alcohols alcohols r o h

Alcohols R-O-H
Classification CH3, 1o, 2o, 3o

Nomenclature:
Common names: “alkyl alcohol”
IUPAC: parent = longest continuous carbon chain
containing the –OH group.
alkane

drop -e, add –ol

prefix locant for –OH (lower number for OH)


CH3
CH3CHCH2CHCH3
OH
4-methyl-2-pentanol
2o

CH3
CH3CCH3
OH
tert-butyl alcohol
2-methyl-2-propanol
3o

CH3
HO-CHCH2CH3

CH3CH2CH2-OH

sec-butyl alcohol
2-butanol
2o

n-propyl alcohol
1-propanol
1o


Physical properties of alcohols:

polar + hydrogen bonding
relatively higher mp/bp

water insoluble!
(except for alcohols of three carbons or less)

CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2-OH
hydrophobic

hydrophilic


Oldest known organic synthesis:
“fermentation”
Sugar

+ yeast



Grape juice => “wine”
Barley => “beer”
Honey => “mead”
Rice => “sake”

~5-11% ethanol

ethyl alcohol

+ CO2


Distillation of fermented beverages to produce “distilled spirits”
with a greater percentage of ethyl alcohol (bp 78.3 oC).
Ethyl alcohol forms a binary azeotrope with water:
95% ethanol + 5% water (bp 78.15oC)

Diluted with water => “vodka” 40% ethyl alcohol in water.

“proof”: when aqueous alcohol is placed on a sample of
gunpowder and ignited, the gunpowder will burn at a minimum
concentration of 50% alcohol. This is called “100-proof”.
(proof = 2 * alcohol percent)


Add oil of juniper => gin
Add peat smoke => scotch
Age in a burned barrel => whiskey

Add peppermint => schnapps
Etc.

Ethyl alcohol is a poison. LD50 = ~10g/Kg orally in mice.
Nausea, vomiting, flushing, mental excitement or depression,
drowsiness, impaired perception, loss of coordination, stupor,
coma, death may occur. (intoxication)


Alcohols, synthesis:
1.
2.
3.
4. Hydrolysis of alkyl halides (CH3 or 1o)
5.
6.
7.
8.


R-H

R-X

R-OH

Acids

NR

NR



Bases

NR

some

Active
metals

NR




Oxidation

NR

NR

1o/2o

Reduction

NR



NR

Halogens

NR

NR

NR




Alcohols, reactions:
R-|-OH
1. With HX
2. With PX3
3. (later)
RO-|-H
4. As acids
5. Ester formation
6. Oxidation


1. Reaction of alcohols with HX: (#1 synthesis of RX)

R-OH +

a) HX:

HX 

R-X +

H2 O

HI > HBr > HCl

b) ROH: 3o > 2o > CH3 > 1o
c) May be acid catalyzed
d) Rearrangements are possible except with most 1o alcohols.


CH3CH2CH2CH2-OH

+

NaBr, H2SO4, heat



CH3CH2CH2CH2-Br

n-butyl alcohol

n-butyl bromide

1-butanol

1-bromobutane

CH3
CH3C-OH
CH3

+

HCl



CH3
CH3C-Cl
CH3

(room temperature)

tert-butyl alcohol

tert-butyl chloride

2-methyl-2-propanol

2-chloro-2-methylpropane

CH3CH2-OH

+

HI, H+, heat



CH3CH2-I

ethyl alcohol

ethyl iodide

ethanol

iodoethane


Mechanism?

CH3-OH and most 1o alcohols react with HX via SN2 mechanism

3o and 2o react with HX via SN1 mechanism

Both mechanisms include an additional, first step, protonation
of the alcohol oxygen:
R-OH + H+ 

R-OH2+

“oxonium ion”

Whenever an oxygen containing
compound is placed into an acidic
solution, the oxygen will be
protonated, forming an oxonium ion.


Mechanism for reaction of an alcohol with HX:
CH3OH or 1o alcohols:

SN2
1)

2)

R-OH

X

+

+

R-OH2

HX

R-OH2

RDS

R-X

+

+

X

H2O


Mechanism for reaction of an alcohol with HX:
2o or 3o alcohols:

SN1
1)

R-OH

2)

R-OH2

3)

R

+

+

HX
RDS

X

R-OH2
R

R-X

+

H2O

+

X


May be catalyzed by acid.

SN2 rate = k [ ROH2+ ] [ X- ]

SN1 rate = k [ ROH2+ ]

Acid protonates the -OH, converting it into a better leaving
group (H2O), increasing the concentration of the oxonium ion,
and increasing the rate of the reaction.

Rearrangements are possible (except with most 1o alcohols):
CH3
CH3CHCHCH3 + HBr



OH

Br

↑


CH3
CH3CHCHCH3
OH2+

CH3
CH3CCH2CH3



Br-

CH3
[1,2-H]
CH3
CH3CHCHCH3  CH3CCH2CH3

+
+
2o carbocation

3o carbocation


In the reaction of most 1o alcohols with HX you don't have
to worry about the possibility of rearrangements. The mechanism
is SN2 and does not involve carbocations.

CH3CH2CH2CH2CH2-OH +

HBr, H+, heat

1-pentanol
CH3CH2CH2CH2CH2-Br
1o alcohol:
No rearrangement, SN2

1-bromopentane


Most 1o? If large steric requirement…
CH3
CH3CCH2-OH
+
CH3
neopentyl alcohol

HBr

CH3

CH3CCH2CH3
Br
2-bromo-2-methylbutane


CH3
CH3CCH2-OH2+ 
CH3


CH3
CH3CCH2+ 
CH3
1o carbocation

CH3
CH3CCH2CH3
+
3o carbocation

[1,2-CH3]


2. With PX3
ROH +

PX3



RX

a) PX3 = PCl3, PBr3, P + I2
b) No rearrangements



c) ROH: CH3 > 1o > 2o
CH3
CH3CCH2-OH
CH3
neopentyl alcohol

+

PBr3 

CH3
CH3CCH2-Br
CH3
2,2-dimethyl-1-bromopropane


3. Dehydration

(later)

4) As acids.

a) With active metals:
ROH +

Na



RONa

+

½ H2 

b) With bases:
ROH +

NaOH

 NR!

CH4 < NH3 < ROH < H2O < HF


CH3CH2OH

+

WA

+



SB

+

NaNH2
SB

+

CH3CH2ONa

SA

CH3MgBr

SA

SA

H2O

WB

CH3CH2OH

CH3OH



NaOH

SB

CH4

+

MgBr(OCH2CH3)

WA



NH3
WA

+

WB

CH3ONa
WB

5. Ester formation.
CH3CH2-OH

+

CH3CO2H, H+

CH3CH2-OH

+

CH3COCl

CH3-OH

CH3SO2Cl

+



Esters are alkyl “salts” of acids.





CH3CO2CH2CH3

CH3CO2CH2CH3

CH3SO3CH3

+

HCl

+

+

H2 O

HCl


O
R C
OH

O
R C
ONa

O
R C
OR'
ester

carboxylic acid

sodium salt

O
R S OH
O

O
R S OK
O

sulfonic acid

potassium salt

O
HO P OH
OH

O
HO P OR
OH

O
HO P OR
OR

monoester

diester

phosphoric acid

O
R S OR'
O
ester
O
RO P OR
OR
triester