Bromine test for unsaturation

Bromine is a hazardous chemical that may cause serious chemical burns. Do not breathe its vapors or allow it to come into contact with your skin. Perform 

Do not use acetone to rinse glassware containing residual amounts of bromine. This prevents formation of a-bromoacetone, a severe lachrymator. Rather, follow the procedure described in Wrapping It Up. 

Preparation Sign in at www.cengage.com/login to read the MSDSs for the chemicals used or produced in this procedure. 

Dissolve 50 mg or 1 or 2 drops of the unknown in dichloromethane, and add to this solution 0.1 M bromine in dichloromethane dropwise until a light orange color just persists. Rap/d disappearance of the bromine color to give a colorless solution is a positive test for unsaturation. 

Decolorize any solutions in which the color of bromine is visible by dropwise addition of cyclohexene then discard the resulting mixtures in the container for halo-genated organic liquids. 

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The double bond of tetrachloroethene is undetectable in the bromine test for unsaturation. Give a plausible explanation... 

Transfer the pot residues from the distillation of spearmint and/or caraway oil to the container for nonchlorinated organic wastes. After performing the prescribed tests on your distillate, put the isolated natural products into appropriately labeled containers. Place the dichloromethane solution from the bromine test for unsaturation in a container for halogenated organic liquids put the manganese dioxide from the Baeyer test for unsaturation in a container for heavy metals. Neutralize and then filter any excess 2,4-dinitrophenylhydrazine solution. Put the filter cake in the container for nonhazardous solids. Flush the filtrate as well as filtrates obtained from recrystallization down the drain. 

Neutralize the residue remaining in the stillpot with 10% aqueous hydrochloric acid then flush it down the drain. Place the dichloromethane solution from the bromine test for unsaturation in a container for halogenated organic liquids put the manganese dioxide from the Baeyer test for unsaturation in a container for heavy metals. 

Chemical Tests. Add several crystals ( 5 mg) of the fra s-dnnamic add to 1 mL of 5% sodium bicarbonate on a watch glass. Does evolution of CO2 indicate the presence of a carboxylic add Does the material give a positive bromine test for unsaturation (see Chapter 9). 

The decolorisation of bromine, usually in CC14 solution, is one of the classical tests for unsaturation, and probably constitutes the most familiar of the addition reactions of alkenes. It normally proceeds readily in the absence of added catalysts, and one is tempted to assume that it proceeds by a simple, one-step pathway ... 

The reaction with permanganate constitutes a valuable and much-used test for unsaturation in an organic compound. The substance is dissolved in cold alcohol, a few drops of sodium carbonate solution are added, and then a drop.of dilute permanganate solution. Rapid disappearance of the red colour indicates the presence of a double bond. The Baeyer test can also be carried out in pure glacial acetic acid, which is stable towards permanganate. Another method of detecting double bonds is by the decolorisation of bromine. As a rule, chloroform is used as solvent. 

Addition of X2 (Bt2 and CI2) to alkenes gives vicinaZ-dihalides. This reaction is used as a test for unsaturation (n bonds), because the red colour of the bromine reagent disappears when an alkene or aUcyne is present. For example, when ethylene is treated with Br2 in CCI4 in the dark at room temperatures, the red colour of Br2 disappears rapidly, forming 1,2-dibro-moethane, a colourless product. 

Electrophilic addition of the halogens and related X—Y reagents to alkenes and alkynes has been a standard procedure since the beginning of modem organic chemistry.1 Anti electrophilic bromination of such simple compounds as cyclohexene and ( )- and (Z)-2-butene, and variants of this reaction when water or methanol are solvents (formation of halohydrin or their methyl ethers, respectively), are frequently employed as prototype examples of stereospecific reactions in elementary courses in organic chemistry. A simple test for unsaturation involves addition of a dilute solution of bromine in CCU to the... 

Testing for Unsaturated Hydrocarbons with Bromine movie... 

Test for unsaturation A few drops of bromine dissolved in an organic solvent are shaken with the hydrocarbon. If it is decolourised, the hydrocarbon is unsaturated. 

Test for unsaturation using bromine in a suitable solvent (Figure 14.13, p. 225). 

The residue is cooled to 40° and slowly hydrolyzed (cooling as necessary) with 900 cc. of cold 6 N sulfuric acid, prepared from 145 cc. of concentrated sulfuric acid and 700 cc. of water. The oily layer is separated, washed once with water, and distilled at 60-70° while the pressure is lowered slowly from about 275 mm. to 65 mm. Finally the distillation is continued to 100° and 20 mm. This procedure permits separation of all the crotyl alcohol from the higher-boiling polymerization products. The aqueous layers are combined and distilled until the distillate no longer gives a test for unsaturation with a dilute solution of bromine in carbon tetrachloride. The distillate is then saturated with potassium carbonate, and the oily layer which separates is added to the product obtained by distillation of the oil. 

Other organic reactions take place between completely uncharged molecules with no dipole moments. One of the old tests for unsaturation was to treat the compound with bromine water. If the brown colour disappeared, the molecule was unsaturated. We don t use tests like these any more (spectroscopy means we don t need to) but the reaction is still an important one. A simple symmetrical alkene combines with symmetrical bromine in a simple addition reaction. 

The additions of halogens such as bromine to alkenes represent a good test for unsaturation in a molecule. The addition of bromine takes place via the formation of a bromonium ion. Proof of this was obtained by carrying out the reaction of ethene with bromine in the presence of sodium chloride, when the product was the bromo-chloride (BrCHjCHjCl). 

B) Tests for Unsaturation. (1) Add 1 ml of benzene to 2 ml of 1 per cent solution of bromine in carbon tetrachloride and allow to stand for a few minutes. (2) Shake 1 ml of benzene with 2 ml of 0.05 per cent potassium permanganate solution and allow to stand for 5 minutes. 

G) Test for Unsaturation. Dissolve 0.4 g (or 7-8 drops) of the fatty acid mixture in 3-4 ml of carbon tetrachloride. Add from a burette, drop by drop, one per cent solution of bromine in carbon tetrachloride until the color of bromine persists even with shaking. Repeat, using about the same amount of stearic and oleic acid. 

The addition of Bt2 to alkenes is used as a simple qualitative test for unsaturation. Bromine, a dark red liquid, is dissolved in a nonpolar solvent. When an alkene is added, the solution becomes colorless as the Bt2 reacts with the alkene to form a colorless compound. This reaction may be used to distinguish between alkanes and alkenes. 

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