Synthesis of diethyl 2-{[3-(triethoxysilyl)propyl]amino}ethylphosphonate

Yuliia I Chuiko ,Yu V Kholin ,Максим А Колосов

doi:10.26565/2220-637x-2020-34-03

Yuliia I Chuiko , Yu V Kholin + Show 1 more

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https://doi.org/10.26565/2220-637x-2020-34-03

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Abstract

Diethyl 2-{[3-(triethoxysilyl)propyl]amino}ethylphosphonate is promising reagent for the modification of silica surface and thus for the creation of chelate adsorbents for extraction of d‑metals ions from water media. Diethyl 2-{[3-(triethoxysilyl)propyl]amino}ethylphosphonate was synthesized by alkylation of 3-aminopropyltriethoxysilane (APTES) with diethyl vinylphosphonate under quick neat heating. The possible alternative approaches to the synthesis of this compound were investigated (alkylation of APTES and N-acetylAPTES) as well as behavior of APTES towards heating in absolute ethanol and THF. APTES was shown to be not stable in absolute ethanol, that is caused by polycondensation processes. Because of this fact, previously reported protocol of diethyl 2‑{[3‑(triethoxysilyl)propyl]amino}ethylphosphonate synthesis in ethanol turned to be impossible.

Highlights

3-Aminopropyltriethoxysilane (APTES) is a widely used agent for development of robust hydrophobic coatings on glass surface [1, 2] and, in general, for obtaining of 3-(aminopropylsilyl)modified surfaces [3,4,5,6]
We have lately proposed a general strategy for N-modified 3-(aminopropyl)silica synthesis, which consisted of N-prefunctionalization of APTES with hydrolytically, air and time stable functional groups and further synthesis of surface-modified silica on the base of the latter precursor
In our previous work we worked up the synthesis of diethyl {[3-(triethoxysilyl)propyl]amino}methylphosphonates, which after grafting of SiO2 surface and further hydrolysis should produce sorption material with five-membered chelate binding structure [15]

Summary

Introduction

3-Aminopropyltriethoxysilane (APTES) is a widely used agent for development of robust hydrophobic coatings on glass surface [1, 2] and, in general, for obtaining of 3-(aminopropylsilyl)modified surfaces [3,4,5,6]. The purpose of the present work is to obtain, starting from APTES, diethyl 2-{[3-(triethoxysilyl)propyl]amino}ethylphosphonate 1 which after a grafting of SiO2 or sol-gel synthesis in reaction with TEOS should create a layer of the uniform substituted 2-(phosphonatoethyl)amino groups on the silica surface, producing after the stage of acidic hydrolysis a promising six-membered chelate binding structures (Figure 1). 1H NMR spectra (CDCl3): 1) diethyl vinylphosphonate 2; 2) APTES; 3) the reaction mixture (ethanol was removed by vacuum distillation) after 19 h. In any case the result was negative, and the starting compound 5 was returned back in the amount of 50–70 % We attribute such a passivity of amide 5 in the basic media to the formation of an anion, which is stabilized by intramolecular complexation by the silicon atom (due to the reversibility of the process after work-up of the reaction mixtures the starting material is regenerated, Scheme 5).

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