Carboxylic Acids &

DerivativesDr. 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, and an antioxidant.

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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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