Experiment 5 - Nitration of chlorobenzene

Experiment 5- - Experiment 5 Nitration of Chlorobenzene Lut Ming Cheng 4957880 CHM2123 Section C TA Wendy Campbell Due Date 1 Theory and Mechanism

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Experiment 5 Nitration of Chlorobenzene Lut Ming Cheng, 4957880, CHM2123, Section C TA: Wendy Campbell Due Date: October 29, 2008 1 – Theory and Mechanism Electrophilic aromatic substitution involves an aromatic ring acting as a nucleophile in attacking strong electrophile. Aromatic ring only reacts when strong electrophile is present, due to its higher stability in result of aromaticity. Therefore, weak electrophile is not able to initiate any aromatic substitution reactions. In this experiment, nitration of chlorobenzene is carried out. The brief reaction is shown as follow, Cl HNO 3 H 2 SO 4 Cl NO 2 + Cl NO 2 + NO 2 Cl Major Minor Trace Nitric acid is first protonated by strong sulfuric acid to form nitronium. Nitronium is a strong electrophile, therefore chlorobenzene acts as an nucleophile to attack the nitrocation on the nitronium. This forms an arenium ion, which also called a σ complex or Wheland intermediate. Chlorine atom is one of the halide atoms that direct substituent to go into ortho and para position. Therefore, when students use chlorobenzene as the starting reagent, most nitro groups is directed to the para and the ortho position, due to a better capability to resonance for stabilization. Step 1 O H N + O O - + O H S O O OH O H 2 + N + O O - + HSO 4 - N + O O + H 2 O N + O O Step 2 Cl + slow CH + Cl NO 2 C H + Cl O 2 N H NO 2 C + Cl C H + Cl O 2 N H Step 3 HSO 4 - + Cl O 2 N H 2 SO 4 +
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Halide group is also a weak deactivating group that withdraws electrons from benzene ring. Therefore, when nitrobenzene is formed, the second nitration reaction goes much slower than the first due to a deficient amount of electrons for the nucleophilic attack. In addition, to minimize secondary reaction, controlling the reaction temperature and relative reagent quantities are very important. Furthermore, the second nitration happens mostly at the meta position. This is due to the higher stability of substituents in the sigma complex at the meta position. Resonance structures determine the stability of the compound. More resonance structures usually means a higher stability. 2 – Table of Reagents Compound Molar Mass (g/mol) Quantity Density (g/mL) mmol equiv. Nitric acid
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/13/2010 for the course CHM CHM2132 taught by Professor Goto during the Fall '07 term at University of Ottawa.

Page1 / 6

Experiment 5- - Experiment 5 Nitration of Chlorobenzene Lut Ming Cheng 4957880 CHM2123 Section C TA Wendy Campbell Due Date 1 Theory and Mechanism

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online