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len
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Benzene Extraction from Petrol/Gasoline
Benzene is a horrible substance. My fat chemical hazards reference book, which admitedly lists most substances as horrible poisons (I think the old
adage of crying wolf applies here) goes bezerk under the entry of benzene, with the words carcinogen repeated about ten times, a multitude of chemical
societies listed which class it as a carcinogen, all its horrible effects on the body catalogued, its a right-to-know substance, minimum allowable
concentration 0.5ppm etc. The entry itself occupies about a page and a half, thats 10 times the volume for most other chemicals. At the end theres a
warning that there might not be a minimum allowable exposure to a carcinogen. In Australia its classed an S7 poison together with cyanides etc,
which means its purchase is registered and controlled.
After reading all this information I was truely shocked and praying I never come into contact with this horrible stuff.
The next shock was finding out that common old petrol, the stuff my garage (as do most garages) whiffs of when a car is being fixed, the stuff I have
seen some people siphon with their mouths, contained up to 5% benzene in 1997 (although in the US and now in the EU legislation is coming up to limit
its concentration to 1%). 5%, thats more than acetic acid in vinegar, and if you can get a good whiff of acteic acid with a boiling point of 117C
from vinegar, then petrol should give you a good whiff of benzene, which boils at only 80C. Nobody informed me of that. It figures, authorities love
to show their overt concern for safety by banning and limiting stuff. This costs them nothing, allows them to demonstrate their high standards, while
exercising their real love - power. But when money gets involved, when its a case of quantifying their concern with something of value to them, then
they start re-evaluating as to how much it really matters to them. Apparently they are worried about benzene less than it costs money to make petrol
benzene-free.
I have found reports on the internet claiming the air at service stations is only 25ppb benzene on average. But that is ambient air, which I know
from experienece does not smell of petrol. One gets a good whiff of the later only when standing over a nozzle, and especially when replacing the
latter as this normally involves spilling some petrol. So one would expect garage mechanics and perhaps people who do motoring in general to show
higher rates of myeloid leukemia than some country folk leading a reclusive life, and in any case, an increase in the incidence of leukemia as the use
of petrol increased from the 1930's onwards. Yet I have read reports that no such trend has been observed!
I could find no figures on the internet for benzene in Australian petrol, but with all the overt concern for safety here (we are not allowed to climb
ladders alone at work) I thought it would be on a par with the EU. In any case I decided to do my own investigation (with such a sensitive issue I
dont know how much one could believe published data anyway).
500ml of petrol were fractionally distilled. The most voluminous fraction was that boiling 40-60C (pentanes etc) 57%. The 60-75C fraction was 8%,
while the benzene containing fraction 75-100C, which includes heptane, was only 12ml (2.4%). So far so good. However the 60-75C fraction should also
include benzene, since the lower boiling point alkanes, of which petrol mostly consists, lower the boiling point of its mixture with them.
I now looked around for a test to separate the aromatic in my two fractions from the aliphatics. Most of the books I looked at suggested nitration.
The benzene ring is stable and nitrates easily in a HNO3/H2SO4 nitrating mixture without cleavage, the alkanes are unreactive, while alkenes oxidize.
Although none of the books looked at this as a quantitative problem, I decided that by measuring the nitrobenzene formed, and asuming the yield quoted
in nitrobenzene preparations, I should get a good idea of how much benzene was present in my original mixture. One concern was as to the separability
of the alkene oxidation products from the nitrobenzene. For this I would need to know what happens when alkenes are oxidised with nitric acid. The
textbooks are useless here. They mostly appear to be copies of each other. They all seem so logical and compelete when one reads them without a
problem at hand, but when you have a specific problem you see the omissions. I think their authors would regard the inclusion of phenomena that are
complex and they can not fully explain as interefering with the aim of their presentation, of a subject they are perfectly in control of, and/or would
undermine their authority.
In any case 30 ml of the second fraction were nitrated, proceeding as in Vogel (or in the nitrobenzene thread in this forum, fortunately I did not
have fuming HNO3 available, else I would have fallen into the same trap as described there). I noticed during the reaction that as well as an orange
oil a green particulate substance which disolved with shaking was formed, and was sure this was oxidation products from other components of petrol.
None of the textbooks make mention of it. Yet reading postings on the forum, I see this same phenomenon mentioned starting with, presumably, real
benzene. As I said before I see this as a really is a advantage of this forum over so-called professional publications. People here do not mind
mentioning things they do not fully understand.
At the separation stage three layers were formed. The upper layer, 17ml, was lighter than water and consists presumably of the alkane/unreacted
portion. The middle layer, 13ml was orange, oily, and heavier than water. This must contain the nitrobenzene, and due to its orange rather than
yellow colour I would have thought it to contain a good portion of unknown alkene oxidation products, however reading the nitrobenzene thread, I see
that a similar result can be obtained with relatively pure benzene. The green stuff was contained in the densest acid layer, and became more apparent
when water was added to it.
I washed the nitro layer with water and carbonate several times, and it became opaque orange-brown and emuslified. Disposing of washings down the
sink I caught a very definite, pleasant, medicinal-almond odour, I could not distinguish it from benzaldehyde. Reading the same on the forum, I am
now confident I have nitrobenzene in good yield.
Now as to the benzene content in Australian winter petrol. Going by the unreacted fraction, if we assume the rest was benzene, we have 13ml out of
30ml in the second fraction. I.e. 43%, while 2nd and 3rd fractions make 10% of petrol. All in all petrol contains 4.3% benzene. Going by the
amount of nitrobenzene formed assuming its essentially pure, we have 13ml nitrobenzene, which equates to 11 ml pure benzene initially present. I.e.
36% of the fraction, or 3.6% in petrol. However if we take into account the 85% yield reported in textbooks for the nitration reaction, this becomes
4.3% again!
Overall a very bad picture for Australia, on the fronts of both safety and hypocricy.
P.S. The final step would be to distil the dryed nitrobenzene, but Im hesitant to do this. The books say it forms explosive hazards whe heated with
many other organic substances, while the distilations performed in textbooks would not contain even trace amount of some of the substances present in
my case. Furthermore I have no definite idea of what these could be. I also noticed the formation of a yellow percipitate if the washing (containing
acid) were allowed to stand overnight (even in the cold). This presumably is dinitrobenzenes, which are explosive when heated. Again this
observation was mentioned in the thread, while books say nothing on this. They all talk about a vigorous nitration environment and 100C needed to
form dinitro. Has anyone had any experience distilling impure nitrobenzene?
[Edited on 18-7-2006 by len]
Edited title. Chemoleo.
[Edited on 18-7-2006 by chemoleo]
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Magpie
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In response to your question I will quote from two university lab manuals that have nitrobenzene synthesis procedures:
1. copyright 1960: "Distill the nitrobenzene using a small distilling flask and an air-cooled condenser." "Collect the portion boiling at 200-215C,
but do not go above this temperature nor distill to dryness because the small quantity of residue contains dinitrobenzene which may decompose
violently at high temperature."
2. copyright 1950: "The boiling point rises rapidly, and the product is collected at 205-212C." "It is important not to distill quite to dryness, as
the residue (mostly m-dinitrobenzene) may decompose violently if heated much above the boiling point of the nitrobenzene."
I followed the first procedure when I made nitrobenzene from homemade benzene (from Na benzoate).
I hope this helps. Nice work, BTW.
The single most important condition for a successful synthesis is good mixing - Nicodem
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len
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Thanks for that Magpie. I have seen these very same distillation instructions in my textbooks, but what worries me is that they presume you would be
distilling nitrobenzene obtained in the nitration of the relatively pure benzene they describe. The hazardous substances book lists a whole pile of
organics with which nitrobenzene forms an explosive hazard, and since none of the publications I consulted revealed a) the relative composition of
petrol b) the full range of oxidation products of alkenes with nitric acid, I really
dont know if theres anything mixed with the nitrobenzene that could make distillation dangerous.
Your benzene would of course have been much purer than mine. What sort of temperature is needed to do the decarboxilation you mention? Is there much
charring? What sort of yield do you get? I presume if done in glassware it would be ruined since hot NaOH attacks glass. I was thinking of using
CaO for the same procedure. Dont know if it would work.
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Magpie
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There is a huge thread here called "Benzene synthesis." It will likely answer all your questions. Use the search function to find it.
I used a large glass test tube, and yes the molten NaOH ruins it after a few runs (cracks). Others have gone to metal containers at a
semi-industrial scale. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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unionised
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A year or 2 back I had occasion to GC some petrol to measure the benzene content. It was about 1.5%
It's an interesting question about banning benzene from petrol. Yes, it's a carcinogen, but then again, it's not a very good one. Alcohol is also
carcinogenic but I can't see anyone banning it (again) in a hurry. People working in labs a few decades ago used to wash up in benzene. Most of them
didn't suffer any harm.
Life is full of risks; one reason for benzene in petrol is that it's a useful anti-knock agent. It was put in to replace tetraethyl lead. I wouldn't
want to go back to that. The risks from being knocked down by a car are vastly greater than the risk of getting cancer from benzene from fuel. If you
really want to reduce the overall risk you need to ban the car rather than benzene.
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chloric1
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nitorarenes
About 7 years ago I played around with 2 or 3 nitroarenes. I believe I made ortho & para nitrotoluenes and chloronitrobenzene. Just the sweet
odors and the literature convinced me of there ominously poisonous nature so I have not messed with them since. I may in the future but...they are
scary I found a quite satisfactor way of drying the compounds though. I
dissolved them in chloroform rapidly stirred the solution with anhydrous calcium chloride. An orange cloudy solution became crystal clear orange
or yellow.
As far as distilling nitrobenzene, I assume it can be done safely but you will have to sit down near it and monitor the temperature closely. Be
careful!
[Edited on 7/20/2006 by chloric1]
Fellow molecular manipulator
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len
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Thanks chloric, thats helpful. Ill follow your procedure with chloroform and report on the results.
As far as sitting next to it closely and monitoring the temperature, I think you might be trying to get rid of me .
I agree about closely monitoring the temperature but I am not ready to die in the name of establishing that Aussie petrol is full of benzene. In fact
devising a way to keep track of the distillation while being a good distance away from it is what is occupying me now.
I have meanwhile found a few worrying reactions in the literature were alkenes (and even some especially reactive alkanes) actually add an NO2
under the influence of nitric acid, rather than being simply oxidised, as my earlier sources have indicated. Aliphatic nitro compunds are explosive.
I do not know their solubility in water though. Maybe they have been washed away (the washings were all dark red). Many of the oxidation products
should certainly have been washed away as they would have an OH group, the NO2 Im not sure about.
Its interesting to see UK petrol is only 1.5% benzene. We are a technological backwater here unfortunately. We try to cast a good image of ourselves
but frequently dont have the technology to follow up on it with actions. I am beginning to agree with unionised that the danger of benzene is
overrated. It should not be S7. The human statistics I have mentioned, and what he said do not support the carcinigenicity it is purported to have.
P.S. I have not established the 4.3% benzene in petrol with absolute certainty yet. I believe that would come with distillation of my product and
comparison of its boiling and melting points.
And yes, thanks Magpie I did not know how to search this site properly at first and so missed the large benzene synth page. I got one page of results
on benzene and thought that was all. I am not entirely to blame though, there were no page numbers at the bottom of the page to indicate more
responses to my search were available.
[Edited on 21-7-2006 by len]
[Edited on 21-7-2006 by len]
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leu
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| Quote: | | Aliphatic nitro compunds are explosive. |
The esters of nitronic acids can be quite explosive when distilled to dryness, but aliphatic nitro compounds are merely flammable  It will take a column of very many theoretical plates to separate benzene from
gasoline, a paper on exactly how it's done might be around somewhere
Chemistry is our Covalent Bond
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len
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OK, thats good, if aliphatic nitro's are merely flamable, Im
happy to do distillation. Are there any references?
Proper separation of benzene from petrol would require many plates. Please note that I did not claim to have done this. I labeled the reactant
merely the 60-105 bp fraction. I clamed a better separation at the nitration stage, since this separates the aromatics from the aliphatic alkanes.
This allows me to deduce how much benzene was present in the 60-105 bp fraction of petrol. This I find at 4.3%, a pretty reasonable amount Please
note also this is in Australian winter petrol. Other countries have more stringent controls, and I hope they are fulfilled in reality.
Benzene in Australia is hard to purchase since its an S7 poison, and now a fairly rare chemical. The 4.3% content in petrol makes this an economic
source for it (and the Australian position concerning benzene fairly hypocritical) I believe, depending on what you want to do. To isolate it further
from the 60-105C fraction, of which it forms 43%, is quite an arduous task, as you point out. The other compounds its mixed with in that fraction all
have very similar boiling points. But if you need it for nitration - and this is often the next step from benzene to other aromatics - then that
separation need not be done. Most of the other components in the mixture do not get nitrated.
My position regarding our authorities is either
1) Benzene is a dangerous poison, put your money where your mouth is and make petrol benzene free
2) Its not so bad - a not very good carcinogen - then remove the S7 rating and all the hoopla
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Magpie
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len if you are especially worried about the alkenes I was thinking it should be possible to destroy them them by shaking the gasoline with either
KMnO4 in water (Baeyer test for unsaturation) or bromine in water. I believe these tests leave benzene intact.
The single most important condition for a successful synthesis is good mixing - Nicodem
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not_important
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Think I would have gone for a 72-92 range for a first benzene cut. After that the KMNO4 oxidation magpie suggests, whash with Na2CO3 to pull out
organic acids acids, dry, and redistil using a narrower cut for the benzene fraction.
After that you might try Br2 + Fe to make bromobenzene, instead of nitrating. Or you could steam distill the nitro layer, salt out the nitrobenzene -
even extract using your pet. ether cut, and distill for the final isolation.
You might have picked up a little toluene in your benzene cut, especially if there was any water in the gas. Dry the gasoline before the first
distillation. Hmmm ... you could apply a more vigorous KMNO4 oxidation to the crude nitrobenzene to convert any nitro-alkylbenzenes to benzoic acids,
remove with a alkaline wash.
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len
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Very interesting Magpie and 'not_important', thank you very much.
I dont know why I did not think of the KMnO4, indeed all the alkenes should be converted to acids and washed out. The KMnO4 is aqueous of course, so
I am not quite sure what sort of conditions are needed to get a good conversion of C5-C8 alkenes. There would be a problem using Br, I think its
reasonably soluble in organics amd might be hard to get rid of, plus I think the nitro is more on the path to other aromatics if synthesis is what you
are after. Br's plus is that its safer to distill, minus that I'd need a fume hood. Id like to try it anyway as a check on my results.
'Not important', I did not know water reduces separability of benzene and toluene. I dont believe it forms an azeotrope with either. Is that because
its boiling point lies between them (I havent heard of this), or is there another reason?
As for the cut, I agree with you in theory, but in practice, almost nothing came over between 85-100C anyway, which surprised me. As the last
distilate came over at 83-84 degrees the bulb temperature jumped almost immediately to 106C (and toluene). The lower range of my cut was actually 65C
and not 60C as I wrote, and there was some instability in the vigreux column I used in the separation. I could only vouch for the temperature in a
five degree range at best. So as far as that part is concerned I effectively did what you suggested.
About the steam distillation. That would be useful if there are dissolved non-volatiles in the nitrobenzene. The volatiles would all come along for
the ride and I might end up with what I started with. Are other nitro products from C5-C8 nitration equaly volatile with steam? What about the alkene
oxidation products? I have so far found very little information on the various branched compounds.
[Edited on 22-7-2006 by len]
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not_important
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Thanks, len.
benzene 91.1% : water 8.9% bp 69.3
toluene 80.4% : water 19.6% bp 84.1
Benzene was, and toluene is, used to force reactions through the azeotropic removale of water.
If you used Br2, you'd need an aq. bisulfite or thiosulfate wash to remove excess. Just that ArBr is less worrysome than ArNO2 to distill.
Steam distallation might decompose non-aromation nitro compuonds, and leave behind some of any dinitro aromatics. All the alkanes + alkenes would come
on over as well, which is why you'd need to dry and second distill.
Yeah, fractionating columns can be a hassle; vigreux usually isn't a problem but usually isn't always.
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len
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Thanks not_important, you obviously know quite a lot about it, pretty impressive to comunicate with someone like that.
Meanwhile I have done the reaction with KMnO4, so can answer some of my own questions, and the degree of unsaturation in petroleum ether (I used the
low bp fraction as I had none of the benzene fraction left).
I shook 10 ml of the 40-60bp fraction in the cold with dropwise addition of KMnO4 (1.4gms in 30 ml H2O acidified with 0.6ml H2SO4). It reacts with
unsaturateds in petroleum ether in the cold but requires vigorous shaking to mix the layers, a brown percipitate of MnO2 was formed, which surprised
me, I though in acidic solution Mn went all the way to Mn2+. Just the fumes of petroleum ether are enough to turn, the tip of an inserted pipette
with KMnO4 solution brown. Its a bit hard to tell the end point of the titration, because a fine layer of MnO2 percipitate sticks to the walls of the
flask. But when the liquid splashed against fresh walls by the shaking no longer showed a purple tinge, I knew all KMnO4 reacted and added more.
I was able to add 1.2 gms KMnO4 this way, which (assuming all alkenes react) gives the degree of unsaturation of the petroleum fraction as 14%. If
the same is true of the benzene fraction, this is quite abit higher than I hoped  .
More concerned now about an explosion during distilation.
I hope everyone wishing to try this realises that to distill petrol one does no use a bunsen burner. A heating mantle and quickfit flask/condenser
are required.
[Edited on 22-7-2006 by len]
[Edited on 22-7-2006 by len]
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not_important
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len - you have too little acid to take that fully to K2SO4 + MnSO4. Even twice as much weight of H2SO4 to KMnO4 will result in MnO2, roughly 1cc 98%
H2SO4 per gram KMnO4; the molar ration for full reaction is 3 H2SO4 : 2 KMnO4. But then it will oxidise alcohols and such as well.
Also any alcohols are likely to consume KMnO4 too, and they will end up in the low cut - azeotropes again.
I'm a bit surprised at the apparent amount of alkenes; might be interesting to titrate a ml with KMnO4 and another with bromine water. Also, as
another project, to oxidize 50 to 100 ml of raw petrol, and try to figure out the oxidation products - ketones and corboxylic acids of what chain
length.
Sounds as if you may need to restart the test. Measure out the sample, KMnO4 to take out alkene, and then dry the petrol, then fractionate and
nitrate.
To distill petrol? Just pour it into the bucket drop the big funnel over the top, and stack a few logs on the fire underneath.
And isn't Astralian winter blend about the same as they use in Canada during the summer? ;-)
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len
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Sorry, you are right not_important I did not do the stoichiometry. 1mol H+ per 1mol MnO4- is not enough to give Mn2+. However I think my degree of
unsaturation is still right (at least it cant be less than the already fairly high figure) since the MnO4- was used up, and I assumed it all went to
MnO2. The Mn couldnt reduce to a higher oxidation state than MnO2.
I think you are right, with the amount of alkenes there I have to repeat my experiment. Before that though, Ill distill the ArNO2 (with suitable
preliminaries) since I cant thrown it away after all the work Ive done. It'll take some time, come to think of it, since I dont want to expose the
indoors to toxic (carcinogenic?) nitrobenzene fumes and an explosion hazard, and I can't distill it outside lest the neighbours think this is on
direct assignment from bin Laden.
Your proposal to analyse the oxidation products sound interesting - but to separate the individual products Ill need and MS and GC wont I. Iff there
are N unsaturateds in petrol, then after oxidation I should get something like 3N products right?
I can just see the petrol distillation on a good fireplace. You wont need many logs to keep warm that night! Mind you some of the things I read on
this site made me think that someone might just try something like that. And then there will be trouble. I wish our winters were like Canadian
summers. Weve had a few -5C at night lately!
[Edited on 23-7-2006 by len]
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unionised
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All of these oxidations and manipulations will expose you to a lot of benzene and its unpleasant nitro derivatives. You have a nasty chance of blowing
yourself up with the distillation too. What's the point exactly?
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not_important
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Most certainly salvage the current batch of products. You've put some effort into this, might as well hve something out of it, and a bit of oil of
mirbane is nice to have around.
Most places I've read suggest that the alkenes are going to be C7 or smaller, meaning the largest product after acid-permanganate will be C6; any 1,2
alkenes will lose their terminal C as CO2. I'd be surprised if you ended up with more than 4 or 5 carboxylic acids and ... 5 ketones. While a GC
would make the task easier and a MS- -would bereal nice, i'd be it could be done without either. If there are as high of percentage of alkenes as you
quick test suggests, along with the degree of aromatics you seem to have found, petrol might be a useful source of reagents.
By the friend in Vancouver I talked a few weeks ago, it was running 3 to 5 C at night, but that was just past Mid-Summer so I'd expect it warmer now.
Suspected of being on assignment from Osama. Ah, the bygone innocent days of standing outside shining the laser up into the falling snow, firing up
the carbon arc furnace in the back yard during the same snow, floating bits of sodium in the runoff from rain, turning off all the streetlamps with a
lofted flash bomb, going down to the tips to blow up old furniture and snog...(sigh)
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len
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unionised - the point is to find out exactly how much benzene Im already being exposed to daily anyway.
not_important, I did see some bubbling, and was wondering what the hell that was. Thanks for that. Yes our Australian variety of petrol seems not as
boring as I had imagined. And I havent investigated the higher bp fractions yet. Mind you its probably coming out of our antiquated refineries. In
a more technologically advanced country petrol might turn out to be a lot more boring.
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not_important
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len - Australian petrol, like Canadian, has MMT in it if I've been told right. Another reason to hit the raw stuff with KMnO4 before starting on
fractionating.
Your comments on the local refineries may have something to do with the apparent high amount of unsaturatedness. Alkenes are a cheap way to boost
octane, within limits, so they may have increased the percentage of alkenes.
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len
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Sorry if this is a dumb question, what is MMT? I couldnt find it anywhere on the web.
Theres been a racket in Australian petrol recently, the petrol companies were getting around the 49c/l govt. excise by mixing in hydrocarbons from
paint thiners (toluene) and the like, which had no tax. So we now have the excise on all hydrocarbons. Wouldnt be surprised if the alkenes are a new
scheme
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not_important
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Not dumb, it's new to Aus (if they haven't dropped it) but the Canadians have been muttering over it for years
MMT :
http://en.wikipedia.org/wiki/Methylcyclopentadienyl_manganes...
http://www.globalleadnet.org/advocacy/initiatives/mmtfactshe...
http://www.sciencemag.org/cgi/content/summary/300/5621/926
I'm not fond of getting stuff with CO ligands in it on my person, a nice oxidising acid wash might be just the thing.
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unionised
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Dear God! will people never learn?
They argued for years about taking the lead out of petrol because it was a known neurotoxin, but they said it was"indispensible". I'm not saying that
any fuel is going to be entirely devoid of toxicity but why did they think this was a good idea? Sure, benzene isn't nice stuff, but at least it burns
to CO2 and water (ideally). Finely divided MnOx isn't a good idea.
Ironicly, alcohol has a relatively low toxicity (Any arguments and I will drink 100ml of it mixed in a pint of cola while inviting people to try the
same with other solvents) but is responsible for an awful lot of poisonings.
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len
Harmless
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Registered: 17-7-2006
Location: Australia
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Good God, the darn thing looks like nickel carbonyl! with a methyl pentadiene ring replacing one of the CO, and a manganese instead of a nickel
central atom. (I guess thats why its called manganese tricarbonyl ..)
Its description reads:
MMT is a viscous yellow liquid with an herbaceous odor
Couldnt find its bp or whether it decomposes, but my 120-150C bp fraction is light yellow and I was wondering why. Even if it does have a high bp I
feel it is likely to come over earlier, say with the xylenes. I dont know how much of it is added and what would be the test for it. Its use hasnt
attracted any attention in Australia at all, I guess the mass populace is largely ignorant here, and the petroleum companies like to keep it that way.
Meanwhile I have done one of the preliminaries, and nitrated the petroleum ether, which earlier gave 14% alkenes. The products showed only two
layers: aqueous and non-aqueous. No middle ring. There was plenty of frothing. I guess the lower bp alkenes are oxidised and do not add NO2. The
results are acids/ketones, which are water soluble, and CO2. This is good. I hope same holds for the 65-100C alkenes.
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not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
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If the acid strength and temperature are right you maybe can oxidise tertiary hydrogens. I assume the frothing was obvious NOx ?
Ah, the other thing that might do it - oxygenates in the gas such as ethanol?
MMT - the following sez 10 to 40 ppm in fuel, bp 231-something, photochemical short-lived. It could co-distill, dunno.
http://www.epa.gov/chemrtk/mthmntri/c14889tp.pdf
Interesting project you have, keep the updates coming.
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