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Friedel Craft Work Up of Aluminum Chloride catalyzed Reaction At Scale

kilomentor | 14 November, 2012 01:53

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Chemical terms aluminum | work

Comments

Re: Friedel Craft Work Up of Aluminum Chloride catalyzed Reaction At Scale

petr | 14/11/2012, 11:03

Addition of four equivalents of sodium fluoride with one equivalent of water is sometimes used to form easily filterable precipitate of NaAlF4.

Re: Friedel Craft Work Up of Aluminum Chloride catalyzed Reaction At Scale

anniechem | 14/11/2012, 17:08

In my previous life as a process chemist, we ran into problems while quenching a reaction that had used aluminum isopropoxide with HCl (6M if I recall correctly). On smaller scale, the issue hadn't been as much of a problem, but on large scale in the reactor, we ended up with a stuck impeller and a big freaking mess. We eventually figured out that the massive precipitation only started to occur after one equivalent of acid was already added. If you kept adding acid to the nasty mixture (and on a smaller scale, shaking the flask...obviously not possible on large scale), everything would eventually go back into solution. It has to do with the insolubility of partially hydrated aluminum salts. We eventually solved the issue by doing the quench as an inverse addition (reaction mixture pumped out of reactor, reactor charged with acid solution, then reaction mixture slowly added to acid). Worked beautifully.

kilomentor update

kilomentor | 14/11/2012, 20:17

Larry asent me a reply about what actually happened as opposite to my conjecture!

Thanks for all of the ideas; the problem has been solved. The solution is to keep the reactor temperature hot during the quench. The solids I saw during the addition of the water and conc. HCl was the product coming out of solution. I thought I should keep the temperature as low as possible during the quench to minimize time spent quenching the reaction, as we need to do this on a large scale, where heat duty of our equipment could limit things. If the temperature is kept elevated then we see a very clean phase separation and can draw off the bottom aqueous acid/dissolved Al salt layer and continue to isolate the product. Kind of obvious in retrospect, but it's not like I have never been stumped by the Goddess of Chemistry before!!

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