As I'm preparing to do my very first extraction, I decided I wanted to make doubly sure of the chemicals I'll be using. I'm confident that my distilled water, salt, citric acid, and sodium hydroxide are all food-grade. I was disappointed in the results of the evap tests I did on my solvents though.

My Bestine left a thin, tenacious, waxy white film, that proved to be very heat-stable and chemical resistant (it was hard cleaning it off my watch glass). My hardware store acetone left an oily residue with a strong odor of petroleum grease, like what you'd pack wheel bearings with. Yuck.

I would surmise that the impurities came from the manufacturing and packaging equipment. The acetone likely pulled grease out of the pumps and valves, and the Bestine could very well have leached nitrile or polyacrylate (or even PTFE) out of the fittings. Regardless, I didn't want any of those contanimants anywhere near something that would be going into my body.

So, being the nerd that I am, I decided to pull out my distillation glassware set and clean them up!

Side note: one thing my distillation kit lacked was boiling stones. Actual boiling stones are expensive, but I discovered that these aquarium filter cartridges contain a baggie's worth of nice, clean pearls of sintered glass. I cut a filter open to get the pearls out, and they make fantastic boiling stones for organic solvents. (I haven't tested them for resistance to acids or bases yet.) They're porous so they're single-use only, and 8-10 pearls was fine for a 1L round bottom flask.




The Acetone

I did the acetone first, heating in a water bath via a simple distillation. In hindsight, I ran this first distillation way too fast, and likely carried over a lot of impurity. It was good enough to get my glassware properly clean though, so for the second round I installed the fractionating (Vigreux) column and distilled at a much more reasonable pace.

I processed a total of 3 liters of acetone in three batches. My thermometer appears to be very accurate, as the vapor held 56°C through the entire distillation. The resulting acetone appears to be very pure, perhaps with just a bit of absorbed water. When each batch got down to the last 100ml or so, I noticed it wasn't evaporating as clean any more. It had a bit more water, and although it exaporated clean, it produced some of that icky "grease" smell for a few minutes after the acetone was gone.

Even down to the last 30-40ml when I stopped collecting distillate, the distillation temperature remained steady. The remaining liquid in the boiling flask went into my Waste Organics can, and I added another liter of acetone and proceeded with the next batch. For the final batch, I evaporated off these dregs; it contained a lot of acetone plus maybe a ml or two of water, which eventually dried down to leave a layer of foul-smelling grease in my watch glass. The distilled acetone evaporates very, very clean!

The Bestine

Distilling the Bestine was a bit more interesting. I did a simple distillation here, really wish I had fractionated it but oh well. I heated this in a sand bath (actually copper-coated BBs) anticipating higher temperatures than I got; in hindsight, a water bath would have been just fine.

The first fraction of Bestine distilled over at almost exactly 69°C: the boiling point of hexane. Out of a liter of Bestine, I probably collected 50ml of presumably hexane, which went into my Waste Organics can. I started collecting with the next fraction at 79°C, which, assuming it was indeed heptane, would have been 2,2-Dimethylpentane. The temperature then rose stepwise until it reached almost exactly 92°C and stabilized.

I probably distilled over about 90% of the Bestine at that 92°C; The temperature never rose higher than that. I never did reach the 98.4°C boiling point of n-Heptane, and I stopped collecting when I got down to the last 50ml or so, still distilling at 92°C.

Now, I'm not entirely sure what I have in my bottle labeled "Distilled Bestine". 3-Methylhexane boils at 91.6°C and 3-Ethylpentane boils at 93.3°C, but the SDS for Bestine specifically lists its composition as 100% n-heptane. Perhaps I was actually dealing with some sort of azeotropic mixture of n-heptane and other light hydrocarbons? Or heck, maybe I had the thermometer positioned wrong in the distillation head. The acetone temperature was spot-on though...

Anyway, whatever it is, I'm very pleased with how clean my distilled Bestine evaporates, and I'll be comfortable extracting with this. I still have another quart of it (two, actually) so I'm debating putting another liter under the Vigreux column and see what happens.

So that's my book report! Thoughts? Has anyone else analyzed their NPS, and Bestine in particular, to this degree?

PTFE is resistant to most chemicals, so it is unlikely to be found in Bestine.


Assuming you heat with a magnetic hotplate, do not distill to dryness and the internal temperature never exceeds 260°C, a regular magnetic stir bar (oval if your boiling flask is round-bottom, straight if flat-bottom) is a good reusable substitute for boiling stones.


I did notice a large 92°C fraction in my batch and threw it away. The rest was mostly 96°C and it did reach 98°C in the end.

Cheap lab thermometers are rarely accurate. They can take a while to be heated up by solvent vapors and begin showing the right temperature. Their accuracy varies depending on the temperature range. They can be heated (radiant heat) by the glassware that surrounds them. Measurements within 2°C are usually considered within the margin of error.

By the way, I don't think I'll ever buy Bestine again. It has served me well, but these days it is easy to find pure n-Heptane.

Sadly, a good heating mantle is outside my price range these days. If I feel like I'll get $100 worth of use out of it then I'll totally get one, until then I like the versatility of an inexpensive electric hot plate.

Oddly enough, I don't remember ever using a stir bar as a boiling aid in the O-chem lab. Dunno why, maybe it was just because the volumes we were distilling were too small for that.




I considered that, but like I said, this cheap thermometer appears to be remarkably accurate, far more so than my other cheap thermometer. I tested it multiple times against several other thermometers I own, and it appears to be as accurate as my best digital thermometer. It reads boiling water at 99.8°C and condensing acetone at 56°C. Like I said, either this Bestine is not actually pure n-heptane, or I had the thermometer improperly positioned in the distillation head. If I do distill another liter of Bestine, I'll use the column and watch the thermometer placement and report back.




Yeah, I agree, in hindsight I should have just spent the extra money to order lab-grade heptane. If I ever run out of Bestine (I have three quarts of it) I'll absolutely do that.

A stir bar is a suboptimal choice - it does not work very well under vacuum, or with high-bumping liquids like sulfuric acid. In a lot of cases it is sufficient, however.


I can recommend flat-bottom, round flasks that can stand directly on a hot plate. You will not want to pull strong vacuum on large ones, but for simple distillations they work just fine.

...For round-bottom flasks, a convenient (far more convenient than oil or sand baths) option is a series of aluminum blocks like the one below. They are best used on round (not square) hotplates, which they are designed to grip (so they will not slide around). There also exist modular variants with inserts for various flask sizes. The small holes are for hotplate-connected thermometers. They are made of aluminum, so magnetic stirring still works. The only downside of these blocks is that that flasks should not be left in them when cooling down. They can be quite expensive but used ones do show up from time to time; they can serve a lifetime unless you spill something corrosive on them.