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-17.1 Carboxylic Acids and Their Derivatives: Carboxylic acids have an –OH group bonded to the carbonyl C atom. Esters have an -OR group bonded to the carbonyl C atom. Amides have an –NH2, -NHR, or –NR2 group bonded to the carbonyl C atom. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 1 ► Carboxylic acids behave as weak acids. They surrender the hydrogen of the carboxyl group, COOH, to bases and establish acid–base equilibria in aqueous solution. ► Like alcohols, carboxylic acids form hydrogen bonds with each other so that even formic acid (HCOOH), the simplest carboxylic acid, is a liquid at room temperature with a boiling point of 101ºC. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 2 ► Acids with saturated straight-chain R groups of up to 9 C’s are volatile liquids with strong, sharp odors; those with up to 4 C’s are water soluble. Acids with larger saturated R groups are waxy, odorless solids. Their water solubility falls off as the size of the hydrophobic, alkane-like portion increases. ► Carboxylic acids are named in the IUPAC system by replacing the final -e of the alkane name with -oic acid. If other functional groups are present, the chain is numbered beginning at the –COOH end. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 3 ► Dicarboxylic acids, which contain two –COOH groups, are named systematically by adding the ending -dioic acid to the alkane name. ► Unsaturated acids are named systematically in the IUPAC system with the ending -enoic. ► The acyl group that remains when a carboxylic acid loses its –OH is named by replacing the -ic at the end of the name with -oyl. An exception is the acyl group from acetic acid, which is traditionally called an acetyl group. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 4 Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 5 ► When the –OH of the carboxyl group is converted to the –OR of an ester group the ability of the molecules to hydrogenbond with each other is lost. ► Simple esters are therefore lower boiling than the acids from which they are derived. ► Esters are colorless, volatile liquids with pleasant odors, and many of them contribute to the natural fragrance of flowers and ripe fruits. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 6 ► The nitrogen atom is bonded to a carbonyl-group carbon in an amide, but not in an amine. ► The positive end of the carbonyl group attracts the unshared pair of electrons on nitrogen strongly enough to prevent it from acting as a base by accepting a hydrogen atom. As a result, amides are NOT basic like amines. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 7 ► Unsubstituted amides are named by replacing the -ic acid or -oic acid of the corresponding carboxylic acid name with -amide. ► If the N atom of the amide has alkyl substituents on it, the compound is named by first specifying the N-alkyl group and then identifying the amide name. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 8 17.2 Some Common Carboxylic Acids ► Formic acid, HCOOH: Chemical that is present in the sting of ants. ► Acetic acid, CH3COOH: dilute (5%) aqueous acetic acid is known as vinegar. ► Butyric acid, CH3CH2CH2COOH: Chemical responsible for odor of rancid butter. ► Caproic acid, CH3CH2CH2CH2CH2COOH: First isolated from the skin of goats-which has a distinct smell. ► Citric acid: Present in citrus fruits and blood. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 9 17.3 Acidity of Carboxylic Acids Carboxylic acids are weak acids that establish equilibria in aqueous solution with carboxylate ions, The carboxylate ions are named by replacing the -ic ending in the carboxylic acid name with –ate. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 10 Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 11 17.4 Reactions of Carboxylic Acids: Ester and Amide Formation ► Ester formation, known as esterification, is carried out by warming a carboxylic acid with an alcohol in the presence of a strong-acid catalyst. ► Esterification reactions are reversible. Ester formation is favored either by using a large excess of the alcohol or by continuously removing one of the products. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 12 17.5 Aspirin and Other Over-theCounter Carboxylic Acid Derivatives Aspirin is a white, crystalline solid. Chemically, aspirin is acetylsalicylic acid, an ester formed between acetic acid and the –OH group of salicylic acid. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 13 ► An alternative to aspirin for pain relief is acetaminophen (better known as Tylenol), an amide that also contains a hydroxyl group. ► Acetaminophen reduces fever, but unlike aspirin it is not an anti-inflammatory agent. The major advantage of acetaminophen over aspirin is that it does not induce internal bleeding. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 14 17.6 Hydrolysis of Esters and Amides Acid-catalyzed hydrolysis is simply the reverse of the esterification. An ester is treated with water in the presence of a strong acid and hydrolysis takes place. An excess of water pushes the equilibrium to the right. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 15 Ester hydrolysis by reaction with a base such as NaOH or KOH is known as saponification (after the Latin word sapo, “soap”). The product of saponification is a carboxylate anion rather than a free carboxylic acid. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 16 17.8 Phosphoric Acid Derivatives ► Phosphoric acid is an inorganic acid with three ionizable hydrogen atoms (red), allowing it to form three different anions. ► Just like a carboxylic acid, phosphoric acid reacts with alcohols to form phosphate esters. It may be esterified at one, two, or all three of its groups by reaction with an alcohol. Copyright © 2010 Pearson Education, Inc. Chapter Seventeen 17