How Is Ethanol Converted to Ethanoic Acid?

How Is Ethanol Converted To Ethanoic Acid?

Ethanol is converted to ethanoic acid through an oxidation reaction

The first catalysed reaction

The conversion of ethanol to ethanoic acid, commonly known as acetic acid, was the first reaction to be attempted in the presence of a catalyst. This introduction was done in the late 1700 by Johann Wolfgang D’bereiner, even before the term catalyst was introduced. Ethanoic acid had been first identified by German chemist George Stahl earlier that century, produced by air oxidation of ethanol present in alcoholic drinks. Although this process was quickly applied to the production of a weak solution of acetic acid called “vin aigre” which literally means “sour wine”, it wasn’t until 1949 that American chemist Frank Westheimer finally unveiled the complicated mechanism behind this reaction.

Although more sophisticated synthetic methods have been developed to synthesise ethanoic acid, the production of wine vinegar still maintains the tradition of relying on this oxidation reaction to convert ethanol into ethanoic acid.

Ethanol is converted to ethanoic acid through an oxidation reaction

The early process merely involved leaving an alcoholic drink (containing ethanol) exposed to air to obtain vinegar. This basic procedure has been significantly improved, and the reaction is now conducted using a catalyst at 150 degree Celsius under reflux and high pressure. Under these conditions, a 90% yield can be obtained, representing a simple and eco-friendly way to generate ethanoic acid. The reaction can be subdivided in two stages:

  • First stage: Partial oxidation generating ethanal
  • Second stage: Ethanal oxidation to ethanoic acid (full ethanol oxidation)

The reaction can be catalysed with potassium dichromate (K2Cr2O7) or sodium dichromate (Na2Cr2O7) in combination with sulphuric acid, to generate the reactive oxygen. Conventionally, this oxygen is represented as [O].

K2Cr2O7 + H2SO4 à Na2SO4 + Cr2(SO4)3 + H2O + [O]

Partial oxidation to ethanal

The first stage involves the production of ethanal (which is an aldehyde). During the initial stages, excess ethanol (CH3CH2OH ) means not enough oxidising agent is able to continue the reaction to the second stage, and there is a temporary accumulation of ethanal (CH3CHO).

CH3CH2OH + Cr2O72- + H+ à CH3CHO + Cr3+ + H2O

Full oxidation to ethanoic acid

As the ethanol is consumed in the partial oxidation, the oxidising agent (now present in excess) is free to convert ethanal to ethanoic acid and the full oxidation can be completed. Once all reagents are consumed, the solution is allowed to cool and ethanoic acid is removed by distillation.

CH3CHO + Cr2O72- à CH3COOH + Cr3+ + H2O

In reality, this reaction has very little importance in an industrial setting, as acetic acid is produced more efficiently via the Monsanto and Cativa processes using methanol. There are some applications which use ethanal as a raw product, but in that case, this product is generated by oxidation of ethylene. This reaction remains however, a favourite amongst chemistry teachers to explain the oxidation of a primary alcohol partially to aldehyde and completely to carboxylic acid.

Rich Hudson
I'm Managing Director of a leading UK chemical supplier. My company supplies most of the chemicals I blog about, you can buy them online at Chemicals.co.uk. I also keep a personal blog at RichHudson.co.uk.
Rich Hudson
Rich Hudson
Rich Hudson

Latest posts by Rich Hudson (see all)

Comments

  1. Marie Hibbert says:

    hi there, your website has really helped me, but i was wondering if you could help me a little more. I am doing an experiment in chemistry where i need to detect the amount of ethanol within a wine sample. I know i need to conduct some experiments involving electrochemical fuel cells- similar to what is used in breatherlisers. 1st i need to do experiments with different concentrations of ethanol and then draw a graph. then i need to test my wine sample and mark where on the graph it sits so i can get the ethanol content from it. all this i understand but i dont know how to go about with the experiment. my teacher has said set up 2 fuel cells, a salt bridge and a voltmeter, but i do not know what to put in the fuel cells, and what would my cathod and anode me made of? thank you i hope i have givent you enough information so you can help me.

    • Hi Marie, I’m afraid I have no experience in testing alcohol this way so I’m unable to advise you. Perhaps one of The Chemical Blogs other readers will be able to answer?

Leave us a comment - we'd love to hear from you!

*