Catalytic Amination of Polylactic Acid to Alanine

Abstract

In comparison to the traditional petroleum-based plastics, polylactic acid, the most popular biodegradable plastic, can be decomposed into carbon dioxide and water in the environment. However, the natural degradation of polylactic acid requires a substantial period of time and, more importantly, it is a carbon-emitting process. Therefore, it is highly desirable to develop a novel transformation process that can upcycle the plastic trash into value-added products, especially with high chemical selectivity. Here we demonstrate a one-pot catalytic method to convert polylactic acid into alanine by a simple ammonia solution treatment using a Ru/TiO2 catalyst. The process has a 77% yield of alanine at 140 °C, and an overall selectivity of 94% can be reached by recycling experiments. Importantly, no added hydrogen is used in this process. It has been verified that lactamide and ammonium lactate are the initial intermediates and that the dehydrogenation of ammonium lactate initiates the amination, while Ru nanoparticles are essential for the dehydrogenation/rehydrogenation and amination steps. The process demonstrated here could expand the application of polylactic acid waste and inspire new upcycling strategies for different plastic wastes.

Expanding Plastics Recycling Technologies: Chemical Aspects, Technology Status and Challenges

“…The products include polymers with new properties, 898 liquid fuels, 899 waxes, 900 and platform molecules. 901 The C-H bonds in PE (HDPE, LDPE, LLDPE) can be oxidized to ketone or hydroxyl groups, which generates functionalized polymers with unique physical properties (e.g., strong adhesion, ability to be painted with common paint etc.). 898 The high-valent ruthenium-oxo species (polyfluorinated ruthenium porphyrin) catalyzes this process in the presence of 2,6dichloropyridine N-oxide and shows high reactivity without the incorporation chlorine or overoxidation to form esters at 120 °C.…”

“…Tian et al reported that Ru/TiO2 can catalyze the amination of ether groups in PLA in ammonia solution at 140 °C. 901 Alanine can be produced by this process with high selectivity in the absence of hydrogen. In most of the cases, other chemicals (e.g., light alkanes, water, halogens) need to be cofed for the functionalization of the waste plastics.…”

Selective Hydrogenation of Naphthalene to Decalin Over Surface‐Engineered α‐MoC Based on Synergy between Pd Doping and Mo Vacancy Generation

“…Traditional hydrogenation catalysts based on Pt group metals (e.g., Pt, Pd, and Ru) [12][13][14][15][16][17][18][19][20] offer the benefits of comparatively mild operation conditions, high selectivity, high efficiency, and excellent stability but are costly, which has inspired the development of cheaper yet efficient alternatives. The selection of a suitable support was found to be important for improving catalytic performance at reduced noble metal loadings.…”

Efficient conversion of lactic acid to alanine over noble metal supported on Ni@C catalysts

“…The addition of Ru not only provides an active metal site for dehydrogenation, but also greatly promotes the NH 3 adsorption for amination reaction. 39 The role of metallic oxide in amination has also been discussed in many research studies. Zhang et al designed a Ru/ZrO 2 catalyst in the aldehyde/ketone amination, where RuO 2 acted as a Lewis acid and activated the carbonyl group.…”