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United States Patent 0 Ice Patented July 26, 1966

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United States Patent 0 Ice Patented July 26, 1966 1 3,262,971 United States Patent 0 ice Patented July 26, 1966 1 2 Still another object is to provide novel doubly un 3,262,971 saturated compounds of phosphorus and methods of PHOSPHORUS COMPOUNDS Cli?ord N. Matthews, University City, St. Louis, Mo., making the same. - assignor to Monsanto Research Corporation, St. Louis, A further object is to provide a novel method of making Mo., a corporation of Delaware precursors of the said salts. ' No Drawing. Filed Aug. 7, 1964, Ser. No. 388,292 These and other objects will become evident from a 23 Claims. (Cl. 260-515) consideration of the following speci?cation and claims. The novel mesomeric salts provided by this invention This application is a continuation-in-part of my co are salts wherein the cation is a monovalent mesomeric pending .application S.N. 154,874, ?led November 24, system comprising a methylidyne radical linking two 1961; and a continuation-impart of my copending applica phosphorus atoms, including inner salts with the stated tion S.N. 230,266, ?led October 12, 1962, both now cationic structure and thus designated mesomeric inner abandoned. salts. This invention relates to compounds of Third Period Novel and unexpectedly e?ective methods are provided elements and, more particularly, provides novel unsatu by this invention for producing the presently provided rated compounds, including mesomeric phosphorus salts novel salts, which may be effected by methods comprising and methods of preparing the same. treating a methylene bis phosphonium salt with a base. A mesomeric compound or radical is one which contains The e?Fect of alkali treatment on phosphonium salts a resonance (resonating) system. The carboxyl group was investigated in the early history of phosphorus chem of carboxylates is an example of a mesomeric radical. istry, a century ago. It was found that the phosphonium The carboxylate ion may be written as salts were cleaved by alkali, so as to lose an organic 0 radical and form a phosphine oxide, as illustrated by JLOe the equation: NaOH but since the two oxygen atoms are equivalent and the 25 (CHmP‘BBrG -—-> (ensure charge resonating between them is distributed over both In the 20th century, Wittig showed that organolithium oxygen atoms, rather than showing the negative charge compounds, which have a basic character, could be used on one or the other oxygen atom, it would be more to remove an organic radical from a phosphonium salt accurate to show the charge as distributed between them, and form a phosphorane ylide (or, as it may be called, thus: 30 an “ylene”), as illustrated by the equation: l c Extensions of this work have demonstrated that other . 6 bases can be used to form ylides (“ylenes”) also, includ As this distributed charge formula illustrates, in a mes ing sodamide, alkali metal alkoxides and, where an omeric radical, the central carbon atom is surrounded organic phosphorus substituent is acyl or carbalkoxy by an environment of charged atoms. substituted, even an alkali metal hydroxide like NaOH. Phosphorus resembles oxygen in various respects. This Bis-phosphonium salts have been investigated in the element, like oxygen, can be either singly or doubly latter connection, with the result that the bis-ylides bonded to a carbon atom. As an onium group, while covalently bonded to carbon, it can carry an electrical (ceHs) sPzCH (CH2) XCHZP (ceHs) 3 charge and form ionic salts. The onium radical, how where x is 2 or 4 were successfully produced using basic ever, in contrast to oxygen in the carboxylate ion, car reagents such as phenyl or butyllithium, sodarnide and ries a positive charge. Thus, substitution of such an sodium ethoxide (Angew. Chemie, 71, 261). However, onium-forming element for ‘oxygen in formula of the the ethylene bis-phosphonium salts behave otherwise: in carboxyl radical, in a valence state adapted to form stead of the expected [—CH=P(C6H5)3]2 product, one onium groups, would produce a cationic analog of the of the phosphorus atoms separates from the alkylene or carboxyl radical. This would be a mesomeric salt of the ganic radical to form a phosphine, the reaction appar formula ently proceeding as shown in the following equation: 6 6B 69 9 ¢L1 GB 6 Br¢31>-0HlGHz—-P¢3Br -—~> ¢3P + CHz=CH—P¢3Br Treating ethy-lenebisphosphonium salts with sodium |al— koxides was also found to produce loss of an organic 55 radical to form a phosphine, thus or a diphosphine 60 Such mesomeric salts have not previously been known. While phosphonium cationic salts are well known in the art, mesomeric cationic analogs of carboxyl com Thus, the ethylene bisphonium salts were shown to tend pounds have nevertheless remained unknown. to lose an organic radical, rather than losing the elements It is an object of this invention to provide novel mes 65 of a hydrogen halide as do the bisphosphonium salts omeric cationic analogs of carboxyl compounds. where the alkylene group is trimethylene or longer chain A particular object of this invention is to provide novel length. mesomeric cationic salts of phosphorus. Surprisingly, the methylene bisphosphonium salts do Another ‘object is to provide novel methods of making not undergo the cleavage of a P-C bond which the ethyl such novel mesomeric salts. 70 ene salts exhibit. On the other hand, they do notresem Still another object is to provide novel cationic mes ble the higher alkylene salts in eliminating the anion and omeric phosphorus inner salts. an alpha-carbon substituent at each phosphonium group. 3,262,971 3 4 Instead, the methylene bis(onium) salts eliminate an that the product isolated is an ‘ionizable salt, in which the anion and an alpha-carbon atom substituent from one anion can be dis-placed by metathesis: - - - phosphonium group only, to form a mesomeric salt of the ‘above-stated novel type. V The stated me-someric salts in turn will react with a (These types of salts, in which the negative charge is not strong base to eliminate the anion and the methylidyne located in the same covalently bonded molecule as that carbon atom substituent, to form a carbodiphosphorane, in which the positive charge is located, may be called an allene analog wherein ‘a single carbon atom links two “outer salts,” to distinguish them from inner salts.) phosphorus atoms each having three additional substitu However, when the carbodiphosphorane is reacted with ents. the Lewis acid, it is now found that the product is the These allene-type compounds can be regarded as ana inner salt, logs of carbon dioxide, in parallel to the analogy of the presently provided mesomeric salts to carboxylate radi cals. Such allene analogs are also provided as new com :pounds by this invention. 15 The invention as set forth in the foregoing description Further, it has been found that a carbodiphosphorane will be more readily understood from a consideration of can be added to unsaturated carbon compounds wherein the following equations, illustrating a particular embodi a doubly bonded carbon atom is disubstituted by electro ment of this invention: negative substituents capable of forming a double bond 2O with carbon, as represented, for example, by the reaction ‘ (11) :vwhere ¢ is phenyl. The invention thus provides methods of producing a The product of Equation I is a salt comprising the 25 variety of inner salts with different anions wherein the .mesomeric cation of this invention. It.m»ay be written mesomeric cation is a trisubstituted phosphonium methyl to show the resonating system, as ene trisubstituted phosphorane group. The presently provided novel salts are useful for a wide variety of chemical and agricultural purposes. For example, they may be employed in analytical chemistry, as for forming identi?able salts with particular anions. The mesomeric “outer salts” (the salts which are not inner salts) undergo metathesis readily, to form salts or it may be written to show the equivalence of the two with anions other than the original anion. Thus, for ex P atoms, as‘ 35 ample, the bromide ion of the above-shown mesomeric phosphorus bromide salt can be replaced by a tetraphen I? ylboronate ion. /C\ Members of the class of novel salts provided by this ¢aP"'-“\P¢a invention, including the inner salts, have photochromic 6B (phototropic) properties adapting them for use as light Bre indicators. For example, the stated tetraphenylboronate salt undergoes a distinct color change on exposure to or it may be‘ written as a single resonance form, as light. Exposure to ultraviolet light produces a distinct color change in the inner salts. Thus, these compounds o i‘ 45 can be used as indicators of light exposure, employed, Br9¢,P~_o=P¢. for example, on photographic ?lm packs, whereby unde ' The presently provided inner salts are also salts hav sired exposure of the ?lm to light can be detected. More ing -a mesomeric cation as provided by this invention. over, the stated photochromic reaction is associated with Inner salts are compounds having a positive charge lo formation of free radicals. Thus these products canbe 'calized in one portion of the molecule and a negative 50 used as a light-activatable source of free radicals. charge localized in another portion of the same covalently The class of mesomeric salts of this invention also has bonded molecule. Familiar examples of such salts are important utility as a chemical intermediate. The “outer” the betaines (zwitterions) such as salts release the elements of an acid to form a compound of the type 55 in which the positively charged cationic ‘group is a sub as, for example, in the embodiment vstituted ‘ammonium radical.‘ The presently provided novel inner salts are compounds wherein the positively charged group comprising the cation of the inner salt is a trisubstituted phosphonium methylene trisubstituted The resulting class of allene analogs also provided as phosphorane group.
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