Dinitroaniline purification with inorganic acid halides

The present invention is directed to a process for reducing the concentration of nitrosamines in dinitroanilines, which comprises treating a nitrosamine-containing dinitroaniline with PCl.sub.3, PCl.sub.5, PBr.sub.3, POCl.sub.3, SCl.sub.2, SOCl.sub.2, SO.sub.2 Cl.sub.2, SOBr.sub.2, or TiCl.sub.4.

SUMMARY 
The dinitroaniline class of compounds includes numerous commercial 
herbicides. Recently a new analytical device, known as a thermal energy 
analyzer (TEA), has been developed (J. Chromatogr. 107 (1975), 351 and 
references there cited; and "N-Nitroso Compounds in the Environment," IARC 
Scientific Publication #9 (International Agency for Research on Cancer, 
Lyon, 1974), p. 40). The TEA analyzes specifically for the nitroso (--NO) 
group, and is capable of detecting the nitroso group at concentrations as 
low as 0.02 ppm--much lower than prior analytical techniques. Analysis of 
various dinitroanilines by the TEA reveals that some of the 
dinitroanilines contain very small amounts of nitrosamines. Certain of the 
nitrosamines have been shown to be carcinogenic in animals. Therefore, it 
is desirable to reduce the concentration of nitrosamines in the 
dinitroanilines. 
DETAILED DESCRIPTION 
The present invention is directed to a process which comprises 
(1) contacting a nitrosamine-containing dinitroaniline selected from the 
group consisting of 
trifluralin, 
isopropalin, 
benefin, 
ethalfluralin, 
butralin, 
tendimethalin, 
fluchloralin, 
profluralin, 
dinitramine, 
4-trifluoromethyl-2,6-dinitro-3-chloro-N,N-diethylaniline, 
4-methyl-2,6-dinitro-N,N-bis(2-chloroethyl)aniline, 
oryzalin, and 
nitralin, 
(a) in liquid phase, 
(b) with a reagent selected from the group consisting of PCl.sub.3, 
PCl.sub.5, PBr.sub.3, POCl.sub.3, SCl.sub.2, SOCl.sub.2, SO.sub.2 
Cl.sub.2, SOBr.sub.2, and TiCl.sub.4, until the concentration of the 
nitrosamine has been reduced, and 
(2) thereafter recovering the dinitroaniline. 
Dinitroanilines with which the present invention can be practiced (and 
their generic names where available) are 
(1) 4-trifluoromethyl-2,6-dinitro-N,N-di-n-propylaniline (trifluralin); 
(2) 4-isopropyl-2,6-dinitro-N,N-di-n-propylaniline (isopropalin); 
(3) 4-trifluoromethyl-2,6-dinitro-N-n-butyl-N-ethylaniline (benefin); 
(4) 4-trifluoromethyl-2,6-dinitro-N-ethyl-N-methallylaniline 
(ethalfluralin); 
(5) 4-tert-butyl-2,6-dinitro-N-sec-butylaniline (butralin); 
(6) 3,4-dimethyl-2,6-dinitro-N-(1-ethylpropyl)aniline (tendimethalin); 
(7) 4-trifluoromethyl-2,6-dinitro-N-propyl-N-(2-chloroethyl)aniline 
(fluchloralin); 
(8) 4-trifluoromethyl-2,6-dinitro-N-propyl-N-(cyclopropylmethyl)aniline 
(profluralin); 
(9) 4-trifluoromethyl-2,6-dinitro-3-amino-N,N-diethylaniline (dinitramine); 
(10) 4-trifluoromethyl-2,6-dinitro-3-chloro-N,N-diethylaniline 
(intermediate to dinitramine); 
(11) 4-methyl-2,6-dinitro-N,N-bis(2-chloroethyl)aniline; 
(12) 4-sulfamoyl-2,6-dinitro-N,N-di-n-propylaniline (oryzalin); and 
(13) 4-(methylsulfonyl)-2,6-dinitro-N,N-di-n-propylaniline (nitralin). 
Preferred dinitroanilines with which the present invention is carried out 
are trifluralin, isopropalin, benefin, and ethalfluralin. 
Generally, the dinitroanilines are prepared by a reaction route of which 
the following, for trifluralin, is typical: 
##STR1## 
It is believed that small amounts of nitrogen oxides remaining from the 
nitration step react with a portion of the amine during the amination 
step, generating small amounts of nitrosamine which may appear in the 
final dinitroaniline product. Therefore, any nitrosamine contaminant is 
expected to be the nitroso derivative of the alkylamine employed. However, 
it is conjectured that exceedingly small amounts of yet other nitrosamines 
may also be formed. The removal of nitrosamines, regardless of identity, 
is desirable, and the present process meets that objective. 
The mechanism by which the present process operates is not known with 
certainty. It is known, however, that the nitrosamine is converted, 
"denitrosated," to a substance not containing the nitrosamine group. The 
present process provides substantial reduction in nitrosamine 
concentration, regardless of the initial amount of nitrosamine. In most 
cases, the nitrosamine concentration is reduced to less than about 10 ppm. 
The present process is conducted in a liquid phase. In the case of those 
dinitroanilines melting at lower temperatures, such as below about 
140.degree. C., this is preferably achieved by heating the 
nitrosamine-containing dinitroaniline to its melting temperature or 
somewhat higher. Trifluralin melts at about 54.degree.-5.degree. C., 
benefin, at about 65.degree.-6.degree. C., and ethalfluralin, at about 
57.degree.-9.degree. C. Isopropalin melts at about 30.degree. C. but 
because of minor impurities is generally liquid at room temperatures. 
Additionally, a liquid phase can be achieved by dissolving the 
nitrosamine-containing dinitroaniline in a solvent. Suitable solvents 
include aromatic solvents such as benzene and toluene; and halogenated 
aliphatic hydrocarbons, such as chloroform, methylene chloride, and carbon 
tetrachloride. 
The amount of reagent to be employed is not critical, so long as the amount 
is sufficient to reduce the initial amount of nitrosamine to a lesser 
amount. In general, 0.1 to 2.0 grams of reagent per 100 grams of 
dinitroaniline is satisfactory. 
The reaction can be conducted at temperatures over a wide range, such as 
from room temperature to about 140.degree. C. When conducting the process 
neat, the reaction is conducted at temperatures above the melting 
temperature of the particular dinitroaniline. Good results have been 
obtained at temperatures of from 70.degree. to 90.degree. C. when 
conducting the process neat with trifluralin, isopropalin, benefin, and 
ethalfluralin. The reaction can be conducted at atmospheric pressure or at 
elevated pressures. 
The rate at which the present process proceeds will vary with the 
concentration of the nitrosamine, temperature, the reagent, the rate of 
its addition, and other factors. The presence of water is deleterious. The 
progress of nitrosamine removal can be monitored by gas chromatography or 
by TEA analysis. Denitrosation is generally complete in less than an hour. 
Time studies of the present process have shown an early drop in levels of 
nitrosamine, followed in some instances by a slight rise in levels of 
nitrosamine upon extended reaction time. It is believed that extended 
exposure of (1) the dinitroaniline and (2) the denitrosation products, to 
the reaction conditions may result in further nitrosamine formation. 
Therefore, minimizing reaction times is desirable. 
Workup desirably takes the form of neutralization and separation of the 
purified dinitroaniline. 
The following examples illustrate the present invention and will enable 
those skilled in the art to practice the invention. 
Unless otherwise noted, determination of nitrosamine concentration in the 
following examples was done by a gas chromatographic method sensitive down 
to about 0.5 ppm. A "non-detectable" reading (reported below as "N.D.") 
was considered to represent less than about 0.5 ppm of nitrosamine. A 
Hewlett-Packard Model 5711A gas chromatograph was used but the method can 
be carried out with any gas chromatograph apparatus equipped with a flame 
ionization detector. The column was a glass coil 4 ft..times.1/8 inch 
i.d., packed with 3% Carbowax 20M on 100/120 mesh AW DMCS Chromosorb G 
operated at 100.degree. C. After the nitrosamine peak eluted, the column 
was heated to 230.degree. C. and held there for about 15 minutes. The 
helium flow rate was 60 ml/min. A standard of approximately the same 
concentration of the nitrosamine expected in the sample was employed. Both 
standard and sample were prepared in methylene chloride. 
Those examples utilizing TEA analysis are so indicated. Analyses by this 
method were carried out in essentially the same procedures as described at 
J. Chromatogr. 109 (1975), 271. In the context of the present invention, 
this method is considered to be sensitive to nitrosamine concentrations as 
low as about 0.05 ppm. Where TEA analysis of the samples reported below 
showed no nitrosamine, it is reported as "N.D.

EXAMPLE 1 
NITROSAMINE REMOVAL FROM TRIFLURALIN, PCL.sub.3 
A 30-gram portion of a lot of trifluralin with an average assay of 68 ppm 
of nitrosamine and 0.5 gram of PCl.sub.3 were mixed and heated to 
70.degree. C. The reaction mixture was maintained at 70.degree. C., with 
stirring, for one hour. Samples were taken at 30 minutes and 1 hour and 
analyzed for nitrosamine concentration. Thereafter, the reaction mixture 
was neutralized with 2 ml of 10% sodium carbonate solution, the layers 
were separated, and the aqueous layer was extracted with an equal amount 
of methylene chloride. The methylene chloride extract was also analyzed 
for nitrosamine content. The results were as follows: 
______________________________________ 
Time when Nitrosamine 
Sample taken Concentration 
______________________________________ 
30 min. 1.2 ppm 
1 hour N.D. 
(methylene chloride 
extract) N.D. 
______________________________________ 
EXAMPLE 2 
NITROSAMINE REMOVAL FROM TRIFLURALIN, PCL.sub.3 
The reaction reported in Example 1 was repeated except that (1) only 0.2 
gram of PCl.sub.3 was used; (2) the temperature was 90.degree. C.; and (3) 
the reaction was terminated at 30 minutes. A sample was analyzed for 
nitrosamine content and 0.9 ppm was detected. 
EXAMPLE 3 
NITROSAMINE REMOVAL FROM TRIFLURALIN, PCL.sub.3 
The reaction reported in Example 2 was repeated except that only 0.02 gram 
of PCl.sub.3 was used. A sample was analyzed for nitrosamine content; none 
was detected. 
EXAMPLE 4 
NITROSAMINE REMOVAL FROM TRIFLURALIN, PCL.sub.3 
The reaction reported in Example 3 was repeated except that the temperature 
was 120.degree. C. Analysis of a sample showed no nitrosamine. 
EXAMPLE 5 
NITROSAMINE REMOVAL FROM ETHALFLURALIN, PCL.sub.3 
A 30 gram sample of ethalfluralin with a nitrosamine assay of 8.6 ppm was 
heated to 90.degree. C., 0.2 gram of PCl.sub.3 was added, and the reaction 
mixture was stirred for 1 hour at 90.degree. C. A 10% sodium carbonate 
solution (5 ml) was added and the layers separated. A sample of the 
ethalfluralin layer was taken and analyzed for nitrosamine content by TEA; 
the analysis showed 5 ppm of nitrosamine. 
EXAMPLE 6 
NITROSAMINE REMOVAL FROM ISOPROIN, PCL.sub.3 
A xylene solution of isopropalin (50 ml, representing 35 grams of 
isopropalin with a nitrosamine assay of 33.5 ppm) was stripped on a rotary 
evaporator for 20 minutes at 90.degree. C. PCl.sub.3 (0.5 ml) was added 
and the reaction mixture stirred at 80.degree. C. for 30 minutes. A 5% 
sodium carbonate solution (20 ml) was added and the mixture stirred for 10 
minutes, then stripped on a rotary evaporator (15 minutes at 100.degree. 
C.) and analyzed for nitrosamine content. The analysis showed 1.9 ppm of 
nitrosamine. 
EXAMPLES 7-9 
NITROSAMINE REMOVAL FROM TRIFLURALIN, SOCL.sub.2 
A series of three reactions was conducted, varying the amount of SOCl.sub.2 
employed, the reaction temperature, and the reaction time. In each 
reaction, the SOCL.sub.2 and a 30 gram portion of a lot of trifluralin 
with an average assay of 68 ppm of nitrosamine were mixed and heated to 
the reaction temperature. The reaction mixture was maintained at that 
temperature for the specified period, then neutralized with 2 ml of 10% 
sodium carbonate solution. The layers were separated and in the first 
reaction of the series, the organic layer was extracted with an equal 
amount of methylene chloride. Samples were analyzed for nitrosamine 
content with the following results. 
______________________________________ 
Amount Reaction Time when Nitrosamine 
of SOCl.sub.2 
Temperature 
Sample taken 
Concentration 
______________________________________ 
Ex. 7 0.5 g 70.degree. C. 
30 min. 22 ppm 
1 hour 11 " 
methylene 
0.7 .mu.g/ml 
chloride 
extract 
Ex. 8 0.2 g 90.degree. C. 
30 min. 3.9 ppm 
Ex. 9 0.1 g 120.degree. C. 
30 min. 3.2 " 
______________________________________ 
EXAMPLE 10 
NITROSAMINE REMOVAL FROM ETHALFLURALIN, SOCL.sub.2 
A 30 gram sample of ethalfluralin with an assay of 8.6 ppm of nitrosamine 
was heated to 90.degree. C., 0.2 gram of SOCl.sub.2 was added, and the 
reaction mixture was stirred at 90.degree. C. for an hour. A 10% sodium 
carbonate solution (5 ml) was added and the layers were separated. 
Analysis of the organic layer by TEA showed 0.44 ppm of nitrosamine. 
EXAMPLES 11-13 
NITROSAMINE REMOVAL FROM TRIFLURALIN, PBR.sub.3 
In a first reaction, a 30 gram portion of a lot of trifluralin with an 
average assay of 68 ppm of nitrosamine was heated to 70.degree. C. and 0.5 
gram of PBr.sub.3 was added. The reaction mixture was maintained at 
70.degree. C. for 30 minutes, then neutralized with dilute sodium 
carbonate solution and the layers separated. The organic layer was 
analyzed for nitrosamine and showed 1.1 ppm. 
The reaction was repeated under essentially the same conditions except that 
the reaction temperature was 90.degree. C. and only 0.1 gram of PBr.sub.3 
was used. Nitrosamine concentration was reduced to 2.3 ppm. 
The reaction was carried out again under essentially the same conditions, 
except that the reaction temperature was 120.degree. C. and the amount of 
PBr.sub.3 was 0.1 gram. Assay for nitrosamine showed none detectable. 
EXAMPLE 14 
NITROSAMINE REMOVAL FROM TRIFLURALIN, TICL.sub.4 
A 30 gram portion of a lot of trifluralin with an average assay of 68 ppm 
was heated to 90.degree. C. and 0.1 ml of TiCl.sub.4 added. The reaction 
mixture was maintained at 90.degree. C. and samples periodically removed 
and analyzed without workup for nitrosamine content. Results were as 
follows. 
______________________________________ 
Time when Nitrosamine 
Sample taken Concentration 
______________________________________ 
15 min. 59 ppm 
30 min. 16 " 
1 hour 21 " 
2 hours 3.8 " 
______________________________________ 
EXAMPLE 15 
NITROSAMINE REMOVAL FROM TRIFLURALIN, SULFUR DICHLORIDE 
To 100 grams of molten trifluralin, 0.2 gram of sulfur dichloride was 
added, and the reaction mixture was stirred for one hour at 90.degree. C. 
Samples were removed and analyzed for nitrosamine without workup. The 
results were as follows: 
______________________________________ 
Time when Nitrosamine 
Sample taken Concentration 
______________________________________ 
0 50 ppm 
30 min. 7.4 " 
1 hour 7.3 " 
______________________________________ 
EXAMPLES 16-18 
NITROSAMINE REMOVAL FROM TRIFLURALIN, POCL.sub.3 
Three reactions were conducted with POCl.sub.3. In each, a 30 gram portion 
of a lot of trifluralin with an average assay of 68 ppm of nitrosamine was 
heated to a reaction temperature, an amount of POCl.sub.3 was added, and 
the reaction mixture was maintained for 30 minutes at the reaction 
temperature. The reaction mixture was neutralized with sodium carbonate 
and a sample of the organic layer analyzed for nitrosamine. The reaction 
conditions and results were as follows. 
______________________________________ 
Amount of Reaction Nitrosamine 
POCl.sub.3 Temperature Concentration 
______________________________________ 
0.5 g 70.degree. C. 
5 ppm 
0.1 g 90.degree. C. 
10 ppm 
0.1 g 120.degree. C. 
14 ppm 
______________________________________ 
EXAMPLE 19 
NITROSAMINE REMOVAL FROM TRIFLURALIN, PCL.sub.3, EFFECT OF BASE 
A 30 gram portion of a lot of trifluralin with an average nitrosamine assay 
of 68 ppm was mixed with 0.2 gram of PCl.sub.3 and 0.05 gram of sodium 
carbonate. The reaction mixture was heated to 90.degree. C. and maintained 
at 90.degree. C. for 30 minutes, then neutralized with 2 ml of 10% sodium 
carbonate solution and the layers separated. A sample of the trifluralin 
layer was then analyzed for nitrosamine content; none was detected. 
EXAMPLE 20 
NITROSAMINE REMOVAL FROM TRIFLURALIN, PCL.sub.3, TIME STUDIES 
A 30 gram portion of a lot of trifluralin with an average nitrosamine assay 
of 68 ppm was heated to 90.degree. C. and PCl.sub.3 (0.03 ml) was added. 
The reaction mixture was maintained at 90.degree. C. for two hours with 
samples taken periodically and analyzed. Results were as follows: 
______________________________________ 
Time when Nitrosamine 
sample taken Concentration 
______________________________________ 
15 min. 6.6 ppm 
30 min. &lt;1 ppm 
1 hour 4.9 ppm 
2 hours 8.5 ppm 
______________________________________ 
EXAMPLE 21 
NITROSAMINE REMOVAL FROM TRIFLURALIN, SO.sub.2 CL.sub.2 
A 30 ml. portion of trifluralin with a nitrosamine assay of 36 ppm was 
heated to 120.degree. C. and 0.5 ml of SO.sub.2 Cl.sub.2 was added. The 
reaction mixture was maintained at 120.degree. C. for 1 hour. Samples were 
taken at 30 minutes and 1 hour. Each sample was washed with 10 ml of 
water, dried on a rotary evaporator for 15 minutes at 60.degree. C., and 
analyzed for nitrosamine content. Results were as follows: 
______________________________________ 
Time when Nitrosamine 
Sample taken Concentration 
______________________________________ 
30 min. 4 
1 hour 2 
______________________________________ 
EXAMPLE 22 
NITROSAMINE REMOVAL FROM TRIFLURALIN, PCL.sub.5 
The reaction reported on Example 21 was repeated except that PCl.sub.5 (0.5 
gram) was employed instead of SO.sub.2 Cl.sub.2. Results were as follows: 
______________________________________ 
Time when Nitrosamine 
Sample taken Concentration 
______________________________________ 
30 min. 8 
1 hour 4 
______________________________________