Transcript Biochem09_Carboxylic_Acid

Carboxylic Acids &
Derivatives
Dr. Michael P. Gillespie
Introduction
• Carboxylic acids contain a carboxyl group (COOH).
• The name carboxyl is derived from terms
carbonyl and hydroxyl, the two structural units
that make up the carboxyl group.
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Carboxylic Acids: Structure
& Properties
• Carboxylix acids are characterized by the
carboxyl group.
• The carboxyl group consists of two very polar
functional groups, the carbonyl group and the
hydroxyl group.
• Carboxylic acids are therefore very polar
compounds.
• They can hydrogen bond to one another and
to water.
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Carboxylic Acids: Structure
& Properties
• Consequently, they are soluble in water and
boil at higher temperatures.
• As the carbon content increases, the solubility
decreases because the carboxylic acids
become more hydrocarbonlike.
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Carboxyl Group
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Some Important Carboxylic
Acids
• Methanoic (formic) acid causes the burning
sensation of ant bites.
• Ethanoic (acetic) acid provides the zip to
vinegars.
• Polymers of lactic acid are used as
biodegradable sutures and biodegradable
plastic bags (potato peels are a great source
of this lactic acid).
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Some Important Carboxylic
Acids
• Butanoic (butyric) acid is the odor associated
with rancid butter.
• When these carboxylic acids react with
alcohols they produce esters, which contribute
to the fragrance and flavor of many fruits.
• Octanoic (caprylic) acid contributes to hunger
sensations.
• Citric acid provides sharp taste to foods, is a
food preservative, and7 an antioxidant.
Dr. Michael P. Gillespie
Some Important Carboxylic
Acids
• Lactic acid provides a tangy flavor.
• Oxalic acid is found in spinach and rhubarb and
contributes to the formation of kidney stones.
• Benzoic acid is a preservative in soft drinks,
pickles, jellies, etc.
• Salicylic acid is a disinfectant.
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Some Important Carboxylic
Acids
• Acetylsalicylic acid is aspirin. Hippocrates
identified a bitter extract from willow bark
that reduced fevers and relieved pain.
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Biodegradable Plastic
• Polymers of lactic acid make sheets of plastic.
• Polylactic acid (PLA) is produced by the
fermentation of sugars.
• Bacteria in soil can readily break down PLA.
• When french fries are produced, nearly half of the
potato is wasted (approximately 10 billion pounds
of potato waste each year).
• This potato waste can be used to make PLA.
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Preparation of Carboxylic
Acids
• Carboxylic acids are prepared by the oxidation
of aldehydes and primary alcohols.
• The primary alcohol is oxidized into an
aldehyde, which is further oxidized into a
carboxylic acid.
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Acid-Base Reactions
• When strong bases are added to a carboxylic
acid neutralization occurs.
• This produces a carboxylic acid salt and water.
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Esterification
• Carboxylic acids react with alcohols to form
esters and water.
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Esters: Structure &
Properties
• Esters are mildly polar and have pleasant
aromas.
• Their boiling points and melting points are
comparable to those of aldehydes and
ketones.
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Preparation of Esthers
• Esters are formed from the reaction between
a carboxylic acid and an alcohol.
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Hydrolysis of Esthers
• An ester can undergo hydrolysis to revert back
to the parent carboxylic acid and alcohol.
• Saponification is the base catalyzed hydrolysis
of an esther. Soaps are made by this process.
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Acid Chlorides
• Acid chlorides are noxious chemicals formed in
the reaction of a carboxylic acid and reagants
such as PCl3 or SOCl2.
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Acid Anhydrides
• Acid anhydrides are formed by the
combination of an acid chloride and a
carboxylate anion.
• Acid anhydrides can react with an alcohol to
produce an ester and a carboxylic acid.
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Chemistry of Flavor &
Fragrance
• Carboxylic acids are
often foul smelling.
• Butyric acid produces
the smell of rancid
butter.
• When carboxylic acids
are converted to esters
they produce pleasant
smells.
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Phosphoesters
• An alcohol can react with phosphoric acid to
produce a phosphate ester (phosphoester).
• When two phosphate groups are joined, the
resulting bond is a phosphoanhydride bond.
• These two functional groups are important to
the structure and function of adenosine
triphosphate (ATP), the universal energy
currency of all cells.
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Thioesters
• Thioesters are produced by the reaction
between a thiol and a carboxylic acid.
• This reaction is catalyzed by cellular enzymes.
• This reaction helps with fatty acid metabolism.
• Coenzyme A is the most important thiol in
these reactions.
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