Acetoxy group
Encyclopedia
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 alcohol is not a particularly strong nucleophile
and, when present, more powerful nucleophiles like amine
s will react with the above mentioned reagents in preference to the alcohol.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
of the structure CH3-C(=O)-O-. It differs from the acetyl
Acetyl
In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...
group CH3-C(=O)- by the presence of one additional oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
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 acetylationAcetylation
Acetylation describes a reaction that introduces an acetyl functional group into a chemical compound...
):
- Acetyl Halide, such as Acetyl chlorideAcetyl chlorideAcetyl chloride, CH3COCl, also known as ethanoyl chloride or acyl chloride, is an acid chloride derived from acetic acid. It belongs to the class of organic compounds called acyl halides. It is a colorless liquid. Acetyl chloride does not exist in nature, because contact with water would hydrolyze...
in the presence of a base like triethylamineTriethylamineTriethylamine is the chemical compound with the formula N3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine, for which TEA is also a common abbreviation.... - Activated ester form of acetic acid , such as a N-hydroxysuccinimideN-HydroxysuccinimideN-Hydroxysuccinimide is a compound with a molecular weight of 115.09 and a melting point of 95 °C.As it is slightly acidic, it is an irritant to skin, eyes and mucous membranes....
ester, although this is not advisable due to higher costs and difficulties. - Acetic anhydrideAcetic anhydrideAcetic anhydride, or ethanoic anhydride, is the chemical compound with the formula 2O. Commonly abbreviated Ac2O, it is the simplest isolatable acid anhydride and is a widely used reagent in organic synthesis...
in the presence of base with a catalyst such as pyridinePyridinePyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
with a bit of DMAP added.
An alcohol is not a particularly strong nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
and, when present, more powerful nucleophiles like amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
s 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
- AnhydrousAnhydrousAs a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another...
base such as sodium methoxideMethoxideMethoxides are organic salts and the simplest alkoxides. Sodium methoxide and potassium hydroxide have widespread use, though other variants such as lithium hydroxide, rubidium methoxide, caesium methoxide, and francium methoxide exist as well.- Methoxide ion :In organic chemistry, the methoxide...
in methanol. Very useful when a methyl esterEsterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
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 groupFunctional groupIn organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
- AcetylAcetylIn organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...
- AcetylationAcetylationAcetylation describes a reaction that introduces an acetyl functional group into a chemical compound...