Bond scission in sulfur compounds. 13. Reactivity-selectivity correlations. 3. The .alpha. effect at saturated carbon. Reactivity studies of methyl phenyl sulfates with nucleophiles

Buncel, Erwin; Chuaqui, Claudio; Wilson, H.K.

doi:10.1021/jo01306a016

Cited by 35 publications

(24 citation statements)

References 11 publications

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“…The plot between log k 2 and pk a for the corresponding arylthiols [30] shows considerably more scatter correlation than that obtained from the Hammett plot and has slope , Figure 2. As the transition state of a nucleophile implies (partial) donation of an electron pair from the nucleophile to the reaction center, the Bronsted coefficient ␤, is related to the extent of bond formation of the nucleophile to the reaction center, i.e., the ␤ values are generally positively associated with the degree of bond formation in the transition state [27,31,32]. Moreover, a transition state where bond breaking is so much advanced over bond making requires that the reaction center bears a sizable positive charge (with respect to the initial state) which in turn requires a negative with large substituent effect [33].…”

Section: Resultsmentioning

confidence: 99%

Nucleophilic substitution at the pyridine ring. Kinetics of the reaction of 2-chloro-3,5-dinitropyridine with arylthiolates in methanol

Hamed¹

1997

Int. J. Chem. Kinet.

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The reaction rates of 2-chloro-3,5-dinitropyridine 1 with a series of arylthiolates 2a-h in methanol have been measured at 25°C. The products are the corresponding 2-thioaryl-3,5-dinitropyridine 3a-h. Good Hammett correlation with value Ϫ1.19 was obtained suggesting an elimination-addition mechanism S N Ar and the formation of Meisenheimer-like intermediates. Plot of log k 2 vs. pK a values of arylthiols gave straight line with ␤ ϭ 0.38 indicating that the -bond breaking in the pyridine ring is so much advanced over bond making between the nucleophile and the carbon that bears the chlorine atom. Excellent correlation between log k 2 and log K (carbon basicity of arylthiolates) was obtained. sitions [2 -4, 10 -14]. This increased lability of pyridines towards nucleophilic attack is further reflection of the electron-attracting character of the ring nitrogen [4,15]. Protonation or quaternisation of the ring enhances its electron-attracting capability; pyridinium salts and N-oxides are thus even more susceptible than the parent pyridines to nucleophilic attack at the 2-and 4-positions [4,16,17]. In contrast, pyrrole derivatives show low reactivity towards nucleophilic substitution because the nitrogen atom with a lone pair acts as electron release [4]. Moreover, the acid nature of the hydrogen bound to the ring nitrogen and the tendency of the pyrrole to form a conjugate base in the presence of sufficiently strong bases make the formation of Meisenheimer-type adduct even more difficult to occur [15]. Continuing the previous studies on the transmission of substituent electronic effect in the thioaryl ring [8,9,19] and in order to investigate the effect of

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Section: Resultsmentioning

confidence: 99%

Nucleophilic substitution at the pyridine ring. Kinetics of the reaction of 2-chloro-3,5-dinitropyridine with arylthiolates in methanol

Hamed¹

1997

Int. J. Chem. Kinet.

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“…Among the following three major factors responsible for the a-effect, namely, (I) destabilization of the ground state of the a-nucleophile by repulsion between the adjacent lone electron pairs (5), (2) stabilization of the transition state by the extra pair of electrons, and (3) reduced solvation of the a-nucleophile by the adjacent lone electron pair, the last two factors have been fairly well substantiated by both theoretical (6)(7)(8)(9) and experimental studies (10)(11)(12)(13). Stabilization of the transition state by the a-nucleophile, namely the second factor, has recently been considered quite important and possibly the major factor for the enhanced reactivity in the nucleophilic attack of the a-nucleophile on the electropositive reacting center, especially in solution.…”

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confidence: 81%

Importance of repulsion of lone electron pairs in the enhanced reactivity of 1,8-naphthyridine and the large α-effect of hydrazine in the aminolyses of p-toluenesulfonyl chloride

Ōae¹,

Kadoma²

1986

Can. J. Chem.

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SHIGERU OAE and YOSHIHITO KADOMA. Can. J. Chem. 64, 1184 (1986.The rates of aminolyses of p-toluenesulfonyl chloride with primary and tertiary amines have been determined both in acetonitrile and in ethanol. The Bronsted plots of log k, , again pKac values of amines (except hydrazine and 1,8-naphthyridine in acetonitrile) gave a good correlation when the aminolyses were carried out in acetonitrile. In ethanol, however, although Bronsted plots with all tertiary amines show a good correlation, less basic hydrazine shows a higher reactivity than n-butylamine. The abnormal rate enhancement found with hydrazine is undoubtedly due to the a-effect, while that with 1,8-naphthyridine in acetonitrile is considered to be due to the repulsion of two lone electron pairs on the two nitrogen atoms in 1,8-naphthyridine.

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“…From Figure 5 it is apparent that this would give a specific rate constant ~H O O -= 4.6 f 1.2M-l s-l. One hence obtains for the CY effect kHOO-/kMeO-= 8.8 f 2.2. The effect is clearly greater in magnitude than that observed with hydrazine [8], which is a significant finding. The error limit on K given above can be improved upon as a result of a corresponding study with methyl rn-nitrophenyl sulfate.…”

Section: Estimation Of Khoo-using the Derived K Valuementioning

confidence: 58%

The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pK_a of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure

Buncel

Chuaqui

Wilson

1982

Int J of Chemical Kinetics

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A kinetic spectrophotometric investigation of the reaction of the hydrogen peroxide anion with methyl p-nitrophenyl sulfate in methanol solvent resulted in the evaluation of the pKa of HOOH in methanol at 25'C as 15.8 f 0.2. Since normal kinetic procedures for the determination of the equilibrium constant K for the process CH30-+ HzOz i=t CH30H + HOT were found to be associated with high uncertainty, another procedure was devised to establish the magnitude of K. This method is based on an analysis of the changing slopes of plots of pseudo-first-order rate constants against the total base concentration as the stoichiometric amount of hydrogen peroxide is varied. The method is applicable to any system in which anionic nucleophiles generated in situ compete with solvent anions. Such B corroboration of kinetically determined equilibrium constants is believed essential. The kinetic data allow the specific rate constant kHOO-for the reaction of methyl p-nitrophenyl sulfate with hydrogen peroxide anions to be evaluated and yield the rate constant ratio kHOO-/kMeO-= 8.8 f 2.2. This confirms the existence of an (Y effect at saturated carbon in this system.

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Bond scission in sulfur compounds. 13. Reactivity-selectivity correlations. 3. The .alpha. effect at saturated carbon. Reactivity studies of methyl phenyl sulfates with nucleophiles

Cited by 35 publications

References 11 publications

Nucleophilic substitution at the pyridine ring. Kinetics of the reaction of 2-chloro-3,5-dinitropyridine with arylthiolates in methanol

Nucleophilic substitution at the pyridine ring. Kinetics of the reaction of 2-chloro-3,5-dinitropyridine with arylthiolates in methanol

Importance of repulsion of lone electron pairs in the enhanced reactivity of 1,8-naphthyridine and the large α-effect of hydrazine in the aminolyses of p-toluenesulfonyl chloride

The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pK_a of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure

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Bond scission in sulfur compounds. 13. Reactivity-selectivity correlations. 3. The .alpha. effect at saturated carbon. Reactivity studies of methyl phenyl sulfates with nucleophiles

Cited by 35 publications

References 11 publications

Nucleophilic substitution at the pyridine ring. Kinetics of the reaction of 2-chloro-3,5-dinitropyridine with arylthiolates in methanol

Nucleophilic substitution at the pyridine ring. Kinetics of the reaction of 2-chloro-3,5-dinitropyridine with arylthiolates in methanol

Importance of repulsion of lone electron pairs in the enhanced reactivity of 1,8-naphthyridine and the large α-effect of hydrazine in the aminolyses of p-toluenesulfonyl chloride

The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pKa of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure

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The reaction of methyl p‐nitrophenyl sulfate with hydrogen peroxide anion determination of pK_a of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure