Phenol and acetonitrile

Any analytical method [312] suitable for determining equilibrium compositions of a reaction mixture at several temperatures can be used to obtain the enthalpy and the entropy of that reaction. The first example we describe involves a common analytical technique (infrared absorption spectroscopy) and addresses the energetics of the hydrogen bond between phenol and acetonitrile. This careful study on the equilibrium 14.6 was made by Sousa Lopes and Thompson more than 30 years ago [313]. 

Minh Tho Nguyen, Eugene S. Kryachko and Luc G. Vanquickenborne C. Hydrogen Bonding between Phenol and Acetonitrile... 

The PES of the interaction of the phenol and acetonitrile molecules consists of two lower-energy minimum structures displayed in Figure 53. The first, named PhOH-ACN-1, is the conventional structure which has been explored by experimentalists for four decades. It occupies the global minimum on that PES and is characterized by a binding energy (PhOH-ACN) of 22.3 kJmol (see Table 40). It agrees fairly with the exper-... 

FIGURE 53. Complexes of phenol with acetonitrile. The bond lengths are in A. Values in parentheses correspond to the optimized geometries of the free phenol and acetonitrile molecules. Adapted from Reference 761 with permission... 

However, we have shown that the novel bond formation between phenol and acetonitrile plays a role on increasing the concentration of the acetonitrile. By postulating its existence under conditions in which phenol interacts with two acetonitrile molecules, we were able to explain the experimental data that have seemed to be rather unclear during the last four decades. Moreover, we have predicted the existence of another structure formed from phenol and two molecules of acetonitrile, which is characterized by a significant downshift by 244 cm of the v(OH) stretching mode of phenol, never observed experimentally in phenol-acetonitrile complexes. We have suggested that it is likely to exist in the gas phase and non-polar solvents at lower temperatures and showed its fingerprints in order to facilitate its possible experimental detection. 

Acetonitrile (methyl cyanide, cyanomethane) is frequently used with other solvents such as chloroform and phenol, and particularly with acetic acid. It enables very sharp end points to be obtained in the titration of metal acetates6 when titrated with perchloric acid. 

Various extraction methods for phenolic compounds in plant material have been published (Ayres and Loike, 1990 Arts and Hollman, 1998 Andreasen et ah, 2000 Fernandez et al., 2000). In this case phenolic compounds were an important part of the plant material and all the published methods were optimised to remove those analytes from the matrix. Our interest was to find the solvents to modily the taste, but not to extract the phenolic compounds of interest. In each test the technical treatment of the sample was similar. Extraction was carried out at room temperature (approximately 23 °C) for 30 minutes in a horizontal shaker with 200 rpm. Samples were weighed into extraction vials and solvent was added. The vials were closed with caps to minimise the evaporation of the extraction solvent. After 30 minutes the samples were filtered to separate the solvent from the solid. Filter papers were placed on aluminium foil and, after the solvent evaporahon, were removed. Extracted samples were dried at 100°C for 30 minutes to evaporate all the solvent traces. The solvents tested were chloroform, ethanol, diethylether, butanol, ethylacetate, heptane, n-hexane and cyclohexane and they were tested with different solvent/solid ratios. Methanol (MeOH) and acetonitrile (ACN) were not considered because of the high solubility of catechins and lignans to MeOH and ACN. The extracted phloem samples were tasted in the same way as the heated ones. Detailed results from each extraction experiment are presented in Table 14.2. 

Photochemistry of Model Compounds. Preliminary photochemical studies have been carried out on l,3-diphenoxy-2-propanol (3)8 as a model compound for bisphenol A-epichloro-hydrin condensates 1. The utilization of 3 as a model compound for thermal degradation of 1 has been reported. Irradiation (254 nm) of 3 in acetonitrile (N2 purge) provides two major volatile products, which have been identified as phenol and phenoxyacetone (4), by comparison of retention times (gas chromatography) with known samples. A possible mechanism for... 

Retention volumes of monosubstituted benzenes, benzoic acid, phenols, and anilines have been measured in RPLC [76]. Buffered acetonitrile/water and tetrahydrofuran/water eluents were used with an octadecylsilica adsorbent. From the net retention volumes, a substituent interaction effect was calculated and described with the linear free energy relationship developed by Taft. The data was interpreted in terms of hydrogen bonding between the solutes and the eluent. 

It is important to note that the calculation of the initial concentrations of phenol ( 10-2 mol dm-3) and acetonitrile (possibly 1 mol dm-3) were corrected for the density of the solvent at each temperature. The temperature effect on the molar absorption coefficient (e) was also considered when relating [PhOH] to the absorbance of the O-H free band. This was empirically made by measuring the absorbances (A) of a phenol solution (in the same solvent and with a concentration similar to that used in the equilibrium study) over the experimental temperature range. For each temperature, the Lambert-Beer law [312],... 

Figure 3.6 Test for active silanols on octadecyl-bonded silica gels. Column 5 pm octadecyl-bonded silica gel, 15 cm x 4.6 mm i.d. eluent, 60% aqueous acetonitrile flow rate, 1ml min-1 temperature, ambient detection, UV 254 nm. Peak 1, pyridine 2, phenol, and 3, toluene. A, Column with no active silanol groups B, some active groups and C, numerous active groups.

FIGURE 6.3 Plot of column efficiency against sample mass for three neutral compounds (3-phenylpropanol, caffeine, phenol), and three charged compounds (propranolol, nortriptyline, 2-NSA [2-naphthalenesulfonic acid]) on XTerra MS (15 x 0.46 cm, 3.5 pm particles). Mobile phase acetonitrile-formic acid (overall concentration 0.02 M) pH 2.7 (28 72, v/v) except for caffeine (12.5 77.5, v/v). Flow rate 1 mL min . Column temperature 30°C. Injection volume 5 pL. 

Kinetic studies of various systems have been carried out as follows the reaction of 2,2 -dichlorodiethyl sulfide and of 2-chloroethyl ethyl sulfide with diethylenetriamine and triethylamine in 2-methoxyethanol ° the catalysed reactions of substituted phenols with epichlorohydrin the reactions of para-substituted benzyl bromides with isoquinoline under high pressure the reactions of O-alkylisoureas with OH-acidic compounds [the actual system was N, N -dicyclohexyl-0-(l-methylheptyl)isourea with acetic acid] and tlie ring opening of isatin in aqueous binary mixtures of methanol and acetonitrile cosol vents. 

Photolytic. Under artificial sunlight, river water containing 2-5 ppm chlorobenzene degraded to phenol and chlorophenol. The lifetimes of chlorobenzene in distilled water and river water were 17.5 and 3.8 h, respectively (Mansour et al, 1989). In distilled water containing 1% acetonitrile exposed to artificial sunlight, 28% of chlorobenzene photolyzed to phenol, chloride ion, and acetanilide with reported product yields of 55, 112, and 2%, respectively (Dulin et al., 1986). 

The anthocyanins exist in solution as various structural forms in equilibrium, depending on the pH and temperature. In order to obtain reproducible results in HPLC, it is essential to control the pH of the mobile phase and to work with thermostatically controlled columns. For the best resolution, anthocyanin equilibria have to be displaced toward their flavylium forms — peak tailing is thus minimized and peak sharpness improved. Flavylium cations are colored and can be selectively detected in the visible region at about 520 nm, avoiding the interference of other phenolics and flavonoids that may be present in the same extracts. Typically, the pH of elution should be lower than 2. A comparison of reversed-phase columns (Ci8, Ci2, and phenyl-bonded) for the separation of 20 wine anthocyanins, including mono-glucosides, diglucosides, and acylated derivatives was made by Berente et al. It was found that the best results were obtained with a C12 4 p,m column, with acetonitrile-phosphate buffer as mobile phase, at pH 1.6 and 50°C. 

N2-purged solutions of 5x1 O 4 mol dm"3 of the sterically hindered phenols in acetonitrile were photolyzed with fs-pulses. After tens of picoseconds a band between 400 and 450 nm... 

Figure 25-12 Isocratic HPLC separation of a mixture of aromatic compounds at 1.0 mL/min on a 0.46 x 25 cm Hypersil ODS column (C,8 on 5-jxm silica) at ambient temperature ( 22 C) (1) benzyl alcohol (2) phenol (3) 3, 4 -dimethoxyacetophenone (4) benzoin (5) ethyl benzoate (6) toluene (7) 2,6-dimethoxytoluene (8) o-methoxybiphenyl. Eluent consisted ot aqueous buffer (designated A) and acetonitrile (designated B). The notation 90% B in the first chromatogram means 10 vol% A and 90 vol% B. The buffer contained 25 mM KH2P04 plus 0.1 g/L sodium azide adjusted to pH 3.5 with HCI.

The reactions of 0-naphthol and 4-methoxyphenol with acetyl, propionyl, butyryl, 0-chloropropionyl and chloracetyl chlorides in acetonitrile produce some striking kinetic results109. The behaviour of acetyl, propionyl and n-butyryl chlorides fit reasonably well into the pattern for acetyl chloride in nitromethane and acetyl bromide in acetonitrile. However, with chloracetyl chloride the mechanism is essentially a synchronous displacement of covalently bound chlorine by the phenol and this process is powerfully catalysed by added salt with bond breaking being kinetically dominant. When no added salt is present the rate of hydrolysis of chloracetyl chloride is ca. 8000 times slower than that of acetyl chloride. Although, normally, in second-order acylation reactions, substituents with the greatest electron demand have been found to have the fastest rates, the reverse is true in this system. Satchell proposes that a route such as... 

Alkylation of phenols and alcohols.1 Both KF and CsF impregnated on alumina are highly effective as catalysts for alkylation of phenols and alcohols. Acetonitrile or DME are superior solvents for this reaction. 

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