Transcript 15.1 Amines

Chapters 16-19 (short version)
• AMINES, ALDEHYDES, KETONES,
CARBOXYLIC ACIDS, ESTERS,
ANHYDRIDES
16-1
AMINES
Ch 16……what to know
16-2
Structure and Classification
Amines are classified as 1°, 2°, or 3° depending on the
number of carbon groups bonded to nitrogen.
CH3 -NH2
Methylamine
(a 1° amine)
H
CH3 -N-CH3
Dimethylamine
(a 2° amine)
CH3
CH3 -N-CH3
Trimethylamine
(a 3° amine)
Aliphatic amine: All carbons bonded to nitrogen are
derived from alkyl groups. See the three above.
Aromatic amine: One or more of the groups bonded to
nitrogen are aryl groups.
NH2
Anilin e
(a 1° aromatic amine)
H
N-CH3
N -Methylan iline
(a 2° aromatic amine)
CH3
CH2 -N-CH3
Ben zyldimethylamine
(a 3° aliph atic amin e)
16-3
Structure and Classification
• Heterocyclic amine: An amine in which the nitrogen
atom is part of a ring.
• Heterocyclic aliphatic amine: A heterocyclic amine in
which the ring is saturated (has no C=C bonds).
• Heterocyclic aromatic amine: The amine nitrogen is
part of an aromatic ring.
N
N
H
N
H
Pyrrolidin e Pip eridin e
(h eterocyclic aliph atic amin es)
N
N
N
N
N
N
N
N
H
H
Pyridin e Pyrimidin e Imid azole Purine
(heterocyclic aromatic amines )
*DNA bases are classified as Purines and Pyrimidines
(only 2 specific ones you have to know for test)
16-4
Nomenclature
IUPAC names
• We derive IUPAC names for aliphatic amines just as we
did for alcohols.
• Drop the final -e of the parent alkane and replace it by
-amine.
• Use a number to locate the amino group on the parent
chain.
NH2
CH3 CHCH3
2-Propanamine
NH2
H2 N
Cyclohexanamine
NH2
1,6-Hexanediamine
16-5
Nomenclature
• IUPAC names (cont’d)
• IUPAC nomenclature retains the common name aniline
for C6H5NH2, the simplest aromatic amine.
• Name simple derivatives of aniline by using numbers to
locate substituents or, alternatively, use the prefixes
ortho (o), meta (m), and para (p).
• Several derivatives of aniline have common names that
are still widely used; among them is toluidine:
NH2
NH2
NH2
CH3
A niline
NO2
4-N itroaniline
(p-N itroan iline)
3-Methylaniline
(m-Tolu idine)
16-6
Nomenclature
IUPAC names (cont’d)
• Name unsymmetrical secondary and tertiary amines as
N-substituted primary amines.
• Take the largest group bonded to nitrogen as the
parent amine.
• Name the smaller group(s) bonded to nitrogen, and
show their location on nitrogen by using the prefix N(indicating that they are bonded to nitrogen).
CH3
NHCH3
N-Meth ylan ilin e
N
CH3
N,N -D imethylcyclopentan amin e
16-7
Nomenclature
Common names
• For most aliphatic amines, list the groups bonded to
nitrogen in alphabetical order in one word ending in the
suffix -amine.
NH2
Propylamine
NH2
NH2
N
sec-Butylamin e D ieth ylmethylamin e
Cyclohexylamine
CW- Name the above by IUPAC
16-8
Physical Properties
Like ammonia, low-molecular-weight amines have very
sharp, penetrating odors.
• Trimethylamine, for example, is the pungent principle
in the smell of rotting fish.
• Two other particularly pungent amines are 1,4butanediamine (putrescine) and 1,5-pentanediamine
(cadaverine).
H2N
NH2
1,4-Butane diami ne
(Putrescine )
H2N
NH2
1,5-Pentanedi amine
(Cadave ri ne )
16-9
Physical Properties
Amines are polar compounds:
• Both 1° and 2° amines have N-H bonds, and can form
hydrogen bonds with one another.
• 3° Amines have no N-H bond and cannot form
hydrogen bonds with one another.
16-10
Physical Properties
• An N-H---N hydrogen bond is weaker than an O-H---O
hydrogen bond, because the difference in
electronegativity between N and H (3.0 - 2.1 = 0.9) is
less than that between O and H (3.5 - 2.1 = 1.4).
• We see the effect of hydrogen bonding between
molecules of comparable molecular weight by
comparing the boiling points of ethane, methanamine,
and methanol.
MW (amu)
bp (°C)
CH3 CH3
CH3 NH2
CH3 OH
30.1
-88.6
31.1
-6.3
32.0
65.0
16-11
Physical Properties
• All classes of amines form hydrogen bonds with water
and are more soluble in water than are hydrocarbons of
comparable molecular weight.
• Most low-molecular-weight amines are completely
soluble in water.
• Higher-molecular-weight amines are only moderately
soluble in water or are insoluble.
16-12
Basicity of Amines
Like ammonia, amines are weak bases, and aqueous
solutions of amines are basic.
• The acid-base reaction between an amine and water
involves transfer of a proton from water to the amine.
H
+
CH3 -N-H :O-H
H
Meth ylammoniu m
hydroxide
: :
: :
H
CH3 -N: + H-O-H
H
Methylamin e
(a bas e)
(*Conjugate acid)
*lone pr of e- accepts H+
16-13
Basicity of Amines
• Given the basicities of amines, we can determine which
form of an amine exists in body fluids, say blood.
• In a normal, healthy person, the pH of blood is
approximately 7.40, which is slightly basic.
• If dissolved in blood, it is present predominantly as its
protonated (conjugated acid) form.
HO
NH 2
HO
D opamine
HO
NH3 +
HO
Con jugate acid of d op amine
(the major form p res ent
in b lood p lasma)
16-14
Reactions of Amines
The most important chemical property of amines is their
basicity.
• Amines, whether soluble or insoluble in water, react
quantitatively with strong acids to form water-soluble
salts.
HO H
HO
HO
NH2
+ HCl
HO
(R)-N orepinep hrin e
(on ly s ligh tly solub le in w ater)
H2 O
HO
H
+
-
NH3 Cl
HO
(R)-N orep ineph rine h yd roch loride
(a w ater-soluble s alt)
HW- 1-What is norepinephrine?; 2-What is
epinephrine?; 3- Explain their functions in the
body
16-15
Amines
Another connection to
Biology/Biochemistry:
How are amines applicable to proteins?
16-16
Summary: Amines
•Amines –NH2. There are primary, secondary and tertiary
amines.
•Nomenclature: IUPAC-Name amines like alcohols;
Common- end with “amine”
•EX-CH3NH2-IUPAC: methanamine; Common: Methyl
amine (both are primary)
•Aliphatic amines- Have alkyl groups (methyl amine)
•Aromatic amines- one or more of the groups bonded to
nitrogen are aryl groups Ex-aniline (aminobenzene);
•Heterocyclic- N is part of the ring (ex-purines, pyrimidines)
•Amino acids-monomers of proteins. Have both amino
group and Carboxyl group
•Reactions: Amines are weak bases. The lone electron
pair attracts H+ (Remember-acids donate H+ and bases
accept H+)
•Physical properties- smaller ones are polar, but weaker
than alcohols (O eneg is 3.5; N is 3.0)
16-17
ALDEHYDES & KETONES
CH 17
16-18
Structure
The functional group of an aldehyde is a carbonyl group
bonded to a hydrogen atom.
• In methanal, the simplest aldehyde (formaldehyde), the
carbonyl group is bonded to two hydrogens.
• In other aldehydes, it is bonded to one hydrogen and
one carbon group.
The functional group of a ketone is a carbonyl group
bonded to two carbon groups.
O
O
O
HCH
CH3 CH
CH3 CCH3
Methanal
Ethanal
Propanone
(Formaldehyde) (Acetaldehyde) (Acetone)
17-19
Nomenclature
IUPAC names for aldehydes
• To name an aldehyde, change the suffix -e of the parent
alkane to -al.
• Because the carbonyl group of an aldehyde can only
be at the end of a parent chain and numbering must
start with it as carbon-1, there is no need to use a
number to locate the aldehyde group.
• For unsaturated aldehydes, indicate the presence of a
carbon-carbon double bond by changing the ending of
the parent alkane from -ane to -enal. Numbering the
carbon chain begins with the aldehyde carbonyl
carbon. Show the location of the carbon-carbon double
bond by the number of its first carbon.
17-20
Nomenclature
• The IUPAC system retains common names for some
aldehydes, including these three.
O
CHO
CHO
H
OCH3
t rans-3-Phenyl-2-prop enal
(Cinn amald ehyd e; in
oil of cin namon)
Ben zaldehyde
(in almond s)
OH
Van illin
(from van illa
bean s)
17-21
Nomenclature
IUPAC names for ketones.
• The parent alkane is the longest chain that contains the
carbonyl group.
• Indicate the presence of the carbonyl group by
changing the -ane of the parent alkane -one.
• Number the parent chain from the direction that gives
the carbonyl carbon the smaller number.
• The IUPAC retains the common name acetone for 2propanone.
O
O
1
Acetone
O
2
3
4
5
1
6
5-Meth yl-3-h exanone
2
2-Methylcycloh exanone
17-22
Nomenclature
To name an aldehyde or ketone that also contains an -OH
(hydroxyl) or -NH2 (amino) group:
• Number the parent chain to give the carbonyl carbon
the lower number.
• Indicate an -OH substituent by hydroxy-, and an -NH2
substituent by amino-.
• Hydroxyl and amino substituents are numbered and
alphabetized along with other substituents.
O
OH O
5
4
3
1
H
3-Hydroxy-4-meth ylp entanal
6
4
3
2
1
NH2
3-Amino-4-ethyl-2-h exanone
17-23
Nomenclature
Common names
The common name for an aldehyde is derived from the
common name of the corresponding carboxylic acid.
• Drop the word "acid" and change the suffix -ic or -oic to
-aldehyde.
• Name each alkyl or aryl group bonded to the carbonyl
carbon as a separate word, followed by the word
"ketone”. Alkyl or aryl groups are generally listed in
order of increasing molecular weight.
O
O
CH3 CH
O
O
CH3 COH
Acetald ehyde Acetic acid
Meth yl ethyl ketone Ethyl isoprop yl ketone
17-24
Physical Properties
A C=O bond is polar, with oxygen bearing a partial
negative charge and carbon bearing a partial positive
charge.
• Therefore, aldehydes and ketones are polar molecules.
• Figure 17.1 The polarity of a carbonyl group.
17-25
Physical Properties
• In liquid aldehydes and ketones, there are weak
intermolecular attractions between the partial positive
charge on the carbonyl carbon of one molecule and the
partial negative charge on the carbonyl oxygen of
another molecule.
• No hydrogen bonding is possible between aldehyde or
ketone molecules.
• Aldehydes and ketones have lower boiling points than
alcohols and carboxylic acids, compounds in which
there is hydrogen bonding between molecules. See the
table on the next screen.
17-26
Physical Properties
Name
die th yl e th e r
pe n tan e
bu tan al
2-bu tan on e
1-bu tan ol
propan oic acid
Mol e cu l ar bp
S tru ctu ral Formu l a W ei gh t (amu )(°C )
CH3 CH2 OCH 2 CH3
34
74
CH3 CH2 CH2 CH2 CH 3 72
36
CH3 CH2 CH2 CHO
72
76
72
80
CH3 CH2 COCH3
74
117
CH3 CH2 CH2 CH2 OH
CH3 CH2 COOH
74
141
• Formaldehyde, acetaldehyde, and acetone are infinitely
soluble in water.
• Aldehydes and ketones become less soluble in water
as the hydrocarbon portion increases in size.
• Flammable
• Simple ones are toxic (ex- formaldehyde/methanal)
• FYI- aldehydes found in some flavorings (cinnamon,17-27
vanilla); dyes; perfumes
Properties
• Reduction (hydrogenation) of aldehydes yields
primary alcohol; reduction of ketone makes a
secondary alcohol
• Ketones cannot be further oxidized
• Simple ketones are excellent solvents. Dissolve in
both polar and non polar substances. Simple ones
low in toxicity
• FYI- Some ketones found in some perfumes,
camphor
17-28
Oxidation
• Aldehydes are oxidized to carboxylic acids by a variety
of oxidizing agents, including potassium dichromate.
O
O
K2 Cr2 O 7
H2 SO 4
H
He xanal
OH
He xanoi c aci d
• Liquid aldehydes are so sensitive to oxidation by O2 in
the air that they must be protected from contact with
air during storage.
O
C
2
H
O
C
+ O2
Be nz al de hyde
2
OH
Be nz oi c acid
17-29
Oxidation
• Ketones resist oxidation by most oxidizing agents,
including potassium dichromate and molecular
oxygen.
• **Not on test: Tollens’ reagent is specific for the
oxidation of aldehydes. If done properly, silver
deposits on the walls of the container as a silver
O
mirror.
R-C-H + 2 Ag( NH3 ) 2 + + 3 OHA ldehyde Tollens'
reagen t
O
R-C-O- + 2 Ag + 4 NH3 + 2 H2 O
Carboxylic Silver
an ion
mirror
17-30
Reduction
• The carbonyl group of an aldehyde or ketone is reduced
to an -CHOH group by hydrogen in the presence of a
transition-metal catalyst.
• Reduction of an aldehyde gives a primary alcohol.
• Reduction a ketone gives a secondary alcohol.
O
H + H2
Pen tanal
O + H2
Cyclopentanone
tran sition
metal catalyst
transition
metal catalyst
OH
1-Pen tanol
OH
Cyclopentanol
17-31
Reduction
*specifics of slides 32-34 NOT
on THIS test. You need to correct your copy!
The most common laboratory reagent for the reduction of
an aldehyde or ketone is sodium borohydride, NaBH4.
• This reagent contains hydrogen in the form of hydride
ion, H:-.
• In a hydride ion, hydrogen has two valence electrons
and bears a negative charge.
• In a reduction by sodium borohydride, hydride ion adds
to the partially positive carbonyl carbon which leaves a
negative charge on the carbonyl oxygen.
• Reaction of this intermediate with aqueous acid gives
the alcohol.
17-32
Reduction
-
H:
+
C O
H
C O
H3 O +
-
H
C O-H
Hydride
ion
O
O-
NaBH4
H
+
H3 O
O-H
H
• Reduction by NaBH4 does not affect a carbon-carbon
double bond or an aromatic ring.
O
C
H
1 . NaBH4
CH2 OH
2 . H2 O
Cin namaldehyde
Cinnamyl alcoh ol
17-33
Reduction
• In biological systems, the agent for the reduction of
aldehydes and ketones is the reduced form of
nicotinamide adenine dinucleotide, abbreviated NADH
(Section 27.3B)
• This reducing agent, like NaBH4, delivers a hydride ion
to the carbonyl carbon of the aldehyde or ketone.
• Reduction of pyruvate, the end product of glycolysis,
by NADH gives lactate (anaerobic respiration)
O
CH3 -C-COO
Pyruvate
-
NADH
O
CH3 -C-COO
H
H3 O+
O-H
CH3 -C-COO
H
Lactate
17-34
Addition of Alcohols
Addition of a molecule of alcohol to the carbonyl group of
an aldehyde or ketone forms a hemiacetal (a half-acetal).
• The functional group of a hemiacetal is a carbon
bonded to one -OH group and one -OR group.
• In forming a hemiacetal, -H of the alcohol adds to the
carbonyl oxygen and -OR adds to the carbonyl carbon.
O
H
C + O-CH2 CH3
H
Benzaldehyde Ethanol
O-H
C OCH2 CH3
H
A hemiacetal
*For this test, just know that Aldehyde + Alcohol  Hemiacetal
*Hemiacetal product contains –OH and ether
17-35
Addition of Alcohols
• Hemiacetals are generally unstable and are only minor
components of an equilibrium mixture except in one
very important type of molecule.
• When a hydroxyl group is part of the same molecule
that contains the carbonyl group and a five- or sixmembered ring can form, the compound exists almost
entirely in a cyclic hemiacetal form.
O
5
4
3
2
1
H
O-H
4-Hyd roxypentanal
redraw to
show the -OH
an d -CHO clos e
to each other
3
2
1
4
5
O
H
C
H
O
H
O-H
O
A cyclic hemiacetal
• -H of the alcohol adds to the carbonyl oxygen
and –O (from –OH) adds to the carbonyl carbon,
closing the ring. *This is how glucose becomes
cyclic in our bodies! (Next unit)
17-36
Carboxylic Acids
• Ch 18
17-37
Carboxylic Acids
• Carboxylic acids: another class of organic compounds
containing the carbonyl group.
• The functional group of a carboxylic acid is a carboxyl
group, which can be represented in any one of three
ways.
O
C-OH
COOH
CO2 H
18-38
Nomenclature
IUPAC names
• For an acyclic carboxylic acid, take the longest carbon
chain that contains the carboxyl group as the parent
alkane.
• Drop the final -e from the name of the parent alkane
and replace it by -oic acid.
• Number the chain beginning with the carbon of the
carboxyl group.
• Because the carboxyl carbon is understood to be
carbon 1, there is no need to give it a number.
18-39
Nomenclature
• In these examples, the common name is given in
parentheses (do not have to know for test).
O
6
O
1
3
OH
Hexanoic acid
(Caproic acid )
1
OH
3-Methylbu tanoic acid
(Isovaleric acid)
• An -OH substituent is indicated by the prefix hydroxy-;
an -NH2 substituent by the prefix amino-.
OH
5
O
1
OH
5-Hydroxyhexanoic acid
H2 N
COOH
4-Aminobenzoic acid
18-40
Nomenclature
• To name a dicarboxylic acid, add the suffix -dioic acid
to the name of the parent alkane that contains both
carboxyl groups; thus, -ane becomes -anedioic acid.
• The numbers of the carboxyl carbons are not indicated
because they can be only at the ends of the chain.
O
HO
2
O
1
3
OH
HO
O
1
OH
O
Ethan edioic acid Prop aned ioic acid
(Malonic acid )
(Oxalic acid )
O
HO
4
O
5
1
OH
O
Butaned ioic acid
(Succinic acid)
HO
O
O
1
OH
Pen tanedioic acid
(Glutaric acid)
HO
6
1
OH
O
Hexan edioic acid
(Ad ipic acid)
18-41
Name these
18-42
Nomenclature
Structure
HCOOH
CH3 COOH
CH3 CH2 COOH
CH3 (CH2 ) 2 COOH
CH3 (CH2 ) 3 COOH
CH3 (CH2 ) 4 COOH
CH3 (CH2 ) 6 COOH
CH3 (CH2 ) 8 COOH
CH3 (CH2 ) 1 0 COOH
CH3 (CH2 ) 1 2 COOH
CH3 (CH2 ) 1 4 COOH
CH3 (CH2 ) 1 6 COOH
CH3 (CH2 ) 1 8 COOH
IU PAC N ame
(acid)
methanoic
ethan oic
propanoic
bu tanoic
pen tanoic
hexan oic
octanoic
decanoic
dodecanoic
tetradecan oic
hexad ecanoic
octadecanoic
eicosan oic
Common
N ame
formic
acetic
propionic
bu tyric
valeric
cap roic
cap rylic
cap ric
lauric
myristic
palmitic
stearic
arachid ic
D erivation
Latin : formica, ant
Latin : acet um, vinegar
Greek: propion, firs t fat
Latin : buty rum, b utter
Latin : valere, to be s trong
Latin : caper, goat
Latin : caper, goat
Latin : caper, goat
Latin : laurus , laurel
Greek: my ris tikos, fragrant
Latin : palma, palm tree
Greek: st ear, solid fat
Greek: arachis, p eanut
18-43
Physical Properties
The carboxyl group contains three polar covalent bonds;
C=O, C-O, and O-H.
• The polarity of these bonds determines the major
physical properties of carboxylic acids.
18-44
Physical Properties
• Carboxylic acids have significantly higher boiling
points than other types of organic compounds of
comparable molecular weight.
• Their higher boiling points are a result of their polarity
and the fact that hydrogen bonding between two
carboxyl groups creates a dimer that behaves as a
higher-molecular-weight compound.
hydrogen bonding
between two
molecules
H3 C
O
+
H O
C
C
O
H
+
CH3
O
-
18-45
Physical Properties
Carboxylic acids are more soluble in water than are
alcohols, ethers, aldehydes, and ketones of comparable
molecular weight.
Boilin g
Solubility
Molecular Poin t
Weigh t
(°C) (g/100 mL H 2O)
Structu re
N ame
CH3 COOH
CH3 CH2 CH2 OH
CH3 CH2 CHO
acetic acid
60.5
1-prop anol
prop anal
CH3 (CH2 ) 2 COOH butan oic acid
CH3 (CH2 ) 3 CH2 OH 1-pentan ol
pentan al
CH3 (CH2 ) 3 CHO
60.1
58.1
118
97
48
infinite
infinite
16
88.1
88.1
86.1
163
137
103
infinite
2.3
slight
18-46
Fatty Acids
Fatty acids: Long chain carboxylic acids derived from
animal fats, vegetable oils, or phospholipids of biological
membranes.
• More than 500 have been isolated from various cells
and tissues.
• Most have between 12 and 20 carbons in an
unbranched chain.
• In most unsaturated fatty acids, the cis isomer
predominates; trans isomers are rare.
18-47
Fatty Acids
Table 18.3 The Most Abundant Fatty Acids in Animal Fats,
Vegetable Oils, and Biological Membranes.
C arbon Atoms :
Dou ble Bon ds * S tru ctu re
S atu rate d Fatty Acids
12:0
CH3 ( CH2 ) 1 0 COOH
C omm on
Name
Me l ti n g Poi n t
(°C )
l au ric aci d
44
14:0
CH3 ( CH2 ) 1 2 COOH
myris tic acid
58
16:0
CH3 ( CH2 ) 1 4 COOH
palmi tic acid
63
18:0
CH3 ( CH2 ) 1 6 COOH
s te ari c acid
70
arach idi c aci d
77
CH3 ( CH2 ) 1 8 COOH
20:0
Un s atu rate d Fatty Acids
16:1
CH3 ( CH2 ) 5 CH= CH( CH2 ) 7 COOH
palmi tol e ic acid
ole i c aci d
18:1
CH3 ( CH2 ) 7 CH= CH( CH2 ) 7 COOH
18:2
CH3 ( CH2 ) 4 ( CH= CHCH2 ) 2 ( CH 2 ) 6 COOH l in ole i c aci d
18:3
CH3 CH2 ( CH= CHCH2 ) 3 ( CH 2 ) 6 COOH
20:4
CH3 ( CH2 ) 4 ( CH= CHCH2 ) 4 ( CH 2 ) 2 COOH arach idon ic aci d
l in ole n i c aci d
1
16
-5
-11
-49
* Th e firs t n u m ber i s the n u mber of carbon s i n th e fatty acid; the se con d is th e
n u mbe r of carbon -carbon doubl e bon ds i n i ts h ydrocarbon ch ai n.
18-48
Fatty Acids
Unsaturated fatty acids generally have lower melting
points than their saturated counterparts.
COOH S te aric acid (18:0)
(mp 70°C )
COOH O l e ic acid (18;1)
(mp 16°C )
COOH Lin ol e ic acid (18:2)
(mp-5°C )
COOH Lin ol e ni c aci d (18:3)
(mp -11°C )
18-49
Fatty Acids
Saturated fatty acids are solids at room temperature.
• The regular nature of their hydrocarbon chains allows
them to pack together in such a way as to maximize
interactions (by London dispersion forces) between
their chains.
COOH
COOH
COOH
COOH
COOH
18-50
Fatty Acids
In contrast, all unsaturated fatty acids are liquids at room
temperature because the cis double bonds interrupt the
regular packing of their hydrocarbon chains.
COOH
COOH
COOH
COOH
COOH
18-51
Link to Biology
• Amino Acids (monomers of proteins)
have carboxyl groups, as well as amino
groups (see amine section of PPt)
18-52
Soaps
• Natural soaps are sodium or potassium salts of fatty
acids.
• They are prepared from a blend of tallow and palm oils
(triglycerides).
• Triglycerides are triesters of glycerol. (Esters will be
covered shortly)
• The solid fats are melted with steam and the water
insoluble triglyceride layer that forms on the top is
removed.
18-53
Soaps
Preparation of soaps begins by boiling the triglycerides
with NaOH. The reaction that takes place is called
saponification (Latin: saponem, “soap”). Boiling with KOH
gives a potassium soap.
O
O CH2 OCR
saponification
+
3
N
aOH
RCOCH
O
CH2 OCR
A trigl yce ri de
( a tri e ste r of gl yce rol )
CH2 OH
CHOH
+
O
+
3 RCO N a
CH2 OH
1,2,3-Propan etriol S odiu m soaps
(Glyce rol; gl yce rin )
What triglyceride did you use in your lab?
18-54
Soaps
In water, soap molecules spontaneously cluster into
micelles, a spherical arrangement of molecules such that
their hydrophobic parts are shielded from the aqueous
environment, and their hydrophilic parts are in contact
with the aqueous environment.
18-55
Soaps
When soaps and dirt, such as grease, oil, and fat stains
are mixed in water, the nonpolar hydrocarbon inner parts
of the soap micelles “dissolve” the nonpolar substances.
18-56
Acidity of Carboxylic Acids
Carboxylic acids are relatively weak acids, however,
substituents of high electronegativity, especially -OH, Cl, and -NH3+, near the carboxyl group increase the
acidity of carboxylic acids.
Formula: CH3 COOH
N ame:
pK a:
Acetic
acid
4.76
ClCH2 COOH
Cl2 CHCOOH
Cl3 CCOOH
Chloroacetic D ichloroacetic Trich loroacetic
acid
acid
acid
2.86
1.48
0.70
In creasing acid strength
18-57
Ch 19
• Esters, Anhydrides, Amides
18-58
Carboxyl Derivatives
Three classes of compounds derived from carboxylic
acids: anhydrides, esters, and amides.
• Each is related to a carboxyl group by loss of H2O
(DEHYDRATION SYNTHESIS).
O
O O
RCOH
RCOCR'
A carboxyli c aci d An an h ydri de
-H2 O
O
O
RC- OH H- OCR'
O
RCOR'
An e s te r
-H2 O
O
RCN H 2
An ami de
-H2 O
O
O
RC- OH H- OR' RC- OH H- NH 2
19-59
Fischer Esterification (Ch 19)
Fischer esterification is one of the most commonly used
methods for the preparation of esters.
• In Fischer esterification, a carboxylic acid is reacted
with an alcohol in the presence of an acid catalyst,
most commonly concentrated sulfuric acid.
O
O
H2 SO4
CH3 C-OH + H-OCH2 CH3
Ethanoic acid
Ethanol
(Acetic acid) (Ethyl alcohol)
CH3 COCH2 CH3 + H2 O
Ethyl ethanoate
(Ethyl acetate)
*-H is removed from alcohol and –OH from carboxylic acid
ALCOHOL + ACID  ESTER + WATER
18-60
Triglycerides
• Glycerol (1,2,3 –propantriol) +
3 Fatty acidsTriglyceride
+H2O
• Triglycerides are esters
18-61
Esters
Ch 19
• Alcohol + Acid  Ester + Water
• Many have pleasant, fruity odors
• General formula: RCOOR
• Naming: 2 words. First, name the alkyl group (next to
the O), then name the parent (from the acid) and
change the –ic ending to –ate
• Ex- draw methyl ethanoate (ethanoate’s common
name is acetate)
18-62
Anhydrides
The functional group of an anhydride is two carbonyl
groups bonded to the same oxygen.
• The anhydride may be symmetrical (from two identical
acyl groups), or mixed (from two different acyl groups).
• To name an anhydride, drop the word "acid" from the
name of the carboxylic acid from which the anhydride
is derived and add the word "anhydride”.
O O
CH3 C-O-CCH3
Acetic an hydrid e
*We will use anhydrides to synthesize aspirin in lab
19-63
Amides (will not test, just FYI)
The functional group of an amide is a carbonyl group
bonded to a nitrogen atom.
• To name an amide, drop the suffix -oic acid from the
IUPAC name of the parent acid, or -ic acid from its
common name, and add -amide.
• If the amide nitrogen is also bonded to an alkyl or aryl
group, name the group and show its location on
nitrogen by N- ; two alkyl or aryl groups by N,N-di-.
O
O
CH3 CNH2
CH3 CNHCH3
Acetamide N-Methylacetamide
(a 1° amide)
(a 2° amide)
O
HCN(CH3 ) 2
N,N-Dimethylformamide
(a 3° amide)
19-64
Hydrolysis The “reverse” of dehydration
synthesis.Decomposition by the addition of water
• Esters: hydrolyze very slowly, even in boiling
water.
• Hydrolysis becomes considerably more rapid,
however, when the ester is heated in aqueous acid or
base.
• Hydrolysis of esters in aqueous acid is the reverse of
Fischer esterification.
O
CH3 COCH2 CH3
Eth yl acetate
+
H2 O
H+
O
CH3 COH + CH3 CH2 OH
Acetic acid
Ethanol
19-65
Hydrolysis of Esters (for lab only)
• We can also hydrolyze an ester using a hot aqueous
base, such as aqueous NaOH.
• This reaction is often called saponification, a reference
to its use in the manufacture of soaps.
• The carboxylic acid formed in the hydrolysis reacts
with hydroxide ion to form a carboxylic acid anion.
• Each mole of ester hydrolyzed requires one mole of
base.
O
CH3 COCH2 CH3+ N aOH
Eth yl ace tate
H2 O
h e at
S odiu m
h ydroxide
O
CH3 CO - N a++ CH3 CH2 OH
S odiu m
ace tate
Eth an ol
19-66
Hydrolysis of Anhydrides
• Carboxylic anhydrides, particularly the low-molecularweight ones, react readily with water (hydrolyze) to
give two carboxylic acids.
O O
CH3 COCCH3 + H2 O
Acetic an hydrid e
O
O
CH3 COH + HOCCH3
Acetic acid Acetic acid
19-67
Hydrolysis of Amides (not on test)
Amides require more vigorous conditions for hydrolysis
in both acid and base than do esters.
• Hydrolysis in hot aqueous acid gives a carboxylic acid
and an ammonium ion.
• Hydrolysis is driven to completion by the acid-base
reaction between ammonia or the amine and the acid to
form an ammonium ion.
• Each mole of amide hydrolyzed requires one mole of
acid.
O
CH3 CH2 CH2 CNH2 + H2 O + HCl
Butan amide
H2 O
heat
O
+ CH3 CH2 CH2 COH + NH4 Cl
Butan oic acid
19-68
Hydrolysis of Amides
• Hydrolysis of an amide in aqueous base gives a
carboxylic acid salt and ammonia or an amine.
• Hydrolysis is driven to completion by the acid-base
reaction between the carboxylic acid and base to form
a salt.
• Each mole of amide hydrolyzed requires one mole of
base.
O
CH3 CNH
A cetanilide
+
NaOH
H2 O
heat
O
+
CH3 CO Na + H2 N
Sodiu m
acetate
An iline
19-69
Reaction with Alcohols
Anhydrides react with alcohols and phenols to give an
ester and a carboxylic acid.
O O
CH3 COCCH3 + HOCH2 CH3
Ace ti c an h ydride Eth an ol
O
O
CH3 COCH 2 CH 3 + HOCCH3
Eth yl ace tate
Ace ti c aci d
Aspirin is prepared by the reaction of salicylic acid with
acetic anhydride.
COOH
OH
S ali cyl ic acid
+
O
O
CH3 C- O-CCH3
Ace ti c an h ydride
COOH
+
OCCH 3
O
Ace tyls ali cyl ic aci d
(Aspi ri n )
O
CH3 C- OH
Ace ti c aci d
19-70
Reaction with Amines
Anhydrides react with ammonia and with 1° and 2° amines
to form amides.
• Two moles of amine are required; one to form the
amide and one to neutralize the carboxylic acid byproduct.
O
O
CH3 C- O-CCH3 + N H3
O
CH3 C- OH + N H3
O
O
CH3 C- O-CCH3 + 2 N H3
Ace ti c
an h ydri de
O
O
CH3 CN H2 + CH3 C- OH
O
CH3 CO - N H4 +
O
O
CH3 CN H2 + CH3 CO - N H4 +
Ace tami de
Amm on iu m
ace tate
19-71
Reaction with Amines
• Esters react with ammonia and with 1° and 2° amines to
form amides.
O
O
OCH2 CH3 + NH3
Eth yl 2-ph e n yl ace tate
NH2 + CH3 CH2 OH
2-Ph e n ylace tami de
• Thus, an amide can be prepared from a carboxylic acid by
first converting the carboxylic acid to an ester by Fischer
esterification and then reaction of the ester with an amine.
• Amides do not react with ammonia or with amines
19-72
Phosphoric Anhydrides
The functional group of a phosphoric anhydride is two
phosphoryl (P=O) groups bonded to the same oxygen
atom.
O O
HO-P-O-P-OH
OH OH
D iphosph oric acid
(Pyroph os phoric acid)
O O
O-P-O-P-OO- OD iphosph ate ion
(Pyroph os phate ion)
O O O
HO-P-O-P-O-P-OH
OH OH OH
Triphosp horic acid
O O O
O-P-O-P-O-P-O
O- O- OTriph os phate ion
19-73
Phosphoric Esters
• Phosphoric acid forms mono-, di-, and triphosphoric
esters.
• In more complex phosphoric esters, it is common to
name the organic molecule and then indicate the
presence of the phosphoric ester by either the word
"phosphate" or the prefix phospho-.
• Dihydroxyacetone phosphate and pyridoxal phosphate
are shown as they are ionized at pH 7.4, the pH of
blood plasma.
O
CH3 O-P-OH
OCH3
D imethyl ph os phate
CH2 OH
CO O
CH2 -O-P-OOD ih yd roxyacetone
p hosphate
O
CHO
HO
CH2 O-P-OOH3 C N
Pyridoxal ph os phate
19-74
Step-Growth Polymerization
Step-growth polymers are formed by reaction between
two molecules, each of which contains two functional
groups. Each new bond is created in a separate step.
• in this section, we discuss three types of step-growth
polymers; polyamides, polyesters, and polycarbonates.
19-75
Polyamides
Nylon-66 was the first purely synthetic fiber.
• It is synthesized from two six-carbon monomers.
rem ove H2O
H
N
O
H
h e at
+
N
H
OH
- H2 O
O
H
He xan edi oi c acid
1,6-He xan e diami n e
(Adi pic acid)
(He xame th yle n e di ami n e)
HO
O
O
N
H
Nylon -66
(a pol yam ide )
H
N
n
19-76
Polyamides
The polyaromatic amide known as Kevlar is made from an
aromatic dicarboxylic acid and an aromatic diamine.
remove H 2O
O
nHOC
O
COH
H
H
heat
+
N
N
-H2 O
H
H
1,4-Benzen edicarboxylic 1,4-Benzen ediamine
acid
(p-Phen ylened iamin e)
(Terep hthalic acid)
O
C
O
CNH
NH
n
Kevlar
(a p olyaromatic amide)
19-77
Polyesters
The first polyester involved polymerization of this diester
and diol.
remove CH 3 OH
O
OCH3
HO
+
CH3 O
O
Dimethyl terephthalate
OH
1,2-Ethaned iol
(Ethylene glycol)
O
heat
-CH3 OH
O
O
O
n
Poly(eth ylene tereph thalate)
(D acron , Mylar)
19-78
Polycarbonates
Lexan, the most familiar polycarbonate, is formed by
reaction between the disodium salt of bisphenol A and
phosgene.
+
remove N a Cl
O
CH3
+
-
Na O
-
O Na
+
CH3
D isodium salt of Bis phenol A
+ Cl
Cl
-NaCl
Phosgen e
O
CH3
O
CH3
Lexan
(a p olycarbonate)
O
n
19-79
Hydrolysis
• The “reverse” of dehydration synthesis
• ESTERS: Ex
19-80