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Question
When liquid ‘A’ is treated with a freshly prepared ammoniacal silver nitrate solution, it gives bright silver mirror. The liquid forms a white crystalline solid on treatment with sodium hydrogensulphite. Liquid ‘B’ also forms a white crystalline solid with sodium hydrogensulphite but it does not give test with ammoniacal silver nitrate. Which of the two liquids is aldehyde? Write the chemical equations of these reactions also.
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Solution
Liquid ‘A’ forms a bright silver mirror on treatment with ammoniacal \[\ce{AgNO3}\] solution, therefore, liquid ‘A’ is an aldehyde.
Liquid B does not give test with ammoniacal \[\ce{AgNO3}\] solution, therefore, liquid ‘B’ must be a methyl ketone.
Chemical equations for these reactions are:
\[\begin{array}{cc}
\phantom{........}\ce{R}\phantom{......................}\ce{R}\phantom{.......}\ce{SO3Na}\phantom{}\\
\phantom{...}\backslash\phantom{......................}\backslash\phantom{...}\phantom{..}/\\\
\phantom{}\ce{C = O + NaHSO3 -> \phantom{..}C}\\
\phantom{.............}/\phantom{......................}/\phantom{.....}\backslash\phantom{..........}\\
\phantom{.....}\ce{\underset{Aldehyde(A)}{H}\phantom{................}\underset{(White crystalline solid)}{\phantom{.}H\phantom{.......}OH}}\phantom{..}
\end{array}\]
\[\begin{array}{cc}
\phantom{........}\ce{R}\phantom{......................}\ce{R}\phantom{.......}\ce{SO3Na}\phantom{}\\
\phantom{...}\backslash\phantom{......................}\backslash\phantom{...}\phantom{..}/\\\
\phantom{}\ce{C = O + NaHSO3 -> \phantom{..}C}\\
\phantom{.............}/\phantom{......................}/\phantom{.....}\backslash\phantom{..........}\\
\phantom{....}\ce{\underset{Methyl ketone (B)}{H3C}\phantom{.............}\underset{(White NaHSO3 adduct)}{\phantom{.}H3C\phantom{.......}OH}}\phantom{.....}
\end{array}\]
\[\ce{\underset{Aldehyde (A)}{R - CHO} + \underset{Tollens reagent}{2[Ag(NH3)2]+} OH- ->[Warm] RCOONH4 + \underset{(Silver mirror)}{2Ag + 3}NH3 + H2O}\]
\[\begin{array}{cc}
\ce{O}\phantom{...............................}\\
||\phantom{...............................}\\
\ce{\underset{Methyl ketone (B)}{R - C - CH3} ->[Tollens reagent] No silver mirror}
\end{array}\]
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RELATED QUESTIONS
Write the products formed when CH3CHO reacts with the following reagents: CH3CHO in the presence of dilute NaOH
What is meant by the following term? Give an example of the reaction in the following case.
Aldol
Write structural formulas and names of four possible aldol condensation products from propanal and butanal. In each case, indicate which aldehyde acts as nucleophile and which as electrophile.
Describe the following:
Cross aldol condensation
Complete the synthesis by giving missing starting material, reagent or product.
\[\begin{array}{cc}
\ce{C6H5CHO}\phantom{............}\\
\phantom{........}\ce{+\phantom{......}\ce{->[dil.NaOH][\Delta]}}\phantom{...}\\
\ce{CH3CH2CHO}\phantom{............}
\end{array}\]
Write a chemical equation for the following reaction:
Propanone is treated with dilute Ba( OH)2.
Explain aldol condensation reaction in detail.
Compounds A and C in the following reaction are:
\[\ce{CH3CHO ->[(i) CH3MgBr][(ii) H2O] (A) ->[H2SO4, Δ] (B) ->[Hydroboration oxidation] (C)}\]
Which of the following compounds do not undergo aldol condensation?
(i) \[\ce{CH3 - CHO}\]
(ii) 
(iii) \[\begin{array}{cc}
\phantom{}\ce{O}\\
\phantom{}||\\
\ce{CH3 - C - CH3}
\end{array}\]
(iv) \[\begin{array}{cc}
\phantom{}\ce{CH3}\\
|\phantom{...}\\
\ce{CH3 - C - CHO}\phantom{..}\\
|\phantom{...}\\
\phantom{}\ce{CH3}\\
\end{array}\]
Why are carboxylic acids more acidic than alcohols or phenols although all of them have hydrogen atom attached to a oxygen atom \[\ce{(-O-H)}\]?
Identify A and B from the following reaction:
\[\begin{array}{cc}
\ce{CH3}\phantom{.................}\\
|\phantom{....................}\\
\phantom{}\ce{2CH3 - C = O ->[Ba(OH)2] A ->[Δ] B + H2O}
\end{array}\]
Convert the following:
Acetaldehyde to But-2-enal
Predict the reagent for carrying out the following transformations:
Ethanal to 3-hydroxy butanal
Why is the α-hydrogens of aldehydes and ketones are acidic in nature?
Assertion (A): The final product in Aldol condensation is always α, β-unsaturated carbonyl compound.
Reason (R): α, β-unsaturated carbonyl compounds are stabilised due to conjugation.
