Oxidation Reactions of Sugars

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Oxidation Reactions of Sugars
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This is the third (and final) quarter of the organic chemistry series. Topics covered include: Fundamental concepts relating to carbon compounds with emphasis on structural theory and the nature of chemical bonding, stereochemistry, reaction mechanisms, and spectroscopic, physical, and chemical properties of the principal classes of carbon compounds. Index of Topics: 00:50 - Ether Formation 04:09 - Esterification 06:02 - Biosynthesis of Glucose 6 Phosphate 06:46 Reducing vs Non-reducing Sugars 11:48 - Oxidizing Agent: Tollen's Reagent 15:11 - Oxidizing Agent: Bromine/H2O 21:57 - Oxidizing Agent: Nitric Acid 24:13 - The Killiani Fisher Synthesis 30:52 - The Ruff Degradation 39:30 - Reduction Reactions of Sugars 41:22 - Disaccharides
Glucose Acetate Hydroxyl Methylgruppe Optische Aktivität Alpha particle Monosaccharide Beta sheet Mixture Pyridine Acyl Dimethylether Methyl iodide Asset Carbon (fiber) Chemical reaction Alcohol Glykoside Acetic anhydride Acid Gesundheitsstörung Computer animation Functional group Chemical compound Acetone
Phosphorsäureester Glucose Kohlenhydratchemie Pyrophosphate Chain (unit) Lactone Saccharose Alpha particle Optische Aktivität Biochemistry Aldose Silver nitrate Alcohol Electronic cigarette Wine tasting descriptors Glykolyse Acid Match Chemical compound Bromine Salpetersäure Thermoforming Acetate Biosynthesis Ester Carboxylate Hydroxyl Ammonium dihydrogen phosphate Chalkogene Deterrence (legal) Gluconsäure Lactitol Tachyphylaxie Redox Beta sheet Mixture Process (computing) Oxide Silver Mannose Aldehyde Fructose Asset Deposition (phase transition) Carbon (fiber) Carbonylverbindungen Aldehyde Ammonium hydroxide Man page Glykoside Water Hydrogen Systems biology Computer animation Generic drug Aldosterone Disaccharide
Enantiomere Glucose Cyanide Kohlenhydratchemie Chain (unit) Carboxylate Amine Hydroxyl Lactone Reactivity (chemistry) Abzug <Chemisches Labor> Barium sulfate Molecule Deterrence (legal) Chemische Synthese Cyanohydrine Barium Redox Process (computing) Aldehyde Palladium Setzen <Verfahrenstechnik> Hydrocarboxylierung Walking Honey Carbon (fiber) Aldehyde Chemical reaction Solution Alcohol Electronic cigarette Blausäure Water Acid Computer animation Cyanidion Functional group Azo coupling Disaccharide Chemical structure Salpetersäure Bromine Base (chemistry) Cobaltoxide Thermoforming
Glucose Semiotics Kohlenhydratchemie Chain (unit) Left-wing politics Galactose Cyclische Verbindungen Optische Aktivität Alpha particle Molecule Starch Barium Sodium borohydride Lactose Maltose Walking Chemical reaction Alcohol Electronic cigarette Reducing agent Acid Decarboxylation Azo coupling Bromine Cobaltoxide Thermoforming Surface roughness Ionenbindung Carboxylate Hydroxyl Reactivity (chemistry) Chemische Synthese Redox Monosaccharide Beta sheet Oxide Aldehyde Setzen <Verfahrenstechnik> Ketone Calcium hydroxide Asset Carbon (fiber) Aldehyde Glykoside Water Ice Hydrogen Computer animation Disaccharide Chemical structure
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good afternoon we're gonna get started we're gonna keep working on chapter 27 does anybody have questions before we get started anyone alright okay so where do we leave off last time let's we're talking about reaction of monosaccharides as alcohols and so what we did was we we started off with the glycoside you'll recognize this as a glycoside because instead of an O H at the anomeric carbon we have an O R group some sort of o R group that makes it a glycoside so rather than the anomeric carbon being a and a hemiacetal it's an asset L so that's a glycoside I hope you are able to recognize that and what we did we started with the glycoside and what we did was we basically deprotonated every hydroxyl and treated it with methyl iodide excess so every single free hydroxyl is methylated and once we do that these are now methyl ethers and they're very stable in order in order to cleave a methyl ether you need to use hot hot concentrated hydraulic acid which is really strong conditions so these guys stay but this is still an acetone we know that asset tells come off very easily in the presence of acid so that's part of an acetal sensitive to dilute acid so on the next page we can see that if we treat this with dilute acid then all the methyls that are on the free hydroxyls are going to stay except for this one that's going to be converted into a hydroxyl now all right so I'm just going to draw a squiggly line here to show that I have alpha and beta and the rest of these are ethers and they're going to stay and certainly this this other one here this Oh ch ch 3 here is also going to stay so before when we had it as a glycoside we did not have meter rotation so for this compound on the previous page it's since its a glycoside no meter rotation at all but once we hydrolyze that that as a towel and make it a hemiacetal now now mutarotation can come take place so so having all of those hydroxyls having these methylated does not interfere with me - rotation so what's going to happen again from you - rotation is that as soon as this becomes a hydroxyl now we can the open ring can open and close and open and close and open and close to give us an equilibrium mixture okay so that's what's gonna happen here all right we can also is terrify so these are just reactions of alcohols the same things that we did back in Chapter nine we can is terrify so we can use acetic anhydride and pyridine this is alpha D glucopyranose and of course we would need excess here and what we're going to basically do is we're going to isolate every single free hydroxyl including the one at the anomeric carbon and so here's what the product would look like and I'm just going to use AC for it the acyl group so AC equals an acyl group all right and if we wanted to name this this would be alpha D glucopyranose Penta acetate
all right so that were the names that we're using here the nomenclature in this chapter is very descriptive and tells us exactly how to draw these compounds so in biological systems the most important esters or sugars are phosphate esters I'm not going to be testing you on biosynthesis of glucose 6-phosphate but it's just this of course starts off the process of glycolysis all right so so what we're doing here is we're we're making a phosphate ester here at this hydroxyl right so that's this that's all it is similar concept notice that's only happening at the primary it's only happening at the primary hydroxyl all right not going to be testing you on that that's biochem right unless you want me to okay all right should we finish labeling that though this is just for fun come on I'm not going to test you on this but glucose 6-phosphate and this is adp adenosine diphosphate all right let's talk about oxidation reactions of sugars and so some of these reagents are going to seem familiar to you hopefully there's one thing that's new is talking about reducing sugars versus non reducing sugars reducing sugars or sugars that are easily oxidized by mild oxidizing agents if you hit all sugars with the strong oxidizing agent they'll be oxidized but we're talking about mild oxidizing agents so examples are glucose and fructose non reducing sugars of course are not easily oxidized by mild I oxidizing agents and the reason that they're not easily oxidized is that the carbonyl group is tied up in an acetal linkage so they're glycosides all right so here are some examples here and I want you to be able to recognize whether sugars are reducing sugar and non reducing sugar and what you're gonna look for is you're gonna look for the an American if there's more than one sugar you're going to look for the an America Arbonne on both sugars if one of them is as a hemiacetal then that's a reducing sugar if there are no hemiacetals a tanah Merah carbons it's a non reducing sugar so let's see what we're talking about here all right so you look at this one here this is this is methyl beta-d-glucose iran aside and what we want to do is we want to key in on the anomeric carbon and is the anomeric carbon here is a glycoside or is an asset a you want to think of it that way and so therefore this is a non reducing sugar and that's because the an America Arbonne is tied up in an antenna glycan an acetal linkage so in order for this this sugar to be oxidized it needs to be in the open chain form so it needs to be able to open up if it can't open up then it's a non reducing sugar and it's not going to be easily oxidized so it's oxidized from the open chain form and so we know that glycosides do not undergo mutarotation that ring does not open and therefore they can't they're not easily oxidized alright here's another example here and we want to find it now we have a disaccharide we want to find the anim Arbonne on both so here's the anomeric carbon on this sugar and here's the anomeric carbon on this sugar and it's the carbon that's bonded to two oxygen groups here so we have a lot of we have a lot of alcohols here all throughout we want to zero in on this one here because that carbon here has an O R and an o R and this this carbon right here o R and ORS o both an America Arbenz are tied up as acetal so it is a non reducing sugar so this is sucrose or table sugar and it is a non reducing sugar and that's because the anomeric carbon
is an acetal or you can also say glycoside glycoside is specific to sugars and I'm Eric Carmen is an acetal so a glycoside all right so both of those are not going to react with mild reducing agents but if you look here we're gonna talk about tollans a tree a reagent and that's a mild oxidizing agent and this is going to oxidizes aldoses to al donek acids all right so if you look at this sugar right here this is a reducing sugar so it gets a little confusing it's a reducing sugar that means it's easily oxidized by mild oxidizing agents so that that's a little confusing but remember when you add an oxidizing agent to the sugar the sugar it's the the oxidizing agent is itself reduced while the sugar is oxidized so it is a reducing agent but I can see how that would be a little confusing here all right so tollans reagent oxidizes aldo aldoses to l donek acids so this is since this anime our carbon is an acetate is a hemiacetal that means it's a reducing sugar and so this is alpha D um glucopyranose a hemiacetal all right so that means that the ring can open up and once the ring opens up this is so this is now open chain glucose and when it's open then it's oxidized and so the reagent is silver nitrate in aqueous ammonia so that's tolerance reagent and basically this is a very mild oxidizing agent it's really only going to oxidize the aldehydes okay it's not gonna oxidize any of the other hydroxyls and so that that's why it's mild and so what you're going to get is the aldehyde oxidize to a carboxylic acid everything else stays the same even the primary alcohol on the end is not oxidized and this is called an L donek acid so that's the generic term for a first sugar that's been oxidized just at the aldehyde it's an aldohn ik acid if we want to be more specific it would be d gluconic acid so that would be more specific named equal conic acid we also get a silver mirror which is kind of cool this is how you can make take a round bottom class and turned it into a mirrored round bottom flask which is kind of cool to do so this is a silver mirror on the inside deposits on the inside of the flask all right so that's some tollens reagent and then bromine and water also oxidizes aldoses 2l donek acids yes no it doesn't we're gonna talk about a region that will nitric acid will but not this reagent okay so bromine water also oxidizes aldoses 2l donek acids the product is in L tonic acid again that would be the generic term if you make an L tonic acid of glucose it's gluconic acid if you make an if you make an alder atonic acid of mannose it's man on ik acid so you kind of get the idea alright so this here is the c2 epimer of glucose you notice that right away right this wasn't glucose okay so if it was glucose then this hydroxyl would be equatorial and it's not and remember we number from the right-hand side here so it's the c2 epimer of glucose which happens to be man oh so you don't need to know that but it is now most of Manos this is going to be in the ring in the ring form very little very small amount less than 1% open chain but once it does open up and it is it's going to go back and forth between alpha and beta and I'm showing here of the squiggly lines for a mixture of alpha and beta so remember we talked about that mutarotation we're going to get a mixture alpha and beta we're going to get an equilibrium mixture this equilibrium mixture will not exactly match glucose because it's a little bit different it has one of the hydroxyls in the axial position so there's going to be a different percentage but we could calculate it like we did glucose if we had the those optical rotations all right so this is an open chain mannose d-mannose so bromine and water also is going to oxidize that to a carboxylic acid just the aldehyde notice I'm remembering to put hydrogen's in you've got to do that on the final so generic all donek acid specific man donek acid deema nanak acid let's be as specific as we can do you main men on ik acid now and what's gonna happen with the demon on ik acid is it's gonna want to cycle eyes and so i'm going to have a long arrow here it's on your page it's on this next page here but it's gonna want to cyclize so here's what it's going to look like notice all the rest of the hydroxyls are untouched and so and so basically what this is is a nester in a six membered ring so this is a lactone so this is the nanak acid d man tonic acid lactone everybody see the Esther here let's Circle the Esther right here so lactone is a cyclic ester
all right so since this is bromine in
water and when you have bromine in water you get some HBR in this solution so it's acidic solution and so the lactone is favored and in that the reason we didn't get a lactone on the previous one is because this is base okay so let's go back if you want to go back there and say that this is lactone is not favored in base which is why I wrote the open chain form in the product here so ammonia is a base this bromine waters acidic solutions so we tend to get these things in it in a six membered ring a lactone questions on that point anybody so we have two different reagents to make a lactone one the open chain it's going to be favored and and and then the second one the the ring closed so so what it looks like what it looks like is that we we've really ox all it looks like all we've done is oxidized this hydroxyl when it's in the closed position but it's not it does open up its oxidized and then it closes back down again so that's what you get alright nitric acid is stronger so if you've already gone to discussion this week we've talked about nitric acid it is a stronger oxidizing agent it's going to oxidize the aldehyde and it's going to oxidize the primary alcohol on the other end so hno3 and heat so this is open chain what sugar is this everybody recognize that sugar if you don't good idea to recognize that by next Wednesday open-chain d-glucose right so that's open chain d-glucose when we oxidize that we get both ends oxidized to carboxylic acid it is slower to react with secondary alcohol so we don't do secondary alcohols are not touched so oxidizes aldehydes and primary alcohols this has a different name um it is a an L Doric acid so generic for all sugars al dark acid and specific since this is glucose d gu quark acid alright so do you have to memorize the turmeric acid no if you know what nitric acid does to a sugar then you don't need to know what all dark all dark acid is okay as long as you recognize what the reagent does then you will be in good shape for the final questions on nitric acid anybody a couple more reactions do we want to talk about and then we're going to just tuck a move to talk about disaccharides all right so lengthening and shortening changing carbohydrates and how you do that we're going to talk about lengthening the chain first using kill eonni Fisher synthesis and then we'll talk about shortening the chain and then we'll work then we'll look at an example of how you would use these types of reactions to figure out the structure of unknown sugars and then we'll look at more reactions where we'll have more problems like that at the final review that's on Friday okay so it was I couldn't put it on the discussion worksheet because we hadn't covered it yet all right so this is Kelly honey Fischer synthesis and I the reagents should look a little bit familiar to you HCN we did it differently we're in chapter 21 so this is chapter 21 we did it I'm step one and ACN step two h3o plus but what do we do with it well what if what does that what does that do what are those reagents do with an aldehyde remember that from chapter 21 because cyanohydrin right alright so basically what I have here is this part of the molecule is not changing so rather than taking the time to draw all of those boxes we're just putting ditto marks to say that's staying the same and then we want to just focus on what is actually changing in this molecule as it reacts so we're going to make a cyanohydrin so so remember so remember how that goes we protonate oxygen first if we do it with HCN and then the cyanide attacks if we do it in the two-step process boom like that right if we do the two-step the cyano hide the cyan it the cyanide group attacks the carbonyl without protonating first and then you add acid okay so that's two ways to do it but when you do that you're gonna make you're gonna add a new stereocenter because that is a new stereo Center and since these are a chiral reagents that means we will get two enantiomers for our product all right and again the rest of the molecule is staying exactly the same and then I don't know and I don't know how they did this back in the day Emile Fisher before we had a lot of the techniques that we have now and he I don't know how he worked with hydrogen cyanide without a efficient fume hoods back then I don't know I don't know how he did it without dying honestly he did end up dying it with one of the reactions we have coming up here so anyway so h2 palladium barium sulfate so basically what this is going to do is it's going to partially reduce the nitrile because of the barium sulfate it's a little bit reduced reactivity so we're not going to go all the way we're not going to reduce the cyano group all the way to a ch2 NH 2 we're going to stop at an amine and so what it looks like after that step is so hopefully these reactions are looking soon familiar to you although this is this is a little bit different but what is that functional group at the top there again back to chapter 21 what is that functional group at the top there it's an amine right what happens when we put any median acid what happens what's more stable an amine or the corresponding aldehyde aldehydes more stable so it's going to it's actually going to be converted into the aldehyde so it's almost like we've inserted a CH o H into the into the sugar in the to position so we've extended the chain by one carbon and we have a pair of sugars epimer these are epimers of each other and so if we draw the rest of the molecule we'll see should we let's do it let's take out that let's draw the rest of it here what's the bottom part this is just D glucose right
oops Ling move that over and you could you recognize that as glucose right D glucose and when we draw the other one again the bottom is going to be exactly the same has not changed at all this is the c2 epimer of glucose which we've already seen a couple of times this is de Manos all right question on kill eonni Fisher synthesis yes it's the barium modifies the reactivity of the Palayam tones down the reactivity of the Palladian yeah all right so that's how we add a carbon we want to talk about how to take a carbon off and I your book has wall degradation and I'm choosing rough degradation instead yeah you can draw the cyclize I just drew it open chain yeah it's certainly going to mainly be cycle ice product all right so this is so I'm using rough degradation because these reagents are a little bit more familiar to you but it's a way to shorten the chain so bromine and water we already talked about what that's going to do the calcium hydroxide is just there to remove any of the acid that's present as we said when you have bromine water you do have some hbr so that second step is just to deprotonate and neutralize any acid that is present and then these reagents are not familiar to you but it's h2o to you'll recognize that as an oxidizing agent and fe2 so4 3 so oxidative decarboxylation and what happens is this co2 that's on the top right here goes away and I drew this wrong I have to put a no H here I think I drew it in it just erased it for me it does that sometimes and then so this goes away and then the top at this carbon number two right here ends up becoming an aldehyde all right so let's draw that back again so top carbon is converted to I'm co2 and then the second to the top carbon gets converted into an aldehyde and you could do this stepwise we talked about in the beginning when we talked about D and L sugars you can act you can take a carbon off at the time and two at a time until you get to the bottom and that's how Fischer was able to assign configuration for L sugars and D sugars all right so the rough tag rotation can be used in structure determination here's an example here and we'll see some more examples on the final review and maybe beyond the final what do you think alright so here's an example and what I recommend that you do is you read through the Fischer proof of structure that's in chapter 27 so you can see how all these reactions are used to determine how Fischer was able to come up with the structure and assign all of the stereocenters in glucose without any of the modern technology that we have now is pretty amazing he was able to do that ok so here's an example D altos is an aldohexose so it means it's six carbons and it's not a keto so it as an aldehyde at the top and right rough degradation of D ultros gives the same aldo pentose as does degradation of d aloes the c3 epimer of glucose give the structure of d ultros okay so i'm gonna draw it over here i know what d aloes looks like I know what it looks like because I've been given the information it's the c3 epimer of glucose so if we number from the top 1 2 3 4 5 6 C 3 up immerse so that means we have this is the same as glucose carbon number 4 is the same as glucose carbon number 3 and glucose the hydroxyl would be on the left but now it's on the right and on glucose the hydroxyl is here so that's D aloes and when I had to memorize this - this all the structures of the sugars when I was a student that was really easy to memorize because all of the hydroxyls are on the same side all I see yeah but it sticks it sticks with you that's stuck and that's the only one that I well that's one of the few I have memorized okay so that's d aloes which is the c3 epimer of glucose so at a minimum you need to memorize glucose otherwise you're not going to be able to solve any of these types of problems and what it says is that that d ultros is an aldohexose that gives the same aldo pentose as does degradation of d aloes the c3 up of our glucose so let's do a rough degradation of this one here and see what we get when we do a rough degredation all right so remember what happens here is that the this is oxidized to a carboxylic acid and then we do oxidative decarboxylation so this comes off and then carbon number 2 is converted into an aldehyde so let's draw that so carbon number 2 is now our aldehyde would everybody agree that that's the product you we get from rough degradation of D aloes everybody see that all right so if you're if you're going from the bottom everything's staying the same that carbon is the same that carbon is the same that carbon is the same that carbon is the same the only thing that changes is the top two carbons that's gone and that becomes now carbon one alright so what that means is that if they are going to have if they form the same sugar on rough degradation week that allows us to draw the structure of DL tros so what we're seeing here is that let's number this when we do a rough degradation this part of the molecule stays exactly the same so let's draw a square around that part of the molecule staying exactly the same and so that means that this part of the molecule is staying exactly the same so
it means that this is d ultros questions on how I did that so there's only two possible configurations at the stereo center here has a hydroxyl on the right here has the hydroxyl on the left and so if it's that the hydroxyl was on the right it would be D Alice it's not it's D ultros and so that means that that's the structure of the outros questions anybody too easy too easy for the final you think I heard it yeah out there okay all right let's add the last reaction we want to talk about where sugars you're familiar with this reaction sodium borohydride what does it reduce aldehydes and ketones right okay it's gonna and it needs to be in the open chain form for this to work okay so we're going to reduce this aldehyde it's going to be oxidized and reduced to a and primary alcohol and if you've gone to discussion already some of you have some of you haven't once you make the both ends of the sugar the same you can look for planes of symmetry here and so here's another example of wing making the both ends the same we have three stereocenters right here okay so when we oxidize when we reduce the aldehyde we still have three stereo centers here but notice the mall once we oxidize reduce like people want to say oxidize once we reduce the aldehyde both ends are the same and we actually have a plane of symmetry right here if we slice slice it right through that hydrogen oxygen bond and the hydrogen on the other side this molecule is actually a chiral and this is another thing that Don Fischer used in is proof of structure of glucose things like this to assign configuration of sugars questions on reduction of sugars anybody let's talk a little bit about disaccharides we've already said we've already mentioned that if you take the an americorps bit of a sugar plus an alcohol you have an asset al which is a glycoside right if ROH if the alcohol is another sugar you of a disaccharide which is composed of two monosaccharides you nuts in naturally-occurring disaccharides there are three principal glycosidic bond arrangements I'm going to give you an example of each of these so and I want you to be able to identify these if I give you the structure of a disaccharide I want you to be able to to indicate what type of linkage you have alright it's not that hard a one for prime link the animerica Arvin c1 is bonded to the oxygen atom on c4 ii sugar to form a disaccharide the prime symbol and one for prime indicates that c-4 is on the second sugar i'll show you what that means in just a second I've 1/6 primelink the an American c1 is bonded to the oxygen atom on c6 of the second sugar and in one-one Prime the anomeric carbon of the first sugars wanted through an oxygen to the anomeric carbon of the second sugar okay so let's look at some examples of each of these so this is lacta lactose are right so one of those monosaccharides that makes up lactose is a glucose what which one is glucose this one or this one that's glucose which epimer of glucose is this one 1 2 3 4 c4 epimer of glucose ok so we want to we want to look at our Annie we have two an americorps birds here in America carbon um is an acetal here so it's a glycoside we have a second and Romaric carbon because we have a second sugar here's our second and I'm Eric Cartman is a hemiacetal alright so and this first sugar right here is galactose you don't need to have that memorized I would tell you what that was our first sugar is d co lactose and the first sugar is usually drawn over to the left in fact that's the way I'm going to draw it for you so this is galactose the c4 epimer of glucose so first sugar drawn over to the right second sugar over here is glucose and notice notice here that this is is this carbon right here the glycosidic carbon there is that alpha or beta its beta right so this is beta and we're and and this so sugar number one is bonded to sugar number two through the oxygen on carbon number four one two three four right it's bonded through the oxygen on carbon number four so this is a beta one four prime sugar number one is galactose so it's a galactose siddik linkage beta one four prime galactose CITIC linkage and the galactose itta clink egde that's because sugar number one is galactose alright questions on how I did that so beta one four five galacto civic linkage maltose which is a starch is a one four prime glucose iddah clink which between two glucose units so that means that their first sugar is glucose on the second sugar is glucose all right so we're looking for an American here and America carbon is an acetal so it's a glycoside that's the thing we want to label here's an America carbon number two is a hemiacetal all right so what is the orientation of the hydroxyl in carbon number one which offer right this is alpha and we are bonded through one two three four we're bonded through the four carbon number four of our second sugar so this is an alpha 1-4 prime glucose itta clink äj-- now are either one of these reducing sugars they're both reducing sugars so well we will not oxidize this ring at all but this ring can open and close and soak in that one so they're both reducing sugars well we'll talk more
about that next time