Proton sponge: an aromatic glycolysis catalyst.

Area of Science:

• Polymer Chemistry
• Organic Chemistry
• Materials Science

Background:

• Chemical depolymerization is crucial for recycling poly(ethylene terephthalate) (PET) plastic, especially for waste streams unsuitable for mechanical recycling.
• Glycolysis, using ethylene glycol (EG) and a catalyst, is a promising PET depolymerization technology.

Purpose of the Study:

• To introduce 1,8-bis(dimethylamino)naphthalene (proton sponge, PS) as a novel organocatalyst for PET glycolysis.
• To investigate the efficiency, kinetics, and scalability of PS-catalyzed PET glycolysis.

Main Methods:

• PET glycolysis was performed using ethylene glycol (EG) and 1,8-bis(dimethylamino)naphthalene (PS) as the organocatalyst.
• Reaction kinetics were analyzed, and catalyst performance was compared to non-aromatic bases.
• The process was demonstrated at a 10 g scale with varying catalyst loadings and air tolerance.

Main Results:

• PS enabled an 89% yield of bis(2-hydroxyethyl)terephthalate (BHET) in 45 minutes at 180 °C with 20 mol% catalyst and 10 equiv. EG.
• PS demonstrated faster PET swelling and shorter induction times compared to non-aromatic catalysts.
• The reaction followed pseudo first-order kinetics (R² > 0.98) with an activation energy of 126.3 kJ mol⁻¹.
• PS catalysis was tolerant to air and effective at a reduced loading of 5 mol%, yielding 64% BHET (>99% purity) at 10 g scale.

Conclusions:

• 1,8-bis(dimethylamino)naphthalene (PS) is a highly effective novel organocatalyst for PET glycolysis.
• The aromaticity of PS contributes to its enhanced catalytic activity.
• PS-catalyzed glycolysis presents a viable and efficient method for PET recycling, with potential for further optimization.