Grundmann aldehyde synthesis

Grundmann aldehyde synthesis is a name reaction in organic chemistry and in 1936 by the German chemist Christoph Grundmann (* 1908) discovered. This is the synthesis of aldehydes from carboxylic acid chlorides having the same chain length.

Overview reaction

First, the carboxylic acid chloride is treated with an excess of diazomethane to form a diazoketone which results in having the structural formula R-CO- CHN2. By supply of heat and the addition of an organic acid such as acetic acid, the diazoketone is converted to acetoxyketone R - CO -CH2- OOC- CH3. After further reduction with aluminum isopropoxide followed by hydrolysis to obtain a glycol, which is cleaved by lead tetraacetate to give the aldehyde with the same chain length, such as the carboxylic acid chloride used.

When long chain, unsaturated fatty acids are present, they may be converted to aldehydes by the particularly pure Grundmann aldehyde synthesis.

Mechanism

A possible mechanism ( ethanal ) can be illustrated from acetyl chloride ( acid chloride) in the example of the synthesis of acetaldehyde. First, the diazomethane attacks the carbonyl carbon atom of the acetyl chloride to 1 nucleophilic, so that a diazonium salt 2 is formed. In the next step, acetic acid is added thereto. The chloride ion attacks the hydrogen atom of the acetic acid and cleaved off as hydrogen chloride. It remains a Methyldiazonium cation and an acetate anion. By the nucleophilic attack of the negatively charged oxygen atom of the anion at the α - carbon atom of the cation of nitrogen is eliminated and there is a acetoxypropane -2- 3 with the addition of aluminum triisopropoxide to Meerwein - Ponndorf - Verley reduction is initiated when a large aluminum complex 3 is formed, and finally the 1,2- propylene glycol ( 1,2-propanediol) 4 is formed. Thereafter, the oxidation is Criegee glycol, ie, 1,2-propylene glycol is treated with lead tetraacetate and a lead- complex reacts acetaldehyde 5 This acetic acid, carbon monoxide and lead ( II) acetate may be deposited.

The abbreviations Ac and iPr in the chart above indicate the acetyl and isopropyl.

Practical significance

The Grundmann aldehyde synthesis is a pure laboratory procedures. Due to the formation of stoichiometric amounts of several - some toxic - waste materials, the atom economy of the method is so bad that no one realized a technical synthesis of aldehydes based on this reaction.