Reaction of benzene diazonium salts with different compounds


> 
> **1.** $ \ce{ArN2+Cl-}$ gives addition product with $\alpha,\beta$ unsaturated acids, with decarboxylation being integral part of reaction. For example,
>  $$\ce{ArN2+Cl- + Ph-CH=CH-COOH -> Ph-CH=CH-Ar +CO2 + HCl}$$
> 
> 
> **2.** With $\ce{SnCl2/HCl, ArN2+Cl-}$ given phenyl hydrazine $\ce{ArNH-NH2.HCl}$
> 
> 
> 


I can not find mechanism of any of these reactions, first reaction seems similar to Meerwein reaction (without $\ce{Cu^2+}$), but certainly can't follow similar mechanism. Second reaction is completely different from either. What are the reaction mechanisms of each?




As to your first reaction that does not utilize copper, a reference to the source would be useful. Nonetheless, the Meerwein Arylation Reaction has been [reviewed](https://onlinelibrary.wiley.com/doi/epdf/10.1002/0471264180.or011.03) in Organic Reactions. The reaction is conducted in the presence of catalytic cuprous ion. Meerwein proposed an aryl cation but a radical mechanism appears plausible. Reduction of the aryldiazonium salt **1** produces aryl radical **2** and cupric ion. Addition of the aryl radical to cinnamic acid **3** to the double bond to give the more stable of two possible radicals, ---namely--- the benzylic radical **4**. This radical is oxidized by cupric ion to produce benzylic cation **5** and the catalyst cuprous ion. Loss of CO2 forms the stilbene **6**.  

![](https://i.stack.imgur.com/rGUNj.jpg)


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