Cannizzaro Reaction

Lab #12
Cannizzaro Reaction

Experimental procedure for the Cannizzaro reaction
Dissolve 3.0 gms of solid KOH (corrosive) in 3.0 mL of deionized (distilled) water by gently stirring the mixture in a 50 or 100 mL beaker. Cool the mixture to room temperature. Place 3.0 mL of benzaldehyde (toxic/flammable) (droppers should be marked) in the test tube provided and add the concentrated KOH you have just made to it. Cork the tube securely and shake the tube vigorously until an emulsion is formed. Place the test tube in the rack provided by the instructor. (Do not use separate racks) Allow the test tube to stand until the next lab period. (Or, at least, 4 days)

 Add about 2.0 mL of water to the mixture, stopper and shake the test tube. If the entire solid has not dissolved then decant off the solution into a clean beaker and add more water to the test tube and repeat shaking of the test tube. If there are solid lumps, break them up with a stirring rod and add water and then shake the mixture. Repeat the procedure until all or most of the solid has dissolved. Pour the solution into a separatory funnel, and extract the solution 2 times with 8mL portions of diethyl ether (listed/ Flammable). Combine the ether extracts in one beaker. If a solid separates out of the solution when the ether is added, add water in small quantities until the solid has redissolved, and then proceed with the extraction. Be sure to avoid the formation of an emulsion by shaking the mixture gently at first, and more vigorously once you observe how long it takes the emulsion to breakup after shaking. The ethereal solution is dried using anhydrous MgSO₄. The dried ether solution is analyzed using the GC for the relative amounts of benzyl alcohol to benzaldehyde. Dispose of this product in the designated waste bottle.

The water solution left after the ether extraction is poured into a mixture of 8 mL of concentrated HCl (Corrosive), 5 mL of water and 3 ice cubes. Stir the mixture vigorously during the addition. Cool the resultant mixture in an ice-bath, and collect the solid benzoic acid by vacuum filtration using the 5.5cm Buchner funnels. Dry the solid with the filter paper in the brown envelopes provided at the organic prep table. Fold, do not lick, the envelope closed. Determine its melting point when dry. After taking the melting point remember to dispose of the benzoic acid and its envelope in the designated waste box.

CHEMICALS:
KOH Potassium Hydroxide (corrosive)
benzaldehyde (toxic/flammable)
diethyl ether (listed/ Flammable)
anhydrous MgSO₄ Magnesium Sulfate
benzyl alcohol
HCl ( Corrosive) Hydrochloric Acid
benzoic acid

Waste Spill & Disposal F: Ethyl Ether & mixtures and washes
Waste Spill ONLY Disposal B: KOH, Conc. HCl
Waste Spill ONLY Disposal D: Benzaldehyde, Benzyl Alcohol
DO NOT PUT USED WEIGH BOATS IN THE HW CHEMICAL CONTAINER. CONTAMINATED PAPER TOWELS AND WEIGH BOATS ARE PUT INTO THE CLEAR PLASTIC HW BOX IN THE HOOD. PAPER ENVELOPES W/CHEMICALS SHOULD BE FOLDED MULTIPLE TIMES AND SEALED BEFORE BEING PUT INTO THE SPECIFIED HW CONTAINER.