Oxidative Carbonylierung von aromatischen Diaminen mittels aktiviertem Methylformiat

Hussong, Christine Anna; Leitner, Walter (Thesis advisor); Liauw, Marcel (Thesis advisor)

Aachen (2020, 2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

Aromatic dicarbamates provide a phosgene-free access to the corresponding diisocyanates which are utilized in large quantities as industrial important building blocks in polyurethane chemistry. It is particularly beneficial to use the thermodynamically stable greenhouse gas CO2 for carbamate synthesis. For this purpose methyl formate (MF) can be efficiently produced by CO2 hydrogenation integrated with the subsequent esterification of formic acid with methanol. In this thesis, the oxidative carbonylation of toluene-2,4-diamine (TDA) using MF was investigated in detail. An HPLC-analysis method has been developed which allows the quantification of the target product methyl-toluene-2,4-dicarbamate (TDC) separately from side products in the reaction mixture. An extensive analysis of the product spectrum has provided detailed insight into the complex reaction network, pointing out that the side products are caused by three different reaction paths: N-formylation by MF, electrophilic aromatic substitution/condensation with in situ formed formaldehyde, and N-methylation by in situ formed dimethyl carbonate (DMC). The most prominent side product has been identified as "TDCCH2TDC" (5), which is also an interesting precursor for applications in polyurethane chemistry. However, N-methylations are irreversible and lead to unproductive and undesired compounds, therefore the dual reactivity of DMC must be shifted towards carbamate synthesis. The influence of the catalyst on product distribution was evaluated for PdCl2/CuCl2 and eleven heterogeneous Pd-catalysts. Pd(5%)/ZrO2 showed the highest productivity, closely followed by Pd(5%)/CeO2. Both oxidic support materials were found to partially suppress undesired side reactions leading to higher yields of TDC. Additionally, it turned out that the ratio of TDC and "TDCCH2TDC" (5) is significantly affected by the choice of the support. Furthermore, this synthetic method was extended to the synthesis of dicarbamates from 4,4'-methylenedianiline (MDA) and 2,4-diaminomesitylene (17).