Direct Reaction of Phosphorus Acids with Hydroxy of a Silanol and on the Silica Gel Surface

Abstract

Several phosphorus acids (methyl-and phenylphosphonic, diphenylphosphinic, and ethyl phosphoric acids) were found to give esters on reaction with feri-butyldimethylsilanol. The reactions occurred simply on heating the reactants in an inert solvent (hexane or toluene). The reaction is reversible, and yields of esters were improved by continuous water removal. The dibasic acids gave either mono-or disilyl esters; the latter were more easily purified and characterized. The OH groups on the surface of silica gel were also found to react with various phosphorus acids under similar conditions to give surface-bonded esters. Products were characterized by CP/MAS 3IP and 29Si NMR. In the case of phenylphosphonic acid and ethyl phosphoric acids, the products were spectrally identical with those obtained by phosphorylation of the surface OH groups with the highly reactive 3-coordinate anhydrides of these acids when generated in the presence of silica gel.In recent publications,1•2 we have described the action of alkyl metaphosphates, highly reactive and known only as transient species, on the surface OH groups of silica gel. This produces a phosphate group directly bonded to the silica surface: Three different precursors of metaphosphate have been used in these studies, illustrated in Scheme 1 for the ethyl derivative. The same phosphorylated product is formed in each reaction, as revealed by cross polarization-magic angle spinning (CP/MAS) 3IP NMR spectroscopy. The proposal that phosphorus is indeed bonded covalently to the surface is supported by the position of the31P NMR signal at -10; simple phosphates have shifts around ±1, but upfield shifts of about 10 ppm occur routinely when siloxy groups replace alkoxy or hydroxy groups (cf. (EtO)2P-(O)OH, +1, to (EtO)2P(0)OSiMe3, -91), and a similar shift can be expected for the silica phosphate. The possibility was also considered that the metaphosphate was simply hydrolyzed to ethyl phosphate by water remaining on the surface, and adsorbed

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

“…52,53 One should consider that FT-IR experiments, and for that matter many other characterization techniques to probe acid sites (including 1 H NMR), are performed in the absence of water. Therefore, dehydroxylation is promoted and consequently, although unstable, P-O-Si bonds can form, as proposed in Fig.…”

Reaction of the hydroxy groups of zeolites with phosphorylating agents

“…That the phosphorus was covalently bonded to the surface, and not just present as adsorbed ethyl phosphate, was clearly seen from the 31 P NMR signal (Figure 2a), which occurred at d ‫מ‬ 12.6, with a smaller signal at d ‫מ‬ 17.8. The upfield shifting to d ‫מ‬ 12.6 from the value of the starting acid (d 0.4 [4]) is the result of replacement of H on P-OH by a heavy atom such as Si, an effect well established from studies of phosphorylated silica gel. Adsorbed ethyl phosphate gave a signal at d 0.…”

“…The product was dried in a vacuum desiccator and examined spectroscopically (see later discussion). Phosphorus content was determined on a few samples as described elsewhere [4].…”

“…This species was generated by thermal fragmentation of derivatives of the 2,3-oxaphosphabicyclo[2.2.2]octene ring system [2a] (e.g., 1) or of Oalkyl N-substituted phosphoramidic acids [3] (e.g., 2) as seen in Scheme 1. It was also found that phosphorylation of the surface could be effected simply by direct reaction of the OH groups with readily available phosphorus acids (alkyl phosphoric, phos- phonic and phosphinic acids) [4]. We now have applied our phosphorylation procedures to zeolites, and describe our results in this article.…”

Synthesis of New RuO2@SiO2 Composite Nanomaterials and their Application as Catalytic Filters for Selective Gas Detection

“…This assumption was confirmed by recording 31 P NMR spectra of material 2a which display one main peak at 0.1 ppm in agreement with the presence of a silica phosphate ( Figure 4S, Supplementary Information). 23 The effect of the thermal treatment on the structure and porosity of the host matrix was studied by nitrogen physisorption and X-ray diffraction analysis. The nanomaterials 3a, 3b still present typical adsorption-desorption isotherms of type IV with an H1 hysteresis loop evidencing the preservation of the cylindrical pore volume.…”