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In organic chemistry, I learned a lot of useful reactions but unfortunately I didn't get to try many of them first hand (what's sad is I am a Chemistry major too). I've searched the internet back and forth for the answer to this question which I am fairly sure I know the answer to, but I thought I would just double check.

When reacting lithium with an alkyl halide (the reaction requires 2 mol Li metal per 1 mol of the alkyl halide), one mol of lithium forms the organometallic compound while the other forms the lithium halide salt. The reaction takes place in diethyl ether, so my question is does the halide salt fall out of solution or not? I would assume so considering diethyl ethers low dielectric constant in combination with the ionic character of Lithium salts, but I thought I would ask in hopes someone on here has performed this reaction first hand. Thanks!

Edit: So I read LiCl has minimal solubility in diethyl ether, but LiBr is moderately to highly soluble which makes absolutely no sense to me. I guess perhaps the lone pairs on oxygen might play a role in this but then again why wouldn't this have the same affect on LiCl?

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  • $\begingroup$ Never done it myself, but I'm fairly sure you are correct. $\endgroup$ – Dan Burden Aug 25 '16 at 0:11
  • $\begingroup$ Lattice energy of LiBr is smaller than LiCl, so dissolution is more favourable. $\endgroup$ – orthocresol Aug 25 '16 at 1:25
  • $\begingroup$ @orthocresol The lattice energy for LiCl is only ~50 kj/mol greater than the lattice energy for LiBr, yet the solubility of LiBr is far greater than LiCl (at least the few sources I could find portrayed it this way). Is this a typical occurrence (indicating the realtionship between solubility and lattice energy is non-linear)? $\endgroup$ – KeatonB Aug 25 '16 at 18:22
  • $\begingroup$ If you just think about K = exp(-ΔG/RT) you'll see that 50 kJ/mol can potentially lead to a huge change in K already, so I wouldn't be surprised. $\endgroup$ – orthocresol Aug 25 '16 at 23:57

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