Oxidative photochemical conversion of CHCl3 to COCl2 occurred efficiently in the gas phase with a designed flow photoreaction system. Gram-scale phosgenation reactions for synthesizing chloroformates and carbonate esters, including polycarbonates, were facilitated with the semibatch and continuous flow reaction systems. Taking advantage of this photochemical reaction, which proceeds almost quantitatively in a short time without chemical reagents, catalysts, or solvents, we successfully demonstrated solvent-free continuous flow reactions including the photoconversion of CHCl3 to COCl2 and a base-catalyzed phosgenation reaction with N-methylimidazole or pyridine, whose HCl salts become ionic liquids.

Two new reaction processes involving the in situ oxidative photochemical conversion of CHCl 3 to COCl 2 allowed selective syntheses of N-substituted ureas and isocyanates from amines. (I) A CHCl 3 solution containing an amine and an organic base under O 2 bubbling provided the urea derivative under exposure to UV light generated from a low-pressure mercury lamp at 20−40 °C. (II) A two-step reaction involving the oxidative photodecomposition of CHCl 3 at lower temperatures and subsequent sequential injections of an amine and organic base into the sample solution provided the isocyanate in high yield. The reaction processes of (I) and (II) capitalize on the solution conditions of [COCl 2 ] < [amine] and [COCl 2 ] > [amine], respectively, to result in 1:2 and 1:1 reactions. In general, isocyanates, especially aromatic and haloalkyl ones, readily undergo hydrolysis in the presence of an organic base. However, with the advantage of synthesizing the isocyanates in CHCl 3 solvent, direct addition of monoalcohols and diols to the as-prepared sample solution containing the diisocyanate allowed the one-pot syntheses of biscarbamates and polyurethanes, respectively. The reactions developed in this study are simple, safe, and inexpensive methods of synthesizing Nsubstituted ureas and isocyanates, and derivatives of isocyanates such as carbamates and polyurethanes. The present new methods can replace current synthetic methods using COCl 2 in both academia and industry.