In organic chemistry, the acetoxy group (abbr. AcO or OAc; IUPAC name: acetyloxy^[1]), is a functional group with the formula −OCOCH₃ and the structure −O−C(=O)−CH₃. As the -oxy suffix implies, it differs from the acetyl group (−C(=O)−CH₃) by the presence of an 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^[2]
• Activated ester form of acetic acid, such as a N-hydroxysuccinimide ester, although this is not advisable due to higher costs and difficulties.^[3]
• Acetic anhydride in the presence of base with a catalyst such as pyridine with a bit of DMAP added.^[4]

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.^[5]

Alcohol deprotection

For deprotection (regeneration of the alcohol)

• Aqueous base (pH >9)^[6]
• Aqueous acid (pH <2), may have to be heated^[7]
• 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)^[8]