weiming1998
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Sucrose-HClO reaction: Exact mechanism?
Today I have discovered that cane sugar or sucrose, reacts rapidly, without warning and exothermically with a mix of calcium hypochlorite and vinegar.
When I first made the mixture, it did not do anything, then suddenly, the mix started to boil on its own and all the contents shot out of the test
tube due to the amount of gas generated. I then tried to use a very a beaker of a cold mix of vinegar and sugar, in another beaker filled with cold
water. I thought this would stop the reaction going out of control and also enables me to find out what is generated in such a reaction. The mix did
nothing for a few minutes, then evolved a massive amount of chlorine gas (I could tell because of the colour+horrid smell, and this was also done
outside). After the reaction has finished, I was left with a beaker of cloudy liquid, which I decanted off the remaining Ca(ClO)2. The cloudiness
persisted, even when I added more vinegar, which is puzzling because if the cloudiness was from calcium salts (Ca(OH)2, CaCO3), it would have gone
away, but it didn't.
I searched and looked for the reaction on the net, but I can't find any relevant info. Thus I speculated a few possibilities of what happened in the
reaction:
1, The sucrose acted as a catalyst in the decomposition of HClO to HCl, then to Cl2. Probably unlikely, since I have never heard of something like
sucrose acting as catalysts
2, The acidity/HClO hydrolyzed the sucrose into glucose+fructose, and the HClO reacted via the haloform reaction with fructose. When I thought a while
about this, I found that it would be almost impossible because the lack of the OH- ions will stop the haloform reaction, plus the fructose has a CH2OH
instead of a CH3 group, and thus the the haloform is unable to proceed.
3, Replacement of the hydroxyl groups in sucrose by OCl- to form sucrose octahypochlorite, which would be extremely unstable indeed and would explode,
rendering this hypothesis false. In fact, (I think) any reactions that this compound could go through might trigger an explosive reaction.
4, Same as above, except sucrose is hydrolyzed into glucose and fructose, then reacted with HClO, forming glucose pentahypochlorite and fructose
trihypochlorite, respectively.
5, Partial, not full hypochloritation, making a compound that might decompose into other compounds without exploding
6, The hydrolysis of the bond, then oxidation of glucose to gluconic acid, forming HCl as a byproduct and reacting further with excess HClO to form
Cl2. So far my most likely (I think) hypothesis.
This is as much possibilities as I can think. Anyone got any ideas?
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plante1999
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Could you analyse off gas for Cl2, CO2 and others. It would greatly help to find the mechanism of the reaction.
I never asked for this.
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weiming1998
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The presence of Cl2 (definite) would greatly mess up any non-professional analysation techniques (example the Ca(OH)2 test for CO2 would no longer
work because Cl2 would react first/with the CaCO3, forming soluble CaCl2 and soluble Ca(ClO)2). I do not have any professional analytical equipments,
unfortunately. So I can't do that.
[Edited on 6-5-2012 by weiming1998]
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plante1999
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Yes you can.... make a first gas absorption test tube filled with 30%H2O2 and sodium carbonate then pass the gas from the gas absorption test tube in
calcium hydroxide sol..
[Edited on 6-5-2012 by plante1999]
I never asked for this.
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weiming1998
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Quote: Originally posted by plante1999  | Yes you can.... make a first gas absorption test tube filled with 30%H2O2 and sodium carbonate then pass the gas from the gas absorption test tube in
calcium hydroxide sol..
[Edited on 6-5-2012 by plante1999] |
1, I don't have 30% H2O2, only 6%, and only about 40mls
2, I have to make Ca(OH)2 on site as I don't have access to it
3, All this just to verify if there is CO2 or not, when there could be other gases that I have to waste tons of reagents and days of time to analyze.
Better to just boil the solution down and test that.
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plante1999
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by the way calcium hypochlorite decompose with CO2..... I think you should analyse off gass since the solution will be full of carbon based junk, it
would be a mess to analyse it...
[Edited on 6-5-2012 by plante1999]
I never asked for this.
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stygian
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From http://www.google.com/url?sa=t&rct=j&q=&esrc=s&a...
Sodium hypochlorite reacts readily with various reducing sugars...to produce carbon monoxide!
So chlorine and CO is produce, you may be barking up an ill chosen tree
[Edited on 6-5-2012 by stygian]
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weiming1998
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| Quote: Originally posted by plante1999 | by the way calcium hypochlorite decompose with CO2..... I think you should analyse off gass since the solution will be full of carbon based junk, it
would be a mess to analyse it...
[Edited on 6-5-2012 by plante1999] |
Yes, the solution did slowly decompose on heat, and now it is just a black mix of organics. But the solution liberating CO2? Fairly difficult, as if
the HClO oxidized the sucrose to CO2 gases, there is almost certainly going to be black carbon left in the solution, and there are no trace of carbon
in the unheated solution. Partial oxidation of sucrose to CO2 might be possible, but unlikely, because that is impossible outside a very concentrated
aqueous solution of an extremely strong oxidizer, like HClO3, but such solutions are so powerful oxidizers they char paper on contact, something that
5% HClO isn't even close to doing.
Another possibility is the decomposition of Ca acetate, but this is unlikely as well, because again it requires high temperatures or an oxidizer like
HClO3. The lack of a carbon residue is also unexplainable. Nevertheless, I will do some primary analysis of the gas tomorrow, like the flammability,
solubility in water, etc. But first I will try and boil down the solution carefully so the acetic acid is eliminated, then I can test the acidity of
the solid. If it fizzes on contact with NaHCO3, then my 6th hypothesis is most probably correct.
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bbartlog
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Would take quite a lot of hypochlorite to fully oxidize sugar to CO2. In any case, I doubt that you have a single well-defined reaction - however,
- I would expect the first step to be chlorination of one of the carbons on the sugar
- I would expect the solution to become more acidic as the sugar decomposed
- the cloudiness you noticed could be due to calcium oxalate, as oxalic acid is known to be one possible product of sugar oxidation, and calcium
oxalate would be impervious to vinegar
You could read 'A manual of sugar analysis' by J.H. Tucker, from 1881, for an overview of the reactions of sugar with reagents commonly available at
that time. Though I don't know whether he covers bleaching powder.
The less you bet, the more you lose when you win.
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weiming1998
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The reaction with unacidified hypochlorites is very different from the reaction observed with acidified hypochlorites. The acidified hypochlorite
reacted spontaneously, even when cold, extremely exothermically and the solution did not change colour. The unacidified hypochlorite reaction made a
yellow solution, did not proceed unless heated, and is non spontaneous.
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Adas
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And have you tried just Ca(ClO)2 and vinegar?
Rest In Pieces!
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weiming1998
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Yes... household bleach solution is too dilute and I don't have other weak acids readily available.
Edit: I have just noticed something very interesting. The solution of sugar reacted with HClO decomposes readily to a black, non acidic paste, while
sugar dissolved in vinegar does not decompose while the solution is boiling. I will try to crystallize the crystals of organic out by chilling next
time.
[Edited on 7-5-2012 by weiming1998]
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AJKOER
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I believe some of the reaction you are seeing is as a result of your making strong HOCl (weak acid + Ca(ClO)2) which has disproportionated into some
HClO3 and HCl. As a result, the HOCl and HCl is creating Chlorine and the HClO3, being a strong oxidizer, is having a good time with the sugar.
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weiming1998
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| Quote: Originally posted by AJKOER | | I believe some of the reaction you are seeing is as a result of your making strong HOCl (weak acid + Ca(ClO)2) which has disproportionated into some
HClO3 and HCl. As a result, the HOCl and HCl is creating Chlorine and the HClO3, being a strong oxidizer, is having a good time with the sugar.
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Problem is:
1, HClO3 also reacts with HClO in a complex reaction, ending up with ClO2. ClO2 is explosive and the heat produced in the reaction is probably enough
to set it off.
2, If HClO3 were formed, I would see flames, or at least, the sugar turning to carbon and smoking. I don't see any of these.
Since then, I have done some more experimenting. Pouring vinegar on a watch-glass of Ca(ClO)2 and a tiny amount (about 1/20th) of sugar will cause a
rapid expansion of the mixture, as well as the liberation of huge amounts of Cl2. So it is likely that the sugar catalyzed the decomposition of HClO
to HCl. But the resultant, chilled down, reacted mix of sugar and hypochlorite, even an excess of hypochlorite, caused rapid bubbling of Na2CO3, as
well as the formation of some sort of foam-like substance that became a powder when in contact with ethanol. As sucrose hydrolyzes fast in acidic
solution, it could potentially have hydrolyzed and got oxidized by the hypochlorite. Problem is, because there is so many oxidizable hydroxyl groups
in glucose and fructose, it is almost impossible to tell the product apart from the mix of organic mess. Maybe both hydrolysis and catalysis happened,
or that an oxidized product of the sucrose catalyzed the decomposition.
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AJKOER
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Weiming1998:
I repeated your experiment with dilute NaOCl. The result was very different (also no reaction visible). So, I suspect, the issue relates to
concentration. What happens in higher concentration is the HCl/HClO3 formation, or possibly the liberation of Cl2O from the HOCl by the sugar (via a
simple dehydration).
Note, what you are doing is somewhat akin to a dry salt reaction with moisture, which can follow a different reaction pathway than in an aqueous
environment. For example, Cl2O reacts with CaCl2 (found in Bleaching Powder) to form Cl2 and Ca(OCl)2 (see "Handbook of Detergents: Production by Uri
Zoller, Paul Sosisow, page 461. Link http://books.google.com/books?id=dXn3aB1DKk4C&pg=PA461&a... ).
Please note that DiChlorine monoxide is highly reactive (many times that of HOCl, see "DICHLORINE MONOXIDE, HOCl, HYPOCHLORITES", Vol 8, page 549,
Link: http://www.scribd.com/doc/30121142/Dichlorine-Monoxide-Hypoc... ), increasing explosive with concentration and also more poisonous than Cl2. It
reacts explosively with gaseous NH3 and will cause Turpentine to ignite and perhaps, sugar to turn black?
If I am right, repeat your experiment several times with small doses at different levels of dilution and note the results.
Have fun and be safe.
[Edited on 23-5-2012 by AJKOER]
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weiming1998
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| Quote: Originally posted by AJKOER | Weiming1998:
I repeated your experiment with dilute NaOCl. The result was very different (also no reaction visible). So, I suspect, the issue relates to
concentration. What happens in higher concentration is the HCl/HClO3 formation, or possibly the liberation of Cl2O from the HOCl by the sugar (via a
simple dehydration). This is akin to a dry salt reaction which can follow a different pathway than in an aqueous environment. Please note that
DiChlorine monoxide is highly reactive, increasing explosive with concentration and also more poisonous than Cl2. It reacts explosively with gaseous
NH3 and will cause Turpentine to ignite.
If I am right, repeat your experiment several times with small doses at different levels of dilution and note the results.
Have fun and be safe.
[Edited on 23-5-2012 by AJKOER] |
Vinegar is only about 5% acetic acid, while HClO can be made up to 30% or so without decomposing to Cl2O. How does that work? Does sugar catalyse the
dehydration reaction of HClO to Cl2O? Again, if that was the case, the exotherm generated by the reaction is enough to set off the Cl2O in an
explosive cycle, or at least make visible pops in the air. Again, the HCl/HClO3 formation does not describe why there is no smoke/flames and soot in
the mix, nor why the formation of ClO2 did not happen.
I think the reason why a dilute solution did not react visibly is because it takes a fairly long time (minutes) to react even at high concentrations
at room temperature. Low concentrations would take even longer. Also, a concentration that is too low might not produce any gases as the Cl2 dissolves
in water.
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AJKOER
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One method to prepare Cl2O is to dehydrate conc HOCl with anhydrous Ca(NO3)2. Another methods involves stripping conc HOCl with air or another inert
gas.
There is always some Cl2O presence in HOCl, but in dilute solutions it is just tenths of 1%.
Note, dilute amounts of Cl2O are only mildly explosive (unlike ClO2), but increasing concentrations can produce more significant explosions.
Here is a YouTube comment of interest:
"another gas which should be really toxic too is leading chlorine gas through sodium bicarbonate solution (strong im sure it is) the gas goes bang in
contact with rubber and other organic stuff and even DUST particles! but not metal.. should go off really loudly.. and really toxic too..
dichlorinemonoxide Cl2O it is.. used for making hypochlorites..
antiswattt2 in reply to bergfoot02 (Show the comment) 4 months ago"
Link: http://www.youtube.com/all_comments?v=ZjKDoOBuZbY
Now, the process of passing Cl2 into aqueous NaHCO3 is normally a method for the preparation of HOCl as:
Cl2 + H2O --> HOCl + H(+) + Cl(-)
and the highly ionic HCl is removed by the bicarbonate:
HCl + NaHCO3 --> NaCl + H2O + CO2 (g)
leaving HOCl, for the most part, unreactive and further moving the reaction to the right. The presence of significant bubbling from the CO2 may be
stripping some of the Cl2O from the HOCl, which can be increasing concentrated with continuing Cl2 treatment. Hence the comment above.
Now, the net reaction is:
Cl2 + NaHCO3 --> HOCl + NaCl + H2O + CO2 (g)
The authors of the referenced provided below makes the interesting comment: "At this pH, the hypochlorous rapidly disproportionates to chlorate, which
becomes the major product. Thus, chlorination is stopped when carbon dioxide first begins to evolve."
Another similar method is the treatment of an aqueous solution of a hypochlorite with Cl2. Reactions:
Ca(OCl)2 + 2 H2O <---> 2 HOCl + Ca(OH)2
2 Cl2 + 2 H2O ---> 2 HOCl + 2 H(+) + 2Cl(-)
2 HCl + Ca(OH)2 ---> 2 H2O + CaCl2
---------------------
On net:
Ca(OCl)2 + 2 Cl2 + 2 H2O ---> 4 HOCl + CaCl2
Reference: "See Handbook of Detergents: Production", by Uri Zoller, Paul Sosis, page 454, Link:
http://books.google.com/books?id=dXn3aB1DKk4C&pg=PA453&a...
[Edited on 24-5-2012 by AJKOER]
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Waffles SS
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More violent reaction happen when you mix Calcium Hypochlorite with Motor Oil(Here kids make firecracker with HTH and Motor Oil in the closed bottle)
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