2.4- Xylenols, 6-

We turn now to the methyl disubstituted pyridines (lutidines), phenols (xylenols) and anilines, for which the AG, AH and AS values for the ionization process are available. 

Estimated and observed free energies of ionizoHon for the lutidines (dimethylpyridiries) 

Despite the fact that d is not a simple quantity, but a function oi AH and A S, its variation with change of structural parameters obeys a simple relationship, as may be seen from the additivity of A O values. This term is used here in the sense that the thermodynamic quantities for disubstituted compounds may be predicted from the changes produced when single substituents are introduced separately. The free energies of ionization of some methyl disubstituted pyridines, anilines and phenols are shown in Table 4 (to which we shall refer in detail later). From A G values for the parent and mono-substituted compounds it is possible to estimate A G values for disubstituted compounds. Thus, from the A G values for p ridine and the picolines, the following increments are calculated 2-methyl 1 01, 3-methyl 0-56, 4-methyl 1 03. 

The use of these values leads to the estimated A G values shown in Table 3, and these are in satisfactory agreement -with the observed values. Similar correlations are found for the phenols and anilines. 

6-Xylenol reacts with ammonia to yield 2,6-xylidine, a base material for the fungicide metalaxyl (Ciba Geigy). 

5-Dimethylphenol is not directly accessible by selective alkylation of phenol with methanol it is produced by the aromatization of isophorone at 540 to 650 °C on Cr203/K20/Al203 catalysts, or chrome-nickel steel. 

1 Vaporizer/Heater 2 Reactor 3 Gas separator 4 RDC-extractor 5 Saturation column 6 Phase-separation vessel 

An important product from 3,5-dimethylphenol is the insecticide methiocarb (Bayer), which is manufactured by the reaction of 3,5-dimethylphenol with methylsulfenyl chloride to yield 4-methylmercapto-3,5-xylenol followed by reaction with methyl isocyanate. 

5-Dimethylphenol is also used as a building block in the synthesis of vitamin E (a-tocopherol) and, after chlorination to 4-chloro- and 2,4-dichloro-3,5-dime-thylphenol, as a disinfectant and commercial preservative in addition, ammonoly-sis yields 3,5-dimethylaniline, an intermediate for pigments. 

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Cm.OROCARBONSANDCm.OROHYDROCARBONS - BENZYL CTD ORIDE, BENZAL CTD ORIDE AND BENZOTRICm ORIDE] (Vol 6) p-Chloro-m-xylenol [88-04-0]... 

Triaryl phosphates are produced from the corresponding phenols (usually mixtures) by reaction with phosphoms oxychloride, usually in the presence of a catalyst (94—96). They are subsequently distilled and usually washed with aqueous bases to the desired level of purity. Tricresyl phosphate was originally made from petroleum-derived or coal-tar-derived cresyflc acids, ie, cresols, variously admixed with phenol and xylenols. Discovery of the toxicity of the ortho-cresyl isomers led manufacturers to select cresols having very Httle ortho-isomer. 

X5lenol is an important starting material for insecticides, xylenol—formaldehyde resins, disinfectants, wood preservatives, and for synthesis of a-tocopherol (vitamin E) (258) and i7/-a-tocopherol acetate (USP 34-50/kg, October 1994). The Bayer insecticide Methiocarb is manufactured by reaction of 3,5-x5lenol with methylsulfenyl chloride to yield 4-methylmercapto-3,5-xylenol, followed by reaction with methyl isocyanate (257). Disinfectants and preservatives are produced by chlorination to 4-chloro- and 2,4-dich1oro-3,5-dimethylpheno1 (251). 

Triaryl phosphates are produced by reaction of phosphoms oxychloride with phenoHc compounds at 100—200°C with magnesium or aluminum chloride catalyst. Past use of cresols and xylenols from coal tar or petroleum is replaced for lower toxicity and cost by synthetic phenoHcs, primarily isopropyl phenol, /-butyl phenol, and phenol itself A range of viscosities is achieved by selection and proportioning of the phenols and their isomers used for the starting material. 

Alkylated phenol derivatives are used as raw materials for the production of resins, novolaks (alcohol-soluble resins of the phenol—formaldehyde type), herbicides, insecticides, antioxidants, and other chemicals. The synthesis of 2,6-xylenol [576-26-1] h.a.s become commercially important since PPO resin, poly(2,6-dimethyl phenylene oxide), an engineering thermoplastic, was developed (114,115). The demand for (9-cresol and 2,6-xylenol (2,6-dimethylphenol) increased further in the 1980s along with the growing use of epoxy cresol novolak (ECN) in the electronics industries and poly(phenylene ether) resin in the automobile industries. The ECN is derived from o-cresol, and poly(phenylene ether) resin is derived from 2,6-xylenol. 

Ciesol and xylenol can be prepared by the methylation of phenol with methanol over both acid and base catalysts. It is postulated that phenol methylation on acid catalysts proceeds through the initial formation of anisole (methoxybenzene [100-66-3]) followed by intramolecular rearrangement of... 

Other common names are cresol and xylenol for methyl- and dimethylphenols respectively, eg, o-cresol is 2-methylphenol, and 2,5-xylenol is... 

The solubihty of alkylphenols in water falls off precipitously as the number of carbons attached to the ring increases. They are generally soluble in common organic solvents acetone, alcohols, hydrocarbons, toluene. Solubihty in alcohols or heptane follows the generalization that "like dissolves like." The more polar the alkylphenol, the greater its solubihty in alcohols, but not in ahphatic hydrocarbons likewise with cresols and xylenols. The solubihty of an alkylphenol in a hydrocarbon solvent increases as the number of carbon atoms in the alkyl chain increases. High purity para substituted phenols, through Cg, can be obtained by crystallization from heptane. 

Methylphenol is converted to 6-/ f2 -butyl-2-methylphenol [2219-82-1] by alkylation with isobutylene under aluminum catalysis. A number of phenoHc anti-oxidants used to stabilize mbber and plastics against thermal oxidative degradation are based on this compound. The condensation of 6-/ f2 -butyl-2-methylphenol with formaldehyde yields 4,4 -methylenebis(2-methyl-6-/ f2 butylphenol) [96-65-17, reaction with sulfur dichloride yields 4,4 -thiobis(2-methyl-6-/ f2 butylphenol) [96-66-2] and reaction with methyl acrylate under base catalysis yields the corresponding hydrocinnamate. Transesterification of the hydrocinnamate with triethylene glycol yields triethylene glycol-bis[3-(3-/ f2 -butyl-5-methyl-4-hydroxyphenyl)propionate] [36443-68-2] (39). 2-Methylphenol is also a component of cresyHc acids, blends of phenol, cresols, and xylenols. CresyHc acids are used as solvents in a number of coating appHcations (see Table 3). 

Dimethjlphenol (2,6-xylenol) is produced by the gas phase alkylation of phenol with methanol using modified alumina catalysis. The cmde product contains 2-methylphenol, 2,6-dimethylphenol, a minor amount of 2,4-dimethylphenol, and a mixture of trimethylphenols. The 2,6-dimethylphenol is purified by fractional distillation. The mixture of di- and trimethylphenols is sold as cresyHc acid for use as a solvent. 2,6-Dimethylphenol [576-26-1] is available in 55-gal dmms (208-L) and in bulk shipments in tank wagons and railcars. 

When using a continuous vertical retort, phenols, cresols, and xylenols are collected in one fraction. A typical range of primary distillation fractions is given in Table 2. 

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