oxidise phenyl methanol to benzoic acid with potassium permangenate

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Last updated 1:46 PM on 6/15/26
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4 Terms

1
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Theory

  • Alcohol is oxidised in alkaline conditions to an aldehyde then to a carboxylic acid

  • Alcohol used is phenyl methanol

  • The oxidising agent is potassium permangenate

  • Alkaline conditions is provided by sodium carbonate

2
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Theory (2)

  • Excess potassium permangenate Vii is used in order to ensure the complete oxidation to the carboxylic acid otherwise we will end up with benzaldehyde

  • The potassium permangenate will be reduced to a brown percipitate of Mno2

3
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Sodium cabronate use and Hydrochloric acid

  • Sodium carbonate is used to as the rate of the reacion will increase alkaline solution

  • HCL is added to:

  • percipitate the crystaks

  • neutralise the sodium carbonate used and the potassium hydroxide produced

  • Protonates the benzoate annion to form benzoic acid as the solution cools

4
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Method

  • 1cm cubed of pheylmetjanol a colourless oily liquid was added to a connical flask

  • Then 25 cm cubed of excess Kmno4 and .5g sodium carbonate are added to the connical flask excess is added to ensure the complete oxiditation to benzoic acid

  • If compltete oxidiation doesnt happen then the smell of almons will be noticed benzaldeyde

  • The flask placed in water bath for 20 minutes

  • Aids the full oxidation of to benzoic acid

  • 4cm cubed of HCL is added drop by drop un a fume cupboard as HCL gas is gicen off the hcl helps precipiatte the crystals of benzoic acid it neutralises the excess sodium carbonate used at the beginning and the Koh produced

  • glass rod dipped into crystals with brown MnO2 then the Mno2 is dissolved in 10 c m cubed of 1.5 m sodium sulfitte solution

  • when mno2 has dissolved the connical flask was placed on ice and the benzoic acid recrystalised

  • Crystals are filtered

  • Wahsed with ice to maximise tield

  • warm water would dissolve the crystal and reduce yield

  • Slower cooling bugger crystak

  • faster cooling smaller crystal

  • crystaks are dried in a desicator or warm oven

  • purity of crystals obtained by melting point