haribo - 12-3-2009 at 06:44
For a short while, hyposulfinic acid was popular unto its use became known. Na2SO2 is used widely in electroplating & Na2SO2 + 2HCl + H2SO2. The
acid is only found in solution and 50% is commonplace and works.
Still, not simple enough for me. Ever hear of iodometry? Its used to calculate the amount of starch in a solution.
I2 + Na2S2O3 --> Na2S4O6 + 2I-
The only (and unlikely) side-reaction is the formation of I3-.
Anyone think about this one? There seems to be HODS of reactions that reduce iodine. All one has to do is snap on hydrogen(s) and voila. You could add
an excess to the batch to keep the recycling of the iodine going on.
DJF90 - 12-3-2009 at 06:50
In acid the thiosulfate decomposes to sulfur and sulfur dioxide.
Nicodem - 12-3-2009 at 07:17
I must admit that I never heard about Na2SO2 and don't have a clue what is that supposed to be, but you surely must have confused this forum with some
other. Here, meth cook questions are not tolerated.
I suggest you to remove that "RP/I" cook acronym from the tittle and rephrase your question in a manner comprehensible to chemists, that is by
describing exactly what process are you talking about.
[Edited on 12/3/2009 by Nicodem]
smuv - 12-3-2009 at 07:18
I always wondered if sulfur could be replaced for phosphorous in that reaction; never really had a reason to try it though.
Also while sodium thiosulfate does indeed precipitate sulfur upon acidification, thiosulfuric acid is metastable in cool solutions, long enough to
undergo quick reactions.
[Edited on 3-12-2009 by smuv]
panziandi - 12-3-2009 at 13:32
Haribo...
At least talk some sense! H2SO2 doesn't exist according to any books I have at hand! "hypo" referring to sodium thiosulphate Na2S2O3 does exist. Both
DJF90 and smuv are perfectly correct in their points about its chemistry. You will not get HI from Na2S2O3 and I2.
"All one has to do is snap on hydrogen(s) and voila." ... ah you are not a clandestine interested in drugs, you are actually interested in click
chemistry! Actually click theory is heavily influenced by the pharmaceutical industry for obvious reason, nevermind!
At least talk some sense! Of course sulphur compounds can reduce I2 to HI, if you bothered to do any propper research you would stubble upon the
reduction of I2 by H2S with the deposition of S8.
Perhaps try and be a little more professional in your posts, a reference would be great seeing as you are talking about a chemical neither me nor
Nicodem know about :p
"Still, not simple enough for me. Ever hear of iodometry?" ... can you do iodometry? ... is it simple enough? Side reaction of I3- will not occur
because the thiosulphate effectively reduces the iodine to iodide disrupting the equilibrium and eventually at the end point all iodine is reduced to
iodide so no complexing can occur. ... is it simple enough?
DJF90 - 12-3-2009 at 14:47
Haha if you want click chemistry get a molymod set! An alternative to panziandi's suggestion of using H2S on I2 in solution would be the distillation
of HI from a mixture of phosphoric acid and an iodide salt (NaI for example). The only reason why sulfuric can't be used is because it oxidises the
HI/I- forming SO2, H2S and I2 [IIRC].
@smuv: you are right about the thiosulfate reaction with acid. I remember it being fairly slow at RT so it should last a little while at lower
temperatures.
panziandi - 12-3-2009 at 14:54
The reaction of thiosulphate with acid is often done to show kinetics to kids in school! Yes a molymod set would be much more ideal for haribo I
think! Indeed H3PO4 can be used too. I know why HI is so popular, doesn't take a genious to work it out. But I do feel compelled to suggest that this
should have gone into "general chemistry" forum not "organic chemistry" but I'm sure "whimsy" or "detritus" could be more suited :p
Sauron - 12-3-2009 at 18:40
Thiosulfate and conc HNO3 is not slow, it is instantaneous at RT producing S and NOx (big clous of noxious brown gas.) I suppose the reaction first
produces S and SO2 and the SO2 reacts with the HNO3 to produce NOx (NO2/N2O4) and sulfate.
I do not know how clean the NOx is, it may be mixed with some unreacted SO2 so this is not a very good preparative method. Kiddies, do not gas
yourselves with NOX as it is a Bad Thing.
smuv - 12-3-2009 at 22:14
To be honest, I don't see why acidified sodium thiosulfate wouldn't produce at least some hydroiodic acid. It indeed is capable of reducing iodine to
iodide. Fighting precipitation of free sulfur might be a challenge but in my experiments with the synthesis of sym-trithiane, I found that at cold
temperatures thiosulfuric acid solutions can be suprisingly stable. This being said...I don't really think a thiosulfuric acid/Iodine system could
efficiently reduce a benzylic alcohol because I believe precipitation of free sulfur would become a problem over the course of the reaction
(although...maybe sulfur could react with I2 to form some species that is hydrolized to HI...maybe...)
woelen - 13-3-2009 at 00:19
Na2SO2 does not exist, but I think the OP refers to sodium dithionite, Na2S2O4. This is a strong reductor, but in acidic media, it decomposes. On
acidification, a solution of sodium dithionite becomes bright red and after a while, this color fades again and finely divided sulphur precipitates
and the solution obtains a horrible smell, probably from a mix of sulphur dioxide and hydrogen sulfide.
Na2S2O4 certainly is not suitable for clean reduction of I2, it will give a lot of undesirable by-products!!
Nicodem - 13-3-2009 at 00:37
I don't think the original question was about the reduction of I2 to iodide, but about modification of a certain clandestine cooking method. Yet,
since the original poster was so incomprehensible, I'm moving this thread to the General section because it evolved in a topic not related to organic
chemistry any more.
not_important - 13-3-2009 at 00:43
Elemental sulfur and iodine do not react under useful conditions.
Common ways of making HI fro I2 include:
I2 + H2S => 2 HI + S (mentioned earlier)
I2 + SO2 + 2 H2O => 2 HI + H2SO4 (Bunsen reaction, reverses as H2SO4 concentration increases)
2 I2 + N2H4 => 4 HI + N2
The first two work best when producing dilute solutions, while phosphorus and iodine can yield the concentrated acid or gaseous HI - needed for
reducing ROH groups:
ROH + HI <=> RI + H2O (HI forces to the right, water to the left)
RI + HI => RH + I2
3 I2 + 2 P => 2 PI3, + 6 H2O => 6 HI + 2 H3PO3
or
3 ROH + 3 H2O + 2 P => 3 RH + 2 H3PO3 (iodine in effect acting as a catalyst)