Chemistry

T. G. Gnevysheva, I. I. Levkoev

On Polymethine Dyes Derived from Substituted Thiazolines

(Presented by Academician I. L. Knunyants, 30 V 1962)

Substituents in the hetero-residues of cyanine dyes and of dyes closely related to them in structure, when conjugated with the principal chromophore, cause a considerable deepening of the color of these compounds. This bathochromic shift usually increases with an increase in the polarity of the substituents introduced \((^{1,2})\), and its magnitude is evidently determined mainly by the conjugation effect. The inductive influence of substituents on the coloration of such dyes has scarcely been studied. It has only been shown that the presence of ammonium groups in the 5,5′- and 6,6′-positions of thiacarbocyanines \((^{3,4})\), as well as of electron-donor groupings not conjugated with the nitrogen atoms in 2,2′-chino- \((^5)\) and indocarbocyanines \((^6)\), causes only a very small bathochromic shift of the absorption maximum of the dyes. The study, in such dyes, of the actual inductive influence of substituents on coloration is difficult, especially because of their remoteness from the principal chromophore. It therefore seemed of interest to investigate polymethine dyes derived from substituted thiazolines \((\Delta 2)\) (cf. \((^{7,8})\)), in which the groupings in the hetero-residues are not conjugated with the principal chromophore.

In connection with this, dyes of structures I and II were prepared, containing methyl or phenyl groups in the thiazoline residues, with inductive effects differing in sign, and their absorption spectra were investigated.

\[ \begin{aligned} &\text{(I)}\qquad n=1,2,3 \end{aligned} \]

\[ \begin{array}{c|c} R^{1} & R^{2} \\ \hline \mathrm{CH}_{3} & \mathrm{H} \\ \mathrm{H} & \mathrm{CH}_{3} \\ \mathrm{CH}_{3} & \mathrm{CH}_{3} \\ \mathrm{C}_{6}\mathrm{H}_{5} & \mathrm{H} \\ \mathrm{H} & \mathrm{C}_{6}\mathrm{H}_{5} \\ \mathrm{C}_{6}\mathrm{H}_{5} & \mathrm{C}_{6}\mathrm{H}_{5} \end{array} \]

\[ \text{(II)} \]

It may be assumed that in these dyes the five-membered thiazoline ring has a structure sufficiently close to planar. Therefore the spatial arrangement of the groups \(R^{1}\) and \(R^{2}\), located at tetrahedral carbon atoms and lying outside the plane of the hetero-residues, should not change appreciably as a result of their interaction and under the influence of substituents at the cyclic nitrogen atoms, as occurs in substituted thiazolocarbocyanines (III) \((^{9-11})\).

\[ \text{(III)} \]

2,4- and 2,5-dimethyl-($^{12,13}$) and 2,4,5-trimethylthiazolines ($^{13}$), 2-methyl-4- and 5-phenyl- and 2-methyl-4,5-diphenylthiazolines ($^{14}$) were obtained by the action of phosphorus pentasulfide on the mono- or diacetyl derivatives of the corresponding aminomercaptans in benzene or xylene on heating (cf. ($^{13,15}$)).

\[ \begin{aligned} &\begin{matrix} R^2{-}\mathrm{CHOH}\\ \big|\\ R^1{-}\mathrm{CHNH_2} \end{matrix} \quad \begin{matrix} \nearrow\\[-2mm] \searrow \end{matrix} \quad \begin{matrix} R^2{-}\mathrm{CHOH}\\ R^1{-}\mathrm{CHNHCOCH_3}\\[1mm] R^2{-}\mathrm{CHOCOCH_3}\\ R^1{-}\mathrm{CHNHCOCH_3} \end{matrix} \quad \begin{matrix} \searrow\\[-2mm] \nearrow \end{matrix} \quad \xrightarrow{\ \mathrm{P_2S_5}\ } \quad \begin{matrix} R^2\mathrm{HC}{-}\mathrm{S}\\[-1mm] R^1\mathrm{HC}\ \ \ \ \mathrm{C}{-}\mathrm{CH_3}\\[-1mm] \ \ \ \ \ \ \ \ \backslash \mathrm{N} \end{matrix} \end{aligned} \]

From the ethyl p-toluenesulfonates of these bases, symmetric carbo-, di-, and tricarbocyanines (I, \(n = 1, 2, 3\)) were synthesized by the usual methods.

Table 1

Literature data. In CH₃OH: ¹ 443.5 mµ ($^{17}$), 445 mµ ($^{18}$); ² 545 mµ ($^{19}$); ³ 645 mµ ($^{20}$).

Dimethinemerocyanines (II) were obtained by interaction of the indicated quaternary salts with 3-ethyl-5-ethoxymethylenerhodanine in absolute ethyl alcohol in the presence of triethylamine. In most cases the dyes were purified by chromatography on aluminum oxide to separate by-products (in particular, neocyanines in the synthesis of carbocyanines), followed by crystallization. In the synthesis of merocyanines (II), among the by-products there was observed the formation of a monomethinoxanine derivative of 3-ethylrhodanine, as well as more deeply colored salt-like dyes, the structure of which is being studied.

Table 2

* Literature data: 482.5 mµ (in CH₃OH) ($^{22}$); 482 mµ (in C₂H₅OH) ($^{23}$).

Table 1 gives the positions of the absorption maxima (\(\lambda_{\max}\)) in alcoholic solutions of substituted thiazolinocyanines (I, \(n = 1, 2, 3\)) and the corresponding thiazolocarbocyanines (III) (measured on an SF-2 spectrophotometer), and, for dyes I (\(n = 1\)) and III, also the values \(A\) ($^{16}$), characterizing their basicity.

From the data of Table 1 it is seen that the introduction of methyl groups into the hetero residues of thiazolinocyanines has very little effect on the position of the absorption maximum of the dyes and on the magnitude of their basicity; phenyl radicals in the same positions cause a somewhat greater deepening of color and a marked decrease in the basicity of the dyes. Analogous substitution in the thiazolocarbocyanine molecule leads to significantly larger bathochromic shifts of the absorption maximum (13–49 mµ) and changes in basicity ($^9$). The influence of substituents in the 4,4′- and 5,5′-positions on the color of thiazolinocarbocyanines is practically identical and additive. At present

It is difficult to explain the somewhat reduced basicity of 4,5,4′,5′-tetramethylthiazolinocarbocyanine; it seems unlikely that the introduction of methyl groups causes such a distortion of the valence angles of the thiazoline ring as could affect the basicity of the dye.

Table 2 gives the absorption maxima of the synthesized dimethylmerocyanines II and the values of the “hypsochromic shifts” (21), calculated for these dyes.

The data of Table 2 confirm that only in the case of the introduction of phenyl groups does some lowering of the basicity of the thiazoline heteroresidue occur.

Thus, using cyanine and merocyanine dyes derived from thiazoline as examples, it has been shown that the introduction into the heteroresidue of substituents not conjugated with the principal polymethine chromophore and, consequently, possessing only an inductive effect, has very little influence on the color and, in some cases, on the basicity of the dyes. In the case of methyl groups \((+J_{\text{effect}})\), this influence is manifested more weakly than in the case of phenyl groups \((-J_{\text{effect}})\). It is still unclear whether these differences are connected only with the direction or also with the magnitude of the inductive effects of these substituents.

Scientific Research
Cinema and Photography Institute

Received
12 III 1962

REFERENCES

1. A. I. Kiprianov, I. K. Ushenko, E. D. Sych, ZhOKh, 15, 200 (1945).
2. A. I. Kiprianov, I. K. Ushenko, ZhOKh, 15, 207 (1945).
3. I. I. Levkoev, N. N. Sveshnikova et al., Tr. NIKFI, 7, 29 (1944).
4. A. I. Kiprianov, E. D. Sych, Collection of Works of the Institute of Organic Chemistry, Academy of Sciences of the Ukr. SSR, 13, 17 (1947).
5. W. T. K. Braunholtz, J. Chem. Soc., 121, 170 (1922).
6. E. D. Sych, Ukr. Khim. Zhurn., 19, 657 (1953).
7. P. D. Dreifuss, Bela Gaspar, Pat. USA 2677683; Chem. Abstr., 49, 1458 (1955).
8. J. H. Dessauer, M. A. Insalaco, Pat. USA 2653152; Chem. Abstr., 48, 485 (1954).
9. B. S. Portnaya, I. I. Levkoev, N. S. Spasokukotskii, DAN, 75, 231 (1950).
10. E. W. Knott, J. Chem. Soc., 1952, 4099.
11. E. D. Sych, Ukr. Khim. Zhurn., 22, 80, 217 (1956); 24, 89 (1958).
12. S. Gabriel, C. Freiherr, V. Hirsch, Ber., 29, 2609 (1896).
13. G. Bach, M. Zahn, J. prakt. Chem. (4), 8, 68 (1959).
14. Z. P. Sytnik, I. I. Levkoev, T. G. Gnevysheva, K. I. Pokrovskaya, USSR Author’s Certificate No. 104295 (1956).
15. H. Wenker, J. Am. Chem. Soc., 57, 1079 (1935).
16. A. I. Kiprianov, S. G. Fridman, L. S. Pupko, Collection of Works of the Institute of Organic Chemistry, Academy of Sciences of the Ukr. SSR, 13, 40 (1947).
17. L. G. S. Brooker, J. Am. Chem. Soc., 58, 662 (1936).
18. L. G. S. Brooker, A. L. Sklaret al., J. Am. Chem. Soc., 67, 1875 (1945).
19. F. M. Hamer, R. J. Rathbone, B. S. Winton, J. Chem. Soc., 1947, 1434.
20. N. J. Fisher, F. M. Hamer, J. Chem. Soc., 1933, 189.
21. A. I. Kiprianov, G. T. Pilyugin, Uch. zap. Kharkovsk. gos. univ., 10, 91 (1937); A. I. Kiprianov, Dokl. AN UkrSSR, 12, 3 (1940); L. G. S. Brooker, R. H. Sprague et al., J. Am. Chem. Soc., 62, 1120 (1940).
22. F. M. Hamer, B. S. Winton, J. Chem. Soc., 1949, 1126.
23. M. V. Deichmeister, Z. P. Sytnik, E. B. Lifshits, ZhOKh, 22, 168 (1952).