Douchermann
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Isopropyl Mercaptan Synthesis
I remember many people asking for alkyl mercaptan syntheses over time, however no one posted a definitive synthesis backed with experience. Below is
a summary of my route to isopropyl mercaptan.
--Sodium hydrosulfide--
An excess of hydrogen sulfide was produced with 40g of paraffin wax shavings and 80g of elemental sulfur. This was was passed through a solution of
20g sodium hydroxide and 100ml of distilled water. The excess being neutralized with two wash bottles of hydrogen peroxide. After saturation, It was
evaporated down to a yellow solid, which was recrystallized in 96% ethanol. This yielded 27g of hydrated sodium sulfide. Theoretical being 28g of
anhydrous; there was clearly some decomposition during the evaporation.
--Isopropyl bromide--
65ml of isopropyl alcohol was reacted with 95g of sodium bromide and 200ml of ~50% H2SO4. After second distillation, 65g of clear isopropyl bromide
was obtained. This was only a 66% yield, due to me adding the sulfuric acid too quickly to the solution, oxidizing a portion of the bromine out.
--Isopropyl mercaptan--
The entire yield of sodium hydrosulfide was added to a 250ml RBF and 100ml of ethanol was added. To this, 25ml of the previously prepared isopropyl
bromide was added. Sodium hydrosulfide was used in almost a 2x molar excess here for two reasons: it was of unknown NaHS concentration (due to
hydration), and I chose to use an excess to hopefully react all the isopropyl bromide, making separation easier. This was refluxed for 1.5 hours on a
water bath, until all of the yellow solid was gone. The flask was plastered with sodium bromide, which is only slightly soluble in ethanol
(6.25g/100ml @ 25C)
The flask was set up for simple distillation, and the water bath maintained at 75C until no visible boiling was occurring in the flask. I was not
concerned with yield at this point, since the product was only produced for amusement, not for reactions. To obtain as much as possible, bump the
water bath to around 85C and collect about 40-50ml distillate, then fractionally distill the product boiling between 51C-57C.
I obtained 15.7g of clear, yellow distillate (roughly 78.5% yeild).
Isopropyl mercaptan smells incredibly foul. I made the mistake of transferring containers within my living quarters and the smell still lingers,
after many encounters with the Oust can, and an open window. Do not bring this into your living space unless it is in a tightly sealed container.
The left over sodium bromide can be extracted and purified by first cooling to slightly below room temperature (around 15C) then pouring off the
ethanol. The ethanol should contain any sodium hydroxide produced leaving mostly sodium bromide. This can be dissolved in a minimum of room
temperature water, then rendered neutral, or just barely acidic using sulfuric acid. Chill it in a freezer and filter out any sodium sulfate
decahydrate crystals formed, then evaporate the remaining solution to obtain relatively pure sodium bromide.
[Edited on 16-3-2008 by Douchermann]
It\'s better to be pissed off than to be pissed on.
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Methyl.Magic
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good synthesis !
Don't forget that mercaptan can be synthethised by grignard reagent and sulfur with high yield !
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organometallic
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"Don't forget that mercaptan can be synthethised by grignard reagent and sulfur with high yield !" Hey, cool, is there a writeuop for that anywhere?
In vials of ivory and coloured glass
Unstoppered, lurked her strange synthetic perfumes,
Unguent, powdered, or liquid - troubled, confused
And drowned the sense in odours.
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garage chemist
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Very good synthesis, doucherman!
One thing, the synthesis of mercaptans by alkylation of sodium hydrosulfide gives a substantial amount of dialkyl sulfide byproduct. By using Na2S
instead of NaHS, the formation of dialkyl sulfide becomes the main reaction.
Did your NaHS soution smell strongly of H2S after preparation (indicating excess of H2S)? I don't think the S/paraffin reaction is anywhere near
quantitative.
Methyl Magic, I would be most interested in a writeup for the preparation of mercaptans from grignards as well!
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Nicodem
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That is a surprisingly good yield considering the method you used!
However, the boiling points of isopropyl bromide and isopropyl mercaptane are too close, essentially overlapping (59°C vs. 57-60°C), for a bold
assumption that you got a pure product.
Other possible products luckily have much higher boiling points: diisopropyl sulfide (120°C) and diisopropyl disulfide (175-176°C).
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Klute
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Have you considered using thiourea? It's quite cheap, and avoid generating H2S. Never done the reaction myself, so I can't comment on yields though.
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Douchermann
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Garage chemist - the yeilds are not quantative for parrafin/s, however I used a 2x molar excess and a 1/2 molar weigh sodium hydroxide. For equimolar
portions it would be 20g paraffin 40g sulfur and 40g NaOH. It wreaked of H2S to say the least.
Nicodem, I used what I figured was a 2x excess of NaHS to isopropyl bromide, to ensure a complete conversion of isopropyl bromide. However, I do not
know level of hydration on it, so I can only assume there was an excess in there.
Obviously I'm using a lot of excess here, but for something that can be produced 100% OTC, there aren't any real issues.
BTW, I was able to cause mass disorder in my work place with this. A few drops strageically placed throughout the store rendered a subtle chaos
(oxymoron). The manager was swearing at the store director, the lower managers and personell coordinators were looking for a natural gas leak, and
tons of customers were complaining haha.
It\'s better to be pissed off than to be pissed on.
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