Direct Synthesis of Dimethyl Toluene-2,4-Dicarbamate from 2,4-Toluene Diamine, Urea, and Methanol

Abstract

Dimethyl toluene-2,4-dicarbamate (TDC) was directly synthesized from 2,4-toluene diamine (TDA), urea, and methanol in order to overcome the drawbacks of other technological routes to TDC. First the thermodynamic analysis for this reaction was made and the results show that the reaction is endothermic and can occur spontaneously beyond 413.8 K. Then the effects of catalyst and reaction conditions were studied. TDA conversion of 98.8% and TDC selectivity of 41.6% were attained in the presence of zinc chloride catalyst and under the suitable conditions of molar ratio of TDA/zinc chloride/urea/methanol = 1/0.07/5/80, reaction temperature of 190 °C, reaction pressure of 3.0 MPa, and reaction time of 9 h. Low TDC selectivity is attributed to the difficulty in the conversion of the intermediates, methyl 2-methyl-5-amino N-phenylcarbamate (TMC1) and methyl 3-amino-4-methyl-N-phenylcarbamate (TMC2), to TDC. Finally on the basis of analyses of HPLC–MS, HPLC, and GC, three possible reaction paths were proposed. One path is the reaction of TDA with urea to toluene-2,4-bisurea (TBU) and then the formation of TDC from the succeeding reaction of TBU with methanol. Another path is the generation of TMC1 and TMC2 from the reaction of TDA with first urea and then methanol, and the succeeding reaction of the formed TMC1 and TMC2 with first urea and then methanol to TDC. Still another path is the formation of methyl carbamate (MC) by the reaction of urea and methanol and then the reaction of TDA with MC to TMC1 and TMC2, and finally a further reaction of TMC1 and TMC2 with MC to TDC.

One-Pot Synthesis of Dimethyl Hexane-1,6-diyldicarbamate from CO2, Methanol, and Diamine over CeO2 Catalysts: A Route to an Isocyanate-Free Feedstock for Polyurethanes

“…Up to now, several methods to obtain dicarbamates were reported. For example, oxidative carbonylation of diamines, the reaction of diamines with dimethylcarbonate (DMC) − or carbamates, − of diamines with urea and alcohol, − of polyureas with dialkylcarbonates, of aniline with DMC and subsequent condensation using formaldehyde. , …”

Theoretical analysis and evaluation of reaction routes by “three-parameter difference”

“…19,20 The industrial production methods of TDI mainly include: phosgene process, 21 reduction carbonylation method, 22 oxidative carbonylation method, 23 carbon dioxide method, 24 dimethyl carbonate method 25–27 and urea method. 28 On this basis, we proposed the dimethyl carbonate-ionic liquid hydroxylamine method. The specific reaction equations are as follows.…”

Preparation and catalytic performance of ZrO2‐supported Pt single‐atom and cluster catalyst for hydrogenation of 2,4‐dinitrotoluene to 2,4‐toluenediamine

“…The reduction of 2,4‐dinitrotoluene (2,4‐DNT) is one of the most prevalent industrial processes for the synthesis of 2,4‐toluenediamine (2,4‐TDA), with more than 1 million tons produced globally on an annual basis. The desired 2,4‐TDA product is a value‐added intermediate which is predominantly used in the production of polyurethane foams, elastomers, coatings, sealants and adhesives . More specifically, reducing agents such as iron, zinc and sodium hydrosulfite are used to reduce 2,4‐DNT to 2,4‐TDA .…”