nlegaux - 17-2-2016 at 08:10
I recently distilled diethyl ether out of some engine starting fluid, but I now have a large amount of heptane as a byproduct. Because heptane is
significantly cheaper, it would make an attractive solvent for the synthesis of Grignard reagents. I have been unable to find any references to
synthesizing Grignard reagents that use solvents other than ethers, but I would think alkanes are unreactive enough to be used. What disadvantages, if
any, are there to using alkanes as solvents for synthesizing Grignard reagents?
Thank you,
nlegaux
Dr.Bob - 17-2-2016 at 08:22
The Grignards are stablized by the oxygen in ether or THF, so those are best prepared in ethers. Getting the Grignard to form in a solvent other
than an ether might be tough. It might be possible, but not that I have seen.
However, they made be reacted with substrates dissolved in other solvents sometimes, so you could perhaps use the heptane for dissolving the other
reactant. But better to save the heptane for another use, in all honesty. You could use it anywhere hexane might be used, for example, great for
crystallizations or silica gel chromatography.
zed - 17-2-2016 at 16:20
The organo-metallic reagent is complexed with the Ether present. No ether; no Grignard!
It is a package deal.
Further, adding excessive heptane, even after the Grignard has formed, might cause solubility problems. The organo-metallic/ether complex, is more or
less polar. Heptane isn't.
Like dissolves like. Adding unlike, may cause a precipitation.
Doesn't mean it would surely nix your reaction sequence, but it might.
[Edited on 18-2-2016 by zed]
byko3y - 17-2-2016 at 22:08
There's a hell lot of books written about grignard reagents preparation, it's one of the most extensively studied reactions. Heptane is a bad solvent
for many more or less complex organic substances, every functional group lowers solubility of the substance in heptane.
Usually aromatic solvent like benzene or toluene is used to replace ether in already made grignard reagent. If heptane had solvent properties similar
to ether, why would anyone want to use ether? Ethers form peroxides, so they are inconvenient in storage.