kazaa81
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Thiols (mercaptanes) preparation?
Hallo to all,
I'm interested in preparing thiols (also mercaptanes) without special equipment, in a simple lab. Does anyone know something about?
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budullewraagh
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alkene+H2S. careful man; H2S is madly toxic.
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kazaa81
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Can't i use a sulphide, like Na2S, which is more easy to handle?
From butane (for example) what i will get?
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stygian
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I believe NaHS works. Don't know if Na2S would work or not.
NaHS is made from C2H5ONa + H2S
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kazaa81
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I've made my Na2S from a NaOH concentrated solution boiled with sulphur.....if anyone post any example about a full experiment, i would
appreciate this very much!
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garage chemist
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NaOH solution boiled with sulfur gives a random mix of polysulfides, which is useless for the preparation of pure compounds.
Real Na2S can only be made by first saturating a NaOH solution with H2S, yielding NaHS and then adding an equimolar amount of NaOH, this forms Na2S.
Then boil down and cool to obtain crystals of the nonahydrate.
Thioethers can be made by boiling Na2S with alkyl halogenides.
I've successfully made diethyl sulfide by boiling ethyl bromide (made by distilling ethanol with NaBr and dil. H2SO4 and washing the distillate
with water- rhodium's got a procedure) with Na2S produced by the above method (I've got a fume hood and am therefore able to work safely
with H2S). The H2S was obtained by boiling zinc sulfide (obtained as a pigment from an art store) with dilute HCl.
H2S can also be made by heating sulfur with paraffin (this is the easiest and safest method, since stopping the heating also stops the gas evolution).
Mercaptans can be made by boiling the alkyl halogenide with NaHS (this also yields a small amount of the thioether, which can be removed by
distillation of the mercaptan).
Diethyl sulfide stinks really bad, the smell is horrible, like rotten vegetables or bad breath. The smell is also extremely intense and any spill will
cause your lab to stink for weeks.
I haven't tried ethyl mercaptan.
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kazaa81
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Mercaptanes from higher alcohols are probably harder.....but the smell of the ethyl and methyl is enough for now..... also (NH4)2S smells good!
Any mercaptanes/mercaptines idea wellcomed! 
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praseodym
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Heard that the butyl one stinks, like skunk oil. Is it true? Are most mercaptans normally pleasant or unpleasant, in terms of smell?
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Quibbler
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Forget it!
Mercaptans don't just smell they stink. They cling, you will smell of them for days if not weeks, if you have a spill. Even if you have a
fumehood you will cause panic for miles around as people try to find the gas leak. Believe me I've been there.
It's the S-H that seems to make the smell, make S-Me and the smell starts to become pleasant. One of the most pleasant smelling compound I have
ever used was H-C-(SCH3)3 trismethylthiomethane.
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kazaa81
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Wondering about ethyl mercaptane....anyone got a complete procedure from something?
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kazaa81
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I was thinking to make ethyl sulphide or a
mercaptane but, my problem was find
reagents (and apparatus) to make esterification of an
alcohol.
I've thought up a little, then tried ethyl sulphide synthesis with these reagents:
- Boric Acid (H3BO3) - from sodium perborate and HCl
- Ethyl Alcohol (C2H5OH)
- A Sulphide water-alcohol soluble
(Na2S, (NH4)2S, ecc.)
So, I've added some boric acid to a little
of denaturated ethanol...the color pink
disappeared (bleached out) and I think
which I got a solution of ethyl
borate (correct me if I've wrote a mistake).
To this ethyl borate I added some drops of
Na2S (also polysulphides), made from aq. NaOH
and sulphur. I've stirred a little and then...
a terrible stink appeared. So I think that
this is ethyl (or diethyl) sulphide.
Hope to haven't make any mistake...
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Nicodem
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| Quote: |
So I think that this is ethyl (or diethyl) sulphide.
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No, with the experiment as you described it you got hydrogen sulphide (H2S). Do not snif too much of it. It is only two times less poisonous than
hydrogen cyanide.
| Quote: |
Na2S (also polysulphides), made from aq. NaOH and sulphur.
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Garage chemist already explained it to you that by dissolving sulphur in NaOH you do not get Na2S. You can only get a mixture of several sodium
polysulphides and Na2SO3. It is a disproportionation of elemental sulphur and not its reduction as you would want it to be. Similarly you don't
get get only NaCl by dissolving chlorine in NaOH but also an equivalent of NaOCl. With sulphur you have even less luck since sulphur reacts with Na2S
to form Na2Sx (where x>1) so this is not a viable method to make Na2S.
By the way, who told you that triethyl borate alkylates the sulphide anions?
You might consider starting in a library the next time you plan an experiment.
Edit: The best way to do reactions is by understanding what you are doing: Nucleophilic substitution
[Edited on 15-10-2005 by Nicodem]
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unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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kazaa81
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Nicodem, as I've wrote, in the solution obtained by boiling sulphur in aq. NaOH there are "(also polysulphides)". I've type in
particular Na2S for intending sodium sulphide, not to write all the possible formulas of the polysulphides.
I've smelled H2S before this experiment and doesn't have nothing to do with this smell. If it has formed, why I haven't see any bubble?
Because it has dissolved in the ethanol?
Also, I've tought which if a salt of the ethyl group (ex. ethyl bromide) would react with a sulphide to make ethyl sulphide, why not the borate
salt (C2H5)3BO3?
And, I've handled substances a little much dangerous than H2S, like hydrofluoric acid.
Thanks all for help!
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Nicodem
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Mixing H3BO3 with EtOH does not produce (EtO)3B, it only forms an equilibrium of H3BO3, (EtO)H2BO3, (EtO)2HBO3 and (EtO)3B in
ethanol and water with the equilibrium shifted way to the left (little if any (EtO)3B forms without removing water).
Maybe I was not clear enough. You do not get Na2S by dissolving sulphur in NaOH because any formed Na2S reacts with sulphur.
Evolution of a gas is not nearly always accompanied by the formation of bubbles. If you heat saturated aqueous ammonia it liberates NH3 gas but you
will not see any bubbles forming. Same goes with slow neutralization of aqueous sulphides. H2S is relatively soluble in water and ethanol and thus
tends to escape from the phase boundary rather than bubbling like the formation of N2, O2 or H2 in water solutions, for example.
Anyway, you are right. You could not have made H2S since you did not have any Na2S in the solution. What you had smelled might have been something
more exotic like hydrogen persulphide, for example. At least it sounds more interesting. But I don’t know enough about inorganic chemistry to say for sure.
However I know enough organic chemistry to tell you that triethyl borate is nearly not C-electrophylic enough to react with Na2S. No ethylthiols could
have formed in your experiment.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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kazaa81
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Yes, I was already in know that ethanol + boric acid would make an equilibrium.
Also, is correct to say that NaOH + S will yield polysulphides...but I'm not sure which there is H2S2 in the solution.
I'm sure which there is some dihydrogen oxide in the ethanol mix! What a exotic compound...
Nicodem, could you please write a equation where you show how is ethyl sulphide formed? Bubbling H2S in ethanol seem to me too much risky to get ethyl
mercaptan.
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Nicodem
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You do not get any EtSH or Et2S by bubbling H2S in ethanol. The hydroxide is a teribly bad leaving group.
The general reaction equation of making Et2S by the nucleophylic substitution with Na2S is:
Et-(LG) + Na2S => Et-SNa + Na(LG)
Et-(LG) + Et-SNa => Et2S + Na(LG)
The equations should be written in a ionic form since it happens in solution, but how does one use sub/super script in this forum?
(LG) stands for the Leaving Group. It is a group that withdraws electrons from the carbon at which it is attached in order to make it electrophylic
while at the same time it can also leave as an anion. Se the links listed here (for the 2nd time): Nucleophilic substitution
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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kazaa81
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So, I want to have a halogen attached to the ethyl group.....but first I have to find where to get a bromide.
To bad smelling compound, I will gave a try to ammonium sulphide in solution of... dihydrogen oxide
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Sandmeyer
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| Quote: | Originally posted by kazaa81
So, I want to have a halogen attached to the ethyl group.....but first I have to find where to get a bromide. |
Alkylbromides can easily be made from alcohols (utfse), but for this purpose it is not nescessary to go from alkylhalide. Following the thiourea route
allows to start with alcohol under acidic conditions (though yield is not the best), scroll to part B: http://www.orgsyn.org/orgsyn/prep.asp?rxntypeid=23&prep=... There is also a prep (or at least a discussion) in Vogel if memory serves me.
| Quote: | Originally posted by praseodym
Are most mercaptans normally pleasant or unpleasant, in terms of smell? |
Actually, not all smell bad, IIRC a thiol (or is it a thioether) is responsible for the plesent smell of truffle.
[Edited on 16-10-2005 by Sandmeyer]
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kazaa81
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I would partially agree with you, Sandmeyer....thiols are best famous for their unbearable smell
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Cloner
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Thiols can be made from alkyl halides easily. Oddly, grignard reagents can be made to attack solid sulfur but it must be finely divided sulfur, like
the kind you get when leading H2S through iodine (you may want to make HI first anyway). Perhaps you could toss the grignard reagent into a toluene
solution of sulfur to improve yield.
Besides grignard reagents, I think thiosulphate will react with at least the longer alkylbromides forming a so-called bunte salt, which is then
converted into the the disulfide in a one pot synth (reflux acid and equivalent amount of thiosulfate in aquous dioxane (anything else that dissolves
the acid and the salt somewhat will do) until the solution turns clear, then oxidize the bunte salt to disulfide).
Disulfides will not stink so badly so they are good for intermediate step. Also, they are less water soluble than thiols so will be easy to purify.
They will be reduced to thiols by the means like Sn/HCl, Zn/HCl and of course LiAlH4 etc
[Edited on 10-11-2005 by Cloner]
[Edited on 10-11-2005 by Cloner]
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