Crystallise the hydrazone from 70% aqueous EtOH or EtOH/Et2O. Three forms have been described: “” form m 159o, 160o which mutarotates from [] D -87o to -50o (H2O) [Fischer Ber 20 821 1887, Behrends Justus Liebigs Ann Chem 353 106 1907], “” form m 140-141o, 142o which mutarotates from [] 20D -2o to -50o (H2O) [Behrends & Lohr Justus Liebigs Ann Chem 362 78 1908], and Skraup’s form m 115-116o which mutarotates from []D -70o to -47o (H2O) [Skraup Monatsh Chem 10 406 1889, Butler & Crechter J Am Chem Soc 51 3161 1921]. These mutarotate to the formazan.[Beilstein 1 IV 4322, Mester & Major J Am Chem Soc 77 4297 1955, Stanek et al. The Monosaccharides, Academic Press 1963, pp 539-541, 543.]
