Comparison of Ketone and Aldehyde Syntheses

Acylation of both aromatic and aliphatic compounds can be carried out with relative ease using acyl halides, acid anhydrides, ketenes, nitriles, amides, acids and esters in the presence of Friedel-Craft catalysts to give ketones. Similar substitution reactions with formic acid derivatives are therefore expected to yield the appropriate aldehydes. However, since the anhydride and acyl halides of formic acid, with the exception of formyl fluoride, are either not known or are not sufficiently stable to be used in Friedel-Crafts type acylation reactions, this objective cannot be fully realized. Table 1.1 compares the main ketone syntheses (based on acylating reagents) with the corresponding aldehyde syntheses (based on formylating reagents). 

KETONE Acyl halides Acid Ketenes Nitriles Amides Acids Esters 

ALDEHYDE SYNTHESIS CO + HCI (Gattermann- Koch) Formyl fluoride Acetic-formic anhydride CO HCN (Gattermann) BrCN (Karrer) Formamides (Vilsmeier) Formic acid Ortho- formates 

---