Chemistry - C16: Hydroxy compounds & Alcohols

Reactions of Alcohols

Combustion

1. Excess O2 → burn with Pale blue flame

2. Limited O2 → burn with Yellow flame

With Hydrogen Halide (HX)

1. Reagents: NaX & conc H2So4

2. Condition: Reflux

3. Products: Halogenoalkane

With Phosphorous halide

1. PCl5

   1. Room temp

   2. Product: white fumes HCl, Halogenoalkane, POCl3

2. PCl3, PBr3, PI3

   1. Condition: heating

   2. Products: Halogenalkane, H3PO3

With Thionyl Chloride

1. Reagent: conc. SOCL2

2. Condition: Room temp

3. Products: Halogenoalkane + HCL(g) + SO2(g)

Reaction with Sodium

Sodium sinks/disappear (not melt/dissolve) and bubbles of H2(g) evolved.

Alcohol + Metal → Sodium ethoxide/ Sodium methoxide/ Propoxide + H2 (g)

It is a redox reaction.

Oxidation

1. Reagents: K2Cr2O7 or KMnO4 + diluted H2So4 (dehydrating agent)

2. Condition: Heat or reflux

3. Product:

4. Primary alcohol → aldehydes then carboxylic acid ( gives CO2 w Na2CO3 )

5. Secondary alcohol → ketones (gives orange ppt w 2,4-dinitrophenylhydrazine)

6. Tertiary alcohol ❌ oxidized

7. Aldehydes will only be obtained if K2Cr2O7 is used, then product is immediately distilled off

Dehydration to alkenes

1. Reagent: excess conc H2So4 or Al2O3 or Sio2

2. Condition: heat at 170 DC

3. Products: alkenes + H2O

Formation of esters

1. Reagent: mixture of carboxylic acid & conc H2So4 or H3Po4

2. Condition: reflux

3. Products: Ester + H2O

Tri-iodomethane reaction (iodoform test)

1. Reagent: Iodine(aq) & Naoh(aq)

2. Condition: warm

3. Observation: yellow crystals of tri-iodomethane formed.

4. Compound must have CH3CH(OH-) for reaction to occur

Comparing acidity of alcohols and water

Ethanol is weaker acid than water coz

1. Electron donating alkyl group has +ve inductive effect

2. Intensifies the -ve charge of O2

3. Ethoxide ion readily accepts H+ ion more

4. Ethoxide ion more stable.