12 - CYANATES, ISOCYANATES, THIOCYANATES, AND ISOTHIOCYANATES

Abstract

Publisher Summary This chapter discusses esters of cyanic acid that are referred to as cyanates. It has been found that purified cyanates are stable for several weeks. They can be recrystallized and in some cases, they can even be distilled. The reactions may be carried out in acetone or other solvents such as ether, carbon tetrachloride, benzene, acetonitrile, or ethyl acetate. The cyanogen halides used may be either cyanogen chloride or—if a higher boiling point or higher reaction temperature is desired—cyanogen bromide. Convenient laboratory methods for preparation involve the reaction of alkyl halides or dialkyl sulfate with inorganic cyanates such as silver cyanate. Urethanes decompose either thermally or in the presence of phosphorus pentachloride. A process has been patented for preparing isocyanates by the reaction of nitro compounds with carbon monoxide in the presence of a rhodium oxide catalyst. The chapter discusses a process that has also been reported for preparing aromatic isocyanates by the reaction of aromatic nitro compounds with carbon monoxide in alcohol solution to first form the urethanes. Thermal decomposition of the urethane gives the isocyanate.