Citric Acid, Cream of tartar Condensation Polymer

I was having a think about Condensation Polymers. (as people just do). I was wondering if Citric acid ( 2-Hydroxypropane-1,2,3-tricarboxylic acid) would react with cream of tartar (HOOCCH(OH)CH(OH)COOK) at a reasonable pace to form a condensation polymer.

My concern is the whether the citric acid could act as the acid catalyst as well as take part in the reaction. Everyone seems to use sulfuric acid which as it is a strong acid concerns me as well because citric acid is a weak acid.

I figured I should check before I buy some citric acid powder. Also here is my proposed method just in case there are any obvious problems or improvements.

1) take 5g supermarket citric acid powder and add to 1.25cm³ hot water
2) add 4.5g cream of tartar to the solution and use a match to let the plastic stick to.

My main question is will I add too much water in my method and end up hydrolysing anything I make?

I'm just doing this for fun rather than for any academic reason. I also don't want to use any chemicals at home more dangerous than citric acid.

One last thing is whether I need to worry about the difference between monohydrate citric acid and anhydrous Citric acid?

Thanks to anyone that can help

(edited 1 month ago)

Reply 1

TypicalNerd

Original post by Omnibluey

I was having a think about Condensation Polymers. (as people just do). I was wondering if Citric acid ( 2-Hydroxypropane-1,2,3-tricarboxylic acid) would react with cream of tartar (HOOCCH(OH)CH(OH)COOK) at a reasonable pace to form a condensation polymer.
My concern is the whether the citric acid could act as the acid catalyst as well as take part in the reaction. Everyone seems to use sulfuric acid which as it is a strong acid concerns me as well because citric acid is a weak acid.
I figured I should check before I buy some citric acid powder. Also here is my proposed method just in case there are any obvious problems or improvements.
1) take 5g supermarket citric acid powder and add to 1.25cm³ hot water
2) add 4.5g cream of tartar to the solution and use a match to let the plastic stick to.
My main question is will I add too much water in my method and end up hydrolysing anything I make?
I'm just doing this for fun rather than for any academic reason. I also don't want to use any chemicals at home more dangerous than citric acid.
One last thing is whether I need to worry about the difference between monohydrate citric acid and anhydrous Citric acid?
Thanks to anyone that can help

Let’s first think about the mechanism that esterification follows.

Esterification is nucleophilic addition-elimination and begins with the protonation of the carbonyl oxygen of the carboxylic acid. In general, the pKas of such species are usually around -2 and so you need a decently strong acid to initiate the mechanism. This is why concentrated sulphuric acid is thrown in as a catalyst and why the weak carboxylic acid precusor alone usually isn’t enough.

My suspicion is your proposed method won’t work - I think the water content of the mixture is one problem. The lack of a catalyst is your main problem.

If you were to form a polymer, I reckon you’d get quite a complex network given there are several ways the monomers could connect, given both have multiple carboxylic acid (note the -COOK group of the tartar would protonate due to the acid catalyst) and hydroxyl groups.

Reply 2

Omnibluey

Original post by TypicalNerd

Let’s first think about the mechanism that esterification follows.
Esterification is nucleophilic addition-elimination and begins with the protonation of the carbonyl oxygen of the carboxylic acid. In general, the pKas of such species are usually around -2 and so you need a decently strong acid to initiate the mechanism. This is why concentrated sulphuric acid is thrown in as a catalyst and why the weak carboxylic acid precusor alone usually isn’t enough.
My suspicion is your proposed method won’t work - I think the water content of the mixture is one problem. The lack of a catalyst is your main problem.
If you were to form a polymer, I reckon you’d get quite a complex network given there are several ways the monomers could connect, given both have multiple carboxylic acid (note the -COOK group of the tartar would protonate due to the acid catalyst) and hydroxyl groups.

Thanks for your help.

Let's start with the easier problem about the water. I assume we can increase concentration of reactants through less water and/or more reactants. (I assume it doesn't matter which I choose) to fix that problem. How much less water would I need?

With the catalyst issue, do you know normal pH levels or sulfuric acid concentrations to achieve the reaction? As citric acid is quite a strong weak acid I might be able to solve this through a high concentration of citric acid.

(edited 1 month ago)

Reply 3

TypicalNerd

Original post by Omnibluey

Thanks for your help.
Let's start with the easier problem about the water. I assume we can increase concentration of reactants through less water and/or more reactants. (I assume it doesn't matter which I choose) to fix that problem. How much less water would I need?
With the catalyst issue, do you know normal pH levels or sulfuric acid concentrations to achieve the reaction? As citric acid is quite a strong weak acid I might be able to solve this through a high concentration of citric acid.

You could try a different solvent system.

Diethyl ether might work, but you have said you want to avoid handling anything especially dangerous. A number of synthetic organic chemists have used a reflux system involving something called a Dean-Stark trap to get rid of any moisture in esterification mixtures as they reflux (this only works with nonpolar solvents), but I expect this is very much out of budget and not something you could reasonably set up at home lol.

Oh, and before you even suggest trying concentrated sulphuric acid as a solvent, you should recognise that this would almost certainly ruin your yield due to side reactions - concentrated sulphuric acid is a powerful dehydrator of alcohols and a powerful oxidising agent, hence it would make a terrible solvent choice.

I don’t think you really have “usual” concentrations and pH values per se - usually esterification reactions are carried out using the anhydrous reagents (which are usually all liquids and so you don’t usually have to worry about throwing in a solvent - again, in cases where you have solid reagents, generally you use the Dean-Stark method with a nonpolar solvent).

Citric acid really isn’t that strongly acidic. The first pKa is 3.13 and so the equilibrium constant between it and the protonation of a carbonyl is going to be around 10^-5 (logK = pKa of acidic product - pKa of acidic reactant = -2 - 3.13 ≈ -5, so K ≈ 10^-5). The reaction might begin to proceed, but in all probability, your yield would be terrible by the end of it.

Reply 4

Nitrotoluene

Original post by Omnibluey

Thanks for your help.
Let's start with the easier problem about the water. I assume we can increase concentration of reactants through less water and/or more reactants. (I assume it doesn't matter which I choose) to fix that problem. How much less water would I need?
With the catalyst issue, do you know normal pH levels or sulfuric acid concentrations to achieve the reaction? As citric acid is quite a strong weak acid I might be able to solve this through a high concentration of citric acid.

Using citric acid to start the polyester-making process might not be the best idea. It's a weak acid, and this reaction usually needs something stronger, like sulfuric acid, as you told above. That said, both citric acid and cream of tartar have chemical groups that can bond together when heated. They can link up and make polyester through a process called condensation polymerisation, as you no doubt already know. If you just leave them mixed at room temperature, nothing much would occur.
But if you heat things up to about 100 -150°C, like in a warm oven, the reaction can pick up speed.
I think the polymer that is formed will be sticky rather than hard or brittle due to the stay at high temperature.

My 2 cents!

Reply 5

TypicalNerd

Original post by Nitrotoluene

100°C - 150°C might be okay, but I would caution the OP against going anywhere in excess of the upper limit of that range. Citric acid has a tendency to thermally decompose (likely by dehydration and then decarboxylation).

Reply 6

Omnibluey

I wasn't planning on getting sulfuric acid to do it.
As outside my budget (same as with the ether)
I was thinking about 80-90C as above 100C surely I get no water which I assume is a problem. I'm fine with the polymer being a sticky mess. (I assumed I wouldn't get any resembling a string of polymer due to there being too many hydroxyl/ carboxyl group pairs)
Oh and when I said citric acid was strong I meant relative to other common weak acids like ethanoic acid.
I don't mind if the yield is terrible if it helps?

Reply 7

TypicalNerd

Original post by Omnibluey

Fair enough. In all honesty, I probably wouldn’t bother attempting the synthesis though without any catalyst or suitable aprotic solvent. There are other reactions you can do at home with the same amount of money that might be more interesting.

Water boiling off would solve the hydrolysis problem - but you would need at least one of your reactants to liquefy and therefore act as a solvent. This would mean using a temperature at which at least one of your reactants would begin to decompose, however. Really and truly, you’d want to perform the reaction under reflux with a nonpolar solvent like toluene and a Dean-Stark trap, but you have said that you have a fixed budget to work with and I highly doubt the relevant glassware would be within it.

But how terrible is acceptable? - if you cannot isolate any product, then you may as well have avoided carrying out the synthesis…

Reply 8

Omnibluey

I was thinking the making the minimal amount that I can see by moving a match around and then taking it out of the beaker.
But I also think based on what both of you guys have said that it isn't going to work

(edited 1 month ago)

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