McMurry (Kap. 16,6) - Reactions of esters Flashcards
Are esters widespread?
Yes, among the most widespread of naturally occuring compounds.
Are esters known to smell bad or good?
To smell good - pleasant fragrant odors of fruits and flowers.
The ester linkage is also found in animal fats and many important biological molecules.
What are esters used for in the industry?
As solvents = ethyl acetat.
diakyl phalates = used as plasticizer - voluntary withdrawals have though been taken place because of the health risks of phalates.
What kind of reaction does esters undergo?
The same kind of reactions for other carboxylic acid derivatives - although esters are less reactive towards nucleophiles then (acid chloride and anhydrides).
The reaction are applicable for both cyclic esters (lactones) and acyclic esters.
How do esters convert into carboxylic acids?
Esters are hydrolyzed either by basic or aqueous acid to yield carboxylic acid and alcohol.
Hydrolysis by basic solution = saponification
(see the page 580 for saponification reaction).
Hydrolysis by acid catalyzed reaction can occur in different ways, although the reverse of the (Fischer esterfication reaction) is the usual pathway as can be seen an example of on page 581.
Ester hydrolysis is common in biological chemistry - specially in digestion of fietary fats and oils.
The reaction is catalyzed by various lipase enzymes and involves two sequential nucleophillic acyl substitution reaction.
What is the first and the second called?
1) Transesterfication reaction : an alcohol group on the lipase adds to an ester linkage in the fat molecule to give an tetrahedral intermediate that expels alcohol and forms an acyl enzyme intermediate.
2) Addition of water to an acyl enzyme. Folowed by expulsion of the enzyme to give hydrolyzed acid plus regenerated enzyme.
(see page 582 for example).
