Phosphoric thiophosphoric acid triesters

Table 13.12 Rate Constants kA, N, and kB, Half-Lives, tu2, at pH 7, and /NB Values for Hydrolysis of Some Phosphoric and Thiophosphoric Acid Triesters at 25°C a...

As for other esters, hydrolysis of phosphoric and thiophosphoric acid triester occurs via acid-catalyzed, base-catalyzed, and neutral mechanisms (Table 13.12). We note that in the following discussion we are concerned primarily with acid triesters, although the hydrolysis products of these compounds, that is, the di- and monoesters, are also of environmental concern inasmuch as they usually seem to react at slower rates as compared to the triesters (Mabey and Mill, 1978 Wolfe, 1980). 

As can also be seen from Table 13.12, acid-catalyzed hydrolysis is unimportant for many phosphoric and thiophosphoric acid triesters. Among the exceptions are diax-onon and diazinon (/AN = 6.4 and 5.7, respectively). Try to explain why. 

Compounds with phosphorus as the key element that have been investigated for extreme-pressure additive activity add up to an impressively long list. But only a few of them have turned out to be of practical utility and these are predominantly esters of phosphoric acid or derivatives of thiophosphoric acid. In this section we shall be concerned only with those compounds in which phosphorus in combination with oxygen constitutes the key structure dithiophosphates and related derivatives are discussed in Section 11.2.6. The four main types of phosphorus oxyacid esters treated in the present section are shown in Table 11-12. Phosphoric and phosphorous acids are trifunctional hence there are three or-ganophosphorus structures to be considered the neutral triester, the monoacidic diester and the diacidic monoester. 

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See also in sourсe #XX -- [ ]

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