Aggregating Tendencies of Some Phosphonates and Phosphinates

Abstract

Simple aggregations of phosphorus-containing compounds have been investigated for the first time. The aggregators studied are O-alkyl O-4-nitrophenyl methylphosphonates (1-n and 2), 4-nitrophenyl alkylphenylphosphinates (3-n), and O-n-octyl O-4-nitrophenyl phenylphosphonate (4). Their aggregating tendencies have been evaluated by measuring their critical aggregate concentrations (CAgC's) in dioxane−H2O binary mixtures of graded compositions. Structural effects on aggregating tendencies have been discussed.

Aggregating Tendencies of Some Alkylsulfonates

“…Curve c shows that at φ = 0.30 there are three regions, i.e., a monomeric region, a transition region, and an aggregated region; thus the CAgC value of S-12 at φ = 0.30 can be evaluated to be 1.19 × 10 -5 M. These results also show that the occurrence of aggregation of S-12 depends on the φ value of the medium. This observation is very similar to the observation on the behaviors of the carboxylates 12 or phosphonates 4b. In other words, all our data indicate that the occurrence of aggregation depends on the substrate concentration [Agr] i and the solvent aggregation power (SAgP) of the medium, because within a certain range of the φ value, the SAgP of one specified solvent system is directly correlatable with the φ value. ,,14b

1 Plots of log k ob vs log[S-12] i in DX−H 2 O with graded φ values at 35 °C.

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“…The log values of hydrolytic rate constants of substrates in DX−H 2 O mixtures of graded φ values at various initial substrate concentrations were measured and plotted against the log of initial substrate concentrations ([Agr] i ), and for each target molecule and solvent system, a figure with curves corresponding to different φ values can be obtained. Whenever there is a break point in these curves, a CAgC value can be determined. ,5a Figure shows the dependence of log k ob on log [S-12] i at different φ values. These curves are typical: Curve e shows that at φ = 0.40 there is only a monomeric region in which no aggregation of the target molecule (S-12) occurs.…”

“…Water was deionized, and dioxane (DX) was purified by a standard procedure . Kinetic measurements in DX−buffer systems with graded φ values were performed on a Perkin-Elmer Lambda 5 UV−vis spectrometer equipped with a thermostated cell holder at 35 °C by monitoring the formation of the p -nitrophenolate at 410 nm, as previously described. ,4a,5a,,,14a The experimental uncertainty for the k ob values was within ±5%. The aqueous buffer solutions used were as follows: buffer I, 0.01 M NaOH, 0.01 M NaHCO 3 , and 0.34 M NaCl (pH = 11.90); buffer II, 0.064 M NaOH and 0.05 M KCl (pH = 12.90).…”

“…The aqueous buffer solutions used were as follows: buffer I, 0.01 M NaOH, 0.01 M NaHCO 3 , and 0.34 M NaCl (pH = 11.90); buffer II, 0.064 M NaOH and 0.05 M KCl (pH = 12.90). Buffer I was first used because it had been used in most of the previous CAgC measurements, ,4a,, but it was found that the hydrolysis of the sulfonates was much too slow in this buffer, especially for S-12 and S-16. Buffer II was found to be convenient for measurements for all the sulfonates.…”

“…The “break point” of such a log k ob vs log[Agr] i plot, i.e., the narrow transitional concentration region between the horizontal and slanting lines (see, e.g., curve c in Figure ; curve for S-8 in Figure and curve for P-16 in Figure ), represents the CAgC of that particular Agr under study. In recent years, the reliability and trustworthiness of this kinetic methodology have been firmly established time and again. ,, However, all these previously studied simple Agr's are either purely carbon compounds or some phosphorus-containing compounds, but aggregation behavior of sulfur-containing organic compounds has never been reported. In view of the importance of sulfur-containing compounds in organic, bioorganic, and surfactant chemistry, − it certainly would be of interest to study the aggregation behaviors of some sulfur compounds.…”