Sciencemadness Discussion Board
Not logged in [Login - Register]
Go To Bottom

Printable Version  
 Pages:  1  ..  11    13
Author: Subject: Benzene synthesis
wayne_m
Harmless
*




Posts: 9
Registered: 30-6-2017
Member Is Offline


[*] posted on 22-7-2017 at 16:43


Has anyone ever figured out just what the orange gunk from the benzoateNaOH reaction is?
I can confirm that it is not phenol red (I had heard it proposed as an answer.) I added bromine to my latest batch, which would have turned it into bromophenol blue, but it certainly wasn't that.
Whatever it is, I hope there is a good use for it. I'm growing quite a stock of it in my benzene waste container.

Also, in this last batch, I noticed that the distillate from refining the crude product came over at 73, which indicates an azeotrope of benzene and acetonitrile. (Could be something else, but that's the exact number I found for that mixture.)
I distilled my benzene before washing it with water this time.
I'll wash it out with water and try to isolate it, then post my findings.

[edit]
Apparently not. Acetonitrile should be soluble in water, and 100cc benzene mix + 100 cc water shaken vigorously and allowed to separate yielded: 100 cc of benzene mix and 100 cc of water.

Anyone have any ideas ideas what might have made the BP of the benzene mix so low?

[Edited on 23-7-2017 by wayne_m]

[Edited on 23-7-2017 by wayne_m]
View user's profile View All Posts By User
JJay
International Hazard
*****




Posts: 2442
Registered: 15-10-2015
Location: the cloud fortress
Member Is Offline

Mood: joyous

[*] posted on 22-7-2017 at 17:22


Benzene has an azeotrope with water at 69.3 C.

I'm not quite sure what the pyrolysis reaction between benzoic acid and sodium hydroxide is, but it's something like this:

PhCOOH + 2 NaOH -> PhH + Na2CO3 + H2O







View user's profile View All Posts By User
clearly_not_atara
International Hazard
*****




Posts: 754
Registered: 3-11-2013
Member Is Offline


[*] posted on 22-7-2017 at 20:48


Benzophenone or triphenylmethanol are my first guesses.
View user's profile View All Posts By User
wayne_m
Harmless
*




Posts: 9
Registered: 30-6-2017
Member Is Offline


[*] posted on 23-7-2017 at 04:37


I actually had two temperature rests; one at 68, which stayed there for several minutes, and one at 73.

I didn't bother fractioning at this point, since it was just to get the crude separated into low-boiling and water / high-boiling components. I stopped it at 85 C, and a lot of yellow came over, which seems to indicate that it isn't any of the really high boiling things.
I suppose it could be something like benzophenone, if it evaporates readily in boiling benzene, somewhat like a steam distillation. I don't have any experience with it, so I don't know.

I doubt it's or triphenylmethanol, or tetracene, considering that the leftover tar has a melting point well under 100 C, but given the unknown impurities, there's no way to be sure. It solidifies at room temperature.
Could tricene form the dye Alizarin in the benzoate reaction? It seems unlikely, but you never know until you know.

I'll dry the tar and try dropping some of my potassium in it. (I'll warm it just until it melts, and wait a bit to see if it runs away before applying any more heat! Made that mistake the other day and lost a stopper - I think it's in the neighbor's swimming pool.) If it turns blue or purple, it should confirm benzophenone. If not, then I'll try something else until an answer is found!
View user's profile View All Posts By User
 Pages:  1  ..  11    13

  Go To Top