In T P 0 0 0 , there are only two alternative positions:
of the color of the complex with the B.D.H. ion exchange resin
4. Between OH(1‘) and nitrogen (2’) of the azo group 5. Between OH(1’) and nitrogen (3’) of the azo group
Amberlite IR-45(OH). EVALUATION OF STABILITYCONSTANT.The apparent stability constant of the P d - T P 0 0 0 chelate was calculated from the absorbance data by three methods (Table 111).
Seth and Dey (IO) suggested position 2 in the case of chelation with TPO. Similarly, position 4 is preferred in the case of the TPOOO chelate of palladium and the tentative structure of P d - T P 0 0 0 chelate is believed to be:
P d - T P 0 0 0 Chelate The anionic nature of the chelate has been confirmed by electrophoresis studies and also by the complete adsorption
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RECOMMENDED PROCEDURE
An aliquot of the palladium solution is suitably diluted to contain ca. 2 to 15 ppm of palladium. To 10 ml of the dilute solution, an equal volume of 5-fold concentration of either TPO or TPOOO is added. The pH of the mixture is adjusted to 3.5 (for TPO) and 4.0 (for T P 0 0 0 ) and the total volume raised to 25 ml. The mixture is allowed to equilibrate for 15 minutes and the absorbance is measured with a spectrophotometer using IO-mm glass cells at 550 mp (for TPO) and 570 mp (for TPOOO). The concentration of palladium is read from Beer’s law plots prepared under identical conditions. RECEIVED for review December 1 1 , 1967. Accepted March 14, 1968. Work supported by the Council of Scientific and Industrial Research, New Delhi.
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Determination of Impurities in Bromine by Infrared Spectrophotometric Methods Lynn H. Hahn and Loren E. Pauling Michigan Chemical Corp., 500 North Bankson, St. Louis, Mich. 48880 An analytical method was needed for rapidly determining the concentration of impurities in commercial bromine. Recent improvements in bromine quality have necessitated more sensitive and informative analytical techniques. Much about the quality of bromine can be determined from the infrared spectrum because bromine i s a very effective transmitter of infrared energy. Impurities encountered in bromine produced from brine can include water, hydrogen chloride, hydrogen bromide, carbon dioxide, nitric oxide, carbonyl bromide, carbon tetrachloride, bromotrichloromethane, chloroform, ethyl bromide, and dibromobenrene. One impurity, chlorine, which does not show infrared absorption, can be determined by causing reaction with hydrogen bromide which converts the chlorine to hydrogen chloride. The hydrogen chloride is infrared sensitive and its absorption can be related to chlorine concentrations. Cell path lengths of 2 centimeters have been used to provide detection of impurities in concentrations below 1 pg per ml.
INTHE PAST FEW YEARS, the quality of commercial bromine has been improved significantly through the use of purification techniques. Bromine in the past was sold with a purity specification of 99.8 while today purity specifications exceed 99.95 %. The analysis of 99.8 bromine generally consisted of determining the water content by some sort of absorption train technique, determining the chlorine content using a gravity change procedure, and determining the nonvolatiles concentration by evaporating down a sample and weighing the residue. These analyses do not tell anything about the several other impurities which codistill with bromine and these methods are not sensitive enough to be of practical use when
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analyzing 99.95 or better bromine. Analytical methods were needed which could detect concentrations of impurities in the 1 pg per ml of bromine range. Our laboratory work has shown that infrared methods can be used to detect most of the impurities in bromine and quantitative determinations made. A review of the literature shows that the use of infrared to analyze bromine is not new but has probably been used in some laboratories for at least 10 years. Duvall and Kiley reported in 1958 the use of infrared to determine water in bromine ( I ) . Wagner in 1963 reported that bromine transmits infpared energy (2, 3). Stenger reported in 1964 and 1966 the use of infrared to analyze bromine, particularly for organic impurities ( 4 5 ) . Except for the water determination, these papers do not give details of the technique. This paper describes the technique and also a method for determining chlorine in bromine by infrared techniques. EXPERIMENTAL
Equipment and Procedures. Infrared spectra of bromine are recorded using a cell designed to provide a path length so that sensitivities of the order of 1 pg of impurity per ml of bromine are obtained. A cell thickness of about 2 cm is sufficient. The cell is mainly inert to bromine and when handled with care is safe to use. (1) R. B. Duvall and L. R. Kiley, ANAL.CHEM.,30, 549 (1958). (2) H. Wagner, Narurwissenschaften, 50, 223 (1963). (3) H. Wagner, 2.Anorg. Allgem. Chem., 337, 54 (1965). (4) M. S. Chao and V. A. Stenger, Tulanta, 11, 271 (1965). (5) V. A. Stenger, Angew. Chem. Intern. Ed., 5 , (3), 280 (1966). VOL. 40, NO. 8, JULY 1968
1283
Figure 1. Infrared cell for scanning bromine
The cell consists of a glass body, about 2 cm long and 23 mm in diameter with two legs connected to the body made from 12 mm diameter glass tubing fitted with 10/30 female glass joints at the ends. Each end of the cell body is sealed with a 6-mm thick NaCl crystal using a 0.045-inch thick gasket made of Teflon (Du Pont). The gasket is cut to provide an 18-mm hole for passing the infrared energy. The components are held together with two back plates of a Beckman IR-4 infrared cell and four 2-inch long by S/&xh diameter bolts. Usually 0.065-inch thick silicone rubber gaskets are placed between the crystals and the plates to act as a cushion. The bolts are carefully tightened until the cell does not leak bromine (Figure 1). A cell was also constructed for use in determining chlorine in bromine and which is stable in the presence of hydrogen bromide. A Beckman silica cell, 1-cm path length, No. 231010-89, transmits infrared energy in the wavelength region including 1 to 4.6 p. A 5-inch piece of tubing made of Teflon (Du Pont) is attached to the cell and at the other end is attached a 10/30 ground glass joint with the body cut to be 1 inch long. A plastic tubing connector fitted with a silicone rubber septum is used to cap the end of the ground glass body and provides an air tight seal (Figure 2). Bromine is sampled from a bottle using a glass thief. The thief is constructed from a glass tube about 8 inches long by 6/sinch outer diameter which is fitted with a stopcock made of Teflon on one end and a 10/30 male ground glass joint on the other end. The tip end of the glass joint is shaped to a small opening of about 1'. of an inch (Figure 3). Reagents. Bromine which contains total organic impurity concentrations below 1 pg per ml can be prepared for use as an analytical standard. It is difficult to prepare bromine containing less than 1 pg per ml of water. The procedure used for preparing the analytical reagent is to first obtain some commercial high purity bromine, preferably free of carbon tetrachloride and bromotrichloromethane. If it contains these two impurities, they can be removed by first eluting the bromine through a 1OX molecular sieve column. Ordinarily, a 20 inch long by'/,-inch diameter column filled with the sieve will remove these impurities from 1000 ml of bromine and their complete removal can be determined by infrared. 1284
ANALYTICAL CHEMISTRY
Figure 2. Cell for determining chlorine in bromine
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Figure 3. Bromine sample thief
The bromine treated above, or bromine tree of carbon tetrachloride and bromotrichloromethane, is then treated with anhydrous hydrogen bromide to react with any chlorine, which will produce hydrogen chloride. The bromine is then water washed until the hydrogen chloride and hydrogen bromide are completely removed from the bromine. The bromine is further purified by distilling from sulfuric acid with precautions taken to exclude atmospheric moisture. The dried bromine is then eluted through a column packed with a 1/,6-inch, Type 3a-2 Linde molecular sieve which is held in place with glass wool plugs. The bromine is eluted a t a rate of about 5 ml per minute into a bottle arranged to keep the bromine from being exposed to moisture in the air. A final paper filter is placed between the column and the bottle. Bromine treated in this manner will contain less than 1 pg per ml of organic impurity and with careful handling can result in bromine containing less than 2 pg per ml of water. Another method of purification has been described in the literature (6). PREPARATION OF STANDARDS The preparation of standards can be a problem especially if only small amounts of reagent bromine are available. If the quantity of bromine is no problem, standards can be prepared by the direct addition of small quantities of impurity to the (6) Maurice Codell and George Norwitz, ANAL. CHEM., 29, 967 (1957).
bromine. The addition of gases is accomplished using some special techniques. Some reagent bromine, usually 500 ml, is placed into a graduated funnel fitted with a stopcock made of Teflon (Du Pont) and a glass jointed reducer fitted with a silicone rubber septum to provide a n air tight seal. Appropriate volumes of the gas can be added with a Hamilton gas syringe after the same volume of bromine has been removed from the graduated cylinder. This reduces the pressure and makes adding the gas easier. The weight of the gas can be determined by weighing the syringe before and after the addition. Most all impurities added t o bromine dissolve readily. One exception is water. Water added as a liquid can require considerable time to dissolve depending on the amount to be added. PROCEDURES
To scan a spectrum of bromine, the NaCl cell is filled with the aid of the sample thief. The thief and cell are purged with dry nitrogen after which the stopcock on the thief is closed and cell is stoppered. The bromine bottle is uncapped and the thief inserted in the bottle. The stopcock is opened and the bromine allowed to seek its level in the thief. The stopcock is closed, while one stopper is removed from the cell. The thief is carefully transferred to the cell leg and inserted. The other stopper is loosened and the thief stopcock opened which permits the bromine to drain into the cell. This technique results in negligible moisture pick up by the bromine. For safety purposes, a ready source of water should be close by. A hypo (sodium thiosulfate) solution made by dissolving two pounds of crystals in one gallon of water should also be close a t hand. The spectra are recorded between 1 and 15 p in the usual manner and preferably with an empty cell in the reference beam. RESULTS
An infrared scan of regular grade bromine can show a half dozen or more impurities which vary depending on the source of production. Among the more common impurities and their absorption wavelengths are: Water Hydrogen chloride Hydrogen bromide Carbon dioxide Nitric oxide Carbonyl bromide Chloroform Ethyl bromide
2.8 3.6 4.1 4.2 5.4 5.5 8.2 10.5
Dibrornobenzene Carbon tetrachloride Bromotrichloromethane Chlorine
12.3 13.7 14.0 -
Most of the impurities above at concentrations below 30 pg per rnl do not show serious interferences and concentrations can be determined directly by comparison with synthetic standards. Chlorine in bromine does not show infrared absorption so that its character must be changed, if it is to be determined by infrared. This can be accomplished by chemically reacting the bromine sample containing chlorine with anhydrous hydrogen bromide. This reagent will rapidly react with any free chlorine to produce hydrogen chloride and bromine. The chlorine, now as hydrogen chloride and infrared sensitive, can be observed by infrared using the hydrogen chloride absorption band at 3.6 p , The procedure consists of filling the silica cell with the bromine sample to be analyzed. The cell is made air tight with the septum and holder. The cell filled with bromine is scanned on the infrared between 4.6 and 3 with a blank reference silica cell to determine if any hydrogen chloride is already present. The cell is taken to a hood and about 2 ml of anhydrous hydrogen bromide are injected into the cell via a Hamilton gas syringe with a plunger made of Teflon (Du Pont). The cell is shaken 2 or 3 times and scanned again between 4.6 and 3 p. The absorption due to hydrogen bromide at 4.05 p and the hydrogen chloride at 3.6 p are observed. If the scan shows hydrogen bromide, it means all the chlorine present in the sample has reacted and the hydrogen chloride absorption, if present, can be related to the concentration of chlorine. If hydrogen chloride is present but absorption due to hydrogen bromide is absent, it means there is more free chlorine and more hydrogen bromide needs to be added. Hydrogen bromide is added in increments of 1 to 2 ml until the hydrogen bromide absorption appears which means the chlorine has completely reacted. The hydrogen chloride absorption is determined by the base line technique and related to the chlorine concentrations from previously prepared standards, The precision of the determination of chlorine in bromine was determined by analyzing the same sample six times. The standard deviation a t the 24 ppm level was ~ t 0 . 8ppm. ACKNOWLEDGMENT
The authors acknowledge the technical assistance given by Merrill Potter.
RECEIVED for review February 5, 1968. Accepted March 27, 1968.
VOL. 40, NO. 8, JULY 1968
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