Selective dimerization by a radical chain reaction in γ-irradiated crystals of 1,3-bis(3-acetoxyprop-1-ynyl)-4-methoxy-6-methylbenzene

Abstract

A single dimer is formed by a radical chain reaction upon γ-irradiation of 1,3-bis(3-acetoxyprop-1-ynyl)-4-methoxy-6-methylbenzene (1) crystals, sealed in a glass ampoule under vacuum at room temperature. The dimerization is initiated by the addition of the prop-2-ynyl-type radical attached at the 1-position of the benzene ring to the β-carbon of the triple bond attached at the 3-position of the benzene ring. The resulting vinyl radical undergoes H-abstraction from the prop-2-ynyl methylene of the 3-acetoxyprop-1-ynyl group attached at the 1-position resulting in a chain reaction. The dimerization proceeds after the γ-irradiation is stopped. The kinetic chain length of the dimerization may be more than 2 × 10³. Such an exclusive formation of a dimeric product by the γ-irradiation was observed neither for benzene solutions of 1 nor for crystals of other disubstituted bis(3-acetoxyprop-1-ynyl)benzenes. The crystal structure of 1 is responsible for the selective dimerization by the chain reaction. A mechanism for the chain reaction is proposed on the basis of the crystal structure.

References

1. H. Basseler, Adv. Polym. Sci., 1984, 63, 1.
2. H. Sixl, Adv. Polym. Sci., 1984, 63, 49.
3. V. Enkelmann, Adv. Polym. Sci., 1984, 63, 91.
4. O. Rohde and G. Wegner, Makromol. Chem., 1978, 179, 1999.
5. O. Rohde and G. Wegner, Makromol. Chem., 1978, 179, 2013.
6. M. Hagihara, Y. Yamamoto, S. Takahashi and K. Hayashi, Radiat. Phys. Chem., 1986, 28, 165.
7. Y. Kai, A. Yamamoto, D. Xu, N. Kasai, M. Hagihara, Y. Yamamoto, S. Takahashi and K. Hayashi, Makromol. Chem., 1987, 188, 3047.
8. S. Takahashi, Y. Kuroyama, K. Sonogashira and N. Hagihara, Synthesis, 1980, 627.
9. H. Suzuki, K. Nakamura and R. Goto, Bull. Chem. Soc. Jpn., 1966, 39, 128.
10. E. R. Klinshpont, Organic Radiation Chemistry Handbook, eds. V. K. Milinchuk and V. I. Tupikov, Ellis Horwood, Chichester, 1989, p. 34.