Why is Sucrose a none Reducing Sugar? Detail...Please?

Question

Yes I know what a reducing Sugar is, the ring breaks ot the weakest bond between the O-Carbon 1. It yields a H to C5 and a double bond created between C1 and the O.
Why can this not happen under alkeline conditions of the Sucrose molecule?
By adding acid, what makes it happen then?

Many Many Thanks....

Answer 1

Sucrose is a double sugar (permanently covalently bonded molecule of glucose at its carbon number 1 to fructose at its carbon number 2, by an ether linkage [-C-O-C-]). C-1 of glucose is an aldehyde carbon (R-CH=O), which is sometimes-on sometimes-not bonded in a hemiacetal. Whenever tghe Fehlings (or other) reagent catches glucose in thealdehyde form, it oxidizes it and becomes reduced itself to brick-red Cu2O. Similarly for fructose, except the keto group at C-2.

When glucose and fructose arelocked up togetrher into sducrose, the aldehyde and 2-keto group are unavailable for reaction. The conditions of Fehlings, Benedicts, Barfoeds and Tollens reagent are all alkaline. Touch sucrose with a bit of acvid, however, and it catalyzes dissolution of the bond between the two and frees up the groups of both with the oxidizing reagent (which reduces them LOL).