Hexadecane method

It is difficult to judge the accuracy of these methods because data are scarce. Table 4.9 compares the values obtained by different weighting methods with experimental values for a mixture of n-hexane-n-hexadecane at 25°C. The ASTM method shows results very close to those obtained experimentally. 

Comparison of weighting methods for liquid phase viscosities. Mixture of n-hexane - n-hexadecane at 298 K. 

At low temperatures, using the original function/(T ) could lead to greater error. In Tables 4.11 and 4.12, the results obtained by the Soave method are compared with fitted curves published by the DIPPR for hexane and hexadecane. Note that the differences are less than 5% between the normal boiling point and the critical point but that they are greater at low temperature. The original form of the Soave equation should be used with caution when the vapor pressure of the components is less than 0.1 bar. In these conditions, it leads to underestimating the values for equilibrium coefficients for these components. 

This section deals with the experimental determination of the rate of oil solubilization in aqueous solutions of AOS and IOS [70]. The experimental method [71] consists of injecting 25 pi of n-hexadecane (containing 5 wt % Dobanol 45-3 as an emulsifier) into 50 ml water this produces a turbid macroemulsion upon vigorous stirring. At the start of the experiment, a concentrated solution of the surfactant under test is injected and the decrease in turbidity is followed with a photometer. The time elapsed to reach 90% of the initial turbidity is recorded (t ) and the pseudo rate constant of oil solubilization is calculated from... 

Faller and Wohnsland [18, 19] developed the PAMPA assay using phospholipid-free hexadecane, supported on 10 pm-thick polycarbonate filters, and were able to demonstrate interesting predictions. Their PAMPA method appeared to be a satisfactory substitute for obtaining alkane/water partition coefficients, which are usually very difficult to measure directly, due to the poor solubility of drug molecules in alkanes. Apparently, membrane retention was not measured. 

Wohnsland and Faller ([175] performed measurements using a thin (9-10 //in) supported, phospholipid-free hexadecane layer. To validate their model, they used 32 well-characterized chemically diverse compounds. The permeability values obtained with their model could be correlated with known human absorption values if the maximum permeability obtained at different pH was taken into account. However, several disadvantages are related to this method. For hydrophilic drugs, hexadecane by itself has an increased barrier function in comparison with membranes. In addition, the hexadecane layers are not very stable, which makes this assay difficult to apply as a routine screening method. The advantage of this PAMPA setup is that it appears to be a satisfactory substitute for obtaining alkane-water partition coefficients, which are usually very difficult to measure directly, due to the poor solubility of drug molecules in alkanes. 

The standard test method is described in ASTM D-2873. The actual or accessible porosity can also be determined by the weight of liquid (e.g., hexadecane) absorbed in the pores of the separator. In this method, the separator weight is measured before and after dipping in hexadecane solvent, and the porosity is calculated (eq 7) by assuming that volume occupied by hexadecane is equal to the porous volume of the separator. 

The application of a heavy, late eluting solvent was explored somewhat (3J, using decalin and hexadecane solvents. While this method did show some promise, it was not investigated extensively because of limited resources. 

A very interesting synthetic method of bicyclo[n.l.O]alkanes from cychc ketones via this 1,3-C,H insertion of magnesium carbenoid as a key reaction was reported (equation 22) . 1-Chlorovinyl p-tolyl sulfoxide (76) was synthesized from cyclopentadecanone and chloromethyl p-tolyl sulfoxide in three steps in high overall yield. Lithium enolate of tert-butyl acetate was added to 76 to give the adduct 77 in quantitative yield. a-Chlorosulfoxide (77) in a toluene solution was treated with i-PrMgCl in ether at —78 °C and the reaction mixture was slowly warmed to 0°C to afford the bicyclo[13.1.0]hexadecane derivative 79 in 96% yield through the reaction of the intermediate magnesium carbenoid 78. 

Rank the four compounds (I-FV) indicated below in the order of increasing tendency to distribute from (a) air into hexadecane (mimicking an apolar environment), (b) air to olive oil, and (c) air to water. Use the ah j3 and Vn values given in Table 4.3 and calculated by the method given in Box 5.1. Assume, that the four compounds have about the same nDi value. Do not perform unnecessary calculations. Comment on your choices. Finally, check your result (c) by applying the bond contributions given in Table 6.4. 

Promotion of an SN2 displacement mechanism, and hence greater regioselectivity, may be effected by the addition of liquid bromine to a warm suspension of purified red phosphorus in the appropriate alcohol. The reaction is of general application with primary alcohols (isobutyl alcohol to hexadecan-l-ol) the yields are over 90 per cent of the theoretical, but with secondary alcohols the yields are in the range 50-80 per cent (Expt 5.55). This method is to be preferred to the direct use (rather than the in situ generation) of phosphorus tribromide which is the more hazardous reagent. The outline mechanism may be represented thus ... 

Drop-weight method. To determine the surface tension of a hexadecane (Ci6H34) you let it drop out of a capillary with 4 mm outer and 40 /. m inner diameter. Hexadecane wets the capillary. Its density is 773 kg/m3. 100 drops weigh 2.2 g. Calculate the surface tension of hexadecane using the simple Eq. (2.15) and the correction factor /. It was concluded that / should be a function of rc/V 1/3, with V being the volume of the drop. Values for the correction factor are listed in the following table (from Ref. [1], p. 19). Is it necessary to use the correction ... 

Cotterman et al. (34) showed that hexadecane-cracking activity of AFS and USY zeolites appeared to be a function of total Al content, independent of method of dealumination, implying that hexadecane cracking occurs over both framework- and extra-framework-acid sites. Hence, extra-framework material in mildly steamed synthetic faujasite, USY, makes a significant contribution to catalyst activity, as previously reported (32). Gasoline selectivity is influenced by both the method of dealumination and steam treatment, and depends on both framework-acid sites and the presence of extra-framework material. 

First of all, the capacitance of lecithin-hexadecane membrane is about 0.62 yF/cm. This value is smaller than the capacitance of biological membranes, i.e., 1 yF/cm2. The difference is perhaps partially due to the absence of proteins in artificial membranes. In addition, it is known that the presence of solvents decreases the values of membrane capacitance. For example, membranes formed by the Montal-Mueller Method (21), which are believed to be free of solvents, have a capacitance of 0.7 yF/cm2 (22). Thus, the capacitance of bilayer membranes shown in this figure may be in error by about 0.1 yF/cm2 because of the presence of solvent molecules. However, it is more important to note that membrane capacitance is independent of frequency, which provides unequivocal evidence that there is no relaxation process in lipid membranes in this frequency range. Coster and Smith (23) reported that they observed a frequency dispersion of membrane capacitance of artificial layers at very... 

---