Water soluble menthol?

Unknown Member
im trying to make a garden bug spray that’s water soluble menthol. I don’t want to use anything like sodium or potassium hydroxide I was thinking of using ethanol to dissolve the menthol into a concentrated solution then adding a cup of regular ethanol to my sprayer and a small amount of the menthol solution as well then adding in 2 gallons of distilled water which seems to be my fear that the water will make the menthol crash out of the solution. Anyone ever done a project like this that’s willing to help me? I was thinking about using magnesium sulfate in this mix but am not sure if that would be an aid to my goals I just use magnesium sulfate as a supplement and thought it may be of assistance but I’m no chemist. I also don’t know if magnesium sulfate has an exothermic reaction with menthol crystals or menthol solution. Any help is always appreciated 


  • GuntherGunther Member
    Menthol is not water soluble.
    So you'd need either a semi-polar (co)solvent like alcohol, or an emulsifier.

  • PharmaPharma Member, Pharmacist
    You could use the Uzo effect to your advantage. First, it's better to turn menthol liquid by creating an eutectic mixture. This is easy because mixtures with many essential oils shows that effect. Camphor would be the standard for this experiment (did it at university too) -> see also publication showing growth stimulation by applying menthol/camphor to Thale cress ;) . Then you make a concentrated solution of menthol in ethanol or methanol. Yes, correct, methanol. Plants love foliar methanol (10-30% once a week) way more than ethanol (10-20% max.)! You simply put that stock solution into water and *ZAPP*, it turns milky just like Uzo turns milky when diluted. This microemulsion is only stable for maybe 15 minutes or so, just enough time to drink the Uzo or spray your brew, respectively.
    Do not add Epsom salt to the water, it will break the emulsion faster like it breaks most o/w emulsions.
    Another approach is using a solubiliser. These are added to most lipophilic agricultural pesticides (synthetic ones are usually very lipophilic and poorly soluble). If you take a too good one, you hurt the plants and if it's a not so good one... well, you don't want to treat the plants but the bugs and hence, that'll be what you're looking for. A not so good one means one which doesn't reduce surface tension below a certain level which would allow the brew to enter stomata and/or dissolve cuticular waxes. Take for example common potassium soap (most plants don't like sodium!) and use it at the lowest possible concentration. No harm to the plants and you'll kill some aphids along the way too! How does that sound :smile: ?
    BTW I started mixing fertilisers and 'plant growth cocktails' well before I really went into cosmetics. Half the shake additives I bought ended up on my plants instead of me and now I use them in my creams too LoL. My personal notes regarding plant stimulants and fertilisers are better organised an longer than the ones for my cosmetics hobby.
  • chemicalmattchemicalmatt Member, Professional Chemist
    Curious: where and how does Epsom Salt detract insects? Likewise, menthol? Camphor I know works, but menthol? No worry about exothermic reactions here either. 
  • PharmaPharma Member, Pharmacist
    Curious: where and how does Epsom Salt detract insects?
    It's used as fertiliser, not pesticide ;) .
  • FekherFekher Member, Professional Chemist
    @Mentholidiot the solubility of menthol can be increased by increasing the temperature of water  
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