P-phenylenediamine Production Process

How p-phenylenediamine (PPD) is produced? PPD is used as raw material for Kevlar (Para amid Fiber).




1. React benzene with chlorine in the presence of $\ce{FeCl3}$ to yield chlorobenzene.


According to *Ullmann's Encyclopedia of Industrial Chemistry*:



> 
> Most monochlorobenzene is now produced from benzene and chlorine in continuously operated plants. Depending on the ratio of benzene to chlorine chosen, one can achieve either a low rate of benzene conversion and little dichlorobenzene
> formation, or almost complete conversion of the benzene with a higher degree of dichlorobenzene formation. [...] The composition of a chlorination mixture containing the highest possible proportion of monochlorobenzene has been given as
> 4–5% unreacted benzene, 73% monochlorobenzene, and 22–23% dichlorobenzenes.
> 
> 
> 


2. Nitrate chlorobenzene to obtain a mixture of 2-nitrochlorobenzene and 4-nitrochlorobenzene. Separate the isomers.


In *Ullmann's Encyclopedia of Industrial Chemistry*, we find:



> 
> Nitration of chlorobenzene with mixed acid (30/56/14) typically gives an isomer
> mix in 98 % yield consisting of 34–36% 2-chloronitrobenzene, 63–65 % 4-chloronitrobenzene, and only ca. 1% 3-chloronitrobenzene.
> 
> 
> 


"Mixed acid" refers to a mixture of nitric acid, sulfuric acid and water.


3. React 4-nitrochlorobenzene with ammonia (Nucleophilic aromatic substitution) to obtain 4-nitroaniline.


According to *Ullmann's Encyclopedia of Industrial Chemistry*, the reaction conditions as as follows:



> 
> 4-Nitroaniline is produced in an agitated titanium reactor in 99.3 % yield by reacting 4-chloro nitrobenzene with a tenfold excess of aqueous ammonia at 175 °C and 4.2 MPa (42 bar) for 10 h.
> 
> 
> 


*Ullmann's Encyclopedia of Industrial Chemistry* cites a patent by MONSANTO ([DE1768518](https://depatisnet.dpma.de/DepatisNet/depatisnetaction=bibdat&docid=DE000001768518A)) as the relevant reference.


4. Reduce the nitro group with iron.


 2