Question

The Kiliani synthesis is used to increase the carbon chain in:
A.Acid
B.Alcohol
C.Aldose
D.Ketose

Answer 1

To answer this question, you should recall the concept of Killiani’s synthesis. It is a method for synthesis of monosaccharides.

Complete step by step answer:
Kiliani's synthesis proceeds via synthesis and hydrolysis of a cyanohydrin, thus elongating the carbon chain of an aldose by one carbon atom while preserving stereochemistry on all the previously present chiral carbons. The new resulting chiral carbon is produced with both types of stereochemistry, so the product of a Kiliani's synthesis is a mixture of two diastereomeric sugars, called epimers. For example, a sugar named D-arabinose is converted to a mixture of D-glucose and D-mannose.
It is usually used for the production of sugars that are difficult or impossible to obtain from natural sources. While it does provide access to every possible stereoisomer of any desired aldose, the problem of this reaction is low yield and use of toxic reagents. Also, the process requires having a supply of the previous sugar in the series, which may itself require substantial synthetic work if it is not readily available.

Hence, the correct answer is aldose and the correct option is C.

Note:
You should know about the reverse of Kiliani's synthesis which is known as the Ruff Degradation. It is possible to go in the reverse direction of Kiliani synthesis, where an aldose is reduced in length by one carbon. The procedure for going in this direction is called Ruff Degradation. In the first step, the aldehyde is selectively oxidized to a carboxylic acid by bromine water. Make sure you remember that the secondary and primary alcohols are not oxidized here. The second step involves adding an iron (III) salt like $\left[ {F{e_2}{{\left( {S{O_4}} \right)}_3}} \right]$with hydrogen peroxide, which involves the loss of carbon dioxide and oxidation of the adjacent ${{\mathbf{C}}_{\mathbf{2}}} - {\mathbf{OH}}$to an aldehyde.