Fundamental Properties of Asphalts and Modified Asphalts, III

Dadey et al. [1988] proposed Scheme II for the reaction of DPPC with water to form
diphenylphosphinic acid. We are not sure which scheme more correctly describes the reaction.
However, more recent work seems to agree with Scheme I [Hatzakis et al. 2008].
Other phosphorous compounds can be used to derivatize the labile hydrogen (OH) such as in
phenols and carboxylic acids [Wroblewski et al. 1988; Dadey et al. 1988; Lensink and Verkade
1990]. Dadey et al. [1988] also proposed Scheme III for the reaction of DPPC with phenols. We
have not yet verified the reaction with phenols.
2Ph2POCl + H2O + Ph2P(O)OH +
OH
2Ph2POCl + +
N
Scheme II
N
Scheme III
66
Ph2P(O)O +
In practice, weighed amounts of an internal standard, [MePh3P]I (methyltriphenylphosphoniumiodide),
were placed into oven dried NMR tubes. These tubes were then sealed with rubber septa
to prevent moisture intrusion. A “stock solution” was then made by dissolving Ph2POCl in
CDCl3. An exact amount of stock solution was then added to the sealed tubes via syringe. NMR
data for the stock solution in the sealed tubes was collected to determine how much water was
present in the system. Weighed samples of asphalt were then dissolved in pyridine, added to the
NMR tubes described above, and allowed to react for five minutes at which point NMR spectra
were then acquired. A blank of neat pyridine was tested for water content in the same way the
asphalt samples were tested. All solvents were dried over 4 Å sieves.
The 31 P NMR method was applied to asphalts AAB-1, AAD-1, and ABD-1. Previously, residual
moisture in these asphalts was determined by a commercial laboratory using the Karl Fischer
titration method. 31 P NMR spectra are shown in figure 2-5.8 along with a spectrum of the blank.
The spectra clearly show resonances formed by the reaction of the tagging agent with the water
in asphalt. Although the peak in the blank spectrum of the water reaction product was
subtracted, the NMR results were not in close agreement with those obtained by Karl Fischer
titration (0.46% NMR vs. 0.37% Karl Fischer for ABD; 0.88% NMR vs. 0.37 Karl Fischer for
AAD; 1.28% NMR vs. 0.31% Karl Fischer for AAB). The reasons for the discrepancies are
being investigated.
N +
H
Cl -
N +
H Cl-
L -