Cresol isomers, separation

Displacement-purge forms the basis for most simulated continuous countercurrent systems (see hereafter) such as the UOP Sorbex processes. UOP has licensed close to one hundred Sorbex units for its family of processes Parex to separate p-xylene from C3 aromatics, Molex tor /i-paraffin from branched and cyclic hydrocarbons, Olex for olefins from paraffin, Sarex for fruc tose from dextrose plus polysaccharides, Cymex forp- or m-cymene from cymene isomers, and Cresex for p- or m-cresol from cresol isomers. Toray Industries Aromax process is another for the production of p-xylene [Otani, Chem. Eng., 80(9), 106-107, (1973)]. Illinois Water Treatment [Making Wave.s in Liquid Processing, Illinois Water Treatment Company, IWT Adsep System, Rockford, IL, 6(1), (1984)] and Mitsubishi [Ishikawa, Tanabe, and Usui, U.S. Patent 4,182,633 (1980)] have also commercialized displacement-purge processes for the separation of fructose from dextrose. 

The amount of cresol in the concentrated extract can then be determined by high performance liquid chromatography (HPLC) (DeRosa et al. 1987 Yoshikawa et al. 1986) or gas chromatography (GC) coupled to either a flame ionization detector (FID) or a mass spectrometer detection system (Angerer 1985 Needham et al. 1984). Separation of the cresol isomers by gas chromatography is readily accomplished, and the use of an appropriate internal standard allows the determination of their concentrations. Although exact detection limits were not given for the above GC methods, a concentration of 10 ppm appears to be readily determined. 

The three isomers of cresol are not as readily separated by HPLC, although recent techniques have been developed to accomplish this task. Reversed-phase chromatography columns have been used for the analysis of cresols with limited success. Recently, a new reversed-phase support has been developed that allows complete separation of the three cresol isomers (Bassler and Hartwick 1989). Inclusion complexes of the cresols with p-cyclodextrin cleanly separate the three isomers on commercially available columns (Yoshikawa et al. 1986). Detection limits down to 1 ppm can be obtained by this method. 

Liquid separation Liquid drying Trace impurity removal Xylene, cresol, cymene isomer separation Fructose-glucose separation Fatty chemicals separation Breaking azeotropes Carbohydrate separation... 

The isolation of individual cresol isomers, more particularly, meta- and para-cresols from a mixture of isomeric cresol mixture had been a master problem in organic chemical synthesis. While orf/io-cresol could be more easily separated because of somewhat lower boiling point (approx. 191°C at atmospheric pressure) meta- and para-cresols could not be separated by distillation because of almost identical boiling points (202°C and 201-202°C at atmospheric pressure, respectively). Various processes have been established in the laboratory but only a few have been commercialized. Some of the commercial processes are discussed here in some detail. 

Gas-Liquid Chromatography. Oxidation products were analyzed using either a Pye Argon, Perkin-Elmer Fll or Pye F104 gas chromatograph. The stationary phases and operating conditions have been reported previously 21). An improved method for separating cresol isomers (28) was introduced in this research in place of the previous method which used tris(2,4-xylenyl) phosphate as the liquid phase. 

The phase diagram (Figure 5.23) for the separation of m- and p-cresol shows two eutectics, so that the separation of the cresol isomers is only possible with a p-cresol concentration of over 60%, or a m-cresol concentration of over 88% the application of pressure can facilitate the separation of the cresol isomers. 

These two processes are the simulated moving bed and pressure swing adsorption. The simulated moving bed uses the same packed bed as conventional adsorption, but changes the feed point. This altered feed point means that the stationary adsorbent has a concentration profile more like that which would exist if the feed point were fixed and the adsorbent were moving. The results approximate those that would be possible with countercurrently moving adsorbent but without the curse of particle attrition. This process, developed especially by the American chemical company UOP, is used for the separation of liquid n-paraffins from branched paraffins. It is also used to separate xylene, cymene, and cresol isomers, and aqueous solutions of racemates. 

The cresols occur in cresylic acid, a mixture of the three cresols together with some xylenols and neutral oils, obtained from coal tar distillates. Only the /n-cresol has the three reactive positions necessary to give cross-linked resins and so this is normally the desired material. The o-isomer is easily removed by distillation but separation of the close-boiling m- and p-isomers is difficult and so mixtures of these two isomers are used in practice. 

Gibbard, H.F. andCreek,J.L. Vapor pressnre of methanol from 288.15 to 337.65K,/ Chem. Eng. Data, 19(4) 308-310,1974. Gibbs, H.D. para-Cresol. A new method of separating para-cresol from its isomers and a study of the boiling point, J. Am. Chem. Soc., 49(3) 839-844, 1927. 

The isomers of cresol are excreted in the urine as their glucuronides and sulfates (Biemiek and Wilczok 1986). To analyze for cresols directly, they must first be separated from the biological carrier. This is usually accomplished by heating a urine sample with a concentrated mineral acid for 30 minutes to 1 hour (Angerer and Wulf 1985 DeRosa et al. 1987 Needham et al. 1984 ... 

Sane RT, Sonawane KK. Gas-chromatographic determination and separation of isomers of cresol from pharmaceutical preparation. Indian Drugs 25(10) 420-424. 

Cresol, Cresylic Acid or Methylphenol (called Kresol or Oxytoluol in Ger), CH3.CgH4.OH mw 108.13, 0 14.79% A coml coal tar product of the middle heavy oil fractions. It contains a mixt of o-, m- p- isomers which may be separated by fractional distillation into two fractions o- and a mixt of m- p-cresols. The props of cresol depend upon the compn proportion of isomers in the mixt. See Kirk Othmer (Ref 5) for more details o Cresol, wh crysts, phenol-like odor, poisonous, mp 30.8°, bp 191°, d 1.048 at 20° sol in ale, eth chlf si sol in w (Refs 1 7). Prepn other props are given in Beil (Ref 1)... 

Originally, we believed that the cresol fraction would be obtained as pure -cresol which has considerable value. We found that w-cresol is always formed with -cresol. The mixture of the two isomers is very difficult to separate and, without the separation, has a relatively low economic value. 

Experiments have been carried out to separate m- and p- cresols by sulphonation, as sulphonated m- cresol is a liquid substance, while sulphonated p- cresol is crystalline. The two isomers were then separated by centrifugation. However, the purity of the product obtained was not satisfactory enough, thus the process would not be economical. 

These ptwofactors may influence resolution of isomers in an additive (e.g. mandelic acid enantiomers, ortho and meta cresols) or substractive manner (e.g. mephenytoin enantiomers). Thus for the designing and optimization of resolution one should know the stability constants and adsorption properties of CD complexes with the compounds being separated. 

Structural Isomers. Chromatograms illustrating the separation of ortho, meta and para isomers of cresol (22) and and xylene ( O)on RP columns are shown in Figures 4 and 5. They enable a comparison of the chromatographic properties and selectivities due to <. - and -CD complexation between positional isomers of the above compounds.Similar behaviour was observed for ortho,meta and para isomers of fluoronitrobenzene, chloronitrobenzene, iodoni-trobenzene, nitrophenol, nitroaniline, dinitrobenzene (22), nitrocinnamic acid (22) some mandelic acid derivatives (19,21,34) and ethyltoluene (28). Both [Pg.225]

Fluorescence detection at 284/310 nm (extinction/ emission wavelengths) leads to a detection limit of 1.3 mmol/L (0.14 mg/mL for / -cresol). Identification of phenol and /7-cresol may be confirmed by liquid chroma- tography/mass spectrometry. Because HPLC methods require only simple extraction, e.g., by ethyl acetate, and do not require further steps such as derivatization, they j are simple and rapid compared with gas chromatography or gas chromatography/mass spectrometry. Such methods I are useful for monitoring serum phenols in dialyzed patients as an index of hemodialysis adequacy. How- ever, the separation of the three isomers of cresol can only be performed by adding 3-cyclodextrin to the c liquid phase. q... 

Pure cresol is colorless, yellowish, brownish-yellow, or pinkish liquid. o-Cresol, m-cresol, and p-cresol are the three structural isomers of cresol. The names of the three compounds indicate which of the hydrogens on the benzene ring portion of the molecule have been replaced. They are obtained from coal tar or petroleum. Because the boiling points of these three compounds are nearly the same, a separation of a mixture of the three into its pure components is impractical. 

As in case of cresols, separation of individual isomers of xylenols had been a critical problem in organic chemistry. In case of cresols there are only three isomers whereas there are six isomers of xylenols and that makes it more difficult to isolate them as pure individual isomers. 

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