Ruff degradation of D-arabinose gives D-erythrose. The Kiliani-Fischer synthesis converts D-erythrose to a mixture of D-arabinose and D-ribose. Draw out these reactions and give the structure of D-ribose.

Ruff degradation is employed when carbohydrate chain needs to be shortened or degraded by a single carbon. Aqueous solution of bromine is used in first step which is used for oxidation of aldehyde to carboxylic acid and then in second step, ferric ion catalyses oxidation reaction with hydrogen peroxide and bond cleavage between carbon-1 and carbon-2 occurs forming an aldehyde. D-arabinose on Ruff degradation gets converted to D-erythrose.

D-arabinose D-erythrose

Kiliani-Fischer synthesis is employed when carbohydrate chain needs to be lengthened by one carbon. It involves addition of cyanide ion to aldoses which is then partially reduced and hydrolysed to give a new aldehyde. Kiliani-Fischer synthesis converts D-erythrose into mixture of D-arabinose and D-ribose. A new chiral carbon is generated in this process and due to this, position of hydroxyl group can be on left or right. That’s why we got two products, that is, D-arabinose and D-ribose. Diastereomeric mixture is obtained or products which are diastereomers of each other.

D-erythrose D-arabinose D-ribose