Acetoxy group

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The structure of the acetoxy group.

The 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.

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)) 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

It must be noted that 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.

For deprotection (regeneration of the alcohol)

- An aqueous base (pH >9)

- An 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 acetate esters)