132. Some derivatives of thioxanthen

Mechanism of pseudobase disproportionation. Kinetics and mechanism of the reaction of the pseudobases of 2-(substituted-benzyl)-5-nitroisoquinolinium cations with the 2-methylisoquinolinium cation

“…The kinetic isotope effects increase with the electronwithdrawing effect of the substituent X and thus show a definite dependence on the nature of X (eq 4). This substituent dependence of kp/kp is the electronic reverse of that recently reported17 for the oxidation of the same series of alkoxide ions (13) by ferricyanide ion. This latter reaction has p{kp) = -1.29 which corresponds to a quite "product-like" transition state in contrast to the "reactant-like" transition state that is indicated for the present reaction.…”

“…Basic aqueous solutions of 2-benzyl-5-nitroisoquinolinium cations (8) are pink due to the presence of the pseudobases 12 (Xmax 450-458 nm) and/or the pseudobase anions 13 (Xmax 493-507 nm).17 Quantitative studies17•25 of cation-pseudobase equilibration in these systems indicate that the cations 8 are essentially completely converted to their pseudobases 12 at NO, NO, even the lowest base concentrations (0.01 KOH) investigated in the current kinetic study. Addition of the 2-methylisoquinolinium cation to such pink solutions ([KOH] = 0.01-0.5 M) produces decolorization at rates which can be conveniently measured by conventional spectrophotometry at room temperature.…”

“…Since the 2methylisoquinolinium cation is not involved in a base-dependent equilibrium in this region,6 the equilibrium constant K must be related to a base-dependent equilibrium of the N-benzyl-5-nitroisoquinoline derivatives. In fact, it has been established that alkoxide ion (13) formation from the pseudobases (12) does occur in this region and values of Kd = [13]/ [12][~OH] for this ionization have previously17 been evaluated spectrophotometrically under the current experimental conditions (except for the absence of the 2-methylisoquinolinium cation). Values of K = 7-12 M-1 in Table I are in reasonable agreement with K¿ = 9-12 M-1 previously reported for these species.…”

“…Disproportionation for the 2-methylphthalazinium cation occurs only in the range pH [10][11][12][13], with the pseudobase, itself, being extracted from more basic aqueous solutions in which the pseudobase alkoxide ion (pKrq-= 13.0) predominates. 6 Although there does not appear to have been a detailed kinetic study of the pH dependence of these disproportionation reactions, these qualitative observations suggest that the rate of disproportionation reaches a maximum value at the pH at which the concentration of the pseudobase is at its maximum value.…”

ChemInform Abstract: Synthesis of New Benzylpyridines as Potential Photochromic Compounds.

“…The substituted benzaldehydes 1-4 were prepared according to modified literature procedures [10][11][12][13].…”