DRIVEN
(Stranger)
06-23-03 21:54
No 442105
      NaOCN from urea and sodium carbonate
(Rated as: excellent)
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Production of Sodium Cyanate from Urea and Sodium Carbonate


INTRODUCTION

Various members of the hive have previously theorized and experimented with production of the alkali cyanates.  Alkali cyanates are useful compounds.  They can be used for interesting reactions.  For example, one would find its utility in the production of 4-MAR Post 354295 (Bandil: "trans-4-MAR synth w/o cyanogenbromide writeup!", Methods Discourse) and if one really wants to, they can even be reduced further to the significantly more toxic cyanides Post 385632 (Rhodium: "Yes. Alkali metal cyanide plus bromine gives ...", Stimulants)Post 378904 (Polverone: "I can top that", Chemicals & Equipment)

Potassium cyanate can be prepared through the oxidation of potassium ferro-cyanide by fusing it with lead or manganese dioxide Post 383277 (Aurelius: "Urea", Chemistry Discourse).  In addition, the alkali cyanates can also be prepared by heating alkali carbonates in a mixture with powdered cyanuric acid Post 340082 (Polverone: "Encouraging results", Chemistry Discourse).  Perhaps an even more OTC method for the production of cyanates was explored by Polverone whereby sodium cyanate was produced from sodium bicarbonate and urea.  Sodium carbonate was formed by direct heating of the bicarbonate and then combined with urea to generate sodium cyanate Post 378904 (Polverone: "I can top that", Chemicals & Equipment).  Experimentally, it was reported that direct heating of urea and sodium carbonate at 150C produced an effervescing mixture that evolved large quantities of ammonia.  Sodium cyanate was thereafter reduced to sodium cyanide when heated further in the presence of charcoal.

Another hive member suggested that sodium cyanate could be best formed through melting the urea first, then adding the carbonate, followed by recrystallization of the product Post 379016 (Wraith: "Just an alternative", Chemicals & Equipment).  However, others indicated that this should be avoided as alkali cyanates hydrolyze easily and the conversion of the carbonate to the cyanate can be ensured through the addition of excess urea Post 379434 (Polverone: "First-hand experience", Chemicals & Equipment).

That distinctive and skillful Foxy2, complied a set of patent abstracts which pertained directly to the synthesis of alkali cyanates from sodium carbonate and urea with good yields ranging from 95%-99% Post 214057 (foxy2: "NaOCN and KOCN Production", Novel Discourse).  In addition, these abstracts contained vital information about the starting reagent molar ratios, reaction conditions, yields, and purity of product.  A strong similiarity among these abstracts was evident.  All the authors seem to agree that the production of high quality NaOCN proceeds from the addition of urea to the carbonate at molar ratio of (2.0-2.2):1 with stirring and gradually in 3 equal portions, giving each portion to time to react.  Furthermore, Schunk et al. (1) noted that the reaction progresses through 3 stages: Na allophanate and Na cyanate are formed in the 1st stage at 100-120C, water is evaporated in the 2nd stage at 130-140C, and Na allophanate is converted into Na cyanate in the 3rd stage at 140-180C.  During the entire course, the reaction gases are simultaneously being removed in all stages.  Dragalov et al.(2)recommended, that after the addition of the entire amount of urea, it is important calcine the resulting NaOCN is at 180-300C until the gasification of impurities ceases.  To calcine means to heat (a substance) to a high temperature but below the melting or fusing point, causing loss of moisture, reduction or oxidation, and the decomposition of carbonates and other compounds. 

Taken together, these data suggest that the total reaction can be described by the following chemical equation:

Na2CO3 + 2CH4N2O + heat ---> 2NaOCN + H2O + 2NH3 + CO2

The following experimental method for the production of sodium cyanate from the direct heating of sodium carbonate and urea emphasized a 1:2.2 molar ratio of sodium carbonate to urea.  The slight excess of urea was used to ensure total conversion of the carbonate.  As well, urea was added in 3 equal portions and with good stirring.  This means babysitting it so make sure you have some reading to do as well! The final process of calcine is very important in that unwanted contaminants are vapourized leaving a more pure product.

MATERIALS

Equipment

-hotplate
-stainless steel cup
-small cooking pot
-peanut oil
-thermometer
-clampstand
-stainless steel stir rod

Reagents

-anhydrous sodium carbonate, Na2CO3, FW=106 g/mol
-urea, molecular biology grade, CH4N2O, FW=60 g/mol

PROCEDURE

Warning: Ammonia gas is formed in this reaction, so it is a good idea to work in a fume hood or outside where there is good ventilation.

1) A hotplate was rested on the base of a clampstand.  A cooking pot containing peanut oil was placed on the hotplate stirrer.

2) Into the stainless steel cup there was placed 27g sodium carbonate.  The cup was then placed into the oil and secured with clamps to the clamp stand.  The end of the thermometer was placed in the oil and positioned as close to the cup as possible.

3) Though the sodium carbonate used here in was anhydrous, it was warmed to a temperature of 170C  for 10 minutes to remove any residual moisture.  Throughout the reaction the temperature of the oil was kept at 170C and stirring was done frequently.

4) 11.2 g of urea was added slowly, one scoop at a time and with good stirring.  During this, ammonia was released and moisture (water) formed making the mixture damp.  Over the course of 40 minutes the mixture gradually dried out and the amount of released gas lessened.

5) Another 11.2g of urea was added and allowed to react for 35 minutes.

6) The last 11.2g of urea was added and allowed to react for 30 minutes.

7) After adding the total amount of urea over 1h 45 min, the mixture was dry, contained white and off-white-to-yellow granules, and continued to release gas. The product was calcined at a temperature of 280C directly on the hotplate for 4 hr or until gas evolution ceased.  During this process the mixture was stirred every 15 minutes and off-white-to-yellow granules became more prominent and as white ones lessened.  It is important to give the post reaction time to calcine.  For example, after 2 hr into the calcine, the mixture was cooled and weighed 43g which is way over the theoretical yield of 33g.  This means that contaminants or unconverted carbonates are still present.  After heating the mix for another 2 hrs. The yield came down to 33g.
 
8) The NaOCN was allowed to cool and was weighed. Yield was 33g.  Theoretical yield is 33g.  It will be assumed that this product is 95-99% pure.

Taken together, this reaction felt like a success.  The reaction indicators such as ammonia evolution and water formation were present.  As well, the noted drop in yield of 43g to the more realistic 33g during the calcine process was a good indication that impurities and conversion were occuring.  As well the product was considerably off-white-to-yellow in colour relative to the starting white carbonate.  It would be nice to do a melting point determination on the product but 550C seem a bit difficult to achieve.  Perhaps the only way to know for sure is to try the this product in a reaction wink.

Any suggestions, advice or input is much appreciated.

Keep it easy

DrIvEnsmile
 
REFERENCES

1  Sodium cyanate from urea and sodium carbonate. Schunk, Wolfgang; Hohn, Richard; Jasche, Klaus; Braumann, Dietrich; Schweizer, Heidrun. (VEB Agrochemie Piesteritz, Ger. Dem. Rep.). Ger. (East) (1985), 8 pp. CODEN: GEXXA8 DD 221449 A1 19850424 Patent written in German. Application: DD 84-260213 19840221. CAN 103:162702 AN 1985:562702 CAPLUS
 
2 Sodium cyanate. Dragalov, V. V.; Karachinskii, S. V.; Chimishkyan, A. L.; Izakson, G. Yu.; Shvets, P. K.; Kulygin, A. A.; Kulygina, A. F.; Turlanov, N. N. (Mendeleev, D. I., Chemical-Technological Institute, Moscow, USSR). U.S.S.R. (1984), CODEN: URXXAF SU 1074818 A1 19840223 Patent written in Russian. Application: SU 82-3513458 19820917. CAN 100:158962 AN 1984:158962 CAPLUS

It just seems to go faster...
 
 
 
 
    Osmium
(Stoni's sexual toy)
06-24-03 03:38
No 442139
      Sounds good. Have you tried to recrystallize...  Bookmark   

Sounds good.
Have you tried to recrystallize the sodium cyanate? Does anyone have solubility figures at higher temperatures?

I googled for it and found 110g/l at 20C, MP 550C

KOCN is 750g/l at 20C, MP 315C, thermal decomposition taking place >700C

I'm not fat just horizontally disproportionate.
http://www.whatreallyhappened.com
 
 
 
 
    Polverone
(Hive Bee)
07-06-03 22:04
No 445115
      More cyanate info
(Rated as: excellent)
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Here's the good bits from Ullmann 2002:


Cyanates: Properties

In aqueous solution, sodium and potassium cyanate undergo hydrolysis according to Equations (1) and (2) [8].

OCN + 2 H2O  -->  CO32 + NH4+    (1)
OCN + NH4+  -->  CO(NH2)2    (2)

The rate of hydrolysis depends strongly on temperature, pH and concentration. In dilute strong acids, the reaction proceeds according to Equation (1). The reaction is rapid and complete within a short time. It is therefore used in the chemical analysis of cyanates. In concentrated hydrochloric acid, the trimerization product cyanuric acid can be observed as a byproduct. In alkaline solution, the rate of hydrolysis is very slow. Some cyanate decomposes with the formation of urea according to Equation (2).
The formation of cyanate ions is the first step in the detoxification of cyanide ions in water using hydrogen peroxide [9], followed by the further decomposition of the cyanate according to Equation (1) or (2). Industrially, this is the most important reaction involving cyanate ions in aqueous solution.

In the dry state, cyanate salts decompose above 450 C to form cyanides. The decomposition is influenced by certain metals. Both salts are hygroscopic, potassium cyanate much more so than sodium cyanate. When cyanate salts are heated to around 300 C in moist air, they undergo hydrolysis to the corresponding carbonate with liberation of ammonia.
Sodium and potassium cyanate dissolve only in water. Solubility in organic solvents is very low.

Sodium cyanate solubility, g/100 g solvent:

water: 10.68 at 16 degrees C
ethanol: 0.5 at boiling point
benzene: 0.13 at boiling point
liquid ammonia: 1.72 at -19.8 degrees C, 0.72 at 45 degrees C

Potassium cyanate solubility, g/100 g solvent:

water: 75 at 25 degrees C
ethanol: 0.53 at boiling point
benzene: 0.18 at boiling point.
liquid ammonia: 1.70 at 25 degrees C

[8]  J. A. Kemp, G. Kohnstam, J. Chem. Soc. 1956 no. 11, 900.
[9]  Degussa, DE-OS 2 352 856, 1976 (J. Fischer, H. Knorre). Degussa, DRP 742 074, 1943 (H. Beier). H. Knorre, Galvanotechnik 66 (1975) no. 5, 374 383.

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Cyanates: Production

Sodium Cyanate, Technical-Grade. In production, sodium carbonate is used as sodium source [4]. Sodium hydroxide [5] is only useful for laboratory synthesis. Under production conditions, safety considerations make sodium hydroxide unpractical. Urea is the preferred source for the cyanate part of the molecule, giving rise to ammonium carbonate as byproduct. Sodium allophanate has been postulated as a possible reaction intermediate [6]. The appearance and disappearance of such an intermediate can be observed by HPLC analysis. The reaction equation is therefore postulated as follows (Eqs. 3 5).

H2NCONH2 -->  NH4+OCN    (3)
Na2CO3 + NH4+OCN + H2NCONH2 --> NaOCN + NH2CONHCOONa+ + NH3 + H2O    (4)
NH2CONHCOONa --> NaOCN + NH3 + CO2    (5)

The overall reaction is the formation of two moles of sodium cyanate and one mole of ammonium carbonate from one mole of sodium carbonate and two moles of urea (Eq. 6).

Na2CO3 + 2 H2NCONH2  -->  2 NaOCN + (NH4)2CO3    (6)

The reaction is endothermic and requires strong heating above 200 C for a prolonged period of time to reach completion. The reaction takes place in a urea melt with a high content of dispersed solids.

The product from this process has a purity of 89 92 %. The main impurity is excess sodium carbonate with small amounts of sodium allophanate, cyanuric acid, biuret, and urea.

Sodium Cyanate, High-Grade. Sodium cyanate with at least 95 % purity can be obtained by using technical-grade sodium cyanate and urea as starting materials. The process proceeds in the molten state, as described for potassium cyanate [7]. Because of the high melting point of the sodium cyanate, the reaction temperature must be raised to 550 600 C. At these high temperatures, some cyanate decomposes to sodium cyanide, which can lead to formation of undesired byproducts and requires treatment of the wastewater. Also, the byproduct ammonia may ignite (flash point 600 C). For these reasons, production is not without risk.

Potassium Cyanate, High-Grade. The production of potassium cyanate from potassium carbonate and urea requires reaction temperatures of 400 C or above. The product is obtained from the reactor as a liquid, which must be solidified by cooling and ground after solidification. Since the crystalline structure of the potassium carbonate is destroyed in the melting process, the urea can reach nearly all potassium ions and convert them to potassium cyanate at a much higher rate than in the case of the technical-grade sodium salt. It is therefore easy to reach high purities above 95 %. While possible impurities like urea, biuret, cyanuric acid, and potassium allophanate are unstable at the reaction temperature and therefore are easily eliminated, the temperature is still too low to allow for significant formation of potassium cyanide.

[4]  DuPont, GB 1 145 777, 1969. Sakae Food Suff Industry Co., DE 1 205 065, 1966 (I. Tomiro). Degussa, GB 339 220, 1930. DuPont/Degussa, US 1 915 425, 1933 (H. Kloepfer). FMC, EP 0 122 031 B1, 1987 (W. B. Dodge, M. Halfon).
[5]  Asahi Chemical Industry Co. Ltd., JP 49 042 800, 1966 (Y. Nakayama et al.). Stamicarbon B. V. Neth., DE-OS 2 431 205, 1975 (J. Verstegen).
[6]  VEB Agrochemie Piesteritz, DD 221 449, 1985 (W. Schunk et al.).
[7]  US 2 690 957, 1954 (W. P. Horst).

---

Cyanates: Uses:

A review of the chemical reactions involving cyanate salts has been published [10].

In chemical synthesis, sodium cyanate is often the salt of choice. In most reactions, it can be regarded as a safe alternative to phosgene chemistry. The following reactions are or have been of some commercial value.
Reactions with primary or secondary amines afford monosubstituted ureas [11] (Eq. 7).

RNH2 HCl + MOCN --> RNHCONH2 + MCl    (7)

where, e.g., R = ethyl, tert-butyl, cyclohexyl
Sodium and potassium cyanate behave alike. Potassium cyanate is sometimes preferred to sodium cyanate because of its higher purity and its much higher solubility in water, a popular solvent for this type of reaction. Another solvent used for this reaction is ethyl acetate. Well-known pharmaceuticals produced by this type of reaction are the antiepileptic carbamazepine and the dermatotherapeutic agent hydroxyurea. The fungicides lenacil and terbacil are also produced by this type of reaction, and the herbicides isoproturon and diuron can also be produced.
In alkylation reactions, only sodium cyanate gives satisfactory yields (Eq. 8); potassium cyanate cannot be used.

RX + NaOCN -->  RNCO + NaX    (8)

Suitable alkylating agents are alkyl halides or sulfates. For example, allyl isocyanate is obtained from the reaction of sodium cyanate with allyl chloride. The product trimerizes readily to form triallyl isocyanurate [12]. The reaction of dimethyl sulfate with sodium cyanate results in the formation of methyl isocyanate, an intermediate for a number of plant-protecting agents [13].

Aromatic acid chlorides can react with sodium cyanate to yield benzoylurea derivatives, a novel class of herbizides [14]. Similarly, some sulfonylureas are antidiabetic agents, and sodium cyanate can be used for their synthesis. The reaction of sodium cyanate with sulfonyl chloride to give chlorosulfonylisocyanate in situ, which can be treated further in a one-pot synthesis (Eq. 9) [15]. To obtain high yields, a sodium cyanate with a low sodium carbonate content must be used.

NaOCN + SO2Cl2 --> ClSO2NCO + NaCl    (9)

Sodium cyanate is also used as a building block in the multistep synthesis of the herbizides carfentrazone and sulfentrazone [16].

Unique applications for potassium cyanate are rare. The major application of potassium cyanate is as an ingredient in certain steel-hardening salts for the Tufftride/Tenifer process [17].

The reaction of amidosulfuric acid with potassium cyanate yields potassium hydroxyureasulfonate, which has found a minor application as a polymerization catalyst for acrylonitrile [18].

[10]  Houben-Weyl, 4th ed., vol. VIII, pp. 89, 125; Ethyl Corp., US 2 866 801, 1958 (C. H. Himel, L. Richards). H. Bhme, W. Pasche, Arch. Pharm. 302 (1969) 335. K. A. Jensen, M. Due, A. Holm, Acta Chem. Synd. 19 (1965) 438.
[11]  DuPont, US 3 235 357, 1966 (H. Loux). DuPont, US 3 235 360, 1966 (E. Soboczenski). DuPont, US 3 352 862, 1965 (E. Soboczenski).
[12]  Nippon Kasei Chemical Co., DE-OS 2 839 084, 1979 (T. Nakamuro et al.).
[13]  Degussa, US 4 206 136, 1980 (G. Gieselmann et al.).Degussa, DE 2 828 259 C2, 1980 (G. Gieselmann, K. Gnther).
[14]  Ciba-Geigy Res. Discl. 351, 442-7; Chem Abstr. 119 : 271113.
[15]  Hoechst Agrevo, EP 560 178, 1996 (G. Schlegel); Hoechst Agrevo, EP 507 093, 1996 (G. Schlegel et al.).
[16]  FMC, US 5 256 793, 1993 (A. R. Bailey, M. Halfon, E. W. Sortore).
[17]  Daimler-Benz, DE-OS 2 602 754, 1976 (C. Lovasz et al.), Degussa, DE 1 191 655 OT, 1965 (J. Mller). Degussa, DE 1 149 035 OT, 1963 (J. Mller, C. Albrecht). Degussa, DE 1 234 873 OT, 1967 (J. Mller). Degussa, DE 1 280 018 OT, 1968 (J. Mller).
[18]  Asahi Kasei Kogyo, DE 1 720 202, 1973 (T. Ohfuka, K. Shirode, Y. Ichikawa).



Patent GB710143 inspired me to make cyanates (and then cyanides) from cyanuric acid before I realized I could use urea. Where I'm located, if you want only moderate quantities, it's actually easier to buy cyanuric acid.


19th century digital boy