Crystallization of air sensitive compounds

Clearly the crystallization of air and moisture sensitive compounds must be carried out under an inert atmosphere. The trickiest step in this regard is often the introduction of the crude solid into the crystallization flask. This is best avoided if possible by transferring the material in solution. Alternatively, it may be possible to transfer it very quickly in the air or using a blanket of inert gas under a funnel (Fig. 6.20). For very sensitive compounds the transfer of the solid must be carried out in a glove bag or a glove box. 

Once the solid has been placed in the flask, the methods described above for low temperature crystallizations under inert atmosphere can be used for most crystallization encountered by an organic chemist. The apparatus shown in Figs. 11.3, 11.5 and 11.6 can be used, without the cooling bath, unless it is required. 

One particular problem which arises with compounds that hydrolyse on contact with moisture is that small amounts of decomposition products can block filters. Thus, if a sintered disc is used it must be scrupulously dry 

I Remember that most organic liquids are extremely flammable so great care must be taken to ensure that the vapour does not come into contact with flames, sources of sparks (electrical motors), or very hot surfaces (hot plates). 

Beware of the possibility that ethers and hydrocarbons may be contaminated with peroxides (Section 4.4). Be particularly careful when distilling compounds prepared by peroxide and peracid oxidations and always take precautions to remove peroxide residues prior to distillation  

---