Halogenated diazines and triazines

Abstract

PART I A convenient synthesis of 3, 5, 6-trichloro-1, 2, 4-trlazme was developed using 3, 5-dihydroxy-1, 2, 4-triazine and 6-bromo-3, 5-dihydroxy- 1, 2, 4-triazine as precursors. No product was obtained on photolysis of 3, 5,6-trichloro-1,2 ,4-tnazine but nitrogen elimination occurred on pyrolysis to give trichloroacrylonitrile the red colouration from the pytolyzate (at -196 ) was deduced to be from trichloroazetc. This reaction is the first evidence of azete generation from a 1, 2, 4-triazine. The fluorination of 3, 5, 6-Lrichloro-1, 2,4-triazmc was attempted with potassium and caesium fluorides, with and without a solvent 3,5,6-Trifluoro-1 ,2,4-triizine was formed in many of the reactions but was always detected as a minor product in unstable mixtures. Polyfluoroalkylations of 3, 5, 6-trichloro-1, 2, 4-triazine were attempted with tetiafluoroethylene, hexaluoropropene , n-octafluorobut-2 enc and hexafluorocyclobutene. Alkylation was successful only with hexafluoropropene where perfluoro-3, 5, 6-tris-isopropy1-1, 2, 4-triazine was prepared in good yields. Attempts to prepare mono- and di-alkyl derivatives were unsuccessful. Photolysis of perfluoro-3,5,6-tris-isopropy 1-1,2,4-triazine gave three products, perfluoro-isobutyronitrile and perfluoro-2,5-dimethylhex-3-yne by nitrogen elimination and perfluoro-2,4,6-tris-isopropy1-1,3,5-triazine by rearrangement. Pyrolysis gave nitrogen elimination but there was no evidence of any azete formation. PART II The novel cyclisation observed with 4,6-bis-dimcthylamino-3,5-bis-heptafluoroisopropyipyridazine was studied. A process of internal nucleophilic substitution occurred, with elimination of hydrogen fluoride, to give a product with an ambiguous bicyclic structure. The vivid purple coloured intermediate formed on loss of fluoride ion was trapped as a tetrafluoroborate salt. In an aid to determine the structure of the bicyclic product, various dimethylamino heptafluoroisopropylpyridazines were prepared.