Chemistry of Terephthalic acid

@Boffis,

I made Terephthaloyl chloride by refluxing excess Thionyl chloride with terephthalic acid and then distilling the product.








I also sent requested @Pumukli reference by private message to him according to copy right law

[Edited on 5-8-2015 by Waffles SS]

Quote: Originally posted by Pumukli

Regarding the first stage, the ammonolysis, it works as I expected (silently). My original idea was that PET is an ester and esters usually give amids when reacted with NH3. I hoped that terephtalic acid is no exception and glycolic esters are also working in this regard.

Quote: Originally posted by papaya

Once when storing 15% ammonia in a PET bottle it "corroded" away just in a week, nearly up to making holes in it and all covered in white specs ,especially ABOVE the level of liquid ! As ammonia is not as "basic" as say NaOH, can I speculate that what formed was amide(s)?

Quote: Originally posted by Boffis

@Waffles, Nice to have access to thionyl chloride. I might try with PCl5 to give terephthalylchloride and phosphorus oxychloride. But with the number of published descriptions of esterification of terephthalic acid with methanol or ethanol and sulphuric acid it must be possible. I am going to try it with anhydrous methanol and possibly azeotropic water removal after a reasonable reflux period.

You can use S₂Cl₂ instead of Thionyl chloride(also i have access to Riedel-de Haën S₂Cl₂ )

Esterification of Terephthalic acid with methanol or ethanol is possible if you can bring out formed water from reaction
This is difficult because Methanol and Ethanol have lower bp than water(my suggestion is using Molecular sieve 3A or using large amount of Sulfuric Acid as water absorber)


[Edited on 6-8-2015 by Waffles SS]

Use Chloroform for making ternary azeotrope(Water + Methanol + Chloroform=b.p.azeo. 52˚C)
https://en.wikipedia.org/wiki/Azeotrope_tables

I usually use below apparatus for making this type of ester and another Methyl or Ethyl ester(Oxalate,Tartarate ,..)




At end you should wash your ester with Sodium Carbonate solution for removing unreacted acid and mono ester of Terephthalic acid


[Edited on 7-8-2015 by Waffles SS]

I was so intriged by Papaya's comments about the "corrosion" of a PET bottle by aqueous ammonia I just has to try it. The results were slow but amazing; no pressure vessel, no gaseous ammonia or high temperatures just patience!

I took the thicker parts of a PET water bottle from the top and bottom to see how far the process would penetrate. I smashed them with a hammer to make them fit through the top of a glass soda drink bottle but would wedge in the top out of contact with the liquid, I would estimete the weight to be 3 to 4g. I then added 50ml of 32% ammonia solution so that the plastic was wetted but most of the liquid drained to the bottom of the bottle and replaced the lid. I then left the bottle on a shelf in my office for 3 weeks while I was on holiday. When I returned the plastic had turned white and partly crumbled and all was lying in the ammonia liquid at the bottom of the bottle. On shaking much of the white plastic was reduced to white crumbs which suggests that in the thinner sections were completely altered though the thick disc at the base and the lip on the neck are not completely altered.

White altered PET after 3 weeks

I will let it stand for a further 3 or 4 weks and then filter off the solids, wash them and then gently grind them to see how much PET is left.

I think that if 15% ammonia solution works then you probably only need a 30-40% excess af ammonia solution at 32%. This coupled with the use of only the thinner wall sections of the PET bottles could be an interesting "home" route to various compounds. You just need to be patient.

Thank you Boffis for this excellent work!
Here are my 50 cents... since I also have thought for years about the possible uses of PET and terephtalic acid.

1°) If one has access to NaN3 or to N2H4 he could perform:
°Cutrius reaction via Ar-CO-NH-NH2 and HNO2
°Schmidt reaction with NaN3 and H2SO4
Partial reactions would lead to HO2C-Ar-NH2 and complete reaction would lead to H2N-Ar-NH2
From there diazotation is possible with a lot of possible products.

2°) H2N-Ar-NH2 could be reacted with Cl-CO-Ar-CO-Cl (terephtalyl chloride) or with MeO-CO-Ar-CO-OMe (dimethyl terephtalate) to yield kevlar (-NH-Ar-NH-CO-Ar-CO-)n

3°) H2N-Ar-NH2 reacted with aqua regia (HNO3/HCl) will yield chloranile (O=C(-CCl=CCl-)2C=O), with HBr/HNO3 bromanile and probably with I2/HNO3 iodanile.
The halogens are very labile and may lead to halogen exchange reaction; for example tetrabromo-p-quinone (bromanile) will exchange 2 I (diiodo-dibromo-p-quinone) upon reaction of KI/EtOH and finally 4 I (iodanile) if longer exposure time, heat, reflux and more reactants.
The halogen exchange of chloranile, bromanile and iodanile is characterized by the easy replacement of each halide by azide group upon contact with NaN3 water solution forming the extremely dangerous tetraazido-p-quinone (intermediary stages are possible with mono, di, tri azides). This was covered by Axt in this forum.
Same is seen with NaNO2 what forms nitranilic acid (2,5-dihydroxy-3,6-dinitro-p-quinone) forming primary explosive salts like silver and lead nitranilates (the substitution passes maybe via a transcient tetranitro-p-quinone that hydrolyses spontaneously to the dihydroxy-dinitro compound).
Maybe other easy substitutions are possible like OH(-), C#N(-), NH3, NH2OH and N2H4 (this last one will probably reduce the quinone)...to test also amines like CH3-NH2, (NH2)2C=NH, ...

4°) Reaction of aqua regia or of HBr/HNO3 on terephtalic acid is not clear...
-maybe it remains unaffected
-or it is partially halogenated (and maybe decarboxylated) --> halo (dihalo, trihalo or tetrahalo) terephtalic acid and maybe polyhalobenzenes and polyhalobenzoic acid
-or decomposed into chloropicrin (Cl3C-NO2) or bromonitromethanes (CH2Br-NO2, CHBr2-NO2, CBr3-NO2).
The halopicrines are good ways to guanidine via reaction with concentrated ammonia solutions
Cl3C-NO2 -NH3 conc-> (H2N)2C=NH.HCl + NH4Cl + N2 + H2O
Chloropicrine may be dehalogenated and reduced by H2S in basic media to dichloronitromethane, chloronitromethane, nitromethane, methylamine and finally formaldehyde-methanol.

5°) Reaction of iodination (periodination) reagents (HNO3/I2, Cl-I, I2/SO3) allows one to get acces to iodo-, diiodo-, triiodo- and tetraiodo-terephtalic acid (this last one is a X-Ray contrast media for blood system or urinary system medical study).
Under harsh conditions decarboxylation may occure to yield pentaiodobenzoic acid and hexaiodobenzene...

6°) Hunsdieker reaction is not working well with terephtalic acid (less than 2% yield) but well with benzoic acid what will yield chlorobenzene or bromobenzene from silver benzoate (see point 7°) and Cl2 or Br2 in refluxing CCl4 or other suitable solvents.

7°) Thermolysis (425°C) of dry silver terephtalates generates a lot of products like benzoic acid, benzene, biphenyl as major products and terphenyl, quaterphenyl, quinquephenyl, 3,4-benzocoumarin as minor products.
See in requested documents "Thermal and Photochemical Decomposition of Silver Carboxylates", requested by me.

So from this tread, it is obvious many things (if not everything) can be done from easily got OTC PET...
The only limits are:
-your mind
-time
and as usual
-money

@Papaya, yes I'm pretty sure you're right about the white product being the diamide and it also appears that your observation that moist ammonia gas is more aggressive than the solution is correct. With this in mind I am going to try some further larger scale experiments where the PET is isolated from the ammonia solution.

@Philou, thank you for the ideas you posted. There are some interesting possibilities here. I wonder if hydrazine solution would be more aggressive than ammonia solution? I have some 60% hydrazine hydrate solution (about 40% hydrazine), the aim would be to produce the dihydrazide directly from PET. The lower vapor pressure of hydrazine over this solution means you can probably reflux it at atmospheric pressure with minimal loss of hydrazine.

The direct halogenation would also be interesting if it can be made to work but given the inertness of terephthalic acid to nitration I think very harsh conditions will be required though once introduced these halogen are fairly reactive and can be replaced by OH using KOH.

Update on the ammonia experiment: After a vigorous shaking most of the white alteration product became detached from the residual PET but the the thicker parts of the threads and neck still remain see photo.


The PET in ammonia after about 4.5 weeks, fragments of threads and the star from the base are clearly visible.

OK I've stop my experiment described above with PET plastic and aqueous ammonia.

I shuck the bottle vigorously to seperate as much as possible of the white product from from the residual plastic and then strained the mixture through a plastic tea strainer to remove the coarse fragments. The white suspension was gravity filtered and then washed with copious amounts of water until the smell of ammonia had gone and the wash water was no longer alkaline to red litmus. The filter paper was then air dried. When dry the white powder readily seperated from the filter as a fine, soft white powder. I don't have scales where I am so I can't give yields but after 5 weeks all of the thinner side walls of the water bottles had completely disintegrated only the bottoms and necks remained. If the product proves to be terephthalamide this process represents a very useful route to 1,4-benzene derivatives from PET resin.

The residual pieces of the bottles

The product; terephthalamide?

While I have no means at hand to test the material the only other two likely products are diammonium terephthalate and ammonium terephthalate monoamide but both of these are likely to be pretty soluble in ammonia solution and certainly the wash water. I didn't think to save the ammonia soution and try drying it to see if there was any soluble material.

When I get chance I will try a more scientific version of this with weighed quantities and better control.

Quote: Originally posted by Boffis

... I washed and dried the white solid and will investigate this further. ...

Large scale ammoniolysis of PET resin over aqueous ammonia

Following my earlier small scale experiments exposing PET plastic to the fumes of aqueous ammonia and the reasonable success it appeared to have I decided to carry out a much larger scale experiment.

I set up an old desiccator with a piece of plastic mesh to replace the zinc plate and then placed 206g of plastic water bottles cut into rings so that they did not pack too densely. 350ml of concentrated 0.90 density ammonia solution were then poured over the plastic and allowed to drain into the reagent pit at the base of the desiccator. The mesh kept the plastic out of the ammonia solution and so apart from the initial drenching the plastic was only exposed to moist ammonia vapor. The rim of the desiccator was greased with vaseline and the lid was placed firmly in place and the whole was left in a cool dark corner in my outbuilding for nearly 5 months from early November 2015 until mid March 2016. I estimate that the average temperature during this period was about 7-8 C.

Desiccator after opening and draining the excess ammonia

The now white corroded PET resin

When the experiment was opened the whole of the content had turned completely white and opaque and it had settled considerably. The aqueous ammonia that was left was carefully decanted and the PET residue tipped into a large bowl. The desiccator was washed out with about 400ml of water into the bowl and the now very soft and fragile PET gently crushed to give a thick porridge like slurry. This was filtered using a large Buchner funnel; the filtrate was preserved for recovery of any free acids while the filter cake was dried for several days.

The washed and filtered amide

The dried cake was ground to a fine powder and dispersed into 800ml of hot water, simmered for a short while (about 10 mins) and then cooled. The fine white solid was again collected in a large Buchner funnel washed with about 300ml of cold water and dried. The yield of dried solid was 155g. It is highly insoluble in cold as well as hot water and it is not soluble in dilute sodium hydroxide. It is also very resistant to hydrolysis even by hot 40% sodium hydroxide. The nature of this material was not investigated further at present but the yield is very close to the theoretical yield of terephthalamide.

The rewashed amide product

The combined filtrates were acidified to Congo red paper with 18% hydrochloric acid to precipitate any free acids. The white precipitate was recovered by filtration at the pump and dried, it weighed 18.87g. The nature of this acid is uncertain but the two most like possibilities are terephthalic acid and its half amide, 4-amidobenzoic acid; some short chain partial hydrolysis products are also possible if they contain a free acid group.

The residual ammonia solution was partially distilled into fresh water to recover most of the remaining ammonia and the residue in the distillation flask (now rather cloudy but from which nothing settled out) was acidified with hydrochloric acid and the white precipitate filtered off, washed with about 50ml of water and dried yielded a further 1.002g of acid that was added to that already recovered, giving a toatl yield of 19.9g.

To determine the likely indentity of this compound it was decided to titrate the acid against standard sodium hydroxide using phenolphthalein as indicator. The choice of the indicator is important as the final solution should be sufficiently alkaline to neutralise the second base of any terephthalic acid. An immediate issue, however, is the highly insoluble nature of the acid; to circumvent this problem a known weight of acid was dissolved in a known volume of standard sodium hydroxide solution and back titrate the excess alkali.

0.2477g of the dried acid were dissolved in 25ml of 0.2025M sodium hydroxide solution. When solution was complete 2 drops of phenolphthalein indicator solution were added and the excess sodium hydroxide was titrated against 0.2M hydrochloric acid (note 1). 17.3ml were required indicating that 7.7ml were required to neutralise the acid:

7.7/1000 * 0.2025 = 0.0015593 M of acid - therefore 0.2575g of 4-amidobenzoic acid

Or 0.1295g of terephthalic acid (a dibasic acid so twice as much NaOH required to neutralise it)

Clearly therefore, the monobasic amidobenzoic acid looks the more likely candidate even if it is a little impure. It would appear from the greater than 100% content that the main impurity is likely to be incompletely hydrolysised PET.

For comparision the titration was repeated using the terephthalic acid recovered by the PET/caustic fusion process described previously.

0.2504 of terephthalic acid were dissolved in 25ml of 0.2025M sodium hydroxide. When the acid had dissolved 2 drops of phenolphthalein solution were added and the excess alkali titrated with 0.2M hydrochloric acid. 10.1 cc were added ie 14.9cc of sodium hydroxide solution were consumed neutralising the acid. Therefore:

14.9/1000 * 0.2025/2 = 0.001509 M of terephthalic acid = 0.2506 g ie almost exactly the amount taken, indicating that the terephthalic acid is eceedingly pure.

Further Work
When time permits I will dissolve this monobasic acid in the minimum amout of sodium hydroxide solution and attempt to recrystallise it to remove the partial hydrolysis products and isolate the pure acid. I also intend to attempt a faster process using aqueous ammonia in a pressure reactor that I now have to see if I can produce a purer product and a greater yield of the 4-acetamidobenzoic acid relative to terephthalamide.

Given the very low solubility of the terephthalamide in all the solvents I have tried makes further purification impractical so I am going to try and convert it into 1,4-dicyanobenzene and 1,4-diaminobenzene directly and purify these compounds.

Quote: Originally posted by Boffis

Halogen in his post of 24-9-15 above suggested that the amide may contain short chain oligomers capped with ammonia (he means amide groups I presume). I think this is probably very likely but I couldn't see how to test it at the time. Having thought about it further and in the light of my results trying to test for amides with sodium hydroxide I think that one way to test it may be to heat some of the "amide" with strong (say 15-20%) aqueous ammonia to about 100 C in my newly acquired autoclave for 10-15 minutes. My idea is that the pure amide is rather resistant to further hydrolysis by ammonia but any uncleaved ester linkages will hydrolyse, some to amides and some to the ammonium salt, the latter are water soluble so the presence of water soluble ammonia salts in the aqueous phase is indicative of unhydrolysed ester linkages, ie there are residual oligomers. @Romix, the solubility of normal sodium terephthalate is about 14g of salt per 100ml of saturated solution or about 15g of salt per 100ml of water based on my own experience and this is almost independant of temperature ie you can't recrystallise the sodium salt from water by simply cooling a hot saturated solution. Other sodium salts, particularly NaOH, greatly reduce its solubility so the salt can be precipitated by adding 60% NaOH solution until the concntration of NaOH in the terephthalate solution is about 15% but beware! The resulting slurry is impossible to filter with paper filters and is very fine grained and so washes through all but the finest glass frits. Both bases of terephthalic acid are stronger than carbonic acid and so CO2 will not precipitate terephthalic acid. Terephthalic acid is almost insoluble in water (about 10 milligrams per litre!), the only workable solvent for terephthalic acid appears to be dimethylformamide, solubility 7g per 100ml of solvent at room temperature. I just peel off the labels from the bottles, this leaves small dabs of glue but these do not cause problems with such aggressive conditions so I don't try to remove them with expensive solvents. I have also discovered a few more very basic transformation that PET will go through under modestly amateur friendly conditions: PET can be transesterified to dimethyl terephthalate with methanol and alkali (see US pat 3321510) and that this compound (solid Mp 142 C) can be half hydrolysed to methyl 4-amidobenzoate by alcoholic ammonia. According to another patent I found aqueous ammonia in an autoclave at 180-190 C causes complete hydrolysis to ammonium terephthalate.

Quote: Originally posted by Pumukli

Is the IPA smell lost? Strange. Because it has a strong, characteristic odor. Although there is a process (trans-esterification) of vegetable oils catalysed by NaOH (or another strong base) in methanol what yields biodiesel, but you wrote that you added some extra water to the mix. And water is bad for that trans-esterification, it works against you (at least against the equilibrium). So I'm puzzled, I'm going to cut up some pet-bottles now and try to repeat this IPA-PET-Base "mystery". :-)

The original state, right after I closed the flask two days ago.



Now, after the processes had 48 hours to run:

[Edited on 17-4-2016 by Pumukli]



Another view from the bottom of the flask. You can see the white precipitate better from this angle:

[Edited on 17-4-2016 by Pumukli]



There are no cracks or holes on the PET slices. The mixture does not seem to get yellow(ish) either, just forms that white precipitate. (The original PET bottle I cut up was a mineral water bottle, so the PET should be high quality (food grade), not recycled one. The slices originally had a light-blue hue.)

[Edited on 17-4-2016 by Pumukli]

Quote: Originally posted by Boffis

Hi Eddygp, I don't have access to IR or NMR so no, The melting point is higher than I can measure (about 280 C). For various reasons I think that the terephthalamide is impure and contains a significant amount of short chain partial hydrolysis products. I intend to test this idea in the near future as part of my on-going work on terephthalic acid derivatives. I have observed that these partial hydrolysis products are suceptable to further hydrolysis giving a mixture of terephthalic acid and its monoamide and hope to be able to test the amount of each but I am still working on way to separate the two acids.

Quote: Originally posted by Boffis

Halogen in his post of 24-9-15 above suggested that the amide may contain short chain oligomers capped with ammonia (he means amide groups I presume). I think this is probably very likely but I couldn't see how to test it at the time. Having thought about it further and in the light of my results trying to test for amides with sodium hydroxide I think that one way to test it may be to heat some of the "amide" with strong (say 15-20%) aqueous ammonia to about 100 C in my newly acquired autoclave for 10-15 minutes. My idea is that the pure amide is rather resistant to further hydrolysis by ammonia but any uncleaved ester linkages will hydrolyse, some to amides and some to the ammonium salt, the latter are water soluble so the presence of water soluble ammonia salts in the aqueous phase is indicative of unhydrolysed ester linkages, ie there are residual oligomers.

Nitration of TPA
Trial run.

To 100 cm3 Erlenmeyer flask with 30 g of conc. H2SO4 and magnetic dipole, 4 g of TPA is added, next 3,0 g of powdered KNO3 is added in portions. The white muddy mass is stired (or rather moved) by Nd-magnet (outside the flask) after each portion of KNO3. At the start, only 15 g of H2SO4 was used, but it gave not stirrable mass, so additional portion was added.
Next, the flask was placed on the water bath (exactly like in nitration of phtalic acid given in separate topic).
Heating at ~80-90 C during several hours gave nothing interesting - white mudd, slightly less dense on hot.
Heating was paused for 15 hours and continued the next day, but before heating, additional 0,5 g of KNO3 was added.
Soon after it was placed in hot water bath, I noticed the the white mass turn to bright yellow mass and became markedly less
dense. The clear yellow colour soon turn to brown-yellow one, but still bright. During another several hours of heating, the
colour did not change any more, but the mass started to increase its volume (foaming). The flask was removed from the bath and
set aside to cool down. The muddy mixture was less dense even at r.t., it may indicate that "something happened" (good or not good, hah).
The mass was transfered to 100cm3 of chilled water, giving intesively yellow solution with white foamy suspension, some
nitrogen oxide is generated but in so small amount that no hood is needed. It was set aside to cool down again and filtered*.
The white powder (I was almost sure it is unchanged TPA) in the funnel was washed with 2 x 10 cm3 of warm water and dried to
constant weight (4,1 g). I wanted to discadr it, but I noticed (during washing the equipment) the the powder is rather soluble
in water.
The powder was added to ~130 cm3 of water and heating was started. It dissolved gradually as temp. was increasing giving green solution. Several minutes of boiling caused complete dissolution and clear liquid, so it is not TPA !!!
On slow coolig, the solution deposits nothing during hours, but later small globules set on the bottom the flask, but in very small amouts. Keeping this for some time more at r.t. causes precipitation of white powder, supersaturation in this case is very stable, even if solid is already present.
Fitering gave 3,5 g of white** solid and pale green liquid which was kept for another run.

Another run
This time it was 15 g of H2SO4, 4 g of TPA, 3,1 g of KNO3. Procedure conducted as above, the white mud stirred from time to time with Nd-magnet (but I think it has no effect on the progress of reaction; no solid cake is formed during whole time of heating). First, 5-6 hours of heating, pause ~15 hours, and againg heating during ~8 hours. After ~6 hour of the second period, I noticed partial yellow coloration of the white mud and in a short time (<0,5 hour), the white colour turn to brown-yellow, as earlier. Heating was continued for additional ~2 hours (I had no mor time , it was late at night).
It was cooled, transferred into 75 cm3 of water. cooled and filtered. Obtained cake (~8 g), without washing and drying (it is
loosing the time and the product !) was dissolved on hot in green liquid from earlier run.
This time, some (however it looked like miligrams) solid was still present even on boiling, adding 10 cm3 of water gave nothing.
It was filtered on hot, green solution (but not completely clear) was quickly cooled down by immersing the flask in cold water.
Again, no solid was obserwed even cooled below r.t., solution became more turbid only (most possibly unreacted TPA). Suddenly, the solution turn milky and full of white precipitate.
Filtered, washed (~10 cm3 of ice cold water) and weighted: 4,7 g.
The most possibly it is desired nitro-TPA, unfortunately my melting point determination apparatus cannot be used (too low
temp.). I performed titration of this nitro-TPA, to estimate its purity: 0,44 g was titrated with 0,1 M NaOH. The result is 205
(as molar mass), it fits almost perfecly to 209 (theory).
The synthesis is dirty cheap, long-time heating is no problem, beacuse it can be paused at any time and continued later.
Of course, given proportions are surely not optimal but it works

* the filtrate deposits no solid on cooling (even below 0 C)
** it is purely white in LED-light, colour observed in day-light or incandescent lamp has faint yellow coloration

Boffis, I made this titration with phenolphthalein as indicator, because it changes its colour at pH around 9, so it seems to be good choice. I think that purity you calculated (91%), is too low, but without HPLC I cannot prove it
I did reduction of this nitroacid with Fe. I chose this method because it is cheap and almost always works. However, I expected problems caused by the nature of reduced product.
With Fe powder, reduction is quick and takes 30 minutes to complete (with 4 g of nitroacid, 5 g of NaCl, 8 g of Fe, 75 g of H2O).
Unfortunately, prepared solution of aminoacid contains larger amounts Fe(II) - filtration gives clear solution, but after 1 minute it becomes turbid.
It is extremely hard to remove this iron from the solution (for me). I tried careful oxidation with 3% H2O2, but the solution gradualy turns red, most possibly some quinone is formed from the aminoacid. Additionally, formed Fe(III) hydroxide has very bad filtering properities: it comes through every filter I have.....
I have another reduced sample, without H2O2 treatment. It has dirty-pale-yellow colour, with reddish sedimemnt on the bottom.
Filtration gives clear pale greenesh solution, becoming turbid during almost seconds... I checked this solution for Fe(II) content with K3[Fe(CN)6] - the test is strongly positive. So far, I have no idea how to remove Fe from it in a simple way.
But it is really solution of desired aminoacid - it gives strong fluorescence (white-blue) under black-light lamp.

I am going to use Na2S2O4 as reductor the next time, but first I have to prepare some nitroacid (for now, nothing more left).
-------------
Addendum
The turbid solution, with Fe(II) contamination, has pH=5,5.
I was going to add some HCl(aq), but with bottle of this acid in my hand, voices in my head started to shout " Don't do this !".
Yeah, It was stupid idea, so instead of HCl I took NaOH solution and added some to the solution. The effect was terrific: suddenly whole solution turn blue-black for a moment, then some suspension started to float inside, after few seconds I got clear water-like solution with sediment looking like good old "Fe(OH)3".
It was filtered off (small amount) without problems, the filtrate was clear, with pale green-yellow colour, without tendency to become turbid in the air and pH=7,5.
Test for Fe(II) gave nothing, so damned Fe was removed completely.
The solution of amino-TPA is under further investigation.

ps.
0,1 M NaOH means what it means: 0,1 M NaOH
If you want to know more, the manufacturer says that concentration is between x mol/dm3 and y mol/dm3
But can I/you belive it ?
Discussion the difference between 0,1 and 0,14, accuracy of a balance made in PRC, selection of indicators for titration, pK of weak dibasic acid and its starting concentration.... is very interesting, but for separate topic(s).
I just wanted to know if I have TPA or nitro-TPA, so results 205, 210 or 199 are equally good estimations comparing to 166.
In general, performing accurate calculations for some substance with unknown impurities, is pointless.

[Edited on 2-11-2017 by kmno4]

Quote: Originally posted by Boffis

I don't quite understand your second point. The NaOH titration gives you an equivalence number, which is the molecular weight per mole of ionisable hydrogen. So if you started with say 0.25g of acid and the titer was 33ml of 0.1M NaOH then 0.25g = (33 x 0.1)/1000 = 0.0033 moles if it's a monobasic acid or a MW of 75.76. If its a dibasic acid then there are only half as many moles present so 0.00165 mols = MW151.51. When I do this type of titration on phthalic acids I dissolved about 0.2 g in 50ml of 0.1 or 0.2 M standardized NaOH solution and then titrate the excess NaOH against 0.1M HCl. I make up my own standard NaOH solution but I buy the acid a commercial standardized 1M HCl and dilute it to 0.1M and also use it to standardise my NaOH solution. So the accuracy of your MW determination is usually down to two main sources of error, one is the volume of titer which you can only read to an accuracy of about 0.05ml with my burette and the accuracy of the Molarity of the standard solutions but with my terephthalic acid work I was getting a MW of within 1% of the theoretical value, with the terephthalamidic acid there was a difference of 10+ % indicating that it is rather impure. So kmno4's 205 or MW of 207 indicates a mixture of about 91% nitroterephthalic acid 9% terephthalic acid assuming both are anhydrous and the titration is accurate.

Nitration of TPA
Additional runs and interesting observations.

1) 6 g of TPA, 5 g of KNO3, 40 g of H2SO4 (95,5% by titration), total time of heating 23 hours at 75-80 C (total time of pause
about 37 hours). Even during this long-lasting heating, the "mud" inside the flask remains white. At the very end of heating,
the temperature of water bath was increased to 85 C and after short time, the reaction mixture started getting yellow.
So, this colour is rather some sign of decomposition, not the end of nitration.
2) Input as above, total mass of flask at the beginning of heating was 133,7 g, time of heating is 4+10 hours, with 6 hours
pause, temp. was kept between 70 and 80 C. The mass of the flask at the end of heating was 133,7 g. Cooled, white suspension was added to 100 g of ice-cold water (giving green solution+sediment), filter cake was washed with 2x3 g of cold water and dried. 7,1 g of white powder was obtained.
2a) 8,5 g of TPA, 57 g of H2SO4, 7,11 g of KNO3 (the mass of the flask before and after was 155,9 and 155,5 g), 15 hours of heating... 10,0 g of white powder was obtained.

The mass of combined samples of crude nitro-TPA is 24,0 g. 5 g of this acid was dissolved on hot in 100 g of water, chilled and
precipitated powder filtered. The green filtrate* was used for dissolving another 5 g portion... etc.
During some precipitation, the nitroacid deposited as crystalline powder, much easier to filter than the powder form and containing much less absorbed water.
About 0,5 g of this sample was kept for seeding subsequent solutions**.
Combined powders were combined and weighted: 21,8 g (dried). Titration of 0,32 g sample gave molar mass 214 (not bad).
It was purified in the manner as given above and interesting thing was observed: the hot solution of this partly purified nitroacid was practically colourless,ha.
So, the green coloration does not come from nitro-TPA, but from some highly soluble (fortunately) impurities.
About 21 g of crystalline powder (almost white) was obtained (looks similary to benzoic acid).
* these green solutions look the same as solution of K3[Fe(CN)6], at least for me
** solubility of nitroTPA seems to be 0,3-0,5 g per 100g of water (~10 C) and larger than 7 g (larger amounts were not tested) in boiling water.

Addition.
Boffis, your results and calculations seem to me a little aaa... incoherent. Your "hydrates" may exist only in your posts and the most possibly, it is the case. In this particular case of back titration, I would use methyl orange if your NaOH sol. contains larger amount of carbonate.
Next, I would strongly recommend drying your nitroTPA/TPA at least at 110 C (to constant weight). I have noticed that these acids, in powdery form, absorb rather large amounts of water when filtered off some solution. Vacuum filtration helps nothing, filter cake contains up to 50% water. It has nothing to do with hydrates, because the mass, after drying, does not change when kept in the air at r.t.
My experiments presented in this post were performed independently to yours, just simple coincidence. I have to repeat Fe reduction because it seems that I missed some important thing and the yield of aminoacid was close to zero

[Edited on 20-11-2017 by kmno4]

Quote: Originally posted by unionised

As a slight aside. This looks like a good candidate for a back titration. [Edited on 26-11-17 by unionised]

The yield is increased to slightly above 90%, but rather large amount is needed. It seems that Na2SO3, NaHSO3 and SO2 gives some kind of buffer and really large excess of acid is needed to liberate the amino-TPA.
In this way, my experiments with TPA are finished

Quote: Originally posted by Boffis

Hi kmno4, to get the 90% yield do you mean you had to add a lot more hydrochloric acid? I'll be home in a few days so I'll have a go at this.