FireLion3 - 9-5-2014 at 10:30
A base catalyzed deacetylation reaction can occur if an acyl group is conjugated or nearby other electron withdrawing groups, but I am struggling to
understand what happens to the acyl group?
If COCH3 is removed from the molecule, where does it go? Is it an ion in solution (doubt it)? A radical (doubt it)? Does it react with the base - this
I doubt to, since many deacetylation reactions describe using "dilute base", and call it catalyzed, meaning equimolar quantities are unlikely?
The acyl group is 2 hydrogen short of being acetaldehyde.... since it wont be gaining any hydrogen during base catalyzed deacetylation, then what
happens to it? Most reaction schemes I have seen only show the other desired substrates of a deacetylation but not the acyl group itself, or what
happens to it.
Metacelsus - 9-5-2014 at 11:02
It becomes a carboxylate ion.
FireLion3 - 9-5-2014 at 11:15
How? A carboxylate ion has two oxygen (according to wiki). Acyl group only has one.
DraconicAcid - 9-5-2014 at 11:20
Acyl plus hydroxide gives an acetate ion, plus a hydrogen for what it used to be bonded to. That's my guess, at least.
FireLion3 - 9-5-2014 at 11:28
Ah, that makes sense. So, the hydroxide is not used as a catalyst but as a reactant? Meaning calling it base catalyzed is an inaccurate statement?
Dany - 9-5-2014 at 14:05
Yes hydroxide ion in base hydrolysis of ester is not a catalyst because it is consumed during the reaction. The reaction of an ester with a base is
called saponification reaction. the reaction of HO- with and ester RCOOR' lead to the formation of carboxylate ion RCOO- and the corresponding alcohol
R'OH. however, the hydrolysis of an ester with acid (H3O+) is called acid catalyzed because the proton H+ is regenerated at the end of the
reaction. So for base hydrolysis we say "base promoted hydrolysis" and for acid we say "acid catalyzed hydrolysis".
Dany.