Needing some mineral oil with a boiling point of 400±20°C I assumed that I could obtain this by fractional distillation. My first attempt was to
use some old (>20 yrs) Albertson's USP that I had on hand. Using a 200mm Vigreux column I did manage to distill off some of the light ends until
the distillate temperature reached about 310°C. I didn't want to go any higher fearing I might damage my mantle. Also the pot liquid and the
condensate had taken on a translucent yellow color.
My next attempt was to obtain some fresh mineral USP oil from Target where their website said it was "extra heavy." Here I used vacuum fractionation
to keep the temperature down. My pressure was 0-0.5 mmHg and the distillate bp was 160°C. But the Claisen adapter and the lower 3rd of the column
were flooded so this data may not be of any value.
The mineral oil seems "heavy," ie, viscous, so I think I'll just use it "as is." It is dirt cheap at $2/pint.
You can see my distillation set-up below. The Claisen allowed use of an ebulliator, necessary because of severe bumping. Under the Al foil are
fiberglass blankets.
Deathunter88 - 12-10-2015 at 06:33
Mineral oil turns yellow after heating to 200 degrees Celsius for me too. This is not some dirt cheap mineral oil, this is analytical reagent grade
lab stuff. No idea why though. m1tanker78 - 12-10-2015 at 07:35
Same here, I can always count on mineral oil turning yellow, orange-brown or even black depending on how much heat I apply and for how long. If you
leave the 'burnt' oil in a sep funnel or any other container for a few days, undistrurbed, the colored matter will settle at the bottom and yield
crystal clear oil above it. Most of the gunk can be flushed from the sep funnel or carefully removed from a beaker by decanting or syphoning.
Magpie, why did you run a distillation if you only wanted the higher boiling fraction? I routinely prepare batches of mineral oil for storing sodium.
Part of that entails removing traces of water and other low-boiling stuff that may be in there. I heat the snot out of the batch (well beyond the
smoke point) and then do the procedure I outlined in the above paragraph.
Were you wanting to collect the lower boiling fractions for analysis?Magpie - 12-10-2015 at 08:12
The mineral oil seems "heavy," ie, viscous, so I think I'll just use it "as is."
Upon reflection I'm going to have to do better at isolating a fraction boiling at 400±20°C. I need this fraction as a diluent for making 2-octanol.
During the synthesis the octanol is distilled off. I don't want any light minera oil ends contaminating it.
Thanks to both of you for the input on yellowing. And thank you tank for your method on obtaining a heavy fraction. On my initial attempt with the
Albertson's oil I definitely accomplished some separation as it was evident from the difference in viscosity of the two fractions.
