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Current time:0:00Total duration:11:49

Video transcript

in this video we're going to explore how we can start with acetic acid how we can start with acetic acid and acetic acid looks like this how we can start with acetic acid and end up with and end up with a siedel chloride acetyl acetyl chloride that looks like this that looks like this and it's going to be done in the presence of thionyl chloride and thionyl chloride we haven't seen it before but it just looks like this is a sulfur double bonded to an oxygen and then it has single bonds to two separate chlorines and then if you want to care sulfur has six valence electrons so it has another lone pair right over here and we'll stay focus on this because this is really the simplest the simplest reaction of starting with the carboxylic acid and forming an acyl halide and it can be generalized very easily if you turn this methyl group into just a larger chain and then this will be a larger chain right here and instead of having a chlorine here you could do it with other halides as well so let's think about how this might occur so let's start let's have our acetic acid right over here so acetic acid right over here and then you have this oxygen bonded to a hydrogen bonded to a hydrogen just like that now this guy's got two lone pairs this guy's got two lone players and then the thionyl chloride I'll redraw the thionyl chloride right over here the thionyl chloride and I'll I'll set it up in the right position the thionyl chloride looks like this and this has a this has a lone pair of electrons right over here and all of these molecules chlorine and oxygen or all of these atoms chlorine and oxygen we can look at a periodic table up here you see sulfur over here and then to the right of sulfur is chlorine and above sulfur is oxygen so both Laurine and oxygen are more electronegative than sulfur so sulfur is going to have a is going to have a partial positive charge there even though sulfur is a reasonably electronegative in its own right but these guys these other guys are going to be sucking electrons away from it so you could imagine that this oxygen could act as or this entire molecule could act as a nucleophile with this oxygen right over here giving an electron to the sulphur sulphur ziz sulfur as an electronegative atom but it has a partial positive charge in just this vinyl chloride so it'll be attracted there and then this guy's going to have to give up an electron and he'll give it back to this oxygen up there and so that will be and this reaction could go in either direction so once again I'll draw it I'll draw it in equilibrium but right after that happens we'll have this I guess we could call it a complex that would look like this this oxygen it had two lone pairs it had one pair two pairs and now it has a third it has a third pair because it got this electron it always had that other electron in the covalent bond and now it has a negative charge and now the sulfur is bonded to those two chlorines two chlorines and then it is also bonded to this oxygen over here so let me draw it over here so we have this oxygen which is bonded to this carbonyl carbon just like that and then it is bonded to a hydrogen right over there it has one lone pair now and then the other lone pair is now turned into a covalent bond with the sulfur with the sulfur and so this guy gave away an electron so he now has a positive charge he now has a positive charge now the next step you could imagine that this oxygen this oxygen says hey you know I liked having a double bond with the sulfur the sulfur the sulfur is still bonded to a bunch of things that are more electronegative to it it still has a slightly positive positive charge there so you could imagine that this this electron it gets given back to the sulfur but then the sulfur needs to bump an electron chlorine is pretty electronegative so the chlorine can take oh one of these chlorines can take will be able to take away and elect so this chlorine could take away an electron so then after that happens our situation and once again this is an equilibrium our situation will look like this let me draw so let me draw the original acetyl the original acetic acid or what the part that was part of the original acetic acid and so you have this oxygen right over here bonded to a hydrogen bonded to let me do it in the same color so we can keep track of things bonded to that same this sulfur right over here which now has a double bond which now again has a double bond with this oxygen up here other than that same color it's still bonded to that chlorine up there still bonded to that chlorine up over there but now this chlorine is left it's taken that electron with it so the chlorine had 1 2 3 4 5 6 7 valence electrons it gained this electron this orange electron so now it has it has a negative charge and by the way this guy never lost his positive charge still has a positive charge right like that now the chlorine could act as a as a nucleophile on the carbonyl carbon this guy is bonded to two oxygens more electronegative slightly or partially positive charge this guy can give an electron to the carbonyl carbon and right as that happens this is a nucleophilic attack right as that happens the carbonyl carbon can give up an electron to the carbonyl oxygen and then we will be in equilibrium we will be in equilibrium so make sure you realize we're going to the right then down now we're going to the left with this thing so you have this was the carbonyl oxygen a carbonyl carbon bonded to this oxygen right now which now just took another electron so now it has a negative charge it had one two lone pairs now it will have one more lone pair because it took that electron it always had this end of that bond so now it has both of these electrons over here it has a negative charge it gained electron and then it is bonded to this Oh H group right over here this OS group just like that and then that is bonded to the sulfur that is bonded to the sulfur which is bonded to the chlorine and now double bonded to that other oxygen and now double bonded to that other oxygen and of course we have this chlorine over here that did the nucleophilic attack so you have this chlorine over here and it's nucleophilic attack it gave an electron to what was this carbonyl carbon it gave an electron so it is now neutral and you can kind of imagine that this negative charge got transferred to this oxygen up here and this oxygen right here still has a positive charge don't don't want to forget that now the next step that could happen once again all of these can go in either direction is that this guy doesn't like having a negative charge and this guy might is still going to have a partially positive charge because he's bonded to a bunch of electro more electronegative atoms in itself so he wants to reform the double bond reforms the double bond and that kicks off that kicks off all of this business over here so then this let me do this in a new color I've already used the magenta I'll use the pink this electron right here gets taken back by this oxygen by this oxygen that had a positive charge anyway so it would want to take it back and then we are left with and then we're left with and this is this is we're getting pretty close pretty close to the punchline we are then in equilibrium this part over here will then look like this we now have reformed our double bond it is only going to be bonded to the chlorine just like this and this whole part over here on the right has broken off so you have this oxygen bonded let me do it in the same colors you have this oxygen bonded to a hydrogen it now gained an electron it now gained an electron so it is now neutral and it is bonded to this sulfur letting the sulfur is in green it's bonded to the sulfur which is bonded to a chlorine which has a and then it has a double bond to this oxygen right over here so we've already formed we formed our acetyl chloride we formed our acetyl acetyl chloride and we've really kind of finished with the hard part of the reaction to see that how you could get an acetyl chloride and then to kind of complete this reaction because if you actually perform this in a beaker you'll end up with some hydrogen chloride and some some sulfur oxide as a by-product you could imagine that this oxygen right over here takes back its electron from this proton gives it to this sulphur gives it to this sulphur and then the sulfur since it got an electron will allow the electronegative chlorine to take back its electron to take back its electron and then if we just focus on this the acetyl chloride at this point isn't doing anything anymore this would be in equilibrium this would be an equilibrium with something that looks like this you now have a hydrogen proton floating around you now have this hydrogen proton floating around just a naked proton really there's not even any neutrons there you have this oxygen which is now double bonded it is now double bonded with this sulphur so I'm going to try to keep all of the colors the same this right here was yellow and then that original bond that it had with it was magenta and then you have the chlorine nabbed that electron the chlorine I'll do this chlorine in blue now the chlorine nabbed an electron and it already had it already had seven valence electrons one two three four five six seven it now has a negative charge and then the final step so we already have we already have our sulphur dioxide now the fight the final step is just the chlorine giving one of its electrons to the hydrogen to form hydrogen chloride so then the final step is just this is just this and then we are we end up with so when all is said and done when all is said and done we end up with some acetyl chloride we end up with some acetyl chloride we end up with some hydrogen chloride we end up with some hydrogen chloride and we end up with some sulphur dioxide sulphur dioxide just like that and we're done and once again you can generalize this to get it starting with any carboxylic acid and forming the acyl halide version of it or the acyl chloride version if you want to stick with a chloride right over here now I'll show you this right here is a C till this is a C til chloride anyway hopefully you found that entertaining