2,6-Dimethylphenol, temperature

Dimethylphenol [95-65-8] M 122.2, m 65°, b 225°/757mm, pK 10.36. Heated with an equal weight of cone H2SO4 at 103-105° for 2-3h, then diluted with four volumes of water, refluxed for Ih, and either steam distd or extracted repeatedly with diethyl ether after cooling to room temperature. The steam distillate was also extracted and evaporated to dryness. (The purification process depends on the much slower sulfonation of 3,5-dimethylphenol than most of its likely contaminants.). It can also be crystd from water, hexane or pet ether, and vacuum sublimed. [Kester Ind Eng Chem (Anal Ed) 24 770 1932 Bernasconi and Paschalis J Am Chem Soc 108 29691986.]... 

The catalytic activity of Mg/Al/O sample in m-cresol gas-phase methylation is summarized in Figure 1, where the conversion of m-cresol, and the selectivity to the products are reported as a function of the reaction temperature. Products were 3-methylanisole (3-MA, the product of O-methylation), 2,3-dimethylphenol and 2,5-dimethylphenol (2,3-DMP and 2,5-DMP, the products of ortho-C-methylation), 3,4-dimethylphenol (3,4-DMP, the product of para-C-methylation), and poly-C-methylated compounds. Other by-products which formed in minor amounts were dimethylanisoles, toluene, benzene and anisole (not reported in the Figure). 

The intermolecular reaction of phenols with propiolic esters occurs in the presence of a Pd(OAc)2 catalyst to afford coumarin derivatives directly.48,48a An exclusive formation of 5,6,7-trimethoxy-4-phenylcoumarin is observed in the Pd(OAc)2-catalyzed reaction of 3,4,5-trimethoxyphenol with ethyl phenylpropiolate in TFA (Equation (46)). Coumarin derivatives are obtained in high yields in the cases of electron-rich phenols, such as 3,4-methylenedioxyphenol, 3-methoxyphenol, 2-naphthol, and 3,5-dimethylphenol. A similar direct route to coumarin derivatives is accomplished by the reaction of phenols with propiolic acids (Equation (47)).49 A similar reaction proceeds in formic acid at room temperature for the synthesis of coumarins.50,50a Interestingly, Pd(0), rather than Pd(n), is involved in this reaction. 

Figure 2.2 Separation of aromatic compounds using isocratic elution. Conditions column, 5 pm Cis-bonded silica gel, 15 cm x 4.6 mm i.d. eluent, 0.001 M phosphoric acid in 55% aqueous acetonitrile flow rate, 1ml min-1 temperature, ambient, detection, UV 254 nm. Peaks 1, phenol, 2, 4-methylphenol 3, 2,4-dimethylphenol 4, 2,3,5-trimethylphenol 5, benzene, 6, toluene, 1, ethylbenzene, 8, propylbenzene and 9, butylbenzene.

It is well known that 2,6-dimethylphenol is oxidatively polymerized to poly(2,6-dimethyl-l,4-phenyleneoxide) with a copper amine complex as catalyst in the presence of oxygen at room temperature (Eq. 1)... 

Poly(2,6-dimethylphenylene ether) can be prepared by dehydrogenation of 2,6-dimethylphenol with oxygen in the presence of copper(l) chloride/pyridine as catalyst at room temperature. It is known that the mechanism involves a stepwise reaction, probably proceeding via a copper phenolate complex that is then dehydrogenated. 

A. 3,5-Dimethylphenyl 1-bromo-2-naphthoate (3). Under a nitrogen atmosphere, a 250-mL, oven-dried, round-bottomed flask containing anhydrous dichloromethane (100 mL) is charged with 1-bromo-2-naphthoic acid (1, 2.51 g, 10.0 mmol), 3,5-dimethylphenol (2, 1.23 g, 10.1 mmol), dicyclohexylcarbodiimide (DCC, 2.26 g. 11.0 mmol), and 4-(dimethylamino)pyridine (DMAP, 244 mg, 2.00 mmol) (Note 1). After the mixture is stirred for 12 hr at room temperature, the white precipitate that forms (Note 2) is discarded by filtration through a Buchner funnel. From the clear filtrate, the solvent is removed by rotary evaporation (35°C, 720 mbar, 540 mm) to give a colorless solid. RItration through a short silica gel column (5 x 40-cm column, silica gel 0.063 - 0.2 mm, 150 g eluent hexane / diethyl ether 5 1) delivers 3.35 g (94%) of the ester 3, which Is recrystallized from diethyl ether / hexane to give 3.28 g (92%) of a colorless solid (Note 3). 

The oxidative polymerization reaction is rapid at room temperature. Oxidation of 2.6-dimethylphenol readily gives high polymer with only a minor amount of the diphenoquinone (VIII R=R1=CH3). This polymer is now being produced commercially. In general when the substituents are small (Table 4) the polymer is formed preferentially (35). If one of the substituents is as large as tert-butyl or both as large as isopropyl then the diphenoquinone is preferentially formed. 

In the former case the diphenoquinone is formed exclusively while in the latter case small amounts of low molecular weight polymer have been observed. As would be expected, substituents which raise the oxidation potential of the phenol retard the polymerization. Thus whereas 2.6-dimethylphenol polymerizes readily at room temperature, temperatures in the neighborhood of 60° C are required to polymerize 2-chloro-6-methylphenol at comparable rates and even higher temperatures are necessary to oxidize 2.6-dichlorophenol. 

Methoxy- and amino-substituted disilenes behave differently from 1529. Irradiation of a hexane solution of 20 in the presence of various alcohols at room temperature afforded 1,1-dialkoxyhydrodisilanes 28a-32a together with a small amount of the regioisomers 28b-32b (Scheme 5). Thus alkoxy groups direct the alcohol addition to the alkoxy-substituted silicon atom. The ratios of regioisomers (a/b) were 100/0 (EtOH, 28), 96/4 (i-PrOH, 29) and 93/7 (t-BuOH, 30). Steric bulkiness is not the only factor that determines the regioselectivity, since bulky but acidic alcohols, such as 2,6-dimethylphenol... 

PdCl2(PhCN)2-catalysed Claisen rearrangement of the allyl vinyl ether 474 derived from cyclic ketone at room temperature affords the syn product 475 with high diastereoselectivity [203]. In contrast to thermal Claisen rearrangement, the Pd(II)-catalysed Claisen rearrangement is always stereoselective, irrespective of the geometry of allylic alkenes. The anti product is obtained by the thermal rearrangement in the presence of 2,6-dimethylphenol at 100 °C for lOh. 

The ability to polymerize readily via selective oxidation utilizing the abundant and cheap oxidant 02 often represents a desirable low-cost method for upgrading the value of a raw material. The most successful example is the oxidative polymerization of 2,6-dimethylphenol to yield poly(2,6-dimethyl-l,4-phenylene ether) with copper-amine catalysts under an 02 atmosphere at room temperature. Thiophenol also has a labile hydrogen but is rapidly oxidized to yield thermodynamically stable diphenyl disulfide. This formation is based on the more facilitated formation of S—S bond through radical coupling [82] in comparison with the formation of C—S—C bond through the coupling with the other molecules in the para position (Eq. 9). 

The stability of the furan ring in the environment of acid-catalyzed mixtures was investigated by an experiment where 1 mole of furfural was added to a mixture containing 0.67 mole 1,1-dimethylurea (DMU), 1.33 moles 2,4-dimethylphenol, and acid catalyst. The hindered urea and phenol were chosen to limit products to simple, small compounds. To limit losses of the somewhat volatile furfural (bp 162 °C) over the 3-hour reaction time, the reaction flask was heated by a steam bath, using vapor temperatures (36 to 69 °C) much lower than in previous experiments. 

Reported aqueous solubilities of 2,3-dimethylphenol at various temperatures Erichsen Dobbert 1955... 

FIGURE 14.1.1.5.1 Logarithm of vapor pressure versus reciprocal temperature for 2,3-dimethylphenol. 

TABLE 14.1.1.6.1 Reported aqueous solubilities and Henry s Aqueous solubility law constants of 2,4-dimethylphenol at various temperatures Henry s law constant ... 

FIGURE 14.1.1.6.1 Logarithm of Henry s law constant versus reciprocal temperature for 2,4-dimethylphenol. 

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