Hi and welcome to this video looking at oxidizing alcohols. In this video we'll be looking at classifying alcohols, oxidizing agents and the structures and names of the compounds that are produced upon oxidation for alcohols. So here we have three alcohols. This one here is butan-1-ol.
In the middle we have butan-2-ol. And at the right hand side here we have 2-methylpropan-2-ol. If you're unsure on how to name branched chain alcohols, then I recommend that you check out the video on branched chain alcohols after you've watched this.
We're looking at classifying these alcohols. So we've got three classifications. Primary, secondary, secondary and tertiary. What we need to look at is the carbon attached to the OH group and you're looking for how many carbons is it attached to.
So in this case here we've got our OH group attached to the end carbon. This means it's only attached to one other carbon and this makes it A. primary alcohol.
Now you'll often see this represented as the one with the degree sign there. For our middle alcohol here our oxygen is attached to a carbon in the middle of a chain so it's got two carbons attached to it. This makes it a secondary alcohol.
And then our final alcohol here is attached to a carbon which has branches. This means that it's got three carbons attached to it, no hydrogens at all. This makes it a tertiary alcohol.
We'll be looking at what happens to each of these in turn upon oxidation. But first we'll need to think about what things can we use to oxidise alcohols. So we're going to have a look at two oxidising agents.
So the first one we're looking at here is acidified potassium dichromate. So acidified potassium dichromate is orange. And when you have the reaction with acidified potassium dichromate and you have a successful oxidation reaction, this will turn into a sort of a greeny blue colour.
If you're using copper 2 oxide, you'll get a couple of different things happening. So copper 2 oxide is black. If you get a successful oxidation reaction, you're going to reduce the copper dioxide to copper metal, which will be a sort of red-brown colour.
First of all, we're looking at oxidising primary alcohols. So here we have our butane 1-alt that we had earlier. And we're going to see what happens when we oxidise it using either of those two oxidising agents. So the first thing that would form would be this molecule here.
So you can see that our OH group has changed and we've now got the C double bond O. This is what we call the carbonyl group. Okay, so this part here is the carbonyl group. What we need to have a look at is how did this happen? So how did we get this oxidation happening?
So we've lost one of the hydrogens that was attached here to the carbon. And we've lost this hydrogen as well. well.
You can take this one slightly further because we still have a hydrogen attached here in which we can insert an oxygen and then that would take us all the way to our carboxyl group so you'd recognize this as a carboxyl group. carboxylic acid. So when we're looking at oxidising primary alcohols, we go from having a primary alcohol to what we would call an aldehyde, where this carbonyl group is on the end carbon, to a carboxylic acid.
As you go from here to the aldehyde to the carboxylic acid, you get an increase in the oxygen to hydrogen ratio. So for our primary alcohol, for this one here, we have an oxygen to hydrogen ratio of 1 to 10. And the aldehyde? we have 1 to 8, and in the carboxylic acid, we have 2 to 8, which would also be 1 to 4. So you can see we have this increase in ratio because we're gaining oxygen in comparison to the hydrogen within the molecule.
If you were to use copper dioxide to do this oxidation, you would be able to test for the presence of acid forming as well, as being able to see the copper. Let's have a look now at the secondary alcohols. So if you have a secondary alcohol, you can see that we only have this one hydrogen attached here, which means we can only have one oxidation reaction. So we've got the same group that we had previously forming, it's just this time it's in the middle of the chain.
That means that when the carbonyl is in the middle of the chain we actually have something called a ketone. So we are not able to oxidise a ketone any further, so we don't have a hydrogen here in which to insert more oxygen. So when you go from secondary alcohol, you will form a ketone and you'll get no further oxidation happening. That means if you were to oxidise with copper trioxide, you would not be able to see any acid form.
Finally, our tertiary alcohol. As you can see from the structure, we have no hydrogens attached. That means we do not get any oxidation happening at all.
So, no oxidation reactions. This is as far as we can go. So what happens if you find that you've got some aldehydes and some ketones? They have the same general formula, and therefore the same formulas if you had, say, one with three carbons.
They would both have the same formula. How would you be able to tell them apart? They both look very similar. similar, so we would need to use some sort of test to tell them apart. We can use three different oxidizing agents here to do that.
So these will be able to oxidize the aldehyde, but not the ketone, which will allow you to tell which is which. So like before, when we've got acidified dichromate, it's orange to start with, and then will become a sort of a bluey-green colour when we have our oxidation reaction. Phalings, or benedicts, is something that you may have used previously, and is a blue colour due to the presence of copper ions.
Once it has reacted, you'll get an orangey-red colour forming. And finally, Tollens reagent is colourless to begin with and on reaction forms a silver mirror on the inside of your test tube. So let's have a look at naming aldehydes and ketones. So aldehydes and ketones, we follow the exact same rules that we have followed for all of our other naming.
So if we have a look here, you find the longest chain that contains the carbonyl. So for this example, we have four carbons. You number the chain starting with the carbonyl but for an aldehyde that will always be number one and then if you have any branches you would add those on as you're used to. So for this one here this is an aldehyde with four carbons. So aldehydes just start with the same alkane-based part and it ends in"-al".
So we've got butan-al. Ketones, we do the same thing. We find the longest chain which has the carbonyl group. However, this time we would need to number our chain. So 1, 2, 3, 4, trying to get the lowest number for the carbonyl.
And then if you had any branches, again you would name those as they were. four. So again we start with butan and for this one we don't need to include the number because it would be a symmetrical molecule but usually if it was slightly larger you would have to and for a ketone it ends in on so we have butanone. Here are some examples for you to try yourselves so pause the video see how you get on and then restart. So if we have a look at the first one we're looking for the longest chain which contains our carbonyl group.
So that's going to be 1, 2, 3, 4, 5, 6, this one along the middle here. We need to number the chain such that the carbonyl group ends up with the smallest possible number. So we're going to number from the right hand side.
And then we're going to have a look at our branches. So we've got one branch here, we have a methyl branch today. So if we have a look at building up our name, our methyl branch is on number 4. So we're going to have 4-methyl. We've got six carbons, so it will be hexan.
And our carbonyl group is in the middle of the chain, and it's on number three. So we're going to have hexan-3, and that makes it a ketone. So we're going to end our name in"-one". Looking at the second example, we've got an aldehyde, because this is on the end carbon. We have four carbons, but we do need to number the chain because we have some branches here.
So we've got one, two, three, four. So for an aldehyde, the number one carbon will always be the one with the carbonyl attached. So we have two methyl branches here attached to the number three.
So we're going to have a dimethyl. So we'll have three, three dimethyl. and this time it will be butan-al because we have an aldehyde. Here are some names that you can try drawing out.
Remember to start from the end of the name where forward so pause the video and then come back to it once you've given them a try. Having a look at these names we've got pentan and we have own so we know that we have a ketone. In terms of numbers our carbonyl group is on number three and on the second carbon we have a methyl group so that's got one carbon attached to it. If we try drawing this out, we're going to have five carbons in a row.
On the third carbon, we're going to have our double bond to the oxygen. And on the second carbon, so it doesn't matter which one we choose here, we're going to have our methyl group. Then remember to go around and fill in so that every carbon has four bonds, making sure you're aware that this carbon already has its four bonds.
Looking at the second example, we have butanol. So we have four carbons, and with the al ending, we know that we have an aldehyde, so that must be carbon number one. On the third carbon, we have a methyl. branch, so that's of one carbon. So if we draw this out we're going to have four carbons.
On carbon number one we have an oxygen and our hydrogen and then on carbon number three we'll have a methyl group. Okay and then go in and fill in the hydrogens. I hope that you've enjoyed watching this video on oxidizing alcohols.
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