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KOCN Assay

Magpie - 2-12-2010 at 10:33

KOCN Assay

by Magpie

12/4/10

Rev 1

Introduction
In the presence of moisture cyanate tends to easily hydrolyse to carbonate, ammonia, and carbon dioxide, ie,:

2OCN- + 3H2O --> CO3-- + 2NH3 + CO2

For this reason cyanates are often contaminated with carbonate. This is true even for reagent grade material.

This procedure is an expanded version of that presented by Allen (Ref 1). Allen’s procedure is based on Wohler’s reaction where cyanates are converted by dilute nitric acid into ammonia and carbon dioxide:

AgOCN + 2HNO3 + H2O --> AgNO3 + NH4NO3 + CO2

Allen’s procedure was intended for the analysis of samples of “pure” potassium cyanate.

Reagents
sample size: 1g of KOCN
30mL of 1N HNO3 (close to 1N is OK)
30mL of 1N NaOH (close to 1N is OK)
2.1 g of AgNO3
1.5 g of Ca(NO3)2
pH paper (or meter)
distilled water

Equipment
25mL or 50mL burette w/clamp and stand
10 mL pipette
125 Erlenmeyer flask (2ea)
1 small watch glass cover for Erlenmeyer flask
hotplate w/optional magnetic stirrer
small Buchner funnel (4.5cm) with vacuum source
glass funnel
filter papers for glass funnel and Buchner funnel
2 small ss spatulas
forceps (optional but useful)
100mL beaker
30 mL beaker
2 small test tubes (eg, 13mm x 100mm)
scale for weighing to 0.1g
stirring rod

Procedure
Dissolve 2.1g of AgNO3 crystals (an excess) in 20mL of distilled water in a 100mL beaker. Check the pH. If below 6 add 1N NaOH by the drop until pH =6. If particles of dark brown Ag2O are formed that do not dissolve with mixing add 1N HNO3 by the drop until they just dissolve. Check pH. It should be about 6. Transfer this solution to a 125mL Erlenmeyer flask.

Place 5 mL of distilled water in a small test tube and place in an ice water bath. Dissolve 1.5g of Ca(NO3)2 in a second small test tube and also place in the ice water bath. Label this 2nd tube.

Note: The following steps leading up to the mixing of the KOCN with the AgNO3 solution should be carried out quickly to prevent excessive hydrolysis of the KOCN.

Weigh out 1g of the KOCN to be assayed. Using a small paper funnel add the powder to the test tube containing only water in the ice water bath. Mix with a stirring rod. Mix the contents of each test tube together in a 30mL beaker.

Filter the KOCN solution into the AgNO3 solution, ideally as the AgNO3 solution is being stirred on the magnetic stirrer. Wash the residue and the filter paper with distilled water while allowing the filtrate to mix with the AgNO3 solution.

As the KOCN and the AgNO3 mix thoroughly a white precipitate of AgOCN will form. Catch this precipitate on the Buchner funnel and wash it lightly with distilled water. Transfer the precipitate cake to a 125mL Erlenmeyer flask using the ss spatulas and the forceps. This transfer will be facilitated by allowing the cake to dry first.

Warm 30mL of 1N HNO3 in the 2nd Erlenmeyer flask with a watch glass cover on a hotplate. Then transfer this warmed acid to the Erlenmeyer flask containing the AgOCN cake. This is an excess of HNO3. Place this on the hotplate and keep it warm enough to facilitate the reaction converting the AgOCN per Wohler’s reaction shown above. When the dissolution is complete examine the flask for undissolved material. If a residue is present filter the solution back into the other Erlenmeyer flask.

Back titrate the excess 1N HNO3 using 1N NaOH. The endpoint is reached when enough brown Ag2O turbidity is formed to noticeably discolor the solution. To me it had the color of lemon juice at the endpoint.

Calculation of Result
If the normalities of the HNO3 and NaOH reagents were not already 1N, then convert the volumes of the reagents used to equivalent volumes of 1N.

Subtract the mLs of 1N NaOH used from the mLs of 1N HNO3 added. The amount of KOCN present in the sample, then, is equal to 0.04055g times this difference.

KOCN, g = (difference, mL) (0.04055g/mL)

Discussion
The synthesis of KOCN has long been problematic for me. Recently, however, I tried it again using urea, K2CO3, a new reaction vessel, and the procedure found in Ref 2. The vessel is a Lodge cast iron mini-frying pan, 3.5” in diameter. A qualitative test of the product using Co++ was strongly positive (a dark blue). This showed that cyanate had indeed been produced and it likely was of acceptable strength (purity). Therefore I was anxious to find a quantitative analysis procedure to determine the purity of my product. This procedure is the result of my search.

Cast-iron is not the best material for a reaction vessel as it discolors the cyanate product somewhat, turning it a light brown. I assume this is due to iron oxide from the fry pan. I had earlier tried an aluminum drinking cup sold for camping. This didn’t work too well as I believe it was too thin-walled and therefore would cool off too easily. But an aluminum vessel apparently did work well for Atomisator on versuchschemie.de.

Ca(NO3)2 is used to precipitate out any carbonate. Ref 1 indicates that an equivalent amount of Ba(NO3)2 could likewise be used.

Attached are some pictures taken during the analyses of some KOCN that I have recently synthesized. The result using the original procedure was 66.5% purity. The result using this Rev 1 procedure was 74.2%

Silver Recovery
The silver in all of the wastes can be recovered as a silver ingot or as AgNO3 crystals using the procedure shown in Ref 3.

References
1. Allen’s Commercial Organic Analysis, 1913, vol. VII, p. 540 (available through Google Books).
2. Inorganic Syntheses, vol. II, “Alkali Metal Cyanates,” by Scattergood et al, pp. 86-90.
3. Inorganic Preparations, “Silver Nitrate from Silver Residues,” by Harold Walton, 1948, pp. 155-156 (available in SM library).

[Edited on 2-12-2010 by Magpie]

[Edited on 2-12-2010 by Magpie]

[Edited on 3-12-2010 by Magpie]

[Edited on 5-12-2010 by Magpie]

[Edited on 5-12-2010 by Magpie]

DJF90 - 2-12-2010 at 13:41

So what did your purity come out as Magpie?
Edit: Sorry, I must have missed it as I glazed over! Sorry to hear about your burette too

[Edited on 4-12-2010 by DJF90]

Magpie - 2-12-2010 at 14:00

66.5%, as stated in the Discussion.

Jor - 4-12-2010 at 05:32

Nice procedure Magpie! I have myself been thinking about producing some cyanate myself. What is the ideal vessel for conducting the fusion of K2CO3 and urea in? Is nickel alright? I have 2 nickel crucibles. I also have steel and porcelain crucibles, but I think the latter is attacked by carbonates.

By the way, that is quite lot of silver nitrate!

Magpie - 4-12-2010 at 07:50

Quote: Originally posted by Jor

Nice procedure Magpie! I have myself been thinking about producing some cyanate myself. What is the ideal vessel for conducting the fusion of K2CO3 and urea in? Is nickel alright? I have 2 nickel crucibles. I also have steel and porcelain crucibles, but I think the latter is attacked by carbonates.

By the way, that is quite lot of silver nitrate!

Thanks, Jor. I am working on a modification to the procedure that will eliminate the need for a centrifuge. I'll post it soon I hope.

I think nickel or stainless steel would be fine. Aluminum should also be good if it was sufficiently thick walled. On the other hand Atomisator's (versuchschemie.de) Al vessel wall doesn't look very thick. What I think would be ideal is here, but I can't justify the cost:

http://www.mauvielusa.com/Stainless-Steel-Mini-Saute-Pan-plu...

That is, the 3.5" saute pan. It's ss clad aluminum - perfect!

A large porcelain evaporating dish is called out by the Inorganic Synthesis procedure but I cracked mine when heating - damn!

Back when silver was cheap ($6/troy oz) organizations were giving out 1 oz silver comemorative coins for special events. (There is a large silver mine in my locale.) I acquired 2 of these that way. I melted one down to make mossy Ag. I recently made 58g of AgNO3 out of it, which I show in the bottle.

[Edited on 4-12-2010 by Magpie]

Magpie - 4-12-2010 at 20:14

I revised this procedure to eliminate the need for a centrifuge. It's a better procedure, actually.

I re-analyzed the same KOCN using this new procedure. The result was 74.2% KOCN vs 66.5% using the original procedure.

jon - 11-4-2011 at 03:51

i once did'nt have any quick access to cyanates so i did this
i took 1 gram mole of k2co3
3.5 gram moles of urea
and dissolved this in 7 parts of dmso
heated to 140 a lot of cabon dioxide is evolved and a lot of ammonia.
once there was no more gas evolution this indicated the reaction endpoint so the mixture was allowed to cool.
this took about 15 -30 minutes.
then i added about an equal volume of water and preciptated the kocn with ethanol
and washed the kocn on the filter with etoh this works quite well
the other patents just heat the two together and the reaction takes forever and yeilds are incomplete the dmso dissolves both and allows the reaction to happen in no time.

i wish i could find that patent.

[Edited on 11-4-2011 by jon]

Magpie - 11-4-2011 at 08:02

Quote: Originally posted by jon

i wish i could find that patent.

check Chinese patent 101412523

I tried this 11/3/10 with no luck, and didn't post results. White solids resulted with a weight indicating a yield of 69%. However, qualitative testing with 1M Co(NO3)2 was negative.

I recommend that you try that test with your KOCN. A deep blue color should appear.

jon - 11-4-2011 at 11:02

you did'nt get vigourous evolution of co2 and nh3?
it worked perferctly fine for me.
did you sparge the gasses? sometimes that helps, also try using a higher boiling dimethylsulfone i used that too.
and when i was done i sucessfully made some 2-amino oxazoline from it.

Magpie - 11-4-2011 at 13:27

My scale was much smaller than yours:

100 mL DMSO
15.7g urea (0.262 mole)
10.33g K2CO3 (0.075 mole)

Started with a 250mL beaker in a 130C oil bath. There was a lot of smoking so switched to a 250mL RBF with reflux condenser. Some occasional large gas bubbles evolved. No mention of NH3 or CO2 coming off.

This experiment contained quite a bit of "things not going well so made adjustments." So I don't put a lot of stock in the results.

Since DMSO is somewhat expensive I abandoned this procedure (maybe a mistake based on your results) and went back to the classic synthesis in "Inorganic Synthesis," by Scattergood et al.

If your product worked well in a synthesis then that speaks highly of your KOCN.

jon - 11-4-2011 at 18:58

it did it made a certain stimulant that worked so well i failed to realize how powerful the stimulant was and accidentally took too much of it.
and had seizures so i flushed it down the toilet having realized how dangerous it was.
in that case i used methylsulfonylmethane or dimethylsulfone it had a higher boiling point than dmso.
the msm was the stuff you buy at the supplement stores.
i did'nt even bother to remove the fillers and binders all i had to do was rinse out the kocn when i was done, with water.
then crash out the kocn with ethanol, it gave off plumes of ammonia so i knew it was working well
i probably heated that close to 160 or 170 C
i think i used a salt bath (table salt) to heat it.
the msm will sublime and collect on your condensor (something to be aware of)
i did'nt have any cobalt reagents, so i reckoned at ph's of around 5-6 that any carbonates would evervesce but the kocn would not decompose so i tested it in that manner. using vinegar.

[Edited on 12-4-2011 by jon]