This experiment mainly focuses on the synthesis of benzoic acid using benzyl alcohol through reflux and purification process. Benzyl alcohol and benzoic acid are both aromatic compound used in wide variety of cosmetic formulations. Benzyl alcohol handled in this experiment is a primary alcohol to allow further oxidation into carboxylic acid.
2g of potassium permanganate 5ml of 3molL-1 of sodium hydroxide and a few anti-bumping stones are placed into a 100ml pear-shaped flask before adding approximately 25ml of water. The reflux apparatus is then set up.
Figure 1 : Reflux apparatus
The flask is heated to allow the reaction mixture to boil gently and continuously. Next 1ml of benzyl alcohol is added slowly drop by drop using Pasteur pipette for about 5-10 minutes. Residual benzyl alcohol is then rinsed down the condenser with a few millilitres of water and the reaction is allowed to continue until complete (10-15minutes).
The reaction mixture is cooled in an ice bath. By using a Hirsch funnel with filter paper wetted with a little water manganese dioxide is filtered off. Manganese dioxide that is left on the filter paper is washed with two 3ml portions of water to remove adsorbed sodium benzoate.
The filtrate is transferred to a 100ml conical flask before adding enough sodium metabisulfate to make the solution clear and colourless. Addition of a few millilitres of dilute sulphuric acid might be necessary.
The solution is then acidified with dilute sulphuric acid until a large amount of white solid is precipitated. The suspension is cooled in ice and collection of benzoic acid is done by vacuum filtration. It is then recrystallise from water. Recrystallised product is refiltered and air is drawn through the product until dry before its mass is recorded.
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