An organic compound [A] with molecular formula is obtained when compound [B] reacts with red…
An organic compound [A] with molecular formula $\text{C}_2\text{Cl}_3\text{O}_2\text{H}$ is obtained when compound [B] reacts with red phosphorous and $\text{Cl}_2$. The organic compound [B] can be obtained on the reaction of methyl magnesium bromide with carbon dioxide followed by acid hydrolysis. Upon partial reduction, compound [B] forms compound [C] with molecular formula $\text{C}_2\text{H}_4\text{O}$, which gives yellow precipitate of iodoform on heating with iodine in presence of sodium hydroxide. Compound [C] also reacts with dilute NaOH to form compound [D].
(a)
Identify the compounds [A], [B], [C] and [D].
(b)
Write down the reaction for the formation of [A] from [B]. What is the reaction called?
(c)
Write the chemical test to distinguish between compound [C] and acetone.
(d)
Which will be more acidic, compound [A] or [B]? Why?
Answer
Answer (a)
AIWritten by AI (gemini) - it can contain mistakes.
[A] is trichloroacetic acid, $\text{CCl}_3\text{COOH}$
[B] is acetic acid, $\text{CH}_3\text{COOH}$
[C] is acetaldehyde, $\text{CH}_3\text{CHO}$
[D] is 3-hydroxybutanal (aldol), $\text{CH}_3\text{CH(OH)CH}_2\text{CHO}$
Answer (b)
AIWritten by AI (gemini) - it can contain mistakes.
Reaction:
$\text{CH}_3\text{COOH} + 3\text{Cl}_2 \xrightarrow{\text{Red P}} \text{CCl}_3\text{COOH} + 3\text{HCl}$
Reaction name: Hell-Volhard-Zelinsky (HVZ) reaction.
Answer (c)
AIWritten by AI (gemini) - it can contain mistakes.
Acetaldehyde [C] gives a silver mirror with Tollen's reagent and a red precipitate of $\text{Cu}_2\text{O}$ with Fehling's solution, whereas acetone does not give these tests.
Answer (d)
AIWritten by AI (gemini) - it can contain mistakes.
Compound [A] (trichloroacetic acid) is much more acidic than compound [B] (acetic acid). The three strongly electronegative chlorine atoms exert a powerful electron-withdrawing inductive ($-I$) effect, dispersing the negative charge on the carboxylate anion and stabilizing it.
From ISC 2027 Specimen Chemistry Paper 1, question 19(i).