[zim_lab]

we are having a problem with glassware becoming stained by used diesel engine oil products - these are often heavily contaminated with soot, and appear black.  In capilary tubes, you can only rely on chemical cleaning.

Recommendations vary from using toluene or xylene.  It would seem both appear similar in nature, but before we buy these, can anyone comment on the follwing questions:

1. the cleansing ability, or differences in ability of these two (i.e which is the more "aggressive" of the two?

2. We have also been refered to use Tetrahyrafuran - and again, where does this lie in terms of aggressivness, in relation to toluene and xylene

3. any other recommedations or tips on this kind of cleaning?

Many thanks

[Sam (NG)]

None of these chemicals can be classified as "aggressive" in terms of their cleaning ability as they do not have a negative impact on glassware.  The cleaning ability of toluene, xylene or THF is entirely dependent on the polarity of the molecules that you are trying to remove.

They are simply organic solvents of differing polarities, and each will best dissolve compounds most closely related to their own polarity.

I'm assuming that you've tried cleaning your glassware by soaking it in a saturated solution of potassium hydroxide in iPrOH:Water 10:1 (commonly called base bath)?

[zim_lab]

thanks for the reply, and the explaination of the solvents - makes sense.  I will try the potassium hydroxide.   If I may ask a few further questions?

1. is it feasible or safe to mix the 3 solvents I mentioned to allow each to "attach" to whatever polarity suits best?
2. if not I assume each one can be used to same effect, just a longer process
3. for used oils from engines - is there a more suitable solvent than any of the 3 I mentioned?

Many thanks again for the assistance

[Sam (NG)]

Mixing the three solvents will result in a solution with a polarity different from the original solvents (and so with unique properties in terms of what it can dissolve), but not necessarily able to dissolve all of the things that each of the solvents can dissolve separately.

For hydrocarbon oils, the base bath might not work very well.

My suggestion would be to try something like Petroleum Ether (Pick a boiling range: 40-60, 60-80) or the ones that have already been suggested.

[Don Shelly]

If traditional glassware cleaning methods don't work, try either hexane (polarity index 0) or bake in a muffle furnace at 400 C for four hours.

Don

[srochat]

When 'usual' solvents such as water, acetone, methanol or dichloromethane don't work at properly cleaning my glassware, I leave it in diluted nitric acid overnight, then it looks as brand new... just need to be careful with the acid!