Phosphites, reactions with halogens

In a study of the reactions oi acyclic o-methoxyphenyl-phosphinites (45a), phosphonites (45b) and phosphites (45c) with halogens,the intermediate halogenophosphonium salts (46) are stabilised either by ligand exchange with starting material (not shown) or by elimination of methyl halides to form cyclic phosphoranes ( 47 ) 3 7. ... 

With halogens, triaryl phosphites form phosphoranes which may dissociate into various aryloxy-phosphonium compounds. On the other hand, trialkyl phosphites undergo an Arbusov-type reaction with halogens (except F) at low temperature (6.349). Saturated carboxylic acids produce dialkyl phosphites (dialkyl esters of phosphonic acids), while unsaturated acids give dialkyl phosphonates (6.350, 6.351) and a-diketones give pentaoxyphosphoranes (6.344) above. Diphosphonates can be obtained from trialkyl phosphites (6.747). 

Suitable methods for linking a phosphoms—nitrogen bond to the ayiridine ring are the aminolysis of halogenated phosphoms compounds (2,280—282), the transamination of phosphoramines with excess a iridine (283), the reaction with phosphites (284) and phosphoramidites (285) which have a free OH group, or the reaction of phosphines with a iridines and carbon tetrachloride (286). 

Trialkyl phosphites undergo reaction with molecular halogen via a mechanism reminiscent of the Michaelis-Arbuzov reaction to form the dialkyl phosphorochloridate in good yield (Equation 4.4).7 With cyclic esters, the halogen performing the displacement reaction at carbon remains attached within the molecule. 

Y = OEt) have been detected in the reactions of halogen with a cyclic phosphite 40 the reaction with chlorine gave a resonance at dp +35 and bromine gave a resonance at dp +195 p.p.m. The latter is at higher field than the tribromo-compound (21 X = Y = Br dp +189 p.p.m.) and the chlorodibromo-compound (21 X = Br,... 

Replacement of the hydroxyl group in a phenol by halogen cannot be accomplished by reaction with the hydrogen halides as in the case of alcohols, and reaction with phosphorus halides gives only low yields of halogenobenzenes (except in the case of nitrophenols), the main product being a phosphite or phosphate ester. 

The trimethylsilylated ylides (1), easily generated from trimethyl chlorosilane and ylides, react with aldehydes 2 to form vi-nylsilanes 3 (2,3). The vinylphosphonium silanolates 4 are also formed. Compounds 3 are versatile reagents for further reactions (4). The ylide J (with R1 =H) reacts with aldehydes 2 to give the dienes j). The oxidation of with the adduct 6, from triphenyl-phosphite and ozone, gives access to a generaT synthesis of acyl-silanes (trimethylsilylketones) (2). The silylated ylides react to form phosphonium salts 7 with halogen compounds. The salts 7.can be desilylated by fluorine ions. The disubstituted ylides JO Tormed can be converted in statu nascendi with aldehydes V[ into the tris-substituted olefin J2 (2,3). In the case of R3-I, vinyl... 

By controlling the ratio of ROH to PC13 the dialkyl phosphites can also be obtained. Compounds of this type are hydrolyzed with the rate of hydrolysis depending on the length of the alkyl chains. Generally, the rate is inversely related to the molecular weight of the phosphite. The phosphites can be halogenated by reactions with X2 or PX3 ... 

Flame retardants—Whereas halogen-containing Mannich bases arc mainly used as modifiers of macromolccular materials, as mentioned before, phosphorus derivatives arc employed as additives. These products arc obtained from phosphorous acid or phosphites 584 " and from other analogous phosphorus-containing compounds. N-Heterocyclcs, after reaction with melamine and formaldehyde (585), are also used as (lame retardants. -... 

Opaleva, E.N.. Dogadina, A.V., and lonin, B.L, Reaction of dialkyl hydrogen phosphites with halogen-containing alkenes and alkynes in the presence of potassium fluoride, Zh. Obshch. Khim., 65, 1467, 1995 Russ.. 1. Gen. Chem. (Engl. Transl.), 65, 1344, 1995. 

When a fluorine atom in ( .I is replaced by another halogen, a fluorine atom rather than a chlorine" or iodine atom is eliminated as alkyl fluoride from the reaction with trialkyl phosphites. Trimethylsilyl phosphites react with perfluoroalkenes to give fcrs(ti iiuclhylsilyl) perfluoroalke-nylphosphonates in very good yields (81-95%), - probably because of the greater nucleophilicity of the trimethylsilyl phosphites and the stability of fluorotrimethylsilane. ... 

Perkow, W., Krockow. E.W., and Knoevenagel. K.. Reairangements with alkyl phosphites. Part 2. The reaction with a-halogenated aldehydes, Chem. Ber. 88. 662, 1955. 

The aromatic version of the Michaelis-Arbuzov reaction between trialkyl phosphites and aryl bromides in the presence of Nit II ) chloride has extensively been studied with a variety of substituted halobenzenes. It has been shown that electron-acceptor substituents, regardless of their position on the aromatic nucleus, facilitate reaction with P(III) compounds, whereas electron-donor substituents render tlie reaction more difficult. Substituents lying ortho to the halogen lower the reactivity of aryl bromides, probably because of steric hindrance. Thus, the NiCl2.catalyzed direct phosphonylation of pzzra-bromobenzaldehyde with triisopropyl phosphite at 16O C affords diisopropyl para-formylphenylphosphonate in 54% yield (Scheme 5.43). ... 

With the presence of more than one halogen atom in the a-position of the halo ketone, the formation of 2-oxoalkylphosphonates becomes more difficult, and the reactions proceed exclusively according to the Perkow reaction. Thus, dichloromethyl, dibromomethyl, and tribromomethyl methyl ketones, in reaction with trialkyl phosphites, lead to the corresponding vinyl phosphates... 

Pudovik, A.N., and Biktimirova, L.G., Anomalous reaction of a-halo ketones with esters of phosphorous acid. Part 5. Reactions of halogen derivatives of methyl ketone and acetophenone with triethyl phosphite, Zh. Obshch. Khim., 27, 1708, 1957 Chem. Abstr., 52, 3714b, 1958. 

Dihalogenoethyl cyanides undergo dehalogenation to acrylonitrile on reaction with either secondary or tertiary phosphites, presumably through initial attack of phosphorus on halogen. Surprisingly, bis(diphenylphosphinyl)-amine (65) is the product of the reaction of sodium diphenylphosphide and... 

The reaction of triethyl phosphite with the acetal of 1-bromopropion-aldehyde to give the vinylphosphonate (97) has been reported. The mechanism is thought to involve initial conversion into the vinyl ether (98) followed by attack of phosphite on halogen. A similar reaction with 1-bromopropionaldehyde gives the phosphate (99). 

Essentially, the Michaelis-Arbuzov reaction proceeds well with primary alkyl halides and at least moderately well with secondary halides, the reactivity of the halogen being in the order I > Br > Cl, alkyl fluorides normally being unreactive (the reactive polyfluo-roalkanes and alkenes do undergo reactions with trialkyl phosphites and afford halogeno-... 

As in all Michaelis-Arbuzov and Michaelis-Becker reactions, the usual order of decreasing reactivity at the carbon-halogen bond, I > Br > Cl > F, applies with carbon-fluorine bonds tending to be unreactive, other than in exceptional circumstances. Even for diiodomethane, the most reactive dihalomethane, reactions with trialkyl phosphites can be made to yield esters of (iodomethyl)phosphonic acid (11 R = O-alkyl, R = alkyl, n=, X = I or in the presence of more phosphite ester, the methylenebisphosphonic ester 12... 

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