[COMMUNICATION
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KODAKRESEARCH LABORATORIES]
SOME DYES RELATED TO TOLUIDINE BLUE C.
F.
H. ALLEN, C. V. WILSON,
AND
G . F . FRAME
Received October 8, I941
It was pointed out in a previous paper (1) that the dye Toluidine Blue has uncommon spectral absorption characteristics, and it seemed worth while to examine a few similar dyes. The relation between the color and constitution of anthraquinone dyes is well summarized in Houben (2) ; there are a large number of examples illustrating the effect of different groups by themselves or in combination. However, there are comparatively few instances in which simple homologs or isomers are concerned. The most noticeable effect among the acid anthraquinone dyes is found in the difference between the 1,4- and the 1,5-series; when arylamino groups are present the former are green and the latter are bluish. Toluidine Blue (I) is a sulfonated 1,5-ditoluidino-4,8-dihydroxyanthraquinone, and its isomer (11) , 1,4-ditoluidino-5,8-dihydroxyanthraquinone, is Toluidine Green (1) ; these colors thus fit into the series mentioned above. In these structures the rings A are aromatic nuclei of the benzene series; ring B is that portion of the anthraquinone residue to which the aromatic groups are attached; and C the portion without such groups.
CHaN
I
7L-N
\ d\ S
II
I
0
0
....**..../
H
H
(S = SOsNa)
I
I1
Isomers, homologs, and isologs can be secured by (a) varying the nature of the aromatic nuclei A , (b) introducing different substituents into B or C , and (c) changing the position or number of the sulfonic acid groups. Since rings A are always introduced into the molecule by the use of an aromatic amine, it is possible to determine the effect of substituents by using substituted anilines. In this paper are described several dyes in the blue series obtained by the first and third variations; the second type is more easily secured in the green series, and will be described in the following paper. 68
69
DYES RELATED TO TOLUIDINE BLUE
The new dyes have been obtained, using ortho- and meta-toluidine, p-anisidine, p-t-amylaniline, ortho- and para-chloroaniline, p-xenylamine, and @-naphthylamine. The second, third, and last two of these aremuch more soluble inmater than Toluidine Blue; from the sulfur-nitrogen ratio, determined on the second and third, it was concluded that there were two sulfonic acid groups to each
WAVE LENGTH IN MILLIMICRGNS
WAVE L E N G T H IN MILLIMICRONS
FIG.1
FIG.2 FIG. 1. DYES RELATEDTO TOLUIDINE BLUE, HAVINGDIFFEREXTTYPEOF ABSORPTION
-,
CURVE 3’-CH3;
-,
Toluidine Blue (4‘-CH3) ; -, Effect of oleum on Toluidine Blue.
- - *,
2’-CH3;
------ , OC&; - -
FIG. 2. 4 ‘ 4 - h ~HOMOLOG ~ OF TOLUIDINE BLUE 4’-t-amyl homolog, 1:13,OOO; Toluidine Blue, 1:2O,MH3; homolog, 1 :20,000.
-
-,
e ,
--,
4’4-amyl
> P
600
WA’E
roo V A V E L E N G T U IN MILLIMICRONS
LENGTH IN MILLIMICRONS
FIG.4 FIG.3. DYESRELATEDTO TOLUIDINE BLUE,HAVINQSAMETYPEOF ABSORPTION CURVE FIG.3
- -
-,
-,
Toluidine Blue (4’-CH3);
-,
FIG.4. EFFECT OF POSITION OF SULFONIC ACID GROUPS Toluidine Blue ( 2 ’ 4 0 3 X a ) ; - - isomer (3‘-s03Na),
----_-, 4’-phenyl isolog.
a
e ,
p-naphthyl isolog;
4’-chloro isolog;
e ,
nitrogen in the more soluble dyes. The absorption curves of these dyes (Fig. 1) resemble that of the blue dye that results when Toluidine Blue is treated with fuming sulfuric acid; the latter has a sulfur-nitrogen ratio greater than 1, but a pure sample has never been secured. p-t-Amylaniline gives a dye which resembles Toluidine Blue but does not seem to be as strong (Fig. 2). The dyes from p-xenylamine and /3-naphthylamine absorb in the violet and are greenish (Fig. 3),
70
ALLEN, WILSON, AND FRAME
while the one from p-chloroaniline does not have as high absorption in the far red. From these results it may be concluded that only pura-alkylated amines can be expected to produce dyes closely resembling Toluidine Blue. The third type of variation concerns the location of the sulfonic acid group. Direct sulfonation always introduces this group into the 2'-position, ortho to the NH, when the 4'-position is blocked; the position of the sulfonic acid group has been determined by reductive hydrolysis (1). Since 1,5-substitution is unsymmetrical, the usual procedures (3, 4) for securing 3'-sulfonic acids cannot be employed. Adapting a method of preparation useful for certain monoarylated anthraquinones (5, 6), the desired dye was obtained. This reaction consisted in heating a mixture of 4,s-dichloroanthrarufin and sodium 4-aminotoluene-2sulfonate under pressure. The absorption curve of the isomer of Toluidine Blue, furnished by this procedure, falls off in the far red (Fig. 4). EXPERIMEKTAL
The anthraquinone derivatives were mostly prepared by a general procedure ag described under the m-toluidino derivative. Under these conditions, however, the ortho amines did not react, and the addition of boric acid (second procedure) was employed. Two other isologs needed further modifications and are treated separately. The analyses of the anthraquinones are given in Table I. I n general the melting points are accompanied by decomposition and/or sublimation, so that an accurate determination is not possible. I. THE ANTHRAQUINONES
(a) 4,8-Di-m-toluidino-i ,5-dihydroxyanthraquinone. A mixture of 8 g. of 4,8-dichloroanthrarufin (m.p. ca.337") and 100 g. of m-toluidine was heated for sixteen hours at 160-175". After cooling slowly to 50", the mixture was poured into a large excess of dilute hydrochloric acid. The precipitated dye was filtered and washed thoroughly with warm water, followed by 70% alcohol. The yield of crude product was 11 g. For analysis and for subsequent sulfonation, the product was recrystallized first from chlorobenzene and then from xylene. The 4,8-di-p-toluidino, 4,8-di-p-tertiary-amylanilino, 4,8-di-p-anisidino, and 4,8-di-pchloroanilino derivatives were prepared in exactly the same manner. In all cases recrystallization was from chlorobenzene or xylene. If very insoluble, a digestion with chlorobenzene was found sufficient for purification. (b) 4,8-Di-o-ehloroanilino-1,6-dihydroxyanthraquinone. o-Chloroaniline and o-toluidine failed to react with dichloroanthrarufin under the conditions used in the above experiment. It was found necessary to add boric acid, equivalent to about 2/3 the weight of the dichioroanthrarufin. The dyes were isolated as above and were recrystallized from a large volume of xylene for analysis. (c) ~,8-Di-p-xenylamino-I, 5-dihydroxyanthraquinone. A mixture of 50 g. of p-xenylamine and 5 g. of dichloroanthrarufin was heated for eighteen hours a t 170". On pouring the partially cooled product into dilute hydrochloric acid everything precipitated, as the hydrochloride of the amine is not water-soluble. The product was collected, dried, ground to a powder, suspended in 10% sodium hydroxide solution, and stirred for three hours. It was filtered and the precipitate extracted thoroughly with ether to remove the amine. The residue was digested with chlorobenzene for purification, as its low solubility made crystallization impractical. (d) 4,8-Di-P-naphthylarnino-i, 5-dihydroxyanthraquinone. A mixture of 50 g. of 8-naphthylamine and 5 g. of dichloroanthrarufin was heated for twenty-four hours at 170-180". After cooling partially, the reaction mass was treated with about 15 times its volume of 70% ethyl alcohol and the insoluble portion filtered. This material was then transferred t o a
71
DYES RELATED TO TOLUIDINE BLUE
beaker and stirred for a short time with ether in order to remove the unused p-naphthylamine. Finally, it was collected on a Buchner funnel and washed with ether. The light violet product is only slightly soluble in chlorobenzene, xylene, etc., but can be crystallized from a rather large volume of the former. All the substances dissolve in concentrated sulfuric acid with production of a green color and give brilliant blue solutions when poured into water, except the naphthyl isolog, which gives a dull green. The solutions in xylene are all a brilliant blue.
TABLE I ANALYSES OF SUBSTITUTED ANTHRAQUINONES CALC'D, %
FOUND,
%
AMINE USED
C
o-Toluidine.. . . . . . . . . . . . . . . . 74.7 m-Toluidine . . . . . . . . . . . . . . . . 74.7 0-C hloroaniline . . . . . . . . . . . . .
p-xenylamine.. , , , , , . . , , , . p-Xaphthylamine,. . . . . . . . .
C
4.9 4.9
6.2 6.2 5.7
,I
~
i
H
74.9 1 4 . 8 74.7 5.0
6.2 6.4 5.8
~
14.5
,
.I
~
'
14.5
5.2 5.4
11. SULFONATION
The substituted anthraquinones were sulfonated by the use of concentrated sulfuric acid on the steam-bath; this required two and one-half hours with all except the derivative formed from o-toluidine, in which the time had to be greatly increased. The dye-salt mixtures were extracted by boiling methanol-the only method of purification a t all satisfactory. The procedure is illustrated by sulfonation of the isomer derived from m-toluidine. (a) m-Toluidine isomer. A solution of 10 g. of 4,s-di-m-toluidinoanthrarufinin 75 cc. of concentrated sulfuric acid was stirred on the steam-bath for two hours. After cooling and pouring on ice, there was no separation of dye acid, so the entire solution was neutralized by sodium hydroxide. After several hours, much of the sodium sulfate had crystallized and was removed; the filtrate was evaporated to dryness. The pulverized residue was extracted in a Soxhlet apparatus with 500 cc. of methanol for fifty hours; 3 g. of dye was thus secured. From the analysis, i t was estimated to be about 65% dye; Found: N, 2.3; S, 9.3, 9.5. This gives a 1 : l . S ratio of nitrogen to sulfur, indicating that i t is essentially a tetrasulfonic acid, (two SOaNa groups to each toluidine residue). I n a similar manner, the other isologs, except the one from o-toluidine, were secured. The one from p-anisidine, on analysis, showed 1.5% nitrogen and 6.5, 6.6, 6.5% sulfur, which gives a 1:l.g nitrogen:sulfur ratio. The dye from o-chloroaniline has a 1 : l ratio. Anal. Calc'd for C21HllCllN2Na201&:N, 4.0; S, 9.2. Found: X , 4.0; S,9.0, 8.9. (b) For the ortho toluidino isomer, a mixture of 3 g. of the anthraquinone and 23 cc. of concentrated sulfuric acid was heated on the steam-bath for seven hours; the dye acid precipitated after icing. The methanol extraction required sixteen days, and 2.1 g. of dye resulted; in this, the su1fur:nitrogen ratio is 1 : l . Anal. Calc'd for C2sH20NzNazOl&:S, 9.8. Found: S, 9.7, 9.8. (c) Fuming sulfuric acid on Toluidine Blue. A solution of 5 g. of the dye and 25 cc. of 20% oleum was stirred a t 35-40' for one hour, the solution poured upon ice, the dye acid filtered
72
ALLEN, WILSON, AND FRAME
and dissolved in hot sodium hydroxide. After again filtering, the dye was salted out; 4.75 g. of dye-salt mixture resulted. Upon analysis, 1.7% of nitrogen and 4.8,4.8,4.9% of sulfur were found; this indicated that the dye was of about 35% purity. The nitrogen:sulfur ratio is 1:1.3. 111. 4,8-DI-(3‘-SULFO-~-TOLUIDINO)-~,5-DIHYDROXYANTHRAQUINONE (DISODIUM
SALT)
A mixture of 3 g. each of dichloroanthrarufin, sodium acetate, and boric acid, and 8 g. of 4-aminotoluene-2-sulfonic acid in 20 cc. of water and 20 cc. of acetic acid in a sealed tube was heated a t 225’ for thirty hours. The tube contents were extracted by water and the blue solution filtered from the considerable insoluble material. The filtrate was evaporated to dryness and the residue was extracted with absolute methyl alcohol until all the blue color was removed. On standing, the methyl alcohol deposited a blue solid; this dissolved in water to give a brilliant blue solution comparable in strength and general appearance to the Toluidine Blue. SUMMARY
Several homologs of Toluidine Blue have been prepared in order to compare their absorption characteristics with those of the parent substance. The closest resemblance is found with the p-t-amyl homolog. ROCHESTER, N. Y. REFERENCES
(1) ALLEN,FRAME, AND WILSON, J. Org. Chem. 6,732 (1941). (2) HOUBEN, “Das Anthracen und die Anthrachinone,” Verlag Georg Thieme, Leipzig, 1929, pp. 14-30. (3) SCHULTZ, “Farbstofftabellen,” 7. Auflage. Akademische Verlagsgesellschaft m.b.H., Leipeig 1931, No. 1194,page 528;No. 1202,page 533. (4) German patent 181,879;[Frdl., 8, 318 (1906-7)l. (5) German patent 201,904;[Frdl., 9, 736 (190&10)1. (6) German patent 206,645;[Frdl., 9, 720 (1908-IO)].
