Process for producing cyameluric chloride

A process for the production of cyameluric chloride is disclosed which comprises passing cyanuric chloride, mixtures of cyanuric chloride and cyanogen chloride, or cyanogen chloride, at temperatures of 200.degree. to 700.degree. C., together with oxygen over active charcoal, and separating the resulting cyameluric chloride by desublimation from the gas mixture obtained. Cyameluric chloride is a valuable intermediate.

The present invention relates to a process for producing cyameluric 
chloride. 
2,5,8-Trichlorotri-s-triazine of the formula 
##STR1## 
is designated as cyameluric chloride. Cyameluric chloride is a valuable 
intermediate for producing various products, such as gelling agents for 
aliphatic hyrocarbons (see U.S. Pat. No. 3,089,875), fluorine-containing 
oxidants which can be used as additives for rocket propellants (see U.S. 
Pat. No. 3,202,659), stabilisers for photographic emulsions (see U.S. Pat. 
Nos. 2,704,716 and 2,801,172), and dyes (see German Pat. No. 1,102,321). 
The producing of cyameluric chloride by reaction of cyameluric acid or an 
alkali cyamelurate with phosphorus pentachloride in a closed system is 
known (see J. Amer. Soc., 62, 842 (1940)). This reaction can be performed 
either in a bomb tube at 230.degree. C. (see J. Org. Chem. 27, 4264 
(1962)) or in a suitable inert solvent, for example o-dichlorobenzene (see 
German Pat. specification No. 1,102,321). The cyameluric acid or alkali 
cyamelurate, required as starting material, can for its part be produced 
by alkaline saponification of melon, a process wherein there is firstly 
obtained the alkali salt of the cyameluric acid, from the aqueous solution 
of which can be separated, by the addition of hydrochloric acid, the 
cyameluric acid (see J. Amer. Chem. Soc. 61, 3420 (1939) and Liebigs Anm. 
Chem. 73, 228 (1855)). Finally, the melon required for producing 
cyameluric acid can be produced by pyrolysis of melamine at 500.degree. C. 
(see J. Appl. Chem. 9, 340 (1959)), by slow heating of ammonium 
thiocyanate (see Z. Angew. Chem. 39, 1071 (1926)), or by pyrolysis of 
pseudothiocyanogen which, for its part, is obtained by chlorination of 
sodium thiocyanate in aqueous solution (see J. Amer. Chem. Soc. 61, 3420 
(1939)). 
The application of the aforementioned processes for producing cyameluric 
chloride leads in each case to a multistage process, the individual stages 
of which are in part difficult to carry out and difficult to control. 
Apart from these technical difficulties, a further disadvantage associated 
with the application of the aforesaid processes is that, in consequence of 
numerous secondary reactions, cyameluric chloride is obtained only in low 
yields and in an impure form. The processes mentioned above are therefore 
unsuitable for commercial production of cyameluric chloride. 
It is therefore the object of the present invention to suggest a process 
which renders possible the production of pure cyameluric chloride in a 
simple manner. 
It has been found that very pure cyameluric chloride is formed when 
cyanuric chloride, mixtures of cyanuric chloride and cyanogen chloride, or 
cyanogen chloride are passed, at temperatures of 200.degree. to 
700.degree. C., together with oxygen, over active charcoal. The process 
according to the invention for producing cyameluric chloride comprises 
passing cyanuric chloride, mixtures of cyanuric chloride and cyanogen 
chloride, or cyanogen chloride, at a temperature of 200.degree. to 
700.degree. C., together with oxygen over active charcoal, and separating 
the resulting cyameluric chloride by desublimation from the gas mixture 
obtained. 
The active charcoal used can advantageously be the active charcoal 
customarily employed for producing cyanuric chloride. Cyanuric chloride is 
primarily used as starting material for the process according to the 
invention. Since however cyanuric chloride under the applied reaction 
conditions on active charcoal is partially split back to form cyanogen 
chloride, it is also possible to use mixtures of cyanuric chloride and 
cyanogen chloride in the reaction. And since moreover under the reaction 
conditions cyanuric chloride is formed from cyanogen chloride, it is also 
possible to use pure cyanogen chloride as starting material. 
Within the given temperature range of 200.degree. to 700.degree. C., 
temperatures of 300.degree. to 450.degree. C. are preferred. The contact 
times and the quanitity proportions of the reactants are not critical and 
can be varied within wide limits. It is merely necessary that a small 
amount of oxygen be fed in simultaneously with the reaction mixture. The 
oxygen can be supplied in the pure form, in the form of air or in the form 
of other oxygen-containing or oxygen-yielding gases. The oxygen is 
preferably supplied in the form of air. On account of its low vapour 
pressure, the formed cyameluric chloride can be separated in pure form 
from the reaction mixture in a simple manner by desublimation. This 
desublimation is performed advantageously at a temperature of 200.degree. 
to 250.degree. C., preferably at 200.degree. to 220.degree. C. The 
residual gas containing cyanuric chloride and cyanogen chloride can be fed 
back, optionally after the addition of fresh oxygen, to the reaction 
vessel. In some cases, especially where the oxygen is supplied in the form 
of air, it is however advantageous to further process the residual gas. 
This can be effected for example by cooling the residual gas to room 
temperature to obtain the quantitative separation of the cyanuric 
chloride. From the residual gas obtained after separation of the cyanuric 
chloride, it is then possible to isolate the cyanogen chloride either by 
condensation or by absorption with a suitable solvent, for example carbon 
tetrachloride. The cyanuric chloride and cyanogen chloride recovered in 
this manner can subsequently be passed, together with fresh oxygen, again 
over the active charcoal contact. 
Starting with cheap, readily accessible raw materials, it is possible by 
the process according to the invention to produce very pure cyameluric 
chloride in good yield. A further advantage of the process according to 
the invention is that the cyameluric chloride can be produced with a high 
space-time yield. A certain disadvantage of the process is merely that the 
conversion to cyameluric chloride is low. This can however easily be 
offset by feeding back the residual gas obtained after separation of the 
cyameluric chloride, or the unreacted cyanuric chloride and cyanogen 
chloride contained in this residual gas, to the reaction vessel.

The process according to the invention is further illustrated by the 
Examples which follow. 
EXAMPLE 1 
A vertically arranged, electrically heated pyrex glass tube with an inside 
diameter of 28 mm and a length of 500 mm and containing a concentric tube 
of 5 mm diameter, in which thermocouples are fixed at various heights, 
serves as the reactor. At the lower end of the reactor is located a 
receiver which is used for desublimating the cyameluric chloride and which 
can be thermostatically controlled at a temperature of 200.degree. C. 
After this receiver is inserted a second receiver in which the residual 
gas is cooled to room temperature to effect separation of the cyanuric 
chloride. The receiver for separating cyanuric chloride is connected to an 
exhaust-gas pipe which is provided with devices for sampling and which has 
an absorption column filled with aqueous sodium hydroxide solution. 
The reactor is charged with 20 g (45 ml) of a commercial coarse-grained 
active charcoal having a specific surface area (BET) of 1100 m.sup.2 /g. 
Whilst being flushed with air (0.5 1/min.), the reactor is heated to 
400.degree. C. and is held for one hour at this temperature. There are 
subsequently continuously passed 1.16 kg/h of cyanuric chloride vapour and 
30 1/h of air at 400.degree. C. over the catalyst. After 370 operating 
hours, 1.108 kg of cyameluric chloride has been precipitated in the first 
receiver thermostatically controlled at 200.degree. C. The purity of the 
product on the basis of the chlorine determination according to 
Wurzschmitt is 99.5 to 100% and on the basis of the nitrogen determination 
according to Kjeldahl 98.6 to 100%. 
The space-time yield is 66.5 g of cyameluric chloride per liter of catalyst 
and hour. 
The effective consumption of cyanuric chloride, ascertained from the 
difference between supplied cyanuric chloride and recovered cyanuric 
chloride, is 3.50 kg, which corresponds to a yield of 31.7 percent by 
weight. 
The analysis of the uncondensed gases and of the wash liquor shows that 
these gases contain, in addition to phosgene, chlorine, carbon dioxide and 
small amounts of carbon monoxide, dinitrogen monoxide and carbon 
tetrachloride, also 1.48 kg of cyanogen chloride. There follows from this, 
taking into account the fact that 7 mols of cyanogen chloride or 7/3 mols 
of cyanuric chloride are required for 1 mol of cyameluric chloride, that 
there is a selectivity of cyameluric chloride formation of 85%. 
EXAMPLE 2 
Cyanuric chloride/air mixtures of varying composition are reacted under 
different reaction conditions in the reactor described in Example 1. The 
test results are summarised in the following Table. 
__________________________________________________________________________ 
Test 
[.degree.C.]Temperature 
[kg/h]chlorideCyanuric 
[1/h]Air 
chlorideair/cyanuricMolar ratio 
##STR2## 
__________________________________________________________________________ 
1 300 0,115 
12 0,86 
0,5 
2 400 2,32 
60 0,21 
82,1 
3 400 1,16 
30 0,21 
68,4 
4 400 0,23 
6 0,21 
15,1 
5 400 0,115 
3 0,21 
17,6 
6 400 0,058 
1,5 0,21 
6,5 
7 400 0,029 
0,75 0,21 
4,1 
8 400 0,23 
1,12 0,04 
17,0 
9 400 0,23 
24 0,80 
16,7 
10 400 0,029 
12 3,41 
2,1 
11 430 0,115 
3 0,21 
31,3 
12 450 0,115 
3 0,21 
37,8 
13 500 0,115 
3 0,21 
36,2 
14 500 0,58 
15 0,21 
105,4 
15 400 1,16 
30* -- 0 
__________________________________________________________________________ 
*nitrogen in place of air 
The test results show that the amount of air has only a slight effect on 
the formation of cyameluric chloride. Test 15 shows however that 
definitely oxygen has to be present for the formation of cyameluric 
chloride. The formation of cyameluric chloride increases with the increase 
of the cyanuric chloride throughput and of the temperature. The 
selectivity of the reaction slowly decreases however at temperatures above 
430.degree. C. Moreover, at these temperatures the active charcoal is 
slowly oxidised to carbon dioxide. 
EXAMPLE 3 
The reactor described in Example 1 is charged with 50 g of active charcoal, 
and is heated as in Example 1 to 400.degree. C. There are then passed 
through the reactor at 400.degree. C. 0.06 kg/h of cyanogen chloride and 
1.2 1/h of air. The amount of cyameluric chloride formed is 0.7 g/h.