Chemistry · Aldehyde and Ketones: Nature of carbonyl group, nucleophilic addition to >C=O group, relative reactivities of aldehydes and ketones
Identify
\( \boldsymbol{A} \stackrel{\boldsymbol{H C N}}{\longrightarrow} \boldsymbol{B} \stackrel{\boldsymbol{H}_{3} \boldsymbol{O}^{+}}{\longrightarrow} \boldsymbol{L} \boldsymbol{a} \boldsymbol{c t i c} \boldsymbol{a c i d} \) Identify \( \boldsymbol{A} \)
- A. \( H C H O \)
- B. \( C H_{3} C H O \)
- C. \( C_{6} H_{5} \) СНО
- D. \( C H_{3} \) СОСН \( _{3} \)
Step-by-step solution
Lactic acid is 2-hydroxypropanoic acid. The reaction sequence involves cyanohydrin formation with HCN followed by acidic hydrolysis. For an aldehyde, the cyanohydrin has one more carbon, and hydrolysis yields a hydroxy acid. Acetaldehyde (CH3CHO) has two carbons; its cyanohydrin has three carbons, and hydrolysis gives lactic acid. Formaldehyde (HCHO) would give glycolic acid, benzaldehyde (C6H5CHO) gives mandelic acid, and acetone (CH3COCH3) gives 2-hydroxy-2-methylpropanoic acid. Thus, A is CH3CHO.
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