The Rosenmund reduction is a

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or Saturated ...

process in which an

acyl chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...

is selectively reduced to an

aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...

. The reaction was named after

Karl Wilhelm Rosenmund Karl Wilhelm Louis Rosenmund (15 December 1884 – 8 February 1965) was a German chemist. He was born in Berlin and died in Kiel. Rosenmund studied chemistry and received his Ph.D. 1906 from University of Berlin for his work with Otto Diels. H ...

, who first reported it in 1918. Rosenmund reduction scheme

The reaction, a

hydrogenolysis Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes lysis (breakdown) by hydrogen.Ralph Connor, Homer Adkins. Hydrogenolysis Of Oxygenated Organic Compounds. J. Am. Chem. Soc. ...

, is catalysed by

palladium Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), ...

barium sulfate Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs in nature as the mineral barite, which is the main commercial source of ...

, 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 A poison is any chemical substance that is harmful or lethal to living organisms. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figurati ...

. Originally this was

thioquinanthrene Thioquinanthrene, also known as thiochinathren, is an aromatic organic chemical compound. It has the chemical formula C18H10N2S2 and reacts with alcoholates or alkoxides. One of the key uses is to act as a catalyst poison in the Rosenmund reduct ...

although

thiourea Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), with the oxygen atom replaced by sulfur atom (as implied by the '' thio-'' prefix). The properties of urea and thiourea differ s ...

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 In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

. Rosenmund catalyst can be prepared by reduction of palladium(II) chloride solution in the presence of BaSO₄. Typical reducing agent is formaldehyde. While Rosenmund reduction method can be used to prepare several aldehydes, formaldehyde cannot be prepared, as formyl chloride is unstable at room temperatures. Rosenmund Reaction

See also

References

Further reading