Reimer–Tiemann reaction

The Reimer -Tiemann reaction is a name reaction in organic chemistry. The reaction is named after their discoverers, Karl Ludwig Reimer and Ferdinand Tiemann. The Reimer - Tiemann reaction represents the reaction of phenols with dichlorocarbene is that arises from chloroform in an alkaline solution at a higher temperature and is very unstable. Predominantly the ortho Formylierungsprodukt is then obtained, while others formylation reactions such as the Gattermann - synthesis mainly deliver the para- product.

Mechanism

First, the dichlorocarbene must be obtained for the reaction. For this purpose, first chloroform 1 reacts with the base 2 via the carbanion dichlorocarbene to (3) (singlet - carbene ). This chloroform is deprotonated and then splits off a chloride ion.

Now the dichlorocarbene is brought to reaction with phenol. Phenol 4 is located under the reaction conditions as phenolate 5. The dichlorocarbene (3 ) rearranges the mesomeric phenolate anion in the ortho- position with the formation of 6 at. From the primary product 6, the carbanion formed by proton migration 7 After cleavage of a chloride ion and a subsequent rearomatization the resulting carbenium ion 9 is hydrolyzed and get the phenolate anion 11. After further elimination of chloride ion results in a dienone 12, tautomerizes to aromatic final product 13 after a dienone - phenol rearrangement.

The yield of the reaction is generally below 50 %, so it is rarely used. Their advantage lies in the ortho selectivity. The reaction may be favorably influenced by ultrasound, the reaction time is shortened and the yield increases.