Monosaccharides - Weak Oxidation (Aldonic Acid)


Video Transcript

In this video we're going to learn how to perform a weak oxidation on monosaccharides to yield a functional group called an aldonic acid, let's get going so that monosaccharides are essentially polyols with carbonyls attached or with one carbonyl attached, so that means that they can undergo a series of oxidation or reduction reactions because there's so many reactive functional groups, we have alcohols that can be oxidized, we have ketones that can be reduced, all kinds of stuff okay? Well, it turns out that one of those possible oxidation is called weak oxidation and what weak oxidation is defined as is the Selective oxidation of monosaccharide aldehydes to carboxylic acid, okay? The selective oxidation of just the aldehyde to carboxylic acid is known as weak oxidation. Now, guys think about it all of these different OHS could potentially be oxidized, they could be, this OH could be oxidized to a ketone, this OH is a primary alcohol that could totally be oxidized to a carboxylic acid, if I use a strong enough oxidizing agent I could turn this whole thing into like ketones, carboxylic acids etc. But with the special route with a special oxidizing agent I can simply just select the very top aldehyde and turn it into a carboxylic acid, okay? In fact this reaction doesn't even work with ketosis because ketosis don't have aldehydes, right? So, it's selective for aldehyde to carboxylic acids and the reagents that we use for this actually is called bromine water, okay? So, it's bromine in water, this method can be used to differentiate between aldoses and ketoses because it doesn't work on ketosis, you can't do anything with it works on aldoses but it doesn't work on ketoses. So, it's kind of the basis, the principle of this is the basis for some tests of sugars, some sugar test, a test whether you want to have one functional group or another, this is kind of like one of the test, okay? Now guys we're in luck, the mechanism of this reaction of this oxidation is not fully known. So, you're not going to have to draw the mechanism you just need to be aware of what these regions do and what the product is. So, let's go through a really quick, here I have d-mannose, a sugar you guys should be super familiar with, I'm going to react it with bromine water. Now, specifically it should be mildly, mildly acidic, it shouldn't just be bromine and water she a little bit acidic but just you guys know most textbooks, most professors skip this part, they don't even write it, I'm just putting this here for your benefit so you guys know but in the future I'm going to skip the pH 6 part because most texts and professors don't use it, okay? What this is going to do through a mechanism that we don't fully know it's going to selectively only oxidize my aldehyde to a carboxylic acid and notice that no other groups are going to change even the primary alcohol stays totally is fine, the only thing oxidizes at the top, okay? When this happens the functional group is no longer called a, it's no longer like a monosaccharide, it's a modified model saccharide called an aldonic acid. So, what you would do is you would take your root, which is d-mannose. So, you take the d-mano part and you would add on the suffix of nic acid, okay? Because notice that it's nic acid, aldonic acid. So, you just end add on the nic acid part and that's the way that you would mean it. So, an aldonic acid of d-manose is specifically called d-manonic acid and that means that I have a d-mannose that you oxide the top to a carboxylic acid okay, cool? So, that's it for that, general reaction, let's go ahead and do a practice problem

Problem: Predict the product of the following reaction.