Acetal

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Acetal

An acetal is a molecule

Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
with two single bonded oxygens attached to the same carbon atom.

Traditional usages distinguish ketal

Ketal

A ketal is a functional group or molecule containing a carbon Chemical bond to two -OR groups, where O is oxygen and R represents any alkyl group....
from acetal (whereas the ketal has two carbon-bonded R groups, the acetal has one carbon-bonded R group as H-). Current accepted terminology classifies ketals as a subset of acetals.

The plastic known as acetal is a polyacetal.

Formation of an acetal occurs when the hydroxyl

Hydroxyl

Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl Radical and the hydroxyl anion is called a hydroxide....
group of a hemiacetal

Hemiacetal

Hemiacetals and hemiketals are compounds of the general formula R1R'1COR2, where R2 is not hydrogen....
becomes protonated and is lost as water.

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Encyclopedia

An acetal is a molecule

Molecule

Ketal

Hydroxyl

Hemiacetal

Hemiacetals and hemiketals are compounds of the general formula R1R'1COR2, where R2 is not hydrogen....
becomes protonated and is lost as water. The carbocation

Carbocation

A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer Electron shell#Valence shell instead of the eight valence electrons that ensures maximum stability ....
ion that is produced is then rapidly attacked by a molecule of alcohol

Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
. Loss of the proton from the attached alcohol gives the acetal. Acetals are stable compared to hemiacetals but their formation is reversible as with esters. As a reaction to create an acetal proceeds, water must be removed from the reaction mixture or it will hydrolyse the product. The formation of acetals reduces the total number of molecules present and therefore is not favourable with regards to entropy

Entropy

In many branches of science, entropy is a measure of the disorder of a system. The concept of entropy is particularly notable as it is applied across physics, information theory and mathematics....
. A way to improve this is to use an orthoester

Orthoester

In organic chemistry, an orthoester is a functional group containing three alkoxy groups attached to one carbon atom. The name can also refer to any organic compound that contains this functional group....
as a source of alcohol. Aldehydes and ketones undergo a process called acetal exchange with orthoesters to give acetals. Water produced along with the acetal product is used up in hydrolysing the orthoester

Orthoester