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. It also has low toxicity and unlike some other developers, does not cause dermatitis upon skin contact.^[1]

Phenidone

Names
Preferred IUPAC name 1-Phenylpyrazolidin-3-one
Identifiers
CAS Number	92-43-3 Y
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL7660 Y
ChemSpider	6823 Y
ECHA InfoCard	100.001.960
EC Number	202-155-1
PubChem CID	7090
UNII	H0U5612P6K Y
CompTox Dashboard (EPA)	DTXSID1049433
InChI InChI=1S/C9H10N2O/c12-9-6-7-11(10-9)8-4-2-1-3-5-8/h1-5H,6-7H2,(H,10,12) Y Key: CMCWWLVWPDLCRM-UHFFFAOYSA-N Y InChI=1/C9H10N2O/c12-9-6-7-11(10-9)8-4-2-1-3-5-8/h1-5H,6-7H2,(H,10,12) Key: CMCWWLVWPDLCRM-UHFFFAOYAF
SMILES O=C2NN(c1ccccc1)CC2
Properties
Chemical formula	C9H10N2O
Molar mass	162.192 g·mol−1
Appearance	Crystal leaflets or needles
Melting point	121 °C (250 °F; 394 K)
Solubility in water	10 g/100 ml at 100 °C
Solubility in ethanol	10 g/100 ml (hot)
Solubility in diethyl ether	practically insoluble
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Harmful if swallowed
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H411
Precautionary statements	P264, P270, P273, P301+P312, P330, P391, P501
Safety data sheet (SDS)	External MSDS
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

Phenidone is Ilford's trademark for this material, which 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.^[2]

Phenidone functions as a reducing agent. It converts to the N-phenyl-hydroxypyrazole: