Preparation of methoxy benzene

(1) From alkyl halides

(ii) By heating alkyl halide with dry silver oxide

heat

2RX + Ag₂O ————→ R – O – R + 2AgX,

heat

2C₂H₅Br + Ag₂O ————→ C₂H₅OC₂H₅ + 2AgBr
^{Ethyl bromide Diethyl ether}

(2) From alcohols

(i) By dehydration of alcohols

(a) With conc. H₂SO₄ at 140° C

ROH + HOR ——————→ ROR + H₂O.

^{2 molecules of alcohol} 140^oC ^Ether

• In this reaction alcohol must be present in excess.

• This reaction is mainly applicable for the dehydration of primary alcohols. Secondary and tertiary alcohols form alkenes mainly.

• When this reaction is carried out between different alcohols then there is a mixture of different ethers is obtained.

(b) With Al₂O₃ at 250° C:

Al₂O₃

2ROH ——————→ R – O – R + H₂O
250^oC

(ii) By the action of diazomethane on alcohols : This reaction is in presence of catalyst, boron trifluoride or HBF₄.

BF₃

ROH + CH₂N₂ ——————→ R – O – CH₃ + N₂

(a) This method is very useful for preparing mixed ethers.

(b) In higher cases, there can be 1, 2-hydride or 1, 2-methyl shift to form more stable carbonium ion.

(3) Reaction of lower halogenated ether with Grignard reagent

ROCH₂X + XMgR' ——→ ROCH₂R' + MgX₂
^{Halogeneted Grignard Higher}

^{ether reagent ether}

(i) Higher members can be prepared by the action of grignard reagent on lower halogenated ethers.

(ii) Ether form soluble coordinated complexes with grignard reagent.