Hey guys!
Let's take a look at the following new video dealing with alcohol reactions.
Here it says alcohols can be easily identified by the presence of the hydroxyl group, so
they’re OH group.
Because of the presence of this highly polarized group, alcohols can be involved in many organic
reactions.
Here we’re going to take a look at the three major types of organic reactions that deal
with alcohols.
We're going to say here substitution.
Under this reaction, alcohols react with the hydrohalic acids of HCL or HBr to become alkyl
halides.
All that happens in this reaction here is that the OH here will get replaced by the
halogen in the acid.
That's all that is occurring here.
The OH in the alcohol gets replaced by the halogen.
What happens here is we have CH3CH2CH.
The Br is going to be there now.
CH2CH2CH3.
The reason that this happens is because what's actually happening is the OH and the H are
combining and you're losing them as water.
The Br lost a partner.
That carbon lost an OH.
So what do they do?
They just meet up together and create an alkyl halide.
Remember, an alkyl halide is when you have a carbon connected to a halogen.
Here, the next type of reaction we can do is an elimination reaction.
Under this reaction, under the presence of concentrated acids such as H3PO4 or H2SO4,
an alcohol undergoes dehydration.
We lose water again.
Now we're going to form an alkene, so were going to form a double bond.
Basically what happens here is, here is our acid and usually it'd be good if we used heat
so this triangle here represents heat.
What happens here is this OH is going to be lost and then one of the neighboring carbons
is also going to give up an H. Together they lose water.
This carbon loses an OH.
This carbon loses an H, so now they're one bond short each.
What are they left to do?
They form a double bond with each other so that carbon still makes four bonds.
Remember, carbon is tetravalent.
It wants to continue making four bonds.
That carbon is going to double bond to this carbon here and we have that.
That carbon could have done it to any one of the neighboring carbons because they're
all CH3 groups, they're all the same.
The double bond could be made anywhere around it.
Besides that, we also have our third reaction which is oxidation.
In oxidation reactions, an alcohol can be seen as an alkane that has undergone an initial
oxidation.
The alcohol can then continue to be oxidized to form
either a ketone or carboxylic acid.
This is done with the strong oxidizing agent sodium dichromate, Na2Cr2O7 and the strong
acid sulfuric acid, H2SO4.
There is also an inverse relationship that can change our products back into their reactants.
What we have here is a primary alcohol.
This primary alcohol, what's going to happen to it is the primary alcohol when we use these
reagents, it changes the primary alcohol into a carboxylic acid.
That's what we would do.
We could say that there’s an inverse relationship, meaning we can go backwards if we use a reducing
agent, a strong reducing agent.
This strong reducing agent will be LiAlH4, which is called lithium aluminum hydride.
So lithium aluminum hydride can take us back there.
Also we can say besides a primary alcohol, I could have used an aldehyde so if that carbon
had been an aldehyde, the same thing would have occurred.
This changes primary alcohols and aldehydes into carboxylic acids.
I’d still makes that same exact compound.
A secondary alcohol, this one.
Remember, we've talked about how to classify alcohols in previous sections.
Here the carbon and the OH are counted as one.
You say how many carbons is that carbon connected to?
Two, that's what makes it secondary.
Secondary alcohols can be oxidized into what?
Into ketones.
Basically this carbon here changes into a ketone carbon.
It's going to form a double bond to oxygen.
It's going to lose its H so that it can make a double bond and the oxygen is going to lose
its H so they can make a double bond.
Secondary alcohols get oxidized into ketones.
Again, there's the inverse relationship where we can take the ketone back
to the secondary alcohol if you use that strong reducing agent, LiAlH4.
Here we're doing a reduction going backwards and to go to the ketone, we oxidized.
Finally, here we have a tertiary alcohol because again carbon in the OH is counted as one group.
You say that carbon is only connected to three carbons, so it’s tertiary.
The thing about tertiary alcohols is tertiary alcohols cannot be oxidized.
You’d say here no reaction.
Only primary and secondary alcohols can be oxidized here.
Tertiary alcohols cannot be oxidized.
These are the different types of reactions that alcohols do at this point for you guys.
Again, I said it a million times already, when you get to Organic
1, you’ll learn even further reactions dealing with alcohols.
Here you guys are just getting a small sample of the most popular types of alcohol reactions.