Polymerization of DL-Lactide induced by Protonated Montmorillonite clay as a solid catalyst: Mechanism study

Abstract

29Si NMR spectroscopy. The results show that, the mechanism of the reaction involves both Brønsted and Lewis acid sites on Maghnite surface.

The Structure and Properties of Sepiolite with Partial Lattice Ions Substituted by Aluminum Ions

“…4C, D. The width of the signal reflects the symmetry of Al complex, and the narrower spectrum reflexes the higher symmetry of the complex (Wang et al, 2000). For Sep, two bands of Al O at 7.5 ± 0.5 ppm and −2 ± 1 ppm, deriving from the Al at the edge (Al O 2) and the section (Al O 1) of the octahedron in sepiolite, and two signals of Al T at 65 ± 1 ppm and 74 ± 1 ppm, corresponding to the Al at the center (Al T 2) and edge (Al T 1) of tetrahedron in sepiolite, are very close to the (Caillerie and Fripiat, 1992;Wang et al, 2000;Aslya et al, 2016). The signals at 86 ± 5 ppm are broad, revealing poor symmetry, which might be from the Al in the tetrahedron in the amorphous impurity (Wang et al, 2000).…”

“…The acid and base in silicate minerals show catalytic activity in organic reactions, e.g., the pyrolysis behaviors of organic matters, the methylbutynol conversion, the Biginelli type reaction of aldehydes, and the synthesis of malononitrile prepolymers (Corma and Martín-Aranda, 1993;Hu et al, 2003;Niwa et al, 2010;Pushpaletha and Lalithambika, 2011;Liu et al, 2013a;Jha et al, 2013;Novikova et al, 2013;Bu et al, 2017;Phukan et al, 2017). The acid-base conjugation in minerals plays a role to fix organic molecules during the reaction, for example, in the polymerization reaction of D, L-Lactid catalyzed by acidmodified montmorillonite, the D, L-Lactid molecules were fixed on the accessible tetrahedral Al sites (act as acid sites) through oxygen atoms (Aslya et al, 2016). The amino group in aminobenzodifurandione dye was protonated by the acid bound to the oxygen atom of silanol (Lewis base) when probing the basicity of solid acids (Spange et al, 2005).…”

Synthesis of Polytetrahydrofuran Using Protonated Kaolin as A Solid Acid Catalyst

“…For this purpose, the use of nontoxic heterogeneous catalysts instead the mentioned homogenous catalysts can be an efficient solution method [10]. Regarding the application of heterogeneous catalysis for the polymerization process, over the last few decades, several research groups have valorized and applied some natural materials based on clays that have been already used as solid catalysts for the polymerization of vinyl, heterocyclic and ester monomers [11][12][13][14][15][16][17][18][19][20][21][22][23]. Among these clay materials, the kaolin, a class of inexpensive and a new non-toxic cationic catalyst, exhibited much higher catalytic reactivities in different organic synthesis processes [10,[24][25].…”