thesmug
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Benzene vs toluene toxicity
This is my first time posting in this section, so correct me if this is in the wrong place, and sorry if it is too much of a beginner question.
Anyway, my question: I'm sure everyone knows benzene is toxic, and toluene isn't and for that reason toluene is used a lot more. If the two are (most
of the time) able to be used interchangeably, why is benzene so much more toxic than toluene?
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macckone
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Benzene is slightly less toxic. It is much more carcinogenic.
The oral LD50 of toluene is 636mg/kg
The oral LD50 of benzene is 930mg/kg
Toluene MSDS:
http://www.sciencelab.com/msds.php?msdsId=9927301
Benzene MSDS:
http://www.sciencelab.com/msds.php?msdsId=9927339
I assume that the benzene molecule is just the right size and shape
to disrupt DNA replication during mitosis. If you would do some
research you might find the exact answer. You obviously didn't
research this at all.
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thesmug
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Sorry about that, it came to me all the sudden when I was doing something so I didn't have time to research it but this is what the Wikipedia article
says:
| Quote: |
One way of understanding the carcinogenic effects of benzene is by examining the products of biological oxidation. Pure benzene, for example, oxidizes
in the body to produce an epoxide, benzene oxide, which is not excreted readily and can interact with DNA to produce harmful mutations.
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This led me to this report:
http://opus.bibliothek.uni-wuerzburg.de/files/5509/Lutz79.pd...
which sheds a lot more light on the subject. Sorry for not researching earlier.
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forgottenpassword
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I used to work with someone who worked for a paint manufactures several decades ago. He told me that people used to wash their hands in benzene at the
end of every day. None of them had cancer 20 years later.
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macckone
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Benzene is one of the few known rather than suspected carcinogens.
Not everyone is susceptible to every carcinogen.
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zed
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Back in my lab days, if I got something really odd or unknown on my hands, a quick rinse off with a little benzene was not unheard of. Not good for
you, and might cause aplastic anemia, if you were extremely unlucky, but think of all of the worse things out there.
That benzene could cause cancer was initially determined statistically. Folks that worked around it, showed a increased incidence of certain types of
cancer. If everyone who experienced benzene exposure, got the big C, America would be a giant ghost town.
Some gasolines have a high percentage of benzene. It's around.
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unionised
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OK,so the question was why is the toxicity benzene so different from toluene when they are both very similar- to the extent that they are often
interchangeable?
And your reply is "I assume ...You obviously didn't research this at all"
well, if you are going on an assumption then you too are guilty of failing to do the research.
And it's true that the carcinogenicity of benzene is due to epoxide formation.
So?
Toluene can form similar epoxides and the chemistry would be pretty similar so why isn't toluene a carcinogen?
Part of the reason is that the methyl group is an easy target for metabolism and it gets oxidised to benzyl alcohol and then benzoic acid.
Benzoic acid is relatively water soluble and is excreted more rapidly in the urine (partly after conjugation with glycine to form hippuric acid).
Another part of the explanation is that the methyl group activates the ring towards oxidation (by a different set of enzymes) to form cresols.
So the reason toluene is less carcinogenic is that there is an easier ring oxidation path and another excretion path which, between them ensure that
toluene is removed before it is epoxidized.
[Edited on 3-7-14 by unionised]
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Chemosynthesis
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Quote: Originally posted by unionised  |
Toluene can form similar epoxides and the chemistry would be pretty similar so why isn't toluene a carcinogen?
Part of the reason is that the methyl group is an easy target for metabolism and it gets oxidised to benzyl alcohol and then benzoic acid.
Benzoic acid is relatively water soluble and is excreted more rapidly in the urine (partly after conjugation with glycine to form hippuric acid).
Another part of the explanation is that the methyl group activates the ring towards oxidation (by a different set of enzymes) to form cresols.
So the reason toluene is less carcinogenic is that there is an easier ring oxidation path and another excretion path which, between them ensure that
toluene is removed before it is epoxidized.
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Excellent points, but it should also be noted that the derivatization of benzene and metabolites also must affect binding affinities and ability to
function as a substrate within cell signaling networks.
Even small changes in molecular symmetry or binding topologies can alter the efficacy of the ligand upon a receptor, even reverse the effects in some
pharmacological instances (inverse agonism).
Here is a fairly recent review since the last article I saw posted in thread, though good, was from 40 years ago.
Carcinogenesis (2011)
doi: 10.1093/carcin/bgr297
http://carcin.oxfordjournals.org/content/early/2012/01/17/ca...
[Edited on 14-7-2014 by Chemosynthesis]
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CuReUS
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| Quote: | | Benzoic acid is relatively water soluble and is excreted more rapidly in the urine (partly after conjugation with glycine to form hippuric acid).
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it would be wrong to say that benzoic acid is soluble in water (solubility at 40'C- 5.51 g/L)
but it might become more soluble if it conjugates with glycine
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Etaoin Shrdlu
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5.51 g/L is pretty soluble, considering. How many grams of toluene are you expecting to ingest?
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macckone
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Benzoic acid will combine with sodium in a carbonate buffered system.
Blood is such a system. Sodium benzoate is very soluble and
Will be excreted.
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Chemosynthesis
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It can also be glucuronidated, which is also a biotransformation technique to increase hydrophilicity and excretion.
See PMID:13406041.
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unionised
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| Quote: Originally posted by CuReUS | | Quote: | | Benzoic acid is relatively water soluble and is excreted more rapidly in the urine (partly after conjugation with glycine to form hippuric acid).
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it would be wrong to say that benzoic acid is soluble in water (solubility at 40'C- 5.51 g/L)
but it might become more soluble if it conjugates with glycine |
That's roughly ten times more soluble than the toluene it was made from.
So what I said- that it's relatively soluble- is right.
Also, I'm fairly sure that hippuric acid is less soluble than benzoic acid, but I'd need to check.
[Edited on 24-1-15 by unionised]
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Etaoin Shrdlu
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The solubility of hippuric acids climbs rapidly with temperature. I am finding it difficult to locate any specific numbers, though. Everyone seems to
favor "dissolves readily in hot water."
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CuReUS
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| Quote: Originally posted by Etaoin Shrdlu | | The solubility of hippuric acids climbs rapidly with temperature. I am finding it difficult to locate any specific numbers, though
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Solubility in water: 1g/250 mL cold water. Other solubilities: freely soluble in hot water, 1g/100mL chloroform - 1g/400mL ether, 1g/60mL amyl
alcohol, freely soluble in hot ether, pract.insoluble in benzene, cs2 and petr.ether
http://www.fishersci.com/ecomm/servlet/fsproductdetail_10652...
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Etaoin Shrdlu
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I'm looking for data at higher temperatures...
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