Leia here from ley.com and in this video we'll look at the mechanism for alcohol oxidation using chromic acid peridinium chlorochromate and potassium prominate chromic acid is a common oxidizing Regent for alcohols but you may see it in a different form but if you see chromium with oxygen and an alcohol recognize it's an oxidation reaction it can be made from chromium trioxide in sulfuric acid and acetone or sodium D chromate in sulfuric acid in water chromic acid has a central chromium with two double bound oxygens and two single bound hydroxy groups this means that when the oxygens are pulling on the bonds between themselves and chromium chromium is left partially positive also keep in mind that acids can dissociate in solution so that chromic acid can be in the form of a free acidic proton and the conjugate base hc4 minus that proton can be picked up by anything in solution including chromic acid which will play a key role in understanding the mechanism we'll use propanol as a simple primary starting alcohol keeping in mind that it'll get oxidized Twice first to an alide but then directly to a carboxilic acid because a strong oxidizing agent will not wait and will not stop at the alahh to start the mechanism we have an activated chromic acid because it's accepted a proton and has a positive oxygen on one of the carbonal this makes chromium even more partially positive and oxygen being partially negative will want to attack we'll show oxygen reaching out with a lone pair of electrons to attach that Central chromium giving it two many bonds as a result the bond between chromium and the activated oxygen will collapse onto oxygen this step is critical in understanding why we had to proteinate it first we're in an acidic solution that means means we have protons which are positive and neutral molecules if we did not activate this oxygen collapsing that Pi Bond onto oxygen would give us a negative charge which is not going to form in this type of acidic solution the oxygen that attacked now has three bonds and one lone pair for a formal charge of plus one we have to get rid of that electron and we show an internal proton transfer where one of the hydroxy groups on chromium will reach for that prot giving the electrons back to the oxygen atom chromium now has a positive oxygen oxygen on our starting molecule now has two lone Pairs and is back to being neutral this intermediate is called the chromate Esther because it looks like an ester with chromium at the center an Esther remember has a carbon double bound to oxygen and single bound to an O group here we have a chromium double bound oxygen and the alcohol is our o group The Next Step step will be to break away the oxygen from the chromium and this is allowed to happen because we have at least one alpha hydrogen the alpha carbon is the one that is holding the oxygen the hydrogens attached to that are the alpha hydrogens we show a weak base in solution like water coming in to grab the hydrogen atom but it only grabs the proton leaving the electrons behind instead of collapsing the electrons onto carbon we collapse them towards the oxy atom the two electrons will now sit between carbon and oxygen as a pi Bond and this is the key this is the oxidation step where we form a second bond between carbon and oxygen in this case to form the aldah oxygen however has too many bonds so we have to kick out the bond between itself and chromium collapsing that onto the chromium this gives us our product which is an alahh but it's not our final product if you started with a secondary alcohol instead of a hydrogen you would have an R Group and this would be a ketone your final product but because we have another Alpha hydrogen we can do the entire mechanism again to get a carboxilic acid the key to understanding the next step is to remember that a carbonal dissolved in an acidic solution can undergo hydration to form a dial you learn this with your aldhy and Ketone reactions so I'll fly through it quickly we have protons in solution h3o+ or a proteinated chromic acid we'll activate the carbonal by grabbing that proton we activate the carbonal to make that carbonal carbon more reactive and more susceptible to attack oxygen has a lone pair in a positive charge making it unhappy so the oxygen will start pulling on the electrons that bind it to carbon making that carbon very partially positive a partially negative oxygen on water will take advantage of that charge and attack this gives us a proteinated diod we bring in a water molecule to remove that extra proton giving the electrons back to oxygen for a neutral gem di intermediate this gem dial intermediate is key to the next step when you have two alcohols bound to one carbon it's not very stable it's reactive and in this case with chromic acid still present in solution it's going to react with chromic acid once again we see the LOM Paran alcohol attack and activated chromic acid Breaking the Bond between chromium and the activated oxygen the purple oxygen now has three bonds alone pair in a positive charge so we show an internal proton transfer to make the oxygen neutral once again we have a chromate Esther ready for the oxidation step we still have an alpha hydrogen so we show a water molecule in solution grabbing that hydrogen collapsing the electrons between carbon and the chromate Ester oxygen and breaking off the entire chromium complex this gives me a final product with a double bond between carbon and the oxygen we just reacted and a single bond between the other oxygen on the molecule if you wind up with a product like this and it looks confusing number and redraw the carbon holding both oxygens is number one and then continue down the chain we'll redraw that same carbon chain and add the substituents in a more familiar manner a double bound oxygen going straight up the O going down to the side and there's our carboxilic acid the next mechanism we'll look at is the oxidation of an alcohol using PCC peridinium chlorochromate paradine is a heterocyclic aromatic compound because we have a nitrogen in what looks like a Benzene ring when you protonate it you get peridinium with a positive charge and the counter ion is chlorochromate which is chromium double bound to two oxygen atoms one single bound negative oxygen and a chlorine notice that in this solution we don't have sulfuric acid which is a strong acid allowing us to form an O minus in solution peridinium is very weak so that negative oxygen is allowed your professor may use different versions of PCC in the mechanism you might see the chlorochromate protonated and a neutral paradine just make sure you recognize the concept of the reaction and then use the version that your professor requires we'll start with another primary alcohol and show it reacting with chlorochromate in the same way as we did before oxygen attacks The partially positive chromium causing a bond between chromium and double bound oxygen to collapse we're not in a strongly acidic solution so we allow that second negative to form in fact the problem here is a positive charge having negative and positive oxygens in the same solution is not ideal deal so we instantly have a proton transfer giving oxygen back its electrons to make it neutral and making one of the negative oxygen neutral at the same time and once again we have our chromate Esther intermediate but that second negative oxygen atom is greedy the other one got a hydrogen it wants to get rid of its charge too so it'll take its electrons and collapse it down to form a piie bond between itself and chromium this puts too many bonds on chromium and winds up kicking out the best leaving group in this case a chloride ion but chloride is not happy chloride is very weak base but considering that this entire group is such a good leaving group a weak base is enough to kick it all out the CL minus will grab one of the alpha hydrogens collapsing the electrons up towards oxygen forming that carbonal and kicking out the entire chromium complex we still have the alpha hydrogen giving us a final product that is an alide PCC does not use any water we can't hydrate the alide and we cannot do that second oxidation so it stops right here if you started with a secondary alcohol you would end with a ketone but again it stops after one oxidation the final mechanism we'll look at is oxidation using potassium permanganate or km4 K4 is an ionic compound that'll dissociate to give us k+ a positive spectator ion that does not interact at all and permanganate M4 minus which is the key to this reaction permanganate has manganese double bound to three oxygen atoms and single bound to one oxygen atom with a negative charge this is your first clue that we're dealing with basic conditions we'll show the mechanism for a secondary alcohol which is oxidized to a ketone if we had a primary alcohol it would undergo a second oxidation just like was s for chromic acid and that would give us the carboxilic acid as the final product as with the previous reactions we show the lone pair on oxygen attacking that Central atom and collapsing one of the bonds between manganese and oxygen we form an unstable intermediate with negative and positive oxygens close to each other so we have an internal proton transfer where oxygen grabs the proton and these electrons will collapse onto the oxygen getting rid of that positive charge the next step is an interesting one where we have a cyclic flow of electrons one attacks the next attacks the next to give us our final product pay attention to the colors and what goes where keeping in mind that we still have an alpha hydrogen this is the hydrogen to remove in order to do this oxidation we'll show this as a purple pair of electrons grabbing the hydrogen atom to get rid of the negative charge that causes the electrons between carbon and hydrogen to collapse up towards the oxygen atom forming a pi bond which causes the electrons between oxygen and manganese to collapse onto manganese and this gives us our final product which is a ketone again if this was an aldhy it would happen again and we would get a carboxilic acid be sure to join me in the next video where we look at reduction using hydrides like sodium borohydride and lithium aluminum hydride you can find this entire series along with my redox practice quiz and cheat sheet by visiting my website layers.com ruxx