Purification Methods
The anhydride is purified by distillation in a vacuum and readily solidifies to a crystalline mass on cooling. [Heitman J Am Chem Soc 34 1594 1912.] Alternatively purify it by dissolving it in the minimum volume of toluene and refluxing for 2hours using a Dean-Stark trap. Evaporate under reduced pressure and distil the anhydride at 18mm. It is then recrystallised three times from its own weight of dry *C6H6. It is sensitive to moisture and should be stored in the dark in a dry atmosphere. The O-methyloxime has m 110-112o [Levy Tetrahedron Lett 3289 1972]. If the sample has hydrolysed extensively (presence of OH band in the IR) then treat with an equal bulk of SOCl2, reflux it for 3hours (CaCl2 tube), evaporate and distil the residue in a vacuum, then recrystallise it from *C6H6, Et2O/*C6H6 or CHCl3 (EtOH free by passing through Al2O3, or standing over CaCl2). [Clarke & Dreger Org Synth Coll Vol I 495 1941.] It is used for modifying -amino functions of lysyl residues in proteins [Bagree et al. FEBS Lett 120 275 1980]. [Beilstein 19 I 659, 19 II 137, 19 III/IV 1641, 19/4 V 215.]
