Thomas Winwood
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Hydrochloric / sulphuric acid question
I was reading one of BromicAcid's posts on synthesis of carbon disulphide and have been planning how I myself might go about performing this
reaction. (Nothing like throwing yourself in.)
My question concerns producing carbon for this reaction. Everyone's added sulphuric acid to sucrose and watched it build a Tower of Babel of
carbon, and I was wondering if hydrochloric acid does the same thing?
Google searches have given me nothing helpful, and I'm on holiday for Christmas so I can't ask a teacher or consult a library resource.
Thanks in advance. 
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BromicAcid
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Hydrochloric acid will not do the same thing. Sulfuric acid has the distinction of being a dehydrating agent at high concentrations, it will take the
water molecules right out of the sucrose molecule leaving behind the carbon and becoming more dillute H2SO4 in the process. You can also see the
difference in their reaction with water, if you take a watch glass with concentrated H2SO4 in it and add a few drops of water on the top, they will
boil of pop off, whereas the same display with HCl will do no such thing. Other acids that have an affinity for water include concentrated phosphoric
and perchloric acids, though there are other less common ones. Regardless, when we learn 'Always add acid to water, never add water to
acid' we don't learn that it only really matters with the dehydrating acids.
BTW, which method to produce CS2 were you planning on trying? None of them seemed to work particularly well, the method using carbon obtained from
decomposing sugar over high heat is too pure to allow the reaction to work well, supposedly the addition of alkali metal carbonates increases the rate
of reaction though in catalytic amounts (i.e., less then 1/100 the reaction mixture). And the method using regular carbon obtained from OTC sources
yields H2S.
Edit: Mwa ha ha haaaa! I was first 
[Edited on 12/17/2004 by BromicAcid]
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HNO3
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The reastion with sulfuric acid proceeds as follows: C12H22O11(s) + H2SO4(con)(l) = 12 C(s) + 11 H2O(l) + H2SO4(dil)
No, HCl doesn't give the same result, because it doesn't have nearly the affinity for water that sulfuric does.
BTW, I doubt that you googled, since I did a quick search "Sulfuric acid sugar" the first hit gave the answer. Starting a thread on your
first post is generally locked upon as bad, IMHO. Did you search the Board?
oops, BromicAcid posted while I was typing
[Edited on 12-17-04 by HNO3]
\"In the beginning, God...\" Wait a minute, God doesn\'t exist!!!!!!!!!! \"OK, in the beginning, ummm, hydrogen...\" Wait a minute, what about the
laws of thermodynamics? \"OK, in the beginning, ummm.....UMMMMM, what\'s left to choose from?
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neutrino
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No, it won’t. The reason this happens with H<sub>2</sub>SO<sub>4</sub> is that it is an extremely strong dehydrating agent,
dehydrating sugar according to the following equation:
C<sub>12</sub>(H<sub>2</sub>O) <sub>11</sub> -> 12C + 11H<sub>2</sub>O
the water going to hydrate the acid. HCl possesses no such properties (extreme water affinity).
edit: That was fast. Two posts while I was writing mine.
[Edited on 17-12-2004 by neutrino]
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Thomas Winwood
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| Quote: | Originally posted by HNO3
BTW, I doubt that you googled, since I did a quick search "Sulfuric acid sugar" the first hit gave the answer. Starting a thread on your
first post is generally locked upon as bad, IMHO. Did you search the Board?
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No, I didn't think to search the board (perhaps I should have). And as for the Googling... I did Google - "sugar and sulphuric acid"
and "hydrochloric acid water affinity" if I remember correctly - but you'll have to take my word for it, and it seems I didn't
search for the right things. (Spelling it the British way over the American way might have made a difference...oops.)
Anyway, as for BromicAcid's last question, I was planning on using the standard industrial method of adding the sulphur and carbon together at
high temperatures. The carbon comes from the crushed product of the sucrose-acid reaction, which I figured would work well (although now I'm
doubting things like purity, and some of the observations you made while doing much the same experiment).
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Polverone
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Curiously, heating sucrose with hydrochloric acid will convert it to a charred-looking crunchy black mass over a period of time. The same thing
happens with other organic material like peanut shells ascorbic acid. It does seem to undergo some sort of aqueous "charring" and this
cannot be explained by dehydration.
This has also made me wonder if conc. H2SO4 turns sugar to carbon only because of its great water affinity. Would grinding sucrose and P2O5 together
with the exclusion of moisture produce the charring effect also? What about sucrose and a water-hungry base like sodium amide?
[Edited on 12-17-2004 by Polverone]
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Darkfire
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HCl can be used in dehydration reaction even at consentrations less than that found in the muratic acid sold for the pool. I've used it for
dehydration after an aldol condensation. Is this signifcantly diferent than dehydrating sucrous with the same thing?
\"I love being alive and will be the best man I possibly can. I will take love wherever I find it and offer it to everyone who will take it. I
will seek knowledge from those wiser and teach those who wish to learn from me.\" Duane Allman
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HNO3
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Oh well. Live and learn
\"In the beginning, God...\" Wait a minute, God doesn\'t exist!!!!!!!!!! \"OK, in the beginning, ummm, hydrogen...\" Wait a minute, what about the
laws of thermodynamics? \"OK, in the beginning, ummm.....UMMMMM, what\'s left to choose from?
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