# Why are all 3 of propane, butane and isobutane used in deodorant sprays?

Here are the back ingredient labels of a few popular commercial alcohol-based deodorant sprays.

As one can clearly see, they all have many things in common, but the 3 which are of importance in lieu of this question are-

• Butane
• Isobutane
• Propane

After a quick search on the internet, one can find all 3 have the same common function i.e. acting as a propellant to give a perfect aerosol spray.

My questions lies, why are all 3 of them used together when they have the same function? There are also many deodorant sprays that use only butane as the propellant. Is it something related to pressure factors or its ability to be used in different conditions(hot/cold weather)?

If there's no such strong reason behind it, and if cost effectiveness isn't harmed either, then why not just use one of the 3? And if so, what would be the best of the 3 alternatives?

Image source: Google Images 1 2 3 4

• A mixture can easily be cheaper than any of its ingredients. – Ivan Neretin Jul 24 '20 at 7:40
• Well that's just propane-butane, or LPG! Nothing mysterious, just a fraction of petroleum... It's like ask why is gasoline not one compound. – Mithoron Jul 25 '20 at 0:57
• @Mithoron It's nothing about being mysterious ;) I just wanted to know if there's any special reason for using 3 different things that do the same function, and if we can do it by just one of them, cause there are such deos that use butane only. If one asks why gasoline isn't one, one could ask why water isn't one either?! – Sir Arthur7 Jul 25 '20 at 9:11

Bu/iBu or Bu/iBu/Pr mixtures are easier/cheaper to get instead of pure components as Ivan says, as there is extra effort for their separation, not the extra effort for their mixing.

Butane(Bu)/isobutane(iBu)/propane(Pr) boiling points are $$\pu{0 ^\circ C}$$, $$\pu{-11 ^\circ C}$$ , $$\pu{-33 ^\circ C}$$ respectively. Real boiling points would be higher than boiling points of pure hydrocarbon mixture, as deodorants are solution of active components in volatile liquid hydrocarbons, what increases the boiling point.

Propane (and isobutane too to a lesser extent) shifts usability toward lower temperatures, similar as Pr/Bu mixture of liquefied gas fuel cartridges for outdoor usage. Butane itself does not work well around $$\pu{0 ^\circ C}$$ either as propelent either as fuel, as it has not enough pressure to overcome the external one.

The goal is to provide the vapour pressure within the given pressure range for the given operational temperature range. Pure compounds have usually too low vapour pressure at the minimal temperature or too high vapour pressure at the maximal temperature.

Another reason is the control of evaporation rate of the solvent when it is being sprayed out. Different compositions of deodorant matrix may prefer different rates of hydrocarbon evaporation and different related cooling effect.

• I agree that "there is extra effort for their separation, not extra effort for their mixing", but how much does it convert to cost when we're talking about pricing? I knew one butane-propelled deo, that costed the same. Yes I mentioned that "hot/cold weather" usability thinking about gas canisters. – Sir Arthur7 Jul 25 '20 at 9:07
• Price is not the only parameter. – Poutnik Jul 25 '20 at 15:32
• Exactly my point! I'd argue for hydrocarbon reserves than ease of processing (esp. when it isn't much of a big deal) – Sir Arthur7 Jul 26 '20 at 3:11