Trichloroacetaldehyde (chloral, CCl3CHO) is subjected to the Cannizzaro reaction with aqueous NaOH. The product mixture contains sodium trichloroacetate (CCl3COONa) and which other organic compound?

Introduction / Context:
The Cannizzaro reaction is a well known organic redox reaction in which a non enolisable aldehyde disproportionates in the presence of a strong base. One molecule of the aldehyde is oxidised to a carboxylate, while another is reduced to an alcohol. Trichloroacetaldehyde, also called chloral, undergoes this reaction. Understanding which products are formed tests your knowledge of reaction mechanism and the patterns of oxidation and reduction in carbonyl chemistry.

Given Data / Assumptions:

• Substrate: trichloroacetaldehyde, CCl3CHO (chloral).
• Reagent: aqueous sodium hydroxide, NaOH.
• The reaction is stated to be a Cannizzaro reaction.
• One product is sodium trichloroacetate (CCl3COONa).
• We must identify the other organic product from the options.

Concept / Approach:
In a Cannizzaro reaction, two molecules of an aldehyde without alpha hydrogen atoms react in base. One molecule is oxidised to a carboxylate salt, while the other is reduced to a primary alcohol. For trichloroacetaldehyde, the oxidation product is trichloroacetic acid salt, CCl3COONa. The corresponding reduction product is the alcohol where the aldehyde group CHO becomes CH2OH, giving 2, 2, 2 trichloroethanol, CCl3CH2OH. Other options such as chloroform or trichloroethanol with incorrect carbon chain length do not match the Cannizzaro pattern.

Step-by-Step Solution:
Step 1: Write the structure of trichloroacetaldehyde: CCl3CHO, where the aldehyde carbon is attached to a trichloromethyl group.Step 2: In the Cannizzaro reaction, one molecule of the aldehyde is oxidised to the carboxylate: CCl3COO−, giving sodium trichloroacetate with Na+.Step 3: The other molecule is reduced, where the aldehyde CHO group is converted to a primary alcohol CH2OH.Step 4: The reduction product therefore has the formula CCl3CH2OH, which is known as 2, 2, 2 trichloroethanol.Step 5: Check the options and locate 2, 2, 2 trichloroethanol as option b.Step 6: Verify that chloroform (CHCl3) or trichloromethanol do not correspond to a simple reduction of the aldehyde group of chloral.

Verification / Alternative check:
You can think of the Cannizzaro reaction in terms of oxidation state changes at the carbonyl carbon. In the aldehyde, the carbonyl carbon has a certain oxidation level. Oxidation to the carboxylate increases the oxidation state, while reduction to an alcohol decreases it. Structural logic then dictates that the carbon chain length remains the same. Since the aldehyde carbon in trichloroacetaldehyde is part of a two carbon skeleton (CCl3CH=O), the alcohol must also have two carbons, which fits 2, 2, 2 trichloroethanol, not a one carbon compound like trichloromethanol or chloroform.

Why Other Options Are Wrong:
Option a, chloroform, CHCl3, lacks the hydroxyl group and does not come from direct reduction of the aldehyde function. Option c, trichloromethanol, would have only one carbon and is not the straightforward reduction product of a two carbon aldehyde. Option d, 2, 2, 2 trichloropropanol, would have three carbons and also does not match the starting skeleton. Option e, ethanol, lacks the trichloromethyl group and is unrelated to the chlorinated aldehyde starting material.

Common Pitfalls:
Students sometimes forget that in the Cannizzaro reaction both oxidation and reduction occur on the same aldehyde skeleton, so the carbon chain length of the alcohol and carboxylate products must match that of the starting aldehyde. Another pitfall is to confuse the Cannizzaro reaction with haloform reactions, which do produce chloroform from certain carbonyl compounds. Keeping these reaction types separate and focusing on carbon skeleton conservation in Cannizzaro reactions helps avoid confusion.

Final Answer:
Along with sodium trichloroacetate, the Cannizzaro reaction of trichloroacetaldehyde with NaOH produces 2, 2, 2 trichloroethanol as the other organic product.