Potassium benzoate

Potassium benzoate, the potassium salt of benzoic acid, is a food preservative that inhibits the growth of mold, yeast and some bacteria. It works best in low-pH products, below 4.5, where it exists as benzoic acid.
Acidic foods and beverages such as fruit juice, sparkling drinks, soft drinks, and pickles may be preserved with potassium benzoate. It is approved for use in most countries including Canada, the United States and the European Union, where it is designated by the E number E212.
Potassium benzoate is also used in whistle compositions in pyrotechnics.

Synthesis

One very common way to make potassium benzoate is by oxidizing toluene to benzoic acid followed by a neutralization with potassium hydroxide:
Another way to synthesize potassium benzoate in the lab setting is by hydrolyzing methyl benzoate with potassium hydroxide:

Reactions

Potassium benzoate, like sodium benzoate, can be decarboxylated with a strong base and heat:

Mechanism of food preservation

The mechanism of food preservation begins with the absorption of benzoic acid into the cell. If the intracellular pH changes to 5 or lower, the anaerobic fermentation of glucose through phosphofructokinase is decreased by 95%.

Safety and health

Potassium benzoate has low acute toxicity upon oral and dermal exposure. It is a mild irritant to the skin, and has the potential to cause serious eye damage.