Synthesis and Thermal Properties of Bio-Based Janus Ring Siloxanes Incorporating Terpenes and Terpenoids

Abstract

A mild and highly selective hydrosilylation method was employed to synthesize five novel well-defined Janus ring siloxanes bearing terpenes and terpenoids, which are the main bioactive components of essential oils. The characterization of these new bio-sourced molecular materials, derived from hydrosilyl-substituted all-cis-cyclotetrasiloxane, was conducted through comprehensive analyses using multinuclear NMR, infrared spectroscopy, elemental analysis, and mass spectroscopy. The thermal stability of the newly synthesized Janus rings was investigated, and the siloxane skeleton was shown to confer an enhanced thermal stability compared with free terpenes and terpenoids.

Keywords: Janus ring siloxane; all-cis-cyclotetrasiloxane; hydrosilylation; silsesquioxane; terpenes; terpenoids.

Scheme 1

Functionalization of hydrosilyl-substituted Janus rings has been reported in previous studies and in this work.

Scheme 2

Synthesis of compound 1; red Si: T-unit Si; blue Si: M-unit Si.

Scheme 3

Hydrosilylation of 1 with S-limonene; red Si: T-unit Si; blue Si: M-unit Si.

Figure 1

Zoomed-in view of the incorporated S-limonene moiety in compound 2; red Si: T-unit Si; blue Si: M-unit Si; red circle: an asymmetric carbon atom.

Scheme 4

Hydrosilylation of 1 with different essential oil components; red Si: T-unit Si; blue Si: M-unit Si.

Figure 2

TGA graphs of compounds 2–6.