Phosphinodithioic acids

Flotation Reagents. Only one sulfide mineral flotation collector is manufactured from phosphine, ie, the sodium salt of bis(2-methylpropyl)phosphinodithioic acid [13360-78-6]. It is available commercially from Cytec Industries Inc. as a 50% aqueous solution and is sold as AEROPHINE 3418A promoter. The compound is synthesized by reaction of 2-methyl-1-propene [115-11-7] with phosphine to form an iatermediate dialkylphosphine which is subsequently treated with elemental sulfur [7704-34-9] and sodium hydroxide [1310-73-2] to form the final product (14). The reactions described ia equations 10 and 11... 

PRhC32H38, Rhodium, (l,4-butanediyi)(Ti -pentamethylcyclopentadienyI)(tri-phenylphosphine)-, 22 173 PS2C4H11, Phosphinodithioic acid, diethyl-molybdenum complexes, 23 120, 121 PS3C,2H27, Phosphorotrithious acid tributyl ester, 22 131... 

In the acid-catalyzed thiolysis of nitriles (73) HaS is commonly replaced by appropriate precursors or equivalents. Thus, thioacids, RCOSH, have been used together with HC1 or SnCU. Thioacetamide (77) is a very convenient source of HaS as shown in equation (36), an equilibrium is established which is shifted to the right, if the liberated MeCN is removed by distillation. Alternative sources of HaS are di-thiophosphoric, HSP(=S) (OR)a with R = Et or Pr, " or phosphinodithioic acid derivatives, HSPPha(= S). ° The last mentioned approach allows the elegant synthesis of a-hydroxythioamides (78) in Scheme 11. ... 

Phosphinodithioic acids Phosphorodithioic acid 0,0-diesters Phosphonodithioic acid O-esters... 

Phosphinodithioic acids add to p-benzoquinones, and to (1,2-alkadiene)phosphonic acid derivatives, although... 

Phosphinodithioic acids react with stannic chloride at - 25° C to substitute one of the chlorine atoms/ but the related phosphono-chloridothioate gives (122) with the same reagent, The bis(phosphino-dithioic) acid (123) forms polymeric complexes with transition-metal ions... 

The addition of sulphur to a stoichiometric amount of a secondary phosphine, R2PH, in a solvent and in a non-oxidizing atmosphere, affords the phosphine sulphide, R2P(S)H The further addition of sulphur (a less than stoichiometric amount is recommended ) which, in principle should provide the phosphinodithioic acid, R2P(S)SH, was the method used originally in 1871 by Hofmann, without published details, for the preparation of diethylphosphinodithioic acid, and remains, following modifications, one of the more important means of obtaining such compounds. 

The two principle products from the addition of sulphur to Et2P(S)H are the phosphin-odithoic acid, Et2PSSH, and the trisulphane, 174 (R = Et, Z = Z = S, = 3)(Scheme 48), which can be separated wthout too much difficulty. In many cases, the phosphinodithioic acids may be isolated as the salt of a heavy metal such as nickel, but a better synthesis procedure consists in the addition of the sulphur to the secondary phosphine sulphide in aqueous alkali (ammonia solution provides better yields than sodium hydroxide), when the polysulphane—the principle by-product—is broken down under the influence of the alkali metal sulphide. A phosphinodiselenoic acid may be obtained in essentially the same... 

In common with simple thiols and (9, (9-dialkyl phosphorodithioates, phosphinodithioic acids add to alkenes according to the Markovnikoff rule (propenenitrile is a possible exception to this behaviour) and even in the absence of a catalyst (equation 44). In the presence of sodium methoxide, anti-Markovnikoff behaviour is often observed as the result of Michael addition of the acid anion (equation 45). Addition of the acids to otherwise saturated nitriles leads, following acidolysis of intermediate species, to thiocarboxamides and the phosphinothioyl halide (Scheme. 50). 

The only acid known to exist in thiol form is bis(trifluoromethyl)phosphinothious acid, which can be made in 50% yield by the action of hydrogen sulphide on trifluoromethylphosphinous chloro-phosphine. This acid will add sulphur to form bis(trifluoromethyl)phosphinodithioic acid. 

Phosphinodithioic acids, R2P(S)SH, (9.433a) can be made in up to 90% yields by the action of secondary phosphines on sulphur in dilnte ammonia. The ammonium salts so obtained can then be converted into the corresponding acids with HCl (9.434). Phosphinodithioic adds can in some instances be obtained from phosphinothioic halides and sodium hydrosulphide (9.435). They may also be made by a Friedel-Crafts-type reaction with benzene (9.436). Metal salts may be produced directly by the action of sulphur and alkali sulphide, or sulphur and metal, on diphosphine disulphides (Figure 9.23). 

Many salts of phosphinodithioic acids have been prepared, mainly because of their useful properties (like phosphorodithioic acids above) as lubricating oil and gasoline additives, flotation agents... 

Alkylene-bis-phosphinodithio acids of type R P(S)(SH)(CH2) P(S)(SH) R form highly coloured complexes, some of which are highly polymeric and may have structures such as... 

Esters can be obtained by reacting phosphinodithioic acids with alcohols (9.449), or by reacting alkali metal salts with alkyl halides (9.450) or benzene diazonium chloride (9.451). Phosphinodithioate esters can also be obtained from halophosphoranes and thiols (9.452) or disulphides and secondary phosphines (9.453). 

Many compounds of the types in Table 9.6 can be made by adding sulphur to the appropriate phosphine. Diphosphine disulphides are thus derived from biphosphines, bis(phosphinodthioic) acids from di-secondary biphosphines (9.584), alkylene bis(alkylphosphine sulphides) and aUcylene bis(phosphinodithioic)acids (Table 9.6) from secondary alkylene biphosphines (9.585, 9.586), and alkylene bis(dialkylphosphine sulphides) from alkylene diphosphines. Reaction (9.583) can also be noted. 

The simplest method of preparation of bis(phosphinothiolyl)sulphides (Table 9.6), is to heat phosphinodithioic acids to eliminate hydrogen snlphide (9.599). A more general method is to heat salts of phosphinodithioic acids with phosphino thionic halides (9.600). 

Another method is the oxidation of phosphinodithioic acids by aqueous iodine (9.601) (Figure 9.25). 

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