Synthesis and Properties of N-Bromosuccinimide Derivatives of Ammonium Dialkyl/Alkylene Dithiophosphates

Reaction of N-bromosuccinimide with ammonium salt of alkylene (dialkyl) dithiophosphates, [OGOPS2NH4; G=−CMe2CMe2−CH2CMe2CH2−, CMe2CH2CHMe2−, CH2CH2CHMe2−; (RO)2PS2NH4; R=C2H5, n−C3H7, i−C3H7], in 1 : 1 molor ratio in refluxing benzene solution yields red/brown-colored sticky liquids. These newly synthesized complexes have been characterised by physicochemical and spectroscopic techniques (MW, IR, NMR [1H and 31P]). The computational semiempirical calculations (MOPAC6P/c) have also been studied for these complexes. On the basis of the above studies, the formation of P−S−N chemical linkage has been established.


RESULTS AND DISCUSSION
Reaction of N-bromosuccinimide with ammonium dialkyl (alkylene) dithiophosphates has been carried out in the presence of anhydrous acetonitrile which proceeds to completion within in 6-7 h (refluxing) with the precipitation of ammonium bromide as shown in Scheme 1.
The derivatives shown in Scheme 1 are reddish-or brown-colored sticky liquids. They are nonvolatile even under reduced pressure and are miscible with common organic solvents. On heating, these compounds tend to decompose. Besides, for these compounds are reddish-colored sticky liquids, it could not be possible to have a single crystal X-ray data for correlation. The computational semiempirical calculations (Mopac6p/c) for one representative complex {1-[(diethoxy phosphorothioyl)thio] pyrrolidine-2,5-dione} have been studied and the data regarding the structure of molecule has been tabulated, (see Table 1 and Figure  1). The molecular weight data corresponds with the results obtained. The molecular data indicates a large deviation in the tetrahedral-bond angle values for almost all the atoms. It also indicates a good stability of the molecule (ΔH f = −178.8 K·Cal). The five membered ring at nitrogen atom seems to be puckered. A distorted tetrahedral structure around phosphorus atom has been proposed. These computer-based calculations/data are also in good agreement with the analytical and spectroscopic (IR, PMR, 31 P NMR) data obtained for these compounds.

IR spectra
The IR spectra of these derivatives show the following characteristic changes, (see Table 2).  Table 1 number (20-30 cm −1 ) for six membered (dioxaphosphorinane) ring derivatives.   long-range coupling of these protons with magnetically active phosphorus atom. A singlet appears for CH 2 proton of succinimide ring at δ 1.1-1.5 ppm.

31 P NMR spectra
In the proton decoupled 31 P NMR spectra only one 31 P NMR signal has been observed for each compound (see Table 3). Only one sharp resonance signal at δ 58-62 ppm shows purity of these compounds. An upfield shift (δ 19-22 ppm) is observed for these derivatives in comparison to parent dialkyl (alkylene) dithiophosphates, suggesting the covalent nature of newly formed sulfur-nitrogen linkage as well as the absence of any coordinating tendencies in the above derivatives. Thereby appears a unidentate nature of dithiophosphate moiety. On basis of the above spectral [IR, NMR ( 1 H, 31 P)] and other physicochemical evidences, the formation of [P−S−N] chemical bond has been established and the structures in Figures 2 and 3 have been tentatively assigned for the above derivatives.

Experimental
Solvents were dried by standard methods. Ammonium salt of dialkyl/alkylene dithiophosphate was prepared by the methods reported in the literature [14]. Sulphur was estimated gravimetrically as barium sulphate (messenger method) [15]. Molecular weights were determined by the "Knaur Vapor pressure Osmometer" using a chloroform solution at 45 • C. IR spectra were recorded in Nujol mull (4000-200 cm −1 ) on an FT IR spectrophotometer model Megna-IR-550 MICOLAC-USA. Carbon and hydrogen analyses were performed on a Perkin Elmer CHN/O analyzer. 1 H NMR spectra were recorded in CDCl 3 solution on a 90 MHz JEOL FX 90 spectrometer using TMS as an internal reference. 31 P NMR was recorded in C 6 H 6 using H 3 PO 4 as an external reference (CDRI Lucknow). The experimental details of representative compounds are described below. Analytical results are summarized in Table 4.

Preparation of OC(Me
An anhydrous acetonitrile solution (50 mL) of N-bromosuccinimide (0.98 g) was added into the suspension of ammonium salt of hexylene dithiophosphate (1.33 g) and refluxed for 6-7 h. Ammonium bromide precipitated within the course of reaction was filtered off and the solvent was removed under reduced pressure. A red/brown-colored sticky liquid product (1.8 g, 82.21%) was isolated. Synthetic and analytical data are given in Table 4.