Sciencemadness Discussion Board - picric acid from aspirin

picric acid from aspirin

spirit - 10-11-2012 at 12:03

I need help. I have ran this reaction twice almost to completion. I have seen the color changes but have no precipitate.

I have extracted aspirin from 20, 325mg tablets. I have two procedures both describing the same process. Both are equally vague.

The first adds 5 grams aspirin to 80ml fuming h2so4 on water bath for fifteen minutes. Solution turns yellow. It is removed from heat and 15g KNO3 is added in the additions with stirring. There's no brown gas evolved but there are fumes produced. After the additions solution turns red and with stirring becomes yellow again. It is cooled to room temp and added to 1000ml h2o and crushed ice. Yellow crystals are supposed to precipitate and get filtered. the yellow residue is washed twice with cold water to yield picric acid.

The second method starts by adding 5g aspirin to 80ml fuming h2so4 at 70deg c. Solution turns yellow. It is cooled to 50 def c. And KNO3 is added. Solution turns red. Stirring until it returns to yellow. It is brought to room temp and added to 1000ml ice water. The ice is allowed to melt on it's own and the yellow crystals that precipitate are filtered.

The first time there were no temps to follow and I believe I reduced the aspirin to acetic acid which is why there was no product. The second time seemed to go fine but here I am after the ice melt with no precipitate and 1.5 liters of corrosives I don't want to filter if I've already bombed it.

Boffis - 10-11-2012 at 15:49

Use the search engine, there are probably more picric acid synths on this web site and any other compound, some very detailed indeed. Also during this nitration both acetic acid and CO2 are given off so your comment "I believe I reduced the aspirin to acetic acid" probably indicates that you at least hydroysed the aspirin to salicylic acid.

Mailinmypocket - 10-11-2012 at 16:04

Why on earth are you using so much FUMING sulfuric? Where did you get your synthesis from?

*BTW this should be in the energetics section of the forum.

[Edited on 11-11-2012 by Mailinmypocket]

plante1999 - 10-11-2012 at 16:13

I already made 1 g of picric acid from aspirin. I didn't purified the aspirin. I didn't had any use for the picric acid so I just stored it under water. I don't think I could use it for something, I just made the picric acid because I like how all old Lab had a bottle full of it, I also wanted to make phenol from it but I found it to be quite difficult to do. 1g under water should be quite safe

I used 14 ml 96% H2SO4
2 g KNO3
1 g aspirin

First I dissolved the aspirin in the sulphuric acid and added the KNO3, it turned red. Then I heated it with an alcohol burner, It turned black and made a lot of gas, after few minutes of heating the solution turned very light yellow. Then I added the solution on a 50ml ice cube and I waited until it melted. I filtered the solution and I got 1 g of picric acid when dried.

WARNING!
Picric acid stain really strongly most organic material especially skin and nail! The yellow color fade take about 10 day for skin and doesn't for nail until you cut them!

[Edited on 11-11-2012 by plante1999]

spirit - 10-11-2012 at 16:59

Mailinmypocket- the first comes from an improvised munitions handbook. Most of the precursors are made from other sections in the book. I made my KNO3 only. It calls for boiling battery electrolyte for the fuming h2so4. I was attempting hardware grade that had been clarified by boiling with h2o2. I think the volume it calls for is before boiling until fuming, all other procedures I've seen use around 80ml h2so4.

I noticed how saturated the solution became (that oily look) after the KNO3 addition. If it appeared saturated at this volume, maybe it wouldn't have been able to dissolve a batch this size (roughly 5x plante1999 synthesis). off the top of my head I remember KNO3 dissolves around 1g/16ml h2o and I used 15g...

good point about the energetics section, slipped my mind. my apologies.

Plante1999, thanks for sharing your experience. I will have to try your way. Were you able to see a precipitate in the solution before you filtered? Of the techs i have one way insinuates a residue of picric acid, and the other crashes yellow crystals with the ice water. I'm just wondering if I should be seeing 4-5g of material floating around before I decide to filter this beaker.

plante1999 - 10-11-2012 at 17:09

When I added the picric acid to the ice cube it change color from slightly yellow to a really bright yellow, after the ice cube as melted there was yellow powder floating around. Filter while cold tough.

And please delete one of the two similar reply you made.

Mailinmypocket - 10-11-2012 at 17:42

Battery grade sulfuric acid is 85% If not less, or around that. Boiling it until it fumes does not make it "fuming sulfuric acid" it just concentrates it. Fuming sulfuric acid is made by adding sulfur trioxide to concentrated sulfuric acid (98%+) and having free SO3 in the acid. What you probably have is pretty concentrated sulfuric acid, not fuming. Still, it seems to be a bit much as far as the synth is concerned.

[Edited on 11-11-2012 by Mailinmypocket]

spirit - 10-11-2012 at 19:55

I realize it's garbage in garbage out. The improvised handbook has you boil until fumes because that might be all you can do in the field. I'm going through the book just to see how realistic it's claims are and then I am trying it again for purity.

Might I have success dissolving the aspirin in h2o, generating SO3 FROM cupric sulfate, and bubbling with heat? Buying good acid isn't a problem, I just want to make as much from scratch as I can first.

spirit - 11-11-2012 at 14:27

I let the flask settle and there is a layer of black on the bottom which I think is the sulfuric acid contaminants. I can now see a bunch of particles suspended in solution. Maybe I can decant some while leaving the black behind. Thanks for the help.

caterpillar - 11-11-2012 at 15:33

Quote: Originally posted by plante1999

I already made 1 g of picric acid from aspirin. I didn't purified the aspirin. I didn't had any use for the picric acid so I just stored it under water. I don't think I could use it for something, I just made the picric acid because I like how all old Lab had a bottle full of it, I also wanted to make phenol from it but I found it to be quite difficult to do. 1g under water should be quite safe

I used 14 ml 96% H2SO4
2 g KNO3
1 g aspirin

First I dissolved the aspirin in the sulphuric acid and added the KNO3, it turned red. Then I heated it with an alcohol burner, It turned black and made a lot of gas, after few minutes of heating the solution turned very light yellow. Then I added the solution on a 50ml ice cube and I waited until it melted. I filtered the solution and I got 1 g of picric acid when dried.

WARNING!
Picric acid stain really strongly most organic material especially skin and nail! The yellow color fade take about 10 day for skin and doesn't for nail until you cut them!

[Edited on 11-11-2012 by plante1999]

You had to take at least twice more KNO3. Check your numbers. And remember, that some excess of KNO3 (33% at least) is a must. My first attempt to prepare picric acid was realized with the same mistake. Later I used phenol- 250 gr and 1000 gr of KNO3.

Hawkguy - 7-11-2014 at 22:27

I just did this, but the precipitate colour was that of white people, like a pinkish beige.... Could I have made a wierd isomer?

greenlight - 8-11-2014 at 00:20

I tried a variation of the first procedure stated by Spirit a couple of years ago but had the same problem with no precipitate at all, just yellow ice-water. I tried it two more times before after this before giving up, with more heating time while adding the ASA and slower addition time of the Potassium nitrate with longer stirring and ended up with a small amount of picric acid but not worth the time.
I don't think there was enough Kno3 in the reaction but I will try again in the future with some users variations from the old E&W forum i have written down, or if I can locate phenol.

[Edited on 8-11-2014 by greenlight]

Hennig Brand - 8-11-2014 at 05:30

Look for, "Rosco's Good Old Country Recipe for Picric Acid". It is basically foolproof as long as the instructions are followed. I used to try and get creative with this synthesis back when my scientific background was such that most improvisations done by me were not improvements. Rosco's method seems to be very nearly optimized.

greenlight - 8-11-2014 at 05:43

Thanks, I will look for that document and try his synth if i can find it.

Rosco Bodine - 8-11-2014 at 08:55

Quote: Originally posted by Hennig Brand

Look for, "Rosco's Good Old Country Recipe for Picric Acid". It is basically foolproof as long as the instructions are followed. I used to try and get creative with this synthesis back when my scientific background was such that most improvisations done by me were not improvements. Rosco's method seems to be very nearly optimized.

I think this should help

http://www.sciencemadness.org/talk/viewthread.php?tid=389&am...

forgotpassword - 9-11-2014 at 07:36

I was under the impression that the Aspirin had to be hydrolysed to Salicylic Acid before nitrating it

Hennig Brand - 9-11-2014 at 09:13

If aspirin is used instead of salicylic acid hydrolysis occurs in the hot sulfuric acid sulphonation stage of the process. The products of aspirin hydrolysis are salicylic acid and acetic acid. The salicylic acid is then sulphonated to almost exclusively 5-sulphosalicylic acid from what I understand.

Product of Direct Sulphonation of Salicylic acid.jpg - 41kB

During nitration the sulphonic acid group is easily substituted by a nitro group and finally the dinitro-salicylic acid is decarboxylated and the final nitro group is added producing picric acid. The decarboxylation is witnessed as the foaming that occurs especially during the last third of the nitrate salt addition.

[Edited on 9-11-2014 by Hennig Brand]

TGT - 10-11-2014 at 00:10

Picric acid is one of my favorite energetics to synthesize, second being ETN. I have made it many times over the last couple years and have now got it down to perfection. I have used 70% nitric acid and also ammonium nitrate and have found no difference in yield or quality. One of the most important attributes in a successful batch is temperature control vs time.

If anyone is interested in the details let me know. I have wanted to get it recorded for sometime as my notes are extremely messy, not to mention the hole that goes through them from a large drop of sulphuric acid lol. If someone wants a write up it will push me to make a good copy. I unfortunately have severe procrastination problems.

TGT

greenlight - 10-11-2014 at 05:02

I would be very interested in a reading writeup of your picric acid synthesis from 70% nitric acid as i want to attempt to make this explosive in the next week or two after I purchase some aspirin tablets to extract. I have tried it acouple of times before with low yields (almost nothing).

I will try yours since you say you have got it down to perfection if its uses acetylsalicylic acid.

TGT - 10-11-2014 at 06:35

Okay, I will do a write up as soon as I can and post it. I need to record it anyways for my own personal notes so thanks.

TGT

TGT - 11-11-2014 at 19:13

Well, here is half the procedure. I wrote it very detailed so that there would be hopefully no problems while performing this task. The next part I'll post in a couple days. Also, I am sure there is many Picric Acid procedures here, but I just wanted to post the one I know for me to be the best.
------------------------------------------------------------------------
Picric Acid from ASA Tablets / ASA Extraction

The following will describe in detail how to extract Acetylsalicylic Acid (ASA) from over the counter tablets and then finally convert it to Picric Acid for use as a booster in high explosive caps. You can do this all in one run, but I like extracting the ASA to high purity first and then drying for later use. You can use it before it dries, but for our purposes I will describe how to do it separately for clarity.

First you must find ASA tablets that contain the least amount of ingredients. The no name brands are usually best for this as they contain only Corn Starch and Microcrystalline Cellulose as binders. Both binders are not soluble in alcohol and ASA is, so this will make extraction very easy. I will be using a box with a count of 500 tablets each containing 325 mg. This will give us a theoretical yield of 162.5 grams of pure Acetylsalicylic Acid.

Materials for ASA Extraction:

• 2 1000 ml Beaker - Coffee grinder/Mortar and Pestle
• 2 Coffee Filters - Stir Stick
• Approximately 600 ml of Methanol - 600 ml cold Water
• 500 325 mg ASA Tablets - Ice or access to a fridge

Procedure:

- Crush ASA tablets into a fine powder using the Mortar and Pestle and/or a Coffee Bean Grinder.

- Place powdered tablets into a 1000 ml beaker and add 600 ml Methanol.

- Place ASA/Methanol mixture on a hot plate and heat until hot, but not boiling, while stirring well. Five minutes or so should be enough time to dissolve the ASA. The ASA will dissolve, but the binders will not. Remove beaker from hot plate.

- Place a Coffee Filter on another 1000 ml empty beaker and filter the ASA/Methanol mixture and discard the binders and filter paper. Now there should be only ASA and Methanol in the beaker.

- Place beaker back on hot plate and boil the liquid down to 150 ml. I use Methanol because it has a low boiling point and we want to keep the temperature below 60 degrees Celsius so that the ASA does not hydrolyze and break down into Salicylic acid. For Picric Acid production it probably doesn't matter, but for our purposes we will keep it as ASA. You can use Isopropyl Alcohol or Ethanol if you do not have Methanol, but still keep an eye on the temperature and it will take longer to boil down. Make sure you do this outside or in a fume hood. The vapors are toxic and the liquid flammable.

- Fill an empty 1000 ml beaker with 600 ml of ice cold water and crash the 150 ml of Methanol/ASA liquid into the water. You will instantly see precipitate forming as ASA is not soluble in water. This also gives you very clean product instead of boiling to dryness. Also boiling to dryness could cause the ASA to turn to Salicylic Acid.

- Stir gently and if still warm from the addition of Methanol place in a fridge for a few hours, then filter and dry. The crystals will be pure white and fluffy. You can speed drying by dabbing and pressing the water out with a dry paper towel. Usually the crystals will not stick to the paper. You will have very pure Acetylsalicylic Acid to use for our next step. I like to do this procedure on day 1, and then on day 2 start with the Picric Acid.

to be continued......

greenlight - 11-11-2014 at 23:05

Thanks I will do this step now and as soon as you write up the second part I will give it a go and post results to see if I can get the same high yields as you.
I like the idea of methanol instead of isopropanol to extract the ASA because it is much cheaper here to buy than the isopropyl alcohol.

TGT - 21-11-2014 at 20:17

Picric Acid from ASA Tablets / Part 2

The following will describe in detail how to convert the Acetylsalicylic Acid (ASA) from the previous procedure to Picric Acid, a very powerful explosive material. This is a very dangerous synthesis and should be performed by someone with adequate experience in energetic materials. It should also be performed in a fume hood or outside, never indoors without proper ventilation. There is always a chance of a runaway reaction when adding the Ammonium Nitrate or Nitric Acid (depending on which you choose to use). This happens when the temperature is not kept in the proper range or the materials are added too quickly. That is why it is always a good idea to have a large bowl of water/ice cubes with sodium bicarbonate mixed in as a safety precaution. If something unexpected should happen you can always dump the project into the bowl and avoid being injured.

In the previous experiment we purified more ASA than is needed as the following procedure will only use 35 grams of ASA. The reason for this is to keep the experiment relatively small and simple. After experience in synthesizing Picric Acid you can scale up the procedure. Scaling up is not mathematically consistent and required experimentation. That is why at the end of this document I added some values to follow for larger batches that I have previously completed with excellent yields.

One last important note before we start. In this procedure you can substitute Ammonium Nitrate for 70% Nitric Acid. I have found that 1 milliliter of 70% Nitric Acid is equal to 1 gram of pure Ammonium Nitrate. For every gram of ASA you will need 2 grams or 2 ml of 70% Nitric Acid. Sulfuric Acid will vary with use of Ammonium Nitrate, Nitric Acid or batch size. For this experiment we will be using Nitric Acid.

Materials for Picric Acid Synthesis:

• 250 ml Round bottomed flask - 500 ml Graduated Cylinder
• Thermometer - Glass Stir Stick
• Hot Plate - Hot Water Bath
• 35 grams of ASA - 70 ml of 70% Nitric Acid
• 95 ml of 96% Sulfuric Acid - Digital Scale
• 2, 1000 ml Beakers - Filter Paper

Note: If using Ammonium Nitrate in place of Nitric acid, add 110 ml of sulfuric acid. The rest of the measurements are to stay the same. Just make sure with every addition of Ammonium Nitrate you mix extremely well and dissolve it all before adding more.

Procedure:

- Set up the hot water bath and place on hot plate. Preheat the water to 70 degrees Celsius so that it stays at this temperature consistently. I personally didn’t use a hot water bath. Instead I used a coffee mug heater that maintained my temperature in the proper range and I found this worked well. To be safe use a water bath, but use your own judgment.

- Add 95 ml of Sulfuric Acid to the 250 ml round bottomed flask and place it in the hot water bath.

- Weigh out 35 grams of ASA and set aside.

- With your glass thermometer measure the temperature of the Sulfuric Acid and when it reaches 65 to 70 degrees Celsius start the addition of powdered ASA. Add around a gram at a time while stirring or swirling and watch your temperature. The temperature will increase slightly with each addition, but not nearly as much as when the Nitric Acid is added. Make sure that all of the ASA is dissolved well into the Sulfuric Acid before adding more. Consistent stirring or swirling is very important to avoid hot spots and to dissolve each addition properly. Do not let your temperature increase beyond 95 degrees Celsius. You should try to reach the 95 degree mark at the end of ASA addition.

- After the ASA addition has completed continue heating at 95 degrees Celsius for 45 minutes while stirring or swirling occasionally. The additional heating will sulfonate and decarboxylize the ASA. If your acid is clean you should see a color change from red to very dark brown or black. You probably will not see this color change if your Sulfuric Acid is hardware store grade. Just follow the temperatures and times listed and it will be fine.

- After 45 minutes of heating remove the solution from the hot plate and let it cool down to around 30 to 35 degrees Celsius. After it has cooled to this temperature it is time to add the Nitric Acid.

Note: If your using Nitric Acid over 75% pure you might want to start the addition at room temperature or cooler. The higher the percent the lower your starting temperature should be. The beginning temperature is for 70% because that is what I used for this synthesis.

- Measure out 70 ml of Nitric Acid using your graduated cylinder.

- Add extremely slow your Nitric Acid a few ml at a time to your Sulfuric Acid/ASA solution while stirring or swirling continuously. At the start do the addition of Nitric Acid without the hot water bath and keep an eye on the temperature. Try to increase the temperature gradually so that the beginning nitration is started at 35 degrees while the end of nitration reaches 85 to 90. Use the hot water bath if necessary. This temperature range works reliably well and is much safer than heating too hot. Keep in mind there will be some red Nitrogen Dioxide gas with each addition, but if done slowly this should be kept to a minimum. Near the end of the Nitric Acid addition the bubbling should slow and the reaction mixture takes on a canary yellow to tomato sauce red color, depending on batch size. The entire Nitric Acid addition should take around half to one hour to complete, but this can vary. Remember stirring or swirling is essential.

- Now that the Nitric Acid addition is complete, set up the hot water bath to a consistent temperature of 95 degree’s Celsius and heat the reaction mixture/beaker while swirling often. Continue heating for no less than 1 hour at this temperature. This will complete the reaction. Make sure you always keep a good eye on what is happening and never leave the chemicals unattended. Also, be sure to have your safely bowl of water and Sodium Bicarbonate close by as described earlier. This was not added to the materials list, but should be considered important.

- Now let the reaction mixture cool to room temperature. You will start to see the mixture thicken up and crystals will begin to precipitate.

- Fill a 1000 ml beaker with 500 ml of ice cold water. Next, pour the reaction mixture into it. It will turn a beautiful shade of canary yellow. Picric Acid will begin to drop out of solution. It is very important to leave this beaker in a cool place for 24 hours. A refrigerator would be ideal. Picric Acid crystals sometimes take a long time to form and the longer you wait, the better the yield.

- After the 24 hours filter your crystals with filter paper and the other empty 1000 ml beaker and now you have crude Picric Acid. Wear gloves and do not spill or drip any as it is extremely hard to remove, especially from skin. My lab bench is now a permanent shade of yellow to remind me of my clumsiness. When finished you can press dry the crystals with a paper towel and place in a warm dry environment. Picric Acid is not extremely hydroscopic so it should dry to a nice powdery consistency after crushing. Even at this stage it is relatively pure and can be used for most purposes. In part 3 we will be recrystallizing them to get pure crystals of Picric Acid that can be safely stored for many years.

To be continues…

------------------------------------------------------------------------
Sorry this second part took so long. It was late when I finished it, so if anyone see's any mistakes please let me know. I tried to write it as accurate as I could from my messy notes. I have tried this numerous times and is always reproducible. Any questions let me know.

TGT

[Edited on 22-11-2014 by TGT]

greenlight - 23-11-2014 at 02:35

I just did the second step and everything went perfect but I just have a question about the last part of the nitration.

I added the 70% Nitric acid from an addition funnel in small portions over a 40 minute period and completed the addition fine. After the HNO3 addition, I placed the reaction mix which was 80. C on a heat bath to bring it to 95.C for the hour. When it got close to 95.C the reaction mixture started to give off continuous small amounts of fumes of red Nitrogen dioxide but I continued anyway. Is this normal?
After it had been on the heat bath for about 15 minutes it started giving off more Nitrogen dioxide and went from tomato red to orange with small crystals of picric acid coming out in the mixture.
I took it off heat when this started happening and more crystals came out until it all turned into a slurry of crystals. I dumped it into ice water and it is still precipitating.
The synthesis worked so its not a problem I was just wondering if it has happened to you before?
I was thinking maybe I didn't need the extra nitration time because I'm using reagent grade acids, or maybe my stir bar had small particles of metal it had picked up off the benchtop on it and they reacted with the Nitric acid?

Bert - 23-11-2014 at 09:48

Quote:

the reaction mixture started to give off continuous small amounts of fumes of red Nitrogen dioxide but I continued anyway. Is this normal?

This reaction reliably produces nitrogen oxides, hence the frequent mention of needing a proper fume hood or outdoor setup/fan for vapor extraction and protective gear (mask with correct filters for NOx and sufficient capacity to carry you through the exposure time) in order to avoid injuring or killing yourself.

You DID provide for fume removal and wore protective gear, correct?!

If not, PLEASE tell someone responsible what you just did, and be aware that pulmonary edema from such vapors often takes a while after exposure to become obvious! We don't need any MORE dead amateur chemists.

Quote:

Acute Exposure Nitrogen dioxide is thought to damage lungs in three ways: (1) it is converted to nitric and nitrous acids in the distal airways, which directly damages certain structural and functional lung cells; (2) it initiates free radical generation, which results in protein oxidation, lipid peroxidation, and cell membrane damage; and (3) it reduces resistance to infection by altering macrophage and immune function. There may be an immediate response to exposure to nitrogen oxide vapors that may include coughing, fatigue, nausea, choking, headache, abdominal pain, and difficulty breathing. A symptom-free period of 3 to 30 hours may then be followed by the onset of pulmonary edema with anxiety, mental confusion, lethargy, and loss of consciousness. If survived, this episode may be followed by bronchiolitis obliterans (fibrous obstruction of the bronchioles) several weeks later. Any of these phases can be fatal.

RIP myfanwy

[Edited on 23-11-2014 by Bert]

greenlight - 23-11-2014 at 15:44

Bert, I'm sorry for making that post sound like I didnt have any protection, I do not own a fume hood but did the reaction outside with a respiratory full face mask with a filter that protects against the NOx.
I didn't mean to cause confusion by not adding in my post that I wore protective gear, as am aware of the dangers of NItrogen dioxide. On second look, asking if nitric oxides normal during a nitration does look a bit stupid.
I just wondered if anyone else had the same continuous plume of red Nitrogen dioxide after the Ntric acid addition. I am used to seeing lots of white fumes and small amount of red sometimes during nitrations but never continuous red fumes. Maybe I have nothing to worry about, as the yield is fine, its just unusual how it started precipitating out of nowhere when the reaction mix was still on the heat bath.

[Edited on 24-11-2014 by greenlight]

Hennig Brand - 23-11-2014 at 20:04

Are you providing good mixing for the reactants? If not, you will normally get hot spots and oxidation and NOx.

Gradual nitric/nitrate addition and gradual temperature increases prevent the buildup of reactants which can cause short bursts of fast reaction rate which are exothermic and cause temperature increases (which further increases reaction rate; positive feedback). Really good mechanical stirring is very important to prevent hotspots and oxidation and loss of nitrogen witnessed as the poisonous red gas escaping from the reaction vessel. If you are losing a lot of red gas you are losing nitrogen that could have been used to nitrate the salicylic acid or phenol. When you see a lot of sudden heat and red gas, there are probably some undesirable reactions taking place as well, like oxidations and tar production. A certain amount of red gas is normal, but I almost never see it when I run a picric acid synthesis. I take my time gradually increasing the temperature and adding the nitrate slowly and evenly and I make sure the magnetic stirrer is really moving. The synthesis can be conducted without a mechanical stirrer, if one understands how to compensate, but it is not ideal.

greenlight - 23-11-2014 at 20:17

Thanks Henig brand, I was stirring using a magnetic stirrer on half speed. I think I did the NItric acid addition a little too fast and the temp came up too quick. Maybe I was not stirring fast enough as well as you say to make sure the stirrer is really moving.
Do you have any idea why the sudden precipitation of picric acid that started coming out after 15 minutes off heating at 95.C. When I took tge beaker off heat it just turned into a slurry of crystals.
I have a fine yield which is drying now but I am just curious about the sudden precipitation.

Hennig Brand - 23-11-2014 at 20:35

I would say you reached the saturation limit for the liquid phase, which resulted in picric acid precipitating. Lowering the temperature even more reduced the solubility still furthur (more picric acid precipitated).

[Edited on 24-11-2014 by Hennig Brand]

Rosco Bodine - 23-11-2014 at 21:34

There are several things reported in this thread which causes me to raise an eyebrow as to the credibility or accuracy of the process described, recognizing that there are issues apparent for the manipulations which simply do not compute. The 250ml volume for the reaction flask is just one of the issues and there are a list of them. I for several reasons find the information being shared in this thread suspect and I think other readers would also read along to a point and be struck with incredulity, move along a bit further and have that reoccur, move along a little more, and shrug the shoulders at the same points as I do.

Not meaning to get into making a list .....but putting a foaming agent in a quench bath for a nitration mixture is simply asinine.......for one example. It only makes sense to someone who thinks they have situational awareness because they don't really understand the situation, but only think incorrectly that they do.

TGT - 23-11-2014 at 23:16

Greenlight. I am glad it worked out for you. About your red gas being emitted, this is normal, but if using 70% Nitric Acid you should not get too much if added slowly. I think in your case you were using regent grade at a high concentration so this is probably why. With higher concentrations you should start off at a lower temperature and I think I wrote that somewhere. It seems you didn't need to heat to 95, may be 90 is a good limit. Also, I wrote to heat for no less than 1 hour, probably half hour is enough and I think I should change it. I just wanted to make sure it was nitrated properly. There is some things I intend to change, but I am glad it all went safe and you were successful.

Rosco Bodine, you are correct in saying my materials list (such as the 250 ml reaction flask) cold potentially be incorrect, it should read 500 ml. I was including them from memory as I never recorded what I used. Now that you mention it, 250 ml looks a little small and is probably not safe. Also I took this directly from my notes that I record and they are in point form and in no way in an order that someone can follow, so some things might have been lost in the translation. If there is anything you think should be improved for safety or readability, please let me know. I wrote these for my own records and would also like them to be accurate and safe for others to reproduce. Your opinion would be greatly appreciated and trusted.

TGT

[Edited on 24-11-2014 by TGT]

greenlight - 24-11-2014 at 02:52

TGT, the acid was reagent grade but it was only 70% concentration.
I agree about the temperature and time frame, It only needs to be at about 80-90.C and I only needed 15 minutes before the Trinitrophenol started crashing out.
I also did do it in a 500ml vessel, it would have got a little too close to foaming over in the 250ml.

Rosco Bodine - 24-11-2014 at 10:53

It is entirely possible that using nitric acid for the nitration that the process can run at faster rate and lower temperature than using a nitrate addition to a sulfuric acid solution of the sulfonate precursor. Using free nitric acid would also result in a much thinner and more easily stirred mixture. There are some routes to picric acid using precursors which are nitrated using no sulfuric acid and accomplish the nitration using nitric acid alone. Sulfanilic acid may be nitrated in such manner as can nitroso derivatives of phenols.......no sulfuric acid needed but just azeotropic nitric being sufficient for the trinitration.

Sunlight can cause red fumes to appear in a nitration mixture, or can decompose the nitric acid vapors above a hot mixture particularly and so can excessive heating alone result in red fumes. There will be a temperature driven reaction rate for the nitration where the rate of addition of the nitric acid will be well matched to the rate of nitration, so that the thing being nitrated absorbs the nitrogen with very little loss of nitrogen or other byproducts. The rate of addition and temperature that works best can be different for different batch sizes and will vary according to the precursor being nitrated and the nitrating agent being used, with temperature and stirring also being factors. With most nitrations you will observe a gradually increasing temperature during nitration if the nitration is being pushed by rate of addition and it will sustain the nitration reaction by its own heat of reaction begun at a certain starting temperature that is initially high enough so that nitration proceeds quickly from the start. Generally for aromatic nitrations as the nitration proceeds nearer to completion there is not sufficient concentration of unnitrated material remaining in the mixture for the reaction to proceed to completion by its own heat of reaction and supplemental heating is then required to maintain the heat of reaction for an extended holding time during which the nitration completes. The point of precipitation of end product will be determined by the solubility and concentration of the end product in the reaction mixture, the composition of which is changing during the nitration. Temperature and water content may be deliberately chosen to accomplish lowest solubility for the desired end product in the spent nitration mixture, and the process can be designed to produce a product of highest purity or greatest yield, with both goals not necessarily achievable together. Reactions can be optimized for economy of time, economy of materials, economy of energy requirement, or for purity of end product, depending on what is the priority, the process may differ.
And what holds true for a 1 mole scale may not directly translate for a different scale when the batch process method is employed as is the case for most lab procedures.

When a lab scale method is described pay attention to every detail because every detail has a likely bearing on the process and the result. The devil is in the details when it is desired to optimize a batch process to do what is desired.

When a near saturated hot solvent solution of something is poured into a cold filter it will likely flash crystallize and clog the filter, so generally a decanting of the hot solvent is done as a "clean enough" separation from residue which is left as maybe 10% of the original volume, then diluted with fresh solvent to maybe half saturation and reheated and then filtered to avoid a plugged filter.

You don't want a foam producing "neutralizer" in a quench bath because of the bubble monster it will create if you need to crash the reaction, and the product will be made a near impossible recovery by the mess and overflow as well as the likely reaction of the product itself with the neutralizer so just plain water with ice is what is more sensible for a quench. For some nitrations which may require cooling during nitration the contingency of quenching is provided by the cooling bath itself into which the reaction is going to be dumped anyway after a nitration is completed.

greenlight - 24-11-2014 at 17:13

Thankyou Rosco for clearing that up.
I think the addition rate of nitric acid was a little fast and it was done in sunlight which may have caused the decomposition to red fumes and I quickly reached the point of precipitation as the solution was past saturated which caused the early crystallization of picric acid.

greenlight - 26-11-2014 at 06:55

It all turned out fine regardless, I just weighed the yield and from 35g Acetylsalicylic acid I got 39.79g of Trinitrophenol using a slight variation of TGT's method

:

[Edited on 26-11-2014 by greenlight]

TGT - 27-11-2014 at 21:26

I am going to edit my method using what I found could be improved on by Greenlight reproducing my method and using some of his observations, along with quite a few points Rosco Bodine pointed out that could potentially be a problem or a hazard. I hope to make it as safe and easy to follow as possible. By tomorrow night it should be fixed and thanks for the suggestions.

If anyone wants me to add the measurements for larger and smaller yields that I have found to be reproducible and also the third part on recrystallization let me know.

Greenlight, looks like your final product and yield turned out well!

TGT

[Edited on 28-11-2014 by TGT]

[Edited on 28-11-2014 by TGT]

greenlight - 27-11-2014 at 23:04

Thanks TGT, I would like to see your revised synthesis.
I would also be interested in your reagent amounts and times for your larger successful batches and recrystallization notes if you wish to add them.

[Edited on 28-11-2014 by greenlight]

S.C. Wack - 28-11-2014 at 10:01

Quote: Originally posted by greenlight

It all turned out fine regardless

That doesn't look anything like the picric I've seen.

TGT - 28-11-2014 at 13:45

I think its the exposure, but it could use a recrystallization.

TGT

greenlight - 28-11-2014 at 18:19

I think it's just the shitty camera and lighting.
But, yeah it does need a recrystallization.

Rosco Bodine - 29-3-2015 at 10:25

Quote: Originally posted by Hennig Brand

If aspirin is used instead of salicylic acid hydrolysis occurs in the hot sulfuric acid sulphonation stage of the process. The products of aspirin hydrolysis are salicylic acid and acetic acid. The salicylic acid is then sulphonated to almost exclusively 5-sulphosalicylic acid from what I understand.

During nitration the sulphonic acid group is easily substituted by a nitro group and finally the dinitro-salicylic acid is decarboxylated and the final nitro group is added producing picric acid. The decarboxylation is witnessed as the foaming that occurs especially during the last third of the nitrate salt addition.

[Edited on 9-11-2014 by Hennig Brand]

WRT your earlier post
http://www.sciencemadness.org/talk/viewthread.php?tid=22241&...

It may be a temperature dependent mechanism when the decarboxylation of the 5-sulfosalicylic predominates, but IIRC the most of decarboxylation foaming occurs when the first (rather than the last) nitro group is introduced. This is not a completely prerequisite reaction or necessarily a required sequence because some lesser foaming continues as the nitration proceeds to completion making it appear a different sequence is possible and occurring also but to a lesser extent towards the end of the nitration. Once a 5-sulfosalicyic acid molecule is decarboxylated by an entering nitro group displacing the carboxyl, the resulting nitrophenolsulfonic acid competes for the next available nitronium ion and the summary theoretical reactions occurring will produce a scenario where dinitration and possibly even trinitration proceeds concurrently for the first decarboxylated material, while decarboxylation via nitration has not yet occurred for other 5-sulfosalicylic acid which is still present unreacted. It seems possible that different sequences are possible for nitration and decarboxylation also, to further complicate interpretation of what reaction is preferential and predominating to what extent, which could differ with temperature, and with order of addition. There are certainly "unknowns" operative for this sequence of reactions involving both the sulfonation of aspirin and the nitration of that product of sulfonation.

A potential may exist also for some 2:4:6-trinitrophenol-m-sulphonic acid to be produced as a minority byproduct of nitration in addition to picric acid. This is an unconfirmed hypothesis on my part which seems plausible and consistent with observation, but would require further research to confirm.

http://link.springer.com/article/10.1007/BF03035659

[Edited on 29-3-2015 by Rosco Bodine]

Hennig Brand - 29-3-2015 at 11:16

From what I remember, when producing picric acid from ASA or salicylic acid, there was very little foaming until about the last third or so of sodium nitrate addition and then the amount of foaming was quite large. I do remember that it started gradually, some time after half the nitrate was added, but foamed vigorously during the last third of the nitrate addition. Depending on how well the mixture was mixed, how slow the addition was and how the temperature was controlled foaming could have nearly died away by the last addition or it may take a certain amount more time of stirring at elevated temperature for the foaming to subside. This is what I have noticed, at least the last few times I performed the synthesis which is still relatively fresh in my memory. I wouldn't be surprised at all, however, if at least slightly different things can happen depending on how the reaction is run.

I do wonder about minor contaminants in the produced picric acid. Strange how I was having so much difficulty preparing proper basic lead picrate, even with very well recrystallized picric acid and careful control of the amount of sodium hydroxide and lead nitrate. The couple of time that I obtained what seemed like the correct product, with the correct color and properties, was when a slight excess of sodium hydroxide was added. That whole thing is still a bit mysterious to me.

Rosco Bodine - 29-3-2015 at 11:26

I saw more thickening of the stirred mixture late in the nitration made a yet smaller rate of foaming much more of a stirring issue later in the nitration when the bubbles could not so easily escape as earlier from the thinner less viscous liquid causing expansion of foam to greatly slow additions. But it seemed when the liquid was thinner earlier the foaming was at a much increased rate, just didn't cause an issue since it freely escaped almost instantly from the thinner mixture. The foam was not persistent even though the gas volume seemed greater, there was no complication for it. So it appeared a higher actual rate of gas evolution early in the process was more manageable because the mixture was thin, but a much lower volume of continuing gas evolution would produce a foaming issue later due to the viscosity of the mixture.

I have been looking at the stirring issue and believe there can be gotten refinement of the process, by perhaps using a bit more H2SO4 and perhaps a bit more H2O in the process, perhaps also using a mixed nitrates scheme as well. I think the process can be tweaked, fine tuned a bit to improve.

There are some old patent references where a solution of NaNO3 was used initially and then finishing of the nitration was done using addition of solid NaNO3 intended to accomplish a nitration curve having a desired water content.
See US1309320 attached.

Also see page 2 line 61 of US1380186 attached.

Some of the old references make mention that resinous impurity byproducts have association with reactions with nitrous acid impurity and excessive temperatures and too strong acidity with insufficient water during the introduction of the initial nitro group, and are unintended byproducts of oxidation of the precursor. There was so much industrial production of picric acid in that era it is likely every variable has been studied carefully, but the details of all that work are not summarized in good completeness anywhere I have found.

Attachment: US1309320 Sodium nitrate plus sulfuric acid for nitrations.pdf (582kB)
This file has been downloaded 456 times

Attachment: US1380186 Picric Acid Manufacture temperature control high yield.pdf (440kB)
This file has been downloaded 478 times

[Edited on 29-3-2015 by Rosco Bodine]

Hennig Brand - 29-3-2015 at 14:31

Thanks for the patents. I hope I am not contradicting too much of what I said in my last post, but the more I think about it, the last few times I have performed the nitration the foaming started and increased in intensity very quickly right around the time the last third of the nitrate was starting to be added. Sometimes a little before and sometimes a little after, depending on addition rate, reaction temperature, mixing, etc, but very close to when the last third was starting to be added. This seems to be right in line with the reaction mechanism previously described and which came from a very old journal article which I also posted in the "Picric Acid Different Instructions" thread. I am not sure what analytical techniques that they used at the time, and would need to go back and read the article, but it read like the intermediates and final products had been determined using analytical techniques.
I guess when the foaming starts could be coincidental, but it seems unlikely given how well it can be predicted based on the amount of nitrate that has been added. I always weigh the nitrate out into three even portions and put them in separate airtight containers prior to the nitration which is how I know.

[Edited on 29-3-2015 by Hennig Brand]

Rosco Bodine - 29-3-2015 at 15:16

The other thread I am reviewing again, but something I have seen already is a diagram regarding the hydrolysis of ASA and a speculated sulfonation of salicylic acid at a link you posted there which is a reaction scheme that is not entirely correct

This scheme below is definitely NOT correct AFAIK

For the HCl catalyzed hydrolysis the reaction should be ASA + H2O -----> Salicylic Acid + Acetic Acid

For the sulfonation the same reaction occurs as for the HCl catalyzed hydrolysis, only catalyzed instead by the H2SO4 which then subsequently reacts by sulfonating the salicylic acid to 5-sulfosalicylic acid NOT para phenolsulfonic acid as shown. There is no decarboxylation of the salicylic acid at this point. The decarboxylation is done by displacement by a nitro group.

We have differently interpreted observations, but I think we are seeing the same reaction scheme.

[Edited on 29-3-2015 by Rosco Bodine]

Hennig Brand - 29-3-2015 at 15:39

I think that was posted quite a while ago and there were a lot of reaction mechanisms for various things on the webpage linked to of which the image you just showed has two. A few of the things I saw on that site looked highly suspect at the time, even wrong, but I was still considering all possibilities (still am, just not as much). Yeah, having water going out of a hydrolysis reaction and not in is an obvious mistake. The articles I am referring to are located near the end of the "Picric Acid Different Instructions" thread. I think I have a couple more articles somewhere as well; one article lead to another and so on and so forth.

Here is the link to the articles:
http://www.sciencemadness.org/talk/viewthread.php?tid=389&am...

Attachment: 4-Sulfo Salicylic Acid Nitration.pdf (1.1MB)
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Attachment: 4-Sulfo Salicylic Acid Synthesis.pdf (424kB)
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Many of the websites that I viewed in the past regarding the subject explicitly stated that aspirin was converted to phenol sulfonic acid during the sulphonation stage, which is completely false from what I have read and observed since.

[Edited on 30-3-2015 by Hennig Brand]

Rosco Bodine - 29-3-2015 at 16:32

Yes I have finished reviewing the other thread and replied there with what I think is a needed reference mentioned in one of the articles you posted. Since there isn't any "learned journal" article I have found titled "making picric acid from aspirin, how does it work?" then we are having to research what is already written and try to connect the dots from those references to solve the mystery.

PHILOU Zrealone - 30-3-2015 at 05:59

If starting from ASA, and the resulting sulfo-salicylic acid immediatelly set (one batch) into the nitration process...
Then the presence of the hydrolysed acetic acid will induce oxydation of the later as CO2 and H2O what may be one cause of mild foaming during the all process.

The decarboxylation of the salicylic acid is favourized by electronegative substituants on the aromatic ring (like nitro groups for example).
This is observed when making TNB from TNT via the oxydative route...
TNT is turned into trinitrobenzoic acid what upon mild heating set the CO2 free to generate TNB.

The carboxylic acid moeity doesn't interfere with the nitration of salicylic acid because the OH is para and ortho directing (position 4 and 6) and the carboxylic group is meta directing (also position 4 and 6), as mentionned Hennig Brand, it should only be just before or at the last stage and while heating that the last nitro group may enter in the last ortho position available taking the place of the carboxylic moeity.
But if nitrous acid is present, then it is wel possible that decarboxylation happens also in early stages...see Nitrosodecarboxylation. Note the interesting synthesis of 2-nitrophenol from salycilic acid and nitrite salt

.
Also the following patent USp 3507924 that mention that CO2H moeity may be substitued by NO2 especially if OH or OMe in ortho or para. But their examples speaks about high temperature (250°C) under pressure with HNO3 (50%) so the process involved in their examples is probably radicalar.

If someone has 4.6-dinitro-salicylic acid...could he make a tiny heating test and see if dinitrophenol does result? I'm puzzled by the large melting point 170-174°C what might be a sign of partial decomposition at melting...decarboxylation?

Rosco Bodine - 30-3-2015 at 07:57

Yes the facile thermal decomposition of trinitrobenzoic acid to trinitro benzene was something being considered as well as the similar decomposition route for salicylic acid to phenol simply by a sudden but limited and controlled heating.
These reactions are something like a spring loaded toggle switch flipped by heat alone, transitioning from the metastable precursor to the more temperature stable decomposition product, similar to a crystal transition temperature. When the material is already close to transition all it takes is a little nudge by some contributing factor to flip that switch. I supposed that the nitro group would see that carboxyl as a half open door and simply displace the carboxyl as if invited to take its place there as a more stable ring substituent.

In COPAE there is an ordering of substitution hierarchy activity given by Davis for promoters or inhibitors of nitration of the benzene ring, as compared with hydrogen, that follows the scheme as follows with the greatest promoter being (phenolic) hydroxyl on the left with decreasing activity towards promotion to the right, with all substituents on the right of Hydrogen actually serving to hinder substitution of a ring hydrogen, (or anything else to the left of themselves?) more greatly. That same activity for hindering substitution of a ring Hydrogen would make such substitutents vulnerable to preferential substitution themselves (as compared with a ring hydrogen), if I understand correctly.

-OH> -NH2> -CH3> --Cl> --H> -NO2> -SO2(OH)> -COOH

I am not certain the ordering which Davis gives is correct. This issue has come up before and it may be a perfect example of a "textbook error".

As for the Nitrosodecarboxylation mechanism, yes that could certainly be in play, particularly since the presence of nitrosyl sulfuric acid has been identified in the low water content nitration mixture, and the nitrosylsulfuric acid is itself capable of accomplishing the nitration leading to picric acid according to the commentary and opinion in some of the literature.

[Edited on 30-3-2015 by Rosco Bodine]

PHILOU Zrealone - 31-3-2015 at 06:19

Quote: Originally posted by Rosco Bodine

In COPAE there is an ordering of substitution hierarchy activity given by Davis for promoters or inhibitors of nitration of the benzene ring, as compared with hydrogen, that follows the scheme as follows with the greatest promoter being (phenolic) hydroxyl on the left with decreasing activity towards promotion to the right, with all substituents on the right of Hydrogen actually serving to hinder substitution of a ring hydrogen, (or anything else to the left of themselves?) more greatly. That same activity for hindering substitution of a ring Hydrogen would make such substitutents vulnerable to preferential substitution themselves (as compared with a ring hydrogen), if I understand correctly.

-OH> -NH2> -CH3> -Cl> -H> -NO2> -SO2(OH)> -COOH

I am not certain the ordering which Davis gives is correct. This issue has come up before and it may be a perfect example of a "textbook error".

The order given is simply a relative order for the speed of nitration in relation to benzene as being taken as unity of reference. So hydroxy is maybe 10E6 times faster than benzene and nitro 10E-3 times slower than benzene but combination of those groups depends on orienting effect (additive or antagonist)...if additive the speed remains on the side of the more activating effect.

If for example -CO2H is taken as unity speed and -OH is 10000 x unity speed; then:
-speed of mononitration of phenol is 10000.
-speed of mononitration of benzoic acid is 1.
-speed of mononitration of salicylic acid (2-phenol-benzoic acid; thus additive effect) would be 10000+1 =10001
-speed of mononitration of 3-phenol-benzoic acid (antagonist effect) would be something between 10000 and 1 but much closer to 10000!

This order has nothing to do with substitution ability!
Otherwise you would:
-never be able to get dinitro or trinitrobenzene from benzene and you would stop at nitrobenzene, substituting endlessly the NO2 by NO2 instead of H!
-never be able to get metanitrobenzoic acid or 3.5-dinitrobenzoic acid from benzoic acid nitration and the only result (what is never obtained in normal nitration process) would be nitrobenzene.

[Edited on 31-3-2015 by PHILOU Zrealone]

Rosco Bodine - 31-3-2015 at 06:48

Quote: Originally posted by PHILOU Zrealone

Quote: Originally posted by Rosco Bodine

You think Davis is completely wrong? I don't, the only issue I have is the specific order may not be exactly right for all cases.

Respectfully I disagree this ordering for groups as promoters or inhibitors of entering nitro groups has nothing to do with substitution ability because yes the speed of reaction which you reference decreases to near zero as further substitution is inhibited for the same reaction condition. This explains why for trinitro benzene each entering nitro group is more difficult to introduce, and why for nitration of toluene and for other aromatic nitrations the same general rule applies. The conditions of nitration can require being made more intense to introduce the second nitro, and still more intense for the third, likewise for a fourth. This is not written in stone with no exceptions, but is a general rule.

[Edited on 31-3-2015 by Rosco Bodine]

PHILOU Zrealone - 31-3-2015 at 06:51

Why does nitrous acid allow substitution of a carboxylic acid function in ortho or para of a phenol?

If you take a look at keton chemistry with nitrous acid or nitrosating agents, you will notice the following:

1°)Butanone turns into butandione monoxime:
CH3-C(=O)-CH2-CH3 + HONO --> CH3-C(=O)-CH(-N=O)-CH3 + H2O
CH3-C(=O)-CH(-N=O)-CH3 <-=> CH3-C(=O)-C(=N-OH)-CH3
or
CH3-CO-CH2-CH3 + HONO --> CH3-CO-CH(-N=O)-CH3 + H2O
CH3-CO-CH(-N=O)-CH3 <-=> CH3-CO-C(=NOH)-CH3

2°)Pentan-2.4-dione turns into pentan-2.3.4-trione-3-oxime:
CH3-C(=O)-CH2-C(=O)-CH3 + HONO --> CH3-C(=O)-CH(-N=O)-C(=O)-CH3 + H2O
CH3-C(=O)-CH(-N=O)-C(=O)-CH3 <-=> CH3-C(=O)-C(=N-OH)-C(=O)-CH3
or
CH3-CO-CH2-CO-CH3 + HONO --> CH3-CO-CH(-N=O)-CO-CH3 + H2O
CH3-CO-CH(-N=O)-CO-CH3 <-=> CH3-CO-C(=NOH)-CO-CH3

So hydrogen atoms in alfa of a ketonic group are favourized (the stability of the enol form CH3-C(-OH)=CH-CH3 explains the attack of the nitrosation on the viccinal CH2 and not on the terminal CH3 what would have lead to a aldo-ceton oxime)!
Hydrogen atoms in alfa of two ketonic groups are even more favourized especially if the final compound generate an extended resonance of pi bonds (sp2 carbons) this is the case with the 3 successive keto groups.

What has it to do with phenol and salicylic acid?

-Phenol is easily nitrosated in para-position...because phenol is a discrete form of keton...phenol contains "enol" what means it is the enol form of a keton

.
Phenol is cyclo(-C(-OH)=CH-CH=CH-CH=CH-) and cyclo(-CO-CH2-CH=CH-CH=CH-) or cyclo(-CO-CH=CH-CH2-CH=CH-) are the derived ketonic forms. Have you noticed the CH2 in ortho position or in para position?
Nitrosation will thus happen in ortho or para position. Usually in para but if position is already taken by a non labile group, then it goes in ortho.

-Salicylic acid contains the sequence HO-C=C-CO2H (rest of the aromatic ring left aside for clarity). Note that -CO2H is -CO-OH...
The associated ketonic form will contain the sequence O=C-CH-CO-OH and the CH is thus between two "keto" groups.
Nitrosation will occure at that place very easily.
O=C-CH-CO-OH --> O=C-C(-N=O)-CO-OH
Alfa keto-carboxylic acid usually easily lose their carboxyl group into CO2 (by temperature increase), this effect is facilitated by the nitrosation (lowering of the decarboxylation temperature).
Malonic acid forms acetic acid. HO2C-CH2-CO2H --> CH3-CO2H + CO2
Pyruvic acid forms ethanal. CH3-CO-CO2H --> CH3-CH=O + CO2

In our case O=C-C(-N=O)-CO-OH --> O=C-CH(-N=O) + CO2
Then the enol form is formed again HO-C=C-N=O to form 2-nitrosophenol!

[Edited on 31-3-2015 by PHILOU Zrealone]

Rosco Bodine - 31-3-2015 at 06:58

The nitroso group should have been included but was not provided in the sequence which Davis described ( more or less correctly

) and I think it should probably be inserted there just to the right of the NO2 group and before the SO2(OH)

PHILOU Zrealone - 31-3-2015 at 08:04

Quote: Originally posted by Rosco Bodine

No!
I agree with COPAE/Davis...so we both agree on that

.

But I do not agree with what you wrote:
"That same activity for hindering substitution of a ring Hydrogen would make such substitutents vulnerable to preferential substitution themselves (as compared with a ring hydrogen), if I understand correctly."

[Edited on 31-3-2015 by PHILOU Zrealone]

Rosco Bodine - 31-3-2015 at 08:42

For the nitration of phenolsulfonic acid the sulfonic group is easily replaced by a nitro, and similarly will occur replacing a carboxyl with a nitroso for a nitrosophenol. The nitroso may follow somewhat the same scheme as a nitro, almost as if it were an "incomplete" or partially formed nitro.

Interestingly for the sulfonation of phenol the first entering sulfonic group occurrs easily, but the second sulfonic group is harder to introduce due to the inhibiting effect of the first. And with salicylic acid the introduction of a second sulfonic does not occur at all due to the combined effect of a first sulfonic made even greater by a carboxyl, the inhibiting effect on sulfonation so complete that sulfonation stops at the monosulfonic acid derivative of salicylic acid.

Yet as you have pointed out, the carboxyl of salicylic acid sulfonate is very easily and preferentially itself vulnerable to substitution by replacement with a nitroso.

Thinking further about the sequence of Davis and my suggesting that nitroso should be inserted there would in this case actually put it between the SO2(OH) and the COOH as a ranking in that hierarchy offered by Davis.

The nitroso itself seems to be easily even preferentially replaced by a nitro which I think is probably more of an oxidation to a nitro in that case, since the "substitution" by a nitro is in part already accomplished. I think that is a "special case exception" which is an exception to the simplified linear hierarchy that is a general rule shown by Davis. I think there are other exceptions which can occur for combined effect of more than one substituent already present on the ring so the simplified linear ranking shown by Davis does not hold as an absolute rule, for which there are exceptions.

Quote: Originally posted by PHILOU Zrealone

But I do not agree with what you wrote:
"That same activity for hindering substitution of a ring Hydrogen would make such substitutents vulnerable to preferential substitution themselves (as compared with a ring hydrogen), if I understand correctly."
[Edited on 31-3-2015 by PHILOU Zrealone]

The only plausible explanation for what I have observed / guessed to be probably occurring which would give the illusion such substitutions are preferential, would involve unspecified abstract and algebraic ring resonance effects or "steric influences" at work. Probably elves make it happen that way so that what is observed remains mysterious

[Edited on 31-3-2015 by Rosco Bodine]