Solvent effect anilines

Solvent Effects. The conversion of dihydroanthracene could be increased by adding water to the pyridine solvent (Table III). An 86% conversion to anthraquinone was obtained when 95% aqueous pyridine was used as the solvent. Furthermore, methanol could be substituted for the water with equivalent results. Other solvents were tried in place of pyridine (Table IV). The data indicate that 95% aqueous pyridine gave the best yields, although aniline gave nearly similar results. When acetonitrile and dimethylformamide were used, the large amounts of unreacted starting material indicate that these solvents may have deactivated the base by undergoing a hydrolysis reaction. 

The oxidation of meta- and para-substituted anilines with imidazolium fluorochro-mate (IFC)18 and nicotinium dichromate (NDC),19 in several organic solvents, in the presence of p-toluenesulfonic acid (TsOH) is first order in the oxidant and TsOH and is zero order with respect to substrate. A correlation of rate data in different solvents with Kamlet-Taft solvatochromic parameters suggests that the specific solute-solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute-solvent complexation. The oxidation rates with NDC exhibited negative reaction constants, while the oxidation with IFC did not correlate well with any linear free energy relationships. 

Another example of intramolecular CT complex formation is provided by trans-4-dimethvlamino-4 -(1-oxobutvl)stilbene Solvent effects on the spectrum give a value of 22D for the excited state dipole moment. The effect of electric field on the fluorescence of 4-(9-anthry1)-N.N.-2.3,5,G-hexamethy1-aniline shows this compound forms an excited state whose dipole moment does not change with solvent . Chiral discrimination in exciplex formation between 1-dipyrenylamine and chiral amines is very weak . In the probe molecule PRODAN (6-propionyl)-2-(dimethylamino)—naphthalene the initially formed excited state converts to a lower CT state as directly evidenced by time-resolved spectra in n-butanol. Rate constants for intramolecular electron transfer have been measured in both singlet and triplet states of covalently porphyrin-amide-quinone molecules . Intramolecular excimer formation occurs during the lifetime of the excited state of bis-(naphthalene)hydrazides which are used as photochemical deactivators of metals in polyethylene . ... 

T <- Tj spectrum shows a single peak at 235 nm F 0.35) and a shoulder around 310nm (F 0.12). Vibronic mechanisms in the two-photon spectrum of benzene and also toluene, halobenzenes, and aniline have been studied by Goodman and co-workers. Two-photon excitation of benzene crystals at 4.2 K has been recorded in the 200 nm second absorption system. The data suggest that the transition is in which the vibronic intensity is derived from the state in the one photon and E g in the case of two-photon excitation. Spectral solvent effects on toluene have been reported by Macovei. Traverso and Brunet have examined the 5j Sq transition in biphenyl and confirmed the earlier conclusion that this is a forbidden process. 

The introduction of a methyl group into the para position of aniline causes a decrease in both A H and d. S. A possible explanation of this is in terms of solvent effect. The — CHg group will tend to reduce the positive charge on the —group andthere will, therefore, be less electrorestriction of water and a consequent increase in enthalpy and entropy of the cationic form, BH+. For the para... 

Reactions of 2-Thiophenesulfonyl Chloride with Anilines. Arcoria and coworkers (126) have studied solvent effects on the kinetics of the reactions of 2-thiophenesulfonyl chloride with a series of ring-substituted aniline derivatives. Using the data in the eight of their solvents which are aliphatic and whose solvatochromic parameters are known (18,50,102,103,104,105,111,112), we have found correlations with tt and a to be excellent. 

For a large number of organic functionalities, significant protonation is only achieved in more concentrated acid solutions e.g. alcohols, ethers, ketones, esters, sulfides, sulfoxides). More concentrated acid solutions cannot be treated as ideal, and Ka values cannot be measured in terms of concentrations as in eqn (3.4). In strong acid media, the significantly decreased water concentration results in additional solvent effects on pA"a that are not accounted for by the pH scale. To account for acid-base behaviour in strong acid media, a number of acidity functions have been established. One of the earliest examples was the Hammett Ho acidity function based on a pairwise comparison of spectrophotometric changes in a series of aniline bases in concentrated acid solution. However, this scale could only be applied for structurally similar bases with similar protonation behaviour. Several other acidity functions have been proposed for other classes of bases such as the Hr acidity function for the ionisation of alcohols. As recently reviewed by Scorrano and More O Ferrall, later treatments by Bunnett and... 

Reactivity trends for D substitution at [Fe(CN)sL] anions will depend on solvent effects on the starting anion and on the separating moieties [Fe(CN)s] and L (L ) in the transition state. The activation parameters determined for a series of anions of this type with L = ammonia, amine, or aniline have been held to indicate the importance of transfer of the leaving group L to the solvent, an importance seemingly not recognized in some other studies. Small differences in reactivity between various complexes with L=NH2(CH2) NH2 or NHa-(CH2) NH3+, 3< <6, have also been attributed to solvation effects at the... 

Mechanistic investigations can also provide insight into unexpected side reactions. For example, in Ir(III)-catalyzed indole synthesis, Messerle and coworkers noted an unexpected side product, N-vinyhndole, when 2-(2-phenylethynyl)anihne was used as substrate with acetone as the solvent By probing solvent effects, deuterium-labeling experiments, and isolation of dormant species formed in stoichiometric experiments, two possible reaction pathways were considered. In collaboration with Eisenstein [303], these pathways were compared computationally, yielding a proposed reaction mechanism that proceeds via the initial formation of imine between the aniline and acetone solvent, followed by imine nucleophilic attack of coordinated alkyne for indole formation. 

THE INFLUENCE OF THE SOLVENTS ON THE ELECTRONIC SPECTRA OF SOME AROMATIC MOLECULES AND THEIR DIPOLE MOMENTS IN THE EXCITED STATE. THE SOLVENT EFFECTS ON THE ANILINE ELECTRONIC BAND AT 34,870 cm-1... 

---