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Dr. S. Paul Douglas , Dept. of Engineering Chemistry, A. U. College of Engg. Andhra University 1 SYSTEMATIC PROCEDURE FOR IDENTIFICATION OF THE FUNCTIONALGROUP OF AN ORGANIC COMPOUND S. No. Experiment Observation Inference1 Physical Characteristics: a) State Solid/liquid b) Colour Colourless/ _ _ _ _ _ colour c) Odour Pleasant/ phenolic/ aniline like/oil of bitter almond/characteristic 2 Solubility: a) Cold Water (Test the aqueous solution withBlue and Red Litmus Papers)SolubleBlue Litmus turned to RedRed Litmus turned to BlueAcidicBasic b) NaHCO 3 (10%) Soluble with effervescencePresence of Carboxylic AcidGroupc) NaOH (10%) SolublePresence of Acidic Substance(Acids and Phenols)d) dil HCl (10%) SolublePresence of Basic Substances(Amines) Note: 1) If Water Soluble, do not test with NaHCO 3 , NaOH and dil HCl. Use Litmus Paper 2) If the Compound is insoluble in water and the other reagents, it is NEUTRAL e) Ether (Note: Insoluble in water,acid and alkali)SolubleHydrocarbons, nitrohydro-carbons, alkyl or aryl halides,esters and ethers. Higher molecular weight alcohols,aldehydes and ketonesInsoluble in Ether but solublein water May be Carbohydrates or Urea 3. Flame Test: Glass rod is dipped in thecompound and subjected toflamea) Burns with a sooty flame b) Burns with non-sooty flamec) CharringAromaticAliphaticCarbohydrates, etc 4. Test for Unsaturation: a) Baeyer’s Test: Compound isadded to aq. KMnO 4 solutiona) Decolourisation of KMnO 4 with brown ppt. b) Compound is added toBromine in CCl 4 (2%) b) Decolourisation of Br 2 without evolution of HBr The compound decolourises both the reagentsThe compound does notdecolourise the two reagents(OR)The colour of one reagent isdischarged and the colour of theother is notUnsaturatedSaturatedSaturated Dr. S. Paul Douglas , Dept. of Engineering Chemistry, A. U. College of Engg. Andhra University 2 5. Lassaigne’s Test for Extra Elements: (Nitrogen and Halogens) A small piece of Sodium metal (Freshly cut) is placed in an ignition tube and the tube is heatedstrongly. Small quantity of the compound (one or two crystals if solid or one or two drops if liquid) isadded and the tube heated strongly. The red hot tube is plunged into 10.0ml of distilled water contained in a mortar and is crushed with pestle and the solution filtered. The filterate is calledSodium Fusion Extract. S. No. Experiment Observation Inferencea) Test for Nitrogen: (in theform of NaCN in the Extract)To small quantity of the extractfew crystals of Mohr’s salt areadded and boiled. To thissolution dil H 2 SO 4 is added toget clear solutionIf the colour of the solution after adding dil H 2 SO 4 is intense blue(Prussian Blue) Nitrogen Present Na+C+N ® NaCN6NaCN + FeSO 4 ® Na 4 [Fe(CN) 6 ] + Na 2 SO 4 Na 4 [Fe(CN) 6 ]+ 2Fe 2 (SO4) 3 ® Fe 4 [Fe(CN) 6 ] 3 + 6Na 2 SO 4 (Prussian Blue Clour) b) Test for Halogens: TheSodium Fusion Extract isacidified with dil HNO 3 , boiled,cooled and AgNO 3 solution isaddeda)White Precipitate soluble in NH 4 OH b) Cream coloured Precipitate ,sparing soluble in NH 4 OHc) Yellow Precipitate insolublein NH 4 OHChlorine PresentBromine PresentIodine Present Na+Cl/Br/I ® NaCl/NaBr/NaI NaX + AgNO 3 ® AgX (ppt) + NaNO 3 c) Test for Sulphur: Theextract is acidified with aceticacid and Pb(CH 3 COO) 2 solutionBlack precipitate of PbS isobtainedSulphur is Present 2Na+S ® Na 2 S Pb(CH 3 COO) 2 + Na 2 S ® PbS + 2 CH 3 COONa (ALL THE ABOVE TEST ARE COMPULSORY FOR ANY GIVEN COMPOUND) (Brown) C C OHOH + KMnO4C C (Purple) + MnO2C C+ B r 2 (Brown)(Clear) CBr Br C(Glycol)(Vicinal Dibromide) Dr. S. Paul Douglas , Dept. of Engineering Chemistry, A. U. College of Engg. Andhra University 3 Tests for Functional Group IdentificationS. No. Experiment Observation Inference1Carboxylic Acids: (Acidic, Soluble in NaHCO 3 and NaOH)Add 1 ml of saturated NaHCO 3 solution to one drop of liquid or small amount of solidCO 2 gas is evolvedCarboxylic acid group presentone drop of liquid or smallamount of solid is dissolved in5ml of ethyl alcohol and 2dropsof conc. H 2 SO 4 are added andthe mixture is poured in to 25mlof dil Na 2 CO 3 and stirred wellFruity Odour is observed(due to the formation of esterswhich are sweet smelling)Carboxylic acid group is present(Carboxylic Acids do not have any characteristic tests other than its solubility in NaHCO 3 witheffervescence and NaOH. To know whether the acid is simple acid or phenolic acid test with FeCl 3 ) 2Phenols: (Acidic, Insoluble in NaHCO 3 but soluble in NaOH)a) Test with FeCl 3 The compound is dissolved in1ml of alcohol or suspended inwater and one or two drops of dilute FeCl 3 addedA prominent Colour changeother than the yellow colour of FeCl 3 obtained(Usually blue or violet – somecases red or green)Phenolic hydroxyl group present b) Liebermann’s Nitroso Test Compound is added few crystalsof NaNO 2 , warmed verygently for 20 seconds andallowed to cool and twice thevolume of Conc. H 2 SO 4 addedand rotate the test tube slowly tomixA deep blue or deep greencolouration developed slowlyDilute the contents cautiouslywith water The solution turns red Now add an excess of NaOHSolutionThe green or blue colourationreappearsPhenolic hydroxyl group present(Note: Only some Phenols givethis test as mentioned above) (Note: Phenols where Para Position is vacant only will give Liberman’s Niroso Test)3 Alcohols:a) Ceric ammonium nitratetest: To the aqueous solution of the compound. Add few dropsof ceric ammonium nitrateRed colour observedAlcoholic hydroxyl group present b) Xanthate test: to theaqueous solution add pellets of KOH, heat, cool and then add1.0ml of ether followed by 2-3drops of CS 2 Yellow precipitate formed Alcoholic group present c) Distinction between 1 0 , 2 0 and 3 0 alcohols: To 2 ml of thecompound 8ml of Lucas reagentadded and shake Non insoluble layer separates atonceCloudiness appears after 4-5minutesSolution remains clear 1 0 Alcohol2 0 Alcohol3 0 Alcohol Dr. S. Paul Douglas , Dept. of Engineering Chemistry, A. U. College of Engg. Andhra University 4 S. No. Experiment Observation Inference4 Carbohydrates: (Soluble in Water, Neutral, Aliphatic and Non-Nitrogenous)a) Molisch’s Test: The compound is dissolved inwater and 2-3 drops of 1%alcoholic solution of a -naphtholand then carefully pour 2 ml of conc. H 2 SO 4 down the side of the test tube so that it forms aheavy layer at the bottomA deep violet coloration is produced where the two liquidsmeetCarbohydrate present b) Action of H 2 SO 4 : Thecompound is warmed with 1 mlof Conc. H 2 SO 4 on a smallflameThe compound immediately blackens. As the temperatureraises, CO 2 , CO and SO 2 areevolvedCarbohydrate presentc) To a small amount of thecompound, Fehling’s Reagent isadded and heated on a water bathRed precipitate of CuO 2 isobtainedReducing sugar 5 Carbonyl Compounds: (Neutral Compounds) a) Test with Borsch’s Reagent: Few drops of the compound isdissolved in methanol and a fewdrops of 2,4-dinitrophenylhydrazine reagent are added(gently heat and cool if necessary)Yellow or Orange colouredPrecipitate is formedMay be aldehyde or ketone R OHorR'+H 2 NHNO 2 N NO 2 R HorR' NHNO 2 N NO 2 b) Tollen’s Test: In a clean test tube 2-3 ml of AgNO 3 solution is taken and 2-3drops of NaOH soln. added. Tothis dil. Ammonia added drop by drop until the precipitatedsilver oxide is almostredissolved, then few drops of the compound added themixture is gently warmed on awater bath with vigorousshaking from time to timeA silver mirror is formed Aldehyde group present
