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Synthesis of Benzylamine and Derivatives


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Example 1, Preparation of Benzylamine

  • 28% Aqueous Ammonia, 810g
  • Benzyl chloride, 84.3g
  • 49% Aqueous NaOH, 52.3g
  • Diethyl Ether, 200g

A three-necked flask was equipped with a reflux condenser dropping funnel and an agitator. All of the aqueous ammonium hydroxide solution was poured into the flask, then the benzyl chloride was introduced drop by drop; over a period of two hours with constant stirring of the mixture. The exothermic heat of reaction kept the temperature between 30-34C during this period. When it is desired to introduce the benzyl chloride at a faster rate, conventional cooling means can be employed to control the temperature. A large excess of ammonia was employed as the molar ratio of reactants was 20:1. An additional two hours was allowed to insure completion of the following reaction:

Then the equimolecular quantity of caustic soda solution was added. When quiescent, the mixture split into an aqueous layer and an oily layer. After separating these two layers by use of a separatory funnel, the aqueous phase was made available for further repeated use by merely adding sufficient ammonium hydroxide to bring the total quantity of ammonia up to the original figure. The oily layer was steam distilled until no further oily constituent was visible in the condensed distillate as it dripped down the condenser tube. This distillate was saturated with sodium chloride and successively extracted with an initial 80 and three 40 gram batches of ethyl ether. Upon evaporation of the ether from the extract, 52g of crude benzylamine remain which was distilled at atmospheric pressure. 41g grams of substantially pure benzylamine distilled over in the boiling range 185-192C, while the residue was found to contain an additional 2.3g of benzylamine and 8.7g of other matter which was believed to consist entirely of dibenzyl amine. Thus the total yield of benzylamine was 43.3g or 60.7% based on the weight of benzyl chloride.

Example 2, Preparation of N-Methylbenzylamine

  • 25% Aqueous Methylamine, 6 moles
  • Benzyl Chloride, 1 mole
  • 50% Aqueous NaOH, 1 mole
  • Diethyl Ether, 200 grams

The procedure of Example I was repeated using the above materials. The reaction here took the course:

N-Methylbenzylamine was obtained in 75% yield and with a boiling point of 82C/27 mmHg.

Example 3, Preparation of N,N-dimethylbenzylamine

  • 25% Aqueous Dimethylamine, 1088 grams
  • Benzyl Chloride, 126.6 grams

In the apparatus of Example 1, the benzyl chloride was added dropwise over a two-hour period to the amine (molar ratio 1 to 6) at a rate sufficient to maintain the temperature below 40C. Stirring was continued at room temperature for an additional hour to insure completion of the reaction denoted by the equation below.

Thereafter the reaction mixture was cooled in a separatory funnel while standing in a refrigerator maintained at 5 C. and separated into two layers. The upper oily layer, weighing 111.5g, was removed and steam distilled until no further oleaginous component was observed in the distillate as it came over. The crude distillate was found to contain 103.5g of N,N-dimethylbenzylamine (76.1% of theory), 3.3g of dimethylamine and no quaternary salts. The dimethylamine was distilled off below 29C under atmospheric pressure from the N,N-dimethylbenzylamine (bp 82C/18mmHg).


References

[1] US Patent 2,608,584