ORGANIC CHEM QUENCH RXN?? Help!! 3. Prelab Exercise Questions: (18 points) a. RE
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ORGANIC CHEM QUENCH RXN?? Help!!
3. Prelab Exercise Questions: (18 points) a. REACTION WORK-UP ANALYSIS: The Canizzaro reaction was discovered in 1853. is a disproportionation reaction that converts an aromatic aldehyde into equimolar quantities of an alcohol and a benzoate salt: Ci 2 KOH 2-chlorobenzyl alcohol 2-chlorobenzaldehyde Potassium 2-chlorobenzoate i. How would you QUENCH this reaction? Would you use acid or base? (HINT: look at the reagent over the arrow of the reaction and product 2) Explain, in words and by drawing out acid/base chemistry reactions, what the quench would accomplish. (3 points) ii. After the quench, the products must be isolated from the aqueous reaction mixture. Suppose diethyl ether is added to the quenched reaction mixture. Which layer is on the top and which layer is on the bottom (organic or aqueous)? Which species in the reaction mixture (consider 1, 2, and 3) will be present in the orcanic laver? (2 points)Explanation / Answer
i) The reaction mixture is QUENCHED by adding sufficient amount of water to the reaction mixture. The potassium 2-Chloro benzoate being salt will dissolve completely in water and go into aqueous phase, while 2-Chlorobenzyl alcohol will be immiscible with water. (There is no need to add add acid or base for quenching the reaction mixture.)
ii) After quenching the reaction mixture, if diethyl ether is added to the aqueous reaction mixture then we get two layers. The top layer is organic layer (because the density of diethyl ether is 0.7134 gm/cm3) and the bottom layer is aqueous layer. 2-Chlorobenzyl alcohol being soluble in diethyl ether will move into organic layer.
iii) After quench and addition of diethyl ether, the layers are separated. The organic layer is washed with 1% solution of sodium bicarbonate. Washing with NaHCO3 helps to remove any residual acid present in organic layer. Therefore, only 2-Chlorobenzyl alcohol is now present in organic layer, and the aqueous layer will contain sodium salt of 2-Chlorobenzoic acid.
iv) After extraction with 1% NaHCO3 solution, first the organic layer is washed with aq. saturated solution of NaCl to remove the water remaining in the organic layer. NaCl helps to remove water by absorbing it from organic layer. Then the organic layer is passed over anhydrous sodium sulfate to remove the traces of water remaining in the aqueous layer. So these two work up steps will ensure that the organic layer is completely free from moisture because the contamination of water in compound will interfere during its analysis.
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