Can biphenyl and ammonia react to form carbazole?

From the perspective of existing literature and industrial practice, simply using biphenyl and ammonia (liquid ammonia) under conventional industrial catalyst conditions cannot efficiently produce high-purity carbazole directly. Although structurally, biphenyl appears to be able to form carbazole by introducing a nitrogen atom to close the ring, in practice it is quite difficult to functionalize the C–H bonds between these aromatic rings and insert a nitrogen atom. In the industrial or fine chemical industry, the common method for synthesizing carbazole is: 1. Obtaining carbazole through a cyclization reaction starting from benzidine-based intermediates ； 2. Constructing carbazole rings using biphenyl derivatives and nitrogen-containing reagents (such as aniline derivatives) under the action of a catalyst ； 3. Carbazole derivatives can also be prepared through other special routes, such as palladium-catalyzed cross-coupling reactions and amination cyclization reactions. Using biphenyl and liquid ammonia as the only starting materials, although ammonia \"seems\" to be able to provide a nitrogen source, biphenyl is not reactive enough; direct C–H bond amination and cyclization to form carbazole are difficult to achieve under conventional industrial catalysts and conditions. There are currently no reports indicating that this direct route can produce industrial-grade products with high purity (purity above 98%). From a thermodynamic perspective: Theoretically, the reactions that lead to the formation of carbazole molecular frameworks, starting from biphenyl and ammonia, involve functionalization of aromatic C–H bonds, intramolecular dehydrogenation, ring closure, and other steps; the change in reaction free energy is often significant (and certain conditions as well as catalysts are usually required to reduce the reaction barrier). Although it may not be completely prohibited thermodynamically (based on Gibbs free energy calculations), the kinetic barriers are very significant, making it almost impossible to carry out this reaction under simple catalytic conditions. Conclusion: In summary, there is currently no mature or reliable method in industry or laboratories to directly synthesize carbazole with high efficiency and high purity (>98%) using only biphenyl and liquid ammonia through conventional industrial catalysts. In actual industrial production, it is generally preferred to use more efficient precursors and routes, such as the method of synthesizing through biphenylamine intermediates followed by ring closure. Therefore, the route you described for directly preparing carbazole from simple biphenyl + ammonia is not practical at present, and there are no clear industrial precedents to support this approach. .