hello organic chemistry students in this video we're going to talk about alcohol oxidation and haly formation let's go ahead and focus on the Alcohol oxidation first now what we see right here are several alcohols this alcohol is a primary alcohol because the O that the carbon is on is directly attached to one other carbon so that's a primary alcohol down below the O that the carbon is on is attached to two two other carbons so please keep in mind that this is the alcohol functional group the carbon is included so these two carbons directly attached to make it a secondary alcohol and then lastly we have a tertiary alcohol down below and that's as far as we can go now a primary alcohol could be oxidized to an alahh so if you look over here on the primary alcohol there are two hydrogens on that carbon and when it becomes the alahh there's only one so notice we're losing the hydrogen on the alcohol and one of these protons to become the alide we can also take a primary alcohol and oxidize it all the way up to a carboxilic acid which we're going to find out here in a moment actually comes through the alahh an aldhy can be oxidized to a carboxilic acid as well so if you start with an aldhy species we can oxit up to the carboxilic acid so primary alcohols have multiple paths it looks like primary can go to aldhy aldhy can go to carboxilic acid now on a a secondary alcohol there's only one proton on this carpet so there's only one oxidation we can do to a ketone and that's it nothing else and luckily for us a tertiary alcohol doesn't do anything whatsoever so now what we're going to look into next are the reagents used to do these oxidations and there are a mult multiple different types of oxidizing reagents there are a lot of them I'm just going to mention a couple in here just so we have the basic understanding and look at the mechanisms of them as well the first one that we're going to look at is PCC peridinium chlorochromate we're going to talk about this mechanism we're also going to talk about chromic acid so chromic acid right here now there's some other ones under PCC I'm going to write something called a sworn oxidation we're not going to see that in this class but I'm just going to write it right there and over here we can actually use pottassium permagon mates oops let me go ahead and erase that I'm just going to write potassium promanade since I'm writing everything else potassium Perman Gates now I want to stress one more time there are several other oxidizing reagents we're just going to look at these right now now I'm going to take these and make a little line between them and what we're going to say is the ones on the left are what we call weak o oxidizing reagents and the ones on the right are strong oxidizing reagents now this doesn't matter for a secondary alcohol because there's only one oxidation step so you can use any of these reagents to form the Ketone bam all said and done when does this matter it matters with the primary alcohol if we use a weak oxidizing reagent a primary alcohol will go to an alahh and stop let me say that again weak oxidizing reagents will take a primary alcohol and go to the aldhy and stop if we use strong oxidizing reagents the primary alcohol will get oxidized to an alahh which immediately gets oxidized to the carboxylic acid so strong oxidizing reagents take us all the way to the carboxilic acid weak oxidizing reagents go to the alahh and stop now I did mention that we can take an alahh and oxidize it to a carboxilic acid that can only be done with strong oxidizing reagents right here only those in the next slide let's go ahead and start going over the mechanism for the PCC the purini chlorochromate reaction all right please forgive me for the arrows not corresponding to what I'm speaking I accidentally Drew everything and the mic wasn't recording so I'm now coming back in and putting the Vol the the text in here so now here I'm showing what PCC is purini chlorochromate and I'll have my laser pointer as well so you'll see two on the screen the peridinium part doesn't matter for us but this chlorochromate does because of that super good leaving group that we're showing so the peridinium like I said does nothing so if we look at the alcohol that's added into this system we're going to notice here is that this alcohol is going to do the first attack of this reaction the alcohol with its lone pairs of electrons will attack this chromium species won't do anything to the peridinium once again so there's our lone pairs we attack the chrom the chromium and we break open the pi Bond now as that piie Bond breaks open it's going to donate its electrons back down again and kick out the chlorine it has to kick out the chlorine or else we've added too many electrons around chromium so that chlorine then leaves and what happens we now start the reaction of this oxidation CL minus leaves the molecule and we now have this oxygen attached to the ch chromium with the hydrogen still on it with our double bonds and a single o o on it there's a positive charge on that oxygen of the former alcohol so when this happens right here what we can have is a proton transfer event we can take that negative charge from the oxygen on the chromium and it can pick up the proton of the oxygen from the former alcohol to help neutralize this species and there we form this activated chromium complex once we're at this stage we're now going to draw our attention to the carbon attached to the former alcohol so those two hydrogens they're becoming more and more acidic because this chromium is pulling electrons on this Bond so something needs to come in and help facilitate these hydrogens to leave and the only thing that's left over in this reaction is CL minus the CL minus just kind of tugs on the proton doesn't deprotonate itself it just tugs allowing the hydrogen to leave and the electrons donate down between this oxygen carbon bond that would give eight electrons on carbon but 10 on oxygen way too many so now this bond that the chromium has been really pushing on is going to be able to steal those electrons in the oxidation process we break open another Pi Bond again and therefore we can pick up the free proton that was left over once again let me stress the proton does not get pulled by the chlorine it's just being electrostatically tugged a little bit it leaves on its own and once it's gone the oxygen that becomes negative picks up that free proton from solution what this now gives us is coming down here is our alahh species wonderful as well as this chromium system that we don't really care about whatsoever so this is the oxidation of a primary alcohol to an aldah a secondary alcohol with PCC would undergo the same exact mechanism as shown here and that is PCC oxidation and please bear with me here oh and I was just stressing again the chlorine is very important with PCC it's a super good leaving group and we're going to see the difference here in a moment as we go into a strong oxidizing re reagent called chromic acid so now with the weak oxidation we take the prim Ary to an alahh we can take a secondary alcohol to a ketone and nothing happens to tertiary chromic acid though chromic acid will take an aldhy so we're starting with the aldhy here and we're going to see how it's going to get oxidized to a carboxilic acid now chromic acid must have water present but we never ever show the water it's assumed that when you use chromic acid potassium paginate water is always present but never written whatsoever I know it's horrible I didn't come up with this rule but that's what we do it's a very common thing that we do so the first thing that's going to happen here is that this water the essential water with one of its lone pairs is going to attack the aldhy the aldhy is the best electrophile in the solution we break open the carbon oxygen double bond we form an oxygen with the negative charge and the oxygen from the water that added in will be positively charged as we see here we then do a proton transfer inside the molecule neutralizing everything present inside it it and we form a new functional group this new functional group of carbon bearing two o is is not a diol this is what we call a hydrates a hydrate is where there's a carbon that has two o groups attached to it different chemistry can happen and it's also reversible but now this hydrate the oxygens have two lone pairs of electrons wonderful add in chromic acid chromic acid comes in and now one of the oxygens either one both both of them are the same will attack the chromium breaking open the chromium oxygen Bond we're going to form a positively charged oxygen species from the alcohol that attacks us and we're going to break open this oxygen chromium double bond so that oxygen on the chromium will pick up the proton from the former alcohol and give us this following crazy looking complex wait for the drawings to finish okay so now we have to look at the carbon of the hydrate there is going to be a hydrogen on that carbon of the hydrate and that that car I'm sorry that proton on that carbon is going to be the one that we are going to pull to finish our oxidation step so I'm just waiting for the arrows to catch back up we're just looking at that chromium species right there okay there's the proton now what else is still in solution our good old trusty water water is essential for taking an aldhy to a carboxilic acid the water can pull the proton donate electrons down giving chromium back its electron density and what do we end up forming as a result of these arrows we close our intermediary bracket and we form chromium species gets kicked out don't care about it whatsoever and we form our carboxylic acid and this is how we do the oxidation from an aldhy to a carboxilic acid we're going to wait for a moment and I should be I should zoom out here one thing you want to notice here is water is essential but luckily for us water and chromic acid nothing happens to it chromic acid does not have anything in it that's going to be a good leaving group so if water attacked it the water just gets pushed back out because there's no good leaving group on chromic acid can't stress that enough so here the essential part is water must be present to form the hydrate it's the hydrate that attacks the chromium to do the oxidation the aldhy does not attack the chromium it is not a nucleophile it's an electrophile the hydrate must be formed that is essential cannot stress that concept enough so now when we compare and contrast what is the difference here the mechanisms are basically the same between them aren't they oxygen attacks a chromium and we do our oxidation but the tricky part here is with PCC PCC if water was present wouldn't water attack this chromium break open the double bond kick back down and kick out the chlorine it would so water kills the PCC reagent so if you try to take an alahh you need water to make it into the hydrate and do the oxidation with PCC water will kill the PCC every single time without any hesitation okay so now I showed the aldhy going all the way to a carboxylic acid so we could take a primary oxidize it to the alahh take the alahh oxidize it to the carboxilic acid or we could just take a primary alcohol treat it with chromic acid and let it push through all the way to the carboxilic acid it will go through an aldhy intermediate absolutely but water will add in form the hydrate and the hydrate will attack the chromium to form the carboxilic acid so chromic acid can take a primary alcohol to a carboxilic acid right off the bats so when we're comparing all these mechanisms it's pretty much the same exact thing oxygen will attack the chromium we break open the double bond in PCC we can donate down and kick out the chlorine in the case of chromic acid there's no good leaving group we break open the double bond we pick up a proton that's it please forgive the competing red doth right now so the mechanism between the two is basically the same minus chlorine right here and no good leing group in the chromic acid that's the essential differences between these two mechanisms but please do not forget H2O kills the PCC reagent every single time now secondary alcohols you can use PCC so secondary alcohols you can use PCC or chromic acid and it goes up to the Ketone and that's where it stops no water needed whatsoever even if you had water you'd form a hydrate but nothing else could happen all right let's go ahead and cover haly formation now we we've already formed haly containing molecules before we've done this we've taken a double bond on hydrohalogenation to form the secondary haly and the primary halide all right that's old school stuff we can also take alcohols and form halides that's the new part that's what this video is covering this new part of haly installation we can take a primary alcohol and convert it into a chloride we can also convert it into the bromide we can take it convert the bromide down here and the bromide right here we're not going to talk about the iodine only chlorine and bromine we can do this on a primary alcohol a secondary alcohol and a tertiary alcohol so if we want to take a primary alcohol and convert it into the primary halide we're going to use a reagent called thoc chloride which is s O2 the structure of it looks just like this and we'll go over mechanism here in a moment if you want to put the bromine in we're going to use something called phosphorus tribromide now that's going to be the same on the secondary carbons as well we're going to use these reagents the Thal chloride and the phosphorus um tribromide to do these haly installations in the case of the tertiary alcohol though we're going to use some HCL or we're going to use some hbr for these reagents so let me go ahead and come right here I'm just going to put a little red Dash around these bromine so it color codes a little bit better so the bromine is in red the chlorine is in white we're going to talk about both of these reactions now we're going to find out here that as a whole the Thal chloride the phosphorus tribromide are going to undergo sn2 reactions both of them the HCL hbr is going to undergo an s N1 reaction and this is because of the type of carbon that these groups are on the primary has to go sn2 the secondary is most unlikely going to go sn2 and tertiary must go sn1 let's get into these mechanisms let me try to move this page up some there it is wonderful let's talk about the mechanism of Thal chloride and I'm going to go ahead and do the secondary alcohol so I want to show the implications of stereochemistry so now with Thal chloride what we are going to see happen is is that that alcohol is going to attack the sulfur and break open the sulfur oxygen double bond that will donate back down and kick out a good leaving group such as chlorine now when that happens we have our sulfur double bonded oxygen another CL we also lose a proton in this reaction so I'll go minus H+ that's this proton right here and we have H+ sitting in solution and C L minus if we look at this molecule this is S2 gas and this is something that wants to evolve from this molecule to drive the reaction forward but we have to do something to form that SO2 gas we have to force this oxygen carbon bond to break and this is going to happen by the chlorine attacking that oxygen carbon bond breaking the electrons down to the oxygen sulfur we donate electrons up they donate back down to do what you got it push out the chlorine so now when this is done that chlorine has to attack from the back side of the oxygen and that's why we're showing the stereochemistry of it going into the plane this is a classic sn2 displacement same exact mechanism for a primary alcohol so now let's go ahead and use a primary alcohol for the phosphorus trib bromide reaction so with the phosphorus tribromide we have three oxygen sitting around I'm sorry three bromine sitting around the oxygen will attack the phosphorus and we push out one of these bromines notice no oxygen phosphorus double bonds just oxygen bromine Bond I'm sorry bromine um phosphorus bonds so here's our phosphorus two bromines attached to it and now the BR minus that was kicked out will wrap back around attack that carbon break the phosphorus the carbon oxygen Bond pushing it out and what do we get in its place a bromine and that is also an sn2 mechanism so Thal chloride phosphorus tribromide both undergo sn2 reactions to take their alcohols to their uh chloride C or chloride or bromide counterparts let's move this up oops so now what about the tertiary alcohol why can't we use Thal chloride or phosphorus tribromide on a tertiary alcohol steric incumbrance yes could this oxygen attack any of those complexes sure but the chloride or the bromide could never wrap around and attack this carbon right here because there's too much bulk so it would just fall back apart and give us back our alcohol so the only way that we can do this is with a strong acid why a strong acid the o o will attack the proton will cleave the proton hogen Bond and what do we form o it looks like we're starting to form water on this molecule water wants to leave desperately good thing it's attached to a tertiary carbon it leaves on its own and we form a tertiary carbocation to which the chloride or the bromide come in and attack and we form our tertiary halide same exact mechanism for the bromine same exact one nothing different minus the fact we're writing BR instead of Cl so quick little compare and contrast of all these great reactions we can go ahead and convert primary or secondary alcohols to the chloride using Thal chloride the bromide using phosphorus tribromide so primary secondary alcohols must use those the tertiaries must use strong acids because we have to form a car carboca the Thal chloride the phosphorous tribromide while yes we can activate so the alcohol could attack this Thal chloride or the phosphorus tribromide the hallogen will never attack that carbon so it just falls back apart to the tertiary alcohol so that is why we need to use the T the strong acid have the oxygen attack the proton form a water leaving group that desperately wants to leave luckily it can forming a tertiary carbocation that is attacked by the chlorine or the broing to form our tertiary Heights and that is halight installation if you have any questions over this please feel free to send me an email come to the discussion section and office hours whatever you would like and I'll be happy to answer your questions I hope all of you are doing well and I look forward to chatting with you all soon