# Why do alpha-hydroxy ketones respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests?

I learnt from a certain textbook that aldehydes and formic acid respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests.

However, in another textbook I read that even alpha-hydroxy ketones respond positively to these tests. What is the reason behind this? I thought ketones are not oxidizable (unless under drastic conditions).

Fructose is an alpha-hydroxy ketone, but all alpha-hydroxy ketones are not fructose. In fructose there is a terminal hydroxy group which facilitates Tollens' test, etc. in basic medium. But why do alpha-hydroxy ketones like benzoin give these tests even though there is no terminal hydroxy group? That part is still unclear to me. Could you please answer that part?

• – Loong Dec 12 '16 at 19:30
• I think $\alpha$-hydroxy ketone is being oxidized to a diketone... Still thinking about mechanism of action. – Zhe Dec 13 '16 at 13:36
• I think you should be able to find your answer here: acadblock.com/organic-chemistry/tollens-reagent-l4b2 – electronpusher Dec 14 '16 at 3:17
• There is a nice answer in this link: quora.com/… – santimirandarp May 9 '17 at 4:15
• – user55119 May 11 at 20:51