By paper chromatography, fractional crystallization, or isomerization p-butylphenylglyoxylic acid p-tolylhydrazone (I) was separated into syn- and anti-isomers.MeO2CCOCl with PhBu and AlCl3 gave 55% p-BuC6H4COCO2Me, b0.1 127-32°, n20D 1.5245, saponified to 79% free acid which with p-tolylhydrazine yielded 71% I, double m.p. 118-20° and 135-7°.Fractional crystallization of I (C6H6) gave first the anti-isomer, m. 135-7°.Addition of 3.1 g. I in 10 ml. H2O, 3 ml. MeOH, and 10 ml. N NaOH to diazotized 2,5-Cl2C6H3NH2 gave 57% 1-(2,5-dichlorophenyl)-3-(p-butylphenyl)-5-(p-tolyl)formazan, m. 160-2°.This reaction was used to detect as little as 0.5 γ I on paper chromatograms.Precipitation of I from a NaOH solution by cold HCl gave the anti-isomer, while refluxing the HCl solution 1 hr. produced the syn-isomer, m. 118-20°.The syn-isomer had pK 5.1 (in 8:1 methyl Cellosolve -H2O), Rf 0.37 ((HOCH2CH2)2S as stationary phase and C6H6-Et3N as mobile phase), λmaximum 358 mμ, and a higher solubility in C6H6 and alc.The anti-isomer had pK 6.6, Rf 0.16, λmaximum 338 mμ.The syn-isomer is stabilized by H bonding.