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Author: Subject: Are hexane and petroleum ether interchangeable?
Cou
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[*] posted on 18-11-2020 at 16:33
Are hexane and petroleum ether interchangeable?


a common introductory grignard reaction lab is preparation of triphenylmethanol with bromobenzene. THe coupling side product is biphenyl, which is removed with petroleum ether.

petroleum ether is mainly a mixture of aliphatic pentanes and hexanes. I already have hexane, can't I use that? Is there any reason why lab procedures want you to use petroleum ether instead?

edit: i found a procedure that uses hexane to extract biphenyl http://web.mst.edu/~tbone/Subjects/TBone/chem228/grignard.pd...

[Edited on 11-19-2020 by Cou]




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[*] posted on 18-11-2020 at 16:49


Petroleum ether is a mixture, and is generally cheaper. That's about it.



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[*] posted on 18-11-2020 at 17:53


Weird, because the amazon listings for hexane are cheaper than petroleum ether.



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[*] posted on 19-11-2020 at 02:34


Where I live, hexane also is cheaper. Pentane is more expensive. If I want to buy n-hexane, then I pay a premium price, but simply buying hexane (mix of isomers) is dirt-cheap.



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[*] posted on 19-11-2020 at 02:45


How useful are hexanes, pet ether and similar hydrocarbons in biphasic extractions compared to toluene? They boil lower and are immiscible with water, but do they have similar solvent properties?

They used barrels of gasoline as a solvent in a documentary regarding Colombian's most important export goods, so it must not be too terrible?
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[*] posted on 19-11-2020 at 02:50


It's cheap, that's why. It also depends on the solute itself. If you could narrow down the group of compounds to dissolve, maybe we could come up with an answer?
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[*] posted on 19-11-2020 at 03:59


Whenever possible I use medicinal petrolether, I've bought 10 L barrel of it not more than 1 year ago. It is very cheap in my country (10 L for circa 40 EUR) and it is always hydrogenated so no alkenes present. Sometimes I redistill it through column when I need some fractions boiling at some temperature range (when using it in Dean-Stark trap apparatus so later I can separate the petrolether fraction from the dehydrated organic compound by distillation). For extractions no need to bother to redistill its fractions. I have also pure n-pentane, n-hexane, n-heptane (circa 20 EUR per 1 L bottle of each one) but medicinal petrolether was most of times OK for me and it was circa 5 times cheaper.



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[*] posted on 19-11-2020 at 06:53


Don't buy solvents on Amazon, period. Overpriced and not representative of true prices. Coleman fuel is petroleum ether, might be worth distilling first though.
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[*] posted on 19-11-2020 at 08:15


Quote: Originally posted by Fyndium  
How useful are hexanes, pet ether and similar hydrocarbons in biphasic extractions compared to toluene? They boil lower and are immiscible with water, but do they have similar solvent properties?


Toluene is a pretty good solvent for a lot of things- petroleum ether and similar hydrocarbons are poor solvents for anything that's not completely non-polar.

I say this based on the number of things that I've recrystallized from toluene by adding petroleum ether as an anti-solvent.




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[*] posted on 19-11-2020 at 13:29


For example, salicylic acid is soluble in toluene, but not in hexane.



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[*] posted on 19-11-2020 at 13:43


I see. There is a reason why hexane and pet's aren't used as solvents in any synthesis writeups despite their low cost and ease of availability.

Good thing I just purified a lot of toluene from a canister of paint thinner.
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[*] posted on 19-11-2020 at 14:24


Hexanes or petroleum ether is most commonly used for column chromatography, where it would be paired with a more polar solvent such as DCM or ethyl acetate to make a mixture tuned to effectively separate whatever mixture you have on hand. Other than that, it's a great degreaser!



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[*] posted on 19-11-2020 at 14:37


Also, it's useful as an antisolvent because of its low boiling point. Use it to wash your precipitate, and it dries quickly. Put a test tube of a solution in a larger container of pentane, and let the crystals grow by vapour diffusion.

From experience, I know that piperine, benzoic acid, and triphenylmethanol are almost completely insoluble in pet ether. Substituted arene metal carbonyl complexes (such as RC6H5-Cr(CO)3, for example) *are* soluble in light hydrocarbon solvents.




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[*] posted on 21-11-2020 at 09:56


To answer the original question, hexanes can almost always replace petroleum ether. The only time this can become a problem is when the low boiling pet ether is used for crystallization of low melting compounds. Switching to hexanes or higher boiling pet ether fractions will often result in "oiling out" of the product.

Years ago various hydrocarbon solvents were sold under the "Skellysolve" name and maybe still are. Here is some information regarding these solvents some of which are referred to as petroleum ether. I cannot remember where I originally found this information.

Skellysolve –Petroleum ether solvents

A: Essentially n-pentane, bp 28-30
B. Essentially n-hexane, bp 60-68
C. Essentially n-heptane, bp 90-100
D. Mixed heptanes, bp 75-115
E. Mixed octanes, bp 100-140
F. Petroleum ether, bp 30-60
G. Petroleum ether, bp 40-75
H. Mix of hexanes and heptanes, bp 69-96
L. Essentially octanes, bp 95-127

Purification method.

Shake several times with conc. H2SO4, then 10% H2SO4 and conc KMnO4 until permanganate color persists. This removes unsaturated and aromatic hydrocarbons. Wash with water, sodium carbonate then water. Dry over CaCl2 or Na2SO4 and distill. Filter through activated alumina to remove epoxides.

Simple distillation of Coleman fuel will provide the fractions listed above, especially E - L. I have done this several times.

Hope this is useful.

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[*] posted on 22-11-2020 at 21:46


There is a video of a similar procedure with gasoline on extractions & ire channel.

https://www.youtube.com/watch?v=FP5JaSH4ysA
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