Isomeric solutes, separation

Table 5. Examples of isomeric solutes separated using monomeric and polymeric liquid crystalline stationary phases.

The direct irradiation of cis- and frans-2-butenes in solution separately and in admixture gives stereospecific dimerization along with the more efficient cis-trans isomerization<78) ... 

Isomeric solutes that have closely related structure with slight difference in v.p. and degree of interaction with conventional stationary phases provide difficult separation problems. Liquid crystal, N,N -bis(p-methoxybenzylidene)-a,o -bi-p-toluldine, was used for separation of several PAH, in general, and benzo (a) pyrane and benzo (e) pyrene in particular (27). 

Two geometrically isomeric solutes were easily separated maleate (cis form) and fumarate (trans form). The hydrophobic or hydrophilic nature of a soluble strongly affects the retention time in this system. Thus, the polar effects of the two carboxyl groups gave phthalate a shorter retention time than benzoate, which has a single carboxyl group. In conventional IC, the 2- phthalate anion would be... 

HFCLM-based Isomer Separation Processes. Armstrong and Jin (33) studied liquid membrane permeation through an aqueous SLM in a cellulose filter placed in a batch cell. The feed consisted of a 50-50 mixture of organic isomeric solute systems (structural, stereoisomers, etc.) in an organic solvent with the same solvent present in the permeate side. They incorporated p-cyclodextrin (they also tested a-and y-) in the aqueous solution to develop selectivity for one isomer over the other. Considerable selectivity was achieved initially. With time the selectivity was lost due to the inherent nature of the batch system. 

Since aliphatic hydrocarbons (unlike aromatic hydrocarbons, p. 155) can be directly nitrated only under very special conditions, indirect methods are usually employed for the preparation of compounds such as nitroethane, CjHsNO. When ethyl iodide is heated with silver nitrite, two isomeric compounds are formed, and can be easily separated by fractional distillation. The first is the true ester, ethyl nitrite, C,HiONO, of b.p. 17° its identity is shown by the action of hot sodium hydroxide solution, which hydrolyses it, giving ethanol and... 

Fructose—Dextrose Separation. Emctose—dextrose separation is an example of the appHcation of adsorption to nonhydrocarbon systems. An aqueous solution of the isomeric monosaccharide sugars, C H 2Dg, fmctose and dextrose (glucose), accompanied by minor quantities of polysaccharides, is produced commercially under the designation of "high" fmctose com symp by the enzymatic conversion of cornstarch. Because fmctose has about double the sweetness index of dextrose, the separation of fmctose from this mixture and the recycling of dextrose for further enzymatic conversion to fmctose is of commercial interest (see Sugar Sweeteners). 

The only practical method of preparing 1,4-aminonaphthol is from a-naphthol through an azo dye, the nitroso compound not being readily available. The majority of investigators have reduced technical Orange I with stannous chloride Mi.is.is.ir.is by the procedures discussed above, and benzeneazo-a-naphthol has been reduced by the same reagent. In order to make possible the use of crude, technical a-naphthol a method has been developed for the preparation of the benzeneazo compound, its separation from the isomeric dye coming from the d-naphthol present as well as from any disazo compound by extraction with alkali, and the reduction of the azo compound in alkaline solution with sodium hydrosulfite. The process, however, is tedious and yields an impure product. 

Truxillines, CggH4jOgN2. In 1887 Hesse isolated from Peruvian coca leaves an amorphous alkaloid which he named cocamine a year later Liebermann examined this material, and by fractioimtion of its solutions by addition of petroleum proved it to be a mixture of at least two isomeric bases, which he named a- and jS-truxillines. The pure alkaloids have not been obtained from coca leaves owing to the difficulty of separating them, but each has been prepared synthetically. ... 

No crystalline hydrochlorides eould be obtained from either santalene. tt-Santalene forms a liquid dihydrochloride of optical rotation -n 6°, when dry hydrochloric acid is passed through its ethereal solution. It also forms a crystalline nitrosochloride melting with decomposition at 122°, and a nitrol-piperidide melting at 108° to 109°. /3-santalene forms corresponding compounds, the dihydrochloride having a rotatory power -H 8°. It forms, however, two isomeric nitrosochlorides, CigHj NOCl. They may be separated by fractional crystallisation from alcohol. One melts at 106°, the other at 152°. The corresponding nitrol-piperidides melt at 105° and 101° respectively. 

In conjunction with Bachofen, Chuit has devised a method for separating the isomeric ionones depending on the following facts. The method is based on the insolubility of the sodium salt of the hydrosul-phonic compound of a-ionone in the presence of sodium chloride, whilst the corresponding j8-compound remains in solution. If sodium chloride be added to a hot solution of the hydrosulphonic compounds, separation of the n-salt takes place slowly as the solution cools, and the salt crystallises in fine white scales, which can be recrystallised from hot water. The j8-compound remains in solution. 

This ketone, of the formula Cj H O, isomeric with those above described, is found in the oils of thuja, tansy, wormwood, and sage. It is identical with the bodies formerly described under the names tan-acetone and salvone. It is best prepared in a state of purity from oil of wormwood. According to Semmler, 200 c.c. of the oil, 0 c.c. of a saturated solution of sodium bisulphite, 75 c.c. of water, and 300 c.c. of alcohol are well shaken at intervals during a fortnight. The crystals formed, consisting of the compound of thujone with the sodium bisulphite, are separated, washed with alcohol-ether, and pressed. On treatment with caustic soda solution, the thujone, amounting to over 40 per cent, of the oil used, separates, and can be distilled with steam. 

Mixtures may be separated by chromatography or by using solubility differences. Isomerization often occurs on heating solutions of m-Pt(RCN)2Cl2 give mixtures of the cis- and trans-forms, while solid m-Pt(PhCN)2Cl2 gives the trans-isomer. 

Another case to which we can apply the principle of microscopic reversibility is the isomerization of cis- and rrans-(H20)4CrClJ and the loss of Cl- from each. This system has been studied both by careful chromatographic separation of the components20 in quenched solutions and by simultaneous multiwavelength spec-trophotometric determinations.21 The scheme is as follows, where the subscript c indicates cis, t trans, and m the monochloro complex ... 

The ability of complexes to catalyze several important types of reactions is of great importance, both economically and intellectually. For example, isomerization, hydrogenation, polymerization, and oxidation of olefins all can be carried out using coordination compounds as catalysts. Moreover, some of the reactions can be carried out at ambient temperature in aqueous solutions, as opposed to more severe conditions when the reactions are carried out in the gas phase. In many cases, the transient complex species during a catalytic process cannot be isolated and studied separately from the system in which they participate. Because of this, some of the details of the processes may not be known with certainty. 

Scheme 166 shows application of this methodology for preparation of hydrazide 1007. Thus, the reaction of acid 1004 with 1-hydroxybenzotriazole and EDC [l-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride] gives ester 1005 that can be separated and characterized, but it rearranges slowly to isomeric form 1006 in solutions. However, both derivatives, 1005 and 1006, are found to be equally reactive toward hydrazine and afford hydrazide 1007 in 98% isolated yield <2002JOC9471>. 

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