Successful Approach to Mimic the Solvent Power of Maltenes Based on SARA Analysis, Solvatochromic and Solubility Parameters

We extended the oil compatibility model to the dissolution of asphaltenes (Asps) in maltenes from 10 crude oils (COs). As scales for the power of solvents of interest, vide infra, we used solvatochromic parameters, calculated from the UV–vis spectra of solvatochromic compounds (probes), Hildebrand/Hansen solubility parameters, and the colloidal instability index of COs. As the colors of maltenes or asphaltene-free crude oils CO_(Asp‑free) were too dark to permit recording the absorption spectra of the probes, we formulated models for these fractions (<b>M</b>CO_(Asp‑free)). They were composed of low molar mass hydrocarbons, namely, <i>cis</i> and <i>trans</i> decalines, isooctane, 1-methylnaphthalene and, as model for resins, benzothiazole/<i>n</i>-octyl-1-naphthoate. We based formulations of these <b>M</b>CO_(Asp‑free) on SARA analysis of the COs and elemental analysis of the corresponding resins. We validated <b>M</b>CO_(Asp‑free) as models for the corresponding CO_(Asp‑free) by showing that the correlation between Hildebrand solubility parameter (δ_t) of (COs) and δ_t for <b>M</b>CO_(Asp‑free) is linear with a slope close to unity. Regarding Asp dissolution, we show that the correlations between log­(dissolved Asp, mass %) and each of the following solvent descriptors is linear: empirical polarity of <b>M</b>COs_(Asp‑free); δ_t of COs; colloidal instability index of COs. Furthermore, the multiple correlation between log­(dissolved Asp, mass %) and other solvatochromic parameters showed that solvent dipolarity and polarizability are important factors for Asp dissolution, in agreement with our previous results on Asp dissolution in pure solvents. The formulation of a model that successfully mimics maltenes is potentially very useful, e.g., in rationalizing the efficiency of certain classes of additives employed for Asp stabilization

The Nature of the Sodium Dodecylsulfate Micellar Pseudophase as Studied by Reaction Kinetics

The nature of the rate-retarding effects of anionic micelles of sodium dodecyl sulfate (SDS) on the water-catalyzed hydrolysis of a series of substituted 1-benzoyl-1,2,4-triazoles (1a–f) has been studied. We show that medium effects in the micellar Stern region of SDS can be reproduced by simple aqueous model solutions containing small-molecule mimics for the surfactant headgroups and tails, namely sodium methyl sulfate (NMS) and 1-propanol, in line with our previous kinetic studies for cationic surfactants (Buurma et al. J. Org. Chem. 2004, 69, 3899−3906). We have improved our mathematical description leading to the model solution, which has made the identification of appropriate model solutions more efficient. For the Stern region of SDS, the model solution consists of a mixture of 35.3 mol dm–3 H2O, corresponding to an effective water concentration of 37.0 mol dm–3, 3.5 mol dm–3 sodium methylsulfate (NMS) mimicking the SDS headgroups, and 1.8 mol dm–3 1-propanol mimicking the backfolding hydrophobic tails. This model solution quantitatively reproduces the rate-retarding effects of SDS micelles found for the hydrolytic probes 1a–f. In addition, the model solution accurately predicts the micropolarity of the micellar Stern region as reported by the ET(30) solvatochromic probe. The model solution also allows the separation of the individual contributions of local water concentration (water activity), polarity and hydrophobic interactions, ionic strength and ionic interactions, and local charge to the observed local medium effects. For all of our hydrolytic probes, the dominant rate-retarding effect is caused by interactions with the surfactant headgroups, whereas the local polarity as reported by the solvatochromic ET(30) probe and the Hammett ρ value for hydrolysis of 1a–f in the Stern region of SDS micelles is mainly the result of interactions with the hydrophobic surfactant tails. Our results indicate that both a mimic for the surfactant tails (NMS) and a mimic for the surfactant headgroups (1-propanol) are required in a model solution for the micellar pseudophase to reproduce all medium effects experienced by a variety of different probes