Benzene octadecyl

Octadecyl ether (dioctadecyl ether) [6297-03-6] M 523.0, m 59.4°. Vacuum distd, then crystd from MeOH/ benzene. 

The development of alkylbenzenesulfonates (ABSs) goes back to 1923, when the British chemist Adams discovered that it was possible to obtain water-soluble products by the sulfonation and neutralization of hexadecyl- and octadecyl-benzene. Such products have also soap-like characteristics [1]. In 1926 IG-Farbenindustrie (Hoechst) and Chemische Fabrik Pott, Pirna/Sachsen simultaneously discovered that long-chain ABSs have excellent surface-active properties. 

Ethoxylation of the base alcohol always improves the solubility of the sulfate. As an example, sodium hexadecyl ether (2 EO) sulfate gives a clear 10% solution in water at 40°C, which becomes a viscous gel at 30°C [59]. Alcohol ether sulfates are also more soluble in organic solvents than the corresponding alcohol sulfates. Sodium hexadecyl and octadecyl ether (2 EO) sulfates are soluble at 1% concentration in lubricating oil, at 2.5% in benzene and chloroform, and at 5% in tetrachloroethylene, whereas alcohol-ethoxylated sulfates with 10 mol of ethylene oxide are soluble at 5% in lubricating oil [59]. 

An increase in the number of methylene units in alkyl benzene did not significantly affect the 7t-energy effect on their retention, but the enthalpy effect increased dramatically [80]. This means that a hydro-phobic compound can be adsorbed directly onto an octadecyl-bonded silica gel. The value of enthalpy effect of a methylene unit in alkyl benzene was calculated to be 500 cal/mol. 

Figure 3.13 n-Electron selectivity of different octadecyl-bonded silica gels towards the retention of polycyclic aromatic hydrocarbons. Columns. , LOC-ODS-E, O, LOC-ODS-NE O, HIC-ODS-E, A, HIC-ODS-NE, eluent, 80% aqueous acetonitrile at 30°C. Compounds polycyclic aromatic hydrocarbons 1, benzene, 2, naphthalene 3, pyrene 4, 3,4-benzopyrene. 

Figure 5.3 Resolution related to peak area ratio. (A) theoretical and (B) experimental changes in resolution with volume ratio. Column, 10 pm octadecyl-bonded silica gel, 15 cm x 4.6 mm i.d. eluent, 90% aqueous acetonitrile flow rate, 1 ml min-1 detection, UV 254 nm. Sample, different ratios of 10 /il benzene and toluene in 10 ml ethanol.

Fio. 12. Graph illustrating the dependence of the logarithm of retention factor for aromatic hydrocarbons on the carbon load of octadecyl silica bonded phases prepared from Par-tisil with octadecyhrichlorosilane. Mobile phase methanol-water (70 30) eluitest A, benzene A, naphthalene , phenanthrene , anthracene O, pyrene. Reprinted with permission from Herndon t al. (70). 

Octadecyldimethylamine oxide (CieDAO) was a commercial sample from Onyx Chemical Company, Jersey City, N. J. (25% active). After evaporating the solvent in a rotary evaporator under reduced pressure, the crude product was recrystallised several times from ethyl acetate. The final product was dried and stored in vacuo over P2O5. Sodium octadecyl sulfate (SODS) was a sample prepared in this laboratory previously, and was recrystallised from ethanol before use. Sodium dodecyl sulfate (SDS) was obtained from Aldrich Chemical Company, and was of 98% purity. It was further purified by repeated crystallisation from ethanol followed by ether extraction. Benzene and methanol were gold-label reagent grade, purchased from Aldrich Chemical Company (Metuchen, N. J.). 

R-Octadecyl alcohol [112-92-5] M 270.5, m 61°, b 153-154°/0.3mm. Crystd from MeOH, or dry ethyl ether and benzene, then fractionally distd under reduced pressure. Purified by column chromatography. Freed from cetyl alcohol by zone melting. 

Nonpolar interactions (hydrophobic) typical octadecyl-modified silica, polystyrene-divinyl benzene copolymers, or carbon-based sorbent. 

One system with these desirable features is a suspension of small a 50 nm) silica particles onto which octadecyl chains have been densely grafted (Stober et al. 1968 van Helden et al. 1981 Woutersen and de Kruif 1991). The octadecyl chains have a theta point near room temperature in various solvents, including benzene, dodecane, and hexadecane. 

Below the percolation line, there is predicted to be a sample-spanning cluster of contacting spheres. Woutersen et al. (1994) found that the gel point for 47-nm octadecyl-grafted silica spheres in benzene is in reasonable agreement with the predicted percolation transition. However, Grant and Russel (1993) found that the gelation line is below the percolation ... 

Figure 7-6 shows the viscosity of thermoreversible dispersions (discussed in Section 7.2.4) of a 50-nm silica particles onto which octadecyl chains have been densely grafted in benzene at particle volume fractions 4> — 0.088-0.133, as a function of temperature T (Woutersen and de Kruif 1991). For T > 9 — 316 K, the viscosity relative to that of the solvent, rir = r /f]s, is independent of temperature, and its dependence on volume fraction 0 is exactly as expected for hard spherical particles without attractive interactions. As T is lowered below 9, however, the viscosity rises rapidly, because of the onset of attractive interactions. 

Sams reported the determination of reserpine in plasma by ion-pair chromatography. To obtain high specifity and to increase the sensitivity reserpine - after extraction from plasma with benzene - was oxidized to 3-dehydroreserpine with vanadium pentoxide in concentrated phosphoric acid, to which 9 ml methanol were added. The fluorescent compound was subsequently analyzed on an octadecyl column with methanol - 0.001 M heptanesulfonate in water (65 35) as mobile phase. Reserpine and rescinnamine could not be distinguished by this method. 

On the other hand, adsorbents A and B modified with ODS and adsorbent C unmodified or modified with ODS as well as with ODS+HMDS exhibit higher adsorption capacity. Benzene shows similar adsorption behavior [68]. The above facts are due to the specific structure of adsorption sites which is formed after the chemical modification of the adsorbents. Adsorption energy sites constitute of spacially arranged CH, CH2 and CH3 groups of the octadecyl radical, chemically bonded to the surface of the silica gel and, in the case of carbosils of components of the carbon deposit (i.e. CH, CH2, CH3) planary distributed on the surface of the supporting material. There is an essential difference in the mechanism of the molecular adsorption on chemically modified and unmodified adsorbents [30]. The surface of chemically unmodified adsorbents can be considered as planar, i.e. two-dimensional, while that of the modified sorbents as three-dimensional. 

In contrast, reversed-phase sorbents have non-polar functional groups, e.g. octadecyl, octyl and methyl, and conversely are more likely to retain non-polar compounds, e.g. polycyclic aromatic hydrocarbons. Ion-exchange sorbents have either cationic or anionic functional groups and when in the ionized form attract compounds of the opposite charge. A cation-exchange phase, such as benzene-sulfonic acid, will extract analytes with positive charges (e.g. phenoxyacid herbicides) and vice versa. A summary of the commercially available silica-bonded sorbents is given in Table 8.1. 

Octadecylmethyl sulfoxide (OMS) was prepared in the following manner 15 g of octadecyl bromide and 3.5 g of thiourea were dissolved in 150 cm3 of ethanol. The mixture was refluxed for 1 hr after which 100 cm3 of ethanol were removed by distillation. The residue, after cooling, was made alkaline by an ethanol/sodium hydroxide solution (5 g sodium hydroxide in a minimum volume of ethanol). Methyl iodide, 3.7 g, was then added, and the mixture was left to stand overnight. The resulting thioether was recovered by filtration and washed with cold ethanol. The thioether was dissolved in glacial acetic acid then small quantities of 20 vol % hydrogen peroxide, constituting the stoichiometric amount, were added over several hours. The product was precipitated with water, and the precipitate was collected by filtration. The crude product was washed successively with water, ice-cold ethanol, and a small quantity of diethyl ether it was finally dried at 70°C. OMS was purified by successive recrystallization from benzene purification was... 

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