Sciencemadness Discussion Board

Synthesis of Sodium Sulfamate

Σldritch - 17-3-2018 at 01:41

Im back doing chemistry after a long pause, let's hope it lasts. I need Sodium Sulfamate for an experiment and since Sulfamic acid is unavailable anywhere near me i decided to make it myself by this reaction:

2 NaHSO4*H2O + CO(NH2)2 ---> 2 Na(NH2)SO3 + 3 H2O + CO2

23 g Sodium Hydrogen Sulfate Monohydrate (Pool pH-)
5 g Urea ("Gentle" road salt)
~100 ml Dihydrogen Monoxide (Home brewed from tap water)
~ 20 ml Acetone (Technical)

Procedure: The Sodium Hydrogen Sulfate Monohydrate was placed in a 100 ml beaker and melted on a hotplate. As soon as the material was completely molten Urea was slowly added with stirring and the mixture turned into a foaming paste. No odor of ammonia was present but a slight smell of sulfur dioxide. When all the Urea was added and thoroughly mixed in 60ml of distilled water and a nickel coated magnet was added as a stir bar to dissolve the crude product. The solution was then boiled down to ~40ml and allowed to cool in a fridge.

The now precipitated product was vacuum filtered as a slush and washed twice with distilled water and twice with acetone and allowed to dry on a piece of paper.

Because i do not know any good way to test Sodium Sulfamate i tried burning it in a test tube: The result was a Ammonia - Sulfur Dioxide smell and water vapor. No discoloration was observed of the solid. This is the best i have as characterization.

Really though i doubt the product is very pure, but i can think simple way to improve purity. Guanidine sulfate is a likely byproduct formed from excess Urea and Sodium Sulfamate which could be removed simply by washing the product in alkali. Guanidine is also why i added the Urea to the Sodium Bisulfate in small portions so no local spots of high Urea content are created. The hard part is removing Sodium Sulfates which have fairly similar solubilities, how could i do that?

Here is a picture of the product.

IMG_20180317_103337.jpg - 2.1MB

Edit by Texium: Fixed title

[Edited on 3-19-2018 by Texium (zts16)]

clearly_not_atara - 17-3-2018 at 01:48

Very nice!

Where did you learn about this reaction? Or did you devise it yourself?

Σldritch - 17-3-2018 at 01:49

Thanks, i came up with it myself.

Metacelsus - 17-3-2018 at 06:39

I'm still not convinced that what you have is sulfamic acid. I would think that ammonium sulfate would be the likely product of your reaction, since you used sodium bisulfate monohydrate:

2 (NaHSO4*H2O) + CO(NH2)2 = Na2SO4 + (NH4)2SO4 + CO2 + H2O

Could you attempt converting it to sulfamic acid, and checking the melting point (which should be 205 °C)?

You could also test solubility, see:

[Edited on 3-17-2018 by Metacelsus]

clearly_not_atara - 17-3-2018 at 09:11

Is sodium sulfamate soluble in ethanol? If so, you should be able to convert to the calcium salt by metathesis with CaCl2 in ethanol. This yields sulfamic acid upon treatment with dilute H2SO4. I don't know if you can actually distill sulfamic acid very easily.

Σldritch - 17-3-2018 at 10:24

Im not convinced it is Sodium Sulfamate or Sulfamic acid either but i am leaning on Sulfamic acid now because when i tried washing it with Sodium Hydroxide it pretty much instantly dissolved and the solution was acidic when i was boiling it down.

I doubt it is Ammonium Sulfate because it is so soluble i would never be able to precipitate it the way i did. However i did smell ammonia when i added the Sodium Hydroxide but not much needs to hydrolyse for a strong smell to be produced.

Anyway ill redo it soon but i am out of vacuum filter papers for the cold filtrations.

And no it is probably not soluble in Ethanol.


Sulfamic acid 12.8 wt% in water at 0 deg C; 17.57 wt% in water at 20 deg C; 22.77 wt% in water at 40 deg C; 0.1667 wt% in formamide at 25 deg C; 0.0412 wt% in methanol at 25 deg C; 0.0167 wt% in ethanol (2% benzene) at 25 deg C; 0.0040 wt% in acetone at 25 deg C; 0.0001 wt% in ether at 25 deg C Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed., Volumes 1-26. New York, NY: John Wiley and Sons, 1978-1984., p. V21 950

From the thread:

I doubt the sodium salt is more soluble seeing as it is an ionic compound.

softbeard - 19-3-2018 at 06:56

I think you need to characterize your product better.
Quick ways of differentiating between sulfamate vs. sulfate or bisulfate:
Barium sulfamate is relatively soluble in water, so aqueous BaCl2 is a good spot check for sulfate contamination. CaCl2 should work too.
Silver sulfamate is also soluble, whereas silver sulphate is only slighty solube.

Improved synthesis of Sodium Sulfamate

Σldritch - 20-3-2018 at 08:23

I found two more filter papers so i improved the reaction a bit. If you look at your experiments and think to yourself; "I wonder how that tastes?", this is not the reaction for you because not only does it resemble making pancakes but the foaming also looks like some kind of delicious marshmallow. Proceed at your own risk...


2 NaHSO4*H2O + CO(NH2)2 = 2 NaSO3NH2 + 3 H2O + CO2

Same reaction but it seemed to me that the main faults of the old procedure was that:

1. It did not mix the reagents properly because Sodium Sulfamate is solid below its decomposition temperature.

2. It was hard to control the temperature.

3. The sulfates were not separated.

This method seems to solve those problems.

69 g Sodium Hydrogen Sulfate Monohydrate (Pool pH-)
15 g Urea ("Gentle" road salt)
~3 g Calcium Nitrate (Extracted and purified from fertilizer)
~110 ml Water (Distilled from the tears of a thousand souls)

69 g of Sodium Hydrogen Sulfate Monohydrate was ground to a powder and set aside and 15 g of Urea was ground to a powder and it, too, was set aside. The powdered reagents were mixed on paper and then added to a mortar and the some distilled water was added. This was ground until a thick, mostly transparent and runny paste was obtained.(1)

A microwave dish was heated on a hotplate until the temperature was high enough to instantly boil water dropped on it. The paste was quickly added and pushed around as the water boiled. As the water boiled away a white fluffy paste was obtained. Heating was continued as the paste started to foam giving of odorless gas puffing up as it became thicker. Stirring was continued until the paste was completely solid and was taken of the heat to cool.(2)

The crude product was added to a 400 ml beaker and the volume was adjusted to 100 ml with distilled water. The solution was then neutralized with sodium hydroxide causing the last of the solid to dissolve.(3)

3 g of anhydrous Calcium Nitrate was dissolved in 10ml of water and added drop wise until no precipitation could be observed.4 The solution was filtered through a coffee filter and allowed to stand overnight at room temperature.(5)

The solution was again filtered through a coffee filter and was placed in a fridge at -18 degrees Celsius until it became a slush.(6) The slush was removed from the fridge, vacuum filtered, washed once with water and thrice with acetone. The product was removed from the filter and allowed to dry on a paper.

Yield: 34 g or 57% of theoretical yield of an off-white crystalline powder giving an awful smell on heating.

(1): Adding too much water will give the Urea more time to hydrolyse and gives the mixture more time to become homogeneous as the water boils. You also want to keep it runny enough for it to easily be distributed on the microwave plate.

(2): Heating too long will remelt the mixture turning it brown to black decomposing the product. I heated it too long almost every time but most of the decomposition products can be filtered off with great effort and mechanical losses and some yellow color will stay with the product.

(3): Give it plenty of time, in the end even the sodium hydroxide had trouble dissolving! Also, you rather have a too acidic solution than a too basic solution because basic condition seem to quickly hydrolyse the Sodium Sulfamate as i found out the hard way.

(4): Next to no precipitate could be seen. Why? Probably the same reason as Sulfamic acid is used for cleaning.

(5): For some reason Sodium Sulfate Precipitates. I have no idea why but it is certainly not the product because it only gives of water on heating, forms typically large Sodium Sulfate Crystals and those crystals quickly dry out in air which is also typical of Sodium Sulfate.

(6): It supercooled for me, i suggest agitating it once in a while.

[Edited on 20-3-2018 by Σldritch]