why don't salts react with carbonyl groups?

[Elite Engineer]

Something I've never understood in chemistry is why don't salts (i.e. NaCl, NaBr) react with

 

carbonyl or alkyl halides?

 

-In theory, the Na and Cl dissociate in solution. The carbonyl or alkyl halide is added, and the

 

negative anion (Cl, Br, etc) reacts with the positively influenced carbon atom...but this doesnt

 

happen. Should a catalyst be present, or does theire need to be an immense amount of heat/ energy

 

for the reaction to take place?

 

~ee

[hypervalent_iodine]

Most likely because the resulting carbonyl compound would be very reactive and reform the starting material. Alkyl halides do actually react in the presence of halide salts, as per the Finkelstein reaction.

[John Cuthber]

"-In theory, the Na and Cl dissociate in solution"

In what solvent?

Water is the obvious choice, but it reacts with carbonyl halides.

[hypervalent_iodine]

Presumably if you were to try it, you would do it in acetone for something like NaI or use a PTC.

[Elite Engineer]

but it still wouldn't work would it? Would it need to be under reflux?

[hypervalent_iodine]

What would reflux do to make it work? The Finkelstein reaction doesn't need to be under reflux. You do need anhydrous acetone, though.

 

As I said, akyl halides will undergo halide exchange. See here. The same is unlikely to be true for acid halides or acids. If you performed the reaction in water, the acid halide would hydrolyse. If you performed it in another solvent, the only way I could see it happening is if you used a phase transfer catalyst or some other solvent that exploited differing solubilities. Still, it seems unlikely that it should happen.

[Elite Engineer]

Well I thought that refluxing it would supply enough energy assist the reaction.

 

So you're saying if you have a salt (i.e. NaCl) and anhydrous acetone, and then introduce acetic acid and/or a alkyl

 

halide, the Cl- would react with the carbonyl carbon or the carbon attached to the halide? I see that NaI works, and

 

that's because I is a great nucelophile. However, if you were to use NaCl, NaBr, etc, there would be reaction, even

 

though Cl and Br are decent nucelophiles. I'm asking, why is this?

 

-I was assuming you would need to reflux with the NaCl to give it the extra "kick: of energy it needed to react.

 

~ee

[hypervalent_iodine]

No. NaCl doesn't dissolve in acetone. And it's not to do with carbonyls, only alkyl halides. It's an S_N2 reaction.