hinz - 18-6-2006 at 04:52
I'm though about making some Di- and Tri-ethylamine by gas phase alkylation. The reaction should occur in a catalyst tube filled with AlCl3. The
ammonia will be prepared by refluxing ammionia soulution and colleting the NH3 which comes out at the top of the condensor. Then I will bubble the NH3
through a gas wash bottle filled with a liquid which shouldn't dissolve too much NH3. There I can count the bubbles and later add the stoichiometrical
amount of ethanol in a small tubular furnace. There the mixture will be preheated and will form a gaseous mixture. The gas will then be inserted into
the catalyst tube in my muffle furnace. There it shall react to the ethylamines.
The reason why I don't like to make it by the EtCl or Et2SO4 method is that I don't have a synthesis description and I'm pretty sure that you have to
add some organic base to prevent the protonation of NH3 to NH4+ by the corresponding acid that will form during the reaction. Inorganic bases will
hydrolyse the EtCl or Et2SO4. The protonated NH4+ can't act as a nucleophile on the ethyl group in the alkylation agent.
But I can't find any additional infomations about the reaction conditions and the catalyst, I only know that alkylamines are prepared by gas phase
alkylation in the industry.
I would choose AlCl3 because it's a lewis acid and will form a complex with the OH group in an alcohol, leaving the alkyl cathion, ready to be
attacked by the NH3 as a nucleophile.
Does anyone know anything about the reaction temperature of the reaction tube and improvements of the catalyst?
[Edited on 18-6-2006 by hinz]
guy - 18-6-2006 at 10:29
Why use AlCl3, use Al2O3 it is more stable at higher temperatures. And how will you prevent the ammonia from reacting with the catalyst and poisoning
it?
hinz - 18-6-2006 at 11:02
Thank's guy. I've searched in my books and found a nice description in the Kirk-Othmer Vol.2 (lower aliphalic amines) and they do also mention silica
and Al2O3 and several other oxides. I thought of AlCl3 because it's an strong lewis acid and would form a complex with the OH of the alcohol, leaving
a possitive allkyl rest, but it melting and sublimating point at appr. 180°C limits the reaction temperature strongly. So I will use some Al2O3 or
some dirty silica from column chromatography as a catalyst.