P-Cresol, alkylation

The fert-butyl carbocation acts as an electrophile and alkylates p-cresol. Alkylation occurs ortho to the -OH group for both steric and electronic reasons. 

The food preservative BHT is prepared by Friedel-Crafts alkylation of p-methylphenol (p-cresol) wnth 2-methyIpropene in the presence of acid BHA is prepared similarly by alkylation of p-methoxyphenok... 

The retention indices, measured on the alkyl aryl ketone scale, of a set of column test compounds (toluene, nitrobenzene, p-cresol, 2-phenyl ethanol, and IV-methylaniline) were used to determine the changes in selectivity of a series of ternary eluents prepared from methanol/0.02M phosphate buffer pH 7 (60 40), acetonitrile/0.02 M phosphate buffer pH 7 (50 50) and tetrahydrofuran/0.02 M phosphate buffer pH 7 (25 65). The analyses were carried out on a Spherisorb ODS reversed-phase column. The selectivity changes were often nonlinear between the binary composition [83]. 

Davassy, B., Shanbhag, G., Lefebvre, F., and Halligudi, S. (2004) Alkylation of p-cresol with tert-butanol catalyzed by heteropoly acid supported on zirconia catalyst. J. Mol. Catal. A Chem., 210, 125-130. 

Bennett and Larter (1997) also studied the solvation of alkylphenols in crude oil-water systems at equilibrium to obtain partitioning coefficients under variable temperature, pressure, and water salinity concentration. Alkylphenol depletion from crude oil, expressed by phenol, cresols, and 3,5 dimethyl phenol, versus temperature in a range of 25-125°C, is given in terms of partition coefficient (P) values (Fig. 16.22). Partition coefficient values increase with addition of alkyl groups to the phenol nucleus. Note that the alkylphenol partition coefficient curves for different isomers tend to converge at higher temperatures and, as a consequence, differences between phenol and p-cresol decrease with increases in temperature. Similar results for oil-deionised water and oil-brine experiments show that increasing temperature leads to a decrease in partition coefficient values. 

Fraction 8 (Figure 5 5) is mostly alkylated phenols and indanols with a trace amount of smaller alkanes. The base line shift is due to the co-elution of several large phenolic species in many isomeric forms. Fraction 9 (Figure 5-6) does not contain any alkanes. The ratio of the o-cresols to m, p-cresols increases from fraction 8 to 9. Both m-cresol and p-cresol are structurally longer than o-cresol. Some long aromatic species such as biphenyls also appear in this fraction. Compared to fraction 8, the phenols in fraction 9 are of shorter size... 

Phenols are a major chemical lump present in coal liquids. Phenols have basically one or more aromatic ring structures with alkyl substituents. Methyl, ethyl and propyl are the most common alkyl substituents. The smallest specie is the one with a hydroxyl group attached to a benzene ring. Addition of a methyl group produces three isomers - o-, m-, and p-cresols. It appears that all three are present in more or less same proportion. The number of possible isomers increases as the possible number and size of alkyl substituents increases. It is expected that higher... 

Alkylation of p-cresol with isobutylene to give ter/-butyl-4-methyl phenol [Eq. (38)] is the first step in the synthesis of agidol-2, an antioxidant for polymeric materials (160). 

Similar results have been obtained in the reactions of 1 and sodium salts of p-cresol and - and /J-naphthols. Under SN2 conditions (DMF or DMSO solvent), the alkylation of sodium cresolate occurs exclusively at the oxygen atom. The addition of a protic solvent causes C-alkylation, though the yields of C-alkylated products are low. Thus in acetone-water or dioxane-water, the yield of C-alkylated products 251 and 252 increases only up to 2%. C-Alkylation has also been observed in the reactions catalyzed by trifluoroacetic acid or boron trifluoride etherate at room temperature. The observed C-alkylation in protic media may be a reflection of a mechanism that involves a protonated epoxide or a more polarized transition state than in an SN2 pathway. 

Schuchmann MN, Steenken S, Wroblewski J, von Sonntag C (1984) Site of OH radical attack on dihydrouracil and some of its methyl derivatives. Int J Radiat Biol 46 225-232 Schuler RH, Albarran G, Zajicek J, George MV, Fessenden RW, Carmichael I (2002) On the addition of OH radicals to the ipso position of alkyl-substituted aromatics production of 4-hydroxy-4-methyl-2,5-cyclohexadien-1-one in the radiolytic oxidation of p-cresol. J Phys Chem A 106 12178-12183... 

Antioxidant additives DBPC = 2,6-di-tert-butyl-p-cresol, B = alkyl-diphenyl amine Extreme-pressure additives DBDS = dibenzyl disulfide (C6H5-CH2-S-S-CH2-C6H5 ), DPDS = diphenyl disulfide (C6H5-S-S-C6H5) ... 

Allylphenols and derivatives with substituents in the allyl group can, be prepared by direct C-alkylation of the sodium salt of the phenol in benzene solution.16 This method is not as good for the preparation of allylphenols themselves as the one involving preparation of the allyl ether followed by rearrangement, because a mixture of several products is obtained in C-alkylation. Thus the alkylation of p-cresol in benzene with sodium and allyl bromide yields 20% of allyl 4-methylphenyl ether, 8% of allyl 2-allyl-4-methylphenyl ether, 40% of 2-allyl-4-methyl-phenol, and 15% of 2,6-diallyl-4-methylphenol.16 The rearrangement of allyl 4-methylphenyl ether, however, yields 2-allyl-4-methylphenol in practically quantitative yield, and the ether is easily obtained. 

Our initial investigation included a study of the alkylation of p-cresol with propylene oligomers and with various a-olefins. Because all alkylations were carried out by a well-known procedure and neither novel reactions nor unexpected results were encountered, no detailed experimental work will be reported As shown by the following reaction, all alkylations were carried out using BF3 catalyst at 80°-90°C. and excess olefin as the reaction solvent. 

If we do not consider possible skeletal rearrangements, 1-hexene can produce either a 1-methylpentyl or a 1-ethylbutyl substituent when alkylating p-cresol and thus give three... 

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... 

Figure 1 shows the results for the 2,6-dialkyl-p-cresols. In Figures 1 and 2, the hours-to-failure scale on the right applies to the two most severe tests using the 5-mil film, while the scale on the left is for the less severe tests using 65-mil bars. In general, increasing the size of the alkyl... 

All four types of phenols alkylated by a-olefins are effective antioxidants. However, the alkylated p-cresols are the most effective, followed closely by the 2,4,6-trialkylated phenols. The alkylated xylenols have a lower degree of effectiveness in polypropylene. Of the entire series, 2,6-dioctadecyl-p-cresol has the best over-all properties. It is one of the most effective non-discoloring antioxidants now known for polypropylene. It is especially useful under adverse conditions, such as high temperatures, or in thin films. 

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. 

Regiocontrol Although Michael additions to [Os]-phenol occur selectively at C4, addition at C2 is thermodynamically favored for phenol complexes that are substituted at C4. For C4-substituted phenol complexes, the regiochemistry can be controlled by varying the time, temperature, and catalyst (Figure 6) [29]. Additions of MVK to the estradiol complex 90 and the p-cresol 94 at —40 °C in the presence of an amine base catalyst result in regioselective C4 alkylation in high yields (91 and 95). However, when this reaction is performed at room temperature in the presence of a Zn2+ co-catalyst, the Michael acceptor adds at C2 to afford... 

In other cases substituents compete by directing to different positions. For example, in the synthesis of the food preservative BHT (p. 30) from 4-methylphenol (p-cresol) by a Friedel-Crafts alkylation, the methyl and OH groups each direct ortho to themselves. The -OH group is much more powerfully directing than the methyl group because it provides an extra pair of electrons, so it wins and directs the electrophile (a t-butyl cation) ortho to itself. The t-butyl cation can be made from the alkene or t-butanol with protic acid or from t-butyl chloride with AICI3. 

The substituted phenols and cresols constitute about half the total volume of this group. Para-t-butylphenol is produced by the alkylation of phenol with isobutylene. The principal applications for this derivative are in the manufacture of modified phenolic resins for the rubber industry and in surface coatings. BHT is obtained from isobutylene and p-cresol. Technical-grade BHT is an antioxidant for plastics and elastomers, and is a gum inhibitor in gasoline. Food-grade BHT is an antioxidant in edible oils, preserves, and many other foods. 2,6-Di-t-butylphenol is used to produce a wide range of plastics additives, antioxidants, and gasoline additives. 

BHT is prepared by Friedel-Crafts alkylation of p-cresol with 2-methylpropene. 

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. 

Example 12.2 Determination of the greenness of a reaction The alkylation of p-cresol using a heterogeneous acid catalyst. 

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