Describe the following:
- Acetylation
- Cannizzaro reaction
- Cross aldol condensation
- Decarboxylation
- Acetylation
- Cannizzaro reaction
- Cross aldol condensation
- Decarboxylation
Solution and Explanation
(i) Acetylation
The introduction of an acetyl functional group into an organic compound is known as acetylation. It is usually carried out in the presence of a base such as a pyridine, dimethylaniline, etc. This process involves the substitution of an acetyl group for an active hydrogen atom. Acetyl chloride and acetic anhydride are commonly used as acetylating agents.
For example, acetylation of ethanol produces ethyl acetate.
(ii) Cannizzaro reaction:
The self-oxidation-reduction(disproportionation)reaction of aldehydes having no α-hydrogens on treatment with concentrated alkalis is known as the Cannizzaro reaction. In this reaction, two molecules of aldehydes participate where one is reduced to alcohol and the other is oxidized to carboxylic acid.
For example, when ethanol is treated with concentrated potassium hydroxide, ethanol, and potassium ethanoate are produced.
(iii) Cross-aldol condensation:
When aldol condensation is carried out between two different aldehydes, two different ketones, or an aldehyde and a ketone, then the reaction is called a cross-aldol condensation. If both the reactants contain α-hydrogens, four compounds are obtained as products.
For example, ethanol and propanal react to give four products.
(iv) Decarboxylation:
Decarboxylation refers to the reaction in which carboxylic acids lose carbon dioxide to form hydrocarbons when their sodium salts are heated with soda-lime.
Decarboxylation also takes place when aqueous solutions of alkali metal salts of carboxylic acids are electrolyzed.This electrolytic process is known as Kolbe's electrolysis.
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(ii) Ethylamine is soluble in water whereas aniline is not.
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Top CBSE CLASS XII Aldehydes, Ketones and Carboxylic Acids Questions
What is meant by the following terms? Give an example of the reaction in each case.
\((i)\)\(Cyanohydrin\)
\((ii)Acetal \)
\((iii)Semicarbazone \)
\((iv)Aldol \)
\((v)Hemiacetal \)
\((vi)Oxime \)
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\((vii)Imine \)
\((ix)\)\(2,4-DNP-derivative \)
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\((i) CH_3CH(CH_3)CH_2CH_2CHO \)
\((ii) CH_3CH_2COCH(C_2H_5)CH_2CH_2Cl \)
\((iii) CH_3CH=CHCHO \)
\((iv) CH_3COCH_2COCH_3 \)
\((v) CH_3CH(CH_3)CH_2C(CH_3)_2COCH_3 \)
\((vi) (CH_3)_3CCH_2COOH \)
\((vii) OHCC_6H_4CHO-p\)Write the IUPAC names of the following ketones and aldehydes. Wherever possible, give also common names.
\((i) CH_3CO(CH_2)_4CH_3 \)
\((ii) CH_3CH_2CHBrCH_2CH(CH_3)CHO \)
\((iii) CH_3(CH_2)_5CHO \)
\((iv) Ph-CH=CH-CHO\)
\((v)\)
\((vi) PhCOPh\)Draw structures of the following derivatives.
(i)The 2,4-dinitrophenylhydrazone of benzaldehyde
(ii)Cyclopropanone oxime
(iii)Acetaldehydedimethylacetal
(iv)The semicarbazone of cyclobutanone
(v)The ethylene ketal of hexan-3-one
(vi)The methyl hemiacetal of formaldehydePredict the products formed when cyclohexanecarbaldehyde reacts with following reagents.
(i)\(PhMgBr\) and then \(H3O + \)
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(iv)Excess ethanol and acid
(v) Zinc amalgam and dilute hydrochloric acid
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Concepts Used:
Aldehydes, Ketones and Carboxylic Acids - Chemical Reactions
Chemical Reactions of Aldehydes and Ketones:
- Cross aldol condensation
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