| Revision as of 02:28, 25 February 2009 editAFigureOfBlue (talk | contribs)Edit filter managers, Administrators53,878 editsm Checking Misplaced Pages for WikiSyntax errors and/or general fixes. You can help!← Previous edit |
Latest revision as of 09:23, 18 August 2024 edit undoChristian75 (talk | contribs)Extended confirmed users, New page reviewers, Pending changes reviewers, Rollbackers114,675 edits Same target but to section: Acetal#AcetalisationTag: Redirect target changed |
| (14 intermediate revisions by 11 users not shown) |
| Line 1: |
Line 1: |
|
|
#REDIRECT ] |
|
'''Acetalisation''' is an ] that involves the formation of an ] or ]. One way of acetal formation is the ] of an ] to a ] or an ]. Acetalisation is often used in ] to create a ] because it is a reversible reaction. |
|
|
|
|
|
|
|
{{Redirect category shell|1= |
|
==Acetalisation of carbonyl groups by alcohols== |
|
|
|
{{R to section}} |
|
|
|
|
|
{{R with history}} |
|
Acetalisation is ] ] with elimination of water. The reaction can be driven to the acetal when water is removed from the reaction system either by ] or trapping water with ]s or ]. The general reaction mechanism for acetalisation of a carbonyl group is shown below. |
|
|
|
}} |
|
|
|
|
] |
|
|
|
|
|
The carbonyl group in '''1''' abstracts a proton from ]. The protonated carbonyl group 2 is activated for ] of the alcohol. The structures '''2a''' and '''2b''' are ]s. After ] of '''3''' by water the ] or ] '''4''' is formed. The hydroxyl group in '''4''' is protonated leading to the ] '''6''' which accepts a second alcohol group to '''7''' with a final deprotonation to the acetal '''8'''. The reverse reaction takes place by adding water in the same acidic medium. Acetals are stable towards ] media. In a '''transacetalisation''' or '''crossacetalisation''' a diol reacts with an acetal or two different acetals react with each other. Again this is possible because all the reaction steps are equilibria. |
|
|
|
|
|
==Examples== |
|
|
One typical example is the acetalisation of 3-bromo-3-methyl-butan-2-one: |
|
|
|
|
|
] in ] is slowly added over a stirred mixture of ] ('''1''') and ] at ] in a ]. After workup 3-bromo-3-methyl-butan-2-one ('''2''') is dissolved in ] and ] ] and ] are added. A ] device is fitted to remove generated water and the reaction is ]ed for 4.5 h. The crude reaction is worked up by washing with saturated ] and ] and the organic layer dried over anhydrous ], after that, ] is added to evaporate the ] under reduced pressure. The residue is purified by ] (0.15 mmHg, 32 ºC) to yield the dioxolane compound '''3''' (62% from 1) as a colorless liquid. <sup></sup>]] |
|
|
|
|
|
Other acetalisation examples can be found in ] and ]. |
|
|
|
|
|
==References== |
|
|
{{nofootnotes|date=February 2009}} |
|
|
<sup></sup> 2-(1-Bromo-1-methyl-ethyl)-2-methyl-dioxolane Juan M. Castro, Pablo J. Linares-Palomino, Sofia Salido, Joaquan Altarejos Manuel Nogueras, Adolfo Sanchez ] 2004, M387 ] publication. |
|
|
|
|
|
] |
|
|
|
|
|
] |
|