Home Cosmetic Science Talk Formulating Benzo precipation

  • Benzo precipation

    Posted by Chemist5000 on June 1, 2018 at 9:10 pm

    I am making a water based gel with benzocaine. I have noticed at temps <25C it starts to fall out of solution.  I dissolved it in PG and in Ethoxydiglycol.  It still recrystallizes until I heat the gel and it redissolves.  

    Chemist5000 replied 5 years, 9 months ago 2 Members · 2 Replies
  • 2 Replies
  • gunther

    Member
    June 2, 2018 at 4:22 pm

    Benzocaine is only slightly soluble in water:

    Soluble in water (0.4 mg/ml at 20° C), methanol, chloroform (500 mg/ml), ethanol (50 mg/ml), and ether (250 mg/ml)
    https://www.scbt.com/scbt/product/benzocaine-94-09-7
    Click on ‘Technical Info’ tab

    Most chemical substances become less soluble as temperature decreases.

    You may wish to add another, or switch solvents
    This 1945 patent lists its solubility in several solvents
    https://patents.google.com/patent/US2457188

    You may wish to stick to a proven pharma recipe.

    It looks like many of them use polyethylene glycol
    …In addition, the vehicle composition might have an effect. Polyethylene glycol is used as the solvent in benzocaine solutions because the local anesthetic is poorly soluble in water.61,62 In our study, the concentrations of polyethylene glycol in the 20 percent benzocaine, 10 percent benzocaine and vehicle gels were 77 percent, 87 percent and 97 percent, respectively…
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3844156/

    Just curious on what you plan to use the benzocaine for?

  • Chemist5000

    Member
    June 4, 2018 at 3:04 pm

    @Gunther
    Thank you for the info.  this will be used as a lubricant to reduce sensitivity. I am concentration lower than 3%.

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