Diaryl ureas, formation

The Beckmann rearrangement of ketoximes to the corresponding amides (31), the Fischer indole cyclization, isomerization of epoxides to the corresponding aldehydes, ketones, or alcohols, hydration and ammo-nolysis of epoxides, oxygen-sulfur interchange, formation of diaryl-ureas and -thioureas from condensation of aniline and carbonyl sulfide, and olefin carbonylation occur over zeolite catalysts (62). The oxo reaction over rhodium and cobalt containing zeolites recently has been claimed (22). 

The relative rates of these reaction sequences were found to depend on the nature of the medium (homogeneous or heterogeneous), rate of addition of water, temperature, reactivity of the amine (formed by the decomposition of the carbamic acid) with the isocyanate, concentration, and other factors. For example, in the reaction with phenyl isocyanate, cold water and heterogeneous medium favored the formation of diaryl urea while with boiling water the main product was aniline. Dilution also favored aniline formation. 

This relatively simple compound 231 requires the 4-C1 picolinic acid chloride 227 easily made in high yield by the S0C12 reaction described earlier. This has the advantage of simultaneously turning the acid into the acid chloride. Formation of the amide 228 and then the diaryl ether is followed by coupling with an isocyanate 230 to make the unsymmetrical urea 231. This large scale synthesis is planned for manufacture.33... 

R-Y-COCl plays the key role in phosgenation reactions that are of a stepwise nature the major part of these processes is COCl (chlorocarbonyl) transfer to R-Y-H generating chloroformates, carbamoyl chlorides, etc. R-Y-COCl is of limited (low) stability and this is the driving force behind its intermediacy in the synthesis of chlorides and isocyanates under elimination conditions (eliminating CO2 and/or HCl), and also determines the character of a reactive substrate in further nucleophilic substitutions to form symmetrical and unsymmetrical substituted carbonic acid derivatives carbonates, carbamates, ureas) or diaryl ketones. Commonly, chloro-formylation and isocyanate formation are independent of the nature of R. Obviously, the reactivity is very different due to the relative basic/nucleophilic ratio. For example, Ar-Cl cannot be prepared through a chloroformate intermediate nor by direct phosgenation, but the reaction does work well in the aliphatic series. 

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