2.6- Xylenol, alkylation with

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). 

Because of the high antioxidant value of the p-cresol products, the work was extended to study the alkylation with a-olefins of three other readily available phenols phenol, 2,4-xylenol, and 2,6-xylenol. The nominal products were 2,4,6-tri(sec-alkyl)phenols, 6-(sec-alkyl)-2,4-xylends and 4-(sec-alkyl)-2,6-xylenols, as shown in the following reactions. Remember that these structural designations are for convenience the actual products are complex mixtures. Again, yields of the desired alkylated phenol were very high. The trialykylated phenol products were... 

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. 

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. 

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. 

While phenol is the most common monomer for novolac manufacture, it is far more common to see incorporation of other phenolic materials with novolacs than with resoles. Cresols, xylenols, resorcinol, catechols, bisphenols, and a variety of phenols with longer alkyl side chains are often used. While most resoles are made with a single phenolic monomer, two or more phenolic materials are often seen in novolac formulae. These additional monomers may be needed to impart special flow characteristics under heat, change a glass transition temperature, modify cure speed, or to adjust solubility in the application process among others. 

Many derivatives of phenol are now made by a synthetic process. Homologous series of substituted derivatives have been prepared and tested for antimicrobial activity. A combination of alkyl substitution and halogenation has produced useful derivatives including clorinated phenols which are constituents of a number of proprietary disinfectants. Two ofthe most widely used derivatives are/ -chloro-m-cresol (4-chloro-3-methylphenol, chlorocresol, Fig. 10.7C) which is mostly employed as a preservative at a concentration of 0.1%, and / -chloro-m-xylenol (4-chloro-3,5-dimethylphenol, chloroxylenol. Fig. 10.7C) which is used for skin disinfection, although less than formerly. Chloroxylenol is sparingly soluble in water and must be solubihzed, for example in a suitable soap solution in conjunction with terpineol or pine oil. Its antimicrobial capacity is weak and is reduced by the presence of organic matter. 

The optical yield was found to be very sensitive to structural modifications of the achiral agent. For example, use of the more bulky FV or Bu substituents in the 3,5-positions of phenol resulted in lower optical yields. In some cases a reversal of the sense of asymmetric induction was observed. Systematic variation of reaction conditions using the best achiral component, 3,5-xylenol, established that optimum results were obtained in ether solvent at about - 15°C. There was also a minor but definite influence of the rate of addition of ketone as well as an effect of concentration on optical yield, with a slower rate being advantageous. The results of reduction of aryl alkyl ketones are shown in Table 9, along with comparative results of reduction with similar chiral auxiliary reagents. 

Figure 14. Time on stream dependence of (a) phenol conversion, and (b) orthoalkyl phenol selectivity on Cu0.5Co0.5Fe204 at optimum reaction conditions, described earlier. Different alkylation is indicated by the name of the alkylation agent in the left panel. 2,6-xylenol selectivity is given for methylation with MeOH/DMC.

We have prepared a number of new phenolic antioxidants by alkylating phenol, p-cresol, 2,4-xylenol, and 2,6-xylenol with a-olefins. All show appreciable antioxidant effectiveness in high temperature accelerated tests. In over-all potency, 2,6-dioctadecyl-p-cresol is the best, followed closely by 2,4,6-trioctadecylphenol. For the tests used in this study, molecular weight was found to be the controlling factor in the relationship of structure to effectiveness. 

Alkylphenols may be produced via the alkylation of phenol with methanol. This reaction produces predominantly anisole and o-cresol with methylanisole and xylenol also being obtained. Strong Bronsted acids are not required to effect these transformations, as both amorphous aluminas and silica/aluminas are active catalysts. Often o-cresol can be produced in 100% isomeric selectivity, particularly when the reaction is run over amorphous alumina based catalysts. When zeolites are used isomer selectivities are changed. 

Alkylation of phenol with methanol has been carried out over Lewis acid ion-exchanged Y-zeolites, FeY, ZnY, CdY and LaY at temperatures of 523, 573, 623, 673 and 698 K to give orfto-cresol, 2,6-xylenol and anisole. Selectivity to ortto-cresol decreases with increase of temperature, as it further reacts to give 2,6-xylenol . ... 

Alkyl phenols as mentioned earlier are phenol derivatives wherein one or more of the benzene ring hydrogens are substituted by an alkyl group. Cresols are monosubstituted methyl phenols, xylenols are dialkyl phenols with two methyl groups. Similarly other alkyl groups such as butyl phenols, butyl cresols are also examples of alkyl phenols. Some of them... 

However, production of xylenols from isomeric xylene mixtures or individual isomers via propylene alkylation has not been attempted so far, neither established commercially nor even been tried in a laboratory or pilot plant. As in benzene and toluene alkylation processes it has been reported that Mitsubishi Gas Chemical Co., Japan obtained 3,5 xylenol by oxidation of 3,5-dimethyl cumene by alkylation of m-xylene with propylene to 3,5-dimethyl cumene hydroperoxide and thereafter its cleavage to 3,5-xylenol. Economics of the process did not justify its commercialization [1,38]. 

Sulfur compounds such as alkyl and aryl thiols are treated with concentrated alkaline solutions in a process known as sweetening and cresols and xylenols are recovered from spent caustic washes, producing sodium cresolates/ xylenolates. 

Alkylation of phenols and phenol derivatives with olefins like isobutene, octene, and nonene to synthesize industrially very important alkylphenols, -cresols, or -xylenols is typically performed at temperatures between 80°C and 120°C. High yields and good selectivities are obtained at these temperatures by using Deloxan catalysts. The very good thermal stability of the Deloxan catalysts allows their use at even higher operating temperatures, like 110°C to 150°C, which results in a higher productivity. 

The ortho alkylation of phenol (6.24) has been carried out with a catalyst that was a solid solution of cerium(IV) and magnesium oxides.86 At 32% conversion, the selectivity was 90% for o-cresol and 8.6% for 2,6-xylenol. [The latter is a monomer for a poly(phenylene oxide), an engineering plastic.] There was no decay of activity. 

Pharmaceutical creosote preparations are derived from the processing of such woody plants as beechwood (von Burg and Stout 1992). Wood creosote (beechwood creosote) is a yellow, transparent liquid with a characteristic smoky odor, obtained by fractional distillation of wood tar. It is composed primarily of phenol, phenols, cresols, guaiacols, xylenols, and small amounts of alkyl-2-hydroxy-2-cyclopenten-l-ones. It has been used as an expectorant, a gastric sedative, a gastrointestinal antiseptic, and particularly as an antidiarrheal agent (Ogata et al. 1993). Wood creosote and coal tar creosote are chemically distinct, and should not be confused with one another (see Chapter 4). 

In certain cases side chains of aromatic compounds can be oxidized in an oxidizing alkali melt — the substance is heated at 200-300° with 3-4 parts of solid sodium hydroxide or potassium hydroxide to which a little water is added. This process has been recommended specifically for homologous phenols since the experiment can be made with the free phenol. An example is the conversion of 2,4-xylenol into 2-hydroxy-5-methylbenzoic acid, which shows also that the alkyl group next to the hydroxyl group is preferentially oxidized.400... 

The formation of cresols (and xylenols) by Friedel-Crafts type alkylation in the reaction of phenol with methanol at 300-450°C over a solid catalyst usually a modified metal oxide is an important and well established synthetic route (ref.22) and typically can result in predominantly o/p substitution (o-cresol,54%, p-cresol,30%, and m-cresol, 17%). Selectivity can be achieved with a magnesium oxide or metal oxide-iron oxide mixture to afford o-cresol and... 

The zeolite-catalysed alkylation of phenol or anisole (methoxybenzene) with methanol is a complex sequence of reactions taking place within ZSM-5 and ZSM-11 at 200-300 °C. As shown in Figure 4.3 (overleaf), the primary products are anisole and cresols (ortho-, rneta- and /7ara-methylphenols), but lesser amounts of xylenols (dimethylphenols) and methylanisoles are also found. Alkylation of both the benzene ring and the oxygen atom is faster when zeolite Y is used, but the selectivity for ortho-crQsol is greater when ZSM-5 or ZSM-11 is the catalyst. 

Alkylation of aromatic rings with an olefin or alcohol was thought to be an acid-catalysed process until MgO was found to be an excellent catalyst. In fact, alkylation of phenol with methanol to yield 2.6-xylenol is much more selective on MgO than on SIOt-AItOj. The... 

One of the more common difficulties in bonding pine veneers and chips is adhesive dryout. Dry-out is associated with the high liquid absorbancy of pine sapwood and it appears especially during long assembly times. This problem can be overcome by using resins modified through reaction with alkylated phenols, especially 3,4-xylenol [52]. Another technique used to achieve similar results is the manipulation of synthesis procedures used in preparing a standard PF resin [52]. The dry-out resistance imparted by alkylated phenols is due to an initial semithermoplastic character in the resin. This is derived from their monomer bifunctionality and the linear polymer that is consequently formed. 

Alkylation of mixed cresols using isobutylene, co-oxidation of cyclohexane and acetaldehyde, and chlorination of mixed xylenols are examples of gas-liquid organic reactions in which absorption of a gas is followed by reaction with two reactants in the liquid. This class of reactions can be represented as... 

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