Dimerization of aniline to biphenyl

I've been looking for ways to synthesize biphenyl - $\ce{(C6H5)2}$.


The Ullmann coupling is inaccessible, as bromobenzene is inaccessible in my country due to the manufacture of PCP.


I had the idea to use a version of the Sandmeyer coupling between 2 molecules of aniline - $\ce{C6H5NH2}$.


My assumptions that this is possible are because of the synthesis of diphenic acid, wherein anthranilic acid is diazonated and coupled using a copper(I) ammonia hydroxylamine complex, as per this paper: <http://orgsyn.org/demo.aspx?prep=cv1p0222>.


I believe it would involve dimerization of the phenyl radical, similar to how the Sandmeyer reaction involves radical addition to copper(II), where the phenyl radical comes from copper(I) induced expulsion of nitrogen from diazonium salts. Is this mechanism correct?


Is is possible to do something similar with anilin? Is there literature for this method?


Please be mindful that I'm not too experienced in the mechanisms of these types of reactions.




As OP commented that they don't want benzene in the synthesis due to its carcinogenicity, here is an alternative route involving halobenzene:


1. Sandmeyer reaction to form halobenzene


[![enter image description here](https://i.stack.imgur.com/jSCsk.jpg)](https://i.stack.imgur.com/jSCsk.jpg)


2. Wurtz reaction or Ullmann reaction


[![enter image description here](https://i.stack.imgur.com/fY6xo.png)](https://i.stack.imgur.com/fY6xo.png)


[![enter image description here](https://i.stack.imgur.com/NBn8a.jpg)](https://i.stack.imgur.com/NBn8a.jpg)


The coupling reaction can be greatly improve (in terms of selectivity and % yield) by using high-end catalyst and improved reaction conditions. Here are some methods:


* Fluorobenzene and phenyllithium


[![enter image description here](https://i.stack.imgur.com/pwCqT.jpg)](https://i.stack.imgur.com/pwCqT.jpg)


* Using palladium based catalyst


	+ Palladium on carbon. Here is [a paper](https://pubs.acs.org/doi/10.1021/op010047k) describing the reaction
	[![enter image description here](https://i.stack.imgur.com/Au3OW.jpg)](https://i.stack.imgur.com/Au3OW.jpg)
	+ Suzuki-Miyaura coupling
	[![enter image description here](https://i.stack.imgur.com/EAupB.jpg)](https://i.stack.imgur.com/EAupB.jpg)
* Kharasch coupling


[![enter image description here](https://i.stack.imgur.com/My9Iq.jpg)](https://i.stack.imgur.com/My9Iq.jpg)


**Reaction sources:**


1. Continuous Processes for the Synthesis and Isolation of
Functionalized Biphenyls via Suzuki-Miyaura Cross-Coupling
Reactions by Georg Johannes Lichtenegger ([pdf](https://diglib.tugraz.at/download.php?id=5990d18a11a16&location=browse))
2. Zenish J. Jain, Paraag S. Gide, Rani S. Kankate, Biphenyls and their derivatives as synthetically and pharmacologically important aromatic structural moieties, Arabian Journal of Chemistry, Volume 10, Supplement 2,
**2017**, DOI: [10.1016/j.arabjc.2013.07.035](https://www.sciencedirect.com/science/article/pii/S1878535213002359)




---


OP's route through Diphenic acid can also work. Diphenic acid can be decomposed thermally as well as catalytically to form various PAH and its derivative, one of the product being biphenyl. [**Beware**: PAH are carcinogenic]


[![enter image description here](https://i.stack.imgur.com/Kowyn.jpg)](https://i.stack.imgur.com/Kowyn.jpg)


**Ref**.: Oxidative Ring-Opening of Aromatics: Decomposition of Biphenyl
Carboxylic Acids and Zinc Biphenyl Carboxylates by Natalia Montoya Sanchez and Arno de Klerk. ([pdf](https://pubs.acs.org/doi/pdf/10.1021/acs.energyfuels.5b02066))


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