NCERT

1 To identify the functional groups present in an organic compound. Organic compounds containing > C = C < and / or C C bonds are calledunsaturated compounds. These compounds undergo addition reaction withbromine water or the solution of bromine in carbon tetrachloride, chloroform orglacial acetic acid. Addition of bromine to an alkene results in the formation ofvicinal dibromide. The reddish orange colour of the solution of bromine in carbontetrachloride disappears on reaction with an alkene. The reaction is as follows :Alkenes decolourise the neutral/alkaline KMnO4 solution and vicinal glycolsare formed (Bayer s test).

2 Reaction takes place as follows :Both the above reactions are used as tests for Test tubes:Two Test tube holder:One Potassium hydroxidesolution:1 2 mL Carbon tetrachloride/chloroform:2 mL Bromine water/solutionof bromine in CCl4 orchloroform:2 mL Potassium permanganatesolution:As per need Compound to be tested:As per need water testDissolve g or 5 drops of organic compound in 2 mL of carbontetrachloride in a test tube and add 2% solution of bromine incarbon tetrachloride or bromine water drop by drop withcontinuous shaking.

3 Decolourization of bromine solution indicatesthe presence of unsaturation in organic s testDissolve 25-30 mg of organic compound in 2 mL of water oracetone (free of alcohol) and add 1% potassium permanganatesolution containing equal volume of 1% sodium carbonatesolution. The discharge of the colour of more than one drop ofpotassium permanganate indicates the presence of unsaturationin the organic compound. Carrying out the reaction under alkalineconditions removes the possibility of confusion due to substitutionin aromatic :(i)Unsaturation in an organic compound is confirmed only whenboth of the above tests are positive.

4 (ii)In place of CCl4 any other solvent such as CHCl3/dioxan andeven water can be used to dissolve the organic compound forcarrying out the reaction. (a)The tests should be performed at room temperature.(b)Handle bromine solution carefully. Do not inhale the vapours and also avoid itscontact with the Alcoholic compounds on reaction with ceric ammonium nitrategive a red colouration due to the formation of a complex.(NH4)2 [Ce(NO3)6] + 3 ROH [Ce(NO3)4(ROH)3] + 2NH4NO3 Ceric ammonium Red complex nitrateDistinction between primary, secondary and tertiary alcoholscan be done on the basis of iodoform test and Lucas and secondary alcohols which contain CH3 CH(OH)Rgroup (iodoform reaction) give positive iodoform test.

5 To carry outreaction, potassium iodide and sodium hypochlorite solution areadded to the compound in the presence of sodium hydroxidesolution. Probably sodium hypochlorite first oxidses potassiumiodide into potassium hypoiodite, which oxidises CH3 CH(OH)Rgroup to CH3 COR group and then iodinates it in the alkalinemedium of the reaction mixture by replacing the -hydrogenattached to the carbon atom adjacent to carbonyl group by is formed after cleavage of C C Potassium hypoioditehypoioditeNaOHCHCHOHCHCHOCICHO CHI + HCOONa Lucas TestLucas reagent contains zinc chloride and concentratedhydrochloric acid.

6 This reagent reacts with primary, secondaryand tertiary alcohols at different rates. Tertiary alcohols reactalmost instantaneously, secondary alcohols react in about 1-5minutes and primary alcohols react very slowly. The reaction maytake 10 minutes to several +HClNo reaction/Slow reaction 222 ZnCl2 RCHOH+HClRCHCl+HO 332 ZnCl2 RCOH+HClRCCl+HO Alcohols are soluble in Lucas reagent but the formed alkylhalides are not soluble. Therefore, formation of two layers in thereaction medium indicate the occurrence of the alcohols Layers do not separateSecondary alcohols Layers separate within 1-5 minutesTertiary alcohols Layers separate immediately24-04-2018 *Potassium iodide-iodine reagent is prepared by dissolving 20 g of potassiumiodide and 10 g of iodine in 100 mL of water.

7 Ceric ammoniumnitrate solution:As per need Sodium hydroxide:As per need Iodine solution:As per need Lucas reagent:As per need Dioxan:As per need Test tube holder:One Test tubes:As per need ammonium nitrate testTake 1 mL solution of organic compound dissolved in a suitablesolvent. Add a few drops of ceric ammonium nitrate of red colour shows the presence of alcoholic OH :The red colour disappears after keeping the reaction mixture forsometime. The colour also disappears if excess of cericammonium nitrate solution is added.

8 Therefore, use of excessof ceric ammonium nitrate solution should be testFirst methodTake mL of the compound in a test tube, add 10 mL of 10%aqueous KI solution and 10 mL of freshly prepared NaOCl gently; yellow crystals of iodoform methodDissolve g or 4 to 5 drops of compound in 2 mL of water. If itdoes not dissolve, add dioxane drop by drop to get a homogeneoussolution. Add 2 mL of 5% sodium hydroxide solution followed bypotassium iodide-iodine reagent* dropwise with continuousshaking till a definite dark colour of iodine persists.

9 Allow thereactants to remain at room temperature for 2-3 minutes. If noiodoform separates, warm the reaction mixture in a water bath at60 C. Add more drops of potassium iodide iodine reagent. If colourof iodine disappears continue addition of reagent till the colour ofiodine persists even after two minutes of heating at 60 C. Removeexcess iodine by adding a few drops of sodium hydroxide solutionwith shaking. Dilute the mixture with equal volume of water andkeep it at room temperature for 10-15 minutes. A yellow precipitateof iodoform is obtained if test is C.

10 Lucas testTake 1 mL of compound in a test tube. Add 10 mL of Lucas well and note the time for the separation of two distinct : Lucas test is applicable to only those alcohols which are solublein the reagent because the test is based on separation of alkylhalides as separate layer. The OH group attached directly to the ring carbon of an aromaticring is called phenolic OH group. Phenols are weakly acidic,therefore they are soluble in NaOH solution but at the same timethey are not sufficiently acidic to be soluble is sodiumhydrogencarbonate solution.