2,847,458 United States Patent Office Paieated Aug. 2, 1958 2 products of the reaction. Thus it is not surprising that either no structures or incorrect structures have been 2,847,458 assigned to them. Generally these reaction products of the prior art have been reacted with other materials PREPARATION OF ARYLPHOSPHONCACDS such as organic and inorganic bases, metal sulfides, al Tsai H. 'Chao, Somerville, Hans Z. Lecher, Painfield, and cohols, phenols, thiols, aluminum chloride and other Ruth A. Greenwood, Somerville, N. J., assignors to hydrocarbons in order to produce products which were American Cyanamid Company, New York, N. Y., a to be used as additives to mineral oils to prevent cor corporation of Maine rosion or to impart extreme pressure lubricating or de No Drawing. Application March 25, 1955 tergent properties to the oils. Some of these products Serial No. 496,934 have also been proposed as flotation agents. The prior art reaction products of aromatic hydrocar 15 Claims. (Cl. 260-500) bons with phosphorus pentasulfide have never been corn pletely hydrolyzed to form phosphonic acids. Some such This invention relates to a new process of preparing crude reaction products have been blown with steam or arylphosphonic acids. It also relates to arylthionophos nitrogen to remove malodorous thiocompounds which are phine sulfides which are new compounds and are inter formed as by-products. However, the prior art empha mediates in said process. sized that after this treatment the products still contained A number of arylphosphonic acids having the formula substantial amounts of sulfur, that is to say they were ArPO(OH) in which Ar is an aryl radical have been 20 not completely hydrolyzed. known but until recently they have been laboratory curi According to the present invention, phosphorus penta osities because the only way of preparing them was by sulfide is heated with an aromatic compound at temper round-about and expensive processes which precluded atures of 140-250° C., the aromatic compound being free their practical utilization. from polar substituents capable of reacting with phos The first process which permitted production of aryl phorus sulfides. Hydrogen sulfide is evolved and an aryl phosphonic acids with sufficient efficiency to make them thionophosphine sulfide is formed. The latter is then practical on a commercial scale is described and claimed completely hydrolyzed by heating with water to produce in Patent No. 2,717,906, issued September 13, 1955, on good yields of the corresponding arylphosphonic acid the copending application of Lecher, Chao, and White without a substantial loss of phosphorus in the form of house, Serial No. 345,264, filed March 27, 1953, which phosphoric acid or phosphorus oxychloride. is a continuation-in-part of an earlier application, Serial A second advantage of the present invention is that the No. 286,614, filed May 7, 1952, and now abandoned. phosphorus sulfides do not catalyze the condensation of According to this process carbocyclic aromatic compounds aromatic compounds such as naphthalenes, alkylbenzenes -free from polar groups capable of reacting with phos and the like, and therefore this drawback of the earlier phoric anhydride-were phosphonated with hexagonal process is likewise substantially eliminated by the present phosphoric anhydride within a temperature range of from invention. 250-325 C. Reaction products were obtained which The process is applicable in general to aromatic com on hydrolysis with water yielded arylphosphonic acids. pounds that are free from polar groups capable of re The reaction products were also convertible into aryl acting with phosphorus sulfides such as hydrocarbons, phosphonic dichlorides by reaction with phosphorus pen 40 e.g. benzene and its homologues, naphthalene and its tachloride as described and claimed in the copending ap homologues, anthracene, phenanthrene; phenol ethers, plication of Greenwood, Scalera and Lecher, Serial No. e.g. anisole, phenetole. The ethers of monocyclic Inono 357,368, filed May 25, 1953, now U. S. Patent No. hydric phenols react with especial ease and give very high 2,814,645, dated November 26, 1957. yields of the thionophosphine sulfides and the phosphonic While this new process gave satisfactory yields of aryl 45 acids. phosphonic acids based on the real usage of the aromatic The reaction temperature will vary with the compounds; compounds (an excess of the aromatic compound was thus for example, some of the phenol ethers such as used but could be recovered and re-used), the process anisole react very Smoothly and quantitatively at about still possessed certain drawbacks from the cost stand the boiling point. Naphthalene gives best results at point. The most serious factor is that only one or two 50 about 160-180° C. but on the other hand benzene and at most of the phosphorus atoms of the phosphoric an some of its homologues such as o-Xylene require temper hydride P.O. reacted with the aromatic compound. The atures of about 225 C. for best results. In general with remaining phosphorus was either lost as phosphoric acid each compound it is desirable to operate at as low a in the case of water hydrolysis or had to be removed as temperature as possible in the range of optimum temper phosphorus oxychloride in the case of production of 55 atures, that is to say as low temperatures as produce phosphonic dichlorides. In both cases this represented reasonably fast evolution of hydrogen sulfide. Higher a waste of raw materials and added to the cost of the temperatures in the case of each compound while still finai arylphosphonic acids. giving good yields are less desirable as there is some Another drawback was that with certain aromatic effect on the yield and purity of the products obtained. compounds, such as naphthalene or alkyl derivatives of 60 A very important, one might say very critical, require benzene the phosphoric anhydride catalyzed condensa ment is that there be a large excess of aromatic com tion reactions forming by-products which complicated the pound. In general the excess should be at least five moles isolation of the phosphonic acids and, of course, lowered of aromatic compound per mole of P4S10. Larger ratios the yields. such as 10 or even 20 to 1 are preferable but, of course, The present invention avoids the disadvantages of the 65 after the optimum results are obtained, further excess prior process by using phosphorus pentasulfide or its of aromatic compound, while it does not adversely affect chemical equivalents instead of the hexagonal phosphoric the reaction, does reduce the output of the equipment, anhydride. Reactions of phosphorus pentasulfide with and therefore very large excesses over that required for hydrocarbons, including aromatic hydrocarbons, are not optimum results are not economically attractive. new in the art. However, the resulting products have The main reaction proceeds according to the equation been mixtures containing not only thionophosphine Sul 70 fides but also lower sulfides of phosphorus and other by 4ArH-I-PS1->2(ArPS)2+2HS 2,847,458 3. 4. where Ar stands for aryl. However, side reactions take corresponding to the dimer when the occluded solvent place in varying degrees with some aromatic compounds was taken into account. resulting in the production of lower sulfides of phosphorus While these dimers are stable at ambient temperature, which are not reactive. In the case of ethers of mono they undergo further gradual polymerization on heating, cyclic, monohydric phenols this side reaction is insignifi forming brittle, transparent resins having probably the cant, but with benzene and naphthalene it takes place to Structure a considerable extent. When a sparingly soluble lower sulfide of phosphorus is formed it crystallizes together Af Ar with the arylthionophosphine sulfide contaminating the -P-S-I-P-S- latter. This is of little consequence if it is to be used C. S S t only as intermediate in further reactions, e. g. in the hydrolysis to give the phosphonic acid or in the chlorina where 'x' stands for an indefinite whole number. In the tion to give an aryltetrachlorophosphorane or arylphos case of p-anisylthionophosphine sulfide polymers of the phonothioic dichloride. However, it renders the prepara formula tion of pure arylthionophosphine sulfides more difficult. The prior art has described the reaction product of 7 naphthalene with PAS as a compound having the formula CHO- -{ D-Pés-cit, 2 S may also be formed. Both the dimeric and the polymeric thionophosphine sulfides are exceedingly sensitive to moisture which causes slow decomposition with formation of hydrogen sulfide. A most unusual behavior toward solvents is noted. Ordinarily a monomer and dimer is much more soluble 25 than a relatively higher molecular polymer. In the present case however the dimer is almost completely insoluble in organic solvent whereas the polymers show Actually it is a mixture of 2- (not 1-) naphthylthiono fair to good solubility. While it is not intended to limit phosphine sulfide with a lower sulfide of phosphorus. the invention to any particular theory we believe that the This reference was badly misleading since a compound 30 following is a possible explanation of the surprising be having the above formula would give on hydrolysis not havior of the dimers and polymers toward solvents. a mono- but a di-phosphonic acid with the phosphorus group not in 2 but in 1 position. Since a formula with a 4-membered ring In the phosphonation of naphthalene the side reaction can be Suppressed to a large degree by using a very great 35 excess of naphthalene (50 mol for 1 mol PS): then the pure 2-naphthylthionophosphine sulfide is highly improbable it is assumed that the dimer is a (CHPS2) 2 salt-like compound formed by semi-polar P-S bonds: can be isolated. Carrying out the reaction in a ratio 4.0 of 10C10H8: P4S10 and adding 40C10Hs afterwards has Ar-P- not the same effect: the thionophosphine sulfide is con -- taminated with a lower sulfide of phosphorus and does S -Air not crystallize in pure form.