Patent GB-875619-A (GB)
Title: Process for the desulphurization of tetraorganodiphosphine disulphides
IPC: C08G79/14
Filed: 1959-04-16
Abstract: Tetraorganodiphosphine disulphides are desulphurized by contacting them with an inorganic reductant selected from metals which do not readily form ionic hydrides of the 4th, 5th and 6th Periods of Group Ib, IIb, IVa, Va and VIII of the Periodic Table and metal hydrides of Group Ia and IIa of the Periodic Table, said metals and hydrides being in finely divided form, at an elevated temperature and recovering a desulphurized phosphine from the reaction mixture.  The desulphurization product will be a tetraorganodiphosphine, or a diorganophosphine or metal salt thereof, depending on e.g. the amount and nature of the reductant used, the reaction condition and the method of product recovery. Specified metals of the first mentioned class are copper, silver, zinc, cadmium, tin, lead, arsenic, antimony, bismuth, iron, cobalt, nickel, ruthenium, palladium and platinum and specified metals of the second class are lithium, sodium, potassium, beryllium, magnesium, calcium, strontium and barium.  The latter class of metals are used in the form of their hydrides which can either be preformed or formed in situ by contacting the metal with the tetraorganodiphosphine disulphide in an atmosphere of hydrogen.  Raney copper and Raney nickel which contain absorbed hydrogen are especially effective.  The use of an atmosphere of hydrogen with metals of the first mentioned class is not necessary but is beneficial if it is desired to obtain the diorganophosphine as the principal final product; when hydrogen is not used with this class of metals the principal product is generally the tetraorganophosphine.  The number of equivalents of metal or metal hydride used should be at least equal to, and preferably in excess of, the stoichiometric requirement based upon the number of moles of tetraorganodiphosphine disulphide present.  Suitable reaction temperatures are from 125 to 350 DEG C.  A controlled rapid heating tends to drive off the tetraorganodiphosphine as it is formed so that it is the principal product recovered whereas with more gradual heating the intermediate tetraorganodiphosphine stays in the reaction mixture and is converted to the diorganophosphine (or metal salt thereof). A solvent may be used, e.g. an aromatic or hydroaromatic hydrocarbon solvent, ether, dioxane, tetrahydrofuran, or a paraffin. The reaction may be carried out in the presence of an inert gas, e.g. nitrogen.  Suitable starting materials are those having the formula <FORM:0875619/IV (b)/1> in which R1, R2, R3 and R4 are alkyl aryl, alkaryl, cycloalkyl or aralkyl radicals.  When tetraalkyldiphosphines are obtained as products they may be converted in the presence of an alkali metal to a metal salt of the dialkyl phosphine which can be decomposed with a proton donor, e.g. a C1-C6 alkanol, a cycloalkanol, an organic acid, or water to form the dialkylphosphine by the method disclosed in Specification 859,373.  The tetraorganodiphosphines are useful as warning chemicals when added to industrial gases in small amounts and tetramethyldiphosphine on reaction with boranes, e.g. pentaborane, yields heat stable polymers.  Examples are given for the conversion of tetramethyldiphosphine disulphide to:: tetramethyl-diphosphine and dimethylphosphine and mixtures thereof and for the conversion of tetraethyl-, tetra-n-propyl-, tetra-n-butyl-, tetra-tolyl- and tetra-phenyl-diphosphine disulphides to the corresponding tetraorganophosphine and of tetra-phenyl- and tetra-tolyl-diphosphine disulphide to the corresponding di-organophosphines.  Examples are also given in which (a) tetramethyl diphosphine is heated with potassium in the presence of decahydronaphthalene and in a nitrogen atmosphere to form the potassium salt of dimethylphosphine which is then treated dropwise with methanol and the mixture heated at 100 DEG C. to form dimethylphosphine, and (b) tetramethyldiphosphine is heated with Raney copper in the presence of decahydronaphthalene and in a stream of hydrogen to yield dimethylphosphine.