Ethyl benzyl ether via Williamson ether synthesis

Ethyl benzyl ether, or a-ethoxytoluene is an ether used in perfumes and as a flavoring. It also finds limited use in organic synthesis. At room temperature, ethyl benzyl ether exists as a high boiling colourless oily liquid with a pleasant fruity smell reminiscent of pineapple. I have no use for ethyl benzyl ether and only made it because I wanted to try making some kind of ether.

The easiest route to the compound is the famous williamson ether synthesis which involves the SN2 reaction between an alkoxide anion and an alkyl halide. For ethyl benzyl ether, ethoxide and a benzyl halide are used. Here is what I did.

To a two necked round bottom flask, I added 32ml of ethanol (reactant and solvent). I then attached a water circulated liebig condenser to the middle neck. Through the side neck, I added in 1.5g (0.216 moles) of lithium metal granules, then sealed the side neck with a stopper. The lithium began gently bubbling in the ethanol and slowly developed a white crust on the outside. To help the lithium react, I began refluxing the mixture. Lots of white precipitate began forming as the lithium was consumed. This should be lithium ethoxide, our nucleophile for the reaction. Once almost all the lithium had reacted and all that remained was one small piece, I added in 28ml (0.243 moles) benzyl chloride (our electrophile for the reaction) through the condenser and continued refluxing for 2 hours. With addition of the benzyl chloride, the lithium ethoxide dissolved and the mixture became yellow, and upon further reflux, orange. A fine white precipitate slowly built up during the reflux, even to a point where the mixture became noticeably viscous. This precipitate should be lithium chloride, the by-product of the reaction which is insoluble in ethanol. After, reflux, I allowed the mixture to cool to room temperature, then filtered it to remove lithium chloride. I then transferred the orange filtrate to a 250ml separatory funnel (stopcock closed), washing the round-bottom and filter flask out with 15ml of ethanol then transferring this also to the separatory funnel. I added in 50ml of water, then capped, shaked and vented the separatory funnel and allowed the layers to separate which took a while since an emulsion had formed. I drained off the aqueous phase, then washed the orange organic phase again with 50ml of water. After draining the lower aqueous phase off again, I transferred the still orange organic phase to a two necked 500ml round-bottom flask containing anhydrous calcium chloride. The calcium chloride unexpectedly dissolved into the water present and formed a small bottom layer. I sealed the side neck of the flask with a stopper and set the middle neck up for simple distillation.

 The first fraction to come over was a small amount of water carrying some ethyl benzyl ether at 92-102 C. The fraction boiling between 185-190 C was collected in a storage vial. This is the ethyl benzyl ether. After distillation, I discovered that quite a substantial amount of the ethyl benzyl ether had been steam distilled over with the water in the lower fraction. So, I separated off the upper ethyl benzyl ether layer and performed another distillation, again collecting the fraction boiling at 185-190 C. This was then combined with the earlier collected product in the vial. Finally I added some anhydrous calcium chloride to the vial to dry the product. In the end, I got 16ml of dry ethyl benzyl ether as a colourless oily liquid with a strong citrus-pineapple smell. This works out to a reasonable 52% yield.

The density of the product was 0.914/cm³ which is quite close to the established value of 0.938g/cm³ suggesting relative purity. However, there is probably some unreacted benzyl chloride present, as I made computation error and accedently used an excess of benzyl chloride.

The lithium metal first reacts with the ethanol, irreversibly generating the ethoxide anion which is a powerful nucleophile. The ethoxide then undergoes a SN2 reaction with the benzyl chloride which is electrophilic producing ethyl benzyl ether.

2 Li + 2 C2H5OH ==> 2 LiC2H5O + H2

LiC2H5O <==> Li (+) + C2H5O (-)

C6H5CH2Cl + C2H5O (-) ==> C6H5C(+)H2(C2H5O)Cl

C6H5C(+)H2(C2H5O)Cl ==> C6H5CH2OC2H5 + Cl (-)

Li (+) + Cl(-) ==> LiCl