Alkylated cresols, determination

Thin-layer liquid chromatography has been employed for the determination of alkylated cresols and amine antioxidants [102, 103] in polybutadiene, phenolic antioxidants in PE [104-106] and PP [106], dilauryl and distearyl thiodipropionate antioxidants in polyolefins, ethylene-vinyl acetate copolymer, acrylonitrile-styrene terpolymer and PS, UV absorbers and organotin stabilisers in polyolefins [102], and accelerators such as guanidines, thiazoles, thiurans, sulfenamides, diethiocarbamides, and morpholine disulfides in unvulcanised rubber compounds. 

Solvent extraction gas chromatographic methods have been described for determining alkylated cresols (2,6-di-tert-butyl-p-cresol) and amine antioxidants (N-phenyl-2-naphthylamine, p-phenylene diamine type) and Santoflex (NN sec-heptyl phenyl-p-phenylene diamine) in polybutadiene. 

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

Alkyl-substituted phenols have different reactivities than phenol toward reaction with formaldehyde. Relative reactivities determined by monitoring the disappearance of formaldehyde in phenol-paraformaldehyde reactions (Table 7.3) show that, under basic conditions, meta-cresol reacts with formaldehyde approximately three times faster titan phenol while ortho- and para-cresols react at approximately one-third the rate of phenol.18 Similar trends were observed for the reactivities of acid-catalyzed phenolic monomers with formaldehyde. 

A method suitable for quantification of the functional class of bis(ethanol)amine antistatics, which lack UV chromophores, consists of reaction with methyl orange [53]. Atmer 163 (alkyl-diethanol amine) has been determined as a yellow complex at 415 nm after interaction with a bromophenol/cresole mixture [64]. Hilton [65] coupled extracted phenolic antioxidants with diazotised p-nitroaniline in strongly acidic medium and carried out identification on the basis of the visible absorption spectrum in alkaline solution. The antioxidant Nonox Cl in... 

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]. 

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

With the aim of studying the acid-base properties of Mg-Fe mixed oxides we chose the alkylation of m-cresol with methanol as a model reaction. The distribution of products obtained may take account of the different surface properties of the catalysts [3,4]. The catalytic performances were compared with the acid and basic sites distributions, as determined by pyridine and CO2 adsorption and desorption, respectively. 

Equation (2.57) provides a means of determining the relative contribution of the termination and transfer steps. Thus, if kp is largely relative to kt, the molecular weight will be virtually independent of monomer concentration, but if the reverse is true, X will be directly proportional to [A/]. Hence this relation lends itself to a simple experimental test, i.e., a plot of 1/X" (the reciprocal of the initial X value) against 1 /[MY (the reciprocal of the initial monomer concentration). It has actually been found that the polymerization of styrene by SnCU in ethylene dichloride (Pepper, 1949), and of vinyl alkyl ethers by SnCU in m-cresol (Eley and Richards, 1949), showed a dominance of termination over transfer, i.e., X a [M] however, for isobutylene polymerization catalyzed by TiCU in -hexane (Plesch, 1950), the observed polymer molecular weights were independent of monomer concentration, i.e., transfer appeared to predominate. 

The results discussed in the previous section reveal that the reaction rate corresponding to the formation of major by-products of the oxidation reaction is important to determine the lifetime of dimethylphenol in the atmosphere. The rate constants are calculated using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) corrections over the temperature range of 278-350 K. As described in Figure 19.2, the formation of product channels consists of four reaction channels. The rate constants for the formation of alkyl radical (11), peroxy radical (12), m-cresol and the product channels are designated as k, ki2, and kp, respectively, and are summarized in Tables 19.2 and 19.3. The reaction path properties and rate constant obtained for the most favorable product channels, P5 and P6, are discussed in detail. 

As might be expected, the type of feedstock chemical and industrial process play a key role in determining the presence of phenols in wastewater. For example, the nitration of benzene and toluene to produce nitrobenzene and dinitrotoluene also leads to the incidental formation of nitrophenol, dinitrophenol, and dinitro-o-cresol. Similarly, alkylphenols and methyl-phenols may be produced during alkylation and solvent extraction of toluene, xylene, and Cg-Q alkylphenols. Wise and Fahrenthold (1981) suggested that most industrial processes were not sources of priority pollutants because the processes do not involve critical precursor/process combinations. In addition, synthetic production methods generally lead to an increase in complexity of priority pollutant molecules. These in turn exhibit variable toxicity and persistance, which may be comparable to related priority pollutants. 

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