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Fluxor
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[*] posted on 15-6-2010 at 10:03
paradiclorobenzene - possible degradation of


While cleaning out my mother's attic, I found a large jar of 100% paradichlorobenzene as "moth killer". Apparently, it has never been opened. I was informed by her that it had been stored there about 35 years ago but was never used. The attic in which it was found lacks any kind of climate-control. I know for a fact that in the summers, there is an extraordinary heat build-up in this space.

My question is whether this material, because of the intense heat and over such a length of time, has undergone a level of degradation or decomposition that would likely make it not useful to keep around for future experiments. I don't have anything in mind at the moment, as I'm focusing on inorganic hobby chem for now. However, if in the estimation of the more experienced chemists here, it hasn't degraded, I may keep it.

Myself, I think it may have degraded, judging by its appearance inside the jar. The appearance would suggest that the paradichlorbenzene has partially sublimated owing to its (moderate) volatility. That would explain how the bottom of the jar is almost empty of the substance, and almost all what's remained is thrust toward the lid, as if it wanted to get out. Also, I think it's possible that some of it may have already decomposed into water and CO2.

These are just possibilities based on a google search of the basic properties of the substance. If you have a more accurate idea of what has occurred based on actual experience, I welcome your input and ideas.


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[*] posted on 15-6-2010 at 11:08


Don't worry, it is as clean is it was 35 years ago. If you don't trust me, then measure its melting point and see if it is depressed.
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[*] posted on 15-6-2010 at 11:14


I agree with Nicodem, p-dichlorobenzene is pretty hardy stuff, and would take much more of a harsh environment than your attic could throw at it.
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[*] posted on 15-6-2010 at 11:15


IF it is even what it is labelled as. Asked a few people around the lab, doesn't really look like a benzene. After 35 years, not sure I would trust that the label matches the contents.
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[*] posted on 15-6-2010 at 11:25


"Doesn't look like a benzene"? You can't generalize substituted benzenes to such a degree that they should all look the same. Ibuprofen doesn't look much like benzene either.
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[*] posted on 15-6-2010 at 11:34


Okay, that's fair.

Just adding my two cents. This is the important sentence:

"After 35 years, not sure I would trust that the label matches the contents."
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thumbup.gif posted on 15-6-2010 at 11:45
measurement of melting point


Quote: Originally posted by Nicodem  
Don't worry, it is as clean is it was 35 years ago. If you don't trust me, then measure its melting point and see if it is depressed.


That's great to know. Thank you for your response. I will do some research and set out to try to measure the melting point. I think this could be an interesting experiment in its own right.

Quote: Originally posted by DJF90  
I agree with Nicodem, p-dichlorobenzene is pretty hardy stuff, and would take much more of a harsh environment than your attic could throw at it.


Interesting. What type of harshness would be required? I figured that the air outside the jar, over such a length of time, even with it never being opened, would have at some point begun to enter it and cause it to slowly sublimate.
I agree that it really isn't that harsh, though for a few months of the year the temps go above 37 C.

[Edited on 16-6-2010 by Fluxor]

Quote: Originally posted by gutter_ca  
Okay, that's fair.

Just adding my two cents. This is the important sentence:

"After 35 years, not sure I would trust that the label matches the contents."


Well, my mother claims that it was bought new on or about the time the house was purchased, some 35 years ago, and that it was never used. I tend to believe this is correct. It apparently was simply placed on the attic floor, along with a bunch of boxes in which old clothes were deposited and which piled up around the jar. Then it was just forgotten about. On the innumerable times I've entered the attic, I've never smelled the mothball smell.

[Edited on 16-6-2010 by Fluxor]
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[*] posted on 15-6-2010 at 12:58


Yup! Thats the stuff. I can smell it from here. Used to be cheap as dirt.





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[*] posted on 15-6-2010 at 14:05


Quote: Originally posted by Fluxor  
Interesting. What type of harshness would be required? I figured that the air outside the jar, over such a length of time, even with it never being opened, would have at some point begun to enter it and cause it to slowly sublimate.
I agree that it really isn't that harsh, though for a few months of the year the temps go above 37 C.

p-Dichlorobenzene is thermaly stable up to a couple hundreds degrees, completely inert toward oxygen (air), water, nucleophiles, mild electrophiles, nonreactive toward most metals (with the exception of alkali metals), most bases and acids at room temperare, does not easily photodegradate, it can not biodegradate in its pure form...

Sublimation is just a solid-vapour-solid phase transition, that is a physical phenomenon. It does not cause chemical transformations or degradation! Utmost it alters the crystal structure (the sublimated compound often crystallizes into some different polymorph), but it does absolutely nothing to the molecular structure.

PS: Please start using the edit function (the "Edit" button on the top right of your post). I don't know what is the current forum record for multiple posting, but you sure appear like you are doing your best to beat it.

[Edited on 15/6/2010 by Nicodem]




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[*] posted on 15-6-2010 at 17:53



p-Dichlorobenzene is thermaly stable up to a couple hundreds degrees, completely inert toward oxygen (air), water, nucleophiles, mild electrophiles, nonreactive toward most metals (with the exception of alkali metals), most bases and acids at room temperare, does not easily photodegradate, it can not biodegradate in its pure form...

Sublimation is just a solid-vapour-solid phase transition, that is a physical phenomenon. It does not cause chemical transformations or degradation! Utmost it alters the crystal structure (the sublimated compound often crystallizes into some different polymorph), but it does absolutely nothing to the molecular structure.

PS: Please start using the edit function (the "Edit" button on the top right of your post). I don't know what is the current forum record for multiple posting, but you sure appear like you are doing your best to beat it.

[Edited on 15/6/2010 by Nicodem][/rquote]

According to one study it does react with air, with nitrogen to form hydroxl radicals:

Quote:

Reactions with hydroxyl radicals occur in the atmosphere to breakdown p-DCB to produce nitrochlorobenzene, chlorophenol, and aliphatic dicarbonyl product that are further degraded by photolysis (INCHEM, 2004).


source: Environmental Fate of Paradichlorobenzene
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[*] posted on 15-6-2010 at 19:16


I think you failed to read that correctly : Reactions with hydroxyl radicals to produce the products, not "react with air, with nitrogen to form hydroxl radicals". Hydroxyl radicals are extremely reactive, and produced by high energy reactions generally involving peroxides or short wave UV; they are noted for their ability to chew on aromatic rings. This is taking place in the range of 15 to 60 km up, where there's plenty of shortwave UV; I seriously doubt there as much of that around your jar given it was "on the attic floor, along with a bunch of boxes in which old clothes were deposited and which piled up around the jar."

Figure 2 of that PDF shows this, pDCB + ·OH => intermediate radical, which reacts with O2 or NO2 (not N2) to form those other compounds.

When I was quite young and innocent, I tried "doing things" to pDCB as it was an easily accessible organic compound. Dissolving sodium metal in anhydrous alcohol, then adding pDCB and distilling off the excess alcohol, then refluxing for hours did nothing. It turned out to be more difficult to nitrate or sulfonate than nitrobenzene, and unlike nitrobenzene it had no easy-to-reduce attributes.

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[*] posted on 15-6-2010 at 19:51


Quote: Originally posted by not_important  
I think you failed to read that correctly : Reactions with hydroxyl radicals to produce the products, not "react with air, with nitrogen to form hydroxl radicals". Hydroxyl radicals are extremely reactive, and produced by high energy reactions generally involving peroxides or short wave UV; they are noted for their ability to chew on aromatic rings. This is taking place in the range of 15 to 60 km up, where there's plenty of shortwave UV; I seriously doubt there as much of that around your jar given it was "on the attic floor, along with a bunch of boxes in which old clothes were deposited and which piled up around the jar."

Figure 2 of that PDF shows this, pDCB + ·OH => intermediate radical, which reacts with O2 or NO2 (not N2) to form those other compounds.

When I was quite young and innocent, I tried "doing things" to pDCB as it was an easily accessible organic compound. Dissolving sodium metal in anhydrous alcohol, then adding pDCB and distilling off the excess alcohol, then refluxing for hours did nothing. It turned out to be more difficult to nitrate or sulfonate than nitrobenzene, and unlike nitrobenzene it had no easy-to-reduce attributes.



not_important - Thanks for clarifying. I'd be the first to admit I read wrong. You, Nicodem and the others are a beacon of light in the sea of my ignorance.

I was going to keep it based on the posts by Nicodem, DJF90, but it sounds like you're saying its not a very interesting chem to keep around, owing to its lack of reactivity. What experiments for the beginner (if any) would you suggest can be done with it?
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[*] posted on 15-6-2010 at 22:55


Don't throw it away. It is an interesting chemical which can be used for quite a few physics experiments. E.g. melt some in a test tube and let it cool down again. You can get beautiful glass-like structures in the material. It also can supercool and suddenly freeze. Sublimation and crystallization experiments are others which can be done with it. Its melting point is low and it can be lowered by adding other chemicals. E.g. melting point depression experiments can be done with it.

It only is slightly toxic and has a strong smell (good warning properties). This makes it a safe chemical to do these physics experiments.

From a chemical point of view it indeed is not the most interesting chemical. It might be possible to have it reacting with concentrated HNO3/H2SO4 at higher temperatures. I don't know if this gives interesting results.




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[*] posted on 16-6-2010 at 00:01


The mononitration and dinitration of p-dichlorobenzene has been discussed a few times on the forum and I remember that I posted some references about it in some thread in the Energetic materials section. UTFSE and you will surely find a lot, though most posts are from those who still can not see the difference between an alkyl chloride and an aryl chloride (or SN2 and NAS substitutions) and consequently think they can easily do nucleophilic substitutions on p-dichlorobenzene.
It is hard to design a synthesis experiment with this substrate which would strictly use only readily available reagents. The only one I can think of is the synthesis of hexachlorobenzene, but this is not for some beginner as it requires hazardous conditions: heating of p-dichlorobenzene in concentrated sulfuric acid with trichloroisocyanuric acid. Besides the product is toxic and a possible carcinogen (it was used as a fungicide but not anymore). It is not dangerous for an experienced chemist with proper equipment and a fume hood, but certainly not appropriate for a beginner's experiment where things often go wrong when they can go wrong.
It does react with strong nucleophiles under forcing conditions by the addition/elimination mechanism (NAS substitution), but relatively easily with S-nucleophiles. Only one Cl gets substituted with O- and N-nucleophiles, while with S-nucleophiles it is possible to substitute both Cl. It is a good substrate for transition metal catalysed couplings (particularly for Suzuki-Miyaura and Kumada couplings, but Heck and few other couplings are also described). It also works relatively well for Ullmann condensations but again in most literature examples only one Cl gets substituted. In the Buchwald-Hartwig amination both chlorines get substituted. It is also possible to prepare p-chlorophenylmagnesium chloride from it. You can also hydrogenate it to benzene. Under rather extreme conditions it can even be acylated via the Friedel-Crafts reaction (for example with phthaloyl chloride and AlCl3 at 120°C, or acylation with MeCOCl at 150°C!). Sulfonation is also possible. At least one patent also claims that Friedel-Crafts alkylation is possible.

For now, you just add it to your inventory of chemicals - you will find some interesting experiments to do with it later on.




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smile.gif posted on 16-6-2010 at 03:58
THANK YOU


E.g. melt some in a test tube and let it cool down again. You can get beautiful glass-like structures in the material. It also can supercool and suddenly freeze. Sublimation and crystallization experiments are others which can be done with it. Its melting point is low and it can be lowered by adding other chemicals. E.g. melting point depression experiments can be done with it.

It only is slightly toxic and has a strong smell (good warning properties). This makes it a safe chemical to do these physics experiments.

From a chemical point of view it indeed is not the most interesting chemical. It might be possible to have it reacting with concentrated HNO3/H2SO4 at higher temperatures. I don't know if this gives interesting results.[/rquote]


Thanks woelen!:D



Quote: Originally posted by Nicodem  
The mononitration and dinitration of p-dichlorobenzene has been discussed a few times on the forum and I remember that I posted some references about it in some thread in the Energetic materials section. UTFSE and you will surely find a lot, though most posts are from those who still can not see the difference between an alkyl chloride and an aryl chloride (or SN2 and NAS substitutions) and consequently think they can easily do nucleophilic substitutions on p-dichlorobenzene.
It is hard to design a synthesis experiment with this substrate which would strictly use only readily available reagents. The only one I can think of is the synthesis of hexachlorobenzene, but this is not for some beginner as it requires hazardous conditions: heating of p-dichlorobenzene in concentrated sulfuric acid with trichloroisocyanuric acid. Besides the product is toxic and a possible carcinogen (it was used as a fungicide but not anymore). It is not dangerous for an experienced chemist with proper equipment and a fume hood, but certainly not appropriate for a beginner's experiment where things often go wrong when they can go wrong.
It does react with strong nucleophiles under forcing conditions by the addition/elimination mechanism (NAS substitution), but relatively easily with S-nucleophiles. Only one Cl gets substituted with O- and N-nucleophiles, while with S-nucleophiles it is possible to substitute both Cl. It is a good substrate for transition metal catalysed couplings (particularly for Suzuki-Miyaura and Kumada couplings, but Heck and few other couplings are also described). It also works relatively well for Ullmann condensations but again in most literature examples only one Cl gets substituted. In the Buchwald-Hartwig amination both chlorines get substituted. It is also possible to prepare p-chlorophenylmagnesium chloride from it. You can also hydrogenate it to benzene. Under rather extreme conditions it can even be acylated via the Friedel-Crafts reaction (for example with phthaloyl chloride and AlCl3 at 120°C, or acylation with MeCOCl at 150°C!). Sulfonation is also possible. At least one patent also claims that Friedel-Crafts alkylation is possible.

For now, you just add it to your inventory of chemicals - you will find some interesting experiments to do with it later on.


and Thanks Nicodem!?! :o
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[*] posted on 16-6-2010 at 06:46


-
A silly trick is to put roughly equal amounts of solid pDCB and camphor (natural or synthetic) in a test tube together, they soon form a liquid - in effect dissolving in each other. If you crush each finely beforehand, as well as a little naphthalene, and layer pDCB, a thin layer of naphthalene, and then camphor, in a test tube, they will remain solids for awhile - to a casual view the tube appearing to contain a white powder as the 3 layers are not greatly different in appearance. Shake the tube, the camphor and pDCB mix and liquefy, and dissolve the small amount of naphthalene, giving a single transparent liquid in the test tube.

Liquid pDCB is a solvent for polystyrene, and for sulfur at temperatures from around 100 C to around the melting point of sulfur; the camphor-pDCB liquid also dissolves polystyrene. On cooling back to room temperature some of the dissolved material comes out of solution, giving a somewhat milky to fractured glass appearance to the solid. If left to sit exposed to the air for some time, the pDCB sublimes away, leaving the polystyrene or sulfur as a network of fine threads and thin plates forming a sparse, fragile sponge.

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[*] posted on 16-6-2010 at 10:29


Quote: Originally posted by not_important  
-
A silly trick is to put roughly equal amounts of solid pDCB and camphor (natural or synthetic) in a test tube together, they soon form a liquid - in effect dissolving in each other. If you crush each finely beforehand, as well as a little naphthalene, and layer pDCB, a thin layer of naphthalene, and then camphor, in a test tube, they will remain solids for awhile - to a casual view the tube appearing to contain a white powder as the 3 layers are not greatly different in appearance. Shake the tube, the camphor and pDCB mix and liquefy, and dissolve the small amount of naphthalene, giving a single transparent liquid in the test tube.

Liquid pDCB is a solvent for polystyrene, and for sulfur at temperatures from around 100 C to around the melting point of sulfur; the camphor-pDCB liquid also dissolves polystyrene. On cooling back to room temperature some of the dissolved material comes out of solution, giving a somewhat milky to fractured glass appearance to the solid. If left to sit exposed to the air for some time, the pDCB sublimes away, leaving the polystyrene or sulfur as a network of fine threads and thin plates forming a sparse, fragile sponge.



Thank you friend!:) ....And to think I was about to get rid of it...(actually, take it to a hazardous waste facility). Glad I had second thoughts and posted here.

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[*] posted on 17-6-2010 at 17:05


Quote: Originally posted by Nicodem  
The only one I can think of is the synthesis of hexachlorobenzene, but this is not for some beginner as it requires hazardous conditions: heating of p-dichlorobenzene in concentrated sulfuric acid with trichloroisocyanuric acid. Besides the product is toxic and a possible carcinogen (it was used as a fungicide but not anymore). It is not dangerous for an experienced chemist with proper equipment and a fume hood, but certainly not appropriate for a beginner's experiment where things often go wrong when they can go wrong.
It does react with strong nucleophiles under forcing conditions by the addition/elimination mechanism (NAS substitution), but relatively easily with S-nucleophiles. Only one Cl gets substituted with O- and N-nucleophiles


:o I wouldn't try to substitute -Cl for -OH on hexachlorobenzene! My guess is that under the basic conditions the pentachlorophenol condenz to give octachlorodibenzodioxin. I do not know the dangers associated with this compound, but I know that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is nothing I would like to produce in my lab since it is extremely potent mutagen (remember the chlor-acne face of that former Ukraine prezident). Even if the condensation to the heterocycle is a minor side reaction it might make enough compound to ruin your life (and your coming children) if you are not cautious. TCDD is nasty since the organisms have trouble metabolizing it and I can't see where metabolizm would attack octachlorodibenzodioxin either, although it might not be as toxic, but Fluxor, I would advise you not to mess around mixing hexachlorobenzene with NaOH/KOH to make the pentachlorophenol...




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[*] posted on 18-6-2010 at 09:32


Don't make Fluxor afraid. You are talking about hexachlorobenzene, he has p-dichlorobenzene. Fluxor will need to go along a difficult route before he has hexachlorobenzene. With p-dichlorobenzene you can do some funny physics experiments and from a chemical point of view it indeed is best for Fluxor to wait some time before he has more experience/knowledge.



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[*] posted on 19-6-2010 at 07:01


Quote: Originally posted by Sandmeyer  
Quote: Originally posted by Nicodem  
The only one I can think of is the synthesis of hexachlorobenzene, but this is not for some beginner as it requires hazardous conditions: heating of p-dichlorobenzene in concentrated sulfuric acid with trichloroisocyanuric acid. Besides the product is toxic and a possible carcinogen (it was used as a fungicide but not anymore). It is not dangerous for an experienced chemist with proper equipment and a fume hood, but certainly not appropriate for a beginner's experiment where things often go wrong when they can go wrong.
It does react with strong nucleophiles under forcing conditions by the addition/elimination mechanism (NAS substitution), but relatively easily with S-nucleophiles. Only one Cl gets substituted with O- and N-nucleophiles


:o I wouldn't try to substitute -Cl for -OH on hexachlorobenzene! My guess is that under the basic conditions the pentachlorophenol condenz to give octachlorodibenzodioxin. I do not know the dangers associated with this compound, but I know that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is nothing I would like to produce in my lab since it is extremely potent mutagen (remember the chlor-acne face of that former Ukraine prezident). Even if the condensation to the heterocycle is a minor side reaction it might make enough compound to ruin your life (and your coming children) if you are not cautious. TCDD is nasty since the organisms have trouble metabolizing it and I can't see where metabolizm would attack octachlorodibenzodioxin either, although it might not be as toxic, but Fluxor, I would advise you not to mess around mixing hexachlorobenzene with NaOH/KOH to make the pentachlorophenol...

Hm, I guess my review of the p-dicholorobenzene reactivity had an ambigous start. The reactions listed are in regard to p-dichlorobenzene and NOT hexachlorobenzene. Hexachlorobenzene is not that scary. We have half a kilo of it at my job, but nobody yet figured out what to do with it. Still I do agree and like I already said before, it is not an appropriate target for a beginner. But some other reactions on p-dichlorobenzene can be interesting for amateur chemists. Some that can be run under relatively mild conditions should be fine for beginners as well (for examples, bisarylating it by a Suzuki coupling is a nice introduction to the Pd- or Ni-catalysed coupling reactions).




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[*] posted on 28-6-2010 at 02:46


I did a funny little experiment with p-dichlorobenzene. I took approximately 2 grams of the solid and put this in a test tube. I heated this material, such that it became a colorless mobile liquid (I didn't measure the temperature, but it was not really hot, at most 75 C or so). To this liquid I added a tiny speck of solid iodine. This dissolves with a beautiful purple color. Next, I let the liquid cool down slowly. At a certain point in time, it solidifies, but when this happens a peculiar effect can be observed. The liquid first solidifies at the glass walls (which is expected, heat is lost through the glass walls of the test tube), but the solidified material is colorless! Slowly the solidification goes more inwards and the colorless layer reaches a thickness of well over 3 mm. Finally, when all of the material has solidified, a dark core is in the middle of the sample and a colorless/transparent layer is around the core.

So, two remarkable effects can be observed:
1) The freezing process removes the impurity of the iodine to quite a large extent.
2) The color of the dissolved iodine changes from purple to brown when the liquid solidifies.

This is a cute and safe experiment, which may be interesting for Fluxor as well. Iodine can be made from KI, some acid and dilute H2O2. You just need a few specks.

Cleanup after this experiment can be done by heating the material again, such that it becomes liquid again. Then the liquid can be poured out on a paper tissue (do this outside) and the paper tissue can be put in the household waste. The test tube then can be rinsed with 1 to 2 ml of acetone or petroleum ether. The liquid can be evaporated outside on a paper tissue and when most of the liquid has evaporated the tissue can be put in the household waste. Two or even three rinses may be necessary to make the test tube really clean.

[Edited on 28-6-10 by woelen]




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[*] posted on 28-6-2010 at 07:20


Thanks for that, woelen. This sounds like something I'd like to do. I may try the experiment today, in fact!

I don't have KI in stock in my home lab right now, but I do have tincture of iodine, H2O2 (3%), HCL (10.3M) from which I can make I crystals by mixing the three chemicals, filtering, and then evaporating the precipitate to dryness.

I know this is an inefficient way to obtain elemental iodine but I'm planning to place a large order in about a month to round out my lab stock, so I will soon have KI. I checked the Readily Available Chems website but an OTC source for KI is not mentioned.

Greatly appreciate your ideas for experimentation. Thank you once again.
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[*] posted on 28-6-2010 at 10:16


I wouldn't be surprised if the purity of your sublimed product exceeds that of the original contents.

p-DCB can also be obtained from urinal cakes.

It looks like p-DCB can be reacted with sodium sulfide (Na2S) to give poly(p-phenylene sulfide), which might be interesting:

http://en.wikipedia.org/wiki/Poly(p-phenylene_sulfide)

I attached a paper detailing the preparation (and mechanism) of this polymer.

Cheers,

O3

[Edited on 28-6-2010 by Ozone]

Attachment: Poly(p-phenylene sulfide)_Fahey et al, 1997.pdf (341kB)
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[*] posted on 28-6-2010 at 12:02


Ozone, your reaction must be done using N-methylpyrrolidinone as a solvent. This does not sound like something most home chemists have on their shelves. In aqueous solution this polymerization reaction cannot work, because p-dichlorophenol does not dissolve in water.



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[*] posted on 28-6-2010 at 19:03


I thought N-methylpyrrolidinone could be had from "green" paint strippers:

http://www.popularwoodworking.com/features/finish7.html

A fairly "innocent" product that is NMP, 99%:

http://talasonline.com/photos/msds/MSDS_NMP.pdf

I suspect that other polar aprotic solvents might work as well, e.g. N,N'-DMF. See:

http://www.freepatentsonline.com/4038263.html

Specifically, "The organic amides for use in the process of this invention should be substantially liquid at the reaction temperatures and pressures employed. The amides can be cyclic or acyclic and can have 1 to about 10 carbon atoms per molecule. Examples of some suitable amides include formamide, acetamide, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-ethylpropionamide, N,N-dipropylbutyramide, 2-pyrrolidone, N-methyl-2pyrrolidone, ε-caprolactam, N-methyl-ε-caprolactam, N,N'-ethylenedi-2-pyrrolidone, hexamethylphosphoramide, tetramethylurea, and the like, and mixtures thereof."

I attached the supplimentary material from this patent.

Cheers,

O3



Attachment: US4038263-phenylenesulfide.pdf (230kB)
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