A detailed investigation of the dediazoniation of 2,4,6-trimethylbenzenediazonium tetrafluoroborate in 2,2,2-trifluoroethanol is presented. The dediazoniation rate, the isotopic N,-Np rearrangement, and the exchange reaction of the diazonio group with external nitrogen in p-lsN labeled diazonium salts were monitored under a constant pressure of 300 atm mixed nitrogen/argon gas, as a function of the partial pressure of nitrogen. The results obtained provide evidence additional to that presented in the preceding paper for the presence of two reaction intermediates during the course of the dediazoniation. A statistical treatment of the kinetic data excludes the possibility that one reaction intermediate can account for all the phenomena observed. The reaction mechanism of eq 7 is proposed. Rearrangement occurs at the first intermediate, a tight molecule-ion pair, while the exchange with external nitrogen takes place via the second, free aryl cation, intermediate.The results concerning solvent effects on the decomposition of benzene-and 2,4,6-trimethylbenzenediazonium ion described in the preceding paper' support the existence of two reaction intermediates during the course of the dediazoniation: (1) This paper deals with a detailed kinetic investigation of the dediazoniation of a convenient system, 2,4,6-trimethylbenzenediazonium tetrafluoroborate in 2,2,2-trifluoroethanol (TFE) under a constant pressure (300 atm) of mixed nitrogen/argon gas, but different partial pressures of nitrogen. The results provide evidence, additional to that already presented,' for the validity of the proposed two-intermediate mechanism.A statistical treatment of the kinetic data excludes the possibility that one reaction intermediate can account for all the phenomena observed. Experimental SectionMaterials, In the study of the rearrangement and exchange reaction reagent grade (Fluka puriss.) TFE was used without further purification. The solvent which was used for kinetic and solubility measurements was recovered and was used repeatedly after purification by the following methods4 TFE was dried over potassium carbonate and distilled. Phosphorus pentoxide was then added to the distillate, and the solvent was distilled again (bp 73-74 "C). The GLC analysis of the recovered solvent showed no impurities. 2-Naphthol was recrystallized from ethanol (mp 121 "C). The disodium salt of 2naphthol-3,6-disulfonic acid (R-salt) was recrystallized twice from water and charcoal. 2,4,6-Trimethylaniline was distilled under reduced pressure (bp 120 OC, 20 mmHg), and the GLC of the distillate showed no impurities. Reagent grade potassium thiocyanate, potassium fluoride, and sodium nitrite were used without purification.2,4,6-Trimethylbenzenediazoni~m-~-~~N Tetrafluoroborate. Fluoroboric acid (2 mL, 50% aqueous solution) and water (2.5 mL) were added to 0.489 g (3.62 mmol) of 2,4,6-trimethylaniline. The solution was cooled in an ice-salt bath and 0.250 g (3.57 mmol) of NaI5N02 (99.2% nitrogen-15, Stohler Isotope Chemicals) in 0.5 mL of water was added slowly ...
The kinetics of the azo-coupling reactions of various active methylene compounds with diazobenzene-4-sulfonic acid have been studied spectrophotometrically. In the reactions of all the active methylene compounds used, it was found that the reaction rate was proportional to both the concentration of the diazonium salt and the carbanion (or enolate ion) of the azo component. In the reactions of a series of β-dicarbonyl compounds, a plot of the logarithms of the rate constants against the pKa values of active methylene compounds gave a straight line. However, the correlation between the reactivity and pKa was found unsatisfactory in the case of active methylene compounds with such electron-withdrawing substituents as NO2, CN, COR, SO2R, and Cl. These results are discussed in terms of the nucleophilicity of these carbanions.
The azo coupling reaction of p-methoxybenzenediazonium tetrafluoroborate with N,N-dimethylaniline has been investigated in a water-1,2-dichloroethane system. It has been found that, among the several additives examined, the phenolate ion, generated from picric acid or 2,4-dinitro-1-naphthol, acted as an effective phase-transfer catalyst. Further, the reaction of p-diethylaminobenzenediazonium tetrafluoroborate with dimedone, an active methylene compound, has also been investigated in the same two-phase system; a remarkable acceleration in the rate was observed in the presence of tetraalkyl onium salts, and even in their absence.
The stability constants for 18-crown-6 complexes with arenediazonium salts have been determined spectrophotometrically. The Hammett plot for m- and p-substituted benzenediazonium salts showed good correlation with a reaction constant 0.98 in methanol. The solvent effect on the stability of the complexes has been discussed.
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