Phosphite ions, reactions

In addition to the dialkyl phosphite ions, discussed in the previous section, a number of other phosphanions readily undergo photostimulated F-arylation in liquid ammonia. The yields for these reactions, which have to date only been studied for F-phenylations are collected in Table 5.23 Iodobenzene is more reactive than bromobenzene, which fails to react with the PluP—0 ion.23... 

Table 4 Yields of Dialkyl Arylphosphonates Formed in the Photostimulated Reaction of Dialkyl Phosphite Ions with Aryl Halides ArX + (ROhPO" - (RO>2P( —Q)Ar ...

Potassium dialkyl phosphite ions react rapidly with aryl iodides in liquid ammonia under irradiation to form diethyl esters of arylphosphonic acid in almost quantitative yields238. The photostimulated reaction of (EtO)2PO ions with 5-chloro-7-iodo-8-isopropoxyquinoline gave 70% of the substitution product with retention of the 5-chloro substituent239. The same nucleophile was formed in THF, and in a mixture of solvents (1 4 THF MeCN) reacts under irradiation with ArX (o-, ra-,/ -iodoanilines, 2-iodo, 3-iodo, 2-bromo and 3-bromopyridines and 3-bromoquinoline) rendering the substitution product in high yields (70-98%) (equation 130)240. 

The effectiveness of this anticorrosive is attributed to the ability of phosphite ions to inhibit anodic corrosion reactions by formation of iron phosphites and phosphates. 

The acid and its salts, the phosphites, arc powerful reducing agents. Its reaction with silver ion is used as a test for phosphite ion a black precipitate is formed, which consists of silver phosphate, AgaPO, colored black by metallic silver formed by reduction of silver ion. Phosphite ion also reduces iodate ion to free iodine, which can be detected by the starch test (blue color) or by its coloration of a smaU volume of carbon tetrachloride shaken with the aqueous phase. ... 

The dialkyl phosphite ion, however, can itself dealkylate the phosphonate product 300 and finally one may have to reckon with a competitive alkylation of the dialkyl phosphite ion by still unchanged phosphorous diester 301 and the use of allyl halides in the Michaelis-Becker reaction may lead also to diphosphonates owing to the ability of dialkyl phosphite ions to add to unsaturated systems (see Section 9.1).302... 

Phosphite ion coordinated to dinuclear 06ISDIEN dicobalt-p-hydroxo-p-peroxo complex is oxidized to phosphate via apparent 0-atom insertion into the P-H bond, which resembles a hydioxylation reaction The proposed mechanism (Figure 51) of phosphite to phosphate oxidation within the p.-phosphito- x-pCFOXo complex involves the intermediate in Figure 52. 

The synthesis of nucleoside-derived pyridylphosphonates under metal-free conditions was reported (Scheme 4.216) [355]. The chemistry was operationally straightforward and entailed treatment of a nucleoside-derived secondary phosphite with pyridine/trityl chloride and DBU to generate the arylphosphonates in excellent yields. It was noteworthy that the reaction was regioselective for substitution at the 4-position of the pyridine moiety. Based upon an investigation of potential intermediates, the mechanism was proposed to proceed through the initial generation of an A-tritylpyridinium ion. Reaction of this species with the secondary phosphite and DBU afforded a dihydropyridine intermediate that could be observed by NMR spectroscopy but could not be isolated as it underwent conversion... 

Heat treatment of related glasses melted under reducing conditions can yield a unique microfoamed material, or "gas-ceramic" (29). These materials consist of a matrix of BPO glass-ceramic filled with uniformly dispersed 1—10 p.m hydrogen-filled bubbles. The hydrogen evolves on ceranarning, most likely due to a redox reaction involving phosphite and hydroxyl ions. These materials can have densities as low as 0.5 g/cm and dielectric constants as low as 2. 

Zinc chloride is a Lewis acid catalyst that promotes cellulose esterification. However, because of the large quantities required, this type of catalyst would be uneconomical for commercial use. Other compounds such as titanium alkoxides, eg, tetrabutoxytitanium (80), sulfate salts containing cadmium, aluminum, and ammonium ions (81), sulfamic acid, and ammonium sulfate (82) have been reported as catalysts for cellulose acetate production. In general, they require reaction temperatures above 50°C for complete esterification. Relatively small amounts (<0.5%) of sulfuric acid combined with phosphoric acid (83), sulfonic acids, eg, methanesulfonic, or alkyl phosphites (84) have been reported as good acetylation catalysts, especially at reaction temperatures above 90°C. 

Iron(Il) hydrogen phosphite, FeHPO, is oxidized by hypochlorite ions in basic solution. The products are chloride ion, phosphate ion, and iron(lll) hydroxide. Write the balanced equation for each half-reaction and the overall equation for the reaction. 

The mechanism of the reaction of tertiary phosphites with halogeno-acetylenes has been investigated by two groups of workers. - Initial attack of phosphite could be on carbon to give the anion (78), which can eliminate halide, or on halogen to give the ion pair (79) which leads to the same intermediate (80). In both cases an Arbusov reaction would give the isolated product (81). 

The reaction with phosphite esters is known as the Michaelis-Arbuzov reaction and proceeds through an unstable trialkoxyphopsphonium intermediate. The second stage is another example of the great tendency of alkoxyphosphonium ions to react with nucleophiles to break the O—C bond, resulting in formation of a phosphoryl P—O bond. 

Mechanism 3 involves NiOH in at least three reactions, and Ni(OH)2 as the active Ni reactant in solution. Since increasing the concentration of the complex-ant(s) in solution will reduce the concentration of both unhydrolyzed and hydrolyzed metal ions, arguments of complexation cannot be readily employed to either support or discount this mechanism. However, it has been this author s experience in formulating electroless Co-P solutions with various complexants for Co2+ that improper complexation which results in even a faint precipitate of hydrolyzed cobalt ions yields an inactive electroless Co-P solution. Furthermore, anodic oxidation of hypo-phosphite at Ni anodes does not proceed at a significant rate under conditions where the surface is most probably covered with a passive film of nickel oxide [48], e.g. NiO.H20, which would be expected to oxidize the reducing agent via a cyclic redox mechanism. 

In addition to the decay of hydroperoxides, metal complexes accelerate the reaction of phosphite with peroxyl radicals [90,91]. Phosphite forms a complex with the metal ion, and the formed complex terminates the chains more rapidly than phosphite does alone. For example, triphenyl phosphite terminates the chains in oxidized styrene with fkq = 2 x 103L mol-1 s-1 at T 393 K and the complex of this phosphite with CuCI does it with fkq = 2 x 105L mol-1 s 1, i.e., two orders of magnitude more rapidly. The values of / and kq for three phosphites and six complexes (phosphite with CuCI) are given in Table 17.10. 

Yoneda, S., Kawase, T., and Yoshida, Z.-i., Synthesis of [l-(alkylthio)]- and (1-mercapto)cycloalkanephosphonic esters by the reactions of cycloalkaneth-iones with trialkyl phosphites, /. Org. Chem., 43, 1980, 1978. 

The use of transition metals for the facilitation of substitution reactions on vinylic carbon has proven to be quite successful. For example, vinylic chlorides in the presence of nickel(II) chloride react with trialkyl phosphites to substitute phosphorus for the halide (Figure 6.17j.71-72 While reminiscent of a direct Michaelis-Arbuzov reaction, including final dealkylation by a chloride ion, the reaction actually involves an addition-elimination process. It appears that chloride provides a more facile reaction than bromide, a characteristic noted in several reaction systems. 

Some examples of the dioxolenium ion alkenylation reaction are shown in Scheme 8.29 [58], The use of AgC104 on Celite (easier to handle than pure AgC104) and triphenyl phosphite was stated to improve the reproducibility in these reactions. At present, the method is not applicable to alkylzirconocene chlorides. 

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