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bfesser
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Quote: Originally posted by Pyro  | | bfesser, are you sure there is one for toluene? I just had a look under purification of common lab. reagents, there is no procedure for toluene.
However there is one for benzene, which is exactly the same. |
Yes, I'm sure. It's essentially the same
procedure.<a href="http://library.sciencemadness.org/library/books/vogel_practical_ochem_3.pdf#page=195"> | Quote: | 16. Toluene. Toluene, free from sulphur compounds, may be purchased. If required dry, it is
treated with anhydrous calcium chloride, followed by sodium wire (see under Benzene, 15).
Commercial toluene contains methyl thiophenes (thiotolenes), b.p. 112–113°, which cannot be removed by
distillation. It may be purified by shaking or stirring several times with about 10 per cent, of its volume of concentrated sulphuric acid as in the
case of benzene (15), but, owing to the greater ease of sulphonation of toluene itself, some temperature control is necessary. The simplest procedure
consists in mechanically stirring one litre of technical toluene with 100 ml. of concentrated sulphuric acid for about 30 minutes; the temperature is
not allowed to rise above 30° by occasional cooling. The lower acid layer is removed, and the process is repeated twice. The subsequent working up is
carried out as described under Benzene.
Pure toluene has b.p. 110·5°/760 mm. <img src="../scipics/_pdf.png" /> |
</a>
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Baffled
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I did the synthesis from Vogel more than a year ago for college, but instead of salting out the pTsOH we decided to neutralize any remaining sulfuric
acid with calcium carbonate and calcium hydroxide (seperately) after the x min of reflux mentioned in Vogel. After letting the neutralized reaction
mixture stand for a few days in between labs we heated the reaction mix for a bit, filtered it and concentrated the filtrate to a small volume after
which it was placed in an oven at 80° C to crystallize. I don't remember the specific yeild of calcium-p-toluenesulfonate (I must add identification
of the product was difficult since our nmr quenched, and mp's were too high, we did get IR-spectra but couldn't find any references) but I do know we
beat Vogel by a long shot. Both calcium carbonate and hydroxide worked pretty well too for sulfonating p-xylene and bromobenzene. http://library.sciencemadness.org/library/books/Weygand_and_Hilgetag_Preparative_Organic_Chemistry.pdf
We got a 70% yeild by refluxing 30 grams of toluene and 40 grams of sulfuric acid for 90 minutes at 110° C, adding 150 ml of dH2O after
the mix had cooled and adding to that 60g of calcium carbonate or 46g of calcium hydroxide.
[Edited on 24-1-2014 by Baffled]
[Edited on 24-1-2014 by Baffled]
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Pyro
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sorry about that, not only did I not find it, I posted the exact page that has the procedure!
now I'm mad at myself 
all above information is intellectual property of Pyro.  |
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Paddywhacker
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| Quote: Originally posted by Baffled | I did the synthesis from Vogel more than a year ago for college, but instead of salting out the pTsOH we decided to neutralize any remaining sulfuric
acid with calcium carbonate and calcium hydroxide (seperately) after the x min of reflux mentioned in Vogel. After letting the neutralized reaction
mixture stand for a few days in between labs we heated the reaction mix for a bit, filtered it and concentrated the filtrate to a small volume after
which it was placed in an oven at 80° C to crystallize. I don't remember the specific yeild of calcium-p-toluenesulfonate (I must add identification
of the product was difficult since our nmr quenched, and mp's were too high, we did get IR-spectra but couldn't find any references) but I do know we
beat Vogel by a long shot. Both calcium carbonate and hydroxide worked pretty well too for sulfonating p-xylene and bromobenzene. http://library.sciencemadness.org/library/books/Weygand_and_Hilgetag_Preparative_Organic_Chemistry.pdf
We got a 70% yeild by refluxing 30 grams of toluene and 40 grams of sulfuric acid for 90 minutes at 110° C, adding 150 ml of dH2O after
the mix had cooled and adding to that 60g of calcium carbonate or 46g of calcium hydroxide.
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With those ratios you neutralized *all* of the acids, including the TsOH.
How did you know that the calcium p-toluene sulfonate would not also precipitate with the CaSO<sub>4</sub>?
Generally, people want the free TsOH acid, and preparing it from the calcium salt would not be a shortcut.
On the other hand, if you determined the amount of free H<sub>2</sub>SO<sub>4</sub> in your reaction mixture and just added
the stociometric amount of calcium carbonate you might be on to a winning protocol, but I cannot see an easy way of making that determination.
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Baffled
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I found the solubility of the calcium salts in an old book full of solubility tables translated from Russian. I don't have it at hand right now.
Could one prepare the free acid by titration with HCl (or even CO2?) and extraction the acid with a nonpolar solvent?
[Edited on 26-1-2014 by Baffled]
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Paddywhacker
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| Quote: Originally posted by Baffled | ...
Could one prepare the free acid by titration with HCl (or even CO2?) and extraction the acid with a nonpolar solvent?
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Then you'd be back to the same problem from before you neutralised it. The problem being how to produce pure crystalline TsOH. The standard way is
to crystallize from concentrated HCl, which is awkward enough that anybody would want an improved method.
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Baffled
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Jes, sure. However, removing the remaining acids from the crystallized product would be a lot easier when there is no free sulfuric acid (there might
be some sulfate, but that's minimal) left after workup. Just dry in vacuüm.
On an industrial scale sulfuric acid could be easily regenerated from the calcium sulfate residue, but that might not be of our concern.
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HeYBrO
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could someone suggest a method of disposal for the left of sulphuric acid and the waste washes? I don't really want to flush thiophenes down the
drain if you get what i mean. is it possible to neutralise them or something?
[Edited on 28-1-2014 by HeYBrO]
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Metacelsus
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You could neutralize the acid with sodium bicarbonate. As for the thiophenes, I'm not too sure; you could look into burning them in a controlled
manner (be careful!).
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HeYBrO
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Just a question (its really noobish, my apologies) But if i were to scale down this procedure by 10 times, obviously the water coming off is going to
be much less, so how much of my 10 ml dean stark should i fill with toluene. I know that the toluene must be in excess and the amount of water will be
probably under a ml ( according to the vocal fifth edition procedure ) I presume about 9 ml toluene in the dean stark from the begging would work to
drip over and begin water collection? Or do i have it wrong?
[Edited on 15-3-2014 by HeYBrO]
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