Sciencemadness Discussion Board - Parrafin

Parrafin

brightwonder - 26-3-2009 at 16:49

I recall reading on a forum that parrafin wax heated with sulfur will result in H2S. Does anyone know if this will create quantities sufficient to be considered dangerous? I was contemplating making this experiment for my nephew but I am concerned about health risks

thank you so much

not_important - 26-3-2009 at 17:10

Depends on how much you heat at once. The demo often used "a pea-size bit of paraffin" and about the same amount of sulfur in a test tube. That small of an amount will cool down quickly, stopping production of H2S.

Old motor oil will work, too, as well as mineral oil.

brightwonder - 26-3-2009 at 17:59

I see. Well then its all depends on the amount used.. several ounces of motor oil combined with sulfur for example would produce H2S at potentially harmful levels?

thank you not_important

rgds,

chris

JohnWW - 26-3-2009 at 18:02

Sulfur can react with alkenes by cross-linking the double bonds, which is how the "vulcanization" (hardening) of natural rubber (consisting of long-chain alkenes) by heating with sulfur occurs. However, PURE "paraffin wax", which is supposed to consist purely of medium to long-chain alkanes, i.e. saturated hydrocarbons with no double bonds, should theoretically not normally react with sulfur, except under quite extreme conditions ("cracking", usually catalytic, which may produce H2S as a byproduct), and of course in the absence of air. The organic chemistry textbooks have NOTHING about any ordinary direct reaction of sulfur with alkanes, let alone to produce H2S. If paraffin wax does react with sulfur under ordinary conditions, with no more than mild heating, it may be be contaminated with some alkenes.

kclo4 - 26-3-2009 at 18:29

Mixing sulfur and paraffin wax to produce H2S works well, and can easily produce dangerous amounts if you use a lot of each.

brightwonder - 26-3-2009 at 18:31

well there seems to a diversity of opinion here

hmmm. well.. anyone else?

thanks people

S.C. Wack - 26-3-2009 at 21:23

http://books.google.com/books?id=inIGAQAAIAAJ&pg=PA209

not_important - 27-3-2009 at 00:13

Thanks, SCW. I was going to comment that sulfur is a long used dehydrogenation agent, from before catalytic methods came into use. Sulfur and selenium both will remove hydrogen from organic compounds, in cases where rings exist often forming the aromatic equivalent - useful for structural elucidation in those early days. I suspect that it relates to the way the S rings break at around 150 C on up, forming diradicals and smaller fragments which abstract hydrogen.

Cheap kerosene and heating oils also work, they also habe a high enough boiling point to not contaminate the H2S.

panziandi - 28-3-2009 at 17:50

I had thought that CS2 was also a by-product of this reaction because isn't it analogous to combustion? Methane reacts with sulphur in teh vapour phase to produce carbon disulphide and hydrogen sulphide, I'd expect this to be similar to what is seen with higher alkanes also.

chief - 29-3-2009 at 04:27

I did this when I was a kid and it works quite well ; but during class it was more practical to use the FeS + HCl method ...

[Edited on 29-3-2009 by chief]

PHILOU Zrealone - 31-3-2009 at 03:54

Quote: Originally posted by panziandi

I had thought that CS2 was also a by-product of this reaction because isn't it analogous to combustion? Methane reacts with sulphur in teh vapour phase to produce carbon disulphide and hydrogen sulphide, I'd expect this to be similar to what is seen with higher alkanes also.

Oxygen has an electronegativity of 3.5, carbon is 2.5 so does sulfur so there is a big difference between oxygen and sulfur attack of alcanes...I think one must heat to the cracking temperature of alcanes to get C-C bond break.

Methane is already isolated carbon atom and so no C-C bond break is needed.

JohnWW - 31-3-2009 at 12:11

I agree with Philou. The close similarity in electronegativity between C and S means that there would not be any significant energetic favoring of a reaction between S and saturated paraffin hydrocarbons in which elemental S abstracts H atoms under ordinary conditions. It could only happen under strongly endothermic conditions such as "catalytic cracking" which would also break C-C bonds.

I have long been aware of the use of elemental Se to reduce and remove all electronegative side-groups (e.g. -OH, -COOH, -NH2) from organic compunds, leaving hydrocarbons. Such groups, of course, do not exist in straight-chain alkanes. It is quite possible that S could also be used to achieve this under certain, probably more rigorous, conditions.

kclo4 - 31-3-2009 at 14:42

Quote:

.I think one must heat to the cracking temperature of alcanes to get C-C bond break.

Would it really need to break the bonds to produce H2S?

I think you guys should heat a small amount of sulfur with wax in a test tube and see what happens

Paddywhacker - 31-3-2009 at 17:20

I had to give this a go. Heated about 10 ml of oil or wax with about 0.5 g sulphur. I tried Olive Oil, Beeswax, and Petrolium Jelly. In all cases the sulphur melted to form a dark red lower layer, and on higher heating the mixtures boiled vigorously. Some sublimed sulphur was seen on the cold parts of the boiling tubes. All oils produced some H2S, but not a great deal. I don't see myself using this method instead of a Kipps Apparatus.

Maybe with a lot of sulphur moistened with a little oil the action would have been more apparent.

The sulphur completely dissolved in the olive oil and in the beeswax to form dark red solutions that stayed in solution when cooled. The sulphur was less soluble in the paraffin, forming floating blobs and later, solid residue.

Now my house stinks and I have the front and back doors open.

kclo4 - 31-3-2009 at 17:26

Did you test for H2S formation with the paraffin?

You could do a test for it - have a strong solution of ammonia around and it should fume, =burn the gas on a glass plate.. notice the sulfur residue, or mix with SO2 and notice the sulfur that forms.

[Edited on 1-4-2009 by kclo4]

PHILOU Zrealone - 1-4-2009 at 07:24

Quote: Originally posted by kclo4

Quote:

.I think one must heat to the cracking temperature of alcanes to get C-C bond break.

Would it really need to break the bonds to produce H2S?

I think you guys should heat a small amount of sulfur with wax in a test tube and see what happens

-I was refering to the quote of panziandi in my reply

No CS2 will form without C-C bond breaking, the example of methane is casual, other paraffins (alcanes) will not produce CS2 the same way O2 does produce CO2....unless high temps are used; temperatures close or higher than cracking temps.

[Edited on 1-4-2009 by PHILOU Zrealone]

not_important - 1-4-2009 at 08:02

Note that when you use unsaturated hydrocarbons such as vegetable oils the addition of sulfur to the C=C double bonds is a competing reaction. Also the glycerol portion of the oils can react with the sulfur if heated enough.

Paraffin wax and petroleum jelly are mixtures of simple hydrocarbons and don't undergo those other reactions.

sparkgap - 1-4-2009 at 09:22

"Note that when you use unsaturated hydrocarbons such as vegetable oils the addition of sulfur to the C=C double bonds is a competing reaction."

Long story short, you "vulcanized" the fatty acids...

sparky (~_~)

Paddywhacker - 2-4-2009 at 12:21

Quote: Originally posted by sparkgap

"Note that when you use unsaturated hydrocarbons such as vegetable oils the addition of sulfur to the C=C double bonds is a competing reaction."

Long story short, you "vulcanized" the fatty acids...

sparky (~_~)

And the resulting oil had interesting stinkey properties. I wish I had known about this when I was a schoolboy.

Edit... and I just tried out glycerol and can confirm that on strong heating there is a reaction that liberates H2S or something that smells like it. Another day with a stinky house.

Edit again ... Polyethylene glycol 6000 also reacts to give H2S, which surprised me somewhat.

[Edited on 3-4-2009 by Paddywhacker]