Kinetic and synthetic investigation of the reactions os halogeno and arlyosycyclophosphazenes

Abstract

The reaction of hexafluorocyclotriphosphazene, N?P?F? (14), with sodium phenoxide in THF yields phenoxy?substituted fluorocyclotriphosphazenes of all degrees of substitution. The results obtained in this investigation reveal that the fluorine?replacement pattern is non?geminal, and trans derivatives are formed exclusively at the bis? and tris?stages. Information regarding the reactivity, stereospecificity of the hexafluoride (14), and the stability of the derivatives N?P?F???(OPh)? (n = 1–5) may be of immense use in extending such reactions to the more challenging polymeric system, polybis(fluoro)phosphazene. The fluoro(phenoxy)phosphazene derivatives, N?P?F???(OPh)? (n = 1–6), can serve as useful starting materials for the synthesis of phosphazene polymers (containing fluorine) by various methods, particularly Friedel–Crafts reactions with haloalkanes. Studies in this direction will be rewarding.

4.8 Reaction of Hexafluorocyclotriphosphazene (14) with Sodium Phenoxide Experimental Section 4.8.1 General All reactions of hexafluorocyclotriphosphazene (N?P?F?) with sodium phenoxide were carried out in THF. The course and extent of reactions were monitored by thin?layer chromatography (TLC) and gas–liquid chromatography (GLC). Separation of the reaction mixtures into pure components (fluorophenoxy derivatives) N?P?F???(OPh)? (n = 1–6) was effected by column chromatography using either silica gel or acid?washed alumina. Considerable loss of material occurred during chromatographic separation in addition to the usual losses due to volatility, transfer, and purification. Isolation of the bis? and tris?derivatives in pure form was particularly difficult, requiring multiple chromatographic separations. Details of the experimental conditions used to prepare the mono?, bis?, tris?, tetrakis?, pentakis? and hexakis?phenoxy derivatives (N?P?F???(OPh)?; n = 1–6) are summarised in Table 4.5. The yields refer to pure compounds obtained after column chromatography. Instrumental methods used were identical to those described in Chapter 3 (Section 3.4.3).

4.8.2 Preparation of Fluoro(phenoxy) Derivatives Typical procedure: Reaction of N?P?F? (14) with two molar equivalents of sodium phenoxide in THF A solution of sodium phenoxide (1.16 g, 10 mmol) in dry THF (100 mL) was added dropwise (30 min) to a stirred solution of N?P?F? (2.5 g, 10 mmol) in dry THF (100 mL) maintained at 0°C. The reaction mixture was allowed to warm slowly to room temperature and then refluxed for 2 hours. The solvent was removed using a rotary evaporator. The residual oil (~2.5 g) was washed with water (50 mL) and extracted with diethyl ether (150 mL). The ether layer was dried (Na?SO?) and evaporated to give an oil (2.08 g). TLC (silica gel; benzene/light petroleum 2:1) showed three spots with R_f = 0.94, 0.89, 0.83. GLC revealed three peaks at retention times 3.5, 6.5, 15.2 min with intensity ratio 1 : 6.8 : 0.5.

Column Chromatography The oil was chromatographed over silica gel (35 g) and fractions were collected:

FractionEluentProduct isolatedA10% benzene in light petroleum (200 mL)(OPh)? derivative, 0.20 g (6.2%)B20% benzene in light petroleum (250 mL)(OPh)? derivative, 1.65 g (41.5%)C20% benzene in light petroleum (250 mL)(OPh)? derivative, 0.15 g (3.2%) Fraction A contained a mono?phenoxy derivative N?P?F?(OPh). Fraction B contained a bis?phenoxy derivative N?P?F?(OPh)?; confirmed by ³¹P NMR and IR of the methoxy derivative. Fraction C corresponded to N?P?F?(OPh)?, matching the data of an authentic sample. Preparations of higher phenoxy?substituted derivatives were similar, though acid?washed alumina gave better separation for tris?, tetrakis? and pentakis?products. Purity of all derivatives N?P?F???(OPh)? (n = 1–6) was confirmed by GLC, with retention time increasing with degree of phenolysis.