The sensitized photodehydrochlorination of poly(vinyl chloride)—II. Model compound studies

p-Cresol, a model compound for an additive shown previously to be a potent photosensitizer of dehydrochlorination in poly(vinyl chloride) PVC, has been shown to sensitize dehydrochlorination in t-butyl chloride, a model for PVC. A quantitative study of the effect of chlorinated alkanes upon the fluorescence of p-cresol in solution reveals that quenching is due to charge transfer interactions, the halogenated compound acting as electron acceptor. Since the mono-halo compound t-butyl chloride does not quench p-cresol fluorescence, it was concluded that the photosensitization occurs via the triplet state of the p-cresol, and this view was confirmed by addition of triplet quenchers. A mechanism for the reaction is proposed, initial exciplex formation being followed by electron transfer.     

Improved cross-metathesis of acrylate esters catalyzed by 2nd generation ruthenium carbene complexes

The performance of cross-metathesis reactions between acrylate esters and olefins catalyzed by Grubbs catalysts have been enhanced by the simple addition of p-cresol. For example, the efficiency of the cross metathesis reaction between methyl acrylate and 1-decene catalyzed by 2 was significantly increased by addition of p-cresol to the reaction mixture, resulting in increased product yields and E/Z ratios.     

Liquid-phase oxidation of 2-methoxy-p-cresol to vanillin with oxygen catalyzed by a combination of CoCl2 and N-hydroxyphthalimide

Liquid-phase oxidation of 2-methoxy-p-cresol to vanillin (4-hydroxy-3-methoxybenzaldehyde), in methanol, with molecular oxygen at atmospheric pressure as oxidant and a combination of cobaltous chloride and N-hydroxyphthalimide (NHPI) as catalyst, has been investigated. The effect of reaction conditions on conversion and selectivity for vanillin was studied systematically. Selectivity for vanillin could be enhanced by optimizing the molar ratio of 2-methoxy-p-cresol to NHPI, the amount of sodium hydroxide, reaction time, reaction temperature, and the volume of methanol, which determined the concentration of the reactants. Under the optimized conditions the yield of vanillin was 90.1 %.     

Electrochemical determination of p-cresol concentration using zeolite-modified electrodes

Carbon paste electrodes modified with different zeolites (MFI and FAU) were studied in order to evidence the electro-oxidation of p-cresol. Cyclovoltammetric experiments were applied by direct measurement in p-cresol-containing aqueous solution, or during release in solution without p-cresol after impregnation. In both cases, the electro-oxidation signal of p-cresol led to two oxidation peaks. Different concentrations of p-cresol were studied. Influences of charge compensating cations, electrode impregnation time and zeolite type were investigated. It was shown that electrochemical measurements could be used as a detection method for p-cresol in aqueous solution with a high sensitivity.     

Synthesis of 2-substituted quinones, vitamin K3, and vitamin K1 from p-cresol. BF3·OEt2-catalyzed methyl migration of 4-tert-butyldioxycyclohexadienones

BF₃·OEt₂-catalyzed methyl group migration of 4-methyl-4-tert-butyldioxycyclohexadienone, which is obtained by ruthenium-catalyzed oxidation of p-cresol with tert-butyl hydroperoxide, in hexafluoro-2-propanol/toluene gave toluquinone efficiently. The reaction can be applied to the regio-selective short-step syntheses of vitamin K₃ and vitamin K₁ from p-cresol.     

Partial oxidation of toluene with nitrous oxide under supercritical conditions

The partial oxidation of toluene with nitrous oxide over the H-ZSM-5 catalyst under supercritical conditions at temperatures of 370–420°C and pressures of 70–160 atm has been investigated for the first time. The maximum cresol selectivity under these conditions is 32%. The amounts of the resulting cresol isomers form the following decreasing sequence: m-cresol > o-cresol > p-cresol. The partial oxidation of toluene is accompanied by disproportionation and biphenyl formation.     

Degradation mechanism of <Emphasis Type="Italic">p</Emphasis>-cresol in aqueous solutions by gamma-ray irradiation

Degradation mechanism of p-cresol in aqueous solutions by gamma-ray irradiation was investigated at various initial p-cresol concentrations with different absorbed doses. The results show that p-cresol in aqueous solutions can effectively be degraded by gamma-ray irradiation. Chemical oxygen demand was used to assess the degree of mineralization of p-cresol. The degradation can be enhanced by the additions of free Radical Scavengers. The degradation products were identified by high-performance liquid chromatography with tandem mass spectrometric. Degradation mechanism of p-cresol in aqueous solutions were proposed according to the products analysis.     

Phase equilibria in systems containing o-cresol,p-cresol,carbon dioxide,and ethanol at 323.15–473.15 K and 10–35 MPa

Phase equilibria in binary and ternary systems containing o-cresol, p-cresol, carbon dioxide, and ethanol have been investigated experimentally at temperatures between 323.15 K and 473.15 K and pressures ranging from 10 MPa to 35 MPa. The experimental results provide a systematic basis of phase equilibrium data, yielding the effect of temperature on the influence of the position of the methyl groups of cresols that are in phase equilibria with carbon dioxide. Based on the different solubilities of the cresol isomers in carbon dioxide, the separation of o-cresol and p-cresol was investigated. The dependence of the separation factor between both cresol isomers on concentration, temperature, and pressure is obtained from experiments in the ternary system, o-cresol+p-cresol+carbon dioxide. The influence of ethanol added to each of the binary systems, cresol isomer+carbon dioxide, in order to enhance the solubility of the cresols in the carbon dioxide-rich phase is also shown. The experimental data have been correlated using seven different equations of state, whereof four explicitly account for intermolecular association: Statistical Association Fluid Theory (SAFT) by Chapman, Gubbins, Huang and Radosz, the SAFT modification by Pfohl and Brunner for near-critical fluids, a modified cubic-plus-association equation of state (CPA EOS) according to the ideas by Tassios et al., and one of the EOS by Anderko. The mixing rule proposed by Mathias, Klotz, and Prausnitz, with two binary interaction parameters per binary system influencing intermolecular attractive forces, is used for all EOS as a basis for an objective comparison of the EOS.     

Kohonen artificial neural networks as a tool for wavelength selection in multicomponent spectrofluorimetric PLS modelling: application to phenol,o-cresol,m-cresol and p-cresol mixtures

Different strategies for wavelength selection for partial least squared (PLS) calibration models have been proposed. In this article, Kohonen artificial neural networks (K-ANN) are used to select optimal sets of wavelengths for PLS calibration of mixtures with stray overlapping. This kind of variable selection appears simple and very effective due to the well known high correlation of spectroscopic data; a measure of the multivariate correlation of the different wavelength subsets is also given. This strategy has been applied to the resolution of mixtures of phenol, o-cresol, m-cresol and p-cresol by spectrofluorimetry. The number of samples to obtain the calibration matrix is also reduced with respect to the number necessary when the full spectrum is used, and the predictive ability of the PLS method is improved.     

The determination of p-cresol in chloroform with an enzyme electrode used in the organic phase

An enzyme electrode that operates in chloroform is described. Polyphenol oxidase (tyrosinase; EC.1.14.18.1) is used to detect p-cresol via electrochemical reduction of the product, 4-methyl- 1,2-benzoquinone, at a graphite foil electode. The response is linear for p-cresol concentrations of 0–0.10 mM, with a limit of detection of 1 μM. After an initial rise from 1.9 μA to 4.0 μA in the first three assays, the response of the electrode to 0.10 mM p-cresol remained stable for twelve consecutive assays ($\text{x}$=4.6, SD=0.49). After intermittent usage for 204 days with appropriate storage, the enzyme electrode remained active. The electrode is sensitive to a broad range of phenols. The feasibility of detecting p-cresol contamination of water is demonstrated.     

The coulometric titration of acids and bases in m-cresol medium

A method is described for the coulometric titration of acids and bases in the solvent m-cresol. The method is suitable for bases with pK_a values greater than 11 in m-cresol, or for acids with pK_a values below 13 in m-cresol. Amounts of 5–50 μeq of acid or base can be determined with a relative accuracy of ±1%.     

Sensitive, selective spectrophotometric determination of phenols with periodic acid

A new spectrophotometric determination of phenols with periodic acid has been developed. The colored product of phenol periodic acid reaction has a λ_max 380 nm. The determination of phenol, pyrocatechol, α-naphthol, β-naphthol, quinol, p-cresol, m-cresol, 8-quinolinol, resorcinol, phloroglucinol, and gallic acid has been done. The effects of possible variables e.g., temperature, reagent, pH buffers have been studied. A study of interferences is made. Mechanism of the reaction is discussed.     

Nitrosation kinetics of phenolic components of foods and beverages

The kinetics of the reactions between sodium nitrite and phenol or m-, o-, or p-cresol in potassium hydrogen phthalate buffers of pH 2.5–5.7 were determined by integration of the monitored absorbance of the C-nitroso reaction products. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of a diffusion-controlled attack on the nitrosatable substrate by NO⁺/NO₂H₂⁺ ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities (o-cresol ≈ m-cresol > phenol ≫ p-cresol) is explained by the hyperconjugative effect of the methyl group in o- and m-cresol, and by its blocking the para position in p-cresol. Analysis of a plot of ΔH^# against ΔS^# shows that the reaction with p-cresol differs from those with o- and m-cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO⁺/NO₂H₂⁺. © 1997 John Wiley & Sons, Inc.     

Flow injection-spectrophotometric determination of cresol compounds in water by reaction withp-aminophenol

A spectrophotometric method has been developed for the simultaneous determination ofo-cresol andm-cresol in water by reaction withp-aminophenol (PAP). Three different methodologies have been assayed; (i) batch analysis, after reaction in an alkaline medium in the presence of dissolved molecular oxygen as oxidizing agent, (ii) a stopped-flow procedure, carried out in the presence of KIO₄ and (iii) a flow injection method based on the same approach. The batch procedure requires 22 min for the full development of colour witho-cresol and 12 min form-cresol. In the stopped-flow mode, using KIO₄ and a reaction time of 12 min, better sensitivity can be obtained for both compounds and limits of detection of 10 g 1^–1 foro-cresol and 30 g 1^–1 form-cresol were found. The flow injection method has a lower sensitivity but permits more than 80 injections per hour. Based on the different maximum absorbance wavelengths obtained for the reaction products of PAP witho-cresol (614 nm) andm-cresol (632 nm), both compounds can be simultaneously determined in water samples and recoveries of 90 to 115% were found in spiked water samples of different types.     

Dipole moment characterization of phenol–, o-cresol–, and p-cresol–formaldehyde resins

Dipole moments and their temperature dependence have been measured in p-dioxane for fractionated novolac phenol–, o-cresol–, and p-cresol–formaldehyde polymers. The phenol–formaldehyde fractions covered a molecular weight range of 200 to 6100, and the limiting dipole moment ratio 〈μ²〉/xm² is 1.48. The p-cresol–formaldehyde dipole-moment ratio at a DP of 4 is 2.47, whereas the phenol–formaldehyde dipole-moment ratio is 1.40. That for o-cresol–formaldehyde is intermediate in value. The dipole-moment temperature coefficients are positive for p-cresol chains and negative for the phenol–formaldehyde chains. These results indicate that the hydroxyl groups along the p-cresol–formaldehyde polymer are highly ordered, with the aromatic rings closer to the sterically hindered planar position than in the phenol–formaldehyde polymers.     

Neue,ungewöhnlich verlaufende Arylierungen der 1,5-Dihydroxy-4,8-diaminoanthrachinon-2,6-disulfonsäure mit Kresolen

A novel course of a phenylation reaction of 1,5-dihydroxy-4,8-diaminoanthraquin-one-2,6-disulfonic acid with cresols . The arylation of 1,5-dihydroxy-4,8-diaminoanthraquinone-2,6-disulfonic acid with m-cresol in conc. sulfuric acid gives in the presence of boric acid a mixture of monosulfonic acids which differ in the substitution of the m-cresol moiety. The main product ( 8 , 95%) is substituted at the p-position to the methyl group, the side product ( 12 , 5%) at the p-position to the OH group. The monosulfonic acid 8 , which could not be isolated is further sulfonated under the reaction conditions to the disulfonic acid 9 . In the case of o-cresol, the cresol moiety is substituted in the p-position ( 16 ) to OH group and in the case of p-cresol in the o-position ( 20 ) to OH group. The obtained monosulfonic acids 16 and 20 resp. are partially sulfonated further under the reaction conditions. The new structures are elucidated by ¹H- and ¹³C-NMR. spectroscopy and the pattern of arylation reaction with phenol is discussed.     

Long-chain double SO3H-functionalized Brønsted acidic ionic liquids catalyzed selective alkylation of phenol and p-cresol with tert-butanol

A simple, efficient, and selective approach for the tert-butylation of phenol and p-cresol using two double SO₃H-functionalized long-chain Brønsted acidic ionic liquids as recyclable catalysts is reported. Under optimum reaction conditions, 89.4% conversion of the phenol and 73.7% selectivity of 2,4-tert-butyl-phenol and 93.2% conversion of the p-cresol and 89.2% selectivity of 2-tert-butyl-p-cresol were obtained. Two ionic liquids could be recovered readily and their catalytic activity almost completely retained after five recycles.     

Non-targeted detection of chemical contamination in carbonated soft drinks using NMR spectroscopy, variable selection and chemometrics

An efficient method for detecting malicious and accidental contamination of foods has been developed using a combined ¹H nuclear magnetic resonance (NMR) and chemometrics approach. The method has been demonstrated using a commercially available carbonated soft drink, as being capable of identifying atypical products and to identify contaminant resonances. Soft-independent modelling of class analogy (SIMCA) was used to compare ¹H NMR profiles of genuine products (obtained from the manufacturer) against retail products spiked in the laboratory with impurities. The benefits of using feature selection for extracting contaminant NMR frequencies were also assessed. Using example impurities (paraquat, p-cresol and glyphosate) NMR spectra were analysed using multivariate methods resulting in detection limits of approximately 0.075, 0.2, and 0.06 mM for p-cresol, paraquat and glyphosate, respectively. These detection limits are shown to be approximately 100-fold lower than the minimum lethal dose for paraquat. The methodology presented here is used to assess the composition of complex matrices for the presence of contaminating molecules without a priori knowledge of the nature of potential contaminants. The ability to detect if a sample does not fit into the expected profile without recourse to multiple targeted analyses is a valuable tool for incident detection and forensic applications.     

Magnesium chloride supported high-mileage catalysts for olefin polymerization. I. Chemical composition and oxidation states of titanium

The chemical composition of a MgCl₂-supported, high-mileage catalyst has been determined at every stage of its preparation. Ball milling of MgCl₂ with ethyl benzoate (EB) resulted in the incorporation of 95% of the EB present to give MgCl₂·EB_0.15. A mild reaction with a half-mole equivalent of p-cresol (PC) at 50°C for 1 h resulted in near quantitative retention of p-cresol by the support. The composition is now approximately MgCl₂·EB_0.15P?_0.5. Addition of an amount of AlEt₃ corresponding to half-mole equivalent of p-cresol liberated one mole of ethane per mole of p-cresol, thus signaling quantitative reaction between the two components. The support contains on the average one ethyl group per Al. Further reaction with TiCl₄ resulted in the incorporation of titanium of approximately 8, 38, and 54% in the oxidation states of +2, +3, and +4, respectively. The ratio of Al to Ti in the catalyst lies in the range of 0.5–1.0. Only 19% of all the Ti⁺³ species in the catalyst can be observed by electron paramagnetic resonance (EPR); these are attributable to isolated Ti⁺³ complexes. The remaining EPR silent Ti⁺³ species are believed to be bridged to another Ti⁺³ by Cl ligands. The total Cl content is equal to the sum of 2 × Mg + 3 × Al + 3.5 × Ti. Most of the p-cresol moiety apparently disappeared from the support, leaving much of ethyl benzoate in the catalyst. Activation with AlEt₃/methyl-p-toluate complex reduces 90% of the Ti⁺⁴ in the catalyst to lower oxidation states. The ester apparently moderates the alkylating power of AlEt₃ to avoid excessive formation of divalent titanium sites. There appears to be a constant fraction of 1/4–1/5 of the titanium which is isolated and the remainder is in bridged clusters independent of the oxidation states of titanium.     

Cyclodextrin-based artificial oxidases with high rate accelerations and selectivity

Three cyclodextrin derivatives with one to four 2-O-formylmethyl groups attached to the secondary rim were prepared and investigated as catalysts for the oxidation of aminophenols in buffered dilute hydrogen peroxide. The derivatives were found to be Michaelis–Menten catalysts and to give rate accelerations of up to 20,000 for the oxidation of 2-aminophenol to 2-amino-phenoxazin-3-one, and 12,000 for the oxidation of 2-amino-p-cresol to 2-nitro-p-cresol. While a range of differently substituted substrates was oxidized the success of the reaction was highly dependent on the substituent pattern. The ability of one of the new artificial enzymes to oxidize selectively one aminophenol from a mixture of two was investigated giving substrate selectivities of up to 16:1.