Pivalic acid

Pivalic acid is a carboxylic acid with a molecular formula of (CH₃)₃CCO₂H. This colourless, odoriferous organic compound is solid at room temperature. Two abbreviations for pivalic acid are t-BuC(O)OH and PivOH. The pivalyl or pivaloyl group is abbreviated t-BuC(O).

Pivalic acid

Names
Preferred IUPAC name 2,2-Dimethylpropanoic acid
Other names Pivalic acid Dimethylpropanoic acid Neopentanoic acid Neovaleric acid Trimethylacetic acid
Identifiers
CAS Number	75-98-9 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:45133 Y
ChEMBL	ChEMBL322719 Y
ChemSpider	6177 Y
ECHA InfoCard	100.000.839
PubChem CID	6417
UNII	813RE8BX41 Y
CompTox Dashboard (EPA)	DTXSID8026432
InChI InChI=1S/C5H10O2/c1-5(2,3)4(6)7/h1-3H3,(H,6,7) Y Key: IUGYQRQAERSCNH-UHFFFAOYSA-N Y
SMILES O=C(O)C(C)(C)C
Properties
Chemical formula	C5H10O2
Molar mass	102.133 g·mol−1
Density	0.905 g/cm3
Melting point	35 °C (95 °F; 308 K)
Boiling point	163.7 °C (326.7 °F; 436.8 K)
Acidity (pKa)	5.03
Related compounds
Related compounds	neopentyl alcohol neopentane Pivalamide Pivaldehyde
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Pivalic acid is an isomer of valeric acid, the other two isomers of it are 2-methylbutanoic acid and 3-methylbutanoic acid.

Preparation

Pivalic acid is prepared on a commercial scale 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.^[1] Pivalic acid is also economically recovered as a byproduct from the production of semisynthetic penicillins like ampicillin and amoxycillin.

It was originally prepared by the oxidation of pinacolone with chromic acid:^[2]

An alternative oxidative route uses aqueous bromine and proceeds by oxidation of pinacolone.^[3] The hydrolysis of tert-butyl cyanide has also been described.^[4] Another laboratory route involves carbonation of the Grignard reagent formed from tert-butyl chloride^[5]

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.^{[citation needed]}

Use in the laboratory

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.^{[citation needed]}

Pivalic acid is employed as co-catalyst in some palladium-catalyzed C-H functionalization reactions.^[6][7]

Alcohol protection

The pivaloyl (abbreviated Piv or Pv) group is a protective group for alcohols in organic synthesis. Common protection methods include treatment of the alcohol with pivaloyl chloride (PvCl) in the presence of pyridine.^[8]

Alternatively, the esters can be prepared using pivaloic anhydride in the presence of Lewis acids such as scandium triflate (Sc(OTf)₃).

Common deprotection methods involve hydrolysis with a base or other nucleophiles.^{[9][10][11][12]}

See also

• Methyl pivalate