Oxidation of 4-chlorobenzyl alcohol to 4-chlorobenzoic acid

Objective

The purpose of this experiment is to obtain a carboxylic acid by oxidation of a primary alcohol using hypochlorite as oxidant.

Experimental procedure

An alternative method to the use of carcinogenic chromium(VI) salts for the oxidation of alcohols is the use of a green oxidizing agent such as hypochlorite. One of the most common sources of hypochlorite is bleach, which is actually an aqueous solution of calcium hypochlorite.

In the case of primary alcohols, oxidation with hypochlorite allows carboxylic acids to be obtained if an excess is used, since the reaction proceeds through an aldehyde which is subsequently oxidized to acid.

Experimental procedure

In an Erlenmeyer dissolve 0.5 g of 4-chlorobenzyl alcohol in 5 ml of acetonitrile. On the other hand, 2.4 g of commercial calcium hypochlorite (65 %) are weighed and transferred to a round bottom flask. They are added 20 ml of water while stirring with a magnet. Maintaining the agitation 2 ml of glacial acetic acid is added, drop by drop. The reflux condenser is coupled and the set is introduced in a water bath.

With the aid of a Pasteur pipette the alcohol solution is added through the condenser. Once the addition is finished, the reaction is heated, during 1 h, to bain-marie shaking vigorously, and avoiding that the temperature of the bath exceeds the 50 ºC. Subsequently, it is cooled down to room temperature.

The reaction crude is transferred into a separating funnel, 10 ml water is added and the flask is washed with 10 ml diethyl ether and poured over the separatory funnel and extracted. Then it is extracted again with diethyl ether (2 x 10 ml). The ether extracts are pooled and treated with two 10 ml portions of saturated aqueous sodium bicarbonate solution.

The aqueous phases are brought together and acidified with 5 % HCl up to pH = 3, obtaining a precipitate (4-chlorobenzoic acid) which is separated by filtration under vacuum. The product is recrystallized from MeOH.

International Chemical Identifier

The IUPAC InChI key identifiers for the main compounds used in this experiment are provided to facilitate the nomenclature and formulation of chemical compounds and the search for information on the Internet for these compounds.

4-chlorobenzyl alcoholPTHGDVCPCZKZKR-UHFFFAOYSA-N
acetonitrileWEVYAHXRMPXWCK-UHFFFAOYSA-N
acetic acidQTBSBXVTEAMEQO-UHFFFAOYSA-N
4-chlorobenzoic acidXRHGYUZYPHTUJZ-UHFFFAOYSA-N
diethyl etherRTZKZFJDLAIYFH-UHFFFAOYSA-N
hydrochloric acidVEXZGXHMUGYJMC-UHFFFAOYSA-N
calcium hypochloriteZKQDCIXGCQPQNV-UHFFFAOYSA-N
MeOHOKKJLVBELUTLKV-UHFFFAOYSA-N

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