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Topic: phenols  (Read 4258 times)

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Offline AMEDIO

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phenols
« on: January 27, 2011, 12:16:42 PM »
what will be the product of the given reaction?

phenol + P2S5 -> ?

thought quite a lot about it...but cant seem to figure it out!!!
can anyone tell the proper mechanism as well , if possible?? ???

Offline AndersHoveland

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Re: phenols
« Reply #1 on: January 27, 2011, 12:54:31 PM »
I do not know with any certainty, but I would think that
(PhO)3P=S and H2S would form. (where Ph is a phenyl group C6H5-- of course  ;) )

Offline nox

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Re: phenols
« Reply #2 on: January 27, 2011, 08:47:11 PM »
http://en.wikipedia.org/wiki/Lawesson%27s_reagent

You'd probably end up with the unmethylated version of Lawesson's reagent.

Offline AndersHoveland

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Re: phenols
« Reply #3 on: January 28, 2011, 02:30:01 PM »
A more likely possibility:
(8)PhOH + P2S5 --> (2)H3PO4 + (3)Ph2S + (2)PhSH

I think this reaction might dominate if regular phenol, rather than methoxy-phenol, is used.

I have been doing some research, and will show what I found.
"Preparation of phosphorothioate esters from benzyl alcohol and phosphorus pentasulfide"
(United States Patent 3102130)
These esters have the formula (C6H5CH2O)3P=S.

In a different paper, ("Preparation of fluoroolefins by reaction of polyfluorochlorocarbinols with phosphorus pentasulfide" R. A. Bekker, G. V. Asratyan, É. P. Lur'e and B. L. Dyatkin),
CH3C(CF2Cl)2OH with at least a five-fold excess of P2S5 was refluxed for 2 hours, producing CH2=C(CF2Cl)2 in 58% yield.
« Last Edit: January 28, 2011, 03:27:51 PM by AndersHoveland »

Offline AndersHoveland

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Re: phenols
« Reply #4 on: January 28, 2011, 03:41:40 PM »
“The present invention relates to a process, wherein an alcohol and/or phenol is reacted with phosphorus pentasulfide in the presence of a catalyst <,such as an ammonium salt,> with the resultant formation of O,O-dialkyl-, O,O-diaryl- or O-alkyl-O-aryldithiophosphoric acids.” (United States Patent 4397791)
These would have a general formula of (PhO)2PS2H. Here is a diagram of a similar acid ester:  http://www.lookchem.com/UserFilesUpload/5%2820%29.png

From "Science Madness": "An alcohol plus phosphorous pentasulphide will make a thiol"
(an example of a thiol is CH3CH2SH )
I also found this: "The mercaptans may be prepared... by heating the alcohols with phosphorus pentasulfide."
("Introduction to Sulfur Functional Groups" by James Richard Fromm) Thiols are often referred to as mercaptans.

"...state that O,O,S-trimethyl phosphorodithioate was obtained from the reaction of methanol with phosphorus pentasulfide." Alfred E. Lippman, 1966 This has a formula (CH3O)2P(=S)(SCH3).

However, apparently alcohols can still be used as solvents for reactions involving P2S5,
Babak Kaboudin and Dawood Elhamifar in Iran "...found that reaction of benzonitrile with phosphorus pentasulfide in ethanol under reflux gave thiobenzamide in 82% yield after a much shorter reaction" with high yields.
Basically C6H5CN reacted to produce C6H5C(=S)NH2.

One note to mention is that the exact formula of phosphorous(V) sulfide can cause confusion.
Generally, P2S5 is not the molecular structure, but rather the compound's ratio of elemental composition, in a similar way that elemental sulfur is often expressed as plain "S". The formula P4S10 can be more descriptive, but this would only correctly apply if the substance was vaporized and then condensed. A similar parallel exists for P2O5 and
P4O10. They are both basically the same compound. The fused solid has a formula of (P2O5)n, whereas the gas and the solid which has been condensed have the actual formula P4O10. However, unlike the oxide, with heat the phosphorous sulfide can easily break into more reactive individual molecules of P2S5.
« Last Edit: January 28, 2011, 04:10:28 PM by AndersHoveland »

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