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I recently bought a product called Prestone De-Icer for Windows and Wipers which claimed to contain Methanol. I was puzzled when using it to note that it did not smell much like Methanol so I looked up the SDS for the product which stated that it contained 50-100% Methanol, 1-10% Ethylene Glycol & 1-5% Carbon Dioxide.

Out of curiosity I decided to carry out a fractional distillation to see just what the constituents were and was puzzled to see the thermometer shoot up through the Methanol BP at 66C mark without stopping and the first stop was about 76C which would suggest Carbon Tetrachloride. It then stopped at about the 79C mark which would indicate Ethanol and then carried on up to about 98C which would suggest Heptane.

So my question is this - Is there something wrong with my methodology or interpretation of what I am seeing or is it possible that the manufacturer is in error in the SDS. The latter would be very serious if true since the SDS would be the resource used should it be suspected that someone has been poisoned by the product.

My instinct is to suspect that I am doing something wrong but for the life of me I can't see what it could be. The thermometers I have used ( three in all ) are calibrated to 0.1 degree and were one mercury, one alcohol and one digital and all agreed to within 0.4C max deviation.

I should point out that I am not a professional chemist, just an amateur who has taken the hobby up in retirement so I am quite prepared to be told that I have got it wrong. It's all part of learning in my opinion.

Here is a link to the SDS - http://www.homedepot.com/catalog/pdfImages/2c/2cd5847a-9dd0-4cf0-a5ef-83efbd532f4c.pdf

I am including a photo of the setup I am using to do the separation. The Vigreaux column is actually wrapped in aluminium foil.

enter image description here

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    $\begingroup$ I would be stunned if there was carbon tet in antifreeze. It's very toxic and dangerous to the environment. $\endgroup$ – jerepierre Feb 4 '16 at 18:44
  • $\begingroup$ I can't imagine heptane either. In the rain heptane would separate out and make a mess on the windscreen. $\endgroup$ – MaxW Feb 5 '16 at 2:22
  • $\begingroup$ The product is for de-icing frozen windscreens so all it has to do is lower the freezing point of water so the ice melts. $\endgroup$ – Kintekobo Feb 5 '16 at 7:52
  • $\begingroup$ My question boils down to this - if you have a substance which is at least 50% Methanol, then when heated the thermometer at the top of the Vigreaux column should rise to the BP temperature and remain steady until most of the Methanol has boiled off, then carry on up to the next highest product. If it is not stopping at the BP of Methanol is there anything that can explain this other than the absence of Methanol? $\endgroup$ – Kintekobo Feb 5 '16 at 8:05
  • $\begingroup$ Maybe they use ethanol or isopropanol as a safer alternative to methanol and haven't updated the SDS? Isopropanol has a characteristic (pleasant) smell easy to recognise. Also, it should be an aqueous solution which explains the $\mathrm {98 \ ^\circ C}$ fraction. $\endgroup$ – K_P Feb 6 '16 at 1:54
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Best Answer is this: Your observations are consistent with the SDS for the reasons below.

A couple of issues see below.

  1. Fractional distillation is much more complicated than you suppose. You have no way to control reflux ratio, (amount of distillate vs reflux) which right away will limit your separation. The column is not insulated or temperature controlled.

  2. Vigreux columns are good for distilling one component from non-volatiles, but are not made for fractional distillations. You will need a much more efficient column, the cheapest choice being a vacuum jacketed Hempel column with some sort of packing, ie Raschig rings.

  3. With the equipment you are using, a range of 10 C between ideal boiling points would be considered normal, you will not see the sharp cut offs you are expecting.

  4. The first component is likely methanol, and the boiling point range you are seeing is due to the above reasons.

  5. Ethylene glycol does not boil to almost 200 C, when you end the distillation, is there any liquid left in the distilling flask?

  6. As far as I could quickly check, methanol and ethylene glycol do not form an azeotrope, but the tables I checked were on Wikipedia and not thorough, you might want to check that. The formation of an azeotrope definitely explains the observations especially if it boils in the range of 98C +/- 20 C

  7. Not sure on the exact conditions or if the MSDS is wrong, but it is conceivable dimethoxyethane (dimethyl glycol) formed or was the original constituent, this has a boiling point of 85 C, it could have even formed in the distilling flask depending on conditions.

  8. Note the MSDS or SDSs are they are now called are not complete, and there are usually other minor constituents that might appear and could possible catalyze the formation of dimethoxyethane, assuming the SDS was correct in the first place.

  9. Distillation is not the appropriate method here, GC-MS would be the way to go.

Hope that helps! I suggest you purchase Handbook of Laboratory Distillation, it is the fundamental text for distillation in theory and practice, the price is well worth it.

In conclusion your observations could be explained by: azeotrope formation, incorrect SDS, formation of dimethoxyethane, and incorrect set up.

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  • $\begingroup$ A very comprehensive answer. I'm not sure that I fully understand all of it but it has given me some useful insights. The book recommendation is a good starting point. Thanks again. $\endgroup$ – Kintekobo Dec 4 '16 at 8:07

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