Cannizzaro Reaction R A M SUNIL KUMAR L. ASST. PROF. , DEPT OF CHEMISTRY KIRORI MAL COLLEGE, UNIVERSITY OF DELHI Table of Contents 1. Introduction of Cannizzaro Reaction 2. General Reaction 3. Mechanism 4. Experimental Evidence 5. Application of Cannizzaro Reaction 6. Further reading and References Introduction ❑Named after an Italian Chemist Stanislao Cannizzaro. ❑ It is characteristic of those aldehyde (aliphatic and aromatic) devoid of a hydrogen atoms ❑In other words non-enolisable aldehydic functional groups give this test. ❑This is base induced reaction. ❑In this reaction, one molecule of aldehyde oxidizes another to the acid and is itself reduced to the primary alcohol. General reaction Reaction: a hydrogens No a hydrogen Why this restriction? What if the a hydrogen atoms are available ? It’s relationship with Aldol Condensation! Mechanism Step 1 Hydroxide as nucleophile Hydroxide as base Step 2 Hydride is least bad leaving group Mechanism continued Step 3 Experimental evidence These deuterium atoms are obtained from aldehydes and not from water. Remember it is the deuteride that will migrate to give alcohol counterpart Application of Cannizzaro Reaction 1) Formaldehyde is disproportionated to formic acid and methyl alcohol in strong alkali. 2) Benzaldehyde can be converted to benzoic acid and benzyl alcohol. 3) Furfural gives furoic acid and furfuryl alcohol in presence of strong alkali. • 4) Crossed Cannizzaro reaction: When a mixture of formaldehyde and a non enolizable aldehyde is treated with a strong base, the later is preferentially reduced to alcohol while formaldehyde is oxidized to formic acid. This is known as crossed Cannizzaro reaction.E.g. a.the initial nucleophilic addition of hydroxide anion is faster on formaldehyde. b.it is utilized in the quantitative reduction of some aldehydes. • 5) Internal Cannizzaro :Phenylglyoxal undergoes internal Cannizzaro reaction by giving Mandelic acid (α-hydroxyphenylacetic acid or 2-Hydroxy-2-phenylethanoic acid) 6) Phthalaldehyde can undergo intramolecular Cannizzaro reaction by giving (o- hydroxymethyl) benzoic acid. 7) Solventless reaction FOOD FOR THOUGHT Why does Chloral (CCl3CHO) which does not have any alpha hydrogen atom still it does not undergo Cannizzaro reaction? Further reading and Refernces 1. Michael B. Smith and Jerry March Sixth Edition 2. Jonathan Clayden, Nick Greeves and Stuart Warren Second Edition 3. Wikipaedia With special reference to Be careful Thank you.