Mass Spectra of 3-Methyl-2(3H)benzoxazolone Hydrazone Phosphorylated Compounds

Abstract

The interpretation of the mass spectra of new phosphorus containing organic compounds is presented. In these compounds, the phosphorylated hydrazono group, > C = N-NH-P(X)(OR) 2 , (X = O, S; R = CH 3 , C 2 H 5 ), is condensed on the annular carbon from the 3-methyl-2(3H)benzoxazolone ring. Elucidation of the fragmentation pathways was aided by exact mass measurements and the observation of metastable transitions. © 1997 by John Wiley & Sons, Ltd. Received 27 June 1996; Revised 5 December 1996; Accepted 21 December 1996 Rapid Commun. Mass Spectrom. 11, 235-240 (1997 Compounds containing the N-methylene benzoxazolone group bonded to phosphorus and having biological properties, constitute the subject of several studies of fragmentation under electron ionization conditions. 1,2There has also been a very extensive study concerning N-substituted derivatives of 2-aminobenzoxazole. 3The present paper analyses the fragmentation patterns, under electron ionization, characteristic of new hydrazono phosphorus esters, in which the unstable N-methylbenzoxazolone-hydrazone group, 4 becomes stabilized through bonding to a phosphorylic or a thiophosphorylic radical (-P(X)(OR) 2 X = O (compounds 1,2), S (compounds 3,4); R = CH 3 , C 2 H 5 ). EXPERIMENTALThe compounds studied are O,O-dimethyl (or diethyl)-3-methyl-, 2(3H)benzoxazolone hydrazone phosphates(1,2) and the corresponding thiophosphates (3,4). They are solids, which exist as white crystals with clearly defined melting points.Measurements were made on a MAT 311 doublefocusing mass spectrometer (Bremen, Germany) with electron energy 70 eV, electron emission 100 µA, and ion source temperature maintained at the optimum evaporation temperature for use of the direct probe inlet viz. 150°C for compound 1, 130°C for 2, 130°C for 3 and 100°C for 4.To confirm the fragmentation schemes, precise mass measurements were made and metastable transitions were also studied for compound 2. RESULTS AND DISCUSSIONThe electron ionization mass spectra of compounds 1-4 are shown in Figs 1-4. The fragmentation patterns shown in Scheme 1 for Compound 2 present a general frame for the compounds studied and the specifications for the corresponding ions are contained in Table 1. The confirmatory exact mass measurements are presented in Table 2.For all of the compounds 1-4, the molecular ion, M + ., is the base peak, following the stabilization of the charge through resonance effects. The high abundance of the ions common to all spectra (Scheme 1) may be explained by resonance effects which stabilize the charge mainly on N-methylbenzoxazolone hydrazone group and derived fragments.The main fragmentation is based on cleavage of the NH -P bond following two pathways. (a) The transfer (T α ) 5 of a hydrogen to the N atom bound to phosphorus seems more probable for the ethyl derivatives which generate the odd mass ion, m/z163, by the loss of C 2 H 4 and P -OH formation (Scheme 1). This will then stabilize to an even mass ion, m/z162, by elimination of an H radical. For the methyl derivatives, the transfe...