Triphenylphosphine oxide (often abbreviated TPPO) is the chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula OP(C₆H₅)₃. Often chemists abbreviate the formula by writing Ph₃PO or PPh₃O (Ph = C₆H₅). This white crystalline compound is a common side product in reactions involving triphenylphosphine

Triphenylphosphine

Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...

. It is a popular reagent to induce the crystallizing

Crystallization

Crystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid...

 of chemical compounds.
Ph₃PO is tetrahedral molecule related to POCl₃.