Inorg. Chem. 1996, 35, 4529-4530
4529
Formation of Explosive Chlorine-Nitrogen
Compounds during the Reaction of Ammonium
Compounds with Chlorine
M. Knothe*
Freiberger NE-Metall GmbH, Lessingstrasse 41,
09599 Freiberg, Germany
W. Hasenpusch
Degussa, AG, Abteilung Umweltschutz,
60287 Frankfurt (Main), Germany
ReceiVed NoVember 22, 1995
Introduction
Figure 1. Dependence of NCl3 formation upon the acidity of reaction
solution: (Curve 1) NCl3 quantity formed (mmol); (curve 2) NCl3
quantity formed relative to the NH4Cl quantity used (%); (curve 3)
NCl3 concentration in the reaction solution (mmol/L).
It is known that during the reaction of chlorine or hypochlo-
ride with ammonium compounds chlorine amines of the
composition NH3-nCln (n ) 0-3) may be formed as unstable
intermediate compounds. Of them, NCl3 is especially explo-
sive.1 The following systems are considered to be dangerous:2
(i) amounts of g0.5 mL of liquid NCl3; (ii) mixtures with g10
vol % of NCl3 in inert solvents, e.g., chlorinated hydrocarbons;
(iii) mixtures with g0.5 vol % of NCl3 in the gas phases.
The literature data concerning the formation of NCl3 during
the reaction of NH4Cl with chlorine
The determination of NCl3 was based on the selective separation of
NCl3 (a) from the reaction solution by extraction with CCl4 followed
by conversion with hydrochloric acid to NH4Cl and (b) from the gas
phase by absorption in 12 M hydrochloric acid. The final determination
of NH4+ was performed photometrically.3 The detection limits for NCl3
were in the gas phase 0.007 mmol and in the reaction solution 0.0035
mmol of NCl3. The correctness of the value obtained was verified by
determining the blank value and by model tests using a 0.9 M NCl3
solution in CCl4.
NH4Cl + 3Cl2 ) NCl3 + 4HCl
(1)
are dispersed and, in part, incomplete.2
Results
This especially applies to the dependence of NCl3 formation
upon acidity. In the weakly acidic medium (pH 1-6) NCl3 is
rapidly formed at reaction yields from 30 up to 70%. At pH g
10 and CHCl > 6 M, no NCl3 is formed. As to the acidity range
from 0.1 to 6 M there are not sufficient data.
For this range NCl3 formation was studied with the use of
higher NH4Cl concentration and at different reaction tempera-
tures.
Preliminary tests have also shown that in clearly acidic
solutions relevant quantities of NCl3 have rapidly formed, being
highly dependent on the apparatus conditions and, thereby, on
the intensity of interaction between the chlorine and solution
phases (during the reaction of 0.5 M NH4Cl/0.5 M HCl solution
with chlorine the yield varied between 30 and 65%). Under
equal conditions the formed NCl3 quantity increased nearly
proportionally to the chlorine flow and, thereby, to the chlorine
quantity introduced.
Experimental Section
The experiments were performed with the use of 100-500 mL of
solution. Because of the great influence of apparatus conditions on
NCl3 formation the dependence upon relevant experimental parameters
was always determined with the same apparatus conditions. In View
of the tendency of NCl3 to explode, the following precautions were
taken: assembly of the apparatus behind double glass shields; avoidance
of critical phase composition by continuously agitating the reaction
solution and passing an air flow through the free reaction space.
For a given time chlorine was passed through the reaction solution
under intensive agitation with, at the same time, a given air flow
maintained in the gas space. The chlorine stream was determined, and
from that the chlorine quantity introduced into the system was
calculated. The reaction gases were passed through a system of washing
bottles. The fractions were processed after the completion of chlorina-
tion and a downtime of 5 min.
The quantities of NCl3 passed from the reaction solution into the
gas phase as well as the NCl3 content in the reaction solution after the
experiment had been finished were determined. The total NCl3 quantity
was given in millimoles of NCl3 as well as in fractions of the added
quantities of NH4Cl and chlorine according to eq 1. In addition, the
remaining NH4Cl content in the reaction solution after the separation
of NCl3 was determined.
Dependence of NCl3 Formation upon the Acidity of
Solution. Under constant conditions (using each time 0.1 L of
0.5 M NH4Cl solution of different acidity, reaction temperature
20 °C, chlorination time 30 min, chlorine flow 8-9 L/h, and
chlorine quantity added 180-206 mmol corresponding to 120-
137% according to eq 1) the dependence of NCl3 formation
upon the acidity was determined within the range from pH )
4.6 to 6.8 M. The results are shown in Figure 1.
+
Influence of NH4 Concentration. Under constant condi-
tions (using 0.1 L of 0.5 M HCl solution, reaction temperature
20 °C, chlorination time 30 min, chlorine flow 8.5 L/h, and
chlorine quantity added 185 mmol) the NH4Cl concentration
varied from 0.01 to 2 M. The results are shown in Figure 2.
Influence of Reaction Temperature. Under constant condi-
tions (using 0.1 L of 0.5 M NH4Cl solution in 1.97 M HCl,
chlorination time 30 min) at two different chlorination rates the
reaction temperature was varied as follows. Series A: 5 L/h
of Cl2; chlorine quantity 113 mmol corresponding to 73%
according to eq 1. Series B: 9.0 L/h of Cl2; chlorine quantity
203 mmol corresponding to 132% of the theoretical value. The
results are shown in Figure 3.
(1) Gmelin, Handbuch der anorganischen Chemie; Verlag Chemie:
Weinheim, Germany: (a) System No. 6, Chlorine (Hauptband, 1927;
Erga¨nzungsband, 1969); (b) System No. 23, Ammonium, 1936.
(2) Dokter, T. J. Hazard. Mater. 1985, 12, 207.
(3) De Vries, T.; Savariar, C. P.; Chakrabartty, M. M. J. Am. Water Works
Assoc. 1962, 54, 858.
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