Valeric acid or pentanoic acid is a straight-chain alkyl carboxylic acid with the chemical formula CH₃(CH₂)₃COOH. Like other low-molecular-weight carboxylic acids, it has an unpleasant odor. It is found in the perennial flowering plant Valeriana officinalis. Technically, pentanoic acid has a molecular weight of 102.13 g mol and a pKa near 4.8, a boiling point around 186 to 187 °C at atmospheric pressure and a density near 0.93 g mL at 20 °C. It is a moderately polar, protic liquid that is miscible with many organic solvents and sparingly soluble in water. In industry it is handled as an intermediate for esterification, amide synthesis and other transformations to produce flavor and fragrance esters, plasticizers, lubricants and pharmaceutical intermediates. Standard analytical methods for identity and purity include gas chromatography and titrimetric acid value determination.
Commercial pentanoic acid is typically supplied with high purity; common specifications cite overall purity by GC in the range of 98.0 to 99.8 percent depending on grade. Typical related compounds and impurity levels observed by routine GC are isovaleric acid (branched C5 acid) up to approximately 0.1 to 0.5 percent, pentanol (C5 alcohol) traces typically below 0.1 percent, pentanal (C5 aldehyde) traces typically below 0.05 percent, ethyl or other alkyl valerate esters below about 0.05 percent, and traces of lower carboxylic acids (acetic, propionic) generally below 0.1 percent. Residual water content is usually controlled to 0.1 to 0.5 percent by weight. Technical grade material intended for noncritical industrial use may show the higher end of these ranges, while reagent or high purity grades will be closer to the upper purity figure and have individual impurities below 0.05 percent.
Valeric acid is primarily used as a chemical intermediate for the production of esters, amides and other derivatives employed in flavor and fragrance compounds, plasticizers, lubricants and pharmaceutical intermediates. It is also used in research applications and in syntheses where a five carbon carboxylic acid building block is required.
At typical handling concentrations, valeric acid can cause skin and eye irritation and respiratory tract irritation from vapors; concentrated liquid contact can cause chemical burns. Ingestion or high exposure may produce gastrointestinal distress and central nervous system effects. Proper personal protective equipment, ventilation and handling precautions are recommended to limit exposure.
Free valeric acid is rarely used directly in finished cosmetic formulations because of its strong odor and potential for irritation. Instead, valeric acid is mainly used as a precursor to esters and other derivatives such as pentyl valerate, which serve as solvents, emollients or fragrance ingredients that have more suitable sensory and safety profiles for cosmetic use.
