Mark asks…
Other than THF and diethyl ether, what could one use as a solvent for a Grignard? Why are these suitable?
So THF and diethyl ether are both slightly polar but why is that important? I need to know other solvents that could be used for Grignard and what would make a bad solvent and why? I’m guessing a nonpolar solvent would make a bad solvent, or maybe something very polar and thus easier for water to dissolve in? Help!
weight loss cardiff answers:
You’re partly right, a nonpolar solvent wouldn’t work. The Grignard reagent is polar and would not be very soluble in a nonpolar solvent.
To see what kind of polar solvents work best, first remember that the Grignard reaction proceeds through an SN2 mechanism. Your Grignard reagent has a dipole moment, (δ−)R−(δ+)MgBr. That partial negative charge turns the R group from a bad nucleophile to a strong nucleophile, which SN2 needs. But it also makes it a strong base. Because of that, we have to be careful with our solvent. If the solvent we use is even a little bit acidic, some of the Grignard reagent will be diverted into an acid-base side reaction with the solvent, instead of the desired nucleophilic substitution.
So, to enhance a reagent’s nucleophilicity for SN2, we need to use a solvent that is polar, but cannot act as an acid. THF and Et2O fit this description; they have dipole moments but don’t contain acidic hydrogens. Since they won’t give up H+ (a proton), we call this type of solvent a “polar aprotic” solvent.
Grignard reagents in particular are highly reactive toward many polar aprotic solvents, further reducing the number of solvents that will work. For instance, your Grignard reagent would attack an acetone solvent, (CH3)2C=O, since it contains a ketone. You’re basically forced to use an ether solvent with Grignard. So, another ether solvent you might use for Grignard is dibutyl ether.
Short, cram night before the test version:
1) Grignard is SN2
2) polar aprotic solvents favor SN2
3) Grignard side-reacts with solvents other than ethers
Laura asks…
Is benzoic acid more soluble in water or diethyl ether?
When both water and diethyl ether were added to benzoic acid, which layer(ie the organic or aqueous layer) can the benzoic acid can be found.
i am also curious that if benzoic acid is more soluble in diethyl ether, is it due to the 6 carbon chain of the benzoic acid?
C6H5coo- soluble in water?
weight loss cardiff answers:
Benzoic acid is more soluble in diethyl ether than water.
So benzoic acid would be in the organic layer.
Bear in mind that ether is less dense than water, so the extract would be on top.
Benzoic acid is more soluble in ether because the benzene ring is nonpolar, aye.
Benzoate salts are water soluble, though, because water is better able to stabilize the negative charge on the oxygen.
Maria asks…
what is the difference Between Ethyl Ether and Diethyl Ether?
i was in chemistry the other day and we were talking about Ether
and i was curious what’s the difference between the two.
weight loss cardiff answers:
Nothing, they represent the same compound. Diethyl ether is the correct IUPAC name for the compound composed of an oxygen attached to two ethyl groups. Ethyl ether is a common name for the same compound. Not technically correct, but widely understood to mean diethyl ether.
Note that sometimes, this compound is also refered to simply as “ether”.
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