Cresol from cymene

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. 

This method is capable of producing p- or m-cresol from the corresponding cymene (isopropyltoluene). Alkaline chlorotoluene hydrolysis is used to formulate a cresol mixture with a high m-cresol content. However, information pertaining to domestic use of this process was unavailable (Fiege and Bayer 1987). 

It has been recently announced that technology for separation of para- and meto-cymenes is offered by Chiyoda Corporation in Yokohama, Japan through Kellog. As in the case of phenol from benzene via cumene, acetone is obtained as a co-product during production of cresols from toluene via cymenes. 

Carvacrol and Thymol, CH3.C3H7.C6H3.OH, are phenols derived from cymene (p-methyl-isopropylbenzene). In carvacrol the hydroxyl group is ortho to the methyl radical this is shown by the fact that carvacrol is converted into o-cresol and propylene when heated with phosphorus pentoxide. In thymol the hydroxyl group is ortho to isopropyl. 

The cumene is oxidized to cymene hydroperoxide, which decomposes to cresols and acetone. The process is similar to phenol (qv) production from cumene. 

The oldest cresol production method used in the United States is through the recovery of fractional distillates from coal tars. Most domestic cresols are formed via catalytic and thermal cracking of naphtha fractions during petroleum distillation. Since 1965, quantities of coal tar and petroleum isolates have been insufficient to meet the rising demand. Consequently, several processes for the manufacture of the various isomers have been developed. One General Electric facility produces o-cresol at an annual capacity of 10,000 tons by the methylation of phenol in the presence of catalysts. The Sherman-Williams Company uses the toluene sulfonation process and maintains an annual capacity for p-cresol of 15,000 tons. The Hercules Powder Company produced p-cresol until 1972 by the cymene- cresol process. 

Friedel-Crafts technology and zeolite- or other solid catalyst-based processes are currently used for other aromatic alkylations, in particular for the manufacture of linear alkylbenzenes (LABs) made from C10-C14 olefins (Equation 8), or from the corresponding chloroparaffins and benzene, and also to make m- and p-cymene (isopropyltoluene Equation 9). LABs are used for the production of sulfonate detergents, while cymenes lead to m- and p-cresols through a procedure analogous to that used for the cumene-to-phenol process. 

The proofs for the above constitutions are as follows (i) Thymol yields cymene, i-methyl 4-iso-propyl benzene, by loss of the hydroxyl oxygen by means of phosphorus penta-sulphide. (2) Carvacrol may be synthesized from potassium cymene sulphonate by fusion with potassium hydroxide. Therefore both must be mono-hydroxy cymenes. (3) Thymol by means of phosphorus pentoxide splits off the iso-propyl radical yielding meta-cresol and propylene. (4) Carvacrol by the same reaction yields ortho-cresol. Therefore in thymol the hydroxy group is meta to the methyl group while in carvacrol it is ortho. The following relationships are thus established. 

Thymol is obtained from the volatile oil of thyme Thymus vulgaris Linne (Fam Labiatae)) by fractional distillation followed by extraction and recrystallization. Thyme oil yields about 20-30% thymol. Thymol may also be produced synthetically from p-cymene, menthone, or piperitone, or by the interaction of m-cresol with isopropyl chloride. 

Use Solvents, synthetic-resin manufacture, metal polishes, organic synthesis (oxidation to hydroperoxides used as catalysts for synthetic-rubber manufacture cymene alcohols are made by hydrogenating the hydroperoxides). Purep-cresol and carvacrol are made from p-cymene. 

Production of cresols based on alkylation of toluene, oxidation of cymenes, or isopropyl toluenes and cleavage into cresols and acetone is a direct extension of phenol process from benzene. The process is, however, more complex since three isomeric cymenes and cresols are involved. The chemistry of the process is as follows ... 

Mitsui Petrochemical Industries Limited and Sumitomo Chemical Co. Ltd., Japan have been operating two 20,000 tpa plants wherein they produce mixed cresols (60% m-cresol and 40% p-cresol mixture) for the last many years. However, they do not separate the mixture of meta- and para-cymenes but convert the cymenes mixture to meto-para-cresols. M/s. Yanshen Petrochemicals, China near Beijing have been operating a similar 20,000 tpa meto-para-cresols plant based on alkylation of toluene. Both the Japanese and Chinese plants have been producing pure meto-cresol and BHT. Through a recent agreement, Sumitomo Chemicals sell 10,000 tpa cresols mixture to Merisol and the remaining 10,000 tpa m-p-cresols are converted pure meto-cresol and BHT. From environmental point of view, cresol plants based on alkylation of toluene are much cleaner and more eco-friendly than those based on sulfonation of toluene. 

There are more than 150 natural essential oils and natural extracts from which a large number of important flne chemicals in the field of flavor and fragrances have been extracted, isolated, and sold as blends in predetermined quantities. Table 10.1 gives some details of only those natural substances containing cresols, precmsors such as cymenes, derivatives such as thymol, menthol, and other allied products. 

Treatment of p-cymene, p-methylisopropylbenzene, by the peroxidation-decomposition process yields p-cresol and acetone. Starting with diisopropylbenzene, either the mono- or dihydroperoxide may Be obtained and from these a variety of products including isopropylphenol, isopropylace-tophenone, hydroquinone, diacetylbenzene, and others, depending- on the decomposition technique. 

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. 

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