Sciencemadness Discussion Board

Nitroguanidine from guanidine nitrate dehydration

roXefeller - 28-12-2020 at 19:26

I've done several searches with the SM tool and bing and google to find what I previously read, can't find it again. If you recall, please pass a link. There was a short debate regarding the necessary time for nitration of guanidine nitrate (GN) in sulfuric acid. One side says nitration happens quickly and hydrolysis sets in to reduce yield. Other side says hydrolysis is slower than nitration and the nitration is slow.

I've tried a couple trials on two sides of the coin, rapid nitration and slow nitration. In the first case 1.77 grams GN were added in small portions to concentrated sulfuric acid in an ice bath. Several hours went by because it was cold, I allowed it to age. Adding water to precipitate I came up with around 0.7g nitroguanidine (NQ).

Second trial was 10 grams of GN in the same conditions, but were added quicker allowing the reaction mixture to warm up to 20C by the end. Then the reaction stirred another 30 minutes before water precipitated. The collected precipitate barely dirtied the filter.

Really disappointing. Especially considering that the faster route was supposedly supported by patent literature. I'm really getting jaded on supposed infallibility of patents, as I've seen before they aren't quite the proscription we expect. Like the author sometimes hides something but wants to get authored. Anyway, I offer this document from Hercules Powder that has nitration proceeding at the elevated temperature of 40C and the long duration of 140 minutes.


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DBX Labs - 28-12-2020 at 20:46

Whenever I do the synthesis to produce more NQ, I run the same procedure as AllChemystery:
200g input of GN outputs about >140g NQ most of the time from my experience. Even this measurement is after recrystallization in a 5-liter beaker.
~80% yield
On this scale, the dehydration at no higher than 10C takes about 6 hours with periodic observation and addition.

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roXefeller - 30-12-2020 at 07:14

I'll try the long 10C synthesis next time around.

This current report is the 40C synthesis. In a water bath was placed a beaker of 12.2g 98% H2SO4. The bath was brought to 37C on the hotplate with stirring. 4.96g guanidine nitrate were added in portions over 80 minutes, maintaining around 42C in the beaker and 37C in the bath. At the end of additions, the bath was brought to 40C to maintain temperature for the next 100 minutes. A brief excursion to 50C in the beaker occurred during heating. But mostly it was 40C. After the 100 minutes 48g of distilled water was added. Previously on the abysmal batch, angry red NOx fumes were emitted with a lot of effervescence. This time no NOx or effervescence. That was reassuring.

Precipitate was filtered and washed. Then added to 30mL distilled water and brought up until it dissolved. It was left to cool to room temp and then placed at 24F to finished precipitating. A large bundle of monoclinic crystals formed. Dried overnight it came to 2.25g. Theoretical was 4.26g. This yield was 53%.

Boffis - 1-1-2021 at 03:11

@roXefeller; the key to this preparation is keeping the reaction temperature low <10 degrees. Above this temperature NQ suffers increasingly rapid hydrolysis by sulphuric acid. Some years ago I carried out this procedure and after filtering off the NQ from the diluted sulphuric acid I stored the acid to use to neutralise caustic solutions from other experiments. 3 months later in the depths of winter I noticed long colourless needles growing in the spent acid. I filtered these off and examined them and found them to be NQ. The temperature in the room where I store my chemicals is typically 3 to 7 C in winter. I recovered a couple more grams. However, at about 35-40 C NQ acts as a guanylating reagent towards amines via its hydrolysis with the liberation of nitrogen oxide, NO I believe.

So I suggest low and slow.

roXefeller - 2-1-2021 at 06:22

Boffis that's interesting that the hydrolysis was slowed enough that further precipitation was faster.

The Picatinny document from above mentions a 1% ammonium nitrate inclusion. I still haven't remembered to do it yet. I did the low and slow two days ago, while waiting for the turn of the year. I used rock salt to cool it below 10C. I wanted to work up a small quantity to use for testing the reduction afterwards, started with 27.5 grams guanidine nitrate and 68 g 98% H2SO4 cooled in the bath. It continued stirring another 5.5 hours after the last addition, while I maintained the temperature of the bath. I diluted it with 200g snow, which made it look like melting ice cream, that full of air and viscous effect, complete with all the bits of monoclinics forming. It was amusing to see. Filtered and reboiled in 350mL of water, it crystallized to 15.1g. So 65% yield based on 23.4g theoretical.