Natural vs. Synthetic Phosphate as Efficient Heterogeneous Compounds for Synthesis of Quinoxalines

Abstract

Natural phosphate (NP) and synthetic fluorapatite phosphate (SFAP) were proposed as stable, inexpensive, readily available and recyclable catalysts for the condensation of 1,2-diamines with 1,2-dicarbonyls in methanol to afford quinoxaline at room temperature. NP provided as high as 92–99% yield for quinoxalines in short reaction times (i.e., 1–45 min), while SFAP created quinoxalines with 87–97% yield in 60–120 min. From the chemical analyses, X-ray fluoresecency, X-ray diffraction, energy dispersive X-ray and Fourier-transform infrared spectroscopy methods, two main phases (CaO, P2O5) appeared in NP together with other low content phases (SiO2, Fe2O3). Compared to other phases, apatite (CaO and P2O5 as Ca10(PO4)6) played a major role in the catalytic activity of NP. SFAP with similar Ca/P atomic ratio showed a relatively lower catalytic activity than NP for the condensation of 1,2-diamine with 1,2-dicarbonyl in methanol at ambient temperature. To investigate the recyclability of catalysts, the surface properties of NP and 6-recycled NP were investigated using scanning electron microscopy, energy dispersive X-ray and Brunauer–Emmett–Teller and Barrett–Joyner–Halenda methods. Some differences were observed in NP and 6-recycled NP’s particle size, surface area, the volume and size of pores, and the content of elements; nevertheless, the use–reuse process did not noticeably change the catalytic property of NP.

Acrylonitrile‐butadiene‐lignin thermoplastic rubber adhesive for enhanced metal‐to‐metal joining

“…15 Furthermore, making use of biobased materials can reduce carbon dioxide production because of their higher biodegradability compared to the synthetic materials. 16,17 Nitrile butadiene rubber (NBR), another main component of adhesive in this research, is commonly used in industrial and automotive areas because of its excellent resistance to lubricants and chemicals, low cost, and properties that can be easily designed by adjusting the acrylonitrile content. 18,19 However, its mechanical strength is weak without reinforcements.…”

“…Naturally, lignin is a crosslinked network of amphiphilic molecules that function as the primary adhesive component to maintain the structural integrity of plant cell walls and in the past few years, lignin‐based adhesives have also been used for substrates such as metals 14 and glass 15 . Furthermore, making use of biobased materials can reduce carbon dioxide production because of their higher biodegradability compared to the synthetic materials 16,17 …”