Phosphoric acid derivatives, nucleophilic substitution

Hydrolysis of diphenyl phosphorochloridate (DPPC) in 2.0 M aqueous sodium carbonate is also believed to be a two-phase process. DPPC is quite insoluble in water and forms an insoluble second phase at the concentration employed (i.e. 0.10 M). It seems highly significant that the hydrophobic silicon-substituted pyridine 1-oxides (4,6,7) are much more effective catalysts than hydrophilic 8 and 9. In fact, 4 is clearly the most effective catalyst we have examined for this reaction (ti/2 < 10 min). Since derivatives of phosphoric acids are known to undergo substitution reactions via nucleophilic addition-elimination sequences 1201 (Equation 5), we believe that the initial step in hydrolysis of DPPC occurs in the organic phase. Moreover, the... 

Nucleophilic substitution on derivatives of sulfuric and phosphoric acids... 

NUCLEOPHILIC SUBSTITUTION ON DERIVATIVES OF SULFURIC AND PHOSPHORIC ACIDS... 

Let us now turn to an example of nucleophilic substitution involving a group of pollutants other than alkyl halides. We consider the hydrolysis of thiometon and disulfoton, two insecticides that were among the major contaminants that entered the Rhine River after the famous accident at Schweizerhalle in Switzerland in 1986 (Capel et al., 1988). This example is representative for the hydrolysis of a variety of phosphoric and thiophosphoric acid derivatives (e.g., esters, thioesters, see Fig. 1), and it illustrates that hydrolysis of a more complex molecule may be somewhat more complicated. The kinetic data, as well as the proposed mechanisms of hydrolysis of thiometon and disulfoton, are presented in Table 4 and Figure 2, respectively. In these cases, the base catalyzed reaction... 

DFP is stable and in the absence of moisture can be stored for considerable periods without decomposition. Hydrolysis in neutral aqueous solution occurs slowly. The reaction is catalyzed by both acid and base. At pH>7, hydrolysis is proportional to the hydroxide ion concentration and at high pH is extremely rapid. The product is always diisopropyl phosphoric acid (equation 38), except under more forcing conditions which eventually produce phosphate (and propan-2-ol). The hydrolysis is strongly catalyzed by the addition of a-effect nucleophiles such as hypochlorite, peroxide, hydroxylamine, hydroxamic acid and their substituted derivatives . Under basic conditions, such nucleophiles (HOX) are present as the anion and are responsible for the rapid initial displacement of fluoride ion from DFP to give intermediate 36 shown in equation 39. Displacement of OX by hydroxide ion regenerates the catalytic OX anion. The reaction with hydrogen... 

The same group also developed the asymmetric synthesis of 3-amino 8-lactams 91 by phosphoric acid-catalyzed cyclization reactions involving azlactones 90 as both nucleophiles and electrophiles (Scheme 2.27) [38]. In addition to aromatic amines, substituted aryl ethylamines 92 participated well in such cyclization reactions to afford products 91a, which can be converted to benzo[a]quinolizidine derivatives 93 after being treated with trifluoroborane in high overall yields with excellent enan-tioselectivity, ranging from 90 to 97% ee [38]. 

In addition to nucleophilic aromatic substitution, there are a number of other synthetic routes to poly(aryl ethers). Friedel-Crafts condensation of arylsulfonyl chlorides and aryl carboxylic acid derivatives with aryl ethers has been employed to prepare polysulfones (2b) and poly(ether ketones) (105,106), respectively. Direct polycondensation of various benzoic acids containing a phenyl ether structure has been carried in 1 10 phosphorous pentoxide/methanesulfonic acid (107). The success of this method is a consequence of the high selectivity of the electrophilic reagent for substitution para to the ether linkage. 

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