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greenlight
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[*] posted on 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]
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[*] posted on 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.




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[*] posted on 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.
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[*] posted on 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]




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[*] posted on 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.
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[*] posted on 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]
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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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.

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[*] posted on 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]

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[*] posted on 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]
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[*] posted on 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]
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[*] posted on 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.




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[*] posted on 28-11-2014 at 13:45


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

TGT
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[*] posted on 28-11-2014 at 18:19


I think it's just the shitty camera and lighting.
But, yeah it does need a recrystallization.
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[*] posted on 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]
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[*] posted on 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.




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[*] posted on 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)
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Attachment: US1380186 Picric Acid Manufacture temperature control high yield.pdf (440kB)
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[Edited on 29-3-2015 by Rosco Bodine]
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[*] posted on 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]




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[*] posted on 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]
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[*] posted on 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]




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[*] posted on 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.
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[*] posted on 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?




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[*] posted on 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]
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[*] posted on 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]




PH Z (PHILOU Zrealone)

"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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