Question

write the short note on Rimartiemann Reaction and Rosenmund's Reaction

Answer 1

The Rosenmund reduction is a hydrogenation process in which an acyl chloride is selectively reduced to an aldehyde. The reaction was named after Karl Wilhelm Rosenmund, who first reported it in 1918.

Rosenmund reductionNamed afterKarl Wilhelm RosenmundReaction typeOrganic redox reactionIdentifiersOrganic Chemistry Portalrosenmund-reductionRSC ontology IDRXNO:0000136



The reaction, a hydrogenolysis, is catalysed by palladium on barium sulfate, which is sometimes called the Rosenmund catalyst. Barium sulfate has a low surface area which reduces the activity of the palladium, preventing over-reduction. However, for certain reactive acyl chlorides the activity must be reduced further, by the addition of a poison. Originally this was thioquinanthrene although thiourea has also been used. Deactivation is required because the system must reduce the acyl chloride but not the subsequent aldehyde. If further reduction does take place it will create a primary alcohol which would then react with the remaining acyl chloride to form an ester.

Rosenmund catalyst can be prepared by reduction of palladium(II) chloride solution in the presence of BaSO4. Typical reducing agent is formaldehyde.


Reimer–Tiemann reaction

The Reimer–Tiemann reaction is a chemical reaction used for the ortho-formylation of phenols;[1][2][3][4][5] with the simplest example being the conversion of phenol to salicylaldehyde. The reaction was discovered by Karl Reimer (de)[6] and Ferdinand Tiemann. The Reimer in question was Karl Reimer (1845-1883) not the less known Carl Ludwig Reimer (1856-1921).[7]

Reimer TiemannNamed afterKarl Reimer
Ferdinand TiemannReaction typeSubstitution reactionIdentifiersRSC ontology IDRXNO:0000072


Reaction mechanism



The mechanism of the Reimer-Tiemann reaction

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 of the dichlorocarbene gives an intermediate dichloromethyl substituted phenol (7). After basic hydrolysis, the desired product (9) is formed.[8]


for this the photo in upward