Sciencemadness Discussion Board - Cellulose dissolving in the nitrating bath

Cellulose dissolving in the nitrating bath

Meal - 20-4-2011 at 14:06

This is my first attempt at nitration. I mixed 50 mL of sulfuric acid (pink viscous liquid, concentration unknown but bottle says it's concentrated) with 15 grams of food-grade KNO3. The color turned to a light orange.

I then added cotton balls and pieces of white printing paper into the nitrating bath. The cellulose stayed intact at first but then went into solution. The paper didn't dissolve though. There were no brown vapors of nitric oxides present but I could smell them upon stirring. I removed the paper after 20 minutes.

I took the paper out and added more cotton to the nitrating bath. The cotton very quickly dissolved into solution and it turned an opaque orange. Although the beaker was cold to the touch, It started to emit white fumes that smelled acidic and I could smell SO2 as well. I doused it in a water bath and neutralized with baking soda, which turned it light green and nothing went out of solution.

What's happening here?

symboom - 20-4-2011 at 14:33

that is interesting never heard that happening before there are a few things that devolve cellulose i know of tetraaminecopper dihydroxide could dissolve cellulose but paper has other things in it cotton is pretty much 99% cellulose

Bot0nist - 20-4-2011 at 14:39

The ratio is 50-55ml H2SO4 to 33g-36g KNO3. The nitrate salt must be fully dissolved. If not the left over H2SO4 will eat the cellulose every time. Gently heat the acid when dissolving the nitrate if needed, then cool before nitrating. NH4NO3 works a bit better as the nitrate salt. Better solubility and makes a less viscous nitrating bath. The thick KNO3 mix makes agitation harder IMO.

[Edited on 20-4-2011 by Bot0nist]

Also, if this is your first attempt at cellulose nitrate then you need to know that the cotton goes a bit gooey and mushy when it's soaked in the acid bath. After a good washing and neutralizing it regains its properties. Wash it extra extra good and dry it for a few days ( I use a desiccant bag). With nitrate salts I also find that leaving it nitrate for several hours or nitrating it twice will produce results on par with a nitric/sulfuric acid bath. This is debated among some members here though. Just MHO. I have no empirical results to back that up.

[Edited on 20-4-2011 by Bot0nist]

quicksilver - 21-4-2011 at 06:27

Since the levels of acids are small (50ml) I am going to take a leap and figure that the levels of cellulose are not too large either.
This is best done on a bit larger level as the cellulose is a very complex material & often inconsistent; raise your levels a bit.

Additionally one of the better sources for nitration-cellulose is toilet paper. It is more consistent than many sources except true paper pulp from a processing plant. Many of the really successful 13% nitration were done via that route. Today cotton (especially for medical needs) has adulterants in it to maintain it's form. I had the chance to use true wild-grown cotton and the results were quite different than a commercial example of medical-grade, etc. but from my experience (& a few others) toilet tissue, clean, pure, uncolored, unscented, etc) was the best overall.

Jimbo Jones - 21-4-2011 at 09:34

Test the supposed celluse. If the cotton burns to small, fine ashes it's cellulose. If the cotton melt with nice smell……

[Edited on 21-4-2011 by Jimbo Jones]

Meal - 21-4-2011 at 14:14

Quote: Originally posted by Bot0nist

The nitrate salt must be fully dissolved. If not the left over H2SO4 will eat the cellulose every time.

I think this is what was occuring. The paper that was soaked in the nitration bath did not burn any differently than regular paper suggesting the KNO3 did not dissolve in the cold temperatures. I will double the KNO3 quantity (30-35 g) and perform the nitration in a warm water bath (25-30 C) for 1 hour. My aim is to produce a small quantity (5 grams) of fully nitrated cellulose.

[Edited on 21-4-2011 by Meal]

Bot0nist - 21-4-2011 at 17:42

Since your using an 'improvised' nitrating bath, I would let the cotton nitrate for several hours. Like 3 - 6 hours. Then I would wash thoroughly, neutralize, and dry. After that, repeat the nitration on the dried cellulose nitrate with a fresh acid/nitrate bath again for several hours, as if it were regular cotton, then wash, etc. again . This will assure that the cellulose is fully nitrated. When your done, and the product is fully dried, it will make a satisfying WHOOMP when lit. I have heard that if you place a small piece of your cellulose nitrate in acetone, and it fully dissolves to a clear solution, that it is fully nitrated, and that no acetone insoluble cellulose is left. If fibers are left undissolved, than the nitration wasn't complete, or you had less than pure cellulose to begin with. Properly nitrated cellulose should leave no residue after deflagration. If a spongy like black carbon mass is left after burning, that's another sign of incomplete nitration.

My first synthesis after joining here was C6H7(NO2

3O5 and I really enjoyed the procedure and the finished product. It gave me the confidence to start work with other, more delicate nitrations. I wish you the best of luck, and may all you learning experiences be safe.

Sincerely, Bot.

Mumbles - 21-4-2011 at 19:03

I tend to agree on the increased amount of nitrate. Off hand, I believe I used 60mL 93% acid, and 36g or so KNO3. I added the KNO3 slowly with cooling. Once I was satisfied that the KNO3 was properly dissolved/reacted I added 5g of cotton and stirred while allowing to warm to RT. With good stirring/movement, the reaction should only take 45min or so at RT. Even at RT, it's still quite a slurry, so you need to work your glass rod in there to squeeze out the spent nitrating slurry, and get fresh stuff in there. I would stir every 5-10min. The product came out off white (probably due to dyes in the acid), but burned and dissolved completely.

Another test I've heard that works is washing the product with alcohol. Lower nitrated NC, which would still dissolve in acetone, will also dissolve in alcohol. I never tried it, but I was recently talking with someone who tried to make some NC (without any research on it), and his product turned gooey with ethanol as he was trying to speed up drying.

quicksilver - 22-4-2011 at 06:28

All positive suggestions; you've got some real room to move.
If your sample is not burning in appropriate fashion; you have something that obviously needs adjustment. Do yourself a favor and make one change at a time; that way you'll really know what it was that hindered your synthesis. Take notes, so that you are not repeating issues that could be altered and have reference for the future. When you think about it, you have several wide variables there.
* Purity of estrified material (precursor).
* Acid levels, purity & strength.
* Length of time in exposure.
* Temperature & ratio of mixed acid.
* Wash, processing, treatment of material: weight, condition, ph after exposure.

Meal - 29-4-2011 at 16:34

I tried it again. 33 g KNO3 in 50 mL H2SO4. I added finely powdered KNO3 slowely and with stirring to the acid and it started fuming and clumping. All additions were done within 20 minutes and the white solids kept clumping more.

To help more of it dissolve, I placed the beaker on a hot water bath for 30 minutes and then cooled down to below room temperature. The solution appeared yellow with large white chunks on the bottom.

I added a small piece of toilet paper in and it immediately turned red. After noting that the toilet paper had not dissolved after a few minutes, I kept adding more squares, up to 20, a few at a time.

Shortly after the last addition, paper in the center began vigorously boiling and charring black. I dumped the reaction in cold water. The area smelled of burnt paper for a while, but no nitric oxides could be seen or smelled. What was recovered was washed once in baking soda, twice in water and is now drying.

Something isn't working here.

Bot0nist - 29-4-2011 at 20:35

This works every time for me. Even with less than 98% rooto acid. If I were you I would suspect the salt, acid, or cellulose as not proper until you can rule each one out. If the paper is turning to carbon then I suspect you've got real H2SO4 but you need to do a titration and get a concentration. What is the source/purity of your nitrate salt? Are you quantifying(weighing) the nitrate salt accurately?

If your acid and nitrate salt check out, Mix up some nitrating solution and divide it among several small beakers to test different sources of 'cellulose' under the same conditions. I have always had good luck with unraveled and washed cotton balls. The cheap ones. Never tried TP myself.

grndpndr - 1-5-2011 at 16:54

I hope this isnt off topic but as regards the cellulose I once again dont have ready references OT memory.IIRC cellulose
in the form of wood chips/sawdust-raw cotton was washed
thoroughly in a lye solution prior to nitration.If memory serves (which it isnt so reliable these days) the process was used prior to the nitration/ production of NC for smokeless powder , as well as NC for gelatin dynamite?

As other members have suggested most far more experienced I would also check all of my precursors.I once had a # of failed nitrations traced to the nitrate salt I was using.I assumed it was the same brand as I had used before when in actual fact it was coated with a claylike substance
that fortunately was easily removed by recrystalization

Great learning nitration IMLimited,HO.

[Edited on 2-5-2011 by grndpndr]

retrofit - 12-7-2015 at 16:03

Bringing this thread back to life, because it seems to be the most appropriate. My first attempt at a nitration (of cellulose) failed, with the cellulose dissolving into the mixture.

In a 250mL beaker containing 120mL of ~90% H2SO4, cooled by an ice bath to ~10 degrees C, was added 60.6g of KNO3 in small additions with magnetic stirring, over the course of approximately an hour and a half. The KNO3 was difficultly soluble and and after the final addition, the mixture was let stir for 30 minutes. By this time, it was a reddish color. White fumes were observed during stirring. After 30 minutes, the KNO3 was still not fully dissolved, so it was removed from the bath, and the temperature was raised to 50 degrees C with continued stirring.

Once the KNO3 was mostly dissolved (and herein I think lies my problem), I removed it from heating and stirring. I began adding small strips of pure cotton batting, one by one, and mixing them by hand, 10g in total. A small amount of white fumes were initially observed, and later, slight red fuming was observed, but the temperature dropped over the course of the additions (to 47 degrees C).

Shortly (20 minutes) it was noticed that the cellulose had dissolved entirely and the temperature was rising to 53 degrees C. The red fuming increased and the mixture began to bubble, so it was placed into the ice bath and tipped over to drown it. The mixture separated into two layers, an oily yellow lower layer (?) and a lighter yellow tinged upper layer (acid/water?)

I suspect that the H2SO4 was oxidizing my cellulose. When I attempted to separate the layers, the lower layer began decomposing with heavy red fumes and a change to a greenish color as the upper layer was decanted off. I immediately drowned the lower layer again and continued with cleaning up/neutralizing the results with sodium bicarbonate.

Total loss. The KNO3 was sourced as 99.8% pure and the H2SO4 from battery acid with the water distilled off (appeared perfectly clear/syrupy/with white fumes).

Any ideas?

[Edited on 13-7-2015 by retrofit]

Bot0nist - 12-7-2015 at 16:45

After the nitrate salt if dissolved, it may be worth a try to cool the mix back down before you add the cotton. The mix may thicken when cooled if you use potassium nitrate, but it will begin to thin out agian as you add and "knead" in the cotton. If all is still going smoothly at this point the temp can be gently raised again.

Ammonium nitrate and sodium nitrate may work better, as they create a much less viscous nitrating bath. If you are able to prepare nitric acid, using it with concentrated sulfuric acid will provide even greater results, as the mobile fluid more easily penetrates the cotton.

retrofit - 12-7-2015 at 17:08

Thanks for the tips. Next time, I'll try bringing the mixture back down to 25 degrees C before adding the cotton. Also, the KNO3 wasn't completely dissolved and there were small chunks floating around. I suspect this was the primary issue.

I have 70% reagent grade nitric acid, but only a liter of it, which I'd like to save for planned future experiments. This being my first nitration, I elected to use KNO3 (my only readily available pure nitrate salt at the moment). I would distill over HNO3, but H2SO4 is the chemical I have the least of available (~200mL). I'm reluctant to use drain cleaner as a source without spending the time time to distill over the H2SO4 (more work than boiling the water off battery acid with better purity).

I found it interesting that it formed two layers, one thick oily deep yellow (almost a gel), and one thin, light yellow aqueous layer. I'm not sure what the lower layer would consist of. Dissolved nitrocellulose? The mixture did not turn blacken, which seems to suggest against my idea of the cellulose being oxidized. Additionally, when I tried to use a sep funnel on the thin, upper layer, I clogged it with what looked like very fine fibers of cellulose that took me quite some effort to clean out.

Could it have been perfectly good product? My strips swelled up first, then dissolved. I found this by Urbanski:

Quote:

The nitration of starch proceeds in this region in a system which is either completely single phase or partly so in contrast with cellulose, which swells only in mixtures rich in nitric acid and low in sulphuric acid.

[...]

It is true that cellulose can be dissolved in mixtures very rich in nitric acid but this requires a longer time and leads to marked degradation of the cellulose.

[Edited on 13-7-2015 by retrofit]

Bot0nist - 12-7-2015 at 19:19

Most drain opener acid should be ok for this. If it chars paper, it is strong enough. Also, make sure your potassium nitrate is finely ground and very dry. If you keep having trouble, try a different source of cotton I suppose.

If you have a ground glass distillation setup, then fuming nitric acid is easily obtained and well worth the effort.

Glad you've seen the library's entries. I hope you've read COPAE, by Davis. Good luck and be safe.

[Edited on 13-7-2015 by Bot0nist]

kecskesajt - 14-7-2015 at 23:46

Your nitrating acid could be hot.Cool it under 10 degree C° and then add the cotton and let it soak for 6 hrs.