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Aldehydes Ketones and Carboxylic Acids question

2021 · 25 Feb · Shift 1 · Q2
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Aldehydes Ketones and Carboxylic Acids question

2021 · 25 Feb · Shift 1 · Q2

JEE MainChemistryAldehydes Ketones and Carboxylic AcidsMCQ+4 / −1
Which one of the following reactions will not form acetaldehyde?
  1. A
    CH3CH2OH⟶573KCuC{H_3}C{H_2}OH\mathrel{\mathop{\kern0pt\longrightarrow} \limits_{573K}^{Cu}}CH3​CH2​OH573K⟶Cu​
  2. B
    CH3CH2OH→CrO3−H2SO4C{H_3}C{H_2}OH\xrightarrow{Cr{O_3} - {H_2}S{O_4}}CH3​CH2​OHCrO3​−H2​SO4​​
  3. C
    CH2=CH2+O2⟶H2OPd(II)/Cu(II)C{H_2} = C{H_2} + {O_2}\mathrel{\mathop{\kern0pt\longrightarrow} \limits_{{H_2}O}^{Pd(II)/Cu(II)}}CH2​=CH2​+O2​H2​O⟶Pd(II)/Cu(II)​
  4. D
    CH3CN⟶ii) H2Oi) DIBAL−HC{H_3}CN\mathrel{\mathop{\kern0pt\longrightarrow} \limits_{ii)\,{H_2}O}^{i)\,DIBAL - H}}CH3​CNii)H2​O⟶i)DIBAL−H​
View written solutionFree

Correct answer: B

  1. We check which reaction does not give acetaldehyde

Acetaldehyde is \ceCH3CHO\ce{CH3CHO}\ceCH3CHO.

  1. Option A

\ceCH3CH2OH→573 KCuCH3CHO+H2\ce{CH3CH2OH \xrightarrow[573\,K]{Cu} CH3CHO + H2}\ceCH3CH2OHCu573K​CH3CHO+H2

Passing ethanol vapours over heated copper at 573 K573\,\text{K}573K causes dehydrogenation of ethanol to ethanal (acetaldehyde).

So, A forms acetaldehyde.

  1. Option B

\ceCH3CH2OH→CrO3/H2SO4\ce{CH3CH2OH \xrightarrow{CrO3/H2SO4}}\ceCH3CH2OHCrO3/H2SO4​

\ceCrO3/H2SO4\ce{CrO3/H2SO4}\ceCrO3/H2SO4 is Jones reagent, a strong oxidizing agent. It oxidizes a primary alcohol beyond the aldehyde stage to the carboxylic acid.

Thus ethanol gives mainly acetic acid:

\ceCH3CH2OH−>CH3COOH\ce{CH3CH2OH -> CH3COOH}\ceCH3CH2OH−>CH3COOH

So, B does not form acetaldehyde.

  1. Option C

\ceCH2=CH2+O2+H2O→Pd2+/Cu2+CH3CHO\ce{CH2=CH2 + O2 + H2O \xrightarrow{Pd^{2+}/Cu^{2+}} CH3CHO}\ceCH2=CH2+O2+H2OPd2+/Cu2+​CH3CHO

This is the Wacker oxidation of ethene, which gives acetaldehyde.

So, C forms acetaldehyde.

  1. Option D

\ceCH3CN→i) DIBAL−Hii) H2OCH3CHO\ce{CH3CN \xrightarrow{i)\ DIBAL-H \quad ii)\ H2O} CH3CHO}\ceCH3CNi) DIBAL−Hii) H2O​CH3CHO

DIBAL-H partially reduces nitriles to aldehydes on hydrolysis.

Hence acetonitrile gives acetaldehyde.

So, D forms acetaldehyde.

  1. Conclusion

Only option B does not produce acetaldehyde.

B\boxed{B}B​

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