Chemistry

Corresponding Member of the Academy of Sciences of the USSR V. V. Korshak, A. M. Sladkov, and Yu. P. Kudryavtsev

Oxidative Dehydropolycondensation of 2,6-Dimethyl-3,5-diethynylpyridine and 9,10-Diethynyl-9,10-dihydroxy-9,10-dihydroanthracene

It was shown earlier that oxidative dehydropolycondensation of acetylene ($^1$) and of certain diacetylenic hydrocarbons ($^{2,3}$) leads to the formation of high-molecular-weight products containing conjugated acetylenic bonds in the chain. The reaction follows the scheme:

$$ n\,\mathrm{HC}\equiv\mathrm{C}-\mathrm{R}-\mathrm{C}\equiv\mathrm{CH} \ \xrightarrow[\mathrm{Cu}^{+}]{\mathrm{O}_{2}}\ -\left[\mathrm{C}\equiv\mathrm{C}-\mathrm{R}-\mathrm{C}\equiv\mathrm{C}\right]_{n}- $$

The high-molecular-weight products formed by this reaction are insoluble and possess electrophysical properties anomalous for organic substances ($^{1-3}$). To obtain soluble compounds, there are apparently three possibilities, namely: carrying out the reaction in the presence of monoacetylenes that terminate the chain, with the aim of obtaining low-molecular-weight products; introducing into the molecules of the initial diacetylenic hydrocarbons bulky groups R; and introducing polar groups R.

To confirm these assumptions, we synthesized 9,10-diethynyl-9,10-dihydroxy-9,10-dihydroanthracene and 2,6-dimethyl-3,5-diethynylpyridine. The oxidative dehydropolycondensation reaction was carried out with these products and jointly with acetylene, p-diethynylbenzene, phenylacetylene, propargyl alcohol, and 2-methyl-5-ethynylpyridine. As a result of the reaction, in all cases both insoluble and soluble products of identical structure were obtained.

The structure of the products was established by comparison of the IR spectra of the starting products, soluble and insoluble polymers, and also on the basis of elemental analysis of the products obtained. Below is given the scheme for formation of high-molecular-weight products by the oxidative dehydropolycondensation reaction.

$$ n\,\mathrm{HC}\equiv\mathrm{C}-\mathrm{A}-\mathrm{C}\equiv\mathrm{CH} +\mathrm{HC}\equiv\mathrm{C}-\mathrm{B} \ \xrightarrow[\mathrm{Cu}^{+}]{\mathrm{O}_{2}}\ \leftrightarrow \mathrm{B}-\mathrm{C}\equiv\mathrm{C} -\left[-\mathrm{C}\equiv\mathrm{C}-\mathrm{A}-\mathrm{C}\equiv\mathrm{C}-\right]_{n} -\mathrm{C}\equiv\mathrm{C}-\mathrm{B} +\mathrm{H}_{2}\mathrm{O} $$

Preliminary data on substances obtained as a result of the oxidative dehydropolycondensation of certain acetylenes are collected in Table 1.

The starting 9,10-diethynyl-9,10-dihydroxy-9,10-dihydroanthracene was obtained by the method ($^4$). 2-Methyl-5-ethynylpyridine was obtained from 2-methyl-5-vinylpyridine ($^5$). 2,6-Dimethyl-3,5-diethynylpyridine was synthesized according to the scheme:

$$ \begin{gathered} 2\mathrm{CH}_{3}\mathrm{COCH}_{2}\mathrm{COCH}_{3} +\mathrm{CH}_{2}\mathrm{O} \xrightarrow{\text{piperidine}} \mathrm{CH}_{3}\mathrm{COCHCOCH}_{3} \\ \qquad\qquad\qquad\qquad \mathrm{CH}_{2} \\ \qquad\qquad\qquad\qquad \mathrm{CH}_{3}\mathrm{COCHCOCH}_{3} \xrightarrow{\mathrm{NH}_{3}} \\[1em] \longrightarrow \text{3,5-diacetyl-2,6-dimethyl-1,4-dihydropyridine} \xrightarrow{\mathrm{PCl}_{5}} \text{3,5-bis(1-chlorovinyl)-2,6-dimethylpyridine} \xrightarrow[\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{OH}]{\mathrm{KOH}} \\[1em] \longrightarrow \text{2,6-dimethyl-3,5-diethynylpyridine} \end{gathered} $$

Table 1

* The polycondensate (insoluble) contains 45,19% ash, apparently complex-bound copper.

** The polycondensate (insoluble) contains an additional 1,84% copper; with this subtracted, the analysis is satisfactory.

M.p. 95°; not described in the literature.

\[ \mathrm{C}_{11}\mathrm{H}_{9}\mathrm{N}. \quad \begin{array}{llll} \text{Found, \%:} & \mathrm{C}\ 85.56;\ 85.36; & \mathrm{H}\ 5.94;\ 5.86; & \mathrm{N}\ 9.04;\ 9.04.\\ \text{Calculated, \%:} & \mathrm{C}\ 85.24; & \mathrm{H}\ 5.76; & \mathrm{N}\ 9.02 \end{array} \]

For the products of the joint oxidative dehydropolycondensation of 9,10-diethynyl-9,10-dihydroxy-9,10-dihydroanthracene with phenylacetylene, p-diethynylbenzene, and acetylene, ESR spectra were recorded.* It is interesting to note that the concentration of unpaired electrons is the same for both soluble and insoluble substances. The largest number of unpaired electrons is found in the product of the joint oxidative condensation of acetylene and 9,10-diethynyldihydroxydihydroanthracene (soluble), \(\sim 2.2 \cdot 10^{17}\), with a signal width of 7.2 oersteds. Apparently, introduction of a 9,10-diethynyldihydroxydihydroanthracene molecule into the polymer chain decreases the degree of conjugation of the \(\pi\)-electrons. However, introduction of such bulky substituents into the acetylene chain leads to the formation of soluble products.

Institute of Organoelement Compounds
Academy of Sciences of the USSR

Received
16 I 1962

CITED LITERATURE

1. V. V. Korshak, V. I. Kasatochkin et al., DAN, 136, 1342 (1961).
2. A. Hay, J. Org. Chem., 25, 1275 (1960).
3. I. L. Kotlyarevskii, L. B. Fisher, E. S. Domnina, Izv. AN SSSR, OKhN, 1961, No. 10, 1905.
4. W. Ried, H. Schmidt, A. Urschel, Chem. Ber. 91, 2472 (1958).
5. A. P. Kost, P. B. Terent’ev, T. Zavada, DAN, 130, 326 (1960).

* The ESR spectra were recorded by N. M. Bazhin at the Institute of Chemical Physics, Academy of Sciences of the USSR.