Salicylic acid (from the Latin word for the willow tree, Salix, from whose bark it can be obtained) is a beta hydroxy acid (BHA) with the formula C₆H₄(OH)CO₂H, where the OH group is adjacent to the carboxyl group. This colorless crystalline organic acid is widely used in organic synthesis and functions as a plant hormone. It is derived from the metabolism of salicin. It is probably best known as a compound that is chemically similar to but not identical to the active component of aspirin (acetylsalicylic acid). In fact, salicylic acid is a metabolite of aspirin, the product of esterase hydrolysis in the liver. It is highly soluble in water.

Plant hormone

Salicylic acid (SA) is a phytohormone; and a phenol, ubiquitous in plants generating a significant impact on plant growth and development, photosynthesis, transpiration, ion uptake and transport and also induces specific changes in leaf anatomy and chloroplast structure. SA is recognized as an endogenous signal, mediating in plant defense, against pathogens It plays a role in the resistance of pathogens by inducing the production of 'pathogenesis-related proteins'. It is involved in the systemic acquired resistance 1 in which a pathogenic attack on older leaves causes the development of resistance in younger leaves, though whether SA is the transmitted signal is debatable.

Production

Salicylic acid is an organic acid biosynthesized from the amino acid phenylalanine.

Sodium salicylate is commercially prepared by treating sodium phenoxide with a high pressure of carbon dioxide at high temperature via the Kolbe-Schmitt reaction. Acidification of the product solution gives salicylic acid:

It can be prepared by the hydrolysis of Aspirin (acetylsalicylic acid) or methyl salicylate (Oil of Wintergreen) with a strong acid or base.

History

main: History of aspirin

The Greek physician Hippocrates wrote in the 5th century BC about a bitter powder extracted from willow bark that could ease aches and pains and reduce fevers. This remedy was also mentioned in texts from ancient Sumer, Lebanon, and Assyria. The Cherokee and other Native Americans used an infusion of the bark for fever and other medicinal purposes for centuries. The medicinal part of the plant is the inner bark and was used as a pain reliever for a variety of ailments. The Reverend Edward (Edmund) Stone, a vicar from Chipping Norton, Oxfordshire, England, noted in 1763 that the bark of the willow was effective in reducing a fever.