Ketals

Acetals

General structure of ketals, a subgroup of acetals in the broader sense. The following applies: R 1 to R 4 are organyl residues (alkyl residues, aryl residues, arylalkyl residues, etc.), but not a hydrogen atom.

Acetals (in the narrower sense) - derived from aldehydes - which, together with the ketals (above) as a subgroup, form the group of acetals (in the broader sense). The following applies: R 1 to R 3 are organyl residues (alkyl residues, aryl residues, arylalkyl residues, etc.), but - with the exception of R 1 - no hydrogen atom.

As ketals is known acetals consisting of a ketone incurred. They are characterized by stability towards alkalis , but can be broken down again into their starting materials by acidic solutions.

The term was temporarily banned from chemical nomenclature , but later reintroduced as a subgroup of acetals. In contrast to the acetals, a ketal in this narrower sense has, in addition to the two alkoxy or aryloxy groups , two further alkyl or aryl radicals on the acetal carbon. Similarly, a distinction is made between the thioketals (mono- and dithioketals, depending on whether one oxygen atom is replaced by sulfur or both) and the thioacetals .

Half-ketals are substituted with an alkyloxy group or aryloxy group and a hydroxyl group on the same carbon atom and belong to the group of the hemiacetals .

synthesis

To synthesize a ketal, a ketone (example: cyclohexanone ) is reacted with a monohydric or dihydric alcohol (example: ethylene glycol ) under acid catalysis with elimination of water:

use

The carbonyl group of ketones is often protected as a ketal during synthesis .

Web links

Commons : Ketale  - collection of images, videos and audio files

Individual evidence

1. ^ Brockhaus ABC Chemie, VEB FA Brockhaus Verlag, Leipzig 1965, p. 144.