SYNTHESIS AND REACTIONS OF 2,2,2-TRIHALOETHYL ALPHA-HYDROXYIMINOBENZYLPHOSPHONATES - THE INFLUENCE OF THE ESTER GROUP ON THE CHEMISTRY OF PHOSPHONATES

Arbuzov reactions of diethyl 2,2,2-trihaloethyl phosphites (3) with benzoyl chloride afforded ethyl 2,2,2-trihaloethyl benzoylphosphonates (4). The reactions of 4 with NH2OH.HCl led to the formation of methyl benzoate and ethyl methyl H-phosphonate as a result of alcoholysis of 4, followed by alkoxy group exchange. Methanol solutions of benzoylphosphonates 4 were found by P-31 NMR spectroscopy to contain considerable proportions of hemiacetals, 7, which undergo base catalyzed C-P bond cleavage. The formation of hemiacetals from benzoylphosphonates 4 is suppressed in 2-propanol, and in this solvent the corresponding oximes 2 could be obtained in good yields. Reactions of methyl benzoylphosphonochloridate (10) with 2,2,2-trihaloethanols, in CH2Cl2, gave methyl 2,2,2-trihaloethyl benzoylphosphonates (11) which could be converted directly to oximes 12 by NH2OH.HCl in a one-pot procedure. In contrast to the previously studied dimethyl (E)-alpha-hydroxyiminobenzylphosphonate, which underwent thermal Beckmann rearrangement to afford N-benzoylphosphoramidates, both (E) and (Z)-trihaloethyl esters 2 and 12 underwent fragmentation to benzonitrile and to the corresponding dialkyl hydrogen phosphate, reflecting the increased electrophilicity of the phosphorus in these compounds. Demethylation of methyl esters 12 was effected smoothly by iodide or bromide ions to yield benzoylphosphonate salts 15, which in tum were converted to oxime salts 14 by treatment with hydroxylamine. In contrast, attempted deethylation of ethyl esters 2 in refluxing acetonitrile led to benzonitrile and pyrophosphate type product as indicated by P-31 spectroscopic examination of the relation mixture. Oxime salts 14 behaved similarly when heated. Acidification of lithium 2,2,2-trifluoroethyl alpha-hydroxyiminobenzylphosphonate (14a) gave the corresponding hydrogen trifluoroethyl phosphonate (19a). The fragmentation of 19a in 0.6 N ethanolic hydrogen chloride to ethyl trifluoroethyl hydrogen phosphate and benzonitrile at room temperature had a T1/2 value of approx 18 hours, which is greater by a factor of 2 than that of the corresponding methyl ester. When the fragmentation of 19 was carried out in solvent mixtures of either water with methanol or 2-propanol, or methanol with t-butanol, the composition of the solvents was reflected in the products, indicating a dissociative type mechanism, involving metaphosphate as reactive intermediates.