Vollhardt  Capítulo 8 (Álcoois)
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Vollhardt Capítulo 8 (Álcoois)

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a p t e r I n t e g r a t i o n P r o b l e m s

322 C h a p t e r 8 H y d r o x y F u n c t i o n a l G r o u p : A l c o h o l s

We now combine the two balanced half-reactions by adding them to each other, that is, (3) 1 (2), a
procedure that cancels out the electrons to give equation (4).

 6 H
� 6 e3 RCH2OH ��3 RCH

O
B

 (3)

 14 H1 1 Cr2O7
22 1 6 e uuy 2 Cr31 1 7 H2O (2)

 3 RCH � 6 H
�

 � 2 Cr3� � 7 H2O3 RCH2OH � 14 H� � Cr2O72�
O
B

 (4)

In this form, (4) contains H1 on both sides. We can simplify it by removing the “excess” H1 to
furnish equation (5).

 2 Cr
3�8 H� Cr2O72� 7 H2O3 RCH2OH ��3 RCH

O
B

�� (5)

Finally, we add nonreacting “spectator ions” of this reaction to show the proper stoichiometry in
equation (6).

 Cr2(SO4)3Na2Cr2O74 H2SO4 7 H2O3 RCH2OH �� Na2SO4�3 RCH
O
B

�� (6)

The balanced equation (6) very nicely reveals why the reaction is run in acidic medium: H2SO4 is
consumed. It also highlights the oxidizing power of dichromate: One mole is suffi cient to effect the
oxidation of three moles of alcohol.

New Reactions
1. Acid-Base Properties of Alcohols (Section 8-3)

OR ROH RO�
�

BH

Alkyloxonium ion

�O
H

H

H�

G

D Base B�

Alcohol Alkoxide

 Acidity: RO – H < HO – H . H2N – H . H3C – H
 Basicity: RO2 < HO2 , H2N2 , H3C2

Laboratory Preparation of Alcohols
2. Nucleophilic Displacement of Halides and Other Leaving Groups by Hydroxide (Section 8-5)

RCH2X RCH2OHHO�� X��
H2O

SN2
X � halide, sulfonate
Primary, secondary (tertiary undergoes elimination)

A

B
RCHX RCHOCCH3CH3CO�

O
B
O

R�
A

RCHOH

R�
A
R�

�
SN2

HO�

Ester hydrolysis

A

A
R�CX

R

R�

A

A
R�COH

R

R�

H2O, acetone

SN1

Best method for tertiary

 C h a p t e r 8 323

3. Reduction of Aldehydes and Ketones by Hydrides (Section 8-6)

B
RCH RCH2OH

O
NaBH4, CH3CH2OH B

RCR�

O
NaBH4, CH3CH2OH A

A
RCR�

OH

H

B
RCH

Aldehyde Primary
alcohol

RCH2OH

O 1. LiAlH4, (CH3CH2)2O
2. H�, H2O

Ketone Secondary
alcohol

1. LiAlH4, (CH3CH2)2O
2. H�, H2OB

RCR�

O
A

A
RCR�

OH

H

Oxidation of Alcohols
4. Chromium Reagents (Section 8-6)

B
RCH

AldehydePrimary alcohol
RCH2OH

O
PCC, CH2Cl2

KetoneSecondary alcohol

Na2Cr2O7, H2SO4 B
RCR�

O
A

RCHR�

OH

Organometallic Reagents
5. Reaction of Metals with Haloalkanes (Section 8-7)

RX Li RLi
Alkyllithium reagent

�
(CH3CH2)2O

RX Mg RMgX
Grignard reagent

�
(CH3CH2)2O

R cannot contain acidic groups such as O – H or electrophilic groups such as C“O.

6. Hydrolysis (Section 8-7)

RLi or RMgX RHH2O�
RLi or RMgX RDD2O�

7. Reaction of Organometallic Compounds to Aldehydes and Ketones (Section 8-8)

RLi or RMgX RCH2OHCH2 O
Primary alcoholFormaldehyde

� P

R�CH

O

Secondary alcoholAldehyde

B A

A
RCR�

OH

H

RLi or RMgX �

R�CR�

O

Tertiary alcoholKetone

B A

A
RCR�

OH

R�

RLi or RMgX �

 Aldehyde or ketone cannot contain other groups that react with
 organometallic reagents such as O – H or other C“O groups.

8. Alkanes from Haloalkanes and Lithium Aluminum Hydride (Section 8-7)

RX LiAlH4� RH
(CH3CH2)2O

C h a p t e r I n t e g r a t i o n P r o b l e m s

Preparation of Alcohols section number

&

B
O

OsO4,
H2O2

1. RCOOH
2. H�, H2O

H2O,
cat. H� or HO�

R�OH,
cat. H� or HO� R� NH2 HCN HO

� H2O, HO� LiAlH4 H2O, H� or HO� R�MgBr LiAlH4
X�cat.

�
N

R

S

HO�, SN2
HO�, SN2

or
H2O, SN1

or

H2O, SN1
NaBH4

or
LiAlH4

R�MgX
or

R�Li
HX H

�
, H2O,

deprotection H
�

, H2O
�Nu

or
NuH

1. Hg(OCCH3)2
2. NaBH4

O
B

1. CH3CO2�Na�
2. HO�, H2O

Other
product:

RX

Other
product:

C(CH3)2CH2P
Product:

OH
Nu

12-10

17-6 17-7 17-9 17-11 18-5 18-9 19-11 20-4 20-4 20-4 23-4

12-78-5 8-5 8-5 8-6 9-8 9-8 9-9 12-48-8

C OH
i

{ O

ROC(CH3)3RCH2X RCHX
R�

A
RCX

R�
A

A
R� ROR

O

RCH(R�)
B

O

RCH(R�)
B O

C CG
D

G
D

P C CG
D

G
D

P

RCH(R�)
O

B
RCH(R�)

O
B

RCH(R�)
O

B
RCH(R�)

O
B

RCH2CH(R�)
O

B
RCOH

O
B

CHCRCH2

O
B

P

O
B

RCOR�

O
B

RCOR�

O
B

RCOR�

O
B

RCH

C CG
D

G
D

P

C CG
D

G
D

P

Product:

Aldol

RCH2C CHCH(R�)
H(R�)

OH
A

R O
A

A
O

B
HOCH2CH2CR

Other
product:

RCOH

O
B

Product:

Hemiacetal

R�O
Product:

Hydrate

OH

R H(R�)

HO
C

G
D

G
D

OH

R H(R�)
C

G
D

G
D

Product:
OH

R H(R�)
C

G
D

G
D

Vicinal diol

G

@ &

Product:

Product:

G@&

O

OH

HO OH

C

&

C

G
@

OC

HO

G

C

(

C

Vicinal diol

Hemiaminal

R�NH
Product:

OH

R H(R�)
C

G
D

G
D

Cyanohydrin

NC
A

A

H

R�COH

R�

Product:

A

A

B
HO

RCCR

OH

Product:Product:
O

B

&

ð 1. BH3
2. H2O2, HO�

12-8

C CG
D

G
D

P

X2, H2O

Product:

G

G@&

O

X

OH
C C

(

C
12-6

C CG
D

G
D

P

12-11

3
2
4

Reactions of Alkyllithium and Grignard Reagents section number

R–H
(R–D) RCH2OH H

OH

R� R C
A

A
OO

R�

OH

R� R C
A

A
OO

R�C Cðq

O

G

G D

D
PC C

C
A

�

RCHPP(C6H5)3
O O O

A

A

A

A
R C C C

OH
J

G
RCOH

B
O

R� C R

R

OH

O O
A

A
R�CR

B
O

R�CR
B

O R2Nð ðCHR
�

ð

�

SS
N R

N
SS

(RLi)
R2NHR�CqN

GD

G GD
PC C

C

CuI, O
B

CO2 B

CuI,
 O

R�CCl
B

R�COR�

ORCH2P(C6H5)3
(RLi)

�

(RLi)

CH2R�

H2O
(or D2O) H2CPO R�CH

B
O

R�CR�
B

O
R�OH R�CqCH

G

G

G

D G

D

D
PC C

C
H

(RLi)
R�

O

R R�

OH

R�O� M� � M�

� M�

RLi or RMgBr

8-7 8-8 8-8 8-8 9-1 9-9 13-3 14-4 15-8

17-12 18-10 19-6 20-2 20-4 20-8 21-4 22-1 23-5 25-6

ð

�

3
2
5

326 C h a p t e r 8 H y d r o x y F u n c t i o n a l G r o u p : A l c o h o l s

Important Concepts
1. Alcohols are alkanols in IUPAC nomenclature. The stem containing the functional group gives

the alcohol its name. Alkyl and halo substituents are added as prefi xes.

2. Like water, alcohols have a polarized and short O – H bond. The hydroxy group is hydrophilic
and enters into hydrogen bonding. Consequently, alcohols have unusually high boiling points
and, in many cases, appreciable water solubility. The alkyl part of the molecule is hydrophobic.

3. Again like water, alcohols are amphoteric: They are both acidic and basic. Complete deprot-
onation to an alkoxide takes place with bases whose conjugate acids are considerably weaker
than the alcohol. Protonation gives an alkyloxonium ion. In solution, the order of acidity is
primary . secondary . tertiary alcohol. Electron-withdrawing substituents increase the acidity
(and reduce the basicity).

4. The conversion of the electrophilic alkyl group in a haloalkane, Cd1 – Xd2, into its nucleophilic
analog in an organometallic compound, Cd – Md1, is an example of reverse polarization.

5. The carbon atom in the carbonyl group, C P O, of an aldehyde or a ketone is electrophilic and
therefore subject to attack by nucleophiles, such as hydride in hydride reagents or alkyl in
organometallic compounds. Subsequent to aqueous work-up, the products of such transformations
are alcohols.

6. The oxidation of alcohols to aldehydes and ketones by chromium(VI) reagents opens up important
synthetic possibilities based on further reactions with organometallic reagents.

7. Retrosynthetic analysis aids in planning the synthesis of complex organic molecules by identifying
strategic bonds that may be constructed in an effi cient sequence of reactions.

Problems
24. Name the following alcohols according to the IUPAC nomenclature system. Indicate stereochem-

istry (if any) and label the hydroxy groups as primary, secondary, or tertiary.

(a) CH3CH2CHCH3

OH
A

 (b) CH3CHCH2CHCH2CH3

Br
A

OH
A

 (c) HOCH2CH(CH2CH2CH3)2

(d)

C
H3C

CH2Cl

H
OH

A

; G^
 (e)

CH2CH3
OH/∑

 (f)

OH

Br

[

~ (g) C(CH2OH)4

(h)
H OH

CH2OH

CH2OH

H OH
 (i)

]

-

OH

CH2CH2OH
 ( j) ClH3C

CH2OH

CH2CH3

25. Draw the structures of the following alcohols. (a) 2-(Trimethylsilyl)ethanol; (b) 1-methylcyclopropanol;
(c) 3-(1-methylethyl)-2-hexanol; (d) (R)-2-pentanol; (e) 3,3-dibromocyclohexanol.

26. Rank each group of compounds in order of increasing boiling point. (a) Cyclohexane, cyclohexanol,
chlorocyclohexane; (b) 2,3-dimethyl-2-pentanol, 2-methyl-2-hexanol, 2-heptanol.

27. Explain the order of water solubilities for the compounds in each of the following groups.
(a) Ethanol . chloroethane . ethane; (b) methanol