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Topic: I need help with 2,6- anthraquinone mechanisms  (Read 8646 times)

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Offline polymer man

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I need help with 2,6- anthraquinone mechanisms
« on: June 12, 2012, 06:52:21 PM »

Hello,

I need your help with two mechanism

The first one is reduction:

http://imageshack.us/photo/my-images/694/78729026.jpg/

The procedure is:

A mixture of 2,6-dibromo-9,10-diphenyl-9,10-dihydroanthracene-9,10-diol (13.5 g, 15.20 mmol), KI (21.8 g, 131.48 mmol), Na2H2PO2.H2O (15.4g, 175.4 mmol) and acetic acid (152 mL) was heated at reflux for 40 min. The precipitate was collected and dissolved in dichloromethane (DCM). The organic solution was washed with brine, dried over anhydrous MgSO4.



The second one is reduction of nitro to amine:

http://imageshack.us/photo/my-images/72/50398641.jpg/

The procedure is:

To a stirred suspension of 2,6-dinitroanthracene-9,10-dione (9.4 g, 31.5 mmol) in ethanol (340 mL) was added a solution of sodium sulfide nonahydrate (34.1 g, 142 mmol) and sodium hydroxide (13.5 g, 338 mmol) in water (590 mL). The mixture was heated at reflux for 6 h and left to stand overnight. The ethanol was removed in vacuo and the residue cooled to 0-5 °C. The resulting precipitate was collected by filtration, repeatedly washed with water, and dried. Recrystallization from ethanol/ water afforded the product as an orange/red solid (7.35 g, 98%)


I appreciate your help.

Offline polymer man

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #1 on: June 13, 2012, 09:38:45 AM »


I got the second mechanism but the first one I could not. I think  a radical needs to be formed in position 9 and 10 but how I do not know.

http://imageshack.us/photo/my-images/232/35173152.jpg/

Offline discodermolide

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #2 on: June 13, 2012, 09:49:45 AM »


I got the second mechanism but the first one I could not. I think  a radical needs to be formed in position 9 and 10 but how I do not know.

http://imageshack.us/photo/my-images/232/35173152.jpg/

I don't think it's a radical, it may be 2 benzylic carbonium ions formed by loss of 2 x water. The ions then re-aromatize.
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Offline orgopete

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #3 on: June 13, 2012, 11:04:04 AM »
I didn't look up a reference to this, but it is an iodide reduction. The other product is I2.
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Offline polymer man

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #4 on: June 13, 2012, 01:07:28 PM »


Thank you for replying.

What is making me to think it is a radical because if ions are formed in position 9 and 10, how double bond will be formed

http://img40.imageshack.us/img40/8558/28239906.jpg

Offline discodermolide

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #5 on: June 13, 2012, 01:16:04 PM »


Thank you for replying.

What is making me to think it is a radical because if ions are formed in position 9 and 10, how double bond will be formed

http://img40.imageshack.us/img40/8558/28239906.jpg

You have the same problem with radicals, somewhere there will be two left over which have to pick up H radicals.
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Offline polymer man

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #6 on: June 14, 2012, 03:45:34 PM »

unfortunately, I could not find clue  about the first mechanism but it looks like iodine reduction.

 ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ???

Offline discodermolide

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #7 on: June 15, 2012, 12:35:01 AM »

unfortunately, I could not find clue  about the first mechanism but it looks like iodine reduction.

 ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ???

Silly question. Is a hypervalent iodine species being formed here with one of the alcohols, this then oxidizes the other position?
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Offline Dan

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #8 on: June 15, 2012, 12:45:09 AM »
How about:
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Offline polymer man

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #9 on: June 15, 2012, 02:12:57 PM »

Thank you for replying,,,,,,

It is really interesting, is it possible that iodine in one side and oxidation the other side and what is the role of NaH2PO2.xH2O

Offline Dan

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #10 on: June 15, 2012, 05:58:09 PM »
Abstraction of I+ by I- to form I2 (which is what I drew) is well known.

I actually didn't read the conditions properly and assumed it was KH2PO4 and was simply acting as an acid catalyst for SN1 in the first step of the mechanism I drew. Realising now that it's potassium hypophosphite and not -phosphate, I doubt my suggestion is correct since there is no acid present. If the KI is catalytic, and not a stoichiometric reductant, it may simply be that it reduces the I2 back to iodide to turn over the catalytic cycle.

I'll have a think about it and try to get back to you, hopefully someone else can shed some light on it...
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Offline discodermolide

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #11 on: June 15, 2012, 11:57:44 PM »
Abstraction of I+ by I- to form I2 (which is what I drew) is well known.

I actually didn't read the conditions properly and assumed it was KH2PO4 and was simply acting as an acid catalyst for SN1 in the first step of the mechanism I drew. Realising now that it's potassium hypophosphite and not -phosphate, I doubt my suggestion is correct since there is no acid present. If the KI is catalytic, and not a stoichiometric reductant, it may simply be that it reduces the I2 back to iodide to turn over the catalytic cycle.

I'll have a think about it and try to get back to you, hopefully someone else can shed some light on it...

This is a potassium salt of phosphonic acid. I don't quite see how it can help but there is a reaction called the Atherton-Todd reaction in which if you react such phosphorus compounds with CCl4  or other halogen sources in the presence of an alcohol they are oxidized to the next highest in this case a phosphonate.
Perhaphs we are getting an intermediate I-P(O)OHO-K+ which reacts with the alcohol to give RO-P(O)OHO-K+  (R = the rest of the anthracene) which is the leaving group - a phosphate!
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Offline Dan

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #12 on: June 16, 2012, 08:43:55 AM »
This is a potassium salt of phosphonic acid.

I don't think it is, potassium phosphonate is KH2PO3

In this reaction it is potassium hypophosphite KH2PO2.

All I can find is vague references to it being a reducing agent. I am also trying to shoe-horn in some kind Atherton-Todd or Appel-type mechanism but not coming up with much. For these sort of things you need to start with an oxidising agent like iodine or a carbon tetrahalide to get the dehydration going. With only KI as the other reagent I don't understand what the hypophosphite is doing.

I can believe AcOH would protonate the OH of the starting material and promote SN1 substitution with I-. Lose water again and you can abstract I+ with I-. The only think I can think of is that the hypophosphite scavenges the I2 to initiate an Atherton-Todd or Appel-like Iodide substitution mechanism.
« Last Edit: June 16, 2012, 09:29:31 AM by Dan »
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Offline discodermolide

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #13 on: June 16, 2012, 09:34:46 AM »
This is a potassium salt of phosphonic acid.

I don't think it is, potassium phosphonate is KH2PO3

In this reaction it is potassium hypophosphite KH2PO2.

All I can find is vague references to it being a reducing agent. I am also trying to shoe-horn in some kind Atherton-Todd or Appel-type mechanism but not coming up with much. For these sort of things you need to start with an oxidising agent like iodine or a carbon tetrahalide to get the dehydration going. With only KI as the other reagent I don't understand what the hypophosphite is doing.

I can believe AcOH would protonate the OH of the starting material and promote SN1 substitution with I-. Lose water again and you can abstract I+ with I-. The only think I can think of is that the hypophosphite scavenges the I2 to initiate an Atherton-Todd or Appel-like Iodide substitution mechanism.


Do you think that you get something like this going on? Compound 1 then iodinates the OH like other P ylids?
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Offline Dan

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Re: I need help with 2,6- anthraquinone mechanisms
« Reply #14 on: June 16, 2012, 09:59:21 AM »
Yeah, exactly. What I was thinking of is attached below, but it doesn't balance the iodine so I don't think it's right (but maybe on the right track).
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