Stanislao Cannizzaro was an Italian chemist. He made his first contribution to chemical research in 1851 when he, along with F.S. Cloez, a French chemist, prepared cyanimide using ammonia and cyanogen chloride in an ethereal solution. Later that year, he became a professor in physical chemistry in Alessandria. It is there where Cannizzaro discovered that aromatic aldehydes can be decomposed into a mixture of the corresponding acid and alcohol by using an alcoholic solution of potassium hydroxide. This is now known as the Cannizzaro Reaction. In 1860, Cannizzaro also contributed much on how to define molecule and atom in his course outline given out at the first international chemical congress. Purpose: The purpose of this lab is to successfully carry out a cannizzaro reaction using potassium hydroxide to convert 4-nitrobenzaldehyde into 4-nitrobenzyl alcohol and 4-nitrobenzoic acid. Reagent Name| Molecular Weight| Drawing of Structure| Physical Properties| Safety/Reference info| 4-nitrobenzaldehydeC7H5NO3| 151.12 g/mol| | Light orange powderMP: 106.5 °CBP: 299.6 °CDensity: 1.338 g/cm3Index of Refraction: 1.617 @ 20°C| www.wikipedia.org| Potassium HydroxideKOH| 56.106 g/mol| | White solidMP: 360 °CBP: 1327 °CWater Solubility: 121 g/100 mL @ 25°CIndex of Refraction: 1.409 @ 20°C| www.wikipedia.org| DichloromethaneCH2Cl2| 84.93 g/mol| | Colorless, volatile liquid; moderately sweet aromaMP: -96.7 °CBP: 39.6 °CWater Solubility: 13 g/L @ 20°CDensity: 1.08 g/cm3Index of Refraction: 1.564 @ 20°C| www.chemspider.comwww.wikipedia.org| 4-nitrobenzyl alcoholC7H7NO3| 153.14 g/mol| | Pale yellow crystalsMP: 92-95 °CBP: 320.8 °CDensity: 1.33 g/cm3Index of Refraction: 1.597 @ 20°C| www.wikipedia.orgwww.chemspider.comwww.lookchem.com| 4-nitrobenzoic acidC7H5NO4| 167.12 g/mol| | Light yellow crystalline powderMP: 237-240 °CBP: 359.1 °CWater Solubility: <0.1 g/100mL @ 26°CDensity: 1.468 g/cm3Index of Refraction: 1.468 @ 20°C| www.chemspider.comwww.wikipedia.orgwww.lookchem.com| Procedure:
1. Place 0.90 g of powdered 4-nitrobenzaldehyde into a clean, dry 125 mL Erlenmeyer flask 2. Add 15 mL of 30% KOH and stir using a magnetic stir bar for the remainder of the time you are in the lab 3. Remove the stir bar and stopper the flask until next week. 4. Next week, add 10 mL water and try to dissolve all the solid material in the flask 5. Pour aqueous solution into a separatory funnel and extract with two 5 mL portions of dichloromethane 6. Combine the dichloromethane extracts and set aside
7. If the 125 mL flask still contains any solids, transfer the aqueous layer back to the flask, add 5 mL of water and try to dissolve the remaining solids 8. Extract the aqueous layer twice more with 5 mL portions of dichloromethane 9. Combine all dichloromethane solutions and extract with 5 mL water 10. Combine the water layers and set aside, labeling the flask ‘acid’ 11. Add 1.2 g anhydrous sodium sulfate to the dichloromethane solution which should contain your 4-nitrobenzyl alcohol product 12. Stopper the flask, label it ‘alcohol’, swirl the flask occasionally, and let the trace amount of water be absorbed by the anhydrous sodium sulfate. 13. While the 4-nitrobenzyl alcohol / dichloromethane solution is drying, prepare an ice bath using a 250-mL beaker 14. Place the aqueous flask labeled ‘acid’ in the ice bath and slowly add 9 mL of 6M HCl 15. Does a precipitate form? What is its color?
16. Collect the 4-nitrobenzoic acid product by vacuum filtration rinsing the flask with water. 17. Transfer the solid to a water glass and let air dry overnight. 18. After drying weigh the crude product, determine its melting point and calculate the percentage yield. 19. Carefully decant or filter the ‘dried’ dichloromethane solution labeled ‘alcohol’ to a clean, labeled, evaporating dish and place in the vent hood. 20. Let the...