four most impotant chamical reaction

4 most chemical reactions coming in all exams

1. Gattermann synthesis
2. reimer taemann reaction 
3. leaderer mannase reaction 
4. hauben hausch reaction 

Gattermann synthesis ;-

When phenol is reacted with liquid HCN and gas HCl in presence of non aqueous AlCl₃ or ZnCl₂ then, one aldehydic group eners in benzene ring and o-Hydroxy benzaldehyde (salidehyde) and some amount of isomer are formed . firstaldemene is formed in this rection which hydrolysed into aromatic aldehyde by water. 

Mechanism ;-

This reaction is example of electrophillic aromatic substitution. In which HCN and HCl react together in presence of non Ag-AlCl3 forms formadiminium ion (I) which attacks at benzene यूring and give aldemine. It gives phenolic aldehyde on hydrolysis of water by mineral acid.

Reimer Tiemann Reaction;-

When basic solution of phenol is heated with chloroform ( CHCl₃ ) then phenolic aldehyde is obtained. this reaction is know as Reimann Tiemann Reaction.

-CHO group goes at O and P position in aromatic ring accordance with -OH group. phenol is refluxed with CHCl₃ and a base then O- and p-hydroxy benzaldehyde is formed.

like this, CCl₄ is used in place of CHCl₃ O- and p- hydroxy benzoic acid is obtained.

Mechanism ;-

By chloroform and Alkali, intermediate strong electrophile product dichlorocarbene or dichloro Methylene is formed which is active carbocation. there are six electrons in their outer most shell. but is is neutral. this attacks o- position of phenoxide ino follows.

Leaderer- mannase Reaction ;-

Phenols are condensed at o- and p- position with aliphatic and aromatic aldehydes.

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example phenol is condensed with formaldehyde in presences of dil.acide or base and a catalyst into bakelite.

hauben hausch Reaction ;-

In this reaction , dihydric or trihydric phenol is heated with alkyl cynide in presence of ZnCl₂ and HCl . The product of this reaction gives phenolic ketons on water- Hydrolysis.

Haube Hausch reaction give a method for indirect acylation of poly hydroxy phenols. phenols do not give this reaction.

Mechanism ;- 

Mechanism of this reaction is similar to gatter mann formylation.