Introduction The Italian scientist Stanislao Cannizzaro (1826-1910) was a professor at the Technical — Organic Chemistry Chemistry Question

Introduction
The Italian scientist Stanislao Cannizzaro (1826-1910) was a professor at the Technical Institute of Alessandria (1851) and subsequently held professorships at Genoa (1855), Palermo (1861), and Rome (1871). In Rome, he also became a member of the senate and of the council of public instruction. He is known for his discovery of cyanamide, for obtaining alcohols from aldehydes – an organic reaction named after him – and for distinguishing between molecular and atomic weights.
The Cannizzaro reaction is a base-catalyzed disproportionation reaction of aromatic or aliphatic aldehydes with no α-hydrogens to the corresponding acid and alcohol. In this disproportionation reaction, one molecule of aldehyde oxidizes another to the acid and is itself reduced to the primary alcohol. Aldehydes with an α-hydrogen do not react in this manner, since for these aldehydes the aldol condensation is much faster.
In cases where two different aldehydes are used, the reaction is called a crossed Cannizarro reaction. In the present reaction of para-chlorobenzaldehyde with formaldehyde, the latter reduces the sooner to the corresponding alcohol, here p-chlorobenzylalcohol, and is itself oxidized to formic acid.

[VISUAL]

Equipment
- three-necked flask (250 cm₃)
- reflux condenser
- dropping funnel
- internal thermometer
- magnetic stirrer with heating plate
- magnetic stirrer bar
- water bath on heating plate
- beaker (500 cm₃ and 250 cm₃)
- heating mantle (250 cm₃) or sand bath on heating plate
- glass rod
- vacuum filter (Ø 5 cm) or Hirsch funnel
- vacuum filtration apparatus
- Bunsen burner
- chromatography tank
- test tubes
- capillary tubes

List of Chemicals
- para-chlorobenzaldehyde
- methanol
- ethanol
- potassium hydroxide
- distilled water
- ethyl acetate
- formalin (aqueous formaldehyde solution, 37 %)
- light petroleum ether (boiling range 40 – 70 °C)
- TLC plates (silica gel 60 F254)

Procedure
Place 28.1 g of para-chlorobenzaldehyde into a 250 cm₃ three-necked, round bottomed flask containing a magnetic stirrer bar and fitted with a reflux condenser, an internal thermometer, and a dropping funnel that contains a solution of 33.7 g of potassium hydroxide in 25 cm₃ of water. Add 60 cm₃ of methanol and 21 g of formalin. Support the flask in a water bath arranged in a way that the level of the water in the bath is at about the same height as the reaction mixture. Stir and heat the solution. When the internal temperature rises to 65 °C, remove the heating source and add the solution of potassium hydroxide dropwise. Ensure that the temperature remains between 65 °C and 75 °C. If necessary, cool the flask with a cold water bath. When the reagent has been added, heat the reaction mixture for 40 minutes at 70 °C followed by further 20 minutes under reflux. If necessary, use a heating mantle or a sand bath instead of the water bath. Allow the reaction mixture to cool down to ambient temperature, transfer the reaction mixture to an appropriate beaker and add 100 cm₃ of water to induce crystallization.
Collect the crude product via vacuum filtration. Wash the crude product with several small aliquots of cold distilled water. Reserve a small sample of the crude product for use in the TLC and for the determination of the melting point.
Recrystallize the crude product from an appropriate solvent, collect the purified crystals by vacuum filtration, dry the product and determine its melting point. In order to determine the appropriate solvent for the recrystallation, place small samples of the crude product in test tubes and recrystallize them from the following solvents:
- water
- water : ethanol (5 : 1)
- ethyl acetate : petroleum ether (1 : 5)
The procedure of the recrystallization from ethyl acetate / petroleum ether is different from standard recrystallization techniques. Dissolve the sample in ethyl acetate at room temperature and slowly add fives times the volume of petroleum ether.
The purity of the crude product and of the recrystallized product are determined by thin-layer chromatography (silica gel 60 F254) using petroleum ether, ethyl acetate or a mixture of these two solvents as the eluting solvent. As a reference, run the starting material on the same plate.

Sources of Error
The starting material para-chlorobenzaldehyde is a solid that is most conveniently transferred in the liquid state by heating the whole storage bottle in a warm water bath. The melting point of para-chlorobenzaldehyde is 47.5 °C. If no crystals of the crude product form or an aqueous emulsion or an oily substance are formed, scratch the base and side of the beaker with a glass rod to initiate crystallization.