Baeyers Test for Unsaturation

Baeyers Test for UnsaturationREACTION OF COLD, DILUTE POTASSIUM PERMANGANATE SOLUTION WITH UNSATURATED HYDROCARBON COMPOUNDSLOGOContentsI. IntroductionII. ObjectivesIII. Reagents & EquipmentIV. ProcedureV. Data & ResultsVI. AnalysisDefinition of TermsHydrocarbons are the simplest organic compounds. Contain only carbon and hydrogen. They can be straight-chain, branched chain, orcyclic molecules. Carbon tends to form four bonds in a tetrahedralgeometry. Hydrocarbon derivatives are formed when thereis a substitution of a functional group at one ormore of these positions.definition of termsAlkanes are hydrocarbon compounds whose molecules contain carbon-carbon single bonds. All have the general formula CnH2n+2 where n is any integer. They are often referred to as saturated hydrocarbons because their molecules contain the maximum possible number of hydrogen atoms per carbon atom, and because they consist only of carbon and hydrogen.Alkenes are hydrocarbon compounds whose molecules contain one or more carbon-carbondouble bonds. They are often referred to as being unsaturated because the presence of a doublebond means that they lack hydrogen atoms as compared with related alkanes. The generalformula for alkenes is CnH2n.

IntroductionTwo common qualitative tests for unsaturation are the reaction of the compounds with bromine in carbon tetrachloride and with potassium permanganate. In both cases a positive test is denoted by decolorization of the reagent.

A. Bromine AdditionWhen a dilute solution of bromine in water (or carbon tetrachloride) is mixed with an alkane, no reaction occurs due to the inertness of saturated hydrocarbon compounds to bromine. The brown colour of the bromine remains. Mixing the same bromine solution with an alkene or alkyne results in the rapid disappearance of the brown colour of the bromine, until a colourless mixture is obtained.www.themegallery.com

Baeyers TestPotassium Permanganate A second qualitative test for unsaturation, the Baeyer test, depends on the ability of potassium permanganate to oxidize the carboncarbon double bond to give alkanediols or the carbon-carbon triple bond to give carboxylic acids

The permanganate is destroyed in the reaction, and a brown precipitate of MnO2 is produced. The disappearance of the characteristic color of the permanganate ion is a positive test for unsaturation. However, care must be taken, since compounds containing certain other types of functional groups (for example, aldehydes, containing the --CH=O group) also decolorize permanganate ion.

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The Baeyer reagent is a cold dilute aqueous solution of potassium permanganate which is a deep purple color.Potassium permanganate does not react with alkanes because they are saturated (single bonds which are all taken).When it is added to alkanes the purple color does not change.

www.themegallery.comWhen it is added to an alkene, the purple color slowly disappears and a brown MnO2 precipitate forms. The appearance of the brown precipitate indicates a positive test for unsaturation.Purple color dilutes to light purple = SATURATEDPurple color disappears and brown ppt forms = UNSATURATED

www.themegallery.comObjectivesTo investigate the physical properties of some hydrocarbonsTo use Baeyer's test to determine if a compound is saturated or unsaturatedwww.themegallery.comReagentsCyclohexaneis a cycloalkane with the molecular formula (CH2)6.

cyclohexaneProperties/Uses:Cyclohexane is mainly used for the industrial production of adipic acid and caprolactam, which are precursors to nylon. Cyclohexane is a colourless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used)

cyclohexaneHazards:Flammablemay cause irritation in eyes, skin,respiratory system; drowsiness,dermatitis,narcosis,comawww.themegallery.comPotassium Permanganateis an inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4 ions

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potassium permanganateProperties/Uses:Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely pink or purple solutions, the evaporation of which leaves prismatic purplish-black glistening crystals. In 2000, worldwide production was estimated at 30,000 tonnes. In this compound, manganese is in the +7 oxidation state.www.themegallery.compotassium permanganateHazards:caustic and can burn the skin. It can irritate skin and repeated use may cause burns. If redness or irritation continues, notify your doctor. When preparing solutions make sure that the crystals or tablets are fully dissolved in water before using.Note that potassium permanganate may leave a brown stain on skin and nails as well as the bath or vessel holding the solution.

Cyclohexeneis produced by the partial hydrogenation of benzene, a process developed by Asahi Chemical Company.

cyclohexeneProperties/Uses:It is converted to cyclohexanol, which is dehydrogenated to give cyclohexanone, a precursor to caprolactam. Cyclohexene is also a precursor toadipic acid, maleic acid, dicyclohexyladipate, and cyclohexeneoxide. Furthermore, it is used as a solvent.EquipmentOrganic Comboplate Microspatulas

equipment PropettesGloves

ProcedureObserve the contents of each well from the side of the comboplate

3 drops of cyclohexane to well A53 drops of cyclohexane to well A4Add 6 drops of cold, 0.1% KMnO4 (aq)Stir the contents of each well vigorously using microspatulaRaise the comboplate.Note the appearance of the contents of each well to see if a colour change has taken place.Data and Results

AnalysisQ1. What do you notice in each well immediately after adding the potassium permanganate solution?

www.themegallery.comQ2. Describe the appearance of the cyclohexane-permangate mixture in well A4 after stirring.Q3. What has happened to the cyclohexene-permanganate mixture after stirring?Q4. How can dilute potassium permanganate solution help the chemist to distinguish between saturated and unsaturated hydrocarbon compounds?Q5. What do you notice about the appearance of bromine-cyclohexene mixture?www.themegallery.comQ6. If cyclohexene is a saturated hydrocarbon compound, why has the colour faded? Use the following reaction to explain your answer.

Cyclohexene + Br2 cyclohexylbromide+Hbrwww.themegallery.comConclusionwww.themegallery.com