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Acetic Acid

What is acetic acid?

Acetic acid also called ethanoic acid has the molecular formula CH3COOH and 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.

Acetic acid structure, formula and resonance hybrid in organic chemistry

Glacial acetic acid is a pungent corrosive liquid solution having a molar mass of 60.052 g 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.

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.

Acetic acid
IUPAC name Ethanoic acid
Chemical formula CH3COOH
CAS Number 64-19-7
Molar mass 60.052 g mol−1
Appearance Colourless liquid
Density (g/cm3) Liquid Solid
1.05 1.27
Melting point 16 to 17 °C
Boiling point 118 to 119 °C
Solubility Miscible in water solution
Acidity (pKa) 4.756
Conjugate base Acetate (CH3COO)
Viscosity 1.22 mPa s
Dipole moment 1.74 D
Heat capacity 123.1 J K−1 mol−1
Entropy 158.0 J K−1 mol−1

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. Therefore, the standard free energy for the ionization of monocarboxylic acid will be more negative than that of alcohol.

Acetic acid uses

  • It is commonly used as a solvent for the preparation of acetates, acetone, and acetic anhydride.
  • It is stable toward oxidizing agents and a useful solvent for the chromium trioxide oxidation process.
  • Acetylene passes over worm acetic acid in the presence of mercuric ions as a chemical catalyst to form vinyl acetate and ethylidene diacetate. Vinyl acetate is used in the plastic industry for the production of plastic 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 CH3COOH

One of the earliest methods for preparing glacial acetic acid by destructive distillation of wood to found pyroligneous acid. This contains ten percent 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 dilutes CH3COOH.

Industrially, CH3COOH is prepared from several organic compounds like alcohol, acetaldehyde, and 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 a 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 synthesized 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 acetic acid?

Vinegar is the 6-10 percent of the aqueous solution of acetic acid that uses for the preservation of food.

It is made in several ways. Melt vinegar in organic chemistry prepared by the oxidation of wort or ethyl alcohol by means of bacteria Mycoderma aceti.

In the quick vinegar process, a barrel containing a specific amount of strong vinegar and a 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 is 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.
2 CH3COOH + 2 Na → 2 CH3COONa + H2

The monocarboxylic acids like CH3COOH chemical bonding with alcohol to form the ester.

Phosphorus trichloride, pentachloride, or thionol chloride act upon monocarboxylic acid to form acid chloride.
3 CH3CO2H + PCl3 → 3 CH3COCl + 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 the reducing agents uses in reaction. Alkane or paraffin is produced when CH3COOH is heated with hydrogen iodide and red phosphorus under pressure.

Acetic acid when heated with hydrogen under pressure at elevated temperature in the presence of a chemical catalyst like nickel produced ethane.