Question

For the determination of fatty acid composition, transesterification is done in a warm aqueous solution of

• A. KCl + methanol
• B. KOH + methanol
• C. NaOH + methanol
• D. H2O + methanol

Hint:

Transesterification is an important step in biodiesel production and fatty acid analysis, typically involving methanol and KOH as a catalyst.

Answer 1

The Correct Option is B

Transesterification of fats into fatty acid methyl esters needs a strong base in methanol to generate methoxide ions that attack the triglyceride's ester bonds.

KCl is a neutral salt and cannot generate methoxide, and water mixed with methanol provides no base at all, so neither can drive the reaction. NaOH can generate methoxide too, but the standard warm aqueous reagent used for this specific fatty acid composition protocol is potassium hydroxide in methanol.

So the reagent used is KOH + methanol.

Answer 2

Thinking about this from the standpoint of standard lipid-analysis protocols used before gas chromatography:

1. KCl + methanol: Never appears in transesterification protocols since it lacks any catalytic base function.
2. KOH + methanol: This exact combination, warmed gently, is the reagent used to convert extracted lipids into their methyl esters before injecting them onto a GC column for fatty acid profiling.
3. NaOH + methanol: Chemically capable of the same base-catalysed reaction, but the specific "warm aqueous solution" protocol referred to in fatty acid composition determination conventionally specifies potassium hydroxide rather than sodium hydroxide.
4. H2O + methanol: A plain aqueous methanol mixture with no base present would not catalyse ester-bond cleavage at all.

Matching the reagent used in the standard protocol described in the question narrows the answer to the potassium hydroxide and methanol combination.

The correct answer is KOH + methanol.