I have been using a reaction with an organozincate starting material. This zincate is freshly prepared from zinc chloride and a Grignard reagent. The experimental procedure ‘handed down’ from more senior members of the lab include fusing the zinc chloride before use. ‘Fusing’ means:
- heating under high vacuum with a heat gun until the salt melted
- cooling the liquid down rapidly with the cold air stream of another heat gun to receive a glass-like solid
This is then dissolved in THF and the Grignard added.
In a recent group seminar I spoke about the trouble I had in achieving consistency with that reaction. Part of the resulting discussion revolved around the method of fusing and what I had been doing wrong. The PI noted how important it is for the fusing to be performed correctly as it influences the reactivity.
What actually happens to the zinc chloride during this process? My little understanding of inorganic solid-state chemistry leads me to believe that the initial crystals break down but the resolidified glass should essentially have the same structure. I am also at a loss how to explain any differences in reactivity following this method.
While it is not the most easy task to search for such references, the concept of fused zinc chloride does exist in the literature; the following two references use it in their experimental sections:
P. Dotta, A. Magistrato, U. Rothlisberger, P. S. Pregosin, A. Albinati, Organometallics 2002, 21, 3033–3041. DOI: 10.1021/om020314q. Synthesis of the ligand 4 on page 3040.
P. G. Gassman, J. G. Schaffhausen, J. Org. Chem. 1978, 43, 3214–3223. DOI: 10.1021/jo00410a024. Synthesis of compound 28 on page 3220.