Why Doesn't Lactose React with Red Tetrazolium in a NaOH Oxidation Process?

[ericvon11]

Hi all,

I was given an unknown in a recent lab and determined it was lactose. However, I'm not quite sure why it reacted the way it did with the reagents used.

I used Red tetrazolium and NaOH which oxidizes aldoses and ketoses. Lactose is made of glucose and galactose, both of which are aldoses. I was wondering first off what NaOH would do in this procedure and if both are aldoses, why doesn't it react with Red tetrazolium? I only got a pink tint when I heated it. But since both are aldoses they should reduce the red tetrazolium right?

 

[Valerie Park]

Thanks in advance for your help!NaOH is an oxidizing agent, meaning that it will react with aldehydes and ketones to form carboxylic acids. In the case of lactose, which is composed of two aldoses, the NaOH will oxidize the aldoses to form the corresponding carboxylic acids, which will then react with Red tetrazolium, resulting in the pink tint.