Gibbs phthalic anhydride process

What is Gibbs phthalic anhydride process?

The Gibbs phthalic anhydride process, also known as the Gibbs-Wohl naphthalene oxidation, was first reported by Gibbs and Conover in 1918, based on a laboratory process developed in 1917. This process offers a simple and direct method for the vapor-phase oxidation of naphthalene to phthalic anhydride, utilizing a catalyst made from Group VB or VIB transition metals.

Gibbs phthalic anhydride process - Gibbs-Wohl naphthalene oxidation - general reaction scheme
Gibbs phthalic anhydride process

The U.S. government strongly supported the Gibbs phthalic anhydride process during the 1910s because phthalic anhydride was a crucial intermediate for dyes (including indigo) and medicinal compounds. Prior to this, all phthalic anhydride had to be imported from Germany, but the outbreak of World War I caused this supply to be cut off.

The Gibbs phthalic anhydride process was actually a modification of a German patent by Sapper at Badische Anilin und Soda Fabrik in 1896, which used sulfuric acid and a mercury salt catalyst to oxidize naphthalene.

However, the 1896 process had significant drawbacks, such as requiring an expensive apparatus to convert SO2 to SO3. The new process, on the other hand, uses air and naphthalene to produce phthalic anhydride as the sole product, making it a much more efficient method for chemical reactions. This breakthrough led to further innovations in the oxidation of aromatic compounds, such as the production of anthraquinone from anthracene and phenanthraquinone from phenanthrene.