1,3,2,4-Dithiadiphosphetane 2,4-disulfides
1,3,2,4-Dithiadiphosphetane 2,4-disulfides are a class of four-membered ring compounds which contain a P2S2 ring, many of these compounds are able to act as sources of the dithiophosphine ylides. The most well known example of this class of compound is Lawesson's reagent.
Other examples of this class of compound have been made; many inorganic chemists are now using Fc2P2S4 (Fc = ferrocene) as a starting material in reactions investigating the general chemistry of the 1,3,2,4-dithiadiphosphetane 2,4-disulfides, one reaction for this is that the Fc2P2S4 compound and all its derivatives are red which make column chromatography of the products more easy. Also the ferrocenyl groups provide an electrochemical handle which provide another means of investigating the properties of the products.
While several different routes to the 1,3,2,4-dithiadiphosphetane 2,4-disulfides exist the most commonly used is the electrophilic aromatic substitution reaction of an arene with P4S10. An alternative reaction is the reaction of a thiol with P4S10 to form a substance like the Davy reagent. The Davy reagent is identical to Lawesson's reagent except in place of the para-methoxyphenyl groups it has aryl sulfide groups. While the Davy reagent is more soluble than the Lawesson's reagent it is likely that the very vile nature of the thiol starting material is likely to make the synthesis of this compound not worth the trouble. In both the patent and academic chemical literature are examples of 1,3,2,4-dithiadiphosphetane 2,4-disulfides with higher solubilities. These highly soluble versions of Lawesson's reagent are created by the reaction of P4S10 with aryl ethers which are different from anisole. For instance butoxybenzene and 2-tert-butylanisole have both been reacted to form more soluble thionation reagents of the 1,3,2,4-dithiadiphosphetane 2,4-disulfide class.
An important subclass of these compounds are the naphthalen-1,8-diyl 1,3,2,4-dithiadiphosphetane 2,4-disulfides; these are intellectually interesting because the two dithiophosphine ylides are fixed together in space by the rigid naphthalene unit. The reactivity of these compounds is very different from that of 1,3,2,4-dithiadiphosphetane 2,4-disulfides.
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