[davon806]

I have done several experiments on last week.The purpose of the experiment is to test the reactivity of the alkanes(combustion,substitution reaction,etc),using cyclohexane as an example.
 My book said the reason of using cyclohexane is because it is cheaper and less hazardous to use than hexane.Why it is less hazardous than hexane?
 Thx

[discodermolide]

Have a look at these pages
hexane   http://en.wikipedia.org/wiki/Hexane

and cyclohexane  http://en.wikipedia.org/wiki/Cyclohexane

and see if you can tell me why cyclohexane is less hazardous.

[davon806]

Yes,I have looked up these pages before.At the beginning,I guess it is because the b.p. of cyclohexane is higher than that of hexane.Thus hexane is more volatile than cyclohexane and hence,it is more harmful.
However,heptane and octane have a higher boiling point than hexane and cyclohexane.That means they are less volatile than cyclohexane.According to my assumption,heptane and octane should be used instead of cyclohexane.I wonder if there are some other metabolic reactions take place between hexane(or other liquid straight-chain and branched alkanes) and body cells but not in cyclohexane and body cells so that cyclohexane is chosen instead of other alkanes?
Thx

[discodermolide]

What about the flame point and flash points of these compounds? What does that tell you?

[davon806]

Yes,from wiki,the flash point of cyclohexane is -20°C,the flash point of hexane is -26°C.
The flash point is just related to the volatility of the liquid.
Under the same condition,the more volatile the liquid,the lower the flash point.
However in this case,I don't think flash point of the compounds will affect the choice of sample to be tested.
As the difference between the size of flash point is too small,they will burn immediately if there is a fire in room condition.
Moreover,as mentioned in the above post,I don't think the volatility of the liquid is the main reason of choosing cyclohexane to be the sample instead of hexane,as there are another compounds with lower volatility can be used.
Any biochemical explanation could account for this?(Or others?)

[fledarmus]

You might also look at these:

MSDS cyclohexane http://www.sciencelab.com/msds.php?msdsId=9927145

MSDS hexane http://www.sciencelab.com/msds.php?msdsId=9927187

You will note that by one authority, hexane is ranked as a higher health hazard (2) than cyclohexane (1). I don't see a lot different in the data except for the lethal concentration, which is twice as high in cyclohexane than in hexane. Both are still pretty high however. The exposure limits for cyclohexane are actually set slightly lower than for hexane. Possibly there is some concern about mutagenicity?

I know that at one company where I previously worked, we were asked to replace hexane with heptane in all possible lab applications, even though heptane was nearly twice the cost. The reasoning for that change was never clearly articulated either, except that it was for "health reasons". I would like to see the comparative data too, so if you find an answer, please post it!

[DrCMS]

Hexane is much more hazardous to people than cyclohexane or heptane.  The OSHA workplace exposure level for hexane is just way too high.

The UK values are:

n-hexane - 8hr TWA - 20ppm
cyclohexane - 8hr TWA - 100ppm
n-heptane - 8hr TWA - 500ppm

Hexane is a known human neurotoxin

[davon806]

Thx,but why heptane is more expensive than hexane?

[fledarmus]

Hexane is a known human neurotoxin

Heptane is also a known human neurotoxin. I'm not arguing with you, just asking for information - do you know any studies that show directly the differences in toxicity between heptane and hexane? The last time I took an interest (some ten years ago now), the best I could find was that they knew hexane was toxic, but since nobody had ever really studied heptane, it was still listed as "suspected" and there was very little toxicity data available. Oddly enough, that seemed to make it easier to get and dispose of.

[DrCMS]

As far as I know there is a metabolic pathway that hexane can interact with that heptane can not.