Phenidone (1-phenyl-3-pyrazolidinone) is an organic compound that is primarily used as a photographic developer. It has five to ten times the developing power as Metol, capable of achieving the same level of development in both less time and at a lower concentration. It also has low toxicity and unlike some other developers, does not cause dermatitis upon skin contact. As a developer, Phenidone is typically used in conjunction with hydroquinone for black and white photography and performs better at lower pH levels. Phenidone is Ilford's trademark for this material, which was first filed on Feb. 24, 1953, but has since expired. Although the compound was first prepared in 1890; it was not until 1940 that J. D. Kendall, in the laboratories of Ilford Limited, discovered the reducing properties of this compound. Large scale production did not become feasible until 1951. Phenidone functions as a reducing agent. It converts to the N-phenyl-hydroxypyrazole. It is oxidized in acidic conditions, contributing the electrons it loses to reduce silver halides such as those found in film: Phenidone is also a dual cyclooxygenase/lipoxygenase inhibitor, capable of blocking the synthesis of arachidonic acid, which plays a role in causing inflammation in systemic inflammatory response syndrome and neuronal damage in kainic acid-induced seizures.

Preparation

Phenidone can be prepared by heating phenyl hydrazine with 3-chloropropanoic acid.