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Chapter 18 Amines and Amides 18.1 Amines Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 1 Amines Amines Are derivatives of ammonia NH3. Contain N attached to one or more alkyl or aromatic groups. CH3—NH2 CH3 CH3—NH CH3 CH3—N—CH3 NH2 2 Classification of Amines Amines are classified as primary, secondary, or tertiary. In a primary (1°) amine, one carbon group is bonded to the nitrogen atom. A secondary (2°) amine has two carbon groups. A tertiary (3°) amine has three carbon groups. H CH3 CH3 | | | CH3—N—H CH3—N—H CH3—N—CH3 1° 2° 3° 3 Models of Amines The three-dimensional models show the shapes of amine molecules with one or more alkyl groups bonded to the nitrogen atom. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 4 Naming Simple 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 dimethylamine CH3 | CH3—N—CH2—CH3 ethyldimethylamine 5 IUPAC Names of Amines In the IUPAC system, Amines are named as alkanamines. The -e in the alkane name of the longest chain is changed to -amine. The chain is numbered to locate the amine group and substituents. NH2 | CH3—CH2—NH2 CH3—CH—CH3 Ethanamine 2-Propanamine 6 Naming Secondary and Tertiary Amines In a secondary or tertiary amine, The longest alkane chain is numbered. Each alkyl group bonded to the N atom is named as a N-alkyl group HN—CH3 | CH3—CH2—CH2—NH—CH3 CH3—CH—CH2—CH3 3 2 1 N-Methyl-1-propanamine 1 2 3 4 N-Methyl-2-butanamine 7 Learning Check Give the common and IUPAC names, and classify as primary, secondary, or tertiary: A. CH3—CH2—CH2—NH2 CH3 | B. CH3—CH2—N—CH3 8 Solution A. B. CH3—CH2—CH2—NH2 1-propylamine, 1-propanamine, 1° CH3 | CH3—CH2—N—CH3 ethyldimethylamine, N,N-dimethylethanamine, 3° 9 Learning Check Write a structural formula for A. 2-pentanamine B. N-methyl-1-butanamine 10 Solution A. 2-pentanamine NH2 | CH3—CH—CH2—CH2—CH3 B. N-methyl-1-butanamine CH3—CH2—CH2—CH2—NH—CH3 11 Aromatic Amines The amine of benzene is aniline. Alkyl groups on the N use the prefix N- and the alkyl name. NH2 NH2 NH CH3 Cl Aniline 3-chloroaniline N-methylaniline 12 Learning Check Give a name for each: A. CH3—NH—CH2—CH3 B. C. CH3 | CH3—CH2—N—CH2—CH2—CH2—CH3 NH2 13 Solution A. CH3—NH—CH2—CH3 ethylmethylamine; N-methylethanamine CH3 | B. CH3—CH2—N—CH2—CH2—CH2—CH3 N-ethyl-N-methyl-1-butanamine C. NH2 aniline 14 Chapter 18 Amines and Amides 18.2 Properties of Amines Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 15 Boiling Points of Amines, Alcohols, and Alkanes The boiling points of amines are Higher than alkanes. Lower than alcohols of similar mass. 16 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Hydrogen Bonding for Amines The polar N-H bond Provides hydrogen bonding in 1°and 2°amines, but not 3°. In amines is not as polar as the O-H bonds in alcohols. 17 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Solubility in Water Amines are soluble in water If they have 1-5 carbon atoms. Because the N atom in smaller amines forms hydrogen bonds with the polar O-H bond in water. 18 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Learning Check Consider the following compounds: 1. CH3—CH2—CH2—NH2 2. CH3—CH2—NH—CH3 3. CH3—CH2—CH2—CH3 A. Which compound has the highest boiling point? B. Which compound(s) is(are) soluble in water? 19 Solution Consider the following compounds: 1. CH3—CH2—CH2—NH2 2. CH3—CH2—NH—CH3 3. CH3—CH2—CH2—CH3 A. Which compound has the highest boiling point? 1. CH3—CH2—CH2—NH2 B. Which compound(s) is(are) soluble in water? 1. CH3—CH2—CH2—NH2 2. CH3—CH2—NH—CH3 20 Amines React as Bases Amines are Bronsted-Lowry bases that attract a H+ from H2O to the N atom. Weak bases in water. NH3 + H2O NH4+ + OH– ammonium hydroxide CH3—NH2 + H2O CH3—NH3+ + OH– methylammonium hydroxide 21 Neutralization forms Amine Salts An amine salt Forms when an amine is neutralized by acid. Is named by replacing the amine part of the name with ammonium followed by the name of the negative ion. CH3—NH2 + HCl CH3—NH3+Cl– methylamine methylammonium chloride Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 22 Properties of Amine Salts Amine salts are Solids at room temperature. Soluble in water and body fluids. The form used for drugs. 23 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Cocaine Cocaine Is sold illegally as an amine salt. Is reacted with NaOH to produce the free amine form known as “crack”. 24 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Learning Check Write the equation for ethylamine when it reacts with each of the following: 1. + H2O 2. + HCl 25 Solution Write the equation for ethylamine when it reacts with each of the following: 1. CH3—CH2—NH2 + H2O CH3—CH2—NH3+ OH– 2. CH3—CH2—NH2 + HCl CH3—CH2—NH3+ Cl– 26 Chapter 18 Amines and Amides 18.4 Amides Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 27 Preparation of Amides Amides are prepared By reacting a carboxylic acid with ammonia or an amine (1° or 2°). Using heat. O || Heat CH3—C—OH + NH3 O || CH3—C—NH2 + H2O O O || Heat || CH3—C—OH + CH3—NH2 CH3—C—NH—CH3 + H2O 28 Amides In amides, an amino group(–NH2) replaces the –OH group of carboxylic acids. O O || || CH3—C—OH CH3—C—NH2 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 29 Naming Amides Amides are named as alkanamides. IUPAC replaces –oic acid ending with –amide. Common names replace -ic acid ending with –amide. O || Methanamide (IUPAC) H—C—NH2 Formamide (common) O || CH3—CH2—C—NH2 Propanamide (IUPAC) Propionamide (common) 30 Naming Amides with N Groups An alkyl group bonded to the N atom is named as N-alkyl in front of the amide name. O H || │ CH3 —C—N—CH3 N-methylethanamide (IUPAC) N-methylacetamide (common) O H || │ CH3—CH2 —C—N—CH2—CH3 N-ethylpropanamide (IUPAC) N-ethylpropionamide (common) 31 Aromatic Amides The amide of benzene is named benzamide. O O C NH2 C NH CH3 Benzamide N-methylbenzamide 32 Learning Check Give the IUPAC and common names for the following: A. O || CH3–CH2–CH2–C–NH2 B. O H || │ CH3–C–N–CH2–CH3 33 Solution A. B. O || CH3–CH2–CH2–C–NH2 butanamide; butryamide OH || │ CH3–C–N–CH2–CH3 N-ethylethanamide; N-ethylacetamide 34 Learning Check Draw the structures of A. pentanamide B. N-methylbutyramide 35 Solution A. pentanamide O || CH3–CH2–CH2–CH2–C–NH2 B. N-methylbutyramide O || CH3–CH2–CH2–C–NH–CH3 36 Classification of Amides Amides are classified according to the number of carbon atoms bonded to the nitrogen atom. O H || | CH3—C—N—H Primary (1°) amide O H || | CH3—C—N—CH3 Secondary (2°) amide O CH3 || | CH3 —C—N—CH3 Tertiary (3°) amide 37 Learning Check Give the common and IUPAC names for the following amides and classify as primary, secondary, or tertiary: A. O || CH3—CH2—CH2—C—NH2 B. O CH3 || | CH3—C—N—CH2—CH3 38 Solution O || A. CH3—CH2—CH2—C—NH2 butryamide (common); butanamide (IUPAC) primary(1°) amide B. O CH3 || | CH3—C—N—CH2—CH3 N-ethyl-N-methylacetamide (common); N-ethyl-N-methylethanamide (IUPAC) tertiary (3°) amide 39 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. 40 Some Amides in Health and Medicine 41 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 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. 42 Hydrogen Bonding of Amides O || CH3—C—N—H | H Hydrogen bonding occurs between primary amides. O || CH3—C—N—H | H 43