# Is 99% Isopropyl Alcohol sold in stores really 99%?

My understanding is that an azeotropic mixture of isopropanol and water is 91%. This makes sense as to why there are so many brands of rubbing alcohol sold at 91%. There are also some sold as 99%, which as far as I know is impossible to reach through distillation. Is there another process that the manufacturers are using to reach 99%, or is it just marketing lies?

• Most brands I find on google sell it at 99.9% even (for cleaning purposes). I checked a few data sheets, inconclusive. The density they give is very close to that on wikipedia (0.786g/ml), whatever that means. Common sense says they sell the azeotrope, but then this stuff is not made via fermentation and distillation. :-) – Karl Mar 19 at 22:14
• Any decent chemical supplier certainly has >91% isopropyl available. Not surprisingly, higher purity costs more, but at least one supplier (a common one, no reason to name) has 99.7% pure isopropyl listed. – Jon Custer Mar 19 at 22:18
• A few different concentrations of isopropyl alcohol are sold as rubbing alcohol. The highest I have seen is 90% – blacksmith37 Mar 20 at 0:20
• There are plenty of ways other than distillation to make pure isopropanol (or other alcohols). And most azeotropes can be broken by adding a suitable third substance. – matt_black Mar 20 at 0:26

The isopropanol can be synthesized without water by hydrogenation of acetone, or water could be removed from the azeotrope using a desiccant. Membrane separation is also efficient. At home, table salt ($$\ce{NaCl}$$) can be used to remove some water.