Phosphorus acid generation

As with other reactions, silyl esters of phosphorus acids constitute an important and useful category of reagents for conjugate addition reactions. With aldehydes, ketones, and esters, the silyl ester linkage is transferred to the carbonyl oxygen, facilitating the completion of the reaction, generating the free carbonyl or ester upon workup with a protic solvent (Equation 3.25). 

Controlled alkylation of phosphorus oxychloride may also be accomplished using a modification of this approach. Reaction of alkyl-aluminum dichloride with phosphorus oxychloride generates the aluminum chloride complex of the alkylphosphonodichlori-date,54 which may be isolated as the simple compound or directly used in reaction to generate other derivatives of the alkylphospho-nic acid. 

Sulphuric and sulphurous acids are dibasic. Sulphonic and sulphinic acids are monobasic. With them we are at the end of the series of acids generated by replacing OH by H. In the phosphorus series the basicity is always one unit higher, so that having passed from phosphoric and phosphorous adds, which are tribasic, to phosphonic and phosphinic acids, which are dibasic, we can proceed a further step to two monobasic acids, for which the recommended names are very naturally phosphonous and phosphinous acids ... 

Complete reduction of sulfonyl chlorides to thiols can be achieved by lithium aluminum hydride [680,693], with zinc [696] and with hydriodic acid generated in situ from iodine and red phosphorus [230]. m-Nitrobenzenesulfonyl chloride, however, was reduced not to the thiol but to bis(m-nitrophenyl)disulfide by hydriodic acid in 86-91% yield [697]. 

Methylcarbazole reacted with 2,6-dimethyl-4-pyrone in the presence of phosphorus oxychloride generating the pyrylium salt 170. Xanthydrol and thiaxanthydrol condensed with carbazole and 9-methylcarbazole under acid catalysis and sulfuric acid oxidation to give the colored salts 171 (X = O or S) the process has been used for the colorimetric determination of carbazole. ... 

Tetracoordinate Si+ complexes may undergo transformations in the mobile ligand, since nucleophilic attack of the counterion may be directed toward electrophilic centers located in the ligand group. Some reactions involving these transformations are of importance in synthesis (86,272-274). For example, the silylation of phosphorus alkyl esters has been broadly explored by bioorganic chemists as a convenient method of generation of phosphorus acids [Eq. (57)] (273). The mechanism of the silylation reaction [Eq. (57)] has been well documented for the cases where X is... 

Quasiphosphonium ions involving oxygen directly bound to the positive phosphorus site are generated as intermediates in numerous other reactions. For example, the Michaelis-Arbuzov reaction (see Section 3.5) produces a quasiphosphonium ion as an intermediate that undergoes attack by the associated amon at the carbon end of the C T P linkage. The reaction follows a different course when aryl ester linkages are present on the starting trivalent phosphorus acid derivative. In such instances, a quasiphosphomum ion is... 

Tims 1 lb. of phosphorus combines with 1.33 lb. of oxygen and 0.9 lb. of water to form 3.23 lb. of pliosphoric acid, which makes phosphorus the best smoke producer, pound for pound, of any know n material. The red phosphorus does not equal white phosphorus for generating smoke and for that reason is seldom used alone, but it ha. lieen mixed with white pliosphonis in the ratio of 1 2 in artillery and trench-mortar smoke shell. 

We have used organo-phosphorus acids [25] as promoters of the reaction of aromatic amines with dimethylcarbonate (DMC) or diphenylcarbonate (DPC) in the presence of carbon dioxide to generate N-alkyl- or aryl-carbamates. We have applied this methodology to the carbamation of aniline, naphtylamine, toluen-diamine, 4,4 -diaminophenyl-methane, among others. 

Improved hydrocyanation, as with catalysts discussed elsewhere in this section, follows from the use of Lewis acid promoters and excess phosphorus ligand. Low-valent cobalt complexes may be prepared by reduction of cobalt(II) chloride with zinc metal in the presence of phosphorus ligand generating in situ the requisite Lewis acid promoter, ZnClj. 

Phosphorus acid is used to generate, by direct alkoxylation with PO, a bis (hydroxypropyl) phosphite. The resulting bis (hydroxypropyl) phosphite is reacted with oxazolidine, under similar conditions to reaction 18.12 and a tetrafunctional phosphonate polyol is obtained (reaction 18.13) [16] ... 

Phosphinous acids represent a promising new class of phosphorus ligands for Suzuki cross-couphngs of unactivated aryl chlorides. The hydrolysis of diorgano-phosphorus halides generates secondary phosphine oxides in an equilibrium with their less-stable phosphinous acid tautomers (Equation 2.29). 

Reaction sequence employed to convert aromatic anilides to aldehydes. Treatment of the anilide with phosphorus pentachloride generates the imidoyl chloride, which is reduced to the imine with a mixture of stannous chloride and hydrochloric acid. Subsequent hydrolysis yields the aldehyde ... 

PolycarbonatG. Polycarbonate, PC, is susceptible to photo-oxidation, and antioxidants are necessary to maintain the low color and high transparency critical to its end-use applications (see Polycarbonates). Phosphites (0.1%) are used to minimized color development dnring processing. It has been shown that the inherent stability of PC is related to the level of phenolic end groups (41). These levels can increase as a result of hmnidity-induced hydrolysis catalyzed by acid. The phosphite chosen must be very stable to avoid the generation of catalytic amoimts of phosphorus acids. 

Aromatic thioamides can be prepared as described in the literature by different ways, either by S -> O exchange between the corresponding benzamides and phosphorus pentasulfide in pyridine solution in the presence of triethylamine (65, 646) as strong base, or by action of H2S on the appropriate nitrile with pyridine and triethylamine solvents using the method of Fairfull et al. (34, 374, 503). In this reaction, thioacetamide in acidic medium can also be used as a H2S generator with dimethylform-amide as the solvent (485). 

Phosphorus [7723-14-0] is a nonmetaUic element having widespread occurrence in nature as phosphate compounds (see Phosphoric acid and phosphates). Fluorapatite [1306-03-4], Ca F(P0 2> is the primary mineral in phosphate rock ores from which useful phosphoms compounds (qv) ate produced. The recovery from the ore into commercial chemicals is accompHshed by two routes the electric furnace process, which yields elemental phosphoms and the wet acid process, which generates phosphoric acid. The former is discussed herein (see Furnaces, electric). Less than 10% of the phosphate rock mined in the world is processed in electric furnaces. Over 90% is processed by the wet process, used primarily to make fertilisers (qv). 

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