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Author: Subject: toluene --> benzaldehyde
benzylchloride1
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[*] posted on 18-3-2009 at 19:57


I did not have very good success with the electrolytic preparation of benzaldehyde. I was able to produce several mililiters of benzaldehyde using this method. I think I will have better luch with the chlorination of the toluene. I put my benzal chloride-benzyl chloride mixture back into the chlorination apparatus and chlornated the product for another 4.5 hours. After distilling, the product had a density of 1.23 and did not have the benzyl chloride odor. The product distilled between 180 to 190 Celsius at a pressure of around 580mm.



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[*] posted on 15-5-2009 at 22:52


Neograviton method seems to work for me and after about 6 hours at about 55 degrees the smell of BnO was strong. Sadly the flask broke when I attempted to steam it out so I will not be able to get an idea of yeild although I did manage to save quite abit but can not attempt a steam distilling until I get all the left over toluene and mess cleared up.

Are the yeilds as Neograviton states at 70%?

Im a little confused on the first step where he stated the need for Mn(IV) IIRC would it not need a 2x molar excess of H2SO4 to form the desired salt instead of the 1:1 he mentions.

Org posted a synthesis from Osmium that stated FeSO4/cupric acetate and sodium persulfate. Im getting ready to run this and was woundering if its really 95% such as stated. Has anyone had experiance with this method. It seems to be largly ignored when it was posted.





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[*] posted on 18-5-2009 at 04:18


I tried it sevral times without getting any definitate results. There was benzoic acid produced, and unreacted benzyl alcohol, depending on the reaction time. But it's worth a try IMHO, I did produce a fair amount at the end. Be carefull to heat above 70°C before adding the persulfate, as there a run-out reaction if you heat to that temp after adding a large amount of persulfate.



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[*] posted on 18-5-2009 at 08:32


I did manage to get the mess cleaned up and steam some out. What came out from the steam distilling smelled of toluene yet it seems the benzaldahyde got let behind judging from the smell. It is quite possible that I didnt let it steam long enough but after the accident its not worth my time to attempt to salvage it.

Hinski posted another means using just Mn(IV) in a electrochemical cell. I think I will proceed in this direction for the time being and keep the persulfate route just for academics. I have heard of the runaway but did not realise that it was caused by preloading the persulfate so thats good to know.





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[*] posted on 20-5-2009 at 20:49


Alkyl hypochlorites as reagents for the side chain halogenation of toluene.

Tert butyl hypochlorite is an interesting chlorinating/oxidizing agent. A safe synthesis of this reagent is given in Organic Synthesis Collective volume 5. Isopropyl hypochlorite can be prepared in a similar method. A US patent describes the chlorination of theyl benzene to a,a-dichloro-1-phenylethane in high yields. This could be applicable to toluene for the synthesis of benzal chloride and other side chain halogenated products. This would be significantly better then passing dry chlorine through refluxing toluene for 12 hours for a 1 mole experiment. Here is an excript from US Patent 5064518 - Method for the selective alpha halogenation of alkylaromatic compounds. Hopefully this is patnet is not totally BS. Tert butyl hypochlorite is the preferred reagent because of its ability to form radicals, an experiment will be conducted with the more easily prepared isopropyl hypochlorite. This may considerably simplify the synthesis of benzal chloride for the home chemist.

Preparation of 1,1-dichloroethylbenzene Using t-butyl hypochlorite.

Into a 5-neck 2-liter flask, equipped with thermometer, mechanical stirrer and a pH probe, is placed 1000 mL of an aqueous bleach solution (~5.25% NaOCl). The flask is placed in an ice bath and cooled to 8° C. and t-butyl alcohol (56.5 mL, 0.59 mole) and glacial acetic acid (34.35 mL) are added with stirring. The temperature rises to about 15° C. and the pH drops from about 11.3 to about 6.5. Stirring is continued for about five minutes and then allowed to phase-separate, during which time a yellow oil floats to the surface. Ethylbenzene (36.9 mL, 0.30 mole) is added, stirring resumed and a 275-watt sun lamp is placed over the flask. The mixture is stirred with illumination for one hour while the temperature is maintained within the range of 8°-18° C., after which stirring is stopped and the mixture is allowed to phase-separate.

The aqueous phase is extracted with two×100 mL portions of methylene chloride and combined with the organic phase. The combined solvent and organic phase is then dried over MgSO4 and the solvent is removed by distillation, leaving 52.01 g of oil. G.C. analysis shows that the product is 73.6% 1,1-dichloroethylbenzene, 10.34% 1-chloroethylbenzene and 10.48% acetophenone and some minor impurities.

The following three experiments (Examples 4, 5 and 6) show the use of other solvents in the reaction using t-butyl hypochlorite as the chlorinating agent.

EXAMPLE 4

Use of Carbon tetrachloride as Solvent

A quantity of t-butyl hypochlorite (7.0 mols, 759.99 g, 775 mL) is chilled to -5° C. in a brine jacketed reaction flask equipped with mechanical stirrer, light well, thermometer and nitrogen supply. Ethylbenzene (2.0 mole, 213.4 g, 246 mL) in CCl4 (10.4 moles, 1594 g, 1000 mL) is added to the reactor and the reaction is started by turning on the lamp (incandescent, 25 watt lamp, General Electric model FG648-X). The reaction temperature is allowed to rise to 10° C. and samples are taken periodically for G.C. analysis. After 4 hours the reaction is complete and the mixture is drained from the reactor and the t-butanol is stripped using a rotary evaporator which leaves 322.62 g of a colorless oil which is 89.4% 1,1-dichloroethylbenzene by G.C. analysis (82.3% yield).

EXAMPLE 5

Use of Benzene as Solvent

The reaction of Example 4 is repeated except that benzene (11.18 moles, 874 g, 1000 mL) is used in place of carbon tetrachloride. The t-butanol is removed on a rotary evaporator and there remains 341 g of a colorless oil which is 91.7% 1,1-dichloroethylbenzene by G.C. analysis (89.3% yield).

EXAMPLE 6

Use of t-butyl hypochlorite as Solvent

Ethylbenzene (4.0 mole, 424.68 g, 492 mL) is charged to a brine jacketed reaction flask equipped with a subsurface N2 sparge, light well, thermometer and condenser. The t-butyl hypochlorite (14.0 mole, 1520 g, 1670 mL) is added to the reactor and the mixture is chilled to -5° C. while sparging with N2. The same lamp employed in Example 4 is switched on to initiate the reaction which is conveniently held at 0° C. by controlling the lamps' output with a temperature controller. Samples are taken periodically and analyzed by G.C. analysis. When the reaction is complete (3 hours) the mixture is drained from the reactor and the t-butanol and excess t-butylhypochlorite is removed on a rotary evaporator, leaving 709.0 g of a clear oil which is 93.2% 1,1-dichloroethylbenzene by G.C. (93% yield).



[Edited on 21-5-2009 by benzylchloride1]




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[*] posted on 21-5-2009 at 01:11


Regarding isopropyl hypochlorite:

http://www.sciencemadness.org/talk/viewthread.php?tid=1896&a...

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[*] posted on 21-5-2009 at 03:08


Regarding t-butyl hypochlorite:

http://www.sciencemadness.org/talk/viewthread.php?tid=1896&a...
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[*] posted on 28-5-2009 at 15:45


The isopropyl hypochlorite chlorination of toluene works fairly well, not explosions or violent reactions, keep mixture below 25C at all times with ice bath, the reaction is very mildly exothermic, the end product had the density of benzyl chloride. A 60W light was used to catalyze the reaction.

Another interesting synthesis of benzaldehyde through benzaldoxime:
Benzaldoxime in practically 100% yield based on NOCl. The nitrosyl chloride could be generated insitu by passing anhydrous HCl into a mixture of toluene and isopropyl nitrite. The oxime can be hydrolyzed with hydrochloric acid to benzaldehyde and hydroxylamine hydrochloride.
THE REACTION OF NITROSYL CHLORIDE ON TOLUENE
BY E. V. LYNN AND HELEN I,. ARKLEY
Received January 19,1923
Some time ago one of us found' that nitrosyl chloride will readily react
with normal heptane in the sunlight to produce a blue material which
easily changes to a colorless oil. The blue compound was later shown2
to be nitroso-dipropylmethane and the rearranged oil, dipropyl-ketone
oxime. It was also demonstrated that this reaction is probably general
for all of the paraffin hydrocarbons, a conclusion reached mainly because
gasoline and petroleum ether give a similar blue color with nitrosyl
chloride.
In experimenting with various substances, it was found that benzene
could not be induced to react at all with the reagent, even in sunlight;
a sample of benzene solution was kept for months without any change in
the brown color of the nitrosyl chloride. In view of this fact, paraffin
derivatives of benzene should react in such a way that only the alkyl
radical is attacked. Toluene, the simplest alkyl drivative, should give,
according to previous experience, phenylnitrosomethane rearranging to
benzaldoxime. CsH5-CHs + NOCl ---j CeHb-CH2-N0 f HC1.
CBHS-CH~---NO --3 C6Hb-cH = N-OH. Experiment has fully
demonstrated the correctness of this reasoning, as toluene reacts readily
in the sunlight with nitrosyl chloride producing benzaldoxime, which has
been converted to benzaldehyde, benzoic acid and benzanilide in the usual
way.
Experimental Part
The nitrosyl chloride was prepared as previously described2 by the reaction
of nitrosyl sulfate and sodium chloride. The toluene was first dried
over sodium hydroxide and then distilled, the portion boiling between 110 '
and 112' being used. This was saturated with the gas, giving a dark
red-brown liquid. In the dark at room temperature there was practically
no change in the appearance, but after some time a heavy, insoluble oil
and some gas were formed. In the sunlight the reaction was quite rapid,
producing large quantities of gas, mostly hydrogen chloride, and an amount
of the heavy oil equal to about 3% of the toluene used. In later experiments
the saturated solution was exposed to the sunlight at temperatures
below 10'. In these cases the reaction proceeded somewhat more slowly
and, in place of the oil, there were deposited beautiful, white, iridescent,
feathery crystals. In all experiments the color of the solution disappeared
with the formation of the precipitate. There was, however, no intermediate
production of a blue color and one can only conclude that phenylnitrosomethane
is very unstable.
In subsequent changes the oil and crystals acted alike and, since it was
just as easy to produce the latter and more convenient to work with them,
they were employed in the reactions recorded below. The crystals had an
indefinite melting point, from 35" to 70". They were dissolved in sodium
carbonate solution and extracted with ether, evaporation of the latter
leaving characteristic crystals of P-benzaldoxime, melting at 128 '. The
primary product was, therefore, undoubtedly a mixture of the hydrochlorides
of both benzaldoximes, since the above procedure transforms the
QC to the 0 form. Hydrolysis of the oxime with dil. acid gave an oil identified
by its odor as benzaldehyde. It was oxidized by nitric acid and the
resulting benzoic acid was precipitated on cooling, and melted at 118". It
was further identified by converting to its ferric salt and to benzanilide,
m. p. 158'.
The amount of benzaldoxime crystals obtained is practically that calculated
based upon the nitrosyl chloride used, about 3% by weight of the
toluene. The time required is dependent upon the temperature and upon
the intensity of the sunlight but in no case was it longer than 2 hours.
Under the right conditions the reaction could undoubtedly be made to
proceed more rapidly and probably continuously. Whether the process
can be utilized commercially under the influence of some catalyst is a
problem which is at present engaging our attention. Furthermore, we are
studying the action of nitrosyl chloride on other substances and will report
the results later.
Summary
Nitrosyl chloride readily reacts with toluene in the sunlight to produce
crystals of benzaldoxime hydrochloride, from which benzaldoxime, benzaldehyde,
benzoic acid and benzanilide can be prepared in the usual way.




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[*] posted on 28-5-2009 at 22:54


Does anyone know how well the above stated reaction would work with substituted toluenes?

For example, how does it treat alkoxy substitutions?
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[*] posted on 28-6-2009 at 10:52


Wow. Has nobody mentioned the "Etard" reaction?
It appears that Chromyl Chloride [Cr(VI)O2Cl2] is excellent at partially oxidizing toluene to benzaldehyde.
While I haven't prepared benzaldehyde from toluene yet, I've successfully prepared chromyl chloride from Chromium(III) oxide via the below process:
--------------------
2 KMnO4 + Cr2O3 + 2 H2SO4 → H2Cr2O7 + 2 KHSO4 + 2MnO2
H2Cr2O7 + 4 KCl + 4 H2SO4 → 2 CrO2Cl2 + 4 KHSO4 + 3 H2O
Overall:
2 KMnO4 + Cr2O3 + 4 KCl + 6 H2SO4 → 2 CrO2Cl2 + 6 KHSO4 + 2 MnO2 + 3 H2O
--------------------
While gaseous hexavalent chromium sounds like a sure-fire recipie for lung cancer, the fumes are dense enough that I feel the risk to be within the realm of reason.
What do you all think? I'm going to try it in the next few weeks and I'll post back with an update. Feel free to PM me with questions or comments.
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[*] posted on 28-6-2009 at 12:48


There's considerable good reading material about this reaction in older publications. Main problems with Etard are hexavalent chromium health hazards, expense of the reagents, violence of the initial reaction, and needing to take careful measures to protect the liberated aldehyde from further oxidation at the end. I will look forward to the results of your experiments.

What form was your Cr2O3 initially in? Was it pottery-grade or something more reactive? Woelen reported not long ago that acid bromate solution would dissolve pottery Cr2O3, which was something of a surprise, since usually it takes high-temperature alkaline-oxidative fusion to get to Cr(VI) from such material. I am curious if the use of KMnO4 was inspired by his posts, derived from some other reference, or discovered independently by you.




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[*] posted on 28-6-2009 at 15:53


I procured the Cr2O3 from the greenish ash left over from the ammonium dichromate volcano demo performed by an old chemistry teacher for a 101 class. I washed it with a dilute acid-peroxide solution to neutralize any residual hexavalent chromium and allowed it to dry. I then packed it into glass vials for future use. Now I'm very happy I did so. :)
The KMnO4-acid discovery was determined entirely by myself. The inspiration came after remarking to a friend that Mn2O7 could oxidize "damn near anything."
In addition, I added some of the liquid formed by:
2 KMnO4 + Cr2O3 + 2 H2SO4 → H2Cr2O7 + 2 KHSO4 + 2MnO2
to water and observed an orange solution with brown precipitate, precisely as expected.
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[*] posted on 28-6-2009 at 16:05


This covers substituted toluenes, but is helpful at any rate for reaction conditions.

You're welcome :P

Attachment: Etard Reaction.pdf (221kB)
This file has been downloaded 2561 times

[Edited on 6-29-09 by UnintentionalChaos]




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[*] posted on 29-6-2009 at 15:08


Thanks for the article, UnintentionalChaos. The preps in the article specify CCl4. Has anyone ever run this reaction in CH2Cl2?

[Edit] By that I meant actual experience, not theorizing. Adding chromyl chloride to neat toluene will result in a fire, if you're lucky.

[Edited on 30-6-2009 by entropy51]
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[*] posted on 29-6-2009 at 15:59


CS2 and CHCl3 are also listed as alternative solvents. CHCl3 has the trouble of forming emulsions apparently, so CH2Cl2 might also suffer from this drawback. Adding chromyl chloride dropwise to excess toluene may work, but care should be exercised when trying this as the reaction may be too exothermic with neat liquid reactants.
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[*] posted on 12-9-2009 at 02:38


The way I thought to do it was to slowly add bromine to an excess of toluene, forming benzyl bromide. This would be separated from any remaining toluene and hydroxylated with NaOH to form benzyl alcohol and NaBr. The salt is separated from the alcohol and recycled, while the benzyl alcohol is then mixed with DMSO and HCl or HBr solution is added - producing benzaldehyde and dimethyl sulfate.

Bromine can of course be made by acidifying NaBr followed by simple oxidation with 3% H2O2. Since it is a liquid at feasible temperatures this would ease the halogenation of the toluene. Since adding NaOH reforms the NaBr, it can be recycled.

acid-catalyzed DMSO can oxidize benzyl alcohol (and similar compounds) to benzaldehyde with as high as 95% yield!
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[*] posted on 12-9-2009 at 06:39


When someone claims such unusual things, like that slowly adding bromine to an excess of toluene, forms benzyl bromide, or that oxidation of benzyl alcohol with DMSO gives dimethyl sulfate besides benzaldehyde, it is expected that some references are provided.

Why would we believe you just for your word? It is experimentally known that bromine reacts only very slowly with toluene at room temperature, and even this via the electrophilic aromatic substitution, thus giving a mixture of o- and p-bromotoluene. Essentially no benzyl bromide is formed unless you use conditions for radical brominations (that is, radical initiators or photochemically). Also, the oxidation of benzyl alcohol with DMSO means that DMSO is getting reduced (basic rule of redox reactions is that the oxidant gets reduced and reductor oxidized). Dimethyl sulfate is in a higher oxidation state than DMSO, so how could it be the product of the reaction? The next sulfur lower oxidation state product forms, that is dimethyl sulfide, as is known experimentally.

PS: You would know all these things if you would just bother to read and cite references.
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[*] posted on 12-9-2009 at 07:59


DMSO (of which I have about a 500 ml bottle) would be reduced to dimethyl sulfide, which being a mercaptan would have an intense garlic odor. Also, being highly volatile, it would probably be toxic like H2S.
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[*] posted on 13-9-2009 at 08:54


Benzyl halides are commonly made by free-radical halogenation of toluene - the same process is used to produce the chloride as is the bromide, only bromide would probably be loads easier since it is liquid at room temperature. Using 2x the molar ratio results in the benzal halides. Given that it was such common info I didn't see a reason to hunt down a reference for it.

http://www.erowid.org/archive/rhodium/chemistry/alcohol2alde... this describes the oxidation of benzyl alcohols to benzaldehydes using DMSO and HBr.

OHH I did mean sulfide - totally didn't mean to type sulfate - told myself over and over not to make that typo :) My bad haha.

[Edited on 13-9-2009 by Rattata2]
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[*] posted on 14-9-2009 at 01:31


Quote: Originally posted by Rattata2  
Benzyl halides are commonly made by free-radical halogenation of toluene - the same process is used to produce the chloride as is the bromide, only bromide would probably be loads easier since it is liquid at room temperature. Using 2x the molar ratio results in the benzal halides. Given that it was such common info I didn't see a reason to hunt down a reference for it.

Using this as an example, I will try to explain in just few words why it is so important to give references and cite sources. If you would have provided a reference for benzylic bromination of toluene, there would have (statistically) been more chances that you would had also read it, and if you would have read it, you would have also read the experimental conditions. This would have given you the knowledge that just adding bromine to toluene does not form benzyl bromide. Instead, you did the classical beginners mistake who seeing a reaction scheme jumps at the conclusion that you just add this to that and out comes the product. The reaction of bromine with toluene can either proceed via electrophilic aromatic bromination or via radical bromination, both requiring different conditions, but none proceeds to any usable extent by just "slowly adding bromine to toluene".

Quote:
http://www.erowid.org/archive/rhodium/chemistry/alcohol2alde... this describes the oxidation of benzyl alcohols to benzaldehydes using DMSO and HBr.

But why? What is the point of reacting benzyl bromide with a hydroxide (which, by the way, gives a mixture of benzyl alcohol and dibenzyl ether) just to then oxidise the benzyl alcohol with DMSO? It sounds completely irrational when you can oxidise benzyl bromide with DMSO directly using the Kornblum oxidation. (And this is another example of lack of reference checking. If you would have checked the references from the paper you linked to you would have read the reference number 3 and 4 as well).




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[*] posted on 14-9-2009 at 03:36


Ratatta2: Listen to Nicodem - he makes very valid points.

JohnWW: I actually had the "pleasure" of smelling DMS as a solution in DCM. It was very cabbage like (not garlic as you describe) and rather strong smelling, although not as strong as I had anticipated (possibly due to it being in solution?). It was actually *quite nice* once the majority of the smell had gone, leaving a faint odour in the room.
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[*] posted on 15-9-2009 at 20:43


toluene + Ca(OCl)2 @105C with no other reagents should make benzyl chloride...
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[*] posted on 15-9-2009 at 20:58


Prove it.
Book learning is all fine and well but unless your Ca(OCl)2 is pure you will run out of room. Not to mention the ugly runaway leading to over heating.
Oh yeh did I mention the product of all that hassle was junk? Im sorry but I toyed with that method and wasted alot of toluene to accomplish nothing useful and it caused my eyes to feel as though sand is in them. You will get a mixture of products doing it that way as well so there are other more focused ways one could go about its synthesis.

Check out Lens threed on the topic in prepublications. You can't beat that kind of excelent work that was performed in that writeup.

BTW: The worst part of the synthesis using the hypochlorite is the runaways. This could be due to my dirty Ca(OCl)2 but either way I think this sucks. I want so bad to try it once more because I hate like hell when a synthesis kicks my ass but I think I know when Im beat and wasting my time.





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[*] posted on 15-9-2009 at 21:58


Ive never tried it, but the stuff on this site should be pretty accurate. http://www.erowid.org/archive/rhodium/chemistry/benzylchlori...

"Toluene and dry Calcium Hypochlorite (bleaching powder) are heated together to 105°C in the abscence of other reagents. This avoids by-product formation. If equal amtounts are used, volume-wise, there is a high conversion. If more bleaching powder is used, the conversion is more robust, but contaminants such as benzal chloride and benzotrichloride are formed [...]"
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[*] posted on 15-9-2009 at 22:21


"there is a high conversion"

Yup that explains the itchy eyes. But the contamination is to much of a pain when there are better means that even I am able to perform. Anyone with good gear should be able to perform other synthesis with ease instead of dicking with this. The part where is says avoids biproduct formation is a load of shit BTW and they dont mention the fact that when it hits 105-110 it runs away to extreamly high temps. You see them little [...] there? Thats the main problem with rhodiums archives is that it does not give the full details and don't mention what the original text states of SLOWLY adding the Ca(OCl)2 in portions. If you can site rhodiums articals then its better to look for the references at the bottom and take the writeup with a grain of salt. I love the fact he put this all out there but care must be taken. Its just bad form to not cross reference your sources.

[Edited on 16-9-2009 by Sedit]





Knowledge is useless to useless people...

"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story before."~Maynard James Keenan
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