Acetic Acid: Chemical Properties and Reactions
Acetic acid is one of the simplest carboxylic acids, and although usually considered a weak acid, undiluted solutions are still corrosive and may burn the skin. It's an important reagent in many industrial applications, such as production of photographic film and wood glue, as well as synthetic fabrics and fibres. In addition to synthetic acetic acid, this compound is also synthesised by certain bacteria, including Acetobacter and Clostridium genus. These microorganisms are found everywhere, and are usually responsible for food deterioration during long periods of storage
The hydrogen in the carboxyl group (COOH) is easily ionised in solution, granting it an acidic character. Acetic acid is classed as a monoprotic acid, as it only generates one proton (H+) and its conjugated base, acetate (CH3COO-). For example, a 1M solution (vinegar) has a pH around 2.4, which represents only 0.5% of dissociated acetic acid molecules.
CH3COOH --> CH3COO- + H+
Acetic acid can dissolve both polar compounds, such as inorganic salts and sugars, as well as non-polar compounds. It also mixes easily with polar and non-polar solvents, including water, hexane and chloroform. However, from octane upwards, miscibility starts to decrease with higher alkanes.
MOST COMMON CHEMICAL REACTIONS
Acetic acid behaves like a standard carboxylic acid, and in the presence of a base, it generates metal acetate, carbon dioxide and water. One example is the popular vinegar (CH3COOH) and baking soda (NaHCO3) reaction.
CH3COOH + NaHCO3 --> CH3COONa + CO2 + H2O
The OH group is also the main reaction site during the conversion of acetic acid into acetyl chloride. Other possible reaction includes loss of water from two molecules of acetic acid to produce acetic anhydride. Furthermore, via Fisher esterification, esters of acetic acid can be generated, and at temperatures above 440 degree Celsius, acetic acid is decomposed to carbon dioxide and methane. Acetic acid is also considered a mild corrosive agent to various metals, including zinc, magnesium and iron, generating acetates and hydrogen. This is why it is always transported in aluminium tanks.
Mg + 2 CH3COOH --> (CH3COO)2Mg + H2
BIOCHEMISTRY AND METABOLISM
In a biochemical context, acetate and acetic acid are equivalent, as under normal physiological conditions, acetic acid is fully ionised to acetate. This compound originates the acetyl group, essential to all life forms. One of its main functions is bound to Coenzyme A and responsible for carbohydrate and lipid metabolism.