How to make TetraEDTA in 39% solution

[emi]

EDTA's aren't my thing, so up until now I didn't know that much about it (other than it's use in medical circles, prior to hearing about it in soaping) and I certainly didn't know it's function in plant growth (which has piqued my interest - I'm going to have a bit of a closer look at that ).

The thing that I didn't know, in the products you all use, is whether you are using the hydrate or anhydrous product, but I kind of concluded that it didn't actually matter (so long as the calculations were kept consistant), so I chose the hydrate version.

Anyway, I checked your numbers, and they look about right - I got 0.215, or 21.5%, as the multiplier, which is roughly equivalent to your 5 grams of H2Y2 to 1 gram of NaOH, to convert to Y4 and some spare water.

I did find a manufacturing document that looks similar to your idea of adding disodium EDTA to the lye solution. The manufacturer added the NaOH solution to the EDTA solution to convert the disodium EDTA to tetrasodium EDTA - it states that the product (Ethylenediaminetetraacetic acid disodium salt dihydrate) is slowly soluble at room temperature up to 0.26M (stated as making a final solution of approx. 96mg in 1 ml) and the solubility increases as the pH increases.

In other bits of research, I found that there's graphs on the pH needed for each conversion step (these should be fairly easy to find - let me know if you need a link), but the bottom line is that the pH of the solution needs to reach over 10.3 for the tetrasodium EDTA to form ... under that and most of the conversion will not have taken place.

Summary:
Yes, 5 parts disodium EDTA to 1 part NaOH is a good way to remember it.
Add the sodium hydroxide slowly to the disodium EDTA solution
Make sure the final pH reaches at least 10.3 to convert to tetrasodium EDTA (higher is ok).

I probably have no business trying all this, but it's fun. I have 2 questions.
1. Do you think KOH will work to convert the DiEDTA to TetraEDTA? (And if so, do I need to discount EDTA because of my 90% purity of KOH? Or is that so tiny it doesn't matter.)
2. And just in reference to reading your post, how does 21.5% translate to 1:5? Wouldn't it be closer to 1:4? What am I missing??

The reason I ask is because I have a LS paste I need to dilute. The recipe asks for it to be diluted with a 39% solution of TetraEDTA. I only have DiEDTA. If I can not use KOH to convert Di to Tetra and have to use NaOH instead and then add that solution diluted to 39% to my paste, will that cause problems since the paste was made with KOH?

 

[emi]

Thank you, Carolyn! One data point from @cmzaha. Do you remember if it was at all difficult to dissolve the disodium EDTA?

I agree with sending white powder over the border, @Misschief. Thanks for the offer, but I think both of us will be happier if you don't.

I've got to run (DH needs oral surgery). I'll get a call-to-action thread started later today or tomorrow.

Oooh I want to test! I have Di and the Tetra's ETA is 1/7. I can send you some DiEDTA if you'd like. I'd love to return the favor of you answering all my pokey questions. Gonna keep an eye out for your call to action!

 

[SaltedFig]

I probably have no business trying all this, but it's fun. I have 2 questions.
1. Do you think KOH will work to convert the DiEDTA to TetraEDTA? (And if so, do I need to discount EDTA because of my 90% purity of KOH? Or is that so tiny it doesn't matter.)
2. And just in reference to reading your post, how does 21.5% translate to 1:5? Wouldn't it be closer to 1:4? What am I missing??

The reason I ask is because I have a LS paste I need to dilute. The recipe asks for it to be diluted with a 39% solution of TetraEDTA. I only have DiEDTA. If I can not use KOH to convert Di to Tetra and have to use NaOH instead and then add that solution diluted to 39% to my paste, will that cause problems since the paste was made with KOH?

1/ Theoretically it should be possible.

By substituting the Sodium Hydroxide with Potassium Hydroxide, you would also need to account for the extra molecular weight of Potassium (Potassium is heavier than Sodium).

You can use the multiplier to change between NaOH and KOH for SAP value calculations (the SAP multiplier is a handy number to remember: 1.403).

If your purity is 90%, or 0.90, then you also need to divide by 0.90 to get the larger weight needed (to account for the lower purity).

I did some rough numbers for you, and the multiplier becomes 0.30, or 30%, by weight at 100% purity, or 0.33, or 33%, by weight for a 90% purity, for use with KOH.

2/ I calculated the multiplier to ensure that my checking of DeeAnna's numbers followed different steps (where possible).
The same sort of idea is used when checking addition of a list of numbers - the check is to add them up from the last to the first - just by changing the technique, the chance of duplicating errors is lowered.

Short answer:
5:1 ratio means that if you start with 5 parts of Disodium EDTA, you need 1 part of NaOH to react with it.
If you have 100 parts of Disodium EDTA, using this ratio, you'll need 20 parts of NaOH to react with it.
That means that you can take the Disodium EDTA weight, and multiply it by 20% to get the amount of NaOH needed.

The bit you were missing is the number juggle needed to go the other way, and convert a percentage (eg. 20%) into a ratio.
You need to convert your percentage to a decimal first (20/100 = 0.2).
Then you need to know how many of these are needed to make 1 (1/0.2 = 5)
The ratio is now known and can be expressed as 5:1
If you have a calculator or spreedsheet, the single line equation for this is:
1 / ("x%" /100), where "x%" is 20 in our example, so 1/(20/100) = 5
Note: The brackets are important.

Long answer:

... The (very small) catch to using Di is every 5 grams of Di will consume about 1 g NaOH. We use so little EDTA in soap that you might not feel the need to adjust for this -- it's such a tiny error. If you're a geek like me, however, you Want To Know These Things so you can decide.

... I'm hoping maybe SaltedFig, GalaxyMLP, or someone else with a chemistry and math background will doublecheck my thinking. I think I've got the numbers straight, but it never hurts to get a second opinion.

...
2. And just in reference to reading your post, how does 21.5% translate to 1:5? Wouldn't it be closer to 1:4? What am I missing??

The method I used to get the number was to work out the molecular weights, and then divide the molecular weight of NaOH by the molecular weight of Disodium EDTA to get the multiplier needed to calculate how much NaOH is needed for a given amount of Di.

The multiplier I got was 0.214898, which I rounded to 21.5% for our use.

The usage rate of 5g of Tetrasodium EDTA for 1000g of oil is a usage rate that DeeAnna described in an earlier post (it is slightly irrelevant from my perspective - I don't use EDTA, so I take your usage rate at face value), but I'll use this amount as a way of describing the "vast" impact of these numbers

Superfat example
1000 grams of Olive Oil has a NaOH saponification value of 0.136 (roughly) . This gives 136grams of NaOH for a zero superfat. For a 5% "superfat", this amount is multiplied by 95% (or 0.95), to give 129 grams of NaOH).

If 5g of Tetrasodium EDTA, and 0.215 is the multiplier to calculate the extra NaOH to convert Disodium EDTA to Tetrasodium EDTA, then there is another 1g of NaOH required.

The extra superfat created, if this 1g of NaOH is not included, is just over 1%. Just about all recipes will be in the range of a superfat increase of 1% to 2%.

Conclusion:
It's probably worth adding the extra hydroxide if you are using Disodium EDTA, but not entirely necessary.

Original Tetrasodium EDTA: 1000g of oil, 5g of Tetrasodium EDTA
Disodium version with NaOH: 1000g of oil, 5g of Disodium EDTA and 1g additional NaOH
Disodium version with KOH: 1000g of oil, 5g of Disodium EDTA and 1.5g additional KOH
Disodium version with KOH: 1000g of oil, 5g of Disodium EDTA and 1.6g additional 90% KOH

I hope DeeAnna (or one of our other resident chemists) will be so kind as to check my thinking on emi's KOH idea?

Anyway - I might leave this all to you that use EDTA.
Good luck!

 

[DeeAnna]

@emi -- You should be able to react disodium EDTA with KOH. Use the same weight of Di as you would Tetra. The reaction of KOH and Di will consume about 1.4 grams of KOH for every 5 grams of Di that you add.

***

I'm feeling overwhelmed at the moment, so SMF is going to have to take a back seat for a few days. My son has just arrived for a couple of days visit. My estranged stepson and his new wife JUST emailed asking to visit Sunday through Monday morning. I have a dog coming home today from having had knee surgery and has a very restricted range of activities for the next couple of weeks.

Life has zoomed from zero to 60 all of a sudden. So I'm not ghosting y'all ... just way too busy.

 

[emi]

1/ Theoretically it should be possible.

By substituting the Sodium Hydroxide with Potassium Hydroxide, you would also need to account for the extra molecular weight of Potassium (Potassium is heavier than Sodium).

You can use the multiplier to change between NaOH and KOH for SAP value calculations (the SAP multiplier is a handy number to remember: 1.403).

If your purity is 90%, or 0.90, then you also need to divide by 0.90 to get the larger weight needed (to account for the lower purity).

I did some rough numbers for you, and the multiplier becomes 0.30, or 30%, by weight at 100% purity, or 0.33, or 33%, by weight for a 90% purity, for use with KOH.

2/ I calculated the multiplier to ensure that my checking of DeeAnna's numbers followed different steps (where possible).
The same sort of idea is used when checking addition of a list of numbers - the check is to add them up from the last to the first - just by changing the technique, the chance of duplicating errors is lowered.

Short answer:
5:1 ratio means that if you start with 5 parts of Disodium EDTA, you need 1 part of NaOH to react with it.
If you have 100 parts of Disodium EDTA, using this ratio, you'll need 20 parts of NaOH to react with it.
That means that you can take the Disodium EDTA weight, and multiply it by 20% to get the amount of NaOH needed.

The bit you were missing is the number juggle needed to go the other way, and convert a percentage (eg. 20%) into a ratio.
You need to convert your percentage to a decimal first (20/100 = 0.2).
Then you need to know how many of these are needed to make 1 (1/0.2 = 5)
The ratio is now known and can be expressed as 5:1
If you have a calculator or spreedsheet, the single line equation for this is:
1 / ("x%" /100), where "x%" is 20 in our example, so 1/(20/100) = 5
Note: The brackets are important.

Long answer:






The method I used to get the number was to work out the molecular weights, and then divide the molecular weight of NaOH by the molecular weight of Disodium EDTA to get the multiplier needed to calculate how much NaOH is needed for a given amount of Di.

The multiplier I got was 0.214898, which I rounded to 21.5% for our use.

The usage rate of 5g of Tetrasodium EDTA for 1000g of oil is a usage rate that DeeAnna described in an earlier post (it is slightly irrelevant from my perspective - I don't use EDTA, so I take your usage rate at face value), but I'll use this amount as a way of describing the "vast" impact of these numbers

Superfat example
1000 grams of Olive Oil has a NaOH saponification value of 0.136 (roughly) . This gives 136grams of NaOH for a zero superfat. For a 5% "superfat", this amount is multiplied by 95% (or 0.95), to give 129 grams of NaOH).

If 5g of Tetrasodium EDTA, and 0.215 is the multiplier to calculate the extra NaOH to convert Disodium EDTA to Tetrasodium EDTA, then there is another 1g of NaOH required.

The extra superfat created, if this 1g of NaOH is not included, is just over 1%. Just about all recipes will be in the range of a superfat increase of 1% to 2%.

Conclusion:
It's probably worth adding the extra hydroxide if you are using Disodium EDTA, but not entirely necessary.

Original Tetrasodium EDTA: 1000g of oil, 5g of Tetrasodium EDTA
Disodium version with NaOH: 1000g of oil, 5g of Disodium EDTA and 1g additional NaOH
Disodium version with KOH: 1000g of oil, 5g of Disodium EDTA and 1.5g additional KOH
Disodium version with KOH: 1000g of oil, 5g of Disodium EDTA and 1.6g additional 90% KOH

I hope DeeAnna (or one of our other resident chemists) will be so kind as to check my thinking on emi's KOH idea?

Anyway - I might leave this all to you that use EDTA.
Good luck!

Wow. Thank you so so much. My brain is fried. I've been crunching numbers for the last 3+ hours learning all kinds of things. Found myself needing to get solid grip on SAP values which led me on a looptyloop with what I'm sure are typos on someones website trying to explain it which led me all the way back to refreshing college chem 101 with youtube vids on moles and the periodic table....and I've gotten though a little over half your reply. But I'm finally confident to proceed with this LS dilution. I caught so many mistakes in my previous calculations! And I now totally understand what I was missing with the 5:1 thing. I was actually confused and asking about the same exact concept that started this thread that DeeAnna answered so well. I think I get it now. percentage of the SOLUTION vs SOLVENT. In the EDTA case, its 21% NaOH of EDTA as if EDTA is like "solvent", not "solution" of both combined. where 5:1 represents the whole solution. (Like bread hydration of flour = "Solvent"). So if 10g of EDTA, 2.1 g is 21.5%of NaOH. anyway, I think I got it. I hope I got it. I'm going to get this paste going, then digest the SF section of your reply tomorrow with a fresh brain! Thank you so much again for taking the time to post this. I'm sure many will benefit from it in the future!
.

That zip lock bag is my paste and that big printed packet is IrishLass's 30+ page recipe (with minimized pics!)

 

[Juhi]

Disodium EDTA can be converted into Tetrasodium EDTA by reacting the Di with NaOH or other strong alkali. I strongly suspect it's as simple as measuring the correct amount of powdered Di and adding it to your lye solution. Di won't dissolve in plain water like Tetra will, but it should dissolve in lye solution and react with the NaOH to form Tetra.

I haven't done the calculations, so I don't have solid numbers at the moment about how much Di to use and how much NaOH it will consume as it converts to Tetra. Here's a link to what appears to be some reputable although not very detailed advice -- https://chemistscorner.com/cosmetic...-to-formulate-tetrasodium-edta-and-etidronate

I can do the math and get some numbers for you, but I'd need someone to test the practical use of Di for me, since I don't have any on hand. (Or someone to send me a small sample.) In particular, I'd want to know how well it dissolves in NaOH solution. Does it clump up on the top and is fiddly to get stirred into the lye? Does it need to be stirred a lot to dissolve once it is mixed into the lye liquid? Does it take a lot of time? Is there any great amount of heating from the reaction? Or is it dump in and swirl a bit and easy-peasy you're done?

edit:
Okay, I worked through the math. It looks like you want to use essentially the same weight of Di as you would Tetra. For example, if I normally use 5 g Tetra per 1000 g oil, I'd do the same for Di -- add 5 g Di per 1000 g oil.

The (very small) catch to using Di is every 5 grams of Di will consume about 1 g NaOH. We use so little EDTA in soap that you might not feel the need to adjust for this -- it's such a tiny error. If you're a geek like me, however, you Want To Know These Things so you can decide.

So for those folks who have Disodium EDTA in their soaping pantries, now's the time to put your mad scientist hat on and try it. Please tell me if there are any tips or tricks to using Di. Remember -- it won't happily dissolve in plain water, but from what I can tell, it will dissolve in the strong alkali solutions we normally use to make soap. Would someone give it a try and report back?

I'll add this information to the EDTA article I have on my Soapy Stuff section. That way others can benefit from this insight.

I too need tp convert disodium EDTA to tetra sodium EDTA.

My recipe calls for a miniscule amount of tetrasodium EDTA. I have to use NaOH solution in the initial steps as well. Can I simply add disodium EDTA in NaOh solution (50% NaOH which will be more than 1 part per 5 part if disodium EDTA, as the amount of NaOH is going to be 10 times or more than the amount of EDTA needed)

 

[emi]

Sorry for the late reply! Yes, I just added the DiEDTA into the lye water with the appropriate amount of lye to convert it. I can't remember the exact numbers but in terms of process that is what I did. But honestly it's impossible for me to tell if it "worked"! It was for a liquid soap recipe and really how would I know if the EDTA did its job or not? I learned a lot on the process though and I do have fun geeking out from time to time. But I also do have really hard water and I figured the tetra will be useful in future recipes, so after going through the Di to Tetra conversion which I hope worked, I went ahead and bought a small pack of the Tetra EDTA on amazon. It looks like amazon doesn't carry it anymore, but it was coming from Making Cosmetics which does still carry it. Below is a link to the TetraEDTA for $5 from Making Cosmetics.
https://www.makingcosmetics.com/EDTA_p_238.html

DeeAnna is very knowledgable about the actual chemistry of soap making. I have learned so much from her alone. Below is a link that might not tell you too much about converting, but it is a page from DeeAnna's website that talks about EDTA. I referenced this page quite a lot when making my laundry soap.
https://classicbells.com/soap/EDTA.asp