Purification Methods
If the IR is good, i.e. no OH bands, then keep it in a vacuum desiccator overnight (over P2O5/paraffin) before use. If OH bands are present then reflux 4g in Ac2O (12.6mL) containing a few drops of conc H2SO4 for 10minutes (use a relatively large flask), pour onto ice, collect the crystals, wash with dry *C6H6 (2 x 2mL), stir with 17mL of cold Et2O, filter and dry in it a vacuum desiccator as above, or store it in dark evacuated ampoules under N2 in small aliquots. It is not very stable in air, the melting point of the crystals drop one degree in the first four days then remains constant (132-134o). If placed in a stoppered bottle, it becomes gummy and the m falls 100o in three days. Recrystllisation leads to decomposition. If good quality anhydride is required it, should be prepared freshly from tartaric acid. It sublimes in a CO2 atmosphere. [Shriner & Furrow Org Synth Coll Vol IV 242 1963, Bell Aust J Chem 34 671 1981, Beilstein 18 III/IV 2296.]
