Catalysts screening, optimization and mechanism studies of dimethylhexane-1,6-dicarbamate synthesis from 1,6-hexanediamine and dimethyl carbonate over Mn(OAc)2 catalyst

Effective Synthesis of m-Xylylene Dicarbamate via Carbonylation of m-Xylylene Diamine with Ethyl Carbamate over Hierarchical TS-1 Catalysts

Carbonylation of m-xylylene diamine (XDA) with ethyl carbamate to produce m-xylylene dicarbamate (XDC), which is the crucial intermediate for the production of m-xylylene diisocyanate (XDI), over the hierarchical TS-1 (HTS-1) zeolite catalyst was studied. The catalysts were characterized by Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and temperature-programed desorption of ammonia techniques systematically. The results showed that the high performance of HTS-1 could be attributed to the weak acidity and high V _meso/V _total ratio of the catalyst. Impacts of reaction time and reusage on the HTS-1 catalyst were also investigated. Under 6 h and 200 °C, XDA conversion could reach 100% with 88.5% XDC yield. Furthermore, partial loss of Ti active sites with Lewis acidity on the catalyst surface led to the decrease of XDC yield during recycling. Moreover, a possible reaction mechanism for the title reaction was primarily proposed.

Developing an epoxy resin with high toughness for grouting material via co-polymerization method

In order to improve the toughness of epoxy resin for grouting material, the flexible hexamethylene diisocyanate (HDI) was utilized to manufacture a new kind of epoxy resin with high toughness via co-polymerization method. In the procedure of preparing bisphenol A epoxy resin, before the reaction between bisphenol A (BPA) and epichlorohydrin (ECH), HDI was introduced to react with BPA for embedding flexible segments into the chain of epoxy resin, then modified epoxy resin (HDI/EP) was manufactured. The mechanical properties, especially the toughness of the HDI/EP, are significantly increased – the fracture elongation is up to 124%. In addition, the compressed specimens can fully recover to their original shape in a few minutes. Thermal performance and corrosion resistance of the HDI/EP specimen were also investigated, which showed that the specimen can be used under 258°C, and can remain stable in H2SO4, NaOH and NaCl solutions with 10 wt% for 100 h, respectively. The present work provides a convenient avenue pathway to prepare an epoxy resin with high toughness, which may be used in many technologies.

Efficient synthesis of epoxybutane from butanediol via a two-step process

A novel approach for the synthesis of epoxybutane via decarboxylation of butenyl carbonate derived from butanediol was developed for the first time. For the carbonylation of butanediol with dimethyl carbonate, NaAlO₂ has exhibited excellent catalytic activity under mild reaction conditions. The yield of butenyl carbonate reached as high as 96.2%. NaAlO₂ provides suitable acid-base active sites to promote the transesterification reaction of butanediol and dimethyl carbonate. For the following step of decarboxylation of butenyl carbonate, ionic liquid 1-butyl-3-methylimidazolium bromide could effectively catalyze the decarboxylation process both in batch or continuous processes. Moreover, the catalytic mechanism for the crucial step of decarboxylation of butenyl carbonate over 1-butyl-3-methylimidazolium bromide was explored using DFT calculations. The results showed that the electrostatic and hydrogen-bond effects of 1-butyl-3-methylimidazolium bromide played a crucial role for the generation of epoxybutane. Briefly, the Br anion of the ionic liquid attacks the methylene of the ring and the H of the ionic liquid cation attacks the carbonyl oxygen, which facilitated the five-ring opening and subsequent decarboxylation to form BO. This study not only provided a new and green synthetic route for producing epoxybutane, but also contributed to the effective utilization of butanediol, which is inevitably produced as by-product in the process of coal to ethylene glycol, suggesting a promising application in the clean manufacture of epoxybutane with inexpensive cost.