these are some reactions wch i thnk u all must know .......... these r imp for jee......!!!!!!
Rosenmund Reduction
The catalytic hydrogenation of acid chlorides allows the formation of aldehydes.
Mechanism
Side products:
The Pd catalyst must be poisoned, for example with BaSO4, because the untreated catalyst is too reactive and will give some overreduction. Some of the side products can be avoided if the reaction is conducted in strictly anhydrous solvents...............................!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Saytzeff's Rule
Saytzeff Rule implies that base-induced eliminations (E2) will lead predominantly to the olefin in which the double bond is more highly substituted, i.e. that the product distribution will be controlled by thermodynamics.
The use of sterically hindered bases raises the activation energy barrier for the pathway to the product predicted by Saytzeff's Rule. Thus, a sterically hindered base will preferentially react with the least hindered protons, and the product distribution will be controlled by kinetics.
Williamson Synthesis
This method is suitable for the preparation of a wide variety of unsymmetric ethers. The nucleophilic substitution of halides with alkoxides leads to the desired products.
If the halides are sterically demanding and there are accessible protons in the ?-position, the alkoxide will act as a base, and side products derived from elimination are isolated instead.
Mechanism
Kolbe Electrolysis
The electrochemical oxidative decarboxylation of carboxylic acid salts that leads to radicals, which dimerize. It is best applied to the synthesis of symmetrical dimers, but in some cases can be used with a mixture of two carboxylic acids to furnish unsymmetrical dimers.
Mechanism
Side products:
The formation of side products depends on the ease of the follow-up oxidation which leads to carbenium ions, and their subsequent rearrangement:
Fries Rearrangement
The Fries Rearrangement enables the preparation of acyl phenols.
Mechanism
The reaction is catalyzed by Brønsted or Lewis acids such as HF, AlCl3, BF3, TiCl4 or SnCl4. The acids are used in excess of the stoichiometric amount, especially the Lewis acids, since they form complexes with both the starting materials and products.
The complex can dissociate to form an acylium ion. Depending on the solvent, an ion pair can form, and the ionic species can react with each other within the solvent cage. However, reaction with a more distant molecule is also possible:
After hydrolysis, the product is liberated.
The reaction is ortho,para-selective so that, for example, the site of acylation can be regulated by the choice of temperature. Only sterically unhindered arenes are suitable substrates, since substituents will interfere with this reaction.
The requirement for equimolar quantities of the catalyst, the corrosive and toxic conditions (HF), and the violent reaction of the catalyst with water have prompted the development of newer protocols. Zeolites have proven to be unsuitable, since they are deactivated, but strong acids, such as sulfonic acids, provide a reasonable alternative.
An additional option for inducing a Fries Rearrangement is photochemical excitation, but this method is only feasible in the laboratory:
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