# Does glycerol give positive silver mirror test with Tollens’ reagent?

From my school lab manual for identification of organic compounds:

Take 2 ml of Tollens’ reagent and add a few drops of organic sample. Heat the contents on boiling water bath for 5 minutes. Silver mirror is formed. The given organic compound is glycerol.

As far as I know, the compounds with aldehyde groups give positive silver mirror test. Also, those which contain α,β-hydroxy ketone are known to react with Tollens’ reagent.

I have never heard of glycerol reacting with Tollens’ reagent. I found that on heating glycerol forms acrolein which contains aldehyde group:

$$\ce{(CH2OH)2CHOH → CH2=CHCHO + 2 H2O},$$

which I think is the reason, but I am not sure.

• It is unlikely under Tollen's conditions that glycerol is converted into acrolein since both compounds are at the same oxidation level. Base is not going to effect the transformation. What ever aldehydic products are formed, they are at a higher oxidation level than acrolein. See: intechopen.com/chapters/66623 @Aniruddha Deb Oct 13, 2021 at 23:59
• Could it happen due to tautomerism? Infact, there is a dynamic equilibrium between the enol (glicerol) and keton form (see: tgc.ac.in/pdf/study-material/chemistry/…) Mar 25, 2022 at 7:50