Molar mass 102.132 g/mol Formula C5H10O2 Melting point 35 °C | Boiling point 163.7 °C Density 905 kg/m³ | |
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Pivalic acid is a carboxylic acid with a molecular formula of (CH3)3CCO2H. This colourless, odiferous organic compound is solid at room temperature. The acronym for pivalate is Piv & for pivalic acid it is PivH.
Contents
Industrial route
Pivalic acid is prepared by hydrocarboxylation of isobutene via the Koch reaction:
(CH3)2C=CH2 + CO + H2O → (CH3)3CCO2H
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 t-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 (abbreviated piv or pv) 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
Pivaloyl (Pv) group is used as a protecting group in organic synthesis. See for example, it is employed in the preparation of Sivelestat.
Common protection methods include treatment of alcohol with pivaloyl chloride (PvCl) in presence of pyridine.
Alternatively, the esters can be prepared using pivaloic anhydride in the presence of Sc(OTf)3 or VO(OTf)2
Common deprotection methods involve hydrolysis with the base or other nucleophiles.
