# Why is isopropyl alcohol (isopropanol) used in rubbing alcohol instead of 'regular' propanol?

Is isopropanol (or 2-propanol) a better solvent than ordinary propanol (or n-propanol, or 1-propanol)?

This is strongly implied, from what I have read, but I can't seem to find a place that distinctly says so....

Several places have said that mixing well with a wide range of substances makes it a better germ-killer...

Also, is it slightly less volatile than 1-propanol? If so, does this make it more useful?

• Imagine water as a ship, holding an alcohol molecule by OH as an anchor, which tries by its lipophilic end to attach to an eventually lipophilic object. On which alkohol would you put your bet ? Additionally – but this is more valid for longer chain alkohols – linear chains of n-alkohols bind their molecules together, forming colloidial micelles. Try e.g. replacing isoamylalcohol ( $\ce{C5}$ ) for extraction from water by n-amylalkohol - there is big visual difference. Isoamylalcohol would form rather clear, quickly separating mixture. n-amylalcohol would form opaque, stable emulsion. – Poutnik Feb 16 at 9:37
• Also isopropyl alcohol became a kind of reference for reasons negligible at small desk scale. One is cost, as for it can be sold at its chemical and market price with no needing of making it disgusting, as it would be for ethanol. Another one is flammability. It makes a big difference if instead of one bottle you think of shipping and entire chemical plant. And so on. If one has to clean microscopy slide, or disinfect hands, there are sure differences, but of no practical impact. – Alchimista Feb 16 at 10:15
• I suspect one element is also that propanols are made industrially by hydration of propylene, and isopropanol is from propylene is simpler (ie less expensive) to make because the markovnikov addition favors that position. – Andrew Feb 16 at 13:54

Let's compare the two compounds.

Solubility: Both compounds are miscible with water, so there is no difference. With the straight chain, 1-propanol may be slightly more lipophilic, and thus better able to act as a surfactant. However, 1-propanol is a really poor surfactant.

Volatility: Isopropanol has a lower boiling point (82.5 degrees C) than 1-propanol (97 degrees C), so isopropanol should evaporate more quickly. This is an important feature when cleaning.

Flammability: Both compounds have similar flammability.

Safety: Both compounds are hazardous to humans, but isopropanol is less so. Below are the three GHS hazard statements for each compound:

1-propanol

• Highly flammable liquid and vapor
• Causes serious eye damage
• May cause drowsiness or dizziness

Isopropanol

• Highly flammable liquid and vapor
• Causes serious eye irritation
• May cause respiratory irritation

While both are highly flammable, 1-propanol poses more serious risks for eye exposure (damage is worse than irritation). 1-Propanol also can also cause drowsiness or dizziness, while isopropanol does not.

Cost: All of these are well and good, but the likely reason that isopropanol was chosen was cost and availability. Isopropanol is easily obtained by direct hydration of 1-propene using water and acid, while 1-propanol requires hydroformylation of ethene via the oxo process. Isopropanol can also be produced by the reduction of acetone, which is a byproduct of several other chemical syntheses (for example, phenol). I'm not going to provide cost data because price is dependent on supplier, purchaser, and location. However, for equivalent grade, isopropanol should be cheaper than 1-propanol.