Reimer–Tiemann reaction
| Reimer–Tiemann reaction also known as RT reaction | |
|---|---|
| Named after | Karl Reimer Ferdinand Tiemann |
| Reaction type | Substitution reaction |
| Identifiers | |
| RSC ontology ID | RXNO:0000072 |
The Reimer–Tiemann reaction is a
[2][3][4] with the simplest example being the conversion of phenol to salicylaldehyde. The reaction was first reported by Karl Reimer and Ferdinand Tiemann.[5]
Reaction mechanism
Chloroform (1) is deprotonated by a strong base (normally hydroxide) to form the chloroform carbanion (2) which will quickly alpha-eliminate to give dichlorocarbene (3); this is the principal reactive species. The hydroxide will also deprotonate the phenol (4) to give a negatively charged phenoxide (5). The negative charge is delocalised into the aromatic ring, making it far more nucleophilic. Nucleophilic attack on the dichlorocarbene gives an intermediate dichloromethyl substituted phenol (7). After basic hydrolysis, the desired product (9) is formed.[6]
Selectivity
By virtue of its two electron-withdrawing chlorine groups, the carbene (3) is highly electron deficient and is attracted to the electron rich phenoxide (5). This interaction favors selective ortho-formylation, consistent with other electrophilic aromatic substitution reactions.
Reaction conditions
Hydroxides are not readily soluble in chloroform, thus the reaction is generally carried out in a
The reaction typically needs to be heated to initiate the process; however, once started, the Reimer–Tiemann Reaction can be highly exothermic. This combination of properties makes it prone to thermal runaways.
Scope
The Reimer–Tiemann reaction is effective for other hydroxy-aromatic compounds, such as
Dichlorocarbenes can react with alkenes and amines to form dichlorocyclopropanes and isocyanides respectively. As such the Reimer–Tiemann reaction may be unsuitable for substrates bearing these functional groups. In addition, many compounds can not withstand being heated with hydroxide.
Comparison to other methods
The direct
Variations
Using carbon tetrachloride instead of chloroform gives a carboxylic acid product instead of an aldehyde.[8] For example, this reaction variant with phenol would yield salicylic acid.
Historical references
Reimer and Tiemann published several papers on the subject.[9][10] [5][11] The early work has been reviewed.[12]
References
- OCLC 642506595
- ^ ISBN 9780471264187.
- ISBN 978-0471861416.
- ISBN 978-0-08-052349-1, retrieved 2022-02-28
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- ^ Reimer, Karl (1883) "Sitzung vom 22. Januar 1883". Berichte der deutschen chemischen Gesellschaft. 16, p. 101.
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