A Safe, Convenient Method of Generating Bromine for QualitativeAnalysis Suzanne W. Slaydent, Thuy H. Do: Kimbedy Y. Smiley,2 and Donna J. NelsonS University of Oklahoma, Norman, OK 73019 Bromine is routinely used as a qualitative test for unsaturation. active methvlene erouns. .~ . ..nhenols. and a m i n e ~However, there are hazards associated with handling the pure hromine reauired to nrenare the test s o l u t i ~ n We . ~ have developed a" alternatfve method of obtaining hromine that is inexpensive, safe, convenient, and suitable for student use. An aqueous mixture of chloramine-T (sodio-h-chloro-ptoluenesulfonamide).6 sodium bromide, and HCI (1:2:1) is a source of bromine, formed hy the oxidation of bromide by chloramine-T. When a suitable solvent, such as CCld, CHC13, CH2Cla or CS2, is added to the mixture, the bromine is extracted into the nonaqueous phase with the concomitant appearance of the characteristic red color of Br2. This reagent solution may he used whenever a bromine test is reouired. For examnle. or 1-hexene reacts instan. .cvclohexene . taneously with loss of the hromine color to give the corres ~ o n d i n 1.2-dibromo e comnound in 72-74% or 75-80% vield. r k ~ ~ e c t i GMost e ~ ~ .of the minor product mixture is the hromohydrin.
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Reagent . Preparation The commonly used 2% Brz/CC4 reagent can be prepared in several ways. The order of additionof the reagents to form the test solution is of no consequence, provided they are well mixed, nor is it crucial that the measurements or molarities of the compounds be exact. For a large-scale preparation, dissolve 11g of chloramine-
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ACS-PRF Summer Fellow 1985 on leave from George Mason University. Fairfax, VA. ACS-PRF Project Seed Participants. Address: Northeast High School, Oklahoma City. OK. Author to whom correspondence should be sent. 'Pasto, D. J.; Johnson, C. R. Organic Srmcfure Determination; Prentice-Hall: Enalewwd Cliffs.NJ. 1969: o 330. (a) Sax, N. ~ . ~ a n ~ e r oProperties us oilndustrial~aterials;Reinhold: New York, 1968: p 486. (b) Burnen, W. T., Jr. J. Chem. Educ. 1975,52, A322-A323. @Campbell.M. M.; Johnson, G. Chem. Rev. 1978, 78,6579. Passing the Br2/CCI4through a plug of glass wool while separating prevents any solid from entering the bottle. However, the solid does not mterfere with the test reagent.
388
Journal of Chemical Education
T trihydrate and 8 g of sodium bromide in 200 mL distilled water in an 800-mL beaker. Add 40 mL of 1 M HCI while stirring; the mixture is an orange-yellow suspension. Then add 100 mL of CC14and stir uigorously until the CCldphase is red. If mixing with a magnetic stirrer, this step requires about 30 s. Pour the contents of the beaker into a large separatory funnel and drain the lower layer into a brown glass bottle.' If a small amount of the reagent is required, it can be conveniently prepared in a test tuhe as needed. Using Pasteur pipets, deliver into a medium-sized test tube one aliquot each of a 0.5 M aqueous solution of chloramine-T and a 1 M aqueous solution of NaBr. Add slightly less than two aliquots of CCla and then one aliquot of 1 M HCI. Stir vigorously. T o use the reagent, transfer the lower layer via pipet into another test tube containing the substrate. Experimental Commercially available (Aldrich) samples of 1-hexene, cyclohexene, and chloramine-T were used as received. Internal standards (n-alkanes, 99%) were used as received from Humphrey Chemical Co. The dibromoalkanes were identified by MS comparison and by GC coinjection with authentic comnonnds. The authentic comnounds were svnthesized by dropwise addition of bromine to a solution of known amounts of alkene and alkane (internal standard) in carbon tetrachloride until no more color disappeared. Product identities and vields were determined usine a Hewlett-Packard 5 7 9 0 ~ 1 3 3 9 0equipped ~ with a 6-ft X '/& column with 10% SE-30 on 100-120 mesh Chromosorb W. Mass spectra were obtained on a Hewlett-Packard 5985 gas chromatograph/mass spectrometer/data system equipped with a 4-mm X 6-ft column with 3% SE-30 on 100-120 mesh Chromosorb W.
Acknowledgment Acknowledement is made to the donors of the Petroleum Research h n d , administered by the American Chemical Society, for the suppon of this researrh. We also appreciate grants from the Research Corporation and from the National Science Foundation.
