Download Esters are reduced by hydride reagents to give alcohols or aldehydes.

Esters are reduced by hydride reagents to give alcohols or aldehydes.
LiAlH4 will reduce an ester to an alcohol. Only half the equivalent of LiAlH4 is
required per ester function.
The use of the milder reducing agent bis(2-methylpropyl)aluminum hydride at low
temperatures in toluene, allows the reaction to be stopped at the aldehyde oxidation
state.
Esters form enolates that can be alkylated.
Treatment of esters with a strong base at low temperatures produces ester
enolates (acidic -hydrogens). These enolates react like ketone enolates,
undergoing alkylations.
The pKa of esters is about 25, thus the ester enolates behave as strong bases. Side
reactions include E2 processes and deprotonations.
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Esters in Nature: Waxes, Fats, Oils and Lipids
Waxes are simple esters, whereas fats and oils are more complex.
Waxes are esters containing a long-chain carboxylic acid and a long-chain alcohol.
Waxes are found in nature as hydrophobic and insulating coatings on skin, fur,
feathers, fruits and leaves.
Some waxes are liquid or very soft at room temperature and are used as
lubricants (spermaceti, beeswax).
Lanolin, a sheep’s wool wax, is used as a cosmetic base.
Carnauba wax, from the leaves of a Brazilian palm, is a mixture of several waxes
used as a floor and automobile wax.
Triesters of 1,2,3-propanetriol (glycerol) with long-chain carboxylic acids, or
triaglycerides, constitute fats and oils
The acids in triglycerides are generally unbranched and contain an even number
of carbon atoms.
Any double bonds present are usually cis.
Lipids are biomolecules soluble in non-polar solvents.
Non-polar solvent extracts a wide range of non-polar substances from biological
materials: terpenes, steroids, fats, oils and other lipids, such as phospholipids.
Phospholipids are important components of cell membranes. Lecithin is a
phosphoglyceride lipid found in the brain and central nervous system.
Long-chain carboxylic acids and phospholipids are termed amphipathic: they have
hydrophobic and hydrophilic ends.
When dissolved in water, fatty acids and some phospholipids form structures
called “micelles.” Most phospholipids form a more complicated structure called a
“lipid bilayer” when dissolved in water.
Lipid bilayers are the basic components of cell membranes.
Amide hydrolysis requires strong heating in a concentrated acid or
base.
Amides are the least reactive of the carboxylic acid derivatives.
Nucleophilic addition-elimination reactions of amides generally require relatively
harsh conditions.
Basic hydrolysis produces the carboxylate salt and the amine.
Amides can be reduced to amines or aldehydes.
Unlike alcohols, reduction of amines using LiAlH4 produces amines instead of alcohols.
Reduction of amides using bis(2-methylpropyl) aluminum hydride produces aldehydes, the
same as the reaction with esters.
In the presence of a base, a primary amide undergoes a special halogenation
reaction called the Hofmann Rearrangement.