DrJekyll (Stranger)
01-18-03 22:21
No 399608
      Why so much Na2SO4 needed for Nitroalkane?  Bookmark   

So SWIM is a newbee working up his first batch of nitroalkane (Et in this case).  The best available start-to-finish procedure swim can find with TFSE is Antoncho's version, with help from Bandil's followup.


SWIM wants to know WHY so much Na2SO4 is needed for this reaction?  As far as swim can tell, it keeps water out of things but at 60g in a total of ~230 ml of liquid, that is a LOT of gunk that doesn't seem to contribute to product... is this reaction THAT sensitive to water?  Or does it GENERATE that much water, necessitating that quantity of drying stuff from start to finish?  Especially since nobody swim has been reading mentions using a drying tube during heating.

I mean, reading past bees' work makes it sound like that much Glauber's salt (talk about convenient, my roommate had some laying around for tie-dyeing) is good for exactly one thing: contributing non-reacting gunk to this matrix.

Is swim COMPLETELY wrong?  (swim knows swim's a newbee but he's trying NOT to sound like an idiot -- fingers crossed).
Or would a smaller amount perform the same function?

And while swim is at it, is there a reference or some theory justifying that quantity (approx .42M Na2SO4 to go with approx 1M each of H2SO4 and EtOH)?
(Chief Bee)
01-18-03 23:25
No 399614
      Water absorbing capacity of sodium sulfate  Bookmark   

Could you please link to the post(s) containing the procedure you are referring to, so that it is easier to discuss it?

In the synthesis of diethyl sulfate from sulfuric acid and ethanol, two moles of water is formed for every mole of diethyl sulfate:

2 EtOH + H2SO4 Et2SO4 + 2 H2O

The water absorbing capacity of sodium sulfate lessens dramatically with increased temperature. Even though Na2SO4 can bind 10 molecules of H2O at room temperature, the capacity is down to 1 molecule above 34.4°C, and at 100°C no water binding occurs.
01-19-03 00:52
No 399622
      Well, I'm working from Post 251119 .  Bookmark   

Well, I'm working from Post 251119 (Bandil: "Nitroethane ala Antoncho succes", Novel Discourse), which was of course inspired by Post 233762 (Antoncho: "Kitchen nitroalkane success!", Chemistry Discourse).

I started w/ same materials and quantities, only after dripping the EtOH into the H2SO4 initially I let it sit, covered, overnight because I had to get some sleep.  Then tonite I heated it back up to <100C (thermometer broke last week, new one is on order) but warmer than body temp (hot to touch water bath but not burning my gloved finger), so maybe 40C.  I measured out 60g's Na2SO4 and poured a bit at a time in, and observed it to bubble, then dissolve slowly each time.  Then I got bold (read that, "stupid") and poured in a bit more, say 10-15g (previous portions had been 3-4g) and it foamed up to way above the liquid line and locked up solid... my little 1" stirbar in 500ml RBF is completely overwhelmed.

I've just come from trying to figure out how to loosen this stuff up, it's not WET anymore, it's the consistency of pizza dough and even replacing the 1" stirbar with a 3" hasn't helped noticeably...  so I grabbed my thermometer (did I mention it broke?) and have been shoving my 3" around, hoping to loosen things up/encourage absorbtion/fix the mess I have made while having followed (I thought) word for word what has worked in two different bees' kitchens.

I don't see a graphic for a sigh, so: <sigh>

(Chief Bee)
01-19-03 01:06
No 399628
      Suggested remedy  Bookmark   

If it is no longer wet, the addition of a liquid seems to be in order. One suitable liquid would be ethanol, as that is a reactant in the reaction. Add 100ml and stir with heating to ~75°C (just below the bp of ethanol) until it loosens up. If it doesn't, try with another 100ml. Let stir at that temperature for another hour, then neutralize with sodium carbonate as in the writeup and continue from there.
01-19-03 02:27
No 399648
      Swim has to assume that swim chose a flask...  Bookmark   

Swim has to assume that swim chose a flask that was too small for the reactants to react.

Swim added ~160mls Ethanol (the same 93% denatured as used in Post 251119 (Bandil: "Nitroethane ala Antoncho succes", Novel Discourse)), and it just *sat* there on top, this stuff is horrible.  So swim capped it and shook it, and finally got it to be a little thinner.  Swim still doesn't think he managed to get to where his 1" stirbar was moving at all, but swim was almost out of flask and certainly out of patience.

Swim is turning it all off for the night.  The references both have FILTERING after cooling at this point...  hahaha. I'm beginning to wonder if my "Glauber's salt" isn't Na2SO4 but something completely different, and I've just wasted a night.  Either that or there is a level of stirring to be had that's beyond my current experience.  But whatever these guys did that I didn't, the pasty white stuff I have filling my 500ml RBF is a terrible mess and a real disappointment.

Thx for the suggestion, tho, Rhodium.
(Official Hive Translator)
01-19-03 04:09
No 399668
      Some problems with nitroethane synth...
(Rated as: excellent)


(keywords: EtNO2, nitroethane, nitroalkane, nitrite, ethylsulfate, NaEtSO4, NaMeSO4)

Well, you see… Na2SO4, of course, is needed to abdorb water….. And one mole of it absorbs 10moles of H2O, BUT.

1) The rationale beehind using 5x xcess was that Na2SO4, however thoroughly you grind it,  won’t bee exactly in “finely dispersed state” and I feared that the hydrated salt on the surface of the granules might prevent it from reacting further.

2) The second rationale is that the more dehydrating agent you use, the faster the rxn goes. It seems to take long enough all by itself.

Please note that I don’t know for SURE neither of the above since neither myself nor anyone else did any analysis of the rxn thus far. SWIM just figured those proportions and durations would work and they did. You may improvize at your own risk if you want to, thoughwink

Now I want to say a couple of things that I never said earlier, although I definitely should haveblush Please forgive me for that, I was planning to work some more on the reaction and then submit the ‘final’ version to the Hive. I haven’t achieved what I planned yet, been too busy w/other stuff. But since you decided to do this, I’ll tell you some things that will bee undoubtedly helpful.

1)  Excessive heating ruins the nitroethane. That is, you can just turn your heater ‘full throttle’ when you do this on MeNO2 and bee fine. But not w/EtNO2. If you heat it above, say, 150 C (the precise temp hasn’t been found out yet – but as the doc on Rh’s about EtONO à EtNO2 conversion suggests, that should bee the critical temp), you’ll get a product contaminated w/all sorts of shit, w/EtNO2 content <40%

2) Unfortunately, since EtNO2 has a rather high bp, it makes it rather difficult to distill it out of the rxn – although, who knows, maybee there is a thin temp margin when you can pull it out and still not ruin it. It’s just we haven’t found it yet. If you have a vacuum source, definitely use it.

Work-up of the rxn by mixing w/water and xtracting w/pet ether is feasible as well, SWIM just never got to it (yet). Probably, this is the best avenue to take at the present state of affairs. Just remember not to overheat it. Drying w/CaCl2 and re-distilling the crude product is also a must. Too bad that it takes really huge amts of salts to produce miserable qtties of the product, so you might have to do this several times bee4 you collect enough to make drying and redistilling feasible.

3) The purer NaEtSO4 you use, the better (less junk to hold the product vapours). It is probably also very important not to overbasify your ethylsulfate when you prepare it (nitroalkanes form salts w/alkalis) . Remember, you can’t overacidify it either since it will ruin all of your NaEtSO4 product rather quickly, although not as quickly if you do that in EtOH (which I advise you to do by all accounts). Lesson: at the last stages of neutralization measure pH literally every second.

4) There is another problem w/the neutralization stage. Unlike w/MeOH, EtOH dissolves significantly less NaOH and huge qtties of alcohol would bee required to dissolve the needed amt. But if you just leave alkali undissolved in the alcohol, it will form a fine suspension that will react w/the acid only gradually, making it very difficult to carefully monitor the pH. That is, the mixtr beecomes acidic and after some time turns basic again – at least, that’s what SWIM saw.
Now KOH is much better soluble in EtOH so maybee it would bee advisable to use it instead.
It is unclear how well it will beehave instead of Na salt, but comradessmile Ennarkont & DMMDA reported a 54% yield of crude (rather impure, as turned later) from pure (reagent grade) KEtSO4.

5) SWIM had an idea of performing this rxn in some high-boiling solvt to circumvent the disadvantages of horrible heterogenicity (solid reacting with solid) – he tried glycerol, planning to simply xtract the rxn w/pet ether afterwards (glycerol isn’t miscible w/naphta, so isn’t DMSO. Unfortunately, DMF mixes w/it. SWIM has no DMSO, alas). Well, the only thing he can say is: use a vessel MUCH larger the the rxn contents. It will foamingly expand enormously and fill all of your apparatus, including the condenser.

Apart from that, I think this idea has a great potential, in terms of improving the yields.

6) And the last thing I want to say – when you get your EtNO2, use the ‘classical’ method in GAA to condense it w/a BA of your choice. The ‘cold’ method that works beautifully w/MeNO2 has been reported to give _oiling_out_ nitropropene even w/a reagent grade EtNO2 (that is still confusing, since evidently it can bee made to work according to the proc on Rh’s; maybee it is specific of 2,5-diMeO-Ph-nitropropene that Ennarkont and DMMDA tried to prepare. Anyhow, that won’t bee a 100% positive test for your nitroethane purity).

That’s all I have to say; bee certain to report your results!

(Chief Bee)
01-19-03 05:20
No 399680
      Henry condensation  Bookmark   

What "cold method" have you had problems with? I have heard no complaints about the cold method using Ethylenediamine Diacetate (../rhodium/chemistry /edda.html)

If you do end up with an oil when making a nitroalkene, pour it into cold water and extract with ether until the aqueous layer becomes colorless, wash the pooled etheral extracts with brine and distill the ether for re-use on a 50°C water-bath (to not overheat the nitroalkene). The nitroalkene should now be crystalline. Dissolve it in a minimum amount of boiling iPrOH and let cool slowly, first at room temp, followed by the fridge. Filter and wash with a small amount of ice-cold iPrOH. The filtrate can be chilled in the freezer to precipitate a few further percent of impure nitroalkene, but this is usually not worth the effort.
01-19-03 14:35
No 399768
      Et2SO4 failure explained  Bookmark   


Since it's never been mentioned explicitly, but should have been obvious...
Since SWIM never considered it, until it made a terrible mess of swim's reaction...

One's Na2SO4 is supposed to be anhydrous. <duuuuuuh>
Swims most definitely was *not*. frown

Guess somebody learned something today.

But while swim is at it: Antoncho, what size flask did/do you use to do this?  Is a 500ml big enough?  Should swim make his second try w/ half-portions?

open mouth, insert foot, broadcast internationally
(Stoni's sexual toy)
01-20-03 01:27
No 399864
      Yes, that was my first thought too.  Bookmark   

Yes, that was my first thought too.
'Glauber's Salt' is hydrated NaSO4 with 10 H2O

I'm not fat just horizontally disproportionate.