November 30, 2017
Breaking carbon-nitrogen bonds with titanium hydride under mild conditions
Processes for removing nitrogen from aromatic compounds such as pyridine and quinoline are important in petroleum refinement. Such processes reduce nitrogen oxides (NOx) from combustion and increase the efficiency of hydrocracking. They are also expected to become increasingly important with growing use of natural resources such as biomass and oil shale, which contain more nitrogen than petroleum.
However, the carbon-nitrogen bonds in aromatic compounds are very stable and it requires a high temperature and pressure (300–500°C and about 200 atmospheres) in combination with a solid catalyst to cleave the carbon-nitrogen bonds. Current processes are energy-intensive, so new catalysts capable of breaking carbon-nitrogen bonds under relatively mild conditions have been long desired.
RIKEN CSRS researchers previously developed a multimetallic hydride with three titanium metals (a titanium hydride compound) that enables cleaving of the highly stable nitrogen-nitrogen bonds in dinitrogen and the carbon-carbon bonds in benzene under mild conditions.
For this research, RIKEN CSRS and Dalian University of Technology attempted to use the titanium hydride compound in a reaction with pyridine. The group successfully removed the nitrogen atom from pyridine and quinoline under mild conditions through the cleavage of the two carbon-nitrogen bonds; hydrolysis also yielded ammonia and cyclic cyclopentadiene. Using X-ray diffraction analysis, spectroscopic methods and computational studies, the team was able to elucidate the mechanistic aspects at the molecular level.
The research demonstrates not only easy removal of the nitrogen atom from pyridine and quinoline via cleavage of two carbon-nitrogen bonds by the titanium hydride compound, but also offers some hints for new chemical transformation through the cleavage of various inert carbon-heteroatom bonds (carbon-sulfur, carbon-oxygen, etc.) by multimetallic hydrides.
Nature Communications doi:10.1038/s41467-017-01607-z
S. Hu, G. Luo, T. Shima, Y. Luo, Z. Hou,
"Hydrodenitrogenation of pyridines and quinolines at a multinuclear titanium hydride framework".
Zhaomin Hou; Group Director
Shaowei Hu; Special Postdoctoral Researcher
Gen Luo; Postdoctoral Researcher
Takanori Shima; Senior Research Scientist
Advanced Catalysis Research Group