The document discusses three reactions: diazocoupling, formylation, and carboxylation. Diazocoupling involves converting amines into diazonium salts that act as electrophiles in aromatic substitution reactions. Formylation uses protonated hydrogen cyanide or alkyl cyanides to introduce aldehyde groups via an imine intermediate. Carboxylation uses phenoxide ions, which are more reactive than phenols, to react with carbon dioxide via electrophilic substitution, delivering the electrophile to the ortho position through coordination with sodium ions.

1. Topic:
Ø Diazo-coupling
Ø Formylation
Ø Carboxylation

2. q Development of amines into diazonium salts as reagents for nucleophilic aromatic
substitution by SN1 mechanism with loss of nitrogen
q Electrophilic aromatic substitution without the loss of nitrogen leads to important azo dyes
q Treatment of the amine with nitrous acid at 0 °C gives diazonium salt
Diazo-coupling

3. q Diazonium salts are good electrophiles for activated aromatic rings, amines and phenols
q Diazotization of salt of sulfanilic acid gives inner salt, combines with N,N-dimethylaniline to
form water-soluble dye, methyl orange

4. q Electrophilic substitution, occurring in para position on activated hindered dialkylamine
q Nucleophilic attack occur on end nitrogen atom of diazonium salt to avoid forming
pentavalent nitrogen

5. Gattermann Reaction (Formylation)
q Useful in preparing aldehydes.
q Use Protonated hydrogen cyanide
q Imine intermediate, ArCH=NH, hydrolyzed to aldehyde
q Lewis acid need not so strong, zinc chloride often used
q With less reactive systems, AlCl3 needed
q Zinc chloride conveniently generated from zinc cyanide, and HCl
• Generating necessary HCN
q Alkyl cyanide RCN use in place of HCN, useful way of preparing ketones from reactive
aromatic species, do not react well under Friedel–Crafts conditions

6. q Electrophile involved R–CºNH+, R(C=NH)Cl, analogue of acyl chloride, RCOCl
q In Gatterman reaction, imine intermediate
q These reactions work when three hydroxyls on benzene ring

7. Carboxylation (Kolbe–Schmitt Reaction)
q Phenoxide ion is more reactive towards electrophilic attack than phenol
q React with such weak electrophiles as carbon dioxide
q industrially used to prepare salicylic acid, precursor in making aspirin

8. q O– substituent is ortho, para-directing, electrophilic substitution step with CO2 gives mostly
ortho product
• Coordination between sodium ion and two oxygen atoms, one from phenoxide and one
from CO2
• Electrophile effectively delivered to ortho position