Reaction of alcohols

Reaction of alcohol

There are two (2) types

First, cleavage (pecah) between O and H, RCO*H

Second, cleavage (pecah) between C and O, RC*OH.

First, cleavage (pecah) between O and H, RCO*H

1. Reaction with electropositive metal. 2. Reaction with Carboxylic acid. 3. Oxidation. Reaction of 1°, 2°, 3° ROH and phenol with KMnO4 / K2Cr2O7.

Second, cleavage (pecah) between C and O, RC*OH

1. Reaction with PCl5, PCl3, SOCl2 and HX. 2. Lucas test and its observations (turns cloudy). Reaction of 1°, 2°, 3° ROH with ZnCl2 + conc. HCl. 3. Dehydration reaction (2 types). Reaction with hot concentrated sulphuric acids. a. primary alcohol (1° ROH) with one alpha hydrogen. b. secondary alcohol (2° ROH) with more than one alpha hydrogen. c. without alpha hydrogen. example: methanol, phenylmethanol. 4. Formation iodoform. Reaction 1° or 2° ROH with hot, iodine, NaOH.

First, cleavage (pecah) between O and H, RCO*H

Reactions:

1. Reaction with electropositive metal.

2ROH + 2Na, Sodium or K, Potassium (electropositive metal) –> 2RO-Na+ (salt, alkoxide) + H2

example: ……

2. Reaction with Carboxylic acid.

ROH + R’COOH (concentrated, heat, H2SO4) –> R’-C=OOR (ester)

example: ……

or… ROH + R’COCl –> R’-C=OOR (ester) + HCl

3. Oxidation. Reaction with KMnO4 / K2Cr2O7.

a. ROH + Hot, acidified, KMnO4

b. ROH + Hot, acidified, K2Cr2O7

1° ROH + KMnO4 or K2Cr2O7 –> R-CH=O (aldehyde)  [O] –> RCOOH (carboxylic acid).

2° ROH + KMnO4 or K2Cr2O7 –> RC=OR (ketone) [O] –> No further oxidation.

3° ROH + KMnO4 or K2Cr2O7 [O] –> No further oxidation.

phenol + KMnO4 or K2Cr2O7 [O] –> No further oxidation.

Second, cleavage (pecah) between C and O, RC*OH

1. Reaction with PCl5, PCl3, SOCl2 and HX.

Nucleophilic substitution;

a. ROH + PCl5 –> RCl + POCl3 + HCl.

b. 3ROH + PCl3 –> 3RCl + H3PO3

c. ROH + SOCl2 –> RCl + SO2 + HCl.

d. 3° ROH + concentrated, HCl or HBr (H2O) –> 3° RX

2. Lucas test and its observations (turns cloudy). Reaction with ZnCl2.

1° ROH + ZnCl2 + conc. HCl (need to heat up) –> 1° RCl + H2O

2° ROH + ZnCl2 + conc. HCl (in 5 minutes) –> 2° RCl + H2O

3° ROH + ZnCl2 + conc. HCl (immediately) –> 3° RCl + H2O.

3. Dehydration reaction (2 types). Reaction with hot concentrated sulphuric acids.

a. primary alcohol (1° ROH) with one alpha hydrogen.
ROH + excess, concentrated, H2SO4, 180°C –> alkene + H2O.

* what is alpha hydrogen? hydrogen that adjacent with OH.

b. secondary alcohol (2° ROH) with more than one alpha hydrogen. produce major and minor alkene follow Saytzeff’s rule.

example:
but-2-ol + excess, concentrated, H2SO4, 180°C –> but-2-ene (major) + but-1-ene (minor)+ H2O.

c. without alpha hydrogen. example: methanol, phenylmethanol. if there is no alpha hydrogen, no alkene will be formed. no reaction.

4. Formation iodoform. Reaction with hot, iodine, NaOH.

1° or 2° ROH + I2, NaOH, heat –> RC=OO- + CHI3 [iodoform (haloform), yellow precipitate, positive test]

 

 

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