Identification of Organic Compounds PDF

**SECTION III:** **IDENTIFICATION OF ORGANIC COMPOUNDS** **INTRODUCTION:** The compound which contains carbon and hydrogen or their derivatives, chiefly those in which the carbon is covalently bonded to carbon, hydrogen, halogen, oxygen, nitrogen and/or sulfur is called organic compound. **Diffe...

**SECTION III:** **IDENTIFICATION OF ORGANIC COMPOUNDS** **INTRODUCTION:** The compound which contains carbon and hydrogen or their derivatives, chiefly those in which the carbon is covalently bonded to carbon, hydrogen, halogen, oxygen, nitrogen and/or sulfur is called organic compound. **Difference between organic and inorganic compounds:** **Organic compounds** **Inorganic compounds** ----------------------- ------------------------------------------------------------------------------------------------------------------------------------------------ ----------------------------------------------------------------------------------- **Definition** Hydrocarbon's derivatives Element's derivative **Source** Usually living, sometimes non-living Non-living **Composition** Restricted to only few elements other than carbon and hydrogen e.g. oxygen, sulfur, nitrogen, halogens and metals (magnesium, iron, zinc) etc. May contain any of the known elements (Na, B, Rb, Pt, Pb etc.) **Solubility** Miscible with non-polar solvents Miscible with water **Chemical bonding** Covalent Ionic **Melting point** Low High **Boiling point** Low High **Catenation** +ive -ive **Isomerism** +ive -ive **Stability** Decompose on heating Do not decompose on heating **Flammability** +ive -ive **Conductibility** Non-electrolyte Electrolyte **Rate of reactions** Slow Fast **Examples** Urea, Acetaminophen, acetanilide, glucose, cinnamic acid Sodium chloride, potassium hydroxide, hydrochloric acid, water, hydrogen peroxide **Systematic procedure for the identification of organic compounds:** **Step 1: Preliminary investigation of the compounds (physical tests):** **Physical state:** This section is useful in consulting the tables of compounds which are subdivided on this basis. A crystalline solid usually consists of a large number of small crystals, each of them having a definite characteristic geometrical shape. Amorphous means shapeless. An amorphous solid has irregular arrangement of solid particles. **Color:** Many organic compounds (solids and liquids) possess a definite color due to the presence of chromophoric group in the molecule. However, sometimes the color of the organic compound may be due to the impurities (formed as a result of slow oxidation of the compound by oxygen in air). The information regarding color is useful in excluding some classes of the organic compounds. **Class of organic compounds** **Color** ---------------------------------------------------------------------------------------- ---------------------------------------------------------------------------- Nitro compounds/quinone Orange yellow Iodoform, iodine containing compounds Yellow Azo compounds Orange/red Anthracene Greenish Hydrocarbons, alcohols, ethers, aldehydes, ketones, acids, phenols and aromatic amines Colorless, however aromatic amines and phenols on exposure become colored. **Odor:** Many organic compounds possess a characteristic odor. The information regarding odor is useful in excluding some classes of the organic compounds. **Class of organic compounds** **Odor** ----------------------------------------- -------------------- Esters, alcohols, aromatic hydrocarbons Pleasant Amines Fishy Benzaldehyde and nitrobenzene Bitter almond like Phenols and salicylaldehyde Phenolic **Solubility in polar and non-polar solvents:** Like dissolves in like phenomenon. Polar organic compound dissolve in polar solvents and non-polar dissolve in non-polar. **Ignition test:** Aromatic and higher aliphatic compound produce smoky flame while aliphatics do not. **Step 2: Preparation of Lassaigne's solution (sodium fusion extract) and detection of elements in the given organic compound** **THEORY** Lassaigne's solution is the aqueous solution containing sodium salts of nitrogen, sulphur or halogens (cyanide, sulphide or halides, respectively) which were previously the constituent elements of organic compound. [Why Lassaigne's solution is used?] Organic compounds are non-polar and do not ionize. To determine the composition of an organic compound, it is essential to convert it to an ionizable form. Lassaigne's solution is used for detecting the presence of nitrogen, sulphur and halogens in the organic compounds. [Why sodium is used for fusion in Lassaigne's test? Can other elements e.g. potassium, calcium or magnesium be used in place of sodium for the same purpose?] Sodium is a soft metal which easily fuses with organic compound. Other elements may also be used in place of sodium, however, potassium is too reactive to handle and calcium and magnesium are much less reactive. [If the organic compound to be fused with sodium metal is volatile, what must be done to ensure, it is not lost?] The fusion tube containing organic compound and the metal must be covered with 0.5g of glucose. **CHEMICALS:** +-----------------------------------+-----------------------------------+ | - Sodium metal | - Organic compound | +===================================+===================================+ | - Ferrous sulphate | - Ferric chloride | +-----------------------------------+-----------------------------------+ | - Hydrochloric acid | - Ammonium sulphide | +-----------------------------------+-----------------------------------+ | - Sodium nitroprusside | - Lead acetate | +-----------------------------------+-----------------------------------+ | - Acetic acid | - Nitric acid | +-----------------------------------+-----------------------------------+ | - Silver nitrate | - Ammonium hydroxide | +-----------------------------------+-----------------------------------+ | - Carbon tetra chloride | - Chloroform | +-----------------------------------+-----------------------------------+ | - Carbon disulfide | - Chlorine water | +-----------------------------------+-----------------------------------+ **SOLVENTS:** Double distilled water **GLASSWARE AND OTHER SUPPLIES:** +-----------------------------------+-----------------------------------+ | - Spatula | - Tong | +===================================+===================================+ | - Fusion tube | - Bunsen burner | +-----------------------------------+-----------------------------------+ | - China dish | - Wire gauze | +-----------------------------------+-----------------------------------+ | - Tripod stand | - Filter papers | +-----------------------------------+-----------------------------------+ | - Funnel | - Beaker | +-----------------------------------+-----------------------------------+ | - Test tubes | - Test tube stand | +-----------------------------------+-----------------------------------+ | - Glass pipette | | +-----------------------------------+-----------------------------------+ **APPARATUS:** - Weighing balance - Water bath **EXPERIMENTAL:** **[Step 2.1: Preparation of Lassaigne's solution:]** 1. Take a small piece of dry sodium in a fusion tube and heat it until melting to a shining globule. 2. Add a pinch of the organic compound in the fusion tube and heat it slowly so that the compound fuses with sodium metal. 3. Now heat the tube strongly till it becomes red hot. 4. Plunge the red hot tube into a china dish containing 30mL of distilled water. 5. Crush the fusion tube with a glass rod and allow the contents to ooze out. 6. Heat the solution to boiling point, cool and remove the insoluble matter by filtration. 7. The clear filtrate is called "Lassaigne\'s solution/extract". **Mechanism:** During fusion, sodium forms water soluble salts of the elements in the organic compound i.e. sodium cyanide with the nitrogen, sodium sulphide with the sulphur and sodium halide with the halogen. If both N and S are present in the compound, sodium sulphocyanide is produced. **Na + C + N → NaCN** **2Na + S → Na~2~S** **Na + X → NaX** **Na + C + N + S → NaCNS** **Precautions:** 1. Use dry sodium metal 2. Fusion tube must be clean and dry since sodium reacts explosively with water and if water is present in the tube, it will inactivate the metal. 2Na + 2H~2~O → 2NaOH + H~2~ ~(gas)~ 3. Sodium fusion extract should be clear and colorless. If the filtrate is colored, discard it and repeat the procedure. 4. Carefully plunge the fusion tube in the china dish containing distilled water. **[Step 2.2: Qualitative test for the elements:]** 1. **Tests for nitrogen** **Ferrous sulphate test:** To 2mL of the Lassaigne's solution, add equal volume of freshly prepared saturated solution of ferrous sulphate and heat. Cool the mixture and add 2-3 drops of ferric chloride solution and acidify with conc. hydrochloric acid. Appearance of a Prussian blue color indicates the presence of nitrogen.  During this test, fresh solution of fresh solution of FeSO~4~ must be used. Otherwise, it is oxidized to ferric sulfate. HCl is added in this test in the end to convert ferrous hydroxide, a green precipitate to ferrous chloride, which is soluble in water. Otherwise the green precipitate may interfere with Prussian blue color. Fe(OH)~2~ + 2HCl \-\-\-\-\-\-\-\-\-\-\-\-\--\> FeCl~2~ + 2H~2~O 2. **Tests for sulphur** **Sodium nitroprusside test:** To 2mL of the Lassaigne\'s solution, add 2mL of freshly prepared sodium nitroprusside solution. Appearance of violet color indicates presence of sulphur. Detection of Elements in Organic Compounds - Learn CBSE **Lead acetate test:** Acidify 2mL of the Lassaigne\'s solution with a few drops of acetic acid and finally add a few drops of lead acetate solution. Appearance of black precipitates indicates the presence of sulphur.  3. **Tests for halogens** **Silver nitrate test:** To 2mL of the Lassaigne\'s solution, add 1 ml of conc. nitric acid and boil for some time to decompose cyanide or sulphide if present. Cool the contents and add silver nitrate solution. 1. A white precipitate soluble in ammonium hydroxide indicate presence of chlorine https://c4.staticflickr.com/9/8781/28349886891\_00d9840be1.jpg 2. Pale yellow precipitate sparingly soluble in ammonium hydroxide indicate presence of bromine  3. Yellow precipitate insoluble in ammonium hydroxide indicate presence of iodine https://c4.staticflickr.com/9/8781/28428588995\_9c14d31959.jpg It is not possible to detect the presence of fluorine since the solubility of AgF is more and thus no precipitate is formed. If N or S are present in the compound, the formation of black ppts may interfere during this test. The function of adding concentrated HNO~3~ and boiling is to decompose any sodium cyanide or sodium sulphide present in the extract. Otherwise these compounds will interfere with the tests of halides since NaCN gives a white ppt. with silver nitrate while Na~2~S gives a black ppt.  **Layer test:** Acidify 2mL of the Lassaigne\'s solution with dil. HCl and add 2mL of carbon tetrachloride/chloroform/carbon disulphide. Now add freshly prepared chlorine water drop by drop and shake vigorously. - Violet coloration of the organic layer indicate presence of iodine - Yellow/brown coloration of the organic layer indicate presence of bromine Chlorine can displace bromine and iodine from their respective halides in solution. Bromine or iodine thus liberated can turn the carbon disulphide layer orange or violet. 4. **Test for nitrogen and sulfur:** To 2mL of the Lassaigne's solution, add equal volume of freshly prepared saturated solution of ferrous sulphate and heat. Cool the mixture and add 2-3 drops of ferric chloride solution and acidify with conc. hydrochloric acid. Appearance of a blood red color indicates the presence of nitrogen and sulfur.  **Step 3: Allocation of class** **INTRODUCTION:** Presence of different functional groups can be indicated by observation of their solubility in various liquids and pH. On the basis of pH, organic compounds may be; 1- Acidic 2- Basic 3- Neutral 4- Inert **Class** **Characteristics** **Example of functional group** ----------- ---------------------------------------------------------------------------- --------------------------------------------------------------------------------- Acidic These compounds, in solution form, change the blue litmus to red (pH \< 7) Carboxylic acid, phenol, Nitrophenol Basic These compounds, in solution form, change the red litmus to blue (pH \> 7) Amines Neutral Do not change the color of litmus Carbohydrates, alcohols, aldehydes, ketones, amides, Anilides, esters, thiourea Inert Only soluble in ether Naphthalene, Anthracene Dissolve the organic compound in various solvents starting from water and followed by methanol, ethanol, ethyl acetate, ether etc. Check the pH of the solution by pH meter or litmus paper. Now allocate the class by following the protocol as under; **CHEMICALS:** +-----------------------------------+-----------------------------------+ | - Organic compound | - Sodium hydroxide | +===================================+===================================+ | - Sodium bicarbonate | - Hydrochloric acid | +-----------------------------------+-----------------------------------+ | - Sulphuric acid | | +-----------------------------------+-----------------------------------+ **SOLVENTS:** Double distilled water, methanol, ethanol, ethyl acetate, ether **GLASSWARE AND OTHER SUPPLIES:** +-----------------------------------+-----------------------------------+ | - Glass test tubes | - Test tube stand | +===================================+===================================+ | - Litmus paper | - Dropper tube | +-----------------------------------+-----------------------------------+ | - Glass pipette | | +-----------------------------------+-----------------------------------+ **Step 4: Determination of functional group** **Preparation of stock solution:** Dissolve 5 g of organic compound in 50 ml of a suitable solvent (water/methanol/ethanol/acetone) and use it for following tests. +-----------------------+-----------------------+-----------------------+ | **Procedure** | **Observation** | **Inference** | +=======================+=======================+=======================+ | **Hydrocarbon | | | | skeleton** | | | +-----------------------+-----------------------+-----------------------+ | **Bromine test** | | | +-----------------------+-----------------------+-----------------------+ | Take 2ml of stock | Orange red color of | Unsaturation compound | | solution in a | bromine solution | | | test-tube, add a drop | disappeared | | | of bromine water and | | | | shake. | | | +-----------------------+-----------------------+-----------------------+ | **Bayer's test** | | | +-----------------------+-----------------------+-----------------------+ | Take 2ml of stock | Pinkish purple color | Unsaturation compound | | solution in a | of KMnO~4~ | | | test-tube, add 1-2 | disappeared | | | drops of alkaline | | | | solution of KMnO~4~ | | | | (1%) and shake the | | | | mixture. | | | +-----------------------+-----------------------+-----------------------+ | **Aromatic system** | | | +-----------------------+-----------------------+-----------------------+ | **Nitration** | | | +-----------------------+-----------------------+-----------------------+ | To 0.2g of the solid | Yellow precipitated | Compound is aromatic | | organic compound in a | formed | | | test tube, add 2ml | | | | conc. sulfuric acid | | | | and 2ml conc. nitric | | | | acid. Heat the test | | | | tube for 5 minutes | | | | and cool the contents | | | | to room temperature. | | | | Now, add 5ml | | | | distilled water. | | | +-----------------------+-----------------------+-----------------------+ | **Alcoholic group** | | | +-----------------------+-----------------------+-----------------------+ | **Ester test** | | | +-----------------------+-----------------------+-----------------------+ | Take 2ml of stock | Fruity smell | Alcoholic group is | | solution in a | | present | | test-tube, add 1 ml | | | | of glacial acetic | | | | acid and 2-3 drops of | | | | conc. sulphuric acid. | | | | Warm the mixture on a | | | | water bath for about | | | | 10 minutes. Pour it | | | | into 20ml of cold | | | | water taken in a | | | | beaker and smell. | | | +-----------------------+-----------------------+-----------------------+ | **Ceric ammonium | | | | nitrate test** | | | +-----------------------+-----------------------+-----------------------+ | Take 2ml of stock | Appearance of pink or | Alcoholic group is | | solution in a | red color | present | | test-tube, add a few | | | | drops of ceric | | | | ammonium nitrate | | | | reagent and shake | | | | well. | | | +-----------------------+-----------------------+-----------------------+ | **Iodoform test** | | | +-----------------------+-----------------------+-----------------------+ | Take 2ml of stock | Formation of yellow | Ethanol, | | solution in a | precipitate | acetaldehyde, | | test-tube, add 1ml of | | sec-methyl alcohol or | | 1% iodine solution. | | methyl | | Then, add dilute | | | | sodium hydroxide | | ketone is present | | solution drop wise | | | | until the brown color | | | | of iodine is | | | | discharged. Warm | | | | gently on a water | | | | bath. | | | +-----------------------+-----------------------+-----------------------+ | **Phenols** | | | +-----------------------+-----------------------+-----------------------+ | **Ferric chloride | | | | test** | | | +-----------------------+-----------------------+-----------------------+ | Take 1ml of neutral | Violet, blue or green | Phenol is present | | ferric chloride | coloration | | | solution in a clean | | | | test-tube and 1ml of | | | | stock solution. | | | +-----------------------+-----------------------+-----------------------+ | **Liebermann's test** | | | +-----------------------+-----------------------+-----------------------+ | Place 2-3 crystals of | Blue or green | Phenol is present | | sodium nitrite in a | appeared | | | clean dry test-tube | | | | and add 1ml of stock | | | | solution. Heat very | | | | gently for half a | | | | minute and allow it | | | | to cool. Then add | | | | about 1 ml of conc., | | | | sulphuric acid and | | | | shake the tube to mix | | | | the contents. A deep | | | | blue or deep green | | | | coloration develops. | | | | Add water carefully, | | | | the color turns red. | | | | Now add an excess of | | | | sodium hydroxide | | | | solution | | | +-----------------------+-----------------------+-----------------------+ | **Aldehydes and | | | | ketones** | | | +-----------------------+-----------------------+-----------------------+ | **2, 4-Dinitrophenyl | | | | hydrazine test** | | | +-----------------------+-----------------------+-----------------------+ | Take 1ml of the stock | Formation of yellow | Carbonyl group is | | solution in a clean | or orange crystals | present | | dry test-tube, add a | | | | few drops of 2, | | | | 4-dinitrophenyl | | | | hydrazine solution | | | | and cork the | | | | test-tube. Shake the | | | | mixture and allow it | | | | to stand for 5 | | | | minutes. | | | +-----------------------+-----------------------+-----------------------+ | **Sodium bisulphite | | | | test** | | | +-----------------------+-----------------------+-----------------------+ | Take 2ml of a | Formations of | Carbonyl group is | | saturated solution of | crystalline | present | | sodium bisulphite in | precipitate | | | a clean test-tube, | | | | and add 1ml stock | | | | solution. Cork the | | | | test- tube, shake and | | | | leave it for 15-20 | | | | minutes. | | | +-----------------------+-----------------------+-----------------------+ | **Fehling's test** | | | +-----------------------+-----------------------+-----------------------+ | Take 1ml each of | Appearance of red | Aldehyde is present | | Fehling's solution A | precipitates | | | and B in a test-tube. | | | | Add 1ml of stock | | | | solution of the given | | | | organic compound and | | | | warm the test-tube in | | | | hot water bath for | | | | 4-5 minutes. | | | +-----------------------+-----------------------+-----------------------+ | **Tollen's test** | | | +-----------------------+-----------------------+-----------------------+ | Take 1 mL of freshly | Formation of a layer | Aldehyde is present | | prepared (\~ 2 %) | of silver metal on | | | silver nitrate | the inner surface of | | | solution in a test | the test tube which | | | tube. Add 1-2 drops | shines like a mirror | | | of sodium hydroxide | | | | solution to it and | | | | shake, a dark brown | | | | precipitate of silver | | | | oxide appears. | | | | Dissolve the | | | | precipitate by adding | | | | ammonium hydroxide | | | | solution drop-wise. | | | | Now add 2ml of stock | | | | solution of the | | | | compound and heat the | | | | reaction in a water | | | | bath for | | | | | | | | 5 minutes. | | | +-----------------------+-----------------------+-----------------------+ | **Benedicts test** | | | +-----------------------+-----------------------+-----------------------+ | Add 2ml stock | Orange-red | Aldehyde is present | | solution of the | precipitate appeared | | | compound in a test | | | | tube containing 2ml | | | | Benedict's reagent. | | | | Place the test tube | | | | in boiling water bath | | | | for 5 minutes. | | | +-----------------------+-----------------------+-----------------------+ | **Sodium | | | | nitroprusside test** | | | +-----------------------+-----------------------+-----------------------+ | Dissolve a crystal of | Red coloration | Keto group is present | | sodium nitroprusside | | | | in 1ml of distilled | | | | water in a clean | | | | test-tube and then | | | | add | | | | | | | | 1ml stock solution of | | | | the given compound. | | | | Shake and add sodium | | | | hydroxide solution | | | | drop wise. | | | +-----------------------+-----------------------+-----------------------+ | **Carboxylic acid** | | | +-----------------------+-----------------------+-----------------------+ | **Sodium bicarbonate | | | | test** | | | +-----------------------+-----------------------+-----------------------+ | To 1ml of the stock | Brisk effervescence | Carboxylic group is | | solution in a | | present | | test-tube, add a | | | | pinch of sodium | | | | bicarbonate | | | +-----------------------+-----------------------+-----------------------+ | **Ester test** | | | +-----------------------+-----------------------+-----------------------+ | To 2ml stock | Fruity smell | Carboxylic group is | | solution, add 1ml of | | present | | ethanol and 1-2 drops | | | | of conc. H~2~SO~4~. | | | | Heat it on a water | | | | bath for 5 minutes | | | | and pour it in a | | | | beaker containing | | | | water. | | | +-----------------------+-----------------------+-----------------------+ | **Amino group** | | | +-----------------------+-----------------------+-----------------------+ | **Carbylamines test** | | | +-----------------------+-----------------------+-----------------------+ | Take 0.2 g of solid | Appearance of | Primary amine is | | potassium hydroxide | unpleasant odor | present | | in a clean dry | | | | test-tube and add 2ml | | | | of ethanol. Warm the | | | | test-tube until the | | | | pallets dissolve. To | | | | this, add a few drops | | | | of chloroform, 1ml of | | | | stock solution of the | | | | given compound and | | | | warm gently. | | | +-----------------------+-----------------------+-----------------------+ | **Azo-dye test** | | | +-----------------------+-----------------------+-----------------------+ | [Solution | Formation of a | Aromatic primary | | 1] | scarlet red dye | amine is present | | | | | | To 2ml of the stock | | | | solution of organic | | | | compound in a test | | | | tube, add 2ml dilute | | | | hydrochloric acid. | | | | Cool the content of | | | | the test tube in ice | | | | and add 2ml of 2.5% | | | | cold aqueous sodium | | | | nitrite solution. | | | | | | | | [Solution | | | | 2] | | | | | | | | In a test tube, | | | | dissolve 0.2 g of | | | | β-naphthol in dilute | | | | sodium hydroxide | | | | solution. | | | | | | | | Add solution 1 into | | | | the cold β-naphthol | | | | solution slowly with | | | | shaking. | | | +-----------------------+-----------------------+-----------------------+ | **Benzene sulphonyl | | | | chloride test** | | | +-----------------------+-----------------------+-----------------------+ | Take 2ml of the stock | Formation of a | Secondary or tertiary | | solution of organic | precipitate | amine is present | | compound in a clean | | | | test-tube, add 2ml of | 1. Dissolved in HCl | 1. Tertiary amine | | 25% NaOH, 2 ml of | | | | water and 1 ml of | 2. Do not dissolve | 2. Secondary amine | | benzene sulphonyl | | | | chloride. Shake the | Precipitated not | Primary amine is | | mixture for 10 | formed and upon | present | | minutes and then cool | addition of HCl, | | | under tap water | insoluble material is | | | | observed | | | Treat the | | | | precipitate, if any, | | | | with 2 ml of cone. | | | | HCl. | | | +-----------------------+-----------------------+-----------------------+ **Step 5: Determination of melting point** The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exists in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atm. **Manual observation of melting point** **Using melting point apparatus**  **Table: Melting point of important organic compounds** **Compound** **Melting point (°C)** ----------------------- ------------------------ Urea 133 Thiourea 182 Benzamide 127-130 Acetaminophen 169 Salicylic acid 158.6 Acetyl salicylic acid 135 Benzoic acid 122.3 Cinnamic acid 133 Ascorbic acid 190 Oxalic acid 189-191 Tartaric acid 171-174 Malic acid 130 Succinic acid 184 Citric acid 153 Adipic acid 152.1 Glucose 146 Fructose 103 Sucrose 186 Resorcinol 110 Gallic acid 260 **Step 6: Confirmatory tests** Based on compound shortlisted by performing abovementioned test