Grundmann aldehyde synthesis

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The Grundmann aldehyde synthesis is a name reaction of organic chemistry and was discovered in 1936 by the German chemist Christoph Grundmann (1908-2003). It is the synthesis of aldehydes from carboxylic acid chlorides with the same chain length.

Overview reaction

First, an excess of diazomethane is added to the carboxylic acid chloride , which leads to the formation of a diazoketone with the structural formula R – CO – CHN 2 . By applying heat and adding an organic acid such as acetic acid , the diazoketone is converted to the acetoxyketone R – CO – CH 2 –OOC – CH 3 . After further reduction with aluminum isopropoxide and subsequent hydrolysis, a glycol is obtained which is cleaved by the lead tetraacetate to form the aldehyde with the same chain length as the carboxylic acid chloride used.

Overview reaction

If long-chain, unsaturated fatty acids are present, these can be converted into particularly pure aldehydes by the Grundmann aldehyde synthesis.

mechanism

A possible mechanism can be illustrated using the example of the synthesis of acetaldehyde (ethanal) from acetyl chloride (acetic acid chloride ). First, the diazomethane attacks the carbonyl carbon atom of the acetyl chloride 1 in a nucleophilic manner , so that a diazonium salt 2 is formed. In the next step, acetic acid is added. The chloride ion attacks the hydrogen atom in acetic acid and is split off as hydrogen chloride . A methyldiazonium cation and an acetate anion remain . Due to the nucleophilic attack of the negatively charged oxygen atom of the anion on the α- carbon atom of the cation, nitrogen is split off and an acetoxypropan-2-one 3 is formed . The addition of aluminum triisopropoxide initiates the Meerwein-Ponndorf-Verley reduction , in which a large aluminum complex with 3 is formed and finally 1,2-propylene glycol ( 1,2-propanediol ) 4 is formed. Then the Criegee glycol oxidation proceeds , i. H. the 1,2-propylene glycol is mixed with lead tetraacetate and reacts to acetaldehyde 5 via a lead complex . Acetic acid, carbon monoxide and lead (II) acetate are separated out.

mechanism

The abbreviations Ac and iPr in the graphic above denote the acetyl and isopropyl radicals .

Practical meaning

The Grundmann aldehyde synthesis is a purely laboratory process. Because of the formation of stoichiometric amounts of several - partly toxic - waste materials , the atom economy of the method is so bad that nobody realizes a technical synthesis for aldehydes based on this reaction.

See also

Individual evidence

  1. ^ Obituary Christoph Grundmann
  2. ↑ Ch. Grundmann: A new process for converting carboxylic acids into aldehydes . In: Justus Liebig's Annals of Chemistry . tape 524 , 1936, pp. 31-48 , doi : 10.1002 / jlac.19365240105 .
  3. ↑ a b c Zerong Wang: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, 2009, ISBN 978-0-471-70450-8 , pp. 1288-1290 .
  4. ↑ H. Krauch, W. Kunz, E. Nonnenmacher: Reactions of organic chemistry . 6th edition. Wiley-VCH Verlag, 1997, ISBN 978-3-527-29713-9 , pp. 50 .
  5. ↑ BP Mundy, MG Ilerd, FG Favaloro, Jr .: Name Reactions and Reagents in Organic Synthesis . 2nd Edition. John Wiley & Sons, 2005, ISBN 0-471-22854-0 , pp. 13-14 .