I poured concentrated sulfuric acid into a pyrex beaker. I placed it outside on the cement patio and, with a fume hood, gently stirred a little sugar
into the acid. Of course, the sulfuric acid dehydrated the sugar, and the reaction took place. I kept a safe distance. When the process ended, the
carbon foam potruded out the beaker.
At the bottom of the container, there were a few mililiters of reddish-brown liquid. I collected it into a boiling flask and observed. With time, it
grew darker. After 20 minutes, it was dark reddish brown, and after about one hour, completely black. I know that this is a percentage sulfuric acid.
The black suggests a possible carbon component. I'm not sure. Does anyone have any idea what this could be? I have the flask right next to me so feel
free to ask about it.
[Edited on 26-1-2009 by BlindedAchievement]kclo4 - 26-1-2009 at 21:01
I would guess that the as the sulfuric acid hydrated, it became weaker desiccant. This may have allowed some sugar to dissolve in the solution with it
only being partially or totally dehydrated over time by some of the remaining sulfuric acid that hasn't lost all of its dehydration abilities. I am
not sure, but that would just be a guess.
You could try to determine if it were carbon instead of some sort of dark organic molecule by dissolving a little bit of the acid mixture in water.
If any small carbon like particles fall to the bottom as a dust like material and the solution is clear it probably is carbon.Ebao-lu - 27-1-2009 at 01:19
Some drink colorants are made from sugar and H2SO4(or alkalines), they consist of partially dehydrated sugar. You seem to obtain something similar
[Edited on 27-1-2009 by Ebao-lu]panziandi - 27-1-2009 at 03:56
This red compound is a partly dehydrated and polymerized amount of sugar. This is common with many hydrocarbons, when they are dissolved in sulphuric
acid. A similar thing I have observed with acetone. A mix of acetone and sulphuric acid first is colorless, but after a few hours it is orange. After
a day it is red and two days later it is black and also becomes quite viscous. What happens is that the acetone becomes more and more polymerized and
a tarry crap is formed. The stronger the polymerization, the darker the tarry crap. I'm quite sure that a similar thing also happens with sugar,
dissolved in sulphuric acid.hissingnoise - 27-1-2009 at 08:04
The dark coloured solution, separated from carbon solids, and fortified by adding an equal volume of 98% H2SO4 will slowly become clear on strong
heating.
H2O is driven off and the remaining carbon is oxidised by hot H2SO4. CO2 bubbles out of solution.BlindedAchievement - 27-1-2009 at 09:01
Ok, I added a little of it to water and waited 10 hours. No carbon sinked to the bottom.
I also found out that if I add more sulfuric acid, it turns redder, more sugar; darker.BlindedAchievement - 27-1-2009 at 09:05
So, does anyone have any idea what elemets are present?
With that info, we could probably sum up an equation:
Ok, sulfuric acid; H2SO4
Possibly carbon; C
Maybe some undehydrated sugar components.woelen - 27-1-2009 at 09:33
You cannot give an equation with this kind of reactions. The red stuff has a highly variable and unpredictable composition.BlindedAchievement - 27-1-2009 at 13:11
Maybe not an exact equation, but we should still find the elements present, and make an estimate of what it is.BlindedAchievement - 27-1-2009 at 13:36
I just checked on the flask, the process has not stopped. It is now like a heavier black. The liquid is denser than before, because it leaves a track
(like a slug) when its container is swirled.querjek - 27-1-2009 at 13:53
Quote:
Originally posted by BlindedAchievement
Maybe not an exact equation, but we should still find the elements present, and make an estimate of what it is.
Just knowing what elements are present won't necessarily allow you to predict what's present in the flask though.
There's carbon, sulfur, hydrogen and oxygen in the flask. There's probably some H2SO4, some C12H22O11, some C, some H2O, and there are probably all
sorts of things in between dehydrated sugar and polymerized sugar.
The reaction should be going toward C and H2O primarily, but polymers can easily result from such a reaction.
[Edited on 27-1-2009 by querjek]hissingnoise - 27-1-2009 at 14:09
With an attitude as insistent as yours, B-A, there's every chance you may find a whole family of exotic new fullerenes swimming around in there.
Way to go!
[Edited on 27-1-2009 by hissingnoise]BlindedAchievement - 27-1-2009 at 15:51
Ok, thanks??
Well, anyway, whatever there is, we know that carbon, hydrogen, oxygen, and sulfur are all present.
Evaluation: sulfuric acid dehydrated the visible pieces of sugar. The more acid, the darker the shade, the more sugar, the lighter the shade. Origin
of black, which is still turning deeper, is unkown. Possibly carbon.
Wait a minute, since the acid, because of the dehydration reaction that produced water, is now low concentration, maybe the undehydrated sugar
molecules are still being slowly dehydrated, which explains the growing black. Perhaps the growing balck is growing carbon level. The increase of
density might mean that it is slowly solidifying, or leaving the obvious liquid state. Or, it can mean that what is left is carbon and water.
The fact that more acid sped up the darkening, might mean that it is helping to dehydrate the undehydrated sugar molecules. More sugar made it
lighter, which means it gradually slowed the process by adding more to do. That is a very likely option to consider.DJF90 - 27-1-2009 at 16:44
Quote:
The liquid is denser than before, because it leaves a track (like a slug) when its container is swirled.
What you describe is an increased viscosity, not density, although it is possible that the reaction mixture has also become more dense. Not sure what
you have there though, it could be anything.BlindedAchievement - 27-1-2009 at 18:46
To be honest, you just defined a new word into my chemistry vovab. Thanks, there.
(can't believe I didn't know what that meant)BlindedAchievement - 27-1-2009 at 19:24
Looks like Polverone has worked his magic.Ozone - 28-1-2009 at 11:26
I'd edit more, but I have to move quickly as I am posting from work (DNS issue? is making it impossible to access the site from home).
OK, first your sugar has inverted. That is, the acid has catalyzed the hydrolysis of the sucrose to give 1 mole each of glucose and fructose. The
fructofuranose then loses 3 moles of water (it will do this at room temperature and pH at all <7. IN this case, it will be fast) to yield
5-hydroxymethylfurfural (HMF). While this is going on, isomerism is taing place between glucose and fructose which continues to feed the reaction.
Competing with the dehydration is an acid catalyzed reverse-aldol type scission of the reducing sugars (either one) to yield smaller, reactive
aldehydes and/or ketones. The HMF can polymerize with the smaller fragments to yield a polymer (strongly fluorescent when small, but as color is
formed it is quenched). HMF cannot homopolymerize (no a-protons). See Antal, et al., 1991 (IIRC) in Carbohydrate Research.
The hexose can also dehydrate yielding maltol derivatives which are largely responsible for the familiar taste and aroma.
Further, as this is taking place, the formation of fructose dianhydrides (~15% or caramel) are also formed (see Pigman, 1957?).
ALL of this can react to form the heterogeneous polymer we call caramel. The molecular weight is, on average, ~5000, but can reach >20,000.
Throw in some amine and your screwed (Maillard reaction sequence).
Cheers,
O3BlindedAchievement - 28-1-2009 at 16:01
So what you're tellin me is that I made some sort of caramel?
I don't know, it may be so.hissingnoise - 29-1-2009 at 06:49
A pretty toxic caramel, mind!BlindedAchievement - 2-2-2009 at 14:03
