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Ch 17. Outline • • • • • • • • Carboxylic Acids and Their Derivatives: Properties and Names Common Carboxylic Acids Acidity of Carboxylic Acids Reactions of Carboxylic Acids: Ester and Amide Formation Aspirin and Other Over-the-Counter Carboxylic Acid Derivatives Hydrolysis of Esters and Amides Polyamides and Polyesters Phosphoric Acid Derivatives AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. Carboxylic Acids and Their Derivatives: Properties and Names Carboxylic acids: –OH group bonded to the carbonyl C atom. Esters: -OR group bonded to the carbonyl C atom. Amides: –NH2, -NHR, or –NR2 group bonded to the carbonyl C atom. (* R = an alkyl group such as ethyl,methyl etc..) AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 1 • Carboxylic acids and derivatives: polar, higher boiling than comparable alkanes. • Carboxylic acids and amides hydrogen bond. • Carboxylic acids and their derivatives undergo carbonyl-group substitution reactions, in which the group bonded to the carbonyl C atom is replaced. AMP_Chem 30B • • Adapted from ©2007 Prentice Hall, Inc. Carboxylic acids are weak acids. They give up the hydrogen of the carboxyl group, COOH, to bases and establish acid–base equilibria in aqueous solution. Write the eqn. for this reaction. Like alcohols, carboxylic acids form hydrogen bonds with each other. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 2 • • Solubility of carboxylic acids: Solubility decreases with increasing length of the carbon chain (>4 C’s) After approximately 9C chain length they are solids. 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. AMP_Chem 30B • • Adapted from ©2007 Prentice Hall, Inc. Most of the time, common names are used for carboxylic acids. When using common names, the carbon atoms attached to the –COOH group are identified by Greek letters rather than numbers. For example, AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 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. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 4 Esters • • Simple esters have 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 (more on esters in lab…) AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. Ester Nomenclature Naming is in two parts: one originating from the parent acid, the other part from the parent alcohol. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 5 Amides • • Unsubstituted amides can form 3 strong hydrogen bonds to other amide molecules. They are higher melting and higher boiling than the acids from which they are derived. Except for the simplest amide (formamide, a liquid), the low molecular-weight unsubstituted amides are solids that are soluble in both water and organic solvents. AMP_Chem 30B • • Adapted from ©2007 Prentice Hall, Inc. 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. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 6 Amides vs. Amines • 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. • AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 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. Citric acid: Present in citrus fruits and blood. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 7 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 AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 8 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. • AMP_Chem 30B • • Adapted from ©2007 Prentice Hall, Inc. Unsubstituted amides are formed by the reaction of carboxylic acids with ammonia. Substituted amides are produced in reactions between primary or secondary amines and carboxylic acids. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 9 Aspirin and Other Over-the-Counter 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. AMP_Chem 30B • • Adapted from ©2007 Prentice Hall, Inc. 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. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 10 • • Benzocaine is a local anesthetic used in many over-thecounter topical preparations for such conditions as cold sores, poison ivy, sore throats, and hemorrhoids. It works by blocking the transmission of impulses by sensory nerves. Lidocaine (Xylocaine) is commonly administered by injection to prevent pain during dental work. Because benzocaine is less soluble than lidocaine, it cannot be used in this manner. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 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. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 11 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. AMP_Chem 30B • • Adapted from ©2007 Prentice Hall, Inc. Amides are extremely stable in water but undergo hydrolysis with heating in the presence of acids or bases. Under acidic conditions, the carboxylic acid and amine salt are obtained, using base produces the neutral amine and carboxylate anion. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 12 Polyamides and Polyesters • Nylons are polyamides produced by reaction of diamines with diacids. Nylon 66 is made by heating adipic acid (hexanedioic acid, a six-carbon dicarboxylic acid) with hexamethylenediamine (1,6-hexanediamine, a six-carbon diamine) at 280°C. ► Nylon being pulled from the interface between adipoyl chloride and hexamethylenediamine. AMP_Chem 30B • • Adapted from ©2007 Prentice Hall, Inc. Diacids and dialcohols react to yield polyesters. The most widely used polyester is made by the reaction of terephthalic acid with ethylene glycol. As a clothing fiber, it has the trade name Dacron. Under the name Mylar it is used in plastic film and recording tape. Its chemical name, poly(ethylene terephthalate) or PET, is usually applied when it is used in clear, flexible soft-drink bottles. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 13 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. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. Phosphate ester: A compound formed by reaction of an alcohol with phosphoric acid; may be a monoester, a diester, or a triester, also may be a di- or triphosphate. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 14 • • If two molecules of phosphoric acid combine to lose water, they form a phosphoric acid anhydride. The resulting acid (pyrophosphoric acid, or diphosphoric acid) reacts with yet another phosphoric acid molecule to give triphosphoric acid. These acids can also form esters, which are known as diphosphates and triphosphates. We will look at diphosphates and triphosphate esters in more detail when looking at DNA structure. AMP_Chem 30B • • Adapted from ©2007 Prentice Hall, Inc. Phosphoryl group: The –PO3-2 group in organic phosphates. Transfer of a phosphoryl group from one molecule to another is known as phosphorylation. In biochemical reactions, the phosphoryl groups are often provided by adenosine triphosphate, ATP, which is converted to adenosine diphosphate, ADP, in a reaction accompanied by the release of energy. AMP_Chem 30B Adapted from ©2007 Prentice Hall, Inc. 15