Aldehydes Ketones And Carboxylic Acids

Aromatic ketones can be prepared by Friedel-Craft's acylation or benzoylation. Acetophenone is prepared by the action of benzene with acetyl chloride in the presence of anhydrous . In this reaction the -atom of benzene is replaced by acyl (- ) group.
This reaction is an example of electrophilic substitution reaction.

During the reaction of carboxylic acids with , the evolves comes from and not from carboxylic acids.

Formic acid can be distinguished from acetic acid since it contains a hydrogen atom instead of methyl group. Therefore, formic acid acts as a reducing agent and decolorise acidified solution.

Electron-donating substituents tend to decrease while electron-withdrawing
substituents tend to increase the acidic strength of substituted benzoic acids relative to benzoic adds. However, due to ortho-effect, -nitro-benzoic add is the stronger add then -nitrobenzoic add.

Gattermann-Koch formyladon When a mixture of and gas is passed through a solution of benzene in the presence of anhydrous and , benzaldehyde is formed.

If in this reaction is replaced by , the reaction is called Gattermann formylation.

When aliphatic carboxylic acids react with bromine in presence of red phosphorus give
-halogenated acids. This reaction is known as Hell-Volhard-Zelinsky reaction.

Acetophenone gives aldol condensation reaction. Benzaldehyde, benzophenone and trichloroacetaldehyde do not contain a- atoms. Hence, do not undergo aldol condensation.

(The reaction is methyl benzoate known as Fischer - Sprier esterification reaction.) (Methyl easters can be prepared by treating carboxylic acid with ethereal solution of diazomethane. Hence, methyl benzoate can be prepared by all these above methods.

Thus, benzaldehyde is obtained when benzal chloride is heated with concentrated aqueous solution of
The obtained aldehyde because of the absence of -hydrogen atom further reacts with concentrated aqueous solution to give benzyl alcohol and potassium benzoate, i.e., it undergoes Cannizzaro reaction

The given reaction is Hell-Volhard Zelinsky (H.V.Z.) reaction. In this reaction, carboxylic acids (except formic acid) react with chlorine or bromine in presence of small quantities of red phosphorus to give -chloro or -bromo acids.

Since, the compound gives a positive iodoform test but negative Tollen's test, so it must be a methyl ketone. From the given molecular formula can be -pentanone

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