Sciencemadness Discussion Board

Reactions between phenol and phosphorous pentasulfide

AndersHoveland - 15-3-2012 at 15:19

The reaction between phenol and phosphorous pentasulfide is apparently fairly complicated. There are several conflicting descriptions in the literature.

One possibility is that
(PhO)3P=S and H2S would form. (where Ph is a phenyl group C6H5—)

Another possibility is:
(8)PhOH + P2S5 --> (2)H3PO4 + (3)Ph2S + (2)PhSH
I think that this reaction might predominate if regular phenol, rather than methoxy-phenol, is used.
Quote:

“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 this acid ester:
0041.gif - 2kB
Quote:

The alcoholysis and phenolysis of phosphorus pentasulfide is accelerated by reacting the phosphorus pentasulfide with an alcohol or phenol in the presence of a catalytic amount of a catalyst consisting essentially of water, phosphoric acid, a phosphate salt, sulfuric acid or mixtures thereof. The dialkyl- or diaryl- dithiophosphoric acids produced...
(US Patent 4681964)

The "diaryldithiophosphoric acid" would presumably have the same stucture:
(C6H5)2P(=S)SH
Quote: Originally posted by ScienceSquirrel  

An alcohol plus phosphorous pentasulphide will make a thiol...

(an example of a thiol is CH3CH2SH )

However, another of the members on this forum had a different opinion:
Quote: Originally posted by Methansaeuretier  

The mainproduct would be trimethylphosphate and not P4O10 I think.


"Phosphorus pentasulfide and ethyl alcohol are reacted slowly to form diethylthiophosphoric acid and hydrogen sulfide."
(CH3CH2O)2P(=S)SH
http://www.cpcb.nic.in/upload/NewItems/NewItem_101_NewItem_1... (p16)
Quote:

"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. The two are the basically the same thing.
Quote:

"...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.
Quote:

"Preparation of phosphorothioate esters from benzyl alcohol and phosphorus pentasulfide"
(United States Patent 3102130)

These esters have the formula (C6H5CH2O)3P=S.
Of course the formula for benzyl alcohol is C6H5-CH2-OH, it may react differently than phenol.

Heating methoxy-benzene (also named "anisole"), CH3-O-C6H5, with phosphorous pentasulfide forms
CH3-O-C6H4-P(=S)S2P(=S)-C6H4-O-CH3
This reaction was described by Sven-Olov Lawesson.
0042.gif - 2kB

In reactions with certain types of acidic alcohols, phosphorous pentasulfide can apparently act as a dehydrating agent, leaving an unsaturated compound.
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.
"Preparation of fluoroolefins by reaction of polyfluorochlorocarbinols with phosphorus pentasulfide" R. A. Bekker, G. V. Asratyan, É. P. Lur'e and B. L. Dyatkin


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.

What is the reaction between phenol and phosphorous pentoxide? If different products can form, under what conditions are each of these different products favored?

[Edited on 15-3-2012 by AndersHoveland]