guy
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Chloranil
I know the standard way of making chloranil is by mixing NaClO3/HCl with phenol. But I do readily have access to chlorates, I wonder if it is
possilble to use TCCA or NaDCCA? I don't see how it wouldn't work but I just want to make sure.
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Boffis
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Not even Baron von Frankenstein had contemplated such a thing.
Lightening pierced the night, the rumble of thunder echoed off distant peaks and then;
A simultaneous flash of lightening and crack of thunder animated the corona bunds sending frenzied blue streamer racing down the insulator stacks.
A darkness returned that seemed to render impotent the faint glow of the IPad screen. But wait, could it be? Still borne and left for dead for almost
ten years, now it stirred. Yes there was life once again in the old chloranil thread. 
Now for something completely sensible.
Preparing chloranil by treating phenol with HCl and sodium chlorate is not a good way to generate chloranil because the initial product is
2,4,6-trichlorophenol which is then difficult to convert to chloranil, although there is a procedure described by Lübbecke and Boldt (1) for a
similar route using hydrochloric acid and hydrogen peroxide with a large amount of magnesium chloride as a catalyst. I have found that it is better to
start with a para-substituted benzene derivative such as quinol, para-phenylenediamine, p-aminophenol or paracetamol which hydrolyses to the former
compound. That said the original poster was about the nature of the oxidising agent.
I did not try the original posters idea with TCCA or NaDCCA because the large amount of isocyanuric acid formed would be difficult to remove from the
chloranil except possibly by leaching in a soxhlet extractor with acetone. If TCCA or the sodium salt are all that you have available as the
chlorinating agent then it is probably better to generate the chlorine externally. There is a published procedure for the use of this method for the
preparation of o-chloranil from catechol via this route although the final oxidation of tetrachlorocatechol to o-chloranil is done externally (2).
A search of the SM forums reveals many references to the preparation of chloranil, some personal others in journals or patents but very little in the
way of actual personal detailed accounts of its preparation have ever been posted. I hope to remedy this over the coming weeks as I intend to post not
only the preparation but the purification of the product which is usually highly impure. I have made many batches of chloranil over the years and
recently I required rather a lot of it to study some of its products. Historically, I used paracetamol in hydrochloric acid with sodium nitrate as the
oxidizing agent but this is the preparation from hell, monstrous toxic foam belching chlorine, nitrogen oxides, chloropicrin and the rest for a final
yield of only 35-40%. Looking for a cleaner method I decided to try oxidizing quinol (hydroquinone) in hydrochloric acid with various oxidizing agent,
I tried sodium chlorate, sodium chlorite and hydrogen peroxide. The first two worked well though the occasional micro explosions in the vapour above
the reaction mixture when using sodium chlorite are a little unnerving but my attempts with 30% hydrogen peroxide failed.
The failure of the hydrogen peroxide method came as a surprise given the number of patents (3, 4 & 5) that describe various modification to this
method. Has anyone on this forum ever tried the hydrogen peroxide method on any substrate? In the paper by Lübbecke and Boldt (1) that describes this
method they us magnesium chloride as a catalyst. However, in the Lübbecke procedure 270ml of concentrate (presumably 36%) hydrochloric acid are used
for just 1.7g of phenol; admittedly the yield is claimed to be 99%.
I would be interested to hear about other people’s experiences preparing this material. I intend to produce a section in the “Pre-publication
forum” eventually.
(1) Lübbecke, H. and Boldt, P.; Tetrahedron 1978; v34; pp1577 to 1579
(2) US patent 4196132
(3) DE 2645114
(4) EP 0326456
(5) US 5334735
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tsathoggua1
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How about using the reaction between hot, concentrated NaOH or KOH and chlorine gas bubbled through to produce chlorates? been a long time (years)
since that road was travelled personally but seem to remember that if cold, hypochlorites are the result of this, whilst chlorates are the result,
along with presumably some chloride.
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nitro-genes
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@Boffis
Did you come to an optimized procedure for producing chloranil from hydroquinone/p-aminophenol? Would be interesting to hear!
[Edited on 21-12-2017 by nitro-genes]
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Boffis
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@nitro-genes; I wouldn't say "optimised". I found, as mentioned in the Lübbecke and Boldt paper, you basically need a very large excess of
concentrated hydrochloric acid over the phenolic compound and oxidizer or you get a lot of partial chlorinated products, di and trichlorobenzoquinones
and sometimes chlorinated hydroquinone derivatives mainly. Hydroquinone is definitely "cleaner" in that much less red alcohol soluble "tar" is
produced.
The important thing is the purification because most of the intermediate stages can be recycled into the next batch. I have found that with
paracetamol I get a high apparent yield of deep orange product after the initial cold water washing and drying (the product gives off a very acrid
vapour while drying, possibly occluded chloropicrin). The crude product is then mixed with an equal weight of isopropanol and left to stand for a
short while at room temperature and the then sucked dry on a buchner funnel and washed with a little more isopropanol. This gets rid of most of the
red tarry material and much of the acrid material. The leachate can be "neutralised" with caustic soda solution before disposal.
The product is now usually cadmium yellow and can be further purified with small volumes of hot isopropanol and/or acetone to give a lemon yellow
pearly powder that consist of chloranil and some trichlorobenzoquinone. The later can be leached out with boil water according to a patent or the
whole can be recrystallised from acetone but it requires a lot of solvent. I usually use it as at this stage since most of the products I make are
easily purified. The materials leached from the product in these later stages can be recycled into subsequent batches. Without recycling a 35% yield
of crude chloroanil is pretty reasonable starting with paracetamol.
With hydroquinone I got much less red tar but the overal yield is about the same. Recycling the lower chloroquinones and hydroquinones greatly
improves the overal yield.
Interestingly I eventually purchased some commercial chloranil but have found it to be much less reactive, particularly towards sodium nitrite in the
nitrite substitution route to nitranilic acid.
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nitro-genes
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Thanks for the info, especially the purification steps are helpful! Been wondering if it would matter if oxidation to benzoquinone or chlorination
would be favourable during the initial stages of the reaction, as most with most available syntheses both seem to occur simultaneously. Can
benzoquinone actually be chlorinated all the way to chloranil? Do the extra chlorine groups attached prevent side reactions, like complete destruction
of the ring e.g? Would it be beneficial to tetra-chlorinate first and form the quinone last?
Attachment: Chlorination of N-acyl Derivatives of p-Aminophenols (Naphthols) and p-Phenylenediamines.pdf (69kB)
This file has been downloaded 273 times
[Edited on 28-12-2017 by nitro-genes]
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Boffis
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@nitrogenes, there are plenty of references to the reductive chlorination of benzoquinone with hydrochloric acid to chlorohydroquinone so I have
always assumed that the process simply progresses via repeating this process and oxidation alternately. I have noticed that with insufficient
oxidising agent the product is a colourless crystalline material that I have taken be be various polychlorohydroquinones. A paper was once posted on
this website, I think by Nicodem, from a Korean or Chinese publication (in English) that looked at the isomer make up of some intermediate
chlorination products.
As the chlorination progresses I think it becomes harder to add further chlorines and that this is why the massive excess of hydrochloric acid may be
required, simply to maintain a high concentration of HCl in the latter parts of the synthesis when some of the HCl has been consumed. If this is the
cases it may be better to carry out the reaction in stages. One problem though that I have noticed is the very low solubility of the tri and
tetrachlorobenzoquinones in the aqueous reaction mixture which may result in a "protective layer" effect reducing the efficiency of the
chlorination/oxidation in the later parts of the synthesis. This may be another reason for the very large volume of hydrochloric acid relative to
reactant in the paper by Lübbecke and Boldt. The paper you attached is very interesting indeed since it uses a non-aqueous solvent in which the
products are probably much more soluble.
I am sure you could use benzoquinone and HCl to start with and then revert to an oxidising agent+hydrochloric acid system.
Incidently in the early days I used sodium nitrate and conc. hydrochloric acid, this required a large amount of hydrochloric acid to keep the salt in
solution, it gave better results but the foam from hell and the lethal fumes were a problem.
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