Preparation of N-benzylurea
Procedure adapted from European patent GB619827 "Process for the Preparation
of Benzylamine and Acyl Derivatives Thereof"
Reagents
43g urea – fertilizer grade prills, but seems pure enough as it has worked fine in
the past for every reaction I have performed with them.
230ml water (plus more for recyrstallization) – ordinary tap water, not treated
with chlorine or fluoride were I live
36ml Benzyl chloride – homemade, dried over anhydrous calcium chloride for a
few hours then over 3A molecular seives for a few days, density is 1.05g/cm 3
indicating high purity
Method
To a 500ml round-bottom flask, was added urea (43g) and water (30ml). Benzyl
chloride (36ml) was then added and a liebig condenser, circulated with cold water
was attached to the flask with a steel keck clip. The mixture was then refluxed on
high heat for 6.5 hours. Upon the first few minutes of heating, all the urea
dissolved giving a cloudy bottom phase with a phase of benzyl chloride fluoting
above. With no stirring, one might expect the limited phase contact to be a
problem, however the the kinetic movement of the boiling mixture seemed
perfectly sufficient to mix the phases. During the first 30 minutes, the phases
dident mix very well, but after this, they were satisfactorily united as an emulsion.
After reflux (While still hot), the mixture consisted of a cloudy bottom phase with
a fair amount of slightly yellow upper phase. Upon cooling, both phases solidified
into a large mass of white crystals. According to the patent, these crystals should
be the crude product, benzylurea.
After reflux, the mass of cyrstals in the flask were broken up into a slurry with a
stirring rod and 100ml of water were added, the apparatus then was rearranged
to performed a simple steam distillation. The perpose of the steam distillation is
to remove unreacted benzyl chloride. The distillate was cloudy and contained a
fair amount of oily droplets1. Upon heating, allmost all the crystals dissolved but
strangely enough, a portion of them appeared to melt and form a slightely yellow
bottom phase. I really have no clue what could cause this. Once 100ml of distillate
had been collected, the distillation was halted and 100ml of hot water was added
to the distilling flask. The steam distillation was then continued continued until
another 100ml of distillate had been collected, after which, the distillation was
ended2. Without delay, the contents of the still hot distilling flask was poured into
a 250ml beaker whereapon (while cooling to room temperature), it solidified once
again into a mass of white cyrstals. Once the cyrstals had cooled completely to
room temperature, they were transferred to a filter paper and pressed to remove
as much liquid as possible. A recyrstallization was performed to purify the
product.
