chapter seventeen carboxylic acids and their derivatives fundamentals of general, organic, and...

Chapter SeventeenCarboxylic Acids and Their

Derivatives

Fundamentals of General, Organic, and Biological Chemistry

5th Edition

James E. Mayhugh

Oklahoma City University

2007 Prentice Hall, Inc.

Prentice Hall © 2007 Chapter Seventeen 2

Outline

► 17.1 Carboxylic Acids and Their Derivatives: Properties and Names

► 17.2 Some Common Carboxylic Acids► 17.3 Acidity of Carboxylic Acids► 17.4 Reactions of Carboxylic Acids: Ester and Amide

Formation► 17.5 Aspirin and Other Over-the-Counter Carboxylic Acid

Derivatives► 17.6 Hydrolysis of Esters and Amides► 17.7 Polyamides and Polyesters► 17.8 Phosphoric Acid Derivatives


17.1 Carboxylic Acids and Their Derivatives: Properties and Names

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.


► Carboxylic acids and their derivatives are all polar, all are 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.


► 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.


► 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.


► Common names of many of the carboxylic acids are used far more often than their IUPAC names, primarily because carboxylic acids were among the first organic compounds to be isolated and purified.

► When using common names, the carbon atoms attached to the –COOH group are identified by Greek letters rather than numbers.


► 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.


► When the –OH of the carboxyl group is converted to the –OR of an ester group the ability of the molecules to hydrogen-bond 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.


Ester names consist of two words. First name the R group, then name the parent acid, with the family name ending -ic acid replaced by -ate. Both common and systematic names are derived in this manner.


► 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. Monosubstituted amides can also form hydrogen bonds to each other, but disubstituted amides cannot do so and are therefore lower boiling.


► 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.


► 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.


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.


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.


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.


► 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.


17.5 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.


► 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.


► Benzocaine is a local anesthetic used in many over-the-counter 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.


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.


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.


► 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.


17.7 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.


► 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.


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.


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.


► 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.


► 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.


Chapter Summary

► Carboxylic acids, amides, and esters undergo carbonyl-group substitution reactions. Most carboxylic acids are weak acids but esters and amides are neither acids nor bases.

► Acids and unsubstituted or monosubstituted amides hydrogen-bond with each other, but ester and disubstituted amide molecules do not. Simple acids and esters are liquids; all amides (except formamide) are solids. The simpler compounds of all three classes are water-soluble or partially water-soluble.

► Many carboxylic acids are known by common names.


Chapter Summary Cont.

► Esters are named with two words: The first is the name of the alkyl group and the second is the name of the parent acid with -ic acid replaced by -ate. For amides, the ending -amide is used.

► Acids have bad odors, whereas esters contribute to the pleasant odors of fruits and flowers. Acetic acid and citric acid occur in vinegar and citrus fruits.

► Aspirin is an ester; acetaminophen is an amide; benzocaine is representative of a family of amides that are local anesthetics. Proteins and nylon are polymers containing amide bonds. Fats and oils are esters, as are polyesters such as Dacron.


Chapter Summary Cont.

► In ester formation, the –OH of a carboxylic acid group is replaced by the –OR group of an alcohol. In amide formation, the –OH group of a carboxylic acid is replaced by -N from ammonia or an amine.

► Hydrolysis of esters or amides restores the carboxylic acid and the alcohol, ammonia, or amine.

► Phosphoric acid forms mono-, di-, and triesters. There are esters that contain diphosphate and triphosphate groups.

► In biochemical reactions, the phosphoryl group is often donated by a triphosphate (such as ATP) with release of energy.


End of Chapter 17

chapter seventeen carboxylic acids and their derivatives fundamentals of general, organic, and...

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common carboxylic acids

reactions of carboxylic

acidity of carboxylic

dicarboxylic acids

weak acids

unsaturated acids

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