Class 12 Chemistry Ethers Notes

Class 12 Chemistry Ethers Notes
Chapter 12 – Ethers | Nepal eNotes
CHEMISTRY • CHAPTER 12

Ether (R−O−R)

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Ether (R−O−R)

Eg

CH3−O−CH3

methoxymethane

(dimethylether)

CH3−CH2−O−CH2−CH3

Ethoxyethane

diethyl ether

CH3−CH(O−CH3)−CH3

2−methoxypropane

O

diphenylether

O−CH₃

methoxybenzene

CH3−CH2−CH2−O−CH3

methoxypropane

Types of ether

1) Aliphatic ether (simple ether)

a) Without benzene ring (symmetrical aliphatic ether) simple ether

Eg:

CH3−O−CH3

methoxymethane

CH3−CH2−O−CH2−CH3

Ethoxyethane

b) Unsymmetrical aliphatic ether (mixed ether)

Eg:

CH3−CH2−O−CH3

methoxyethane

CH3−CH(O−CH3)−CH3

2−methoxypropane

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2. Aromatic ether

having benzene ring

a) Alkyl aryl ether

O−CH₃ methoxybenzene

b) Diaryl ether

O diphenylether

Isomerism in ether

1) Chain isomers

longest chain different.

CH3−CH2−CH2−CH2−O−CH3

methoxybutane

CH3−CH(CH3)−CH2−O−CH3

1−methoxy−2−methylpropane

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2) Position isomers

Eg

CH3−CH2−CH2−O−CH3    and    CH3−CH(O−CH3)−CH3

methoxypropane     2−methoxypropane

3) Functional isomers

Eg

CH3−O−CH3    and    CH3−CH2−OH

methoxymethane     Ethyl alcohol (ethanol)

4) Metamers

The isomers in which the arrangement of alkyl group around the oxygen is different is called metamers.

Eg:

CH3−CH2−CH2−O−CH3    and    CH3−CH2−O−CH2−CH3

methoxypropane     ethoxyethane

General preparation of ether

6) By Williamson’s synthesis (Etherification) (From haloalkane)

Primary haloalkane react with sodium or potassium alkoxide gives ether.

CH3−CH2−Cl + NaO−CH2−CH3 → CH3−CH2−O−CH2−CH3 + NaCl

chloroethane + sod. ethoxide → ethoxyethane

CH3−CH2−Cl + Na−O−CH3 → CH3−CH2−O−CH3 + NaCl

chloroethane → methoxyethane

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CH3−CH(ONa)−CH3 + Cl−CH3 → CH3−CH(O−CH3)−CH3 + NaCl

methoxypropane

Sod. phenoxide + CH3−I → methoxybenzene + NaI

Anisole

Chlorobenzene + NaOCH3 → No rxn

because haloarene are less reactive toward nucleophilic substitution rxn.

7) From alcohol

a) By heating with Al2O3 (Alumina)

Alcohol when heated with alumina at 250°C gives symmetrical ether.

CH3−CH2−OH Al2O3, 250°C→ CH3−CH2−O−CH2−CH3 + H2O

ethoxyethane

b) By heating conc H2SO4 (laboratory preparation of ethoxyethane / diethyl ether)

Ethyl alcohol when heated with conc H2SO4 at 140°C gives diethyl ether. this rxn is used in laboratory.

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preparation of ethoxyethane or diethylether.

2CH3−CH2−OH + H2SO4 140°C, Δ→ CH3−CH2−O−CH2−CH3 + H2O

ethanol (ethyl alcohol) → diethyl ether

Properties

  • lower member of ether are volatile liquid.
  • Ether are soluble in water because they produce inter-molecular H-Bond with water.
Fig: Intermolecular H-bond betn ether and water R O R δ− H−O−H δ+ δ−
VVI: Boiling point of ether is very much lower than that of isomeric alcohol because alcohol produce inter-molecular H-bond but ether doesn’t.

Chemical properties

1) Rxn due to etheral oxygen

a) Rxn with conc H2SO4 or HCl

Ether react with conc H2SO4 or HCl at cold condition gives oxonium salt.

C2H5−O−C2H5 + H2SO4 cold→ [C2H5−O(H)−C2H5]+ HSO4−

diethyl oxonium hydrogen sulphate

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C2H5−O−C2H5 + HCl cold→ [C2H5−O(H)−C2H5]+ Cl−

diethyl oxonium chloride

Imp b) Rxn with air

Ether when react with atmospheric oxygen in presence of sunlight gives peroxide of ether.

C2H5−O−C2H5 + O2 sunlight→ Peroxide of diethyl ether
NOTE: peroxide of ether are thermally unstable. It’s means it can may explosion on long heating. this is the reason for it is dangerous to boil old sample of ether for long time.

Iron wire is used during packaging of ether because iron as high affinity toward oxygen then ether.

2) Rxn due to cleavage of C−O bond

a) Rxn with HX (HI)

Ether react with HI gives alcohol and haloalkane.

CH3−CH2−O−CH2−CH3 + HI → CH3−CH2−OH + CH3−CH2−I

alcohol    Iodoethane

Anisole (methoxybenzene) + HI → Phenol + CH3−I
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If ether is unsymmetrical than smaller alkyl group produce iodoalkane.

CH3−CH2−O−CH3 + HI → CH3−CH2−OH + CH3−I

methoxyethane → ethyl alcohol + Iodomethane

if HI is excess than thus obtain alcohol further react with HI gives Haloalkane it means alcohol is not obtaine as a final product.

CH3−CH2−O−CH3 + HI → CH3−CH2−OH + CH3−I
CH3−CH2−OH + HI excess→ CH3−CH2−I + H2O

Iodoethane

b) Rxn with PCl5

Ether react with PCl5 gives chloroalkane.

CH3−CH2−O−CH2−CH3 + PCl5 → 2CH3−CH2−Cl + POCl3

3) Rxn due to alkyl group (halogenation)

CH3−CH2−O−CH2−CH3 + 2Cl2 dark→ CH3−CH(Cl)−O−CH(Cl)−CH3 + 2HCl

(1,1′)−dichloro diethyl ether

C2H5−O−C2H5 + 10Cl2 sunlight / hν→ C2Cl5−O−C2Cl5 + 10HCl

perchlorodiethyl ether

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Uses of diethylether

  • diethylether is used as general anaesthetic agent.
  • It is used as a solvent in the preparation of grignard reagent.
  • It is good solvent for fats, oil etc.
  • It is used as refrigerator.
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