Topic Qualitative Analysis of Organic Compounds (Chart) Compiled by Dr. Parixit Bhandurge Department Pharmaceutical Chemistry KLE College of Pharmacy, Belagavi. Constituent Unit of KLE Academy of Higher Education and Research.. e-mail:: [email protected] Website:: http://www.klepharm.edu/ Phone:: 0831-2471399 Fax:: 0831-2472777 JNMC Campus,, Beside KLE’’s Dr.. Prabhakar Kore Charitable Hospital and Research Centre,, Nehru nagar,, Belagavi – 590010.. KLE College of Pharmacy, Belagavi. Identification of Unknown Organic Compound The analysis and identification of unknown organic compounds constitutes a very important aspect of experimental organic chemistry. Often, a common first step in the identification of an unknown substance is to determine what elements are present in the sample. Although it is often possible to establish the structure of a compound on the basis of spectra alone (IR, NMR, etc.), the spectra typically must be supplemented with other information about the compound: physical state and properties (melting point, boiling point, solubility, odour, colour, etc.), elemental analysis, and confirmatory tests for functional groups. In this experiment you will carry out several qualitative tests that will allow you to identify functional groups in organic molecules. You will then apply what you have learned by characterizing unknown organic compounds in terms of their functional group and solubility behavior. There is no definite set procedure that can be generally applied to organic qualitative analysis. Various books have different approaches, but a systematic approach based on the scheme given below will give good results. Each functional group has a particular set of chemical properties that allow it to be identified. Some of these properties can be demonstrated by observing solubility behavior, while others can be seen in chemical reactions that are accompanied by color changes, precipitate formation, or other visible effects. In carrying out identification of an organic compound following tests and observations are carried out: I. Preliminary Tests and Physical Examination II. Determination of Physical Constants (M.P/B.P) III. Detection of Elements IV. Determination of Solubility Group V. Detection of Functional Group VI. Special Tests, if any. Test Observation Inference I. Preliminary Test and Physical Examination A State i) Solid Generally high molecular weight, usually having more than 6 carbon atom chain. Eg: Acids, Sugars, Amides, etc. ii) Liquid Generally low molecular weight,. Eg: Alcohols, Ethers, Esters, Aliphatic amines, Aldehydes, Ketones, Hydrocarbons, etc. B Colour Pale Yellow Nitro Compounds s.a. nitrobenzene, dinitrobenzene, nitrophenol, Quinones, Iodoform Yellow Orange Nitro-aniline Pink -Naphthol, -Naphthol, resorcinol, Red Azo compounds, methyl orange Green Nitroso compounds Greenish Yellow o/m-nitrobenzaldehyde Brown-dark Phenols, Amines, (darken due to oxidation) Colourless Compounds not containing strong Chromophore. Eg: Acids, Hydrocarbons, ketones, esters, urea, thiourea, acetamide, acetanilide, benzamide, naphalene, etc C Odour Pleasant Alcohols (low mol. Wt.), Aromatic hydrocarbons, ethers, alkyl halides s.a. chloroform, chlorobenzene. Deep Sweet Chloroform Fruity Esters Phenolic / Carbolic Phenols and cresols Fishy Aromatic amines Kerosene Hydrocarbons Moth Ball Naphthalene Bitter Almond Benzaldehyde, nitrobenzene Pungent/Irritating Aliphatic acids, Acid chlorides, formaldehyde, and side chain halo hydrocarbons CAUTION: Do not taste an unknown compound. To note the odour, cautiously smell the cap of the container and do it only once. Never smell the contents of the container directly. 2. Ignition Test Flame Test: Non-sooty Flame Aliphatic compounds Take a small quantity of compound Sooty Flame Aromatic compounds and put it on a metallic spatula or in a Ammonical odour Urea, thiourea, amides may be present porcelain dish and ignite it directly on the Chars and swells without Sulphur containing compounds melting Melts and chars with a smell of Carbohydrates may be present burnt sugar Produces coughing upon Benzoic acid, salicylic acid etc may be charring present Chars without melting Sulphanilic acid, starch, uric acid may be present Beilstein’s Test: Burns with green flame Urea, Chlorides, Bromides may be Make one end of a copper wire in the present form of a loop and heat it on a burner till flame is no longer coloured. Cool Burns without green flame Flourides may be present the wire and dip the loop in little of the sample and ignite the loop again in flame. 3. Test for Unsaturation a. Action of KMnO4(Baeyers test): Decolourization of KMnO4 Unsaturated compounds may be Sub (solid/Liquid) + Sodium present carbonate solution + few drops of No Decolourization of KMnO4 Saturated compounds may be present 2% KMnO4 solution – Shake vigorously b. Action of Bromine Water (for Decolourization Unsaturated compounds may be freely or sparingly water soluble present compounds): No Decolourization Saturated compounds may be present Sub (solid/Liquid) + Bromine water dropwise – Shake vigorously c. Action of Bromine Water (for Decolourization Unsaturated compounds may be water insoluble compounds): present Sub (solid/Liquid) + 2ml CCl4 or CHCL3 solution dropwise with shaking No Decolourization Saturated compounds may be present + Bromine in CCl4 dropwise – Shake vigorously. 4. Lassaigne’s Test (Elemental Analysis) Place about a pea size of freshly cut sodium metal into a sodium fusion tube and heat the tube gently to melt the sodium to a shining globule. Add a small quantity of the sample (solid/liquid) into the fusion tube. Heat the tube carefully at first and then as strongly as possible until the bottom of the tube is glowing red, holding the tube at this heat for about 2 min. Quickly plunge the hot tube in a china dish containing about 8 ml of distilled water and cover the china dish immediately with a wire gauge. The tube crumbles into pieces and the mass comes out and dissolves in water. Boil the contents of the china dish thoroughly, filter the contents and collect the filtrate (which is also called Stock solution) in a test tube. Divide the filtrate into 3-4 portions and test each portion for the elements separately. Test Observation Inference 1. Test for Nitrogen: a. Prussian Blue test Green or Blue colour Nitrogen present Stock solution + FeSO solution – boil 4 No Green or Blue colour Nitrogen absent and cool. Add conc. H2SO4 2. Test for Sulphur: a. Sodium nitroprusside test Pink colour Sulphur present Stock solution + Sodium nitroprusside No Pink colour Sulphur absent b. Lead acetate Test Black Ppt Sulphur present Stock solution + Acetic Acid + 2 ml No Black Ppt Sulphur absent Lead acetate (5%) 3. Test for Halogens: a. Silver Nitrate test White ppt, which freely Chlorine present Stock solution + dil. HNO3 – heat, boil dissolves in 2 ml of ammonia and reduce to half the volume + a few solution drops of silver nitrate solution. Pale yellow ppt, which is Bromine present difficult to dissolve in 2 ml of ammonia solution Yellow ppt, which is insoluble Iodine present in 2 ml of ammonia solution No Ppt Halogens absent Test for Nitrogen: 6 NaCN + FeSO4 Na4[Fe(CN)6] + Na2SO4 Sodium cyanide Sod. Ferrocyanide FeSO4 2Fe2(SO4)3 Na4[Fe(CN)6] + 2Fe2(SO4)3 Fe4[Fe(CN)6] + Na2SO4dil. H Ferricferrocyanide (Persian Blue) Test for Sulphur: Na2S + Na2[Fe(CN)5NO] Na4[Fe(CN)5NOS] + 2NaOH Sod. nitroprusside Sod. Ferric sulphocyanide (purple-violet colour) Na2S + Pb(CH3COO)2 PbS + 2CH3COOH Lead sulphide Test for Halogens: Dil. HNO3 AgNO3 + NaCl AgCl(s) + NaNO3 White ppt 2NH4OH + - [Ag(NH3)2] Cl + 2H2O Freely water soluble 5. Solubility test: a. Sub + Water Soluble Group I or II present Sub + Ether Soluble Group I or II present Low molecular weight compounds like acids, esters or resorcinol etc. present Insoluble Group II present Sugars, amides (urea) present b. Sub + Dil HCl Soluble Group III present 10, 20 or 30 Amine present c. Sub + Dil NaOH Soluble Group IV present Acids, Phenols or phenolic acids present If Nitrogen is Absent d. Sub + Conc. H2SO4 (In a dry test Soluble Group V present tube) Insoluble Group VI present If Nitrogen is Absent If all the solubility tests failed and the compound contains Nitrogen, then it belongs to Group VII V Solubility Test: Substance (Solid/Liquid) + Solvent (Water (ether) : dil. HCl : dil. NaOH (NaHCO3) : Conc. H2SO4) Don’t change the above order of solubility test. If the substance is soluble in earlier groups do not proceed further. If N is absent If N is present Soluble in water In Conc. H2SO4 (Use dry test tube) Soluble in dil. HCl Soluble in dil. NaOH Soluble/Chemical Indifferent Soluble in Ether changes like heat or Insoluble in Ether Insoluble (Use dry test tube) colour development, ppt etc. Group IV Group I Group II Group III Group V Group VI Group VII Sub + Sodium bicarbonate soln Resorcinol Sugars 10 Amines Soluble Insoluble Aldehydes Hydrocarbons Amides (solid) Acids Phenols Benzaldehyde (special phenol) Glucose (solid) Aniline (liquid) Toluene (liquid) Benzamide (solid) (liquid) Salicylic acid o, m & p – Cresols Naphthalene (solid) Alcohols Ortho and meta Diphenyl(solid) Anilides Benzoic acid (all liquids) Ketones toluidine Aldehydes (both solids) Ketones and Acids (both liquids) Acetophenone Halogen Acetanilide (solid) of Low molecular Urea (solid) (liquid) hydrocarbons Benzanilide (solid) weight (special amide) Para toluidine (solid) Benzophenone Chlorobenzene Nitro Compounds Acetamide (solid) (solid) Bromobenzene 20 Amines Benzylchloride Nitrobenzene