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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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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