What are carboxylic acids, esters, amines, and amides? A carboxylic acid contains a carboxyl group, which • is a carbonyl group (C=O) attached to a hydroxyl group (—OH). • is found on carbon 1 in carboxylic acids. O CH3 — C—OH hydroxyl group or CH3COOH carbonyl group 1 How to name carboxylic acids? IUPAC names • Replace the -e in the alkane name with -oic acid. CH4 methane HCOOH CH3—CH3 ethane methanoic acid CH3—COOH ethanoic acid • Number substituents from the carboxyl carbon 1. CH3 O | ║ CH3—CH—CH2—C—OH 4 3 2 1 3-methylbutanoic acid three-dimensional models 2 Some common carboxylic acids Methanoic acid (formic acid) O ║ H─C─OH ethanoic acid (acetic acid) O ║ CH3─C─OH 3 Aromatic carboxylic acids Benzoic acid • aromatic carboxylic acid. benzoic acid O • locates substituents by numbering the ring from carbon 1 in the carboxyl group. O O C C OH OH C OH Cl NH2 3-chlorobenzoic acid 4-aminobenzoic acid 4 Polarity of carboxylic acids Carboxylic acids • are strongly polar. • have two polar groups: hydroxyl (−OH) and carbonyl (C=O). 5 Solubility in water Carboxylic acids: • form hydrogen bonds with many water molecules. • with 1-4 carbon atoms are very soluble in water. • as carbon atoms increase in chains, solubility decreases. Water molecules 6 Acidity of carboxylic acids Carboxylic acids • are weak acids. • ionize in water to produce carboxylate ions and hydronium ions. 7 Neutralization of carboxylic acids Carboxylic acid salts • product of neutralization of a carboxylic acid • with a strong base. CH3—COOH + NaOH CH3—COO– Na+ + H2O acetic acid sodium acetate (carboxylic acid salt) • are used as preservatives and flavor enhancers. 8 What are esters? Esters give flowers and fruits their pleasant fragrances and flavors. In an ester, the H in the carboxyl group is replaced with an alkyl group. not learning how to name them! O CH3 — C—O —CH3 ester group 9 What is esterification? Esterification is the reaction of a carboxylic acid and alcohol in the presence of an acid catalyst to produce an ester. O H+ CH3—C—OH + H—O—CH2—CH3 O CH3—C—O—CH2—CH3 + H2O ethyl acetate (an ester) 10 Ester products Aspirin • is used to relieve pain and reduce inflammation. • is an ester of salicylic acid and acetic acid. O C OH O O C CH3 O Oil of wintergreen • is used to soothe sore muscles. • is an ester of salicylic acid and methanol. C O CH3 OH 11 Base Hydrolysis (Saponification) Base hydrolysis or saponification, • is the reaction of an ester with a strong base. • produces the salt of the carboxylic acid and an alcohol • Salt- “soap” O || CH3—C—O—CH2—CH3 + NaOH O CH3—C—O– Na+ + HO—CH2—CH3 salt of carboxylic acid alcohol 12 Cleaning action of soap A soap • contains a nonpolar end that dissolves in nonpolar fats and oils, and a polar end that dissolves in water. • forms groups of soap molecules called micelles that dissolve in water and are washed away. 13 Amines Amines • are derivatives of ammonia, NH3. • contain N attached to one or more alkyl or aromatic groups. CH3 CH3 CH3—NH2 CH3—NH CH3—N—CH3 NH2 14 Amines are classified as primary, secondary, or tertiary. • primary (1°) amine, one carbon group is bonded to nitrogen atom. • secondary (2°) amine has two carbon groups bonded to nitrogen atom. • tertiary (3°) amine has three carbon groups bonded to nitrogen atom. H | CH3—N—H 1° CH3 | CH3—N—H 2° CH3 | CH3—N—CH3 3° 15 Naming Amines Simple amines • are named as alkylamines. • List the names of the alkyl groups bonded to the N atom in alphabetical order in front of amine. CH3—CH2—NH2 ethylamine CH3—NH—CH3 CH3 | CH3—N—CH2—CH3 dimethylamine ethyldimethylamine 16 Aromatic Amines • The amine of benzene is named aniline. • Alkyl groups on the N use the prefix N- with alkyl name. NH2 NH2 NH CH3 Cl aniline 3-chloroaniline N-methylaniline 17 Hydrogen bonding for amines The N−H bond • provides hydrogen bonding in 1°and 2° amines, but not in 3° amines. • is not as polar as the OH bonds in alcohols. 18 Solubility in water Amines • with 1-5 carbon atoms are soluble in water. • form hydrogen bonds with the polar O-H bond in water. 19 Amines react as bases Like ammonia, amines are weak bases in water. NH3 + H2O NH4+ + OH– ammonium hydroxide CH3—NH2 + H2O CH3—NH3+ + OH– methylammonium hydroxide forms when an amine is neutralized by acid. 20 Properties of amine salts Amine salts are • solids at room temperature. • soluble in water and body fluids. • the form used for drugs. 21 Alkaloids Alkaloids are • physiologically active nitrogen-containing compounds. • obtained from plants. • used as anesthetics, antidepressants, and in stimulants such as caffeine. • often addictive. 22 Cocaine Cocaine is • sold illegally as the amine salt. • reacted with NaOH to produce the free amine form known as “crack.” 23 Caffeine Caffeine • is a stimulant of the central nervous system. • is found in coffee beans, tea, chocolate, and soft drinks. 24 Nicotine Nicotine • increases the adrenaline level in the blood. • causes addiction to tobacco. N CH 3 25 Morphine and Codeine Morphine and codeine are • alkaloids. • obtained from the oriental poppy plant. • used as painkillers. • modified to make heroin. 26 Amides In amides, • an amino group(–NH2) replaces the –OH group of carboxylic acids. • The aromatic amine is benzamide. O C O || CH3—C—OH O || CH3—C—NH2 NH2 benzamide 27 Some amides in health and medicine • Urea is the end product of protein metabolism. • Saccharin is an artificial sweetener. • Some amides such as phenobarbital, Nembutal and Seconal are barbiturates. • Acetaminophen is used to reduce fever and pain. 28 Physical properties of amides Amides • that are primary (−NH2) or secondary (−NH−) form hydrogen bonds. • that are primary have higher melting points than secondary. • that are tertiary (no H on N) do not form hydrogen bonds and have lower melting points. • all form hydrogen bonds with water. • with 1-5 carbon atoms are soluble in water. 29 Hydrogen bonding of amides O || CH3—C—N—H | H Hydrogen bonding occurs between primary amides. O || CH3—C—N—H | H 30