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enceladus
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[*] posted on 20-10-2018 at 16:01
Unknown RXN of hydrochloric acid and tubing


Yesterday I put some hardware store (conc.~30%) hydrochloric acid in a small bottle for cleaning copper parts to be soldered. I had a length of tubing passing through the cap and down into the acid with a wad of cotton stuffed in the end so I could hold the bottle upright and squeeze just enough acid into the cotton to treat small parts. Anyway, I noticed soon after that there seemed to be a faint smell of H2S when using it but didn't think much of it. I figured the acid might just be mildly contaminated or my sense of smell was off. Today I came back to it to find the dip tube had completely disintegrated into little crumbled yellow bits. It started out as clear, flexible tube. I'm not sure where I got it. It was salvaged. I assumed it was vinyl or PP.

When I opened the bottle to replace the tube the smell of (ostensibly) H2S was overpowering. I spent some time searching for common materials used to make tubing that are both incompatible with HCl and contain sulfur and found absolutely nothing. I'm just trying to figure out what that tubing was made of and what exactly happened to it.

After that I still wanted to use the acid since it was still as effective as ever for cleaning copper parts, but no one wants to deal with that kind of stink so I thought to myself, "What can oxidize H2S but won't affect the HCl or be affected by it? So of course I grabbed some 3% H2O2 and put in about a third as much as there was acid. (The bottle is 100 ml and the tube was perhaps 8cm long and 3mm in diameter btw.)

Some time later I went back to see if the sulfur smell was gone and some other things I wasn't expecting also cropped up. I didn't like hold the bottle up to my face and sniff, but some pressure had built up and whatever gas was in there didn't smell like H2S anymore but still it almost knocked me down. I assume it was Cl2 but I'm not too sure I can't think of any other gas that could form. Maybe it was just a mix of both that made it had to recognize either. In any case it wasn't pleasant. Also a small amount got on my fingers and it started dissolving skin immediately. I've had HCl on my skin plenty of times and it barely affected me and it rinsed off in seconds. This was way different. I wasn't hurt but washing it off felt the same as trying to get NaOH off; slippery and very hard to fully get rid of, leaving my fingertips noticeably less grippy.

So my secondary question(s) are: Does H2O2 enhance the corrosive properties of HCl in a similar fashion as with H2SO4 in a piranha solution? Could any significant quantity of H2SO4 have been produced and if so could it be responsible for increasing the reactivity of the solution?
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macckone
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[*] posted on 20-10-2018 at 16:25


Yes H2O2 increases the reactivity of HCl. It can also oxidize it to chlorine gas given the right conditions.
There are a large number of plastics as well as compounds used to increase the flexibility of plastics.
Sulfur is sometimes used as a crosslinking compound to increase the temperature resistance of plastics or rubbers, aka vulcanization.
Without knowing what your tubing was actually made of it is hard to venture a guess about the chemical reaction.
If it was a clear rubber with sulfur added then it would be very susceptible to HCl and chlorine gas.
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[*] posted on 20-10-2018 at 19:21


If this happens again i think a small amount of sodium metabisulphite be better than peroxide as that would release SO2 with acid and SO2 + 2H2S -> 3S + 2H2O. you can tell if it works by the yellow deposit of sulphur.

Excess SO2 is toxic but not as toxic, or as smelly (burnt match not rotten egg), as H2S and dissolves in water to make sulphurous acid.

I think first the peroxide will create hypochlorous acid HClO which with excess HCl can make Cl2. household bleach is NaClO mixed with some NaOH, the acid form of bleach is more corrosive and a strong oxidiser so it's a good job you got it off quick.

I agree with macckone, vulcanised rubber seems most likely, I bet some of the chopped up (chemically) pieces of rubber dissolved in your acid too so it might leave some unwanted residues on the parts you're trying to flux. Idk if they would be a problem or not though, might be worth testing it still works as you expect before it messes up a job.

IF you made some H2SO4, it would be a small enough concentration not to make much difference in the corrosiveness. HClO is much more of a concern. Only hot or concentrated sulphuric acid acts as an oxidising agent (generally), HClO just want to f*** you up hot or cold.
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enceladus
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[*] posted on 20-10-2018 at 19:45


I appreciate you replying to my very first thread posted to this forum, but your answer is not really specific enough to be useful. No offense. It would be ideal if someone with the exact answers to my questions happened to belong to this forum, see this thread, and also have the time and inclination to give those answers to me comprehensively, but I not only don't expect that to happen, I expect that NOT to happen since almost nothing is ever ideal.

No, what I'm looking for is a short list of plastics, plasticizers, or other common plastic additives that contain sulfur, whether it be present as sulfoxides, sulfones, sulfonic acids, thiocarboxylic acids, thioesters, thioethers, thiols, thiosufates etc. I know the degradation involved a sulfur-containing functional group that was somehow cleaved or otherwise maximally reduced to H2S either by the very low pH or the presence of chloride, or both.

The only polymers I know of that include sulfur (aside from elemental and ionic polymeric sulfur) as part of their fundamental structure are polysulfonic acids which are used as solid acid ion exchange media, and polysulfone. Since its highly unlikely that a scrap of tubing salvaged from a household appliance contains either of those polymers, I have to believe someone could make an educated guess at the additive involved, how and why it decomposed, why the remaining material disintegrated, whether it was a result of it being a reactant or a product, and what it had been doing there in the first place.
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[*] posted on 20-10-2018 at 20:00


Quote: Originally posted by enceladus  
It would be ideal if someone with the exact answers to my questions happened to belong to this forum, see this thread, and also have the time and inclination to give those answers to me comprehensively, but I not only don't expect that to happen, I expect that NOT to happen since almost nothing is ever ideal.


That's not an attitude that is tolerated on this forum, nor is it an attitude one should have when approaching science. After all, the whole point of the sciences is to discover through experimentation. So either you need to revaluate your thought process, or find a different spoon-feeding forum.
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[*] posted on 21-10-2018 at 00:42


Rofl, if you presented the bottle tubing acid blah blah to us Collectively in person to inspect it's still likely a ready answer could not be elucidated.
So to expect more than this from less that this is 'ostensibly' ridiculous.
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[*] posted on 21-10-2018 at 01:04


My best guess would be that the tube was nylon- which is attacked by acids and commonly used to make tubing.
The H2S smell could be due to some additive- perhaps a plasticise/ stabiliser/ whatever.

H2O2 will oxidise HCl to Cl2.
God only knows what you get from chlorinating decomposed plastic.

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[*] posted on 21-10-2018 at 12:04


Quote: Originally posted by unionised  
Only God knows what you get from chlorinating decomposed plastic.
@unionised here ya go:P



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enceladus
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[*] posted on 22-10-2018 at 21:24


Quote: Originally posted by Deathunter88  
Quote: Originally posted by enceladus  
It would be ideal if someone with the exact answers to my questions happened to belong to this forum, see this thread, and also have the time and inclination to give those answers to me comprehensively, but I not only don't expect that to happen, I expect that NOT to happen since almost nothing is ever ideal.


That's not an attitude that is tolerated on this forum, nor is it an attitude one should have when approaching science. After all, the whole point of the sciences is to discover through experimentation. So either you need to revaluate your thought process, or find a different spoon-feeding forum.


Maybe I used too many double negatives or otherwise worded that poorly.. I'm not sure what attitude you perceived, but that post; and especially the bit you quoted, was meant to emphasize that I don't expect to be spoon fed answers.

I just listed some observations, some assumptions, and some of the trouble I'm having with developing a hypothesis. Sulfur is not at all common in the core structure of any but a select few. I don't need anyone to sit here and type up a comprehensive rundown of everywhere it shows up in additives, I just want somewhere to start finding the answers myself.
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[*] posted on 23-10-2018 at 20:21


Sulfur is often added to plastics to improve temperature resistance. It causes crosslinking. Most famously as vulcanization. Clear Urethane rubber with sulfur for crosslinking would be attacked and react exactly as you described. I think I mentioned this in my previous post. But I can't be certain without at least a product number from the tubing as there are simply too many kinds.
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[*] posted on 24-10-2018 at 06:28


Quote: Originally posted by enceladus  
Yesterday I put some hardware store (conc.~30%) hydrochloric acid.....


Apparently what you have experienced with your HCl has been previously reported, see this thread which comes up in a google search:

https://www.reddit.com/r/chemistry/comments/4figqz/contamina...

My guess is a transition metal presence (iron, copper,..) together with H+ (from HCl), a chloride for complexing (like with Cu(l) or other transition metals) and O2 may potentially form radicals (hydroxyl radical, •OH, superoxide radical anion, •O2-,....) and some reactive oxygen species (like H2O2 which interacts with HCl). The action of the hydroxyl radical on chloride is said to proceed as follows:

Fe(ll)/Cu(l)L = Fe(lll)/Cu(ll)L' + e-

O2 + e- = •O2-

H+ + •O2- = •HO2

•HO2 + •HO2 = H2O2 + O2 (slow reaction)

•HO2 + Fe(ll)/Cu(l)L = HO2- + Fe(lll)/Cu(ll)L'

H+ + HO2- = H2O2

Fe(ll)/Cu(l)L + H2O2 --> Fe(lll)/Cu(ll)L' + •OH + OH-

•OH + Cl- --> •ClOH-

If pH > 5: •ClOH- --> •OH + Cl- k = 6.1x10^9 (Source: Supplement Table S1 at: http://www.mdpi.com/1420-3049/22/10/1684 and click on Supplement F1 to download)

If pH < 5: •ClOH- + H+ --> •Cl + H2O k = 2.1×10^10 (Source: Supplement Table S1)

•OHCl- + H+ --> H2O + •Cl (pH < 5)

•Cl + Cl- = •Cl2-

•Cl + •Cl = Cl2

Cl2 + H2O = HCl + HOCl

Fe(ll)/Cu(l)L + HOCl --> Fe(lll)/Cu(ll)L' + •ClOH-

and with the last product, some reaction recycling.

All in all, may explain reports of a color change in contaminated HCl.

Also, there is an electrochemical cell with ferrous or cuprous (which is slowly converted to ferric and cupric), H+ and O2 from air (relatedly think of metal-air battery) producing e- to further attack organics directly or assist in reactive oxygen species formation to corrode your tubing (for details, see my comments and references which are available at http://www.sciencemadness.org/talk/viewthread.php?tid=94078#... ).

Biochemist are also aware of an interesting aspect of copper ions to engage in a cyclic reaction chain/system with select compounds (like blue copper proteins and copper oxidases, see https://pubs.acs.org/doi/pdfplus/10.1021/ba-1990-0226.ch001?... and https://www.sciencedirect.com/science/article/pii/S096098221... ), which may or may not be a play here also (see also http://www.jbc.org/content/270/29/17633.long ).

Welcome to the advanced chemistry class :).

[Edited on 25-10-2018 by AJKOER]

[Edited on 25-10-2018 by AJKOER]
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enceladus
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[*] posted on 24-10-2018 at 22:08


Quote: Originally posted by AJKOER  
Quote: Originally posted by enceladus  
Yesterday I put some hardware store (conc.~30%) hydrochloric acid.....


Apparently what you have experienced with your HCl has been previously reported, see this thread which comes up in a google search:

https://www.reddit.com/r/chemistry/comments/4figqz/contamina...

My guess is a transition metal presence (iron, copper,..) together with H+ (from HCl), a chloride for complexing (like with Cu(l) or other transition metals) and O2 may potentially form radicals (hydroxyl radical, •OH, superoxide radical anion, •O2-,....) and some reactive oxygen species (like H2O2 which interacts with HCl). The action of the hydroxyl radical on chloride is said to proceed as follows:

•OH + Cl- --> •ClOH-

If pH > 5: •ClOH- --> •OH + Cl- k = 6.1x10^9 (Source: Supplement Table S1 at: http://www.mdpi.com/1420-3049/22/10/1684 and click on Supplement F1 to download)

If pH < 5: •ClOH- + H+ --> •Cl + H2O k = 2.1×10^10 (Source: Supplement Table S1)

•OHCl- + H+ --> H2O + •Cl (pH < 5)

•Cl + Cl- = •Cl2-

•Cl + •Cl = Cl2
.......

which may explain reports of a color change in contaminated HCl.

Also, there is an electrochemical cell with ferrous or cuprous (which is slowly converted to ferric and cupric), H+ and O2 from air (relatedly think of metal-air battery) producing e- to further attack organics directly or assist in reactive oxygen species formation to corrode your tubing (for details, see my comments and references which are available at http://www.sciencemadness.org/talk/viewthread.php?tid=94078#... ).

Biochemist are also aware of an interesting aspect of copper ions to engage in a cyclic reaction chain/system with select compounds (like blue copper proteins and copper oxidases, see https://pubs.acs.org/doi/pdfplus/10.1021/ba-1990-0226.ch001?... and https://www.sciencedirect.com/science/article/pii/S096098221... ), which may or may not be a play here also (see also http://www.jbc.org/content/270/29/17633.long ).

Welcome to the advanced chemistry class :).

[Edited on 24-10-2018 by AJKOER]


Haha, YES! this is the sort of response I was after. Some helpful places to start without any snap judgements or bullshit criticism or cynicism. Thank you.
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[*] posted on 25-10-2018 at 01:50


Quote: Originally posted by macckone  
Yes H2O2 increases the reactivity of HCl. It can also oxidize it to chlorine gas given the right conditions.
There are a large number of plastics as well as compounds used to increase the flexibility of plastics.
Sulfur is sometimes used as a crosslinking compound to increase the temperature resistance of plastics or rubbers, aka vulcanization.
Without knowing what your tubing was actually made of it is hard to venture a guess about the chemical reaction.
If it was a clear rubber with sulfur added then it would be very susceptible to HCl and chlorine gas.


I would like to re emphasize that I do appreciate the reply. I feel like even though I did say that, what I went on to say may have still come off a little ungrateful. All I meant was that there was practically nothing to be lost by venturing a guess, but with nothing ventured, there's also nothing to be gained.

Normally I don't need any help investigating minor mysteries like this, but I found this one just puzzling and intriguing enough to submit it to potential outside helpers since the initial conditions were commonplace enough to have been encountered before.

The reason I believe that the list of possible interactions ought to be short is that in spite of the fact that the use of sulfur compounds as initiators has been commonplace since at least the 1970's google still doesn't seem to know what I'm asking about when I try to submit the key terms relevant in the core interaction. I'm sure there's probably some search i could enter to find what I'm after but I just have no idea what it ls.
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AJKOER
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[*] posted on 25-10-2018 at 06:07


I think an interesting experiment would to force air (I have used an old fish tank air pump in some of my experiments) into the mix of HCl/Tubing and see if there is an acceleration in the attack of the tubing.

Also, you may repeat adding a small amount of say powder steel (Fe/Cr), or cast iron (Fe) or some Copper, or transition metal combination, for comparison purposes also.
--------------------------------------------------

Note, I have expanded my original reaction system for completeness and allowing comparison to a system where H2S may be present. For example:

Dissociation: H2S + H2O = H3O+ + HS-

Coupled Redox reactions system:

Fe(lll)/Cu(ll) + HS- → Fe(ll)/Cu(l) + HS•
O2 + Fe(ll)/Cu(l) = O2•- + Fe(lll)/Cu(ll)
HS• + O2•- → S + HO2-
HO2- + H+ → H2O2
Fe(ll)/Cu(l) + H2O2 + H+ → Fe(lll)/Cu(ll) + OH• + H2O (fenton reaction with ferrous, fenton-like with cuprous)
OH• + H2S → H2O + HS•

Note, HS• is oxidized to elemental sulfur and H2O2 (from H+ + HO2-) is created:

HS• + O2•- → S + HO2-

Also, Fe3+ cations are recycled to Fe2+ to feed a fenton reaction:

Fe(lll)/Cu(ll) + HS- → Fe(ll)/Cu(l) + HS•

The possible recycling of transition metal ions means that even small amounts of a metal impurity could eventually produce visible side products with oxygen exposure in time.

Peer reviewed source on the above radical chemistry: See, for example, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4295652/ .
--------------------------------------

Speculated transient creation of colorful sulfur radical anions •Sn-, where n= 2,3 and 4 (see https://pubs.acs.org/doi/abs/10.1021/ic50189a042 ) from the action of solvated electrons acting on elemental sulfur in limited aqueous conditions:

S + e- = •S-

(k-1)S + •S- = •Sk(-) (k=2, 3 or 4, but most readily at k=3) (see also https://pubs.rsc.org/en/content/articlehtml/2016/sc/c6sc0024... )

The basis for this claim is per Wikipedia (https://en.wikipedia.org/wiki/Trisulfur):

"Other methods of production of S−3 include reacting sulfur with slightly dampened magnesium oxide.[12]"

As damp MgO has a high pH (I suspect the pKa of •[S3]- radical anion is high) and as MgO is a photo catalyst forming e- (and also electron holes, h+), this is the basis of my speculation.

However, due to its expected high pKa, in the presence of acid source of H+ (including water), it likely exist in some protonated form:

H+ + •S3(-) = •HS + 2 S (or •HS3)

And, with excess e-, also possible:

•HS + e- (aq) = -HS (aq)

[Edited on 25-10-2018 by AJKOER]
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[*] posted on 25-10-2018 at 10:47


Quote: Originally posted by enceladus  
Quote: Originally posted by AJKOER  
Quote: Originally posted by enceladus  
Yesterday I put some hardware store (conc.~30%) hydrochloric acid.....


Apparently what you have experienced with your HCl has been previously reported, see this thread which comes up in a google search:

https://www.reddit.com/r/chemistry/comments/4figqz/contamina...

My guess is a transition metal presence (iron, copper,..) together with H+ (from HCl), a chloride for complexing (like with Cu(l) or other transition metals) and O2 may potentially form radicals (hydroxyl radical, •OH, superoxide radical anion, •O2-,....) and some reactive oxygen species (like H2O2 which interacts with HCl). The action of the hydroxyl radical on chloride is said to proceed as follows:

•OH + Cl- --> •ClOH-

[Edited on 24-10-2018 by AJKOER]


Haha, YES! this is the sort of response I was after. Some helpful places to start without any snap judgements or bullshit criticism or cynicism. Thank you.


Sorry to burst your bubble, but most of the things AJKOER posts are wild speculation based in some dream reality of his. However, based on your posting history, I guess that's what floats your boat. SMH
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[*] posted on 25-10-2018 at 11:39


Quote: Originally posted by Deathunter88  
......
.......
Sorry to burst your bubble, but most of the things AJKOER posts are wild speculation based in some dream reality of his. However, based on your posting history, I guess that's what floats your boat. SMH


I do agree with the spirit of your comment, and I now try to give less advice based on my experience with say, radical chemistry, to people who have only been imbued in classical procedures and have no level of appreciation or particular knowledge relating to the field I am referencing.

You should checkout some of my recent experiments I posted, complete with pictures of results and source links. See, for example, http://www.sciencemadness.org/talk/viewthread.php?tid=96347#... , http://www.sciencemadness.org/talk/viewthread.php?tid=95543#... , http://www.sciencemadness.org/talk/viewthread.php?tid=94166#... , https://www.sciencemadness.org/whisper/viewthread.php?tid=84... , http://www.sciencemadness.org/talk/viewthread.php?tid=77204#... , http://www.sciencemadness.org/talk/viewthread.php?tid=34429#... and http://www.sciencemadness.org/talk/viewthread.php?tid=27013#... .

Yes, definitely not classic lab prep, but I am legally prescribed from setting up a good lab in my jurisdiction.

So, I resort to learning and employing more science (like radical chemistry, photolysis, electrosynthesis via an electrochemical cell, magnetizer assisted prep, microwave assisted prep, advanced oxidation methodologies involving fenton and fenton-type reactions, electrolysis,....) that may be applied by nearly all home chemists.

[Edited on 25-10-2018 by AJKOER]
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[*] posted on 25-10-2018 at 11:51


As long as there is no peer reviewing in place a lot of bla bla and radical chemistry can go a long way in earning credit.
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[*] posted on 25-10-2018 at 12:52


Quote: Originally posted by Tsjerk  
As long as there is no peer reviewing in place a lot of bla bla and radical chemistry can go a long way in earning credit.


I did quote at least a source reviewed Table of reactions employed:

Quote: Originally posted by AJKOER  
...
.........
If pH > 5: •ClOH- --> •OH + Cl- k = 6.1x10^9 (Source: Supplement Table S1 at: http://www.mdpi.com/1420-3049/22/10/1684 and click on Supplement F1 to download)

If pH < 5: •ClOH- + H+ --> •Cl + H2O k = 2.1×10^10 (Source: Supplement Table S1)
.........................................


Also, I did provide a source reference for the sulfur radical chemistry I cited above that was peer reviewed!

Quote: Originally posted by AJKOER  

.........................
Peer reviewed source on the above radical chemistry: See, for example, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4295652/ .
--------------------------------------


[Edited on 25-10-2018 by AJKOER]
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[*] posted on 25-10-2018 at 20:38


The primary problem with ajkoers reaction mechanism is that it uses exactly as much H2S as it produces.

A much simpler reaction mechanism is

R-S-R + HCl -> R-S-H + R-Cl
R-S-H + HCl -> R-Cl + H2S
R-Cl + H2O -> R-OH + HCl

The actual reaction is more complicated and follows a similar SN2 mechanism to ether hydrolysis in acidic media. Organic sulfides tend to react more readily than ethers.

https://www.masterorganicchemistry.com/reaction-guide/acidic...


This doesn't require any kind of metal contamination.


PS.

enceladus:

I have now spoon fed you the answer. Next time do a little research. And ignore ajkoer's ridiculous overly complicated hypothesis when a simpler one is available.

A cross linked sulphur compound will react with an acid and produce hydrogen sulfide.
Boric acid is regenerated when acid is added to boric acid cross linked compounds as well.


[Edited on 26-10-2018 by macckone]
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[*] posted on 29-10-2018 at 17:48


Quote: Originally posted by macckone  

PS.

enceladus:

I have now spoon fed you the answer. Next time do a little research. And ignore ajkoer's ridiculous overly complicated hypothesis when a simpler one is available.

A cross linked sulphur compound will react with an acid and produce hydrogen sulfide.
Boric acid is regenerated when acid is added to boric acid cross linked compounds as well.


[Edited on 26-10-2018 by macckone]


Holy shit, you and the Deathhunter are brilliantly arrogant douchebags. This is one catty, political forum. Teeming with shit attitudes. Mine wasn't one of them. Stick your spoons up your asses. I'll leave you to your "science madness".
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[*] posted on 29-10-2018 at 17:58


So enceladus is actually PhD pretending a newbie failed? If yes then this can go to rubbish bin.



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[*] posted on 29-10-2018 at 19:45


enceladus:

I gave you the short version of that answer in the first response to your question.
Sulphur cross-linked tubing is attacked by HCl.
You complained noone gave you an answer twice after that.
You said ajkoers answer was a good one without bothering to research a damn thing.
When in reality that speculative mechanism was pure hokum.

This isn't arrogance.
This is annoyance.
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[*] posted on 30-10-2018 at 05:19


Quote: Originally posted by macckone  
enceladus:
......
You said ajkoers answer was a good one without bothering to research a damn thing.
When in reality that speculative mechanism was pure hokum.
.......


Actually, I have little knowledge in sulfur based cyclic systems so as to even suggest speculative reactions. In fact, to be honest, some of the peer reviewed mechanisms in this area, that I have read, appear to me to be weird and unexpected (based, I guess, apparently on backward interpretations of experimental observations to suggest possible pathways), hence my unwillingness to even speculate.

Note, my radical chemistry came completely from published articles which are referenced in the expanded body of the SM thread I provided.

However, that being said, I view the so called peer reviewed science here as likely in flux and basically unsettled. If you have a source that suggests otherwise, my advice would be to research more before relying on poor quality work.
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Here is a comparison of an inorganic viewpoint of say a radical mechanism in a photolysis experiment. It involves the enumeration of all possible chain pathways and then reports the observed product distribution.

My more limited organic viewpoint is that generally there is cited a (like in one) possible named mechanism and then the reported yield, which can vary from high to low (without further explanation as to why the yield is, in fact, low which could be due to other likely pathways). A fair summary?

[Edited on 30-10-2018 by AJKOER]
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[*] posted on 30-10-2018 at 13:21


Quote: Originally posted by macckone  
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A much simpler reaction mechanism is

R-S-R + HCl -> R-S-H + R-Cl
R-S-H + HCl -> R-Cl + H2S
R-Cl + H2O -> R-OH + HCl

The actual reaction is more complicated and follows a similar SN2 mechanism to ether hydrolysis in acidic media. Organic sulfides tend to react more readily than ethers.

https://www.masterorganicchemistry.com/reaction-guide/acidic...

This doesn't require any kind of metal contamination.
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[Edited on 26-10-2018 by macckone]


Most obvious problem with your comment is that Cl2 does not evolve from HCl without a redox reaction.

Also, sulfur treated rubber/plastic is a combination of some sulfur bonding and free sulfur cross-linking, so not R-S-R, more like R-S-H---Sm-R-S-H----..., so your source reference, referring to R-O-R, is a bit weak (see https://polymerdatabase.com/polymer%20chemistry/Vulcanizatio... ) and without reaction condition specifics, perhaps questionable. Supporting this last assessment is the comment (see https://www.quora.com/Why-is-hydrochloric-acid-kept-in-plast... ) to quote:

"Plastics generally do not react with acids, and the plastics that are used with acid storage are especially unreactive."

There is also more evidence suggesting a radical based mechanism at room temperature (see p.513 at https://nvlpubs.nist.gov/nistpubs/jres/4/jresv4n4p501_A2b.pd... ) to quote:

"Fry and Porritt found that hydrogen sulphide is evolved from hard rubber at ordinary temperatures in diffused sunlight and air, due to the decomposition of the rubber-sulphur compound, and that the rate of evolution is increased by exposure to direct sunlight, as well as by a rise in temperature."

where sunlight induces radical formations.

[Edited on 30-10-2018 by AJKOER]
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[*] posted on 30-10-2018 at 13:48




Quote: Originally posted by AJKOER  


Most obvious problem with your comment is that Cl2 does not evolve from HCl without an redox reaction.


How fortunate, then, that there was one.
Quote: Originally posted by enceladus  

So of course I grabbed some 3% H2O2 and put in about a third as much as there was acid.
...
So my secondary question(s) are: Does H2O2 enhance the corrosive properties of HCl in a similar fashion as with H2SO4 in a piranha solution?


[Edited on 30-10-18 by unionised]
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