Acetoxy group
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Acetoxy group, abbreviated AcO or OAc, is a chemical functional group of the structure CH3-C(=O)-O-. It differs from the acetyl group CH3-C(=O)- by the presence of one additional oxygen atom. The name acetoxy is the short form of acetyl-oxy.
Functionality
An acetoxy group may be used as a protection for an alcohol functionality in a synthetic route although the protecting group itself is called an acetyl group.
Alcohol protection
There are several options of introducing an acetoxy functionality in a molecule from an alcohol (in effect protecting the alcohol by acetylation):
- Acetyl Halide, such as Acetyl chloride in the presence of a base like triethylamine
- Activated ester form of acetic acid, such as a N-hydroxysuccinimide ester, although this is not advisable due to higher costs and difficulties.
- Acetic anhydride in the presence of base with a catalyst such as pyridine with a bit of DMAP added.
An alcohol is not a particularly strong nucleophile and, when present, more powerful nucleophiles like amines will react with the above-mentioned reagents in preference to the alcohol.
Alcohol deprotection
For deprotection (regeneration of the alcohol)
- Aqueous base (pH >9)
- Aqueous acid (pH <2), may have to be heated
- Anhydrous base such as sodium methoxide in methanol. Very useful when a methyl ester of a carboxylic acid is also present in the molecule, as it will not hydrolyze it like an aqueous base would. (Same also holds with an ethoxide in ethanol with ethyl esters)