Notes

D E PA RT M E N T O F C H E M I S T RY

CHEM 286L – Organic Chemistry Laboratory II Aldol Condensation – Preparation of Benzalacetophenone

Introduction

The Claisen-Schmidt reaction is a kind of crossed aldol condensation between an aromatic aldehyde and a ketone that yields a α,β-unsaturated ketone. You will perform the condensation reaction by using piperonaldehyde and acetophenone and you will identify the product by its melting point and analysis of its IR spectrum. The 1H NMR spectrum of the product will be provided.

Chemical reaction Textbook reference

O CH3 + O

H O O OH

O O O

As illustrated for the reaction of benzaldehyde with a general ketone, the ketone looses a proton yield, after protonation, a β-hydroxy ketone. This intermediate is, for aromatic aldehydes at least, instable and undergoes base-catalyzed dehydration to yield the unsaturated product.

O

from an α-carbon to form an enolate ion, which attacks the carbonyl carbon of the aldehyde to

Chapter 18.12

R

H O R H H OH R O R R

O

O H2O R

Chapter 18.13

O R R

OH OH R

O

OH - OH R R

O

R

Safety Concerns

Sodium hydroxide is toxic and corrosive, causing severe damage to the skin, eyes and mucous membranes. Wear safety googles and gloves and avoid contact with the solution.

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Procedure Step 1

In a 5 mL conical vial, place 0.150 g of piperonaldehyde (3,4-methylenedioxybenzaldehyde). Using an automatic pipetter add 0.12 mL of acetophenone (Central hood), followed by 0.80 mL of ethanol (95%) using your graduated pipette. Using a spatula, carefully stir the mixture until all solids dissolve: warm the solution in a hot water bath (Hot tap water) if necessary.

Step 2

Allow the solution to cool down to room temperature and add 1.0 mL of the NaOH solution (60%) to the vial. You will find the NaOH solution already prepared, in a burette under the central hood. Stir the mixture with your spatula for few...