Phosphorus ortho

Pyridazinecarboxamides are prepared from the corresponding esters or acid chlorides with ammonia or amines or by partial hydrolysis of cyanopyridazines. Pyridazinecarboxamides with a variety of substituents are easily dehydrated to nitriles with phosphorus oxychloride and are converted into the corresponding acids by acid or alkaline hydrolysis. They undergo Hofmann degradation to give the corresponding amines, while in the case of two ortho carboxamide groups pyrimidopyridazines are formed. 

Phosphorus is not oxidized or reduced biologically, but ortho-P may be formed from organic and poly-P. Ortho-P may be removed by chemical precipitation or biologically with sludges andwih be covered in a later section. 

The synthetic procedure described is based on that reported earlier for the synthesis on a smaller scale of anthracene, benz[a]anthracene, chrysene, dibenz[a,c]anthracene, and phenanthrene in excellent yields from the corresponding quinones. Although reduction of quinones with HI and phosphorus was described in the older literature, relatively drastic conditions were employed and mixtures of polyhydrogenated derivatives were the principal products. The relatively milder experimental procedure employed herein appears generally applicable to the reduction of both ortho- and para-quinones directly to the fully aromatic polycyclic arenes. The method is apparently inapplicable to quinones having an olefinic bond, such as o-naphthoquinone, since an analogous reaction of the latter provides a product of undetermined structure (unpublished result). As shown previously, phenols and hydro-quinones, implicated as intermediates in the reduction of quinones by HI, can also be smoothly deoxygenated to fully aromatic polycyclic arenes under conditions similar to those described herein. 

However an unexpected new cyclic ruthenium phosphorus ylide half-sandwich complex 42 has been obtained by reaction of 41 with dichloromethane as solvent [79]. The cyclisation involves a C-Cl activation and corresponds to the incorporation of the methylene moiety in the P-C bond and to the ortho-metal-lation of one phenyl of the phosphine. An other novel unusual phosphonium ylide ruthenium complex 43 has also recently been described [80]. 

The symmetrical bis(ylidyl)phosphenium chlorides 103, obtained from the reaction of trimethylsilyl ylides 102 with PCI3 are the first phosphenium salts which do not need counterions of low basicity such as AICI4 to be isolated (Scheme 30) [119]. The explanation of their stability lies in the delocalisation of the phosphenium charge in the two phosphonium parts. The reactivity study of these species is reported and for example the phosphenium 103 (R=Ph) adds ortho quinones to the central phosphorus to give the corresponding dioxaphospholenium salts 104 via a [4-1-1] cycloaddition. 

Table 1 The effect of ortho substituents on the flattening of the phosphorus atom (OOP angle) in substituted arylphospholes (10)...

A similar reaction sequence of triisopropylphenylphosphole or mesitylphosphole (17b and 17a, respectively) with phosphorus tribromide afforded the corresponding 2-substituted products. The reaction of dibromophosphine 37 with nucleophiles followed by oxidation or hydrolysis gave phosphonic or //-phosphinic derivatives (39 or 41, respectively) (Scheme 9) [48, 49], The regioselectivity is obviously the consequence of the presence or the lack of the steric hindrance with ortho tert-butyl groups, only position 3 is available, while with the smaller triisopropyl substituent, position 2 may be the appropriate reaction site. 

The reaction of arylphospholes with phosphorus tribromide was extended to di-te/f-butyl-methylphenylphosphole (17c) leading after further steps, to a mixture of 3- and 2-substituted products (43 and 45, respectively) (Scheme 10) [40], The di-tert-butyl-tolyl substituent clearly occupies an intermediate position between the triisopropylphenyl and tri-terf-butylphenyl ones regarding the steric hindrance caused by the ortho alkyl substituents. 

Furo[2, 3 4,5]pyrrolo[l,2-d][l,2,4]triazolo[3,4-/][l,2,4]triazines 667 were prepared by reaction of 664 with phosphorus pentasulfide to give 665 followed by conversion to the hydrazino derivative 666 and subsequent cyclization with ortho-esters (84CCC65, 84M13). Similarly, the indolo analogue 670 was prepared from 668 by sulfurization and hydrazinolysis to give 669, which cyclized with ortho-esters (84CCC1529). 

Cembella et al. [40] have described a method for the determination of total phosphorus in seawater. The procedure used magnesium nitrate to oxidise organic compounds before standard molybdate colorimetric determination of ortho-phosphate. The method was applied to several pure organic phosphorus compounds and gave 93-100% recovery of phosphorus. 

The rhodium-catalyzed arylation of phenols with aryl halides occurs in the presence of phosphinites [PR2(OAr)] as a co-catalyst (Equation (59)).66 The phosphorus atom coordinates to the rhodium atom to facilitate the electrophilic substitution with the rhodium(m) species at the ortho-pos i on. 

At the same time, Knowles team concentrated their efforts on the use of chiral at phosphorus ligands. Four years after the first report, these authors obtained 88% ee in the reduction of a-acylaminoacrylic acids by incorporating cyclohexyl and ortho-anisyl substituents [44] (Scheme 1.11). 

Very recently, Reetz, Ma and Goddard reported phosphoramidites based on BINOL bearing a single ortho-substituent (Scheme 28.10) [69]. These ligands are also chiral on phosphorus, such that the synthesis results mostly in diastereo-mers which have to be separated. In several cases, however, one of the diaster-eomers was formed exclusively. Some of the ligands afford high ee-values in the hydrogenation of methyl N-acyl dehydroalanine and dimethyl itaconate. 

Mnkeni PNS, MacKenzie AF (1985) Retention of ortho- and polyphosphates in some Quebec soils as affected by added organic residues and calcium carbonate. Can J Soil Sci 65 575-585 Ogaard AF (1996) Effect of fresh and composted cattle manure on phosphorus retention in soil. 

Condensed (poly) phosphates may exert different effects on calcium utilization than the aforementioned effects of simple (ortho-) phosphates. Polyphosphates have a much greater affinity for calcium than do orthophosphates, and soluble calcium-polyphosphate complexes are readily formed in the gastric and intestinal environments. In addition, polyphosphates must be hydrolyzed by an intestinal alkaline phosphatase (27) prior to absorption. We have found polyphosphates to be incompletely (80.5%) hydrolyzed to orthophosphate during the digestive process in young adult males when calcium intake was low only 56% of a 1 g phosphorus supplement was absorbed from a polyphosphate sources as compared to 71% from an orthophosphate source (5). 

When an unsymmetrical diyne is used, two regjoisomers of ortho and meta isomers are formed. Then, by choosing the bidentate phosphorus ligand (DPPE or DPPE (l,l -bis(diphenylphosphino)ferrocene), the ratio of their formation could be controlled from 1 4 to 7 1 (Scheme 11.2) [12]. 

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