Production of Individual Cresols

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. 

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Uses of individual cresols, i.e. p-cresol, m-cresol and o-cresol, have been illustrated vide Figs. 5, 6 and 7. A number of downstream derivatives based on individual cresols have been examined in some detail. Properties, technologies, and marketability of these products along with brief details about the existing manufacturers have been highlighted in Chapters 5-7. 

Since before World War II, multimillion pound quantities of cresols have been produced annually in the United States (O Brochta 1949), and domestic production and sales of cresols have steadily increased in recent years. Approximately 57.3 (USITC 1986), 73.3 (USITC 1988), and 82.3 (USITC 1989) million pounds of cresols were produced annually in the United States in 1986, 1987, and 1988, respectively. Respective sales were 56.6 (USITC 1986), 66.8 (USITC 1988), and 72.1 (USITC 1989) million pounds. These production totals include data on the manufacture of cresylic acid and exclude information on cresol production by coke and gas-retort ovens. The commercial mixture of cresol isomers, in which the m-isomer predominates and contains less than 5% phenol, is sometimes referred to as cresylic acid (Windholz et al. 1983). However, cresylic acids generally are composed of cresols, phenols, and xylenols they are defined as those mixtures in which over 50% will boil at temperatures above 204 C (Sax and Lewis 1987). In 1987, the national capacity for producing cresylics was 208 million pounds per year (CMR 1987). Information regarding the production levels of individual isomers and specific mixtures was unavailable. 

Very little information regarding the release of individual isomers was located in the literature. A coal liquefaction waste water effluent contained o- cresol at a concentration of 586 mg/L (Fedorak and Hrudey 1986). o-Cresol was detected at an average concentration of 1.1 pg/L for three samples of retort water from a shale oil production facility (Hawthorne and Sievers 1984). 

Though traditionally obtained from coal tar or from fractions during secondary refining processes of petroleum, they are also obtained as mixed xylenols from a mixture of xylenes CAS no. [1330-20-7] or as pure isomers from individual xylems i.e., m-xylene, o-xylene, or p-xylene. Process chemistry for production of xylenols from xylenes is similar to that of cresols from toluene (see Chapter 2), i.e., sulfonation of the respective aromatic hydrocarbons, followed by neutralization of the sulfonic acids, caustic fusion and acidification of the sodium/potassium salts and purification via distillation. Summary of principal properties of xylene isomers has been shown vide Table 1.1. 

It was heartening to see that for many end products, individual cresols proved to be very effective alternative feedstocks to more conventional and traditional ones such as phenol. For instance, p-hydroxy benzaldehyde was hitherto obtained as a by-product during production of salicyl aldehyde from phenol based on Reimer-Tiemann reaction. In fact, phenol-based p-hydroxy benzaldehyde is only 15% of the mixed aldehydes, and 85% of the product is o-hydroxy benzaldehyde or salicylaldehyde. Direct oxidation of 79-cresol to 187... 

Cresols are used widely by industry. Information from the EPA s Toxic Release Inventory (TRI) on facilities that either manufactured or processed cresols in 1987 is outlined in Table 4-1. The TRI data should be used with caution since the 1987 data represent first-time reporting by these facilities. Only certain types of facilities were required to report. This is not an exhaustive list. According to the United States International Trade Commission (USITC 1987, 1988, 1989) and the 1989 Directory of Chemical Producers (SRI 1989), cresols are currently produced by five manufacturers in New York, New Jersey, Pennsylvania, Illinois, and Texas. USITC (1987, 1988, 1989) and Stanford Research Institute (SRI 1989) data for individual isomers and the mixture o-, p-, and m-isomers are included in Tables 4-2a through 4-2d. Data from the TRI do not agree with those from the USITC and SRI. For example, the Sloss Industries Coke Plant, which appears to meet SRI and USITC production criteria, was not listed with USITC (1987, 1988, 1989) or SRI (1989)-... 

Table 2. Product distribution obtained in 7-radiolysis of deoxygenated and oxygenated solutions of chlorotoluenes and cresols. Taken from Ref 14 [The numbers are the G values of the individual phenolic products formed in deoxygenated (given in parantheses) and oxygenated solutions of chlorotoluenes (X = Cl) and cresols (X = OH). The total yields are based on G( OH) = 5.6 per 100 eV. n.f = not...

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