Abstract

In aminoaerosil, the products of the reaction of γ-aminopropyltriethoxysilane with aerosil. an intraparticular interaction of the basic amino groups with the acidic silanol groups is observed. This behaviour was established a) by adsorption experiments using n-butylamine on aerosil. resp. aminoaerosil of different support density, and b) by microcalorimetric determination of the adsorption energy of acetonitrile using aerosil and aminoaerosils of different support density as substrates.

Aminoaerosils react with isothiocyanates according to (I) with formation of covalently linked thiourea groups. Fig. 3 and Fig. 5 (with trimethylamino) show the time-turnover curves of aminoaerosils of different support density with phenylisothiocyanate. The influence of the tem­perature on the thiourea formation is demonstrated in Table III. Depending on the polarity and the size of the ligands R. the isothiocyanates react with different reaction rates with aminoaerosil (Fig. 6). Aminoaerosils with different coverage density, but with an equal molarity of amino groups and varying specific surfaces, react non-uniformly with phenylisothiocyanate (Table IV).

The comparison of the reaction of phenylisothiocyanates a) with heterogeneously by suspended aminoaerosil and b) with n-butylamine in homogeneous solution, both with equal molar amounts of NH₂, shows characteristic differences (Fig. 8).

The amount of the covalently linked NH₂-groups in aminoaerosils can be determined using Sanger’s reagent.