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Acetic Acid

Organic Chemistry

What is acetic acid?

Acetic acid also called ethanoic acid having the molecular formula CH3COOH prepared industrially by various methods. Commonly it is used as a solvent for the preparation of organic compounds like acetate, acetone, acetic anhydride, acetaldehyde alcohol, vinegar, etc. Glacial acetic acid is a pungent corrosive liquid solution having molar mass of 60 gm mol-1. It is miscible in all proportions with water, ethanol, and ether. The solubility of CH3COOH arises due to the formation of hydrogen bonding with the water molecule.

Acetic acid structure, formula and resonance hybrid in organic chemistry

Properties of acetic acid

Acetic acid ionizes or donates its proton to water to form the conjugate base like acetate ion with two equivalent resonating structures. The internal energy of the anion is lower than the unionized acid. In the case of alcohol, there is no resonance hybrid form in the alkoxide ion. Therefore, it is a stronger acid than alcohol. The standard free energy for the ionization of monocarboxylic acid will be more negative than that of the alcohol.

Acetic acid uses

  • It is commonly used as a solvent for the preparation of acetates, acetone, and acetic anhydride.
  • It is stable towards oxidizing agents and a useful solvent for the chromium trioxide oxidation process.
  • When acetylene passes over worm acetic acid in the presence of mercuric ions uses as a chemical catalyst formed vinyl acetate and ethylidene diacetate. Vinyl acetate used in the plastic industry for the production of plastics toys and daily used equipment.
  • Vinegar (6 to 10 percent aqueous solution of acetic acid) is used commonly in food preparation, in particular pickling liquids, vinaigrettes, and other salad dressings.

Synthesis of acetic acid

One of the earliest methods for preparing glacial acetic acid by destructive distillation of wood to found pyroligneous acid. This contains ten percent of acid solution treated by neutralizing with lime and distilling as the volatile compounds. This volatile compound is a mixture of methanol and acetone. The distillation of methanol and acetone with sulfuric acid gives dilute CH3COOH.

Industrially, CH3COOH is prepared from several organic compounds like alcohol, acetaldehyde, n-butanol. Some synthesis methods are given below the picture.

Synthesis of acetic acid from methanol, acetaldehyde and ethyl alcohol in organic chemistry

Acetaldehyde to acetic acid

CH3COOH is prepared by air oxidation of acetaldehyde in the presence of manganous ion.

Oxidation of n-butane

Acetic acid can be prepared by air oxidation of liquid hydrocarbon like n-butane passes under pressure at 130-230 ºC temperature in the presence of a suitable chemical catalyst like manganous ion.

Methanol to acetic acid

Acetic acid can be synthesis by the reaction between carbon monoxide and methanol under pressure in the presence of cobalt octacarbonyl at about 210 °C.

How to make vinegar from CH3COOH?

Vinegar is the 6-10 percent of the aqueous solution of acetic acid that uses for the preservation of food made in several ways. Melt vinegar in organic chemistry prepared by the oxidation of wort or ethyl alcohol by means of bacteria Mycoderma aceti.

CH3CH2OH + O2 → CH3COOH + H2O

In the quick vinegar process, a barrel containing a specific amount of strong vinegar and 10 percent aqueous solution of ethanol, phosphates, and inorganic salts for the fermentation process for the production of CH3COOH solution. A plentiful supply of air or oxygen necessary otherwise the oxidation is incomplete and acetaldehyde is produced.

Chemical reactions

  • The acids react with strong electropositive metals like lithium or sodium with the liberation of hydrogen (2CH3COOH + 2Na → 2CH3COONa + H2).
  • The monocarboxylic acids like CH3COOH chemical bonding with alcohol to form the ester (CH3COOH + CH3OH → CH3CO2CH3 + H2O).
  • Phosphorus trichloride, pentachloride, or thionol chloride act upon monocarboxylic acid to form acid chloride (3CH3CO2H + PCl3 → 3CH3COCl + H3PO3).
  • CH3COOH is extremely resistant to oxidation but heating with the specific heat with suitable oxidizing agents ultimately produces carbon dioxide and water.
  • The reduction product of monocarboxylic acid depends on the nature of reducing agents uses in the chemical equilibrium reaction. Alkane or paraffin is produced when CH3COOH heating with hydrogen iodide and red phosphorus under pressure.
  • Acetic acid when heating with hydrogen under pressure at elevated temperature in the presence of a chemical catalyst like nickel produced ethane.