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 CH3

CH3CHCH2CHCH3 CH3CCH3

OH OH4-methyl-2-pentanol tert-butyl alcohol

2-methyl-2-propanol 2o 3o

CH3

HO-CHCH2CH3 CH3CH2CH2-OH

sec-butyl alcohol n-propyl alcohol 2-butanol 1-propanol 2o 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 ethyl alcohol + CO2

Grape juice => “wine”

Barley => “beer”

Honey => “mead”

Rice => “sake”

~5-11% ethanol

Alcohols, synthesis:

1.

2.

3.

4. Hydrolysis of alkyl halides (CH3 or 1o)

5.

6.

7.

8.

NR NR NR some

NR NR NR 1o/2o

NR NR

NR NR NR

R-H R-X R-OH

Acids

Bases

Active metals

Oxidation

Reduction

Halogens

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 + HX R-X + H2O

a) HX: 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 CH3

CH3C-OH + HCl CH3C-Cl (room temperature) CH3 CH3

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:

1) R-OH + HX R-OH2 + X

2) X + R-OH2R-X + H2O

RDS

SN2

Mechanism for reaction of an alcohol with HX:

2o or 3o alcohols:

SN1

1) R-OH + HX R-OH2 + X

2) R-OH2 R + H2ORDS

3) R + X R-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 CH3

CH3CHCHCH3 + HBr CH3CCH2CH3 OH Br

Br-

CH3 CH3 [1,2-H] CH3

CH3CHCHCH3 CH3CHCHCH3 CH3CCH2CH3

OH2+ + + 2o carbocation 3o carbocation

CH3CH2CH2CH2CH2-OH + HBr, H+, heat

CH3CH2CH2CH2CH2-Br

1o alcohol:No rearrangement, SN2

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

1-pentanol

1-bromopentane

Most 1o? If large steric requirement…

CH3 CH3

CH3CCH2-OH + HBr CH3CCH2CH3

CH3 Brneopentyl alcohol 2-bromo-2-methylbutane

CH3 CH3 CH3

CH3CCH2-OH2+ CH3CCH2+ CH3CCH2CH3

CH3 CH3 + 1o carbocation 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 CH3

CH3CCH2-OH + PBr3 CH3CCH2-Br CH3 CH3

neopentyl alcohol 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 + NaOH H2O + CH3CH2ONa

WA WB SA SB

CH3CH2OH + CH3MgBr CH4 + MgBr(OCH2CH3)

SA SB WA WB

CH3OH + NaNH2 NH3 + CH3ONa

SA SB WA WB

5. Ester formation.

CH3CH2-OH + CH3CO2H, H+ CH3CO2CH2CH3 + H2O

CH3CH2-OH + CH3COCl CH3CO2CH2CH3 + HCl

CH3-OH + CH3SO2Cl CH3SO3CH3 + HCl

Esters are alkyl “salts” of acids.

R COH

OR C

ONa

OR C

OR'

O

carboxylic acid sodium salt ester

R S

O

O

OH R S

O

O

OK R S

O

O

OR'

sulfonic acid potassium salt ester

HO P

O

OH

OH HO P

O

OH

OR HO P

O

OR

OR RO P

O

OR

OR

phosphoric acid monoester diester triester

"Lasso" chemistry

R CO H

OR C

O R'

OH-O-R'

H+

+ + H2O

CH3CO

O H

+ H-O CHCH3

CH3 H+CH3C

O

O CHCH3

CH3 + H2O

acetic acid isopropyl alcohol isopropyl acetate

R CCl

OR C

O R'

OH-O-R'

H+

+ + HCl

CH3CO

Cl

+ H-O CHCH3

CH3 H+CH3C

O

O CHCH3

CH3 + HCl

acetyl chloride isopropyl alcohol isopropyl acetate

acid chloride + alcohol --> ester

R S

O

O

Cl

sulfonyl chloride

+ H-O-R R S

O

O

O-R + HCl

alcohol sulfonate ester

oxidation states of carbon

- oxidation

CH4 CH3OH CH2O HCO2H CO2

-4 -2 0 +2 +4

reduction -

6. Oxidation

Oxidizing agents: KMnO4, K2Cr2O7, CrO3, NaOCl, etc.

Primary alcohols:

CH3CH2CH2-OH + KMnO4, etc. CH3CH2CO2H

carboxylic acid

Secondary alcohols: OH O CH3CH2CHCH3 + K2Cr2O7, etc. CH3CH2CCH3

ketoneTeriary alcohols:

no reaction.

Primary alcohols ONLY can be oxidized to aldehydes:

CH3CH2CH2-OH + C5H5NHCrO3Cl CH3CH2CHO

pyridinium chlorochromate (PCC) aldehyde

or

CH3CH2CH2-OH + K2Cr2O7, special conditions

Alcohols, synthesis:

1.

2.

3.

4. Hydrolysis of alkyl halides (CH3 or 1o)

5.

6.

7.

8.

Alcohols, reactions:

R-|-OH

1. With HX

2. With PX3

3. (later)

RO-|-H

4. As acids

5. Ester formation

6. Oxidation