Org Prep Daily

June 30, 2007

Base baths

Filed under: Uncategorized — milkshake @ 3:59 pm

The classic soak bath is a mix of isopropyl alcohol with a generous amount of concentrated aqueous KOH. The disadvantage is that is tends to evaporate over time, is flammable and it shouldn’t be poured in the sink because EPA can bust you for sending isopropanol down the drain. There is one good base bath alternative without isopropanol – that contains aqueous KOH with K3PO4 (or any other K-phosphate, with extra KOH to make stuff strongly basic) mixed with some diluted anionic household floor-cleaning detergent. A common grade based on greasy-chain sulfonic acids works best.  The foaming is not much of a problem if you don’t overdo it with the detergent, few spoons is enough for a bucket. Please note that Na-phosphates or NaOH cannot be used as a substitute because Na3PO4 hydrate is poorly soluble and crashes out of the mix. Also some weird detergents tend to form an oily layer if the mix is too concentrated and salty – on the first try one should test the compatibility of the detergent before mixing vats of the bath solution.

This phosphate-based alkaline bath without iPrOH works very nicely for an overnight soak and I would encourage all alkaline bath-lovers to give it a try.


I wash my dirty glassware as soon as it is produced – it is much easier to wash before the stuff dries on.  I prefer doing fewer experiments in parallel but clean and wash inbetween so that at the end of the day the hood is nice and organized again and cleared of the clutter. Hot water and acetone mostly does it for me, for difficult cases the bottles with 2M NaOH, 6M HCl and DMF are at hand. (The particularly nasty pieces of glassware are saved until I feel brave enough to play with piranha mix.) I stopped using base baths because they take space and I don’t like to fish in a bucket full of slippery glassware soaking in a caustic mix. Aluminum parts and frited funnels are eaten in base baths and the forgotten pieces of the glassware are slowly etched. But if you want your flasks picture-pretty then base bath is the way to go.

Update: The actual ratio for a large base bath tank that holds approx 100 liters of of solution is: 1 kilo of common grade 85% KOH pellets dissolved in about 2 liters of water, add 250g of K3PO4 in about 2 liters of water, dilute up to 100 liters total volume, then add a whole bottle of liquid non-scented color-free laundry detergent containing 32 laundry loads (we use a Publix grocery store “Free and Clear” brand with a little dirty boy on the bottle, it is supposed to contain a mix of anionic and non-ionogenic detergents and costs about $3 a bottle)


  1. I just don’t like using piranha if I don’t have to. There are better alternatives like No-Chromix which you can actually store for extended periods of time. I figure I’ll just one-up you and steal your piranha topic for my next post. Thanx! :-P

    Comment by excimer — June 30, 2007 @ 8:21 pm

  2. I am pretty clean with my glassware and never let it stay in the sink dirty for longer than one night. I’ve never had to toss anything in the base bath–aside from PTCDA-clogged frits, soap and water and OCD takes care of everything. (Unless someone else made the mess…)

    Comment by Ψ*Ψ — June 30, 2007 @ 11:26 pm

  3. I work with transition metals (Cu, Ru, Pd, and Pt) and frequently, the compounds that I make are very much like brick dust. What should I use when I collect the compounds on a filter frit and can’t get the metal compound off the frit? Piranha mix?

    Comment by Ron — July 1, 2007 @ 1:51 am

  4. I would do aqua regia

    Comment by milkshake — July 1, 2007 @ 1:52 am

  5. conc nitric acid alone also blasts metal residues pretty well

    Comment by kiwi — July 1, 2007 @ 7:27 pm

  6. A word about nitric acid washing of frits: this method can lead to combustion. Several years ago a colleague of mine was washing a series of frits with conc. nitric acid and one of them exploded. He was doused from head (including his face) to waist in nitric acid and suffered several lacerations from the frit remnants. He was eventually fine, but was in a great deal of pain for several weeks while the burns healed. Thank god the university hospital was literally across the street.

    That said, if one is careful to pre-wash with something else to remove potentially combustible organics, nitric acid is a great way to clean metal contaminated frits.

    Comment by Cat Herder — July 1, 2007 @ 10:42 pm

  7. i use a lot of transition metals and if nitric doesn’t work sulfuric acid with hydrogen peroxide solution usually does.

    Comment by TMTCl — July 2, 2007 @ 1:07 am

  8. I throw my glassware away after selenium dioxide oxidations. It is just not worth the hassle!

    Comment by TWYI — July 2, 2007 @ 3:14 am

  9. Ok, we’re in industry but the convenience of disposable plastic filters can’t be underestimated. Isolute 120-1120-K and smaller, for just filtering off mag sulfate, smaller versions separating a dcm layer from aqueous or isolating your final compound on a small one…
    Nitric acid + organic in a frit isn’t worth the risk, in our risk conscious paranoia. Plus vats of DMF or baths take up space that can be filled with blue liquid for all those corporate photos.

    Comment by DrSnowboard — July 2, 2007 @ 10:50 am

  10. use red fuming nitric acid

    Comment by Wavefunction — July 2, 2007 @ 7:32 pm

  11. Any idea if there’s much risk of explosion from cleaning with conc sulfuric? I’m maybe a little frightened now.

    Comment by Ψ*Ψ — July 3, 2007 @ 3:18 am

  12. None with sulfuric acid only – but if you pour piranha onto Buchner that is soaked in acetone it will immediately detonate – this mishap happened to one of my room-mate chemist friend, working in Evans lab.
    Conc. nitric acid mixtures with organic solvents are pretty bad. I heard that towards the very end of WWII when Nazis were getting short on functioning ammunition factories, improvised bombs were developed for Luftwaffe – instead of a conventional high explosives they contained reservoirs of fuming nitric acid and some organic solvent like methanol-toluene. The binary components were kept separated and got mixed only after the bomb was released.

    Comment by milkshake — July 3, 2007 @ 3:32 am

  13. We have an annealing oven we use for cleaning. We give our stuff a quick solvent rinse then heat it to 575C overnight. At than temp even activated carbon goes away…

    Comment by Milo — July 3, 2007 @ 8:24 am

  14. Green Death – a few crystals of KMNO4 in conc sulfuric acid – good for frits. Probably forms super manganate. But be careful with this stuff – contact with acetone (especially fumes!) causes immediate flames.

    Comment by Anon — July 3, 2007 @ 7:34 pm

  15. I think it forms Mn2O7, a volatile explosive liquid. I have been playing with the mix as a kid, and have seen the metallic-green shiny dropplets condensing on the test tube walls. It’s not nice at all!
    I would rather use the nochromix (ammonium peroxodisulfate). In the presence of a trace amount of AgNO3 it generates Ag2+ species, an agent that can oxidize Mn2+ to permanganate.

    Comment by milkshake — July 3, 2007 @ 8:33 pm

  16. What is the recipe for nochromix? How much ammonium persulfate per L of con. sulfuric acid? I have a few packets left, but would rather save some money and make my own.

    Comment by Anonymouse — July 3, 2007 @ 10:04 pm

  17. I don’t know, the No-chromix composition is proprietary – but ammonium peroxodisulfate is the only hazardous material listed in their old MSDS info and supposedly forms 90-95% of the stuff. The specific density of the solid and its solubility is also a perfect match with data for ammonium perdisulfate. I think one can replace the packet with the equal weight of (NH4)2S2O8 – and maybe compare it side-by side with real No-chromix, by the speed of eating a small piece of paper (or a small chunk of an old bagel) to see if it is the same. But I would be quite careful on the first try. And also, one should never put in a tightly-closed container because the off-gassing .
    There is an old Usenet post that recommends 9.5g of (NH4)2S2O8 per 1 L of conc. H2SO4 as a Nochromix equivalent. I think the only real advantage of Nochromix is that it contains some redox color indicator which tells when the mix is exhausted…

    Comment by milkshake — July 3, 2007 @ 10:10 pm

  18. I’m definitely the type that abuses the base bath. Anything that’s been greased goes in. It’s mostly because I’m lazy – you put your stuff in, leave it overnight, rinse it, and you’re done. I’ll have to try your aqueous KOH/K3PO4 bath some time.

    Comment by Peter — July 4, 2007 @ 1:51 am

  19. no-chromix has no redox color indicator- it’s clear and viscous (since it’s 99% conc sulfuric). It does generate gas but doesn’t set paper on fire- not paper towels, anyway. Batches of no-chromix will be good for a few weeks- piranha decomposes in a matter of hours and has to be made fresh.

    Comment by excimer — July 11, 2007 @ 2:19 am

  20. alison frontier says no-chromix and the peroxodisulfate are pretty much the same thing. good enough for me. Also, on her site, she says for piranha-like solutions to add the acid to the peroxide. that’s fine for really dilute peroxide, but if you need stuff for semiconductor-grade etching, absolutely DO NOT do this. High concentrations of peroxide may cause an explosion. add the peroxide to the acid.

    Comment by excimer — July 17, 2007 @ 2:24 am

  21. I agree – it is just contrary to the water-and H2SO4 mixing order – but that’s what I was instructed to do (and I also found by experiment that reversing the addition order is likely to make a peroxide foam shoot right back at you). In any case, the oversized beaker and properly-trained person is absolute requirement with piranha, things can go wrong in a number of horrible ways.

    I wonder what would happen if one would add just few crystals of AgNO3 to perdisulfate – Ag(2+) is an incredible oxidizer, it takes Mn(2+) all the way to MnO4(-)

    Comment by milkshake — July 17, 2007 @ 2:40 am

  22. Hello!
    Very Interesting post! Thank you for such interesting resource!
    PS: Sorry for my bad english, I’v just started to learn this language ;)
    See you!
    Your, Raiul Baztepo

    Comment by RaiulBaztepo — March 28, 2009 @ 7:40 pm

  23. What concentration of KOH and K3PO4 is needed and does it have to be floor soap what about versa-clean?

    Comment by paul — February 25, 2011 @ 12:55 pm

    • well the mix has been tested with common cheap detergents based on alkyl-substituted benzenesulfonic acids. Versa-Clean looks like a different composition (MSDS gives “coconut diethanolamide and linear alcohol ethoxylate” as active ingredients) so I would not recommend it.
      I dont have exact ratios, it is ” dissolve few spoons of KOH and few spoons of K3PO4 in a half-bucket of warm water, then add a spoon of detergent”
      And you can use potassium hydrogenphosphates too (you just add more KOH, the point is that the mix is strongly alkaline). The result should be a clear solution, with pH about 13-14. If some crap starts oiling out from the mix it means you used a wrong detergent. (Also sodium hydroxide inplace of KOH does not work well because sodium triphosphate hydrate is poorly soluble and crashes out)

      Comment by milkshake — February 25, 2011 @ 2:21 pm

  24. Does anyone have a recipe for this yet with amounts of KOH, K3PO4, and a brand and amount of detergent that works?

    Comment by breitung — April 9, 2012 @ 1:04 pm

    • Here is what we use for a large soak bath (about 3 cubic feet of solution): KOH about 500g dissolved in a small volume of water, diluted with the bulk of water in the bath carboy, K3PO4 solid about 250g dissolved in water separately and added, then liquid laundry detergent, preferably scent- and color free. We use the whole bottle of a generic Publix grocery store brand, 32 loads per bottle/$4, but any anionic detergent should work. (Please make sure not to use cationic detergents – the quat ammonium hydroxides would oil out). Buy a cheap brand, the expensive ones have nice cyclodextrin-encapsulated scents and proteolytic enzymes which won’t help you in the base bath.

      Some cloudiness which gradually settles is OK, it is calcium phosphate – which also forms gradually in the immersed glassware as the Ca slowly leaches from the glass surface – but there should not be any droplets of oiled-out detergent in a correctly prepared bath

      Comment by milkshake — April 9, 2012 @ 2:09 pm

      • Milkshake – – thanks much! I’ll give that a try – assuming the safety department approves it ; )

        Comment by breitung — April 9, 2012 @ 2:25 pm

        • NaOH is used as a drain opener, KOH can’t be much worse. Phosphates down the river act like a fertilizer causing unwanted algal bloom that can turn ponds of standing water into a disgusting spinach soup but I suppose agri business runoff does more damage

          Comment by milkshake — April 9, 2012 @ 2:36 pm

          • I think the big advantage is not losing the IPA to evaporation. We would need to submit the bath to hazardous waste for disposal either way.

            Comment by breitung — April 9, 2012 @ 2:47 pm

          • why dont you just acidify to pH=7 with hydrochloric or sulfuric acid and send it down the drain? The pH adjustment to neutral will be easy, with all that phosphate in there acting like a buffer…

            By the way, what are you de-greasing?

            Comment by milkshake — April 9, 2012 @ 3:53 pm

          • Unfortunately, neutralization isn’t allowed. The bath will be used as a general glass cleaning tool.

            Comment by breitung — April 9, 2012 @ 5:11 pm

  25. Here’s the list of ingredients from Publix’s 2x concentrated liquid detergent:
    Publix Free & Clear 2X Ultra Liquid Laundry Detergent
    Palm Kernelamide DEA
    Methyl Ester Sulfonate
    Sodium Dodecylbenzenesulfonate
    C12-C15 Alcohol Ethoxylate
    Sodium Gluconate
    Derivatives of ethenediyl benzenesulfonic acid (optical brightener)

    Comment by breitung — April 18, 2012 @ 11:01 am

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