Cholesteryl benzoate

Liquid crystals were discovered by an Austrian biologist, Frederich Reinitzer, in 1888. Reinitzer found that cholesteryl benzoate, a biological chemical, melts to form a hazy liquid. At a higher temperature, the haziness disappears. This clear state is what we know now as a liquid crystal. 

Thermotropic cholesterics were officially discovered2 in 1888 by the Austrian botanist Friederich Reinitzer, while studying the melting of cholesterol esters cholesteryl benzoate first melted to give a cloudy liquid that, at higher temperature, turned into an ordinary clear liquid. The cloudy liquid (the mesophase) was a thermotropic cholesteric liquid crystal. These phases... 

The history of liquid crystals started with the pioneer works of Reinitzer and Lehmann (the latter constructed a heating stage for his microscope) at the end of the nineteenth century. Reinitzer was studying cholesteryl benzoate and found that this compound has two different melting points and undergoes some unexpected color changes when it passes from one phase to another [1]. In fact, he was observing a chiral nematic liquid crystal. 

Mesophase materials are possible for all three classes of molecules. Biological mesophases were already discovered in the middle of the 19th Century. Reinitzer later described the special two-stage melting of cholesteryl benzoate. These materials were then named liquid crystals by Lehmann in 1904 5). Small molecule mesophase materials will be referred to from time to time in this review as reference materials. 

All the authors concluded that N20 provides a very high selectivity, which is higher than generally achieved with H202 or 02. In some cases, a virtually quantitative yield of the target product was obtained. This can be exemplified by the N20 epoxidation of cholesteryl benzoate [162] ... 

The reaction was conducted with 0.20 mmol of cholesteryl benzoate and 5.0 mol % Ru(TMP)(0)2 catalyst in fluorobenzene solvent. At the reaction temperature of 413 K and under 1.0 MPa N20 pressure, the catalyst provided a 99% yield with >99% selectivity. 

On cooling [the liquid phase of cholesteryl benzoate] a violet and blue phenomenon appears, which then quickly disappears leaving the substance cloudy but still liquid. 

Internal Standard Dissolve cholesteryl benzoate in Mobile Phase to obtain a solution having a concentration of 2.5 mg/mL. 

The cholesteric mesophase formed by cholesteryl p-nitrobenzoate at 200 °C has been used as the solvent to effect an asymmetric synthesis lrans-but-2-enyl p-tolyl ether gave the product of an ortho-Claisen rearrangement, 2-(but-1 -en-3 -yl)-4-methylphenol. This material exhibited circular dichroism, although neither the optical yield nor the configuration of the product is yet known.262 Decarboxylation of ethylphenylmalonic acid in cholesteryl benzoate at 160 °C (cholesteric liquid-crystalline phase) also proceeded with asymmetric induction to give (R)-(—)-2-phenylbutyric acid, with 18% optical yield.263 Electric dipole moments are reported for some esters of 5a-cholest-8(14)-en-3j8-ol there is some slight correlation with melting points.264... 

Figure 2.1 A schematic representation of the melting of crystalline cholesteryl benzoate (I) at 145.5 °C to form a chiral nematic (cholesteric) phase, which in turn forms the isotropic liquid on further heating to 178.5 °C. ...

With the advent of the chromium trioxide-3,5-dimethylpyrazole complex as an oxidant - allylic oxidation has become far more valuable as a synthetic transfonnation. The reagent was applied by Sala-mond to the allylic oxidation of cholesteryl benzoate to give the correspondbg A -7-ketone (equation 35). However, a 20 molar excess of reagent was still requii to effect the reaction in less than 30 min at room temperature. 

The cis addition of chlorine to 5,6-double bonds has been observed under two distinct sets of reaction conditions. Cholesteryl benzoate (7) reacts with iodobenzeue dichloride under anhydrous conditions (and in the absence of compounds... 

Several hydroxylated analogues of vitamin D have been prepared by irradiation of a steroidal A -diene precursor, following a sequence similar to that used in the synthesis of retroprogesterone. " " Photobromination of cholesteryl benzoate also gave a triene derivative analogous to vitamin D3 (378)/ ... 

A recent study of such irradiations in the presence of -cyclodextrin and various L-amlno acids also revealed asymmetric induction, but the optical yields were low. In one case of asymmetric induction, brief heating of 2-rerf-butyloxaziridine in a medium of cholesteryl benzoate at 148°C yielded a (—)-enriched enantiomer in up to 20% enantiomeric excess. It seems that this experiment requires special attention to the experimental details. ... 

Since the description of liquid crystallinity for cholesteryl benzoate and cholesteryl acetate at the end of the 19th century by Reinitzer [1], an intense activity has been devoted to thermotropic liquid crystals, especially since the early 1970s, owing to the fabrication and application of liquid crystal displays in electronic technology. 

Clindamycin Palmitate Hydrochloride Clindamycin Palmitate Hydrochloride for oral solution Glass, 0.6 M x 3 mm I.D. 1% G36/S1AB (80-100 mesh) Helium 290 FID Cholesteryl Benzoate USP (24, pp. 431 and 432)... 

The term liquid crystal was first applied to compounds that, unlike most compounds that melt in a single step at a definite temperature, show one or more well-defined phases between the solid and the true liquid. Otto Lehmann in 1888 was contacted by Friedrich Reinitzer who had observed that crystalline cholesteryl benzoate, on heating, seemed to have two melting points.At 145.5° C a cloudy liquid forms that, on further heating, changes sharply to a clear liquid at 178.5° C. On cooling the reverse order of phases was found. The turbid liquid is doubly refracting, like the anisotropic crystals described in Chapter 5, hence the... 

A second category of liquid crystals is the type produced when certain substances, notably the esters of cholesterol, are heated. These systems are referred to as thermotropic liquid crystals and, although not formed by surfactants, their properties will be described here for purposes of comparison. The formation of a cloudy liquid when cholesteryl benzoate is heated to temperatures between 145 and 179°C was first noted in 1888 by the Austrian botanist Reinitzer. The name liquid crystal was applied to this cloudy intermediate phase because of the presence of areas with crystal-like molecular stmcture within this solution. 

Although the technical applications of low molar mass liquid crystals (LC) and liquid crystalline polymers (LCP) are relatively recent developments, liquid crystalline behavior has been known since 1888 when Reinitzer (1) observed that cholesteryl benzoate melted to form a turbid melt that eventually cleared at a higher temperature. The term liquid crystal was coined by Lehmann (2) to describe these materials. The first reference to a polymeric mesophase was in 1937 when Bawden and Pirie (2) observed that above a critical concentration, a solution of tobacco mosaic virus formed two phases, one of which was bireffingent. A liquid crystalline phase for a solution of a synthetic polymer, poly(7-benzyl-L-glutamate), was reported by Elliot and Ambrose (4) in 1950. 

A preliminary report" states that reaction of cholesteryl benzoate with (-butyl hydroperoxide and a catalytic amount of cuprous bromide in benzene gave equal parts of A -cholestene-3, 7a- and -3, 7j8-diol dibenzoate. Here allylic attack is not attended with rearrangement. 

Dehydrohalogenation. Hunziker and MUllner effected allylic bromination of cholesteryl benzoate in refluxing petroleum ether, collected the crystalline mixture of 7a- and 7/3-bromocholesteryl benzoate, and treated it with trimethyl phosphite in refluxing xylene. The crystalline reaction product contained 56% of 7-dehydro-cholesteryl benzoate and the amount corresponded to a yield of 52%. It is assumed that the dienic ester is derived from the 7a-cholesteryl benzoate present in the bromination product trans elimination). 

Allylic bromination of cholesteryl benzoate at C7 is the key step in the commercial production of vitamin D3. A carefully developed procedure employs NBS in 20% excess and involves refluxing in petroleum ether under illumination for 4 min. 

Synonym Cholesteryl benzoate Source Huang, Z. Kawi, S. Chiew, Y. C. J. Supercrit Fluids (2004), 30(1), 25-39. 

As early as 1888 the Austrian botanist F. Reinitzer [1] found that cholesteryl benzoate, if heated above its melting point, 146.6 °C, forms a milky, iridescent fluid with some of the typical characteristics of a liquid and some of a crystal [2]. On further heating above 180.6 °C a clear melt is obtained. On cooling the effect was found to be reversible. 

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