Sciencemadness Discussion Board

Benzene from Sodium Benzoate - Dry distillation required? Why?

FireLion3 - 14-7-2014 at 08:41

I was looking at these preps and they all talk about dry distilling benzene from Sodium Benzoate and Hydroxide, but why is a dry distllation required? Both Sodium Benzoate and Sodium Hydroxide is soluble in water, and benzene is hardly soluble in water. Benzene is less than 1% soluble in water, so why can this all not be run in a single reaction flask and then phase separated?

blogfast25 - 14-7-2014 at 08:56

Quote: Originally posted by FireLion3  
I was looking at these preps and they all talk about dry distilling benzene from Sodium Benzoate and Hydroxide, but why is a dry distllation required? Both Sodium Benzoate and Sodium Hydroxide is soluble in water, and benzene is hardly soluble in water. Benzene is less than 1% soluble in water, so why can this all not be run in a single reaction flask and then phase separated?


It [the decarboxylation] only gets going at temperatures well above the BP of water. Also, I'm not sure a solution of the base, as opposed to molten base, is alkaline enough to effectuate the decarboxylation.


[Edited on 14-7-2014 by blogfast25]

UnintentionalChaos - 14-7-2014 at 09:10

Quote: Originally posted by FireLion3  
I was looking at these preps and they all talk about dry distilling benzene from Sodium Benzoate and Hydroxide, but why is a dry distllation required? Both Sodium Benzoate and Sodium Hydroxide is soluble in water, and benzene is hardly soluble in water. Benzene is less than 1% soluble in water, so why can this all not be run in a single reaction flask and then phase separated?


The reaction doesn't start until several hundred degrees C. The hydroxide is there to serve as a high-temp proton donor. Sodium benzoate in water in a sealed tube also produces benzene effectively, but you are at the require temps and enormous pressure.

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FireLion3 - 14-7-2014 at 09:17

That makes sense. I was hoping to make reasonable quantities of Benzene from Benzoate without having to do a dry distillation, but having to distill would make the process unreasonable to perform. I can purchase Benzene, but the price per liter is so much higher than the Benzoate route.

blogfast25 - 14-7-2014 at 10:09

The process is not 'unreasonable to perform'. It takes a fairly simple DIY apparatus and some good safety precautions. See higher up in the relevant sticky thread in 'Organics'.

[Edited on 14-7-2014 by blogfast25]