If the asymmetric system adjoining the COH group, which is that introduced in synthesizing the hexose from the pentose, be eliminated, the formulae at disposal for the two pentoses are CH 2 (OH) - - - COH CH 2 (OH)+-- COH.
The pentose is then obtained from the acetylated compound by successive treatment with ammonia and dilute acids: CH 2 OH ([[Choh) 3 Choh Ch: Noh -)Ch20h (Choh)3 Choh Cn - Ch 2 Oh (Choh) 3 Cho]].
CH20H CH20H CH OH CH OH (CH OH) 2 -> (CH OH)2 CHO CH-OH CN Pentose -> Cyanhydrin on further oxidation gives a mannonic acid, C 5 H 8 (OH) 5 CO 2 H; this acid readily yields a lactone.
Scheibler discovered l-arabinose in 1869, and regarded it as a glucose; in 1887 Kiliani proved it to be a pentose.
Hydrogen peroxide and a trace of a ferrous salt: C 4 H 9 O 4 (CH OH) CHO-->C 4 H 9 O 4 (CH OH) C02H->C4H904 CHO Hexose -> Acid -* Pentose.