Sciencemadness Discussion Board

Exotic choline transesterified/saponified soap ala sciencemadness-style

deltaH - 8-10-2013 at 03:45

Bored of soda or potash soap? Well I have something WAY more fun to play with if you're a bit of a chemistry nut like me.

This was an idea that combined (i) deep eutectic solvents (DES) with (ii) soap making with (iii) exotic cations for soaps with (iv) parallel trans-esterification and saponification reactions into a new experimental soap. I've experimented with this extensively and report my best method info here...

Ingredients:

1. Pure glycerine (I use food grade)
2. Choline chloride (solid) - if prepared properly, it shouldn't have any bad smell of trimethylamine!
3. Sodium hydroxide granules
4. Vegetable fat of your choice (I prefer palm kernel fat)
5. Fragrance: I recommend food almond essence tincture and lemongrass oil

You make the soap thus:

(Any volunteering checkers, please comment if I've made a silly error in the numbers)

Look up your vegetable fat's saponification number (mg KOH required to saponify 1g of YOUR fat fully).

Now HALVE that saponification number and calculate the amount of sodium hydroxide equivalent to that.

Now do the calculations for your first batch, for example based on 1kg of vegetable fat, work out the mass of NaOH needed as well as the number of moles NaOH needed.

You will need to use equimolar amounts of sodium hydroxide, glycerine and choline chloride. So, for example, if you need 4 moles NaOH as half the saponification amount, then you also need 4 moles choline chloride and 4 moles glycerine as well. It's quite simple really!

Ok weigh out all your ingredients, wear rubber gloves and eye goggles please and work with caution!!! Also melt your vegetable oil in the microwave, don't overheat it, stop incrementally and give it a stir, stop microwaving when the last small floating chunk melts. It should be warm but not very hot.

Now blend together the glycerine with choline chloride first (I use an actual blender I reserve for this process only), then add you sodium hydroxide and blend for a minute. The slurry warms up a little and some white precipitate is visible... this is normal. Then add your vegetable oil and blend further. This is where some experience comes in, you want to blend until this solution starts to thicken to the point where it stops swirling throughout. It only takes a short while, so keep watching carefully.

This point is called trace in soap making, quickly mix in any colourants or fragrances you may want to use. I like it colourant free and lightly fragranced, so for that I suggest about 15ml of simple food almond essence tincture/kg fat and a couple ml of lemongrass oil, as preferred.

Now quickly transfer this rapidly thickening slime into a mold, (plastic tupperware containers work just fine). Carefully bang it down on a counter top surface several times to bring trapped bubbles to the top which pop (but not so hard to cause it to jump out and onto you) then put a lid on it and set it aside overnight.

I find that heating this mass [more than what the self heating by the exothermic reaction achieves] results in a smelly product, probably because some trace trimethylamine is formed so I wouldn't suggest being impatient with it!

The next day, eject out the block of soap and cut it into smallish slabs with a knife or metal wire (cheese cutter principle). Then cure it for a few weeks in a closed container before use.

I prefer using smaller blocks because the soap is somewhat hygroscopic, so prefer smaller block that I can finish quicker before replacing with a fresh one from a closed container.

You will find this to be the most beautifully mild and moisturizing soap you have EVER tried. There's good chemical reason for this!

Disclaimer: While I haven't experience any side effects from using this soap and this document suggests choline chloride is safe in soap, the safety of this soap has not been fully evaluated and is reported here for experimental purposes only! Use at your own risk!

Discussion on this chemistry

Firstly, you form a [partial] deep eutectic solvent system between the solid choline chloride and pure glycerol. Really the amount of glycerol you use is somewhat flexible here, you can use less, but I find the soap reactions proceed too rapidly then and you over[self] heat the mass that makes it smelly, also too much and the soap is too soft... you get the idea.

The sodium hydroxide then dissolves into this system, in the absence of water (trace is no disaster), you form one mole equivalent choline hydroxide (soluble in this mix) and one mole equivalent sodium chloride (mostly insoluble).

However this is only half of the amount of base required for saponification of your fat, that's because choline hydroxide has both the hydroxide ion that can saponify, but it also has the hydroxyl group on the choline tail that can transesterify... and DOES in the strongly basic environment of the saponification reaction!

So you end up with a soap that is probably mostly palmitylcholine palmitate, sodium chloride fine crystals and glycerine.

While ordinary soaps don't tolerate the sodium chloride, this stuff, because of the very large size of the cation, is so soluble it has no problem, but it's also very very mild on the skin, I love it!

Isn't the chemistry neat? I loved working on it and making it, though had many many bad smelly batches until I realised what was going on lol

Have fun and be safe!

ASIDE 1: Where to get choline chloride

I was lucky to find an importer in Cape Town fairly easily that sold 80% aqueous solutions to the livestock industry as a nutrient. It's pretty cheap (about $2/l) when sourced from such a source, in fact the supplier simply gave me 20l because it was such a small amount for him (basically they just tapped some leftovers from the hoses they filled up the tankers with).

I'm sure posters here will post their own suggestions for different countries.

ASIDE 2: Make your own solid choline chloride from 80% solutions (the common industrial form)

You will need to crystallise out the choline chloride as a solid, a little easier said than done because it is EXTREMELY hygroscopic.

Please exercise extreme caution as this is a serious scolding hazard that can burn you very easily if you get it on exposed skin, wear long rubber gloves, coat and goggles and good ventilation!

Pour about two liters into a HEAVY saucepan to spread the heat out nicely and then boil it SLOWLY outside until it starts to form a thick skin. At this stage I start folding and scrapping it with a heat resistant spatula (egg lifter) until I get most of it into a semi crystalline half glassy mess(don't expect completely dry looking crystals because even trace water at this stage causes it to not fully crystallise when so hot). Don't overheat or you will start decomposing the choline chloride to trimethylamine that smells TERRIBLE!!! Then set aside to cool only for the minimum time to get to nearly room T and then quickly transfer to an airtight container, you will notice that it will solidify/crystallise almost completely upon cooling, don't worry about minor water left as it's very difficult to dry it more than this without high vacuum or desiccators. This form works just fine!

[Edited on 8-10-2013 by deltaH]

[Edited on 9-10-2013 by deltaH]

Little_Ghost_again - 17-9-2014 at 15:55

Its a shame but in the UK and the rest of Europe (soon), you wouldnt be able to use it unless you could guarantee there was no trimethylamine in the product.
In the UK soap now comes under the rules and regs of cosmetics, all ingredients and processes need a MSD cert with them.

Because trimethylamine has warnings as an irritant etc it would be a huge risk to sell or give to others.
Soap making in the UK under the new regs is a real red tape exercise! If I buy say soya oil from a super market to use in soap making, I have to place a sticker on the oil bottle with a batch number that relates to the record of where and when the oil was purchased. When the oil is used a record of that soap batch must contain the oil batch number and amount ETC ETC ETC ETC.
They charge £185 for each ingredient for a cert of safety. Most people get this from certified chemists, however the regs actually say............ The MSD must be prepared by a COMPETENT person! Obviously this is open to interpretation .
There is currently a Test case before the high court here in the UK, details are scant and for some reason or other its a closed session so I have no way to get details yet

deltaH - 19-9-2014 at 10:05

Initially I made many fishy smelling soaps (containing trace amounts of trimethylamine) until I realised that choline hydrolyses in the presence of water and lye, a problem solved by working in glycerine instead of water when preparing the initial solution for saponification (as described in my method).

I also realised that some trimethylamine is in the initial choline chloride solution (it smells fishy), even though it is a feed grade material, but this is solved by boiling it down to obtain [nearly] anhydrous choline chloride... something one has to do anyhow for my method. The resulting sticky white crystals after cooling are odourless and should be used in good time, all the trimethylamine having boiled off.

The only big disadvantage of my soap in my mind is its tendency to sweat salty glycerine :D Ideally you need to squeeze this out before packaging if you want a decent commercial product.

I and my family have used it quite extensively (in spite of the glycerine sweating) for some time and loved it. I've simply been too lazy to prepare more of it of late, mostly because of the initial choline dehydration step which I find tedious to do.

It has a particularly delicate look about it, as if it were a baby soap, not that I would recommend it be used on babies as it is experimental!

Nevertheless, it is a wonderfully mild soap and I hope many home soap makers will experiment with it!


Little_Ghost_again - 23-9-2014 at 10:28

Quote: Originally posted by deltaH  
Initially I made many fishy smelling soaps (containing trace amounts of trimethylamine) until I realised that choline hydrolyses in the presence of water and lye, a problem solved by working in glycerine instead of water when preparing the initial solution for saponification (as described in my method).

I also realised that some trimethylamine is in the initial choline chloride solution (it smells fishy), even though it is a feed grade material, but this is solved by boiling it down to obtain [nearly] anhydrous choline chloride... something one has to do anyhow for my method. The resulting sticky white crystals after cooling are odourless and should be used in good time, all the trimethylamine having boiled off.

The only big disadvantage of my soap in my mind is its tendency to sweat salty glycerine :D Ideally you need to squeeze this out before packaging if you want a decent commercial product.

I and my family have used it quite extensively (in spite of the glycerine sweating) for some time and loved it. I've simply been too lazy to prepare more of it of late, mostly because of the initial choline dehydration step which I find tedious to do.

It has a particularly delicate look about it, as if it were a baby soap, not that I would recommend it be used on babies as it is experimental!

Nevertheless, it is a wonderfully mild soap and I hope many home soap makers will experiment with it!




Sweating is something I am reading up on and going to work on, as soon as I am upto speed a bit more on Chemistry, its definitely number 3 on my hit list ;).
I also found another great fat to use was the fat from the kidney of chicken! Trouble is getting hold of good quantities of it, you prep it like tallow....Boil is brine for 2-3 hours let cool ect etc.
Gives a great soap! I will give yours a try, I am after anything a little different ;).

deltaH - 1-10-2014 at 11:26

Quote:
...great fat to use was the fat from the kidney of chicken!


OMG, mad science at its best:D:D:D

Anyhow, I would be very grateful if you could check my synthesis on this one, so thanks in advance if you ever get round to it!

As for the sweating, I'm pretty sure it's caused by large amount of glycerine in my procedure. I use glycerine to dissolve the caustic and choline (instead of water) prior to addition to the fat to prevent the choline from hydrolysing to make smelly trimethylamine, something that happens relatively fast in highly basic media... well 'fast' is relative, but fast enough to smell fish :) This synthesis results in the glycerine having quiet a lot of dissolved salt in it, so that salts out the glycerine when cold and hence the 'sweating', well that's my hypothesis for now :P