Preparation of Ethylamine and Diethylamine

About 80 percent of the diethylamine (boiling within 1 degree) can be obtained by two fractional distillations. A further quantity of the mixed bases can be produced from the monoethylamine by treating it with more ethyl bromide. 

Five hundred grams of crude monoethylamine (containing about 10 per cent of diethylamine) were dissolved in 2500 mL of alcohol and 1000 grams of ethyl bromide were added. The mixture must be cooled in ice, since much heat is evolved. After twenty-four hours 200 grams of ammonium bromide were added to fix any free bases, and the solution was treated as described above. 

As the monoethylamine can be again used for the preparation of diethylamine, about 50 percent of the monoethylamine can be converted into diethylamine. Source Gamer 1916 

Test experiments on a small scale with pure alcohol had shown that when ammonium bromide separated in quantity in the early stage of the process, the formation of triethylamine was promoted when the reaction was prolonged. The reason is fairly obvious when the probable mechanism of the process is considered, hence it was found advantageous to use alcohol containing 10 percent water. 

The alcoholic solution, separated from ammonium bromide, was concentrated by distillation (the ammonia evolved was used to charge more alcohol) until nearly all the ammonium bromide formed had separated, 362 grams of which were recovered. 

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