p-toluenesulfonic acid

[Chromic]

Paratoluenesulfonic acid (aka p-tosic acid)

Added 5.0g toluene (1 equiv), 16.4g 94% H2SO4 (3 equiv) to a 50ml flask. Toluene layer went to the top of the flask. Dropped in a stir bar, fitted with a condenser, started stirring, heated to get a gentle reflux (~110C) of 1 drop/sec. 40 minutes passed and the reflux had stopped, the layer of toluene was gone. Easy reaction, nothing to it!

I added 5ml water down the condenser, allowed the flask to cool slowly to room temp, nice crystals of p-tosic acid form. How do I separate them without a sintered glass buncher funnel? Or, would changing this to 1 equiv H2SO4 make tosic acid? (obviously with some 2- & 3- isomers, but that doesn't matter much as it's just going to be used as an acid catalyst, impurities don't bother me much)

[Antoncho]

hmmm... this is very interesting - so, you say that tosic acid is insoluble in aq. H2SO4?? This is really a surprise, i thought, since tosic acid is so water-soluble,... eh...

Well anyway - i suggest you just decant the liquid as much as possible and wash the crystals w/ conc. HCl several times, and then dry over H2SO4/NaOH as described.

Antoncho

[Chromic]

It seems that tosic acid hydrate isn't soluble in ~80% H2SO4, however I did notice that tosic acid does dissolve in 98% H2SO4. (crystals will not form in the above synthesis until the addition of water)

My HCl is only 31%, and I can't decant the crystals, the whole thing is sort of a slush... I'm tempted to try reacting this 1:1. I really want the crystals and don't care about the purity (so long as it's around 80+%) Maybe I should experiment more and post less.    (but I love posting...)

[terbium]

(crystals will not form in the above synthesis until the addition of water)
Yes, this is the same as the procedure in Vogel. He dries the crystals by spreading them on an unglazed porcelain plate.

[Chromic]

Reacting 1:1 toluene to sulfuric acid doesn't work, it gives off lots of SO2. I guess it must be making p-cresol. Trying to get the crystals from spreading out on a porcelin plate didn't work well, I guess I'll have to buy a sintered glass buchner funnel.

[terbium]

I guess I'll have to buy a sintered glass buchner funnel.
Or buy some of the Whatman glass fiber filter disks that I keep touting and use them on your Buchner in place of paper filter disks.

Here is the procedure for p-toluenesulfonic acid from Vogel:
(comments in italics are mine)

Use

Use the apparatus employed for Di-n-butyl ether (a round bottom flask fitted for reflux and with a Dean-Stark water trap). ... Place 87 g (100 ml) thiophene free toluene and 37 g (20 ml) of concentrated sulphuric acid (92 per cent H2SO4 by weight) in the 250 ml ... flask and heat to gentle boiling. When 9 ml of water have been collected in the Dean_Stark trap (4-5 hours), stop heating. The water is derived partly from the reaction (6.25 ml) and partly from the sulphuric acid. Add 6.3 ml of water to the cold contents of the flask; crystallization then occurs. Spread the resulting solid on a porous tile and press well with a glass stopper; toluene and o-toluenesulphonic acid are thus removed. Dissolve the residual solid (47 g) in about 22 ml of water and saturate the solution with hydrogen chloride gas; use any convenient device (e.g., a small funnel) to prevent "sucking back." After several hours the acid crystallises out as colourless prisms. Filter rapidly through a sintered glass funnel, wash with a little concentrated hydrochloric acid, and dry in a vacuum desiccator charged with stick potassium hydroxide and calcium chloride. The yield is 35 g, m.p. 105-106° (sealed tube).

[Dr_Sister]

chromic - its a fuckin mess, i triied to recrysttallize that mushy shit from ipa, and it alot of work to make more mushy shit, i triied washing with toluene, ha! But i have a suspicion that n-butyl alcohol might have a more appropriate solublty curve, but know what, i think fuck it, just distill the stuff, BP 140C next time right out of the rxn flask.

and if you reflux 1st your toluene and drip in the H2SO4 (2 equivalents), you control rxn with stirring and its over in 15 min. then toss the H20 down condenser until it stops trying to reflux out finito! and if you don't decant quik after it goes solid (not slush) really fast .

fun though
7.10.01

[Chromic]

It boils at 140C and 20mmHg.

[Chromic]

Since distilling tosic acid isn't quite possible for me, could I dissolve it into DCM (does it even dissolve well? I've read it dissolves into ether, alcohol, water, etc), then just pour off the H2SO4. Evaporate the DCM, and get my tosic acid?

Would this work? (and if so, could I just store the tosic acid dissolved in DCM?)

[Aurelius]

try dissolving some in DCM- if it works, do as you suggested above.  before storage, however, you should probably recrystallize your product, then dissolve in fresh DCM.

[Chromic]

Ok. I'm still struggling with this. I've tried reacting toluene to sulfuric acid at:

toluene:sulfuric (molar, apx weight:weight tho since MW is similar)
1:3 - works fine
1:2.5 - works fine
1:2 - sulfur dioxide, stopped rxn
3:1 - (as suggested by Vogel) sulfuric dioxide, stopped rxn

I can't stand to breath in the SO2, plus I think it's an indication that the tosic acid is forming 4-methyl-phenol.

The DCM idea didn't work well. Tosic acid didn't move to the DCM layer. Does anyone have any other suggestions? I'm thinking about trying 80% H2SO4 with 3 eq. toluene... is that the right idea, or is there something else I could be doing?

[Chromic]

Nope... 3 equiv 80% toluene isn't working well either, looks like I need a dean-stark trap to use that method. There's a purple toluene layer, and a burgandy H2SO4 layer... doh. The only method so far to work well is 3 equiv 95% H2SO4, 1 equiv toluene.

[Vibrating_Lights]

Chromic_  Are you dreamin what i think you dreamin
VL-

[Chromic]

Not yet. I need decent quality p-tosic acid first.

[Vibrating_Lights]

Someone please help this man. 
Chromic- It looks so easy doesn't it.
VL_

[Chromic]

I'm really at a loss here. I don't have a sintered glass funnel... frig.

[terbium]

I am at a loss to. Procedures from Vogel always work as stated. Do you have crap starting materials? I am guessing that you do because you report a purple color.

[Chromic]

Hey, 3 equiv of toluene does work! My problem was not performing the distillation slow enough. If it is done very slowly there is hardly any SO2 formed.

So, my question is... should I boil off all the toluene to get solid tosic acid or use filter paper in a buchner to filter the mixture? (there is solids)

[Rhodium]

The text below is taken from a japanese patent abstract, and it tells how to produce p-toluenesulfonic acid monohydrate, the product of commerce, which I believe is much easier to isolate than the anhydrous sulfonic acid. It would soon pull that water molecule out of the air anyway.

Toluene is reacted with 80-98% sulfuric acid at 2-4 molar ratio at the boiling point of the toluene and the resultant reaction solution is cooled to about 60°C. Water in an amount corresponding to 0.75mol based on 1 mol p-toluenesulfonic acid in the reaction solution is then added to crystallize monohydrate crystals of p-toluenesulfonic acid while cooling the reaction mixture to 20-60°C. The above-mentioned crystals are subsequently separated to provide a filtrate.

[UTFSE]

are you all sure that SO3 isn't required to make this?

maybe I am thinking of tosyl chloride.
OTEECEE & meeeee!!!!