The results recorded in Table I bear out the conclusions of Emschwiller that free iodine is the first product of photooxidation. If iodine pentoxide were produced, on treatment with water it would yield iodic acid. In the above experiments, the presence of iodic acid was tested for and found to be absent. Analytical Procedure for Ethyl Alcohol Solutions. One to 10 ml. of a solution of iodoform in ethyl alcohol containing not more than 0.1 gram of the substance was pipetted into a 250-ml. conical flask of borosilicate glass, and 10 ml. of benzene with 10 ml. of ether was added. Twenty milliliters of 0.05N sodium thiosulfate (by pipet) and about 80 ml. of water were also introduced into the flask, which, after corking, was placed in a shallow tray containing water a t 20" C., then exposed t o bright sunlight. Rapid decomposition with liberation of iodine was found to take place in the etherbenzene layer. On shaking the flask from time to time with a swirling motion, the iodine liberated was reduced ANALYTICAL CHEMISTRY
yo Error
100.3 ~. -
Table IV. Estimation of Acetone and Its Mixtures Ratio on A4cetone,Mg. Molality Basis Present Found Acetone only 5.8 5.7 1:l Acetone: HCHO 5.8 5.75 1 : 1 Acetone: C6HsCHO 5.8 5.9 1: 1 -4cetone: CCllCHO 5.8 5.7 1: 1 Acetone: CzHsCHO 5.8 5.75
1 138
Error -0.4 -0.5 -0.4 -0.4 -0.3 -0.4
R
1 ml. of 0.05-V iodine = 6.566 mg. of CHI,
Procedure for Iodoform Suspended in Water. Suspensions were prepared by weighing out iodoform into a 250nil. conical flask containing about 100 ml. of water. The iodoform was first dissolved in 20 ml. of ether, and the flask was corked and shaken vigorously, until all the iodoform dissolved. About 10 ml. of benzene and 20 ml. of 0.05K sodium thiosulfate (by pipet) were added. The iodoform was decomposed in the sunlight in a manner similar to that already described. A blank was carried out using 100 ml. of water instead of the suspension. The free iodine liberated froni the iodoform was thus found (Table 111) ~
yc Error -1.7 -0.9 $1.7 -1.7 -0.9
by the sodium thiosulfate solution, This prevented the ether-benzene layer from acquiring a red color which otherwise acted as an autofilter. The best plan for shaking was to shake once every minute for the first 10 minutes, then once every 2 minutes for the next 10 minutes, and later once every 5 minutes until the ether layer remained colorless. Finally, the flask was closely observed for 10 minutes without shaking and the development of no color in the ether-benzene layer during this period was taken as an indication that the reaction was completed. For confirmation, an additional 10 minutes' exposure was given, even after it appeared that the process of photooxidation was over. In all, about 45 minutes were required for complete decomposition. The water in the tray was changed from time to time so that the temperature of the flask did not rise above 25" C. Later, the flask was removed from sunlight and the excess of sodium thiosulfate was titrated vith 0.05N iodine solution after adding to it 1 gram of solid potassium iodide and 1 ml. of starch solution. A blank was carried out in a similar manner, except for the addition of the iodoform solution. The difference in the two iodine readings gave the amount of iodine liberated from iodoform. Dilute sodium thiosulfate solution x i s used here because ether and thiosulfate have a tendency to react when exposed to sunlight. This reaction is negligible when the thiosulfate solution used is very dilute (0,OLV). During photooxidation some gases were produced which developed pressure inside the flask. This was released by opening the cork occasionally. The oxygen
PROCEDURE
FOR ACETONE
dcetone mas first converted to iodoform by employing illessinger's method (4)as described by Mitchell et al. ( 5 ) . Two t o 25 ml. of aqueous solution containing not more than 6 mg. of acetone was pipetted into a 250-ml. conical flask and treated with 100 ml. of water, 20 ml. of 0.liV iodine solution, and 25 nil. of I N sodium hydroxide solution. The flask was swirled and allowed t o stand for 15 minutes for completion of the reaction. Later, its contents were acidified with 25.5 ml. of IN sulfuric acid and the iodine liberated was precisely titrated Kith 0.lX thiosulfate solution to the starch end point. After the titration the hydrogen ion concentration of the solution was reduced as much as possible, by adding 2 drops of phenolphthalein indicator and titrating the excess sulfuric acid with 1N sodium hydroxide solution until the contents of the flask became slightly pink. Then 2 drops of 1N sulfuric acid were added to remove the pink color, followed by 5 mi. of 20% sodium acetate solution. The iodoform suspended in the solution was then estimated by the method described. Only 10 nil. of 0.05N thiosulfate solution was. used for reducing the iodine liberated photochemically. A blank was carried out in a very similar manner, except for the addition of the acetone solution. Thus the amount of iodine liberated from the iodoform produced was found. 1 ml. of 0.05N Is = 0.967 mg. of acetone The procedure described for acetone, although not very simple, is applicable in the presence of other aldehydes and ketones, provided they do not produce iodoform when reacted with hypoiodite solution (Table IV). CONCLUSIONS
The determination of iodoform by the method described presents certain advantages and disadvantages. The procedure is rapid and relatively simple. It can be used for evaluating solutions.
of organic compounds which undergo quantitative iodoform reaction. An obvious disadvantage is the expected interference by other iodine-substituted organic compounds, which must be eliminated from the assay mixture, because most of the iodine compounds are affected by light. Another disadvantage is its dependence on sunlight. The photooxidation takes place in daylight also, but requires many
days for completion. White light from a mercury vapor lamp may be used as a substitute, although trials with such a lamp have not been carried out by the author. LITERATURE CITED
(1) Ellist c . ,
A. Heyrotll, F. F., “The Chemical Action of Ultraviolet Rays,” p. 395, Reinhold, S e w York, 1941.
( 2 ) Emschwiller, G., Bull.
SOC. chim. 6 , 551-60, 561-70 (1939). ( 3 ) Emschwiller, G., Compt. rend. 207, 1201-3 (1938). (4) Messinger, J., Ber. 21, 3366-72 (1888). (5) hlitchell, J., Kolthoff, I. M., Proskauer, E. S., Fpsberger, A., “Organic Analysis, Vol. I, p. 269, Interscience, New York, 1953.
RECEIVEDfor review August 23, 1957. Accepted January 6 , 1958.
Dithizone Method for Determination of Lead in Monazite R. A. POWELL‘ and C. U. S. Geological Survey,
A. KINSER Washington
25, D. C.
b In the determination of lead in monazite-to b e used as the basis for geologic age measurements-it was necessary to eliminate interferences due to the presence of phosphates o f thorium and the rare earth metals. The method involves attacking the monazite samples with hot, concentrated sulfuric acid, then taking them up with dilute nitric acid. Lead i s extracted as the dithizonate and determined spectrophotometrically at 520 mp. Rapid determinations were made with good reproducibility on a series of monazite samples.
I
on the determination of lead in monazite led the authors to believe that thorium-rare earth phosphates were a source of interference. Sandell (8) reported that dithizone extraction fails in the presence of much calcium (or magnesium) and phosphorus because the phosphates of these metals are only slightly soluble in ammoniacal citrate solution and carry down lead strongly. Thorium and rare earth phosphates behave similarly. To minimize or eliminate the interferences in the analysis of monazites and other related materials, it became necessary to study various methods of sample attack, Iead separation, and reagent concentrations. The method developed as a result of this investigation is based on several established spectrophotometric methods (1-3, 6, 8) for the determination of lead, but has been altered a t several points that mere found to be critical when working with samples containing thorium and rare earth phosphates. iJ7ith this procedure lead determinations can be made rapidly on a routine basis. Present address, Union Carbide Ore Co., Sterling Forest Research Lab., Tuxedo, N. Y. SVESTIGATIONS
The method has given excellent reproducibility in the laboratory, and its accuracy was proved by check analysis with two other laboratories using mass spectrographic techniques. PRELIMINARY STUDY
The established method, upon d i i c h the following experimental work is based, consists of dissolution of the sample; addition of citrate to prevent precipitation of metal hydroxides, cyanide to complex other metals, sulfurous acid to reduce iron, and ammonium hydroxide to adjust the pH to 9.2; extraction of lead into a chloroform solution of dithizone; stripping of the lead into a dilute nitric acid solution; reextraction of the lead into a standard dithizone solution; and measurement of the absorbance of the extract a t 520 mp against water as the reference solution. Sample Treatment. Several methods of sample treatment were investigated in an effort t o select the one best suited t o effect solution prior t o the lead determination. Sintering the sample with sodium peroxide (7, 9) seemed promising, but its use was discontinued because of erratic lead analyses obtained after this initial treatment. Later work indicated that the erratic results might have been caused by the difficulty of removing all of the excess peroxide before the lead extraction. Fusion with sodium carbonate, potassium bisulfate, or a 3 to 1 mixture of sodium carbonate and sodium borate failed to give complete decomposition of monazites. Samples seemed to be completely decomposed when the sodium carbonate-sodium borate mixture ratio was changed to 1 to 3; however, the lead results were variable, When so-
dium borate alone was used as the flux, clear melts mere obtained which were exceedingly difficult to dissolve. The treatment with sulfuric acid was the most successful method (4) investigated for the attack of monazite samples. By this means decomposition of samples mas completed within 1 hour, the fusion in platinum vessels, a possible source of error, was eliminated. After the initial treatment with sulfuric acid and the subsequent addition of dilute nitric acid, a trace of residue was usually apparent. However, it was generally insignificant and could be ignored. Of the nine monazite samples analyzed, only one (labeled impure) gave an appreciable residue. Spectrographic analysis showed the major constituent to be silicon, although it also disclosed the presence of lead. This residue was easily decomposed by hydrofluoric and nitric acids. Sample and Reagent Concentration. Cloudiness or precipitation, attributable t o thorium and rare earth phosphates, was observed occasionally in the sample solutions after adjustment of the p H to approximately 9.2. This phenomenon sometimes appeared immediately, while a t other times it was delayed until after the extraction of lead had been completed. As this precipitation seemed to be associated mainly with larger samples, experiments were undertaken to establish the relationship between sample size, time, and amount of precipitation and lead recovery. For the sake of convenience and sample conservation, a synthetic monazite solution was prepared from cerium and thorium nitrates and disodium phosphate. The solution contained the equivalent of 5 mg. of a typical monazite per ml. in dilute nitric acid (I t o I) Preliminary experiments with the esVOL. 30, NO. 6, JUNE 1958
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