The nitrosation of phenol, m-, o-, and p-cresol, 2,3-, 3,5-, and 2, 6-dimethylphenol, 3,5-di-tert-butylphenol, 2,4,6-trimethylphenol, o-chlorophenol, and o-bromophenol was studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the products at 345 nm. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of an attack on the nitrosatable substrate by NO(+)/NO(2)H(2)(+), followed by a slow proton transfer. The finding of an isokinetic relationship supports the idea that the same mechanism operates throughout the series. The observed sequence of nitrosatable substrate reactivities is explained by (i) the preferred para-orientation of the hydroxyl group for the electrophilic attack of nitrosating agents, (ii) steric hindrance of alkyl substituents, which reduces or prevents attack by nitrosating agents, and (iii) the hyperconjugative effect of the methyl substituent, which causes electronic charge to flow into the aromatic nucleus, as well as the opposite electronic withdrawing effect induced by halogen substituents. The results show that potential nitrosation of widespread environmental species such as chlorophenols is negligible, but more attention should be paid to polyphenols with strongly nucleophilic carbon atoms.

Nitrosation reactions of amino acids with an -NH(2) group [namely, six alpha-amino acids (glycine, alanine, alpha-aminobutyric acid, alpha-aminoisobutyric acid, valine, and norvaline); two beta-amino acids (beta-alanine and beta-aminobutyric acid), and one gamma-amino acid (gamma-aminobutyric acid)] were studied. Nitrosation was carried out in aqueous acid media, mimicking the conditions of the stomach lumen. The rate equation was r = k(3)(exp)[amino acid][nitrite](2), with a maximum k(3)(exp) value in the 2.3-2.7 pH range. The existence of an isokinetic relationship supports the argument that all the reactions share a common mechanism. A nitrosation mechanism is proposed, and the following conclusions are drawn: (i) Nitrosation reactions of amino acids with a primary amino group in acid media occur with dinitrogen trioxide as the main nitrosating agent. The finding that the nitrosation rate is proportional to the square of the nitrite concentration suggests that the yield of nitrosation products in the stomach would increase sharply with higher nitrate/nitrite intakes. (ii) Stomach hypochlorhydria could be a potential enhancer of in vivo amino acid nitrosation. (iii) The reactivity (k(3)()(exp)) [alpha-amino acids > beta-amino acids > gamma-amino acids] is the same as that found in a previous work for the alkylating potential of lactones formed from nitrosation products of the same amino acids. This implies that the nitrosation reactions of the most common natural amino acids are the most efficient precursors of the most powerful alkylating agents. (iv) The order of magnitude (10(7)-10(8) M(-1) s(-1)) of the bimolecular rate constants of nitrosation shows that such reactions occur through an encounter process.

We have designed two integrated experiments to serve as an introduction to the study of inclusion phenomena. The first one allows measurement, by UV-Vis spectrophotometry, of the equilibrium constant of the formation of the inclusion complex of an azo-dye (guest molecule) in an a-cyclodextrin (host molecule). In the second experiment, the kinetics of the formation of the inclusion complex of the guest molecule in the host molecule is studied.

2. This complex is a component of a nonsteroidal anti-inflammatory medication possessing analgesic and antipyretic properties.3. The chemical name for mordant yellow 7 is 2-hydroxy-3methyl-5-[(4-sulfophenyl)azo] benzoic acid, disodium salt.4. The chemical name of Biebrich scarlet is 2-[(2-hydroxy-1naphthalenyl)azo]-5-[(4-sulfophenyl)azo] benzenesulfonic acid, disodium salt. The structure is shown in Table 4.5. The azo-dye mordant yellow 7 is not used (20, 21), having been removed from chemical catalogs.6. The chemical name for mordant orange 10 is 2-hydroxy-3-methyl-5- [[4-[(4-sulfophenyl)azo]phenyl]azo]benzoic acid, disodium salt.7. The chemical name for mordant yellow 10 is 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid, disodium salt.

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