Synthesis of m-Dinitrobenzene

 

 

Aim: To prepare and submit  m-dinitrobenzene from nitrobenzene and report its melting point.

Requirement:

a) Chemical required: Nitrobenzene, Conc HNO₃ , Conc H₂SO_{4, ethanol (re-crystallization)}

_{b) Apparatus: RBF (Round Bottle Flask), Conical flask, measuring cylinder, water bath, glass rod, funnel.}

_Principle:

_{Substitution of one or more hydrogen by one or more nitro group(}NO_{2) is known as Nitration.} NO_{2 is a deactivating group, so it directs the second substituent to meta position. Hence it is also called as meta director. This reaction is an example for electrophilic aromatic substitution (}NO_{2 acts as an electrophile).}

_Procedure:

1. _{Place 2.5ml Conc.} H₂SO_{4 and 2.5 ml Conc.} HNO_{3 in a RBF and some porcelain fragments.}
2.  _{Attach reflux condenser and take the set up in the fuming cupboard.}
3. _{Add slowly 1.25 ml of nitrobenzene in portions and shake the flask after each addition to ensure through mixing.}
4. _{Heat the RBF in the water bath for 30mins with frequent shakling.}
5. _{Cool the reaction mixture and pour into the beaker containing ice cold water.}
6. _{Filter the ppt. wash with cold water to remove un-reached acid and calculate the yield.}
7. _{Use: Used in Organic synthesis.}

_Reaction:

_Mechanism:

 

_Calculation:

_{Molecular weight of Nitrobenzene =123g}

_{Molecular weight of m-dinitrobenzene =168 g}

_{123 g of Nitrobenzene -168 g of m-dinitrobenzene}

_{3g of Nitrobenzene should yield - 3x168/123 =}

_{Theoretical yield =}

_{Practical yield= X g}

_{Percentage yield = (Practical yield/Theoretical yield)x100}

_Result:

_{The percentage yield of M-dinitrobenzene was found to be -}

_{Melting point of M- dinitrobenzene is 118} °_C