Sciencemadness Discussion Board

6-hydroxy-2-nitrobenzaldehyde

garage chemist - 20-10-2007 at 23:36

How would one prepare this compound from common reagents?
I tried to come up with viable synthesis strategies but could not think of a method that sounds right.
Nitration of salicylaldehyde (2-hydroxybenzaldehyde) would probably give the wrong isomer (hydroxy group is ortho- and para directing).

Nitration of 2-aminobenzaldehyde or o-toluidine, with the amino and methyl group transformed into the hydroxy and formyl group afterwards also sounds like it would give isomer problems.

Reduction of one of the nitro groups in 2,6-dinitrotoluene followed by conversion of amino and methyl group into hydroxy and formyl sounds better, but I have no idea how the special dinitrotoluene would be made.

m-nitrophenol could perhaps somehow be formylated, but again, the nitro group doesnt like substitution on the ring directly beneath it...

Can someone with more knowledge in organic chemistry help me with a synthesis strategy (not "recipe") for the title compound? This sounds almost like an organic chemistry homework question, but I have just started with Ochem at uni and haven't even had aromatics until now.

Sauron - 21-10-2007 at 01:27

Start with p-toluenesulfonic acid, this blocks the 4-position so you can dinitrate the 2 and 6 positions.

Reduce one nitro to amine, diazotize and convert to phenol.

Oxidize your methyl to carboxaldehyde.

Now get rid of the sulfonyl group.

An old trick but a good one. In Org.Syn there's an example of this strategy being employed to prepare o-nitroacetanilide, the acetyl group is then removed, and the nitro reduced to get o-phenylenediamine. I once considered doing this but instead I bought a Kg of o-nitroaniline and a Kg of o-penylenediamine.

The facile sulfonation and equally facile removal of same, is exploited often in just this way to block one of the favored positions in the ring. Easier than seperating a mixture of isomers.



[Edited on 21-10-2007 by Sauron]

gc.jpg - 2kB

Reference Information

solo - 21-10-2007 at 04:14

Synthesis of 2-Nitrobenzaldehyde from 2-Nitrotoluene
Alexander Popkov
Acta Chim. Slov. 2005, 52, 460–462


Abstract
Comparison of Arthur Lapworth’ one-pot conversion of 2-nitrotoluene to 2-nitrobenzaldehyde with other published synthetic sequences revealed an environmental attractiveness of this reaction. Due optimisation of the procedure was made in order to enhance the safety of this process on a large scale. A highly selective one-pot preparative chemical synthesis of 2-nitrobenzaldehyde from 2-nitrotoluene is described.

Attachment: Synthesis of 2-Nitrobenzaldehyde from 2-Nitrotoluene.pdf (203kB)
This file has been downloaded 2194 times

Sauron - 21-10-2007 at 09:57

No offense to my friend Solo but

I read this paper and what do I see? A 24% yield, which is shite. A switch in solvents supposedly over concerns about peroxides in Et2O. That's pretty bogus because every real practitioner knows how to destroy peroxides if present and how to avoid forming them in the first place (freshly opened cans etc.) 2-propyl nitrite does not strike me as a fun reagent. All the blather about green chemistry does not impress.

I believe we have better methods of taking a benzylic methyl group to carboxaldehyde. Certainly better than 24% and conditions that will not phase a nitro group nor a phenolic hydroxyl. Wasn't there a toluene to benzaldehyde thread?

@gc, here's the Org.Syn. procedure for the removal of the sulfonic acid group from o-nitroaniline, and I believe it references the earlier procedure for nitrating p-acetanilidsulfonic acid. Just do same with p-toluenesulfonic acid (which you can make yourself from toluene, or buy). And crank up the conditions to get the dinitro product. It should not take much.


[Edited on 22-10-2007 by Sauron]

Attachment: CV1P0388.pdf (129kB)
This file has been downloaded 996 times

chemrox - 21-10-2007 at 20:40

Quote:
Quote:
Originally posted by Sauron
Reduce one nitro to amine, diazotize and convert to phenol.


How do you control this? Getting only one nitro reduced?

I'm not doubting you but the devil is in the detail, so Sir Sauron, please walk us through it. I would think the yields would be shitty.




[Edited on 21-10-2007 by Sauron]

Sauron - 21-10-2007 at 21:56

By limiting the amount of reagent of course. For example sodium dithionite/sodium carbonate. Use only enough to satisfy the stoichiometry for one nitro reduction.

Nicodem is the resident authority. If dithionite must be used in excess, then select another reducing agent that will work.

Catalytic hydrogenation you would control very simply by determining the uptake of hydrogen versus that required to reduce one nitro, and stopping the hydrogen flow at that point, cooling (if heated) and releasing the pressure.

I can see how this might be a concern with a dissolving metal reduction but not with something a little more sophisticated.

If uncertain about the technique, I'd try it out on m-dinitrobenzene (cheap) rather than the more valuable target compound that garage chemist is after.

I bet such a conversion of m-dinitrobenzene to m-nitroaniline is in the literature. Maybe even in Org.Syn. Obviously it is not a normal nitration product of aniline (except as a trace).

[Edited on 22-10-2007 by Sauron]

garage chemist - 22-10-2007 at 03:00

Thanks to both of you, Sauron and solo!

I thought of using CrO3/Ac2O/AcOH for the oxidation of the methyl group as in:
http://orgsynth.org/orgsyn/pdfs/CV2P0441.pdf
The yield is not that much better, though.

Wouldnt it be more logical to remove the sulfonyl group directly after nitration of p-toluenesulfonic acid instead of leaving it there throughout the rest of the process, getting 2,6-dinitrotoluene as the intermediate?

The selective reduction of one of the nitro groups seems to be the main problem to me as well.
Sodium dithionite is an excellent reducing agent for aromatic nitro to amine, but its active content is not constant, the commercial material having somewhere around 86% active content.
Furthermore, the dithionite ion decomposes appreciably under the conditions of nitro compound reduction (according to Ullmann, decomposition takes place in aqueous solution more or less rapidly depending on pH and temperature, and there is no stable dithionite solution at and above room temperature) which is why a good excess is always used.
Therefore sodium dithionite does not seem to be a good choice of a reducing agent to me. Correct me if you know better.

It is indeed very good advice to look for a procedure for m-dinitrobenzene ---> m-nitroaniline and then proceed analogously with 2,6-dinitrotoluene. I vaguely remember sodium (poly?)sulfide being used, but I have no idea where I read about such a procedure. I'm going to search for it, but my literature research abilities are very limited.


EDIT: I looked up nitrotoluenesulfonic acids in Ullmann:

2,6-Dinitrotoluene-4-sulfonic acid [88-90-4] (160), 3,5-dinitro-4-methylbenzenesulfonic acid, C7H6N2O7S, Mr 262.20, crystallizes as a hydrate in the form of pale yellow crystals, which soften at 110 °C, dehydrate at 140 °C, and melt at 165 °C.

Production. 2-Nitrotoluene is sulfonated to form 2-nitrotoluene-4-sulfonic acid; the reaction mixture is diluted with 90 % sulfuric acid, and sodium nitrate is added over 6 h at 80 °C. After a further 1 h at this temperature the reaction mass is poured into water and the sodium salt of the product is salted out by addition of sodium sulfate. After being washed acid-free with brine, the yield of 160 is ca. 80 %.


Uses. Reduction of 160 with sulfide gives 2-amino-6-nitrotoluene-4-sulfonic acid (161), and reduction with iron – acid gives 2,6-diaminotoluene-4-sulfonic acid [98-25-9]. 2,6-Dinitrotoluene-4-sulfonyl chloride [80198-19-2] is obtained from 160 by treatment with thionyl chloride. Reaction of this sulfonyl chloride with an alkylamine followed by hydrogenation leads to a readily accessible series of symmetrical diaminotoluenesulfonamides [72].

[72] Bayer, DE 3 012 800, 1980 (R. Kopp et al.).


Note the use of sulfide! Now I need to find laboratory procedures for sulfonation of 2-nitrotoluene and further nitration, and for the sulfide redution.
I'm going to remove the sulfonyl group right after the nitration.


EDIT 2:

6-Nitro-o-toluidine[603-83-8] (122), 2-methyl-3-nitroaniline, C7H8N2O2 , Mr 152.15, mp 92 °C, b p 305 °C, d 415 1.378, crystallizes from ethanol as yellow leaflets.

Production. 6-Nitro-o-toluidine is produced by sulfide reduction of 2,6-dinitrotoluene in a process similar to that for 3-nitroaniline (Section 5.1. Nitroanilines) or by controlled hydrogenation of 2,6-dinitrotoluene with palladium on a carbon catalyst [62].

[62] M. Lounasmaa, Acta Chem. Scand. 22 (1968) 2388 –2390.

and:

3-Nitroaniline[99-09-2] (102), m-nitroaniline, MNA, C6H6N2O2 , Mr 138.13, crystallizes as yellow needles from water. It is moderately soluble in organic solvents and sparingly soluble in water (0.11 %). Its physical properties are listed in Table (12).

Production. 1,3-Dinitrobenzene (Section 3.1. Nitrobenzenes) is added to warm water containing magnesium sulfate. An aqueous solution of sodium hydrogen sulfide (6 molar equivalents) is added gradually to the vigorously stirred emulsion, and reduction is completed by heating to 90 °C. The 3-nitroaniline produced solidifies on cooling and is separated by filtration.


That brings me a lot closer to the target, maybe I wont need explicit preparation instructions.
Also:
"Nitration of 2-nitrotoluene, which is sometimes present in surplus, gives a ca. 67 : 33 mixture of 2,4- and 2,6-dinitrotoluene." (from the section on nitrotoluenes)
2-nitrotoluene is indeed a surplus product from nitration of toluene in the lab.
Now if I find a method to separate 2,4- and 2,6-DNT, this would be an alternative to the sulfonation, considerably shortening the entire procedure.

[Edited on 22-10-2007 by garage chemist]

Sauron - 22-10-2007 at 03:41

The sulfonation is easy on, easy off, and yes you take it off immediately after the dinitration. There will therefore be zero 2,4 dinitrytoluene and negligible to zero 2,3 or 2,5 dinitro product. Sulfonation/desulfonation is a lot easier than seperation of 2,4 DNT and 2,6-DNT.

Dithionite is not the only game in town. Find one that will do the job in stoichiometric qty. There must be lit. examples.

Klute - 22-10-2007 at 06:36

CTH may be well adapted to the reduction of one nitro group. Smooth reaction conditions, and a plethoria of hydrogen donors. Aromatic nitro reduction is well documented, there must be some refs on this subject. I'd love to look this up but can't acces scifinder at the moment.

Nicodem - 22-10-2007 at 10:37

6-hydroxy-2-nitrobenzaldehyde is obtained from m-nitrophenol:


There are only a couple more preparations described in the literature, but they are all crap (=many steps and using expensive/inaccessible reagents) in comparison to the above ones.
As is probably known m-nitrophenol can be (bought or) prepared from nitrobenzene in three simple and high yielding steps (or two steps starting from m-dinitrobenzene; one step from m-nitroaniline).

[Edited on 22/10/2007 by Nicodem]

Sauron - 22-10-2007 at 10:49

Well, bravo, Nicodem.

Excluding Bull.Chem.Soc. Japan, you certainly are the front runner for the Most Obscure Citations award for the month.

chemrox - 22-10-2007 at 17:53

Quote:

The selective reduction of one of the nitro groups seems to be the main problem to me as well.
Sodium dithionite is an excellent reducing agent for aromatic nitro to amine, but its active content is not constant, the commercial material having somewhere around 86% active content.
Furthermore, the dithionite ion decomposes appreciably under the conditions of nitro compound reduction (according to Ullmann, decomposition takes place in aqueous solution more or less rapidly depending on pH and temperature, and there is no stable dithionite solution at and above room temperature) which is why a good excess is always used.
Therefore sodium dithionite does not seem to be a good choice of a reducing agent to me. Correct me if you know better.



This is turning into a really intersting thread, thank you. I was wondering if you might make the dithionite yourself using Zn and NaHSO3? Then the issue is how fast is the decomposition and where one could get data on that or determine by experimentation. I suppose using it on a simpler, cheaper compound, as Sauron suggets, would be a way to see how much the compound affects that. Anyway, NaHSO3 is cheap and abundantly available. Does -S2O4 recrystallize well? Another thought..

UnintentionalChaos - 22-10-2007 at 19:42

Hmm, this topic fascinates me as well. I have been looking to prepare a similar reagent.. Of particular interest to me is 4-bromo, 2-nitrobenzaldehyde since the resulting "6,6-dibromoindigo" is the famous tyrian purple of antiquity, far beyond the price range of anyone but the wealthiest kings.

That strategy of using p-toluenesulfonic acid Sauron put forth seems extremely promising. Thank you. Sometimes simple and well proven techniques are forgotten.

Edited because Im an idiot.

[Edited on 10-22-07 by UnintentionalChaos]

garage chemist - 23-10-2007 at 01:47

Thanks a lot Nicodem, that sort of information is very useful. You opened a new approach to the synthesis- I did not know that formylation of 3-nitrophenol can give the desired compound in useful amounts instead of exclusively the wrong isomer.

Method number 2 and 3 (Reimer-Tiemann) sound most promising. Could you look up how the isomers are separated in method 3, i.e. which isomer is extracted by NaHSO3, under which conditions the separation has to be carried out, and in what proportion the two isomers are obtained?
Or is someone able to access this journal and post the article?


I have now come across a detailed lab synthesis of m-nitroaniline from m-dinitrobenzene: in Gattermann-Wieland, 43th edition, 1982.
It uses ammonium hydrogen sulfide as the reducing agent, prepared in situ from ammonia solution and excess H2S gas.
I have the preparation in german and could post a translation of it if someone is interested.

The same book also contains the preparation of m-dinitrobenzene from nitrobenzene. Mixed acid made from 100% HNO3 and 98% H2SO4 is used and the nitration is carried out at 100°C for 45 minutes.

The diazotation and aqueous thermolysis of m-nitroaniline can surely be done with standard methods.

When the reference to the formylation of 3-nitrophenol can be obtained the synthesis pathway will be essentially complete.

stoichiometric_steve - 10-2-2008 at 16:25

Quote:
Originally posted by garage chemist

Method number 2 and 3 (Reimer-Tiemann) sound most promising. Could you look up how the isomers are separated in method 3, i.e. which isomer is extracted by NaHSO3


yes, that would be most interesting. so Mr. Nicodem, please give us the rest of this sweet 3rd paper!

3-nitroaniline is quite affordable.

Nicodem - 11-2-2008 at 10:32

I don't have the access to such obscure literature. You can try in Wanted references, though the abstract says pretty enough.

nukeB - 12-3-2008 at 22:45

Quote:
Originally posted by Sauron
Start with p-toluenesulfonic acid, this blocks the 4-position so you can dinitrate the 2 and 6 positions.

Reduce one nitro to amine, diazotize and convert to phenol.

Oxidize your methyl to carboxaldehyde.

Now get rid of the sulfonyl group.


In spite of my treating with respect 2 Sauron advices I try to object one, mentioned above. In due course of my search of most convenient method for 2-nitrotoluene synthesis (4 chemstudents training) I couldn't to deny myself to check the route via p-TSA nitration. In all test runs only 2,4-dinitro and sym-TNT in different ratios (in dependence from selected conditions) were isolated. Evidently an usual and ypso- substitutions compete to each other.

Nicodem - 13-3-2008 at 01:46

Either due to an ipso substitution or due to the reversibility of sulfonation under the conditions used (assuming you used HNO3 in H2SO4 for the nitration). Of course, the sulfonation reversibility is also a process involving an ipso substitution with H<sup>+</sup>, so it is just fine to blame it on the ipso substitution in general.
Given the sulfonyl group is strongly deactivating it is hard to imagine nitration conditions where it would be left alone and not succumb to ipso substitutions, but with the plethora of nitrating reagents I would not be surprised if it would be possible. For example, selective ortho-chlorination of p-tosylic acid is possible and was already discussed in another thread in regard of 2-chlorobenzoic acid preparation.

stoichiometric_steve - 12-4-2008 at 10:02

Quote:
Originally posted by Nicodem
As is probably known m-nitrophenol can be [...] prepared from nitrobenzene in three simple and high yielding steps


would you help me out with this one, Nicodem, if you have it at hand?

greatly appreciated!

Sauron - 12-4-2008 at 11:23

It's obvious.

Nitrate the nitrobenzene to m-dinitrobenzene. Purify product

Reduce one (not both) nitro group, you now have 3-nitroaniline. Tin and conc HCl or SnCl4.

Now diazotize the nitroaniline and exchange that with a -OH group.

Voila, m-nitrophenol.

Very very likely all three steps are in Org.Syn.

You can of course, simply purchase DNB, or m-nitroaniline, or m-nitrophenol.

This is a typical first year organic exam question, at least back in the antedeluvian days when I was a student.

All Nicodem was saying was, here's your substrate, now formylate it in between the two groups and you are done, and it's Miller time (or Bass ale.)

[Edited on 13-4-2008 by Sauron]

Nicodem - 13-4-2008 at 23:28

Stoichiometric_steve, reduction of m-dinitrobenzene to m-nitroaniline can be performed selectively with aqueous sodium polysulfide in good yield (check the literature for references). All the other steps are also described somewhere, but I don't have the time to search. (I hope you know all the intermediate products as well as m-nitrophenol are commercially available, so unless you want to prepare it by yourself just for practice…)

stoichiometric_steve - 14-4-2008 at 09:25

Quote:
Originally posted by Nicodem I hope you know all the intermediate products as well as m-nitrophenol are commercially available, so unless you want to prepare it by yourself just for practice…;)


i know that the precursors are available, i just try to keep the total cost low. if you look at the price of m-nitrophenol, you'll freak out. starting from m-nitroaniline is like 1/20 to 1/10 the cost.

and also a little practice on that type of reaction wouldnt hurt, at the university, we've never done any SE/SN reactions on aromatics.

Nicodem - 14-4-2008 at 09:43

Well, if you take m-nitroaniline as the starting point, then it is actually economic. You can find the procedure here: http://www.orgsyn.org/orgsyn/orgsyn/prepcontent.asp?print=1&...

However, starting from nitrobenzene is just way too much work for such simple compound (in this view the price for m-nitrophenol is actually not freaking me out at all).

Sauron - 14-4-2008 at 09:53

Actually he stated the relative costs pretty accurately. A spot check of Acros prices shows m-nitroaniline at $75 for 500 g while m-nitrophenol is $141 for 50 g.

So 15 cents a g vs $3 a g, 1:20 is spot on.

stoichiometric_steve - 14-4-2008 at 11:34

Quote:
Originally posted by Sauron So 15 cents a g vs $3 a g, 1:20 is spot on.


i just estimated, but i'm a sharp shooter ;) also, Acros is the first place i looked, and got scared. but looking again, now it says 75 EUR per 50g for m-nitrophenol. wtf?! i could BET that the last time i looked it was more like 100 EUR per 25g.

the nice thing is, i can get 1,3-dinitrobenzene in small quantities for eh..."free".

Sauron - 14-4-2008 at 11:50

The site shows in US$ for me, go figure. 50 g $141 and change, but, that ought to be about 75 Euros. Anyway too damned much, for something you can make easily from the nitroaniline for 1/20 the cost.

garage chemist - 14-4-2008 at 12:03

Even the whole process starting from benzene would be feasible.
Detailed procedures are readily available for each single step.

1,3-dinitrobenzene from nitrobenzene uses fuming HNO3/H2SO4 at around 100°C and requires proper purification to remove the byproduct 1,2-dinitrobenzene which is formed to the extent of about 10%.
Selective reduction to m-nitroaniline can be done with sulfide, that's the most reliable method since it is well documented.
Diazotation and heating to form m-nitrophenol gives exceptionally good yields for such a reaction.

The crucial information that we need is: Which isomer from the formylation is extracted by NaHSO3? Is it the wanted 6-nitrosalicylaldehyde, or the useless other isomer?
One could theoretically try it out oneself, it's just a yes-no question to be answered. But proper identification of the obtained compounds would be the main concern.

Sauron - 14-4-2008 at 12:17

Aren't the different isomeric nitrosalicaldehydes characterized in the lit.?

Crystallize till pure by tlc than take a mp. Or that of a known derivative. Like the 2,4-dinitrophenylhydrazone.

Nicodem - 14-4-2008 at 12:21

I think the major product is the desired 6-hydroxy-2-nitrobenzaldehyde since in one of the abstracts they isolate it by a single recrystallization which is hardly possible if you would have a mixture of regioisomers of a ratio less than about 2 : 1 for example. Quite probably they don't do any real "extraction" with bisulfite. More likely they just used the bisulfite method to purify the aldehyde and recovered just one product (due to the other being present only in small amounts and being washed off at the bisulfite adduct isolation stage).