Pivalic acid


Pivalic acid is a carboxylic acid with a molecular formula of 3CCO2H. This colourless, odiferous organic compound is solid at room temperature. A common abbreviation for the pivalyl or pivaloyl group is Piv and for pivalic acid is PivOH.

Preparation

Industrial route

Pivalic acid is prepared by hydrocarboxylation of isobutene via the Koch reaction:
Such reactions require an acid catalyst such as hydrogen fluoride. tert-Butyl alcohol and isobutyl alcohol can also be used in place of isobutene. Globally, several million kilograms are produced annually. Pivalic acid is also economically recovered as a by-product from the production of semi-synthetic penicillins like ampicillin and amoxycillin.

Laboratory methods

It was originally prepared by the oxidation of pinacolone with chromic acid and by the hydrolysis of tert-butyl cyanide. Convenient laboratory routes proceed via tert-butyl chloride via carbonation of the Grignard reagent and by oxidation of pinacolone.

Applications

Relative to esters of most carboxylic acids, esters of pivalic acid are unusually resistant to hydrolysis. Some applications result from this thermal stability. Polymers derived from pivalate esters of vinyl alcohol are highly reflective lacquers. The pivaloyl group is a protective group for alcohols in organic synthesis. Pivalic acid is sometimes used as an internal chemical shift standard for NMR spectra of aqueous solutions. While DSS is more commonly used for this purpose, the minor peaks from protons on the three methylene bridges in DSS can be problematic. The 1H NMR spectrum at 25 °C and neutral pH is a singlet at 1.08 ppm.

Alcohol protection

The pivaloyl group is used as a protecting group in organic synthesis. Common protection methods include treatment of alcohol with pivaloyl chloride in presence of pyridine.
Alternatively, the esters can be prepared using pivaloic anhydride in the presence of scandium triflate or vanadyl triflate.
Common deprotection methods involve hydrolysis with a base or other nucleophiles.