Acetoxy group

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The structure of the acetoxy group (blue).

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)

See also

• Functional group
• Acetyl
• Acetylation