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Acetals are stable compared to hemiacetals but their formation is a reversible equilibrium as with esters.As a reaction to create an acetal proceeds, water must be removed from the reaction mixture, for example, with a Dean–Stark apparatus, lest it hydrolyse the product back to the hemiacetal.
Cyclic acetals with aldehydes (6 P) Cyclopentanonides (2 P) P. Pentanonides (2 P) S. Steroid cyclic ketals (1 C, 3 P) This page was last edited on 1 April 2018, at 20
Condensation products from propenal and pentaerythritol were first described in 1950. [4] [5] The synthesis is carried using a general synthesis method for acetals at acid pH (pH 3-5) by reacting an alcohol with an excess of aldehyde, which is stabilized with hydroquinone in the case of propenal, which tends to polymerize at elevated temperature.
Particularly common spiro compounds are ketal (acetal) formed by condensation of cyclic ketones and diols and dithiols. [15] [16] [17] A simple case is the acetal 1,4-dioxaspiro[4.5]decane from cyclohexanone and glycol. Cases of such ketals and dithioketals are common.
Cyclic acetals are very much more stable against acid hydrolysis than acyclic acetals. Consequently acyclic acetals are used practically only when a very mild cleavage is required or when two different protected carbonyl groups must be differentiated in their liberation.
Cyclic acetals (8 C) H. Hemiacetals (1 C, 2 P) K. Ketals (1 C, 11 P) Pages in category "Acetals" The following 17 pages are in this category, out of 17 total.
The ratio of cyclic to acyclic acetals varies with reaction time since acyclic acetals are kinetically favored and cyclic acetals are the thermodynamically favored. [5] This unique formation of cyclic and acyclic acetals leads to varying degradation time because the two acetal groups hydrolyze at different rates.
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.