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15: Organic Acids and Bases and Some of Their Derivatives

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  • Organic acids have been known for ages. Prehistoric people likely made acetic acid when their fermentation reactions went awry and produced vinegar instead of wine. The Sumerians (2900–1800 BCE) used vinegar as a condiment, a preservative, an antibiotic, and a detergent. Citric acid was discovered by an Islamic alchemist, Jabir Ibn Hayyan (also known as Geber), in the 8th century, and crystalline citric acid was first isolated from lemon juice in 1784 by the Swedish chemist Carl Wilhelm Scheele. Medieval scholars in Europe were aware that the crisp, tart flavor of citrus fruits is caused by citric acid. Naturalists of the 17th century knew that the sting of a red ant’s bite was due to an organic acid that the ant injected into the wound. The acetic acid of vinegar, the formic acid of red ants, and the citric acid of fruits all belong to the same family of compounds—carboxylic acids. Soaps are salts of long-chain carboxylic acids. Prehistoric people also knew about organic bases—by smell if not by name; amines are the organic bases produced when animal tissue decays. The organic compounds that we consider in this chapter are organic acids and bases. We will also consider two derivatives of carboxylic acids: esters and amides. An ester is derived from a carboxylic acid and an alcohol. Fats and oils are esters, as are many important fragrances and flavors. An amide is derived from a carboxylic acid and either ammonia or an amine. Proteins, often called “the stuff of life,” are polyamides.

    • 15.1: Carboxylic Acids: Structures and Names
      Simple carboxylic acids are best known by common names based on Latin and Greek words that describe their source (e.g., formic acid, Latin formica, meaning “ant”). Greek letters, not numbers, designate the position of substituted acids in the common naming convention. IUPAC names are derived from the LCC of the parent hydrocarbon with the -e ending of the parent alkane replaced by the suffix -oic and the word acid.
    • 15.2: The Formation of Carboxylic Acids
      Whether in the laboratory or in the body, the oxidation of aldehydes or primary alcohols forms carboxylic acids.
    • 15.3: Physical Properties of Carboxylic Acids
      Carboxylic acids have high boiling points compared to other substances of comparable molar mass. Boiling points increase with molar mass. Carboxylic acids having one to four carbon atoms are completely miscible with water. Solubility decreases with molar mass.
    • 15.4: Chemical Properties of Carboxylic Acids: Ionization and Neutralization
      Soluble carboxylic acids are weak acids in aqueous solutions. Carboxylic acids neutralize bases to form salts.
    • 15.5: Esters - Structures and Names
      An ester has an OR group attached to the carbon atom of a carbonyl group.
    • 15.6: Physical Properties of Esters
      Esters have polar bonds but do not engage in hydrogen bonding and are therefore intermediate in boiling points between the nonpolar alkanes and the alcohols, which engage in hydrogen bonding. Ester molecules can engage in hydrogen bonding with water, so esters of low molar mass are therefore somewhat soluble in water.
    • 15.7: Preparation of Esters
      Esters are made by the reaction of a carboxylic acid with an alcohol, a process that is called esterification.
    • 15.8: Hydrolysis of Esters
      Hydrolysis is a most important reaction of esters. Acidic hydrolysis of an ester gives a carboxylic acid and an alcohol. Basic hydrolysis of an ester gives a carboxylate salt and an alcohol.
    • 15.9: Esters of Phosphoric Acid
      Inorganic acids such as \(H_3PO_4\) form esters. The esters of phosphoric acid are especially important in biochemistry.
    • 15.10: Amines - Structures and Names
      An amine is a derivative of ammonia in which one, two, or all three hydrogen atoms are replaced by hydrocarbon groups. Amines are classified as primary, secondary, or tertiary by the number of hydrocarbon groups attached to the nitrogen atom. Amines are named by naming the alkyl groups attached to the nitrogen atom, followed by the suffix -amine.
    • 15.11: Physical Properties of Amines
      Primary and secondary amines have higher boiling points than those of alkanes or ethers of similar molar mass because they can engage in intermolecular hydrogen bonding. Their boiling points are lower than those of alcohols because alcohol molecules have hydrogen atoms bonded to an oxygen atom, which is more electronegative. The boiling points of tertiary amines, which cannot engage in hydrogen bonding because they have no hydrogen atom on the nitrogen atom.
    • 15.12: Amines as Bases
      Amines are bases; they react with acids to form salts. Salts of aniline are properly named as anilinium compounds, but an older system is used to name drugs: the salts of amine drugs and hydrochloric acid are called “hydrochlorides.” Heterocyclic amines are cyclic compounds with one or more nitrogen atoms in the ring.
    • 15.13: Amides: Structures and Names
      Amides have a general structure in which a nitrogen atom is bonded to a carbonyl carbon atom. In names for amides, the -ic acid of the common name or the -oic ending of the IUPAC for the corresponding carboxylic acid is replaced by -amide.
    • 15.14: Physical Properties of Amides
      Most amides are solids at room temperature; the boiling points of amides are much higher than those of alcohols of similar molar mass. Amides of five or fewer carbon atoms are soluble in water.
    • 15.15: Formation of Amides
      Amides are prepared by the reaction of a carboxylic acid with ammonia or an amine.
    • 15.16: Chemical Properties of Amides: Hydrolysis
      The hydrolysis of an amide produces a carboxylic acid and ammonia or an amine.
    • 15.S: Organic Acids and Bases and Some of Their Derivatives (Summary)
      To ensure that you understand the material in this chapter, you should review the meanings of the following bold terms in the summary and ask yourself how they relate to the topics in the chapter.