Organic Chemistry Tests and Procedures PDF

## **Organic chemistry** ### **Introduction** * **Fehling's reagent:** Initially blue, Fehling's reagent precipitates a brick-red deposit when heated in the presence of aldehydes. This reaction is used to identify the presence of aldehydes, as they are the only compounds that exhibit this property...

## **Organic chemistry** ### **Introduction** * **Fehling's reagent:** Initially blue, Fehling's reagent precipitates a brick-red deposit when heated in the presence of aldehydes. This reaction is used to identify the presence of aldehydes, as they are the only compounds that exhibit this property (e.g., sugars). ### **Tests** #### **1. Tollens' Silver Mirror Test** * **Purpose:** To detect the presence of aldehydes. * **Reagent:** Tollens' reagent, a complex of silver nitrate in an ammoniacal solution ([Ag(NH₃)₂]NO₃). * **Reaction:** Tollens' reagent oxidizes aldehydes to carboxylic acids, resulting in a reduction of silver ions to silver. * **Chemical Equation:** * RCHO + 3HO + 2Ag(NH₃)₂⁺→ RCOO^- + 2H₂O + 2Ag(s) + 4NH₃ * **Half-reactions:** * Ag(NH₃)₂⁺ + e^- → Ag(s) + 2NH₃(aq) * RCHO(aq) + 3HO(aq) → RCOO(aq) + 2H₂O(l) + 2e^- * **Result:** A fine silver mirror forms over the wall of the clean test tube, indicating a positive test. - Aldehydes give a positive result (formation of a silver mirror). - Ketones give a negative result (no mirror formation). #### **2. Lucas' Test** * **Purpose:** To differentiate between primary, secondary, and tertiary alcohols. * **Reagent:** Lucas' reagent: A mixture of concentrated hydrochloric acid (HCl) and zinc chloride (ZnCl₂). * **Reaction:** Lucas' reagent reacts with alcohols to form alkyl chlorides. * **Result:** - **Tertiary alcohols:** The reaction occurs immediately, resulting in a cloudy suspension. - **Secondary alcohols:** The reaction takes about 10 minutes, leading to a cloudy suspension. - **Primary alcohols:** The reaction takes hours or even days to occur, and no obvious cloudiness is formed. #### **3. Jones’ Test** * **Purpose:** To differentiate between primary, secondary, and tertiary alcohols. * **Reagent:** Jones' reagent: A solution of chromic acid (CrO₃) in sulfuric acid (H₂SO₄) and acetone. * **Result:** - **Primary and secondary alcohols:** A blue-green color appears in less than 5 minutes. - **Tertiary alcohols:** The solution remains orange. #### **4. Acidic Carboxylic Acid Test** * **Purpose:** To detect the presence of carboxylic acids. * **Reagent:** Sodium bicarbonate (NaHCO₃). * **Reaction:** Carboxylic acids react with sodium bicarbonate to form a carboxylate ion, water, and carbon dioxide gas. * RCOOH +NaHCO₃ → RCOO^-Na⁺ + H₂CO₃ → H₂O + CO₂(g) * **Result:** Effervescence (the release of carbon dioxide bubbles) indicates a positive test. #### **5. Potassium Permanganate Test** * **Purpose:** To detect the presence of alkenes. * **Reagent:** Diluted potassium permanganate (KMnO₄) in a basic solution. * **Reaction:** Potassium permanganate reacts with alkenes to form vicinal diols. * 3 C=C + 2KMnO₄ + 4H₂O → 3 C-C-C + 2MnO₂ + 2KOH * **Result:** The purple solution of permanganate turns brown-black due to the formation of manganese dioxide (MnO₂). This color change indicates a positive test for the presence of alkenes. #### **6. Amides and Nitriles Test** * **Purpose:** To distinguish amides and nitriles from other functional groups. * **Reagent:** Sodium hydroxide (NaOH). * **Reaction:** Amides and nitriles react with sodium hydroxide to form amines. * **Result:** A positive test is indicated by a basic pH. #### **7. Halogenated Alkyl Test** * **Purpose:** To identify halogenated alkyl compounds. * **Reagent:** Silver nitrate (AgNO₃) in alcoholic solution. * **Reaction:** Halides react with silver nitrate to form a precipitate of silver halide. * **Result:** A precipitate of silver halide (chloride, bromide, or iodide), indicates a positive test. ### **Experimental Part** #### **Procedure** **A. 2,4-Dinitrophenylhydrazine Test** 1. Add 1 mL of 2,4-dinitrophenylhydrazine (DNPH) reagent (yellow solution) to a test tube. 2. Add a few drops of the unknown organic compound. 3. Shake vigorously and observe. **B. Fehling's Test** 1. In a test tube, mix 1 mL of Fehling's solution A and 1 mL of Fehling's solution B. 2. Add 1 mL of the unknown organic compound. 3. Heat gently in a water bath while shaking. 4. Observe any color changes. **C. Lucas' Test** 1. Add 2 ml of Lucas reagent to a clean and dry test tube. 2. Add 5 drops of the unknown organic compound. 3. Shake vigorously and observe. **D. Acidic Carboxylic Acid Test** 1. Add 1 ml of water to a test tube. 2. Add a small amount of sodium bicarbonate (NaHCO₃). 3. Add 10 drops of the unknown organic compound. 4. Observe any bubbling. **E. Potassium Permanganate Test** 1. Add a few drops of potassium permanganate (KMnO₄) in a basic solution to a test tube. 2. Add a few drops of the unknown organic compound. 3. Observe if the purple color of the permanganate solution turns brown-black. **F. Silver Nitrate Test** 1. Add a few drops of silver nitrate (AgNO₃) in an alcoholic solution to a test tube. 2. Add a few drops of the unknown organic compound. 3. Observe if a precipitate forms.