PHOTOCHROMIC MATERIAL

PROBLEM TO BE SOLVED: To obtain a compound that shows a peculiar phenomenon of developing a color only in a solid state by using a pyrazole compound having a specified structure as a photochromic material. SOLUTION: The pyrazole compound is represented by formula I (wherein R to R are each H or a 1-6C linear or branched alkyl). It turns red upon irradiation with ultraviolet rays reducing in the transmittance at a wavelength of near 570 nm. A sample in a colored state is restored to a colorless state when left standing at room temperature for three days. This is prepared in the following way. A ketone compound is reacted with oxalic ester in an organic solvent containing sodium ethoxide to obtain formula II. This compound is reacted with R NHNH2 , and the product is purified to obtain a compound of formula III. (CH2 O)n is added to this compound, the both are reacted, the product is extracted with an organic solvent, and the residue is purified by silica gel chromatography to obtain formula IV (chloromethyl form). This is reacted with potassium acetate to obtain formula V(hydroxymethyl form). This is reacted with BU4 NHSO4 and sodium chloroxide to obtain formula I.