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The runners-up used are also cyclic acetals with 1,2‑hydroxythiols or dithioglycols – the so-called O,S– or S,S-acetals. Ethylene glycol 1,3‑Propadiol Overall, trans-acetalation plays a lesser role in forming protective acetals; they are formed as a rule from glycols through dehydration.
Generic structure of acetals. In organic chemistry, an acetal is a functional group with the connectivity R 2 C(OR') 2. Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments not hydrogen. The two R' groups can be equivalent to each ...
The group is unaffected by treatment with 80% acetic acid, which catalyses the deprotection of O-tetrapyranyl, O-trityl and O-tert-butyldimethylsilyl ethers. It is also unaffected by 50% trifluoroacetic acid (TFA), and survives the harsh acidic conditions used to install and remove isopropylidene or benzylidene acetals. [2]
In organic chemistry, an acetonide is the functional group composed of the cyclic ketal of a diol with acetone. The more systematic name for this structure is an isopropylidene ketal. Acetonide is a common protecting group for 1,2- and 1,3-diols. [1] The protecting group can be removed by hydrolysis of the ketal using dilute aqueous acid.
The degree of conversion to acetal is determined by the equilibrium constant of the reaction: GG-Reaktion zu Acetalen. The most common technique to complete the acetal formation is to remove the reaction water by azeotropic distillation with organic solvents that are not miscible with water, such as benzene or toluene. The tendency of propenal ...
Cyclic hemiacetals often form readily, especially when they are 5- and 6-membered rings. In this case, a hydroxy group reacts with a carbonyl group within the same molecule to undergo an intramolecular cyclization reaction. [6] Formation of a general cyclic hemiacetal Structures of some readily isolable hemiacetals and hemiketals.
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Acid catalyzed acetal formation from the corresponding hemiacetal. Acetals, as already pointed out, are stable tetrahedral intermediates so they can be used as protective groups in organic synthesis. Acetals are stable under basic conditions, so they can be used to protect ketones from a base. The acetal group is hydrolyzed under acidic conditions.