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

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  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.

  1. 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.

  1. 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) as the relevant reference.

  1. Reduce the nitro group with iron.
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  • $\begingroup$ Is this the actual industrial practice? $\endgroup$ – Georg Feb 3 '15 at 16:59
  • $\begingroup$ @Georg Yes, I have updated my answer and added some information from the Ullmann. $\endgroup$ – Klaus-Dieter Warzecha Feb 3 '15 at 21:17
  • $\begingroup$ Mr. Klaus Warzecha, (i).Your answer describes synthesis of para phenylenediamine(PPD) by Reduction of Para Nitroaniline(PNA) with iron. (ii). Thus obtained PPD contains lots of iron impuries with other isomers, and therefore cannot be used as raw material(Monomer)for production of Para amide fiber(Kevlar). (iii). For this purpose catalytic Hydrogenation of PNA is carried out to produce PPD of desired quality(Grade). This is my simple understanding. I am open for edition/addition, please come back. $\endgroup$ – user13275 Feb 8 '15 at 8:53
  • $\begingroup$ @C.M.Padalia You have inadvertently created a second account. Please use the "Contact Us" in the bottom bar to merge your two accounts. $\endgroup$ – jonsca Feb 8 '15 at 10:06

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