Process for recovering zwitterionic diazonium salts by aggregation

Zwitterionic diazonium salts, derived from aromatic amines, are aggregated by: (a) diazotizing said amine to a zwitterionic diazonium salt in the presence of a cationic surfactant or (b) diazotizing said amine and thereafter treating the resulting zwitterionic diazonium salt with a cationic surfactant, so as to give particles of the diazonium salts which are readily separable from the liquid mass in which they are formed.

BACKGROUND OF THE INVENTION 
This invention relates to a process for recovering zwitterionic diazonium 
salts, derived from aromatic amines, which comprises: (a) diazotizing said 
amine to a zwitterionic diazonium salt in the presence of a cationic 
surfactant or (b) diazotizing said amine and thereafter treating the 
resulting zwitterionic diazonium salt with a cationic surfactant. The 
presence of the cationic surfactant during or after diazotization causes 
the zwitterionic aromatic diazonium salt to aggregate so as to give 
particles thereof which are readily separable from the liquid mass in 
which they are formed. 
Amines can be diazotized by the use of several techniques. In the direct 
diazotization process, an acidic slurry of the amine is prepared and a 
nitrite is added thereto. In the so-called reverse method, the amine is 
dissolved in alkali, a soluble nitrite is added, and that mixture is 
poured into an acid, such as hydrochloric acid, so as to effect the 
diazotization. Various difficulties have been encountered with both 
methods. For example, in the diazotization of an aminosulfonic acid by the 
direct method, incomplete diazotization is often encountered if the 
aminosulfonic acid is not freshly precipitated in a finely divided state. 
While the reverse method usually results in complete diazotization of an 
aminosulfonic acid, the resulting insoluble zwitterionic diazonium salt is 
often formed in such a finely divided state that it is difficult to 
isolate. The process of the present invention provides for complete 
diazotization and results in the diazonium salt being in such a state of 
aggregation that it is readily separable from the liquid components in 
which it is formed. 
In U.S. Pat. No. 2,845,326, a stable dispersion of a diazotizable primary 
amine devoid of solubilizing groups e.g. OH or SO.sub.3 H, is obtained by 
the combined use of a cationic compound and non-ionic compound. 
In U.S. Pat. No. 2,812,321, it is disclosed that the addition of a 
surface-active agent of the polyoxyethylene fatty ester class to the 
1,2,4-acid diazotization reaction mixture causes it to remain fluid 
throughout the diazotization process. 
U.K. Patent Specification No. 1,072,702 discloses a process for producing a 
pigment having improved flow properties, dispersibility or gloss retention 
properties which comprises precipitating the pigment in the presence of 
two surfactants, or after-treating a slurry of the pigment with two 
surfactants, one of the surfactants being cationic and the other 
surfactant being anionic in character, and both surfactants having a 
surface tension of not more than 38.5 dynes per cm in a 0.2% by weight 
aqueous solution at 25.degree. C. 
DETAILED DESCRIPTION OF THE INVENTION 
By definition a zwitterionic diazonium compound is one containing a 
substituent that functions as an anion. Common examples of such 
substituents in the dye art are the sulfonic acid group and the hydroxyl 
group. This invention relates to the disclosed processing of diazotizable 
aromatic amines which, because of their proton donor content, are 
zwitterionic. It relates particularly to such processing of diazotizable 
aromatic amines having OH or SO.sub.3 H substituents, for example, 
dehydrothio-p-toluidine sulfonic acid (DHTPTSA) having the formula: 
##STR1## 
2-aminobenzothiazole-6-sulfonic acid, having the formula: 
##STR2## 
4-aminoazobenzene-4'-sulfonic acid having the formula: 
##STR3## 
3-methoxy-4-aminoazobenzene-3'-sulfonic acid; and 2,5-dichloroaniline 
sulfonic acid. 
The cationic surfactant must have at least one long chain (C.sub.10 
-C.sub.18) aliphatic substituent. The best cationic agents have two long 
chains (C.sub.16 -C.sub.18) aliphatic substituents. In particular, the 
cationic surfactants are (1) ammonium compounds of the formula: 
##STR4## 
wherein 
R.sup.1 -R.sup.4 are alkyl containing 1-18 carbons, alkenyl containing 8-18 
carbons, or benzyl; at least one of R.sup.1 -R.sup.4 is a C.sub.10 
-C.sub.18 alkyl or alkenyl; preferably two of R.sup.1 -R.sup.4 are 
C.sub.16 -C.sub.18 alkyl or alkenyl; provided that no more than one of 
R.sup.1 -R.sup.4 is benzyl; 
R.sup.5 -R.sup.9 are hydrogen or R.sup.10 CO--, at least two thereof being 
R.sup.10 CO--; 
R.sup.10 is alkyl or alkenyl containing 11-17 carbons; 
R.sup.11 and R.sup.12 are C.sub.1 -C.sub.4 alkyl; 
R.sup.13 is a bivalent alkylene having 2 to 6 carbons; 
m is 0 to 2; 
n is 0 or 1; and 
X.sup..crclbar. an anion; or 
(2) imidazolium compounds of the formula: 
##STR5## 
wherein R.sup.14 is C.sub.15 -C.sub.17 aliphatic chain. 
The amount of the cationic adjuvant may vary from one diazonium salt to 
another. One would use the minimum amount required to effect the degree of 
aggregation desired. That effect can be determined by observation. 
Generally, one would use between 0.5 and 5 weight % of the cationic 
compound, based upon the weight of diazonium compound. 
The process of this invention can be applied to diazotizations by the 
direct or the reverse method. Moreover, the cationic surfactant may be 
present in the reaction mixture during diazotization or it can be added 
thereto after completion of the diazotization step. 
For example, dehydrothio-p-toluidine sulfonic acid (DHTPTSA) is slurried or 
dissolved in a slight excess of aqueous alkali. The alkali can be sodium 
hydroxide, potassium hydroxide, or lithium hydroxide. A mixture of 
potassium and lithium hydroxide is preferred to form a stable solution of 
DHTPTS. The lithium-potassium DHTPTS solution is drowned in hydrochloric 
acid. Aqueous sodium nitrite is added. After destroying the excess 
nitrite, a cationic adjuvant is added to aggregate the diazo into a 
filterable form. It may be helpful to digest the diazo at 
30.degree.-60.degree. C. to further improve the physical form. The diazo 
is isolated by filtration, washed with water, slurried in water, and then 
coupled with a coupler using a base such as triethanolamine. The cationic 
adjuvant can be removed by filtration of the liquid.

The following examples further illustrate the invention. 
EXAMPLE 1 
The adjuvants shown below have been evaluated in the DHTPTSA process 
described above. After the diazotization was completed, the cationic 
adjuvant was added in a quantity equivalent to 1.57% by weight, based on 
the weight of DHTPTSA, and the resulting mixture was held at 32.degree. C. 
for one hour. The filter leaf test was then performed on the mixture. 
The filter leaf test involves the use of a filter dip disc (3.4 cm dia.) on 
which a vacuum can be drawn. The filter dip disc was put into the diazo 
slurry for 10 sec. (pick up), withdrawn, and allowed to dewater for 10 
sec. The diazo collected was weighed, dried, and weighed again. The volume 
of the filtrate was measured. In another series of tests, the diazo was 
digested at 50.degree. C. for one hour and the filter leaf tests run at 
50.degree. C. The control run contained no adjuvant. 
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Trade Name Chemical Name 
______________________________________ 
"Avitex" ML A quaternary ammonium compound 
represented by the formula: 
##STR6## 
two of the R groups are hydrogen 
and about two thereof are oleyl 
Adogen 442 Di(hydrogenated tallow)dimethyl 
ammonium chloride 
Adogen 471 Tallow trimethyl ammonium 
chloride 
Adogen 477 N-tallow-pentamethyl propane 
diammonium dichloride 
Variquot 60LC 
Dimethylalkyl (C.sub.10-C.sub.18) 
benzyl ammonium chloride 
Variquot K75 Methyl (1) soya amidoethyl 
(2) soya imidazolium methyl 
sulfate 
Varisoft 3690 
Methyl (1) oleylamidoethyl 
(2) oleyl imidazolium methyl 
sulfate 
BTEAc Benzyl triethyl ammonium 
chloride 
TBAc Tetrabutyl ammonium chloride 
______________________________________ 
______________________________________ 
Filter Leaf Tests (10 Sec. Pick-Up 
10 Sec. Dewater) 
32.degree. C. 
50.degree. C. 
Dry ml/ Dry ml/ 
Adjuvant Wt. Wt. Filtrate 
Wt. Wt. Filtrate 
______________________________________ 
Control 8 4 20 13 6 30 
BTEAc 8 4 21 12 6 29 
TBAc 8 4 22 11 5 25 
"Avitex" ML 
10 5 26 22 10 50 
Adogen 442 12 6 33 17 9 50 
Adogen 471 9 4 19 11 5 26 
Adogen 477 9 4 21 12 5 28 
Variquot 60LC 
11 5 22 15 7 34 
Variquot K75 
13 6 29 22 10 48 
Varisoft 3690 
13 6 30 19 9 47 
______________________________________ 
At the concentration used in the tests, all of the foregoing except Adogen 
471, BTEAc and TBAc were found to have some beneficial effect on the 
diazonium salt. "Avitex" ML, Adogen 442, Variquot 60LC, Variquot K75, and 
Varisoft 3690 were found to be particularly effective. 
EXAMPLES 2-4 
The procedure of Example 1 was repeated to give the following results: 
______________________________________ 
Filter leaf 
10 sec 10 sec 
tests pick up dewater 
Wet cake(g) 
ml filtrate 
dry cake(g) 
______________________________________ 
4-Aminoazobenzene-4'-sulfonic acid 
Control (26.degree. C.) 
5.3 33 2.4 
Variquot K75 6.3 39 3.0 
Variquot K75 (40.degree. C.) 
6.7 46 3.4 
2,5-Dichloroaniline sulfonic acid 
Control (15.degree. C.) 
1.9 66 1.0 
Variquot K75 (15.degree. C.) 
1.1 32 0.5 
Variquot K75 (35.degree. C.) 
2.2 90 1.4 
3-Methoxy-4- 
aminoazobenzene-3'-sulfonic acid 
Control (25.degree. C.) 
15.0 58 9.0 
Variquot K75 19.0 86 11.8 
______________________________________ 
EXAMPLES 5 AND 6 
An aqueous hydrochloric acid slurry of 4-aminoazobenzene-4'-sodium 
sulfonate (AABSS) was diazotized in a control run as follows: 
To 380 ml of water were added 70 g of 31.5% HCl and 95 g of 60% AABSS. That 
mixture was cooled to 15.degree. C., then its temperature was allowed to 
rise at will. Over a period of 1 hour, 36 g of 40% sodium nitrite were 
added, and thereafter the mixture was held for 1 hour. At the end of that 
1-hour period, 12 g of 15% sulfamic acid were added over a period of 30 
minutes, and the mixture was held for another 10 minutes so as to destroy 
the excess sodium nitrite. 
The foregoing diazotization reaction was repeated for Examples 5 and 6; 
however, after the HCl had been added and before addition of the AABSS, a 
cationic surfactant was added to the reaction mixture. In the case of 
Example 5, 4 g of Avitex ML were added, and in the case of Example 6, 4 g 
of Avitex Y were added. Avitex Y is the reaction product of 
diethylenetriamine, propylene oxide, stearic acid and methyl sulfate 
having an average structure represented by the formula: 
##STR7## 
wherein about two of R are hydrogen and the remainder thereof are stearyl. 
In a filter leaf test for the reaction masses obtained for the Control and 
for Examples 5 and 6, the rate of filtration and washing were judged by 
the volume of filtrate collected after specific filtration and washing 
times, as recited below. The filtration and washing tests were performed 
using a one-square-inch filter leaf connected to a vacuum source (when 
deadheaded, the source would provide a vacuum of 21 inches of mercury). 
The following data show that Avitex ML and Avitex Y can increase the rate 
of filtration, and more importantly, washing of the diazonium zwitterion 
resulting from the diazotization of AABSS. 
______________________________________ 
Pickup Wash 
Time Time Dewater Filtrate (ml) 
(sec) (sec) (sec) Control Ex. 5 Ex. 6 
______________________________________ 
5 -- 20 2.5 7.5 7.8 
10 -- 20 7.8 15.5 15.5 
5 10 20 9.0 16.0 17.5 
5 20 20 10.5 24.0 23.0 
5 40 20 17.5 37.0 32.5 
______________________________________ 
EXAMPLES 7-9 
In a control diazotization process, 63.3 g of a sulfonation mass containing 
0.07 mole of 2-aminobenzothiazole-6-sulfonic acid (prepared by reacting 
2-aminobenzothiazole with 98% H.sub.2 SO.sub.4 for about 2 hours at about 
120.degree. C.), 15 g of acetic acid, 45 ml of water and 24.2 g of a 38.4% 
solution of nitrosyl sulfuric acid (0.073 mole) were reacted at 25.degree. 
C. for 11/2 hours. In the diazotization processes of Examples 7, 8 and 9, 
0.8 g of a surfactant was added before addition of the nitrosyl sulfuric 
acid. The control mass and those for Examples 7, 8 and 9 were filtered on 
a sintered glass funnel under a vacuum of about 125 mm of Hg. The volume 
of filtrate which was collected in 12 minutes is recorded below. 
______________________________________ 
Example Filtrate (ml) 
______________________________________ 
7 - Avitex ML 32.5 
8 - Varisoft 3690 
54.5 
9 - Variquot 60LC 
28.5 
No surfactant 15 
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