# Looking for chemistry help



## SophomoreOrganicChemist (Dec 30, 2018)

Hello everyone,

My girlfriend has been struggling with some online recipes making liquid soaps. We've decided to do this together and I am rather excited to embark on this exciting journey.  What makes it exciting for me is science! 

My undergrad is in biochem where I did two years of research (organic synthesis). I know about saponification and micelle formation but I am having difficulty finding answers to questions.  I strive for a comprehensive understanding of the underlying mechanisms in soap formation. Unfortunately, I land between two worlds... unable to grasp formulation patents and not getting the answers I want from a recipe website.

I'd love to find a straight forward synthesis with a reaction scheme of liquid soap.

I have:

KOH: (why is K+ > Na+ when it comes to liquid soap? Ionic conc, solubility effects, etc...)

Glycerine: (I can substitute Glycerine for H2O in dilution?  Isn't Glycerine a byproduct of my OIL + KOH? If so, how does my ratio of Glycerine to Oil molecules affect saponification?)

Oils: Palm, castor, coconut, and almond.

If anyone can help point me in the right direction I'd be incredibly grateful. Also, my GLP cringe when I attempt to start making soap without figuring out the mols!


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## atiz (Dec 30, 2018)

Maybe you could have a peek at Kevin Dunn’s Scientific Soapmaking book? It’s about CP soap but might have something relevant for you too. (I just got it but haven’t had the chance to check it really out yet.) Plus, there are a lot of people here on the forum who know these things quite well.


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## DeeAnna (Dec 30, 2018)

SophomoreOrganicChemist said:


> ...KOH: (why is K+ > Na+ when it comes to liquid soap? Ionic conc, solubility effects, etc...)



What do you mean by K+ > Na+? I'm not sure what your question is. Please don't assume we can follow your train of thought.

_"...Isn't Glycerine a byproduct of my OIL + KOH?"_

Yes, glycerin is a byproduct of saponification. You can also add extra glycerin. The extra glycerin is included as part or all of the water-based liquid needed for saponification.

_"...If so, how does my ratio of Glycerine to Oil molecules affect saponification?"
_
If you do add glycerin, the added glycerin apparently catalyzes the saponification reaction. I've not studied this matter to feel confident this is an accurate explanation, but that's the explanation given by a retired pharmacist who explained this method on another soap making forum. (SilverDoctor on The Dish forum for those of you who are wondering.)

I also don't believe the significant relationship is the ratio of glycerin to oil. I suspect the more important relationship is the ratio of glycerin to alkali.

_"...I can substitute Glycerine for H2O in dilution?..."_

Yes, you can add glycerin at the time of dilution as a substitute for water. That doesn't offer any benefits as far as I can tell. The main thing I've seen is glycerin tends to reduce lather compared to only using water for dilution.

_"...Oils: Palm, castor, coconut, and almond...."
_
If you're asking a question here, I'm missing it. Again, please spell out what you are thinking -- we can't read your mind.

_"...my GLP cringe when I attempt to start making soap without figuring out the mols!..."_

Why? Chemists use weights all the time. We can't measure moles, but we can measure mass. So why is the chemistry of soapmaking any different?

The saponification value for each fat is based on the molecular weights and the stoichiometrc ratio between that fat and the NaOH or KOH to saponify. You can calculate a theoretical saponification value for an ideal fat if you like and that might make you feel better about where the moles are hiding. 

Bear in mind the sap values you find in the literature are not calculated values. Sap values are  determined experimentally, because fats are products of nature and vary somewhat in their fatty acid makeup, unsaponifiable content, etc.


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## geniash (Dec 31, 2018)

SophomoreOrganicChemist said:


> KOH: (why is K+ > Na+ when it comes to liquid soap? Ionic conc, solubility effects, etc...)


Welcome SophomoreOrganicChemist! I'll second the suggestion of Scientific Soapmaking book, you will enjoy the read and get science facts you are looking for. KOH is favored for liquid soap making because potassium salts tend to be more soluble in water than sodium salts.


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## DeeAnna (Jan 1, 2019)

Actually few of the OP's questions are answered in the Scientific Soapmaking. Kevin Dunn, the author, doesn't do much more than touch on KOH and liquid soap making. But Dunn's book is still a very good resource for any scientifically minded soap maker.


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## DeeAnna (Jan 5, 2019)

@SophomoreOrganicChemist  -- You might find some answers in this thread -- https://www.soapmakingforum.com/threads/cure-time.35831/ See especially Post 90. Without any response from you, this is the only other tidbit I can offer at this point.


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## dxw (Jan 5, 2019)

SophomoreOrganicChemist said:


> What makes it exciting for me is science!



I’m with you there.  The more I learn the more interesting this becomes – creative chemistry at a grassroots level. The history of the science is also pretty interesting.

The first sentence of Nickerson’s 1932 MSc thesis [1] is: “It is probable that no single class of compounds has been the subject of as much discussion in the chemical literature as have soaps”. That is probably no longer true, given where the materials sciences have been taking us, but it’s a good statement of the then status of soaps.

The Scientific Soapmaking book (K M Dunn) [2] is very good. I almost stopped reading part way through as I found the focus on mensuration (GLP I know) a bit tedious. Just before halfway, though, it gets into the (to me anyway) more interesting stuff.



SophomoreOrganicChemist said:


> My undergrad is in biochem where I did two years of research (organic synthesis).



It sounds to me like you're gonna be in heaven - applied organic chemical synthesis, with fragrances and colourants thrown in



SophomoreOrganicChemist said:


> I'd love to find a straight forward synthesis with a reaction scheme of liquid soap.



I'll have a go at the "why" question later, as I suspect the inevitable wordcount will bounce me from this response, but will try for a more general starter response here.

Firstly, the main difference between liquid and solid soaps is the amount of water. Add water to a solid soap and you can usually make a liquid soap. Remove liquid from a liquid soap, or a detergent preparation, and you can usually make a solid or semi-solid soap /detergent.

Potassium-based soaps are referred to as being 'softer' than their 'harder' sodium counterparts - more on that later. The chemical process for making them is pretty much identical, just substitute a strong K-based alkali (KOH) for the hard-soap NaOH.



SophomoreOrganicChemist said:


> Glycerine: (I can substitute Glycerine for H2O in dilution?  Isn't Glycerine a byproduct of my OIL + KOH? If so, how does my ratio of Glycerine to Oil molecules affect saponification?)



Glycerol could be used to dilute soaps … but water is effective and much cheaper [3].

Glycerol is the backbone of the triglyceride molecules. As a result, when you hydrolyse those fatty acids away to make the soap molecules, the saponification process has glycerol as a natural by-product.

AFAIK glycerol is not an active participant in the saponification reaction. Glycerol is certainly a product of that reaction and is usually considered, at least by CP artisan soap-makers, to be a beneficial by product of the main process. Having extra glycerol in your saponification system might conceivably act to reduce the breakdown of the triglycerides (equilibrium). I have no idea if that has any major practical impact on soap-making or even if it works that way. The main issue for your saponification reaction is the ratio or triglycerides to alkali (lye).

I’ve seen comments suggesting that extra glycerol results in greater heating and speeds the saponification process. I do not know if either or both are true, and have not (yet) found an adequate explanation.




SophomoreOrganicChemist said:


> Oils: Palm, castor, coconut, and almond.



Those are four oils that get a fair bit of use in soap making.

Palm oil contains mostly palmitic and oleic fatty acids. It adds hardness, creaminess, and conditioning characteristics to soap.

Castor oil is mostly ricinoleic fatty acid, with a little bit of oleic. It adds conditioning, bubbliness, and creaminess.

Coconut oil is mostly lauric fatty acid, with myristic next and smaller amounts of palmitic, oleic, stearic, and linoleic fatty acids. It mostly adds hardness, cleansing, and bubbliness.

Almond oil is mostly oleic, followed by linoleic and then palmitic fatty acids. It adds conditioning to a soap.



SophomoreOrganicChemist said:


> If anyone can help point me in the right direction I'd be incredibly grateful. Also, my GLP cringe when I attempt to start making soap without figuring out the mols!



IDK, it seems to me that GLP translates well into good soapmaking. One of the list veterans was explaining to me the likely role of hygiene (i.e. she wears gloves to handle new soaps) in avoiding DOS. It strikes me that that is just GLP, albeit called something else.

The molecules are fun and soap making is dragging so much long-lost biochemistry from the depths of my brain. Lattice enthalpy considerations are also allowing me to engage with the quantum physicists and chemists in my family … which adds an entirely new dimension to mixing oils and alkali.

The moles (stoichemistry) is also fun, although admittedly I seem to be learning a bit too much of that through dreadful mistakes.

____
*Footnotes*
1. Nickerson R F, The mechanism of adsorption at the interfaces of dilute sodium oleate solutions. Masters of Science Thesis University of Massachusetts Amherst. 1932.
2. Scientific Soapmaking.K M Dunn. Clavicula Press, 2010. Rev 1.67 2018. ISBN 978-1-935652-09-0.
3. Biodiesel production has resulted in a lot more glycerol being available on the world market. Glycerol is being widely explored as a potential industrial solvent, for  many reactions, because of it’s availability (cost), chemical profile, non-toxicity, and biodegradability (very good).


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## dxw (Jan 5, 2019)

SophomoreOrganicChemist said:


> KOH: (why is K+ > Na+ when it comes to liquid soap? Ionic conc, solubility effects, etc...)



Brace yourself, this may hurt a little 

*Short answer*
Potassium fatty acid salts tend to be more water soluble than their Sodium counterparts [1].

*Long answer*
Soaps are the water-soluble sodium (Na) or potassium (K) salts of fatty acids (FA). As such they are anionic surfactants. Soaps are, for our purposes, made by the base catalysed hydrolysis of triacyl glycerides [2] using strong alkali.

Using ‘caustic soda’ (NaOH) to hydrolyse the oils and fats produces Na fatty acid salts (Na-FA) while using ‘caustic potash’ [3] (KOH) produces K fatty acid salts [4]. K-FA based soaps are used more widely for liquid soap products than Na-FA based soaps.

Given the oils used in soap-making we’re mostly dealing with 12 - 18 Carbon chain length fatty acids.

K-FA salts are more water soluble than Na-FA salts. This is the core reason that liquid soaps are generally, although not exclusively, made using KOH.

Water solubility is the result of several interactions: cation-anion attraction (lattice energy); cation-water and anion-water interactions (hydration energy); and water-water interactions [5]. The solubility of ionic solids in water depends largely on two things: the energy change that occurs when the ionic solid goes into solution as hydrated ions, and the effect of the hydrated ions on the arrangement of the surrounding water molecules, measured by the organization energy.
Some of the contributory factors:

*Ion charge*. Smaller ion charge tends to favour solubility.  Not an issue in this discussion because K and Na have the same +1 ion charge.​
*Ionic radius*. Larger ions tend to be more soluble. The fact of K having a greater ionic radius than Na, 133 v 95, favours solubility by reduction in lattice enthalpy … more energy is released in the hydration process than is stored in the cation-anion bonds. Cations tend to have more influence on this than the anions, because they are much smaller and there’s a 1/r^2 relationship with hydration energy. Perhaps paradoxically increasing fatty acid chain length (alkyl) tends to correlate with decreasing solubility of a soap – coconut oil, lauric acid (C12) [6], and soap that will lather in seawater.​
Soap mixtures tend to be more soluble than pure soaps. For that matter, soap mixtures tend to do everything soapy better than pure soaps [7].

Fun fact: K-FA salts are widely used as insecticides, herbicides, fungicides, and algaecides. I’ve used liquid soap as an aphid spray with effect. They’re more effective against soft-bodied bugs, like aphids. They kill bugs via desiccation, as does diatomaceous earth, but they achieve the desiccation slightly differently. The structure of those K-FA salts provides water solubility for the fatty acids. The lipophilic carbon chains of the fatty acids penetrate and disrupt the lipoprotein matrix of the insects’ cellular membranes. The membrane disruption leads to evacuation of cellular contents, causing the cell to dehydrate and die. Fatty acid toxicity increases with increasing carbon chain length, typically peaking at C10, and then decreasing. Fatty acid chain lengths of 18 carbons with one or two double bonds (unsaturated) also display insecticidal activity

Hmmm, that didn't end up as long, or as rambling, as I thought it might.  I hope it makes some sense.

___
*Footnotes
1. *In contrast Na halides (e.g. NaCl) are more water soluble than their K counterparts … for #reasons.
*2.* Triacylglycerides, or triglycerides, are esters of glycerol (a polyol alcohol) and fatty acids. One glycerol molecule, because of its three hydroxyl groups, can esterise with three fatty acid molecules – hence triglyceride. The oils and fats used in soap-making contain various triglycerides in differing combinations and proportions.
Fatty acids themselves are poorly soluble in water, but their Na and K salts are relatively hydrophilic.
*3. *The word potassium derives from _potash_. The word potash (_potaschen_ - mid 15th century Middle Dutch etymology) derives from the olden-days method of manufacturing potassium carbonate: water leaching the ashes of burnt plant material in large pots. Caustic potash was then made by treating that potash with slaked lime. cOver time the term potash also came to be applied to mined sources of potassium salts - mainly KCl.
Potassium was first isolated in the early19th century via the electrolysis of caustic potash.
Along the same lines _soda ash_, ash from the burning of marine plants, was originally used to make caustic soda using a similar reaction with slaked lime. Soda ash, mostly Na2CO3, is also the ash that forms on the surface of some handmade soaps.
Early soaps were made using potash and then converted to harder sodium salts by treating the soft potassium soaps with salt (NaCL) solution.
*4. *Other cations can be used to make fatty acid salts. Calcium (Ca) and Magnesium (Mg), along with K and Na, salts are used as food additives. Ca-FA and Mg-FA salts are insoluble in water and part of the scum that forms when many soaps are used in ‘hard’ water. Lead and Magnesium soaps have a range of industrial uses, including an additive to help paints and other surface finishes dry. Calcium soaps are used in synthetic lubricating greases. Zinc soaps are used in talcum powder, and other cosmetic, manufacture.
*5.* It gets messier and less perfect when you start looking at ion pair formation, incomplete dissociation, the formation of complex ions, and pH changes. The fact that we’re talking about soaps, with their micelle-forming behaviour, also reduces the validity of applying purist chemistry reasoning. It gets messy and it probably gets quantum.
*6.* Make soap with shorter chain fatty acids and things can start to smell bad.
*7.* C7 soaps wet better, while C13 soaps best solubilise fats and oils. Differing chain length also helps emulsions maintain their stability, and good thing for soap function. The C7 saturated FA, heptanoic OFC, has an unpleasant rancid smell though.


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## SaltedFig (Jan 5, 2019)

Hah! You know what I took from all that?

No WONDER I don't have aphids on my roses when my straight C12and18 maker neighbour does 
(Thanks)


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## Misschief (Jan 5, 2019)

My brain hurts


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## Meena (Jan 6, 2019)

DeeAnna said:


> ... Dunn's book is still a very good resource for any scientifically minded soap maker.



I think I'll pick it up, as well.  I like having as thorough an understanding of things as time and my brain will permit.   I've preliminarily concluded (because I still haven't made any soap) that success in soap endeavors is highly dependent on getting everything right, chemically:  Too much (lye, water, oils), too little (ditto), incompatible ingredient(s), and probably more factors, and instead of useful soap you have a mess (volcano, refusal to harden, hardening too fast - those are what I remember so far).


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## SophomoreOrganicChemist (Jan 13, 2019)

Thank you so much for all of the knowledge!  

DXW, you provided an elegant explanation of solubility and was exactly what I was looking for! 

DeeAnna, thank you for the straight-forward lathering effects from dilution with glycerol. 

My first attempt seemed to go well, soln wasn't cloudy, lathered well, and skin wasn't dry. Unfortunately, ~1 week later the soap has separated. Two phases: Top layer is cloudy, white in color; the bottom layer is clear and amber in color.  Per everyone's suggestions, I've got some reading to do! 

I will keep everyone updated and again, THANK YOU!


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