Confused About Hydroxy Butanoic Acids and Amide Hydrolysis: Can Someone Explain?

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SUMMARY

The discussion focuses on the distinction between 2-hydroxy butanoic acid (A) and 3-hydroxy butanoic acid (B) in relation to haloform tests, where only B yields a positive result due to the presence of a methyl group adjacent to the carbonyl. Additionally, it addresses the differing roles of hydroxide ions (OH-) in the base-catalyzed hydrolysis of amides versus the Hoffmann degradation, where OH- acts as a nucleophile in the former and as a deprotonating agent in the latter. The reactions are influenced by the conditions that favor either kinetic or thermodynamic products.

PREREQUISITES
  • Understanding of haloform reactions and their requirements
  • Knowledge of hydroxy butanoic acids and their structural differences
  • Familiarity with base-catalyzed hydrolysis of amides
  • Concept of kinetic versus thermodynamic products in organic reactions
NEXT STEPS
  • Study the mechanism of haloform reactions in detail
  • Research the structural characteristics of hydroxy butanoic acids
  • Explore the principles of base-catalyzed hydrolysis of amides
  • Investigate the factors influencing kinetic and thermodynamic product formation
USEFUL FOR

Chemistry students, organic chemists, and anyone interested in understanding the nuances of hydroxy butanoic acids and amide hydrolysis reactions.

zorro
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1) My book says that we can distinguish between 2 hydroxy butanoic acid (A) and 3 hydroxy butanoic acid (B) by haloform tests. It says that B gives positive haloform test. I am fine with it.
I don't get why A doesnot give positive test as it is also a sec. alcohol .

2)In the base-catalysed hydrolysis of amides, they undergo nucleophilic addition of OH- and finally form acetate.
In hoffmann degradation, we use OH- (of an alkali) where it extracts a proton from the -NH2 group and does not add to the amide.

Why is the action of same OH- different in two cases?

Any help appreciated.
 
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1) Regarding the first question: the haloform reaction requires a methyl group to be adjacent to a carbonyl or a secondary alcohol that can be oxidized to a carbonyl. So in alpha-hydroxy butanoic acid, there is no methyl group adjacent to the hydroxyl group. In beta-hydroxy butanoic acid, C-4 is adjacent to the hydroxyl group.

2) I'm speculating a bit here: it sounds like one is the kinetic product (nucleophilic addition) and the other is the thermodynamic product (deprotonation of the amide). I imagine that in practice, the reaction conditions would be tailored to favor one over the other, but that both *could* happen depending on how the hydroxide ion attacks the amide. This is the case with many reactions and is one way that product yields are lowered (competing reactions).
 
Thanks DDTea!