Effect of acyl substituents on the reaction mechanism for aminolyses of 4-nitrophenyl X-substituted benzoates

Second-order rate constants (k(N)) have been measured spectrophotometrically for the reaction of 4-nitrophenyl X-substituted benzoates with a series of alicyclic secondary amines in H(2)O containing 20 mol % dimethyl sulfoxide at 25.0 degrees C. The magnitude of the k(N) values increases with increasing the basicity of amines and with increasing the electron-withdrawing ability of the acyl substituent X. The Hammett plots obtained are not linear but show a break or curvature as the acyl substituent X becomes electron withdrawing for all the amines studied, while the Bronsted-type plots are linear with large beta(nuc) values for all the substrates investigated. The nonlinear Hammett plots suggest a change in the rate-determining step upon changing the acyl substituent X, whereas the linear Bronsted-type plots indicate that the rate-determining step does not change upon changing amine basicity. The Yukawa-Tsuno plots obtained are also linear with positive rho(X) and large r values, suggesting that the nonlinear Hammett plots are not due to a change in the rate-determining step upon changing the acyl substituent X, but due to resonance demand of the pi-electron donor substituent on the acyl moiety. The magnitude of the rho(X) and beta(nuc) values increases with increasing the basicity of amines and with increasing the electron-withdrawing ability of the acyl substituent X, respectively, while that of the r values decreases with increasing rho(X) values and amine basicity.     

Effect of amine nature on reaction rate and mechanism in nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates with alicyclic secondary amines

Second-order rate constants have been measured for reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates with a series of alicyclic secondary amines. The reaction proceeds through S-O and C-O bond fission pathways competitively. The S-O bond fission occurs more dominantly as the amine basicity increases and the substituent X in the sulfonyl moiety becomes more strongly electron withdrawing, indicating that the regioselectivity is governed by the amine basicity as well as the electronic nature of the substituent X. The S-O bond fission proceeds through an addition intermediate with a change in the rate-determining step at pK(a) degrees = 9.1. The secondary amines are more reactive than primary amines of similar basicity for the S-O bond fission. The k(1) value has been determined to be larger for reactions with secondary amines than with primary amines of similar basicity, which fully accounts for their higher reactivity. The second-order rate constants for the S-O bond fission result in linear Yukawa-Tsuno plots while those for the C-O bond fission exhibit poor correlation with the electronic nature of the substituent X. The distance effect and the nature of reaction mechanism have been suggested to be responsible for the poor correlation for the C-O bond fission pathway.     

Aminolysis of O-aryl thionobenzoates: amine basicity combines with modulation of the nature of substituents in the leaving group and thionobenzoate moiety to control the reaction mechanism

A kinetic study is reported for aminolysis of O-Y-substituted phenyl thionobenzoates (1a-f) and O-4-nitrophenyl X-substituted thionobenzoates (2a-f) in 80 mol % H2O/20 mol % DMSO at 25.0 +/- 0.1 degrees C. The reaction proceeds through one or two intermediates (i.e., a zwitterionic tetrahedral intermediate T(+/-) and its deprotonated form T(-)) depending on the basicity difference between the nucleophile and nucleofuge, that is, the reaction proceeds through T(+/-) when the leaving aryloxide is less basic than the attacking amine, but through T(+/-) and T(-) when the leaving group is more basic than the amine. However, the reaction mechanism is not influenced by the electronic nature of the substituent X in the nonleaving group. The Hammett plot for the reactions of 2a-f with benzylamine is consisted of two intersecting straight lines, which might be interpreted as a change in the rate-determining step (RDS). However, the Yukawa-Tsuno plot for the same reactions exhibits an excellent linear correlation, indicating that the nonlinear Hammett plot is not due to a change in the RDS but caused by stabilization of the ground-state of the substrate through resonance interaction between the electron-donating substituent X and the thionocarbonyl moiety.     

Effects of amine nature and nonleaving group substituents on rate and mechanism in aminolyses of 2,4-dinitrophenyl X-substituted benzoates

Second-order rate constants have been measured for the reactions of 2,4-dinitrophenyl X-substituted benzoates (1a-f) with a series of primary amines in 80 mol % H(2)O/20 mol % DMSO at 25.0 +/- 0.1 degrees C. The Br?nsted-type plot for the reactions of 1d with primary amines is biphasic with slopes beta(1) = 0.36 at the high pK(a) region and beta(2) = 0.78 at the low pK(a) region and the curvature center at pK(a) degrees = 9.2, indicating that the reaction proceeds through an addition intermediate with a change in the rate-determining step as the basicity of amines increases. The corresponding Br?nsted-type plot for the reactions with secondary amines is also biphasic with beta(1) = 0.34, beta(2) = 0.74, and pK(a) degrees = 9.1, indicating that the effect of amine nature on the reaction mechanism and pK(a) degrees is insignificant. However, primary amines have been found to be less reactive than isobasic secondary amines. The microscopic rate constants associated with the aminolysis have revealed that the smaller k(1) for the reactions with primary amines is fully responsible for their lower reactivity. The electron-donating substituent in the nonleaving group exhibits a negative deviation from the Hammett plots for the reactions of 1a-f with primary and secondary amines, while the corresponding Yukawa-Tsuno plots are linear. The negative deviation has been ascribed to stabilization of the ground state of the substrate through resonance interaction between the electron-donating substituent and the carbonyl functionality.     

The effect of medium on rate and mechanism: aminolysis of O-4-nitrophenyl thionobenzoate in MeCN and H2O

Pseudo-first-order rate constants (kobs) have been measured spectrophotometrically for reactions of O-4-nitrophenyl thionobenzoate (1) with a series of alicyclic secondary amines in MeCN and H2O at 25.0 +/- 0.1 degrees C. The plot of kobs vs amine concentration exhibits an upward curvature in all cases, indicating that the reactions proceed through two tetrahedral intermediates (a zwitterionic T(+/-) and its deprotonated anionic T-) regardless of the amine basicity and the nature of the reaction medium. However, all the amines investigated have been found to be much less reactive in MeCN than in H2O, although the amines are more basic in the former medium by 7-9 pKa units.     

Spectrophotometric determination of aliphatic primary and secondary amines by reaction with p-benzoquinone

A simple, sensitive and selective spectrophotometric method has been developed for determination of aliphatic primary and secondary amines. It is based on a reaction with excess of p-benzoquinone in ethanol whereby 1:1 (amine:quinone) coloured products are obtained, which have maximum absorption at 510 nm and E(1cm)(1%) in the range 400-650. The effect of solvent, temperature, concentration of quinone and the presence of water have been kinetically investigated by the initial rate method. The conditions for monitoring amine concentrations as low as 0.1 microg/ml are optimized in the light of the kinetic data. Results with an average recovery of 98.5% and mean standard deviation of 1.9% are obtained with 9 different amines without interference from tertiary amines, ammonia, amides, imides, anilides, hydrazines and alpha-amino-acids.     

Protection of primary and secondary amines in the hydroboration reaction

Trimethylsilyl groups are efficient to protect the NH bonds of olefinic amines in the hydroboration reaction with BMS; deprotection is easily run with methanol and affords aminoorganoboranes which can be used without any oxydation.     

Studies on the reaction of primary and secondary amines with phenylseleninic anhydride and with phenylseleninic acid

The dehydrogenation under mild conditions of indolines with phenylseleninic anhydride or acid affords good yields of indoles or of 3-phenylselenenyl indoles. Tetrahydroquinoline and -isoquinoline show comparable behaviour. The dehydrogenation of primary amines gives more complicated mixtures from which nitriles and bis-2-phenylselenenylaldehydes can be isolated.     

Reactions of some 4-methylene-4H-pyran derivatives with primary and secondary amines

4-Dicyanomethylene-4H-pyrans react with secondary amines to give 2-aminopyridine and 2-pyridone derivatives which, in turn, have been used to prepare copyrine derivatives. These pyrans and primary amines gave copyrine and iminopyridone derivatives in addition to the dicyanomethylene-1,4-dihydropyridines, which had been reported previously. Reaction of cyanocarbamoylmethylene-4H-pyrans with secondary amines gave 2-pyrones, and with primary amines, gave copyrines and 1,4-dihydropyridine derivatives.     

Regioselectivity and the nature of the reaction mechanism in nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates with primary amines

Second-order rate constants have been measured for the reaction of 2,4-dinitrophenyl X-substituted benzenesulfonates with a series of primary amines. The nucleophilic substitution reaction proceeds through competitive S-O and C-O bond fission pathways. The S-O bond fission occurs dominantly for reactions with highly basic amines or with substrates having a strong electron-withdrawing group in the sulfonyl moiety. On the other hand, the C-O bond fission occurs considerably for the reactions with low basic amines or with substrates having a strong electron-donating group in the sulfonyl moiety, emphasizing that the regioselectivity is governed by both the amine basicity and the electronic effect of the sulfonyl substituent X. The apparent second-order rate constants for the S-O bond fission have resulted in a nonlinear Br?nsted-type plot for the reaction of 2,4-dinitrophenyl benzenesulfonate with 10 different primary amines, suggesting that a change in the rate-determining step occurs upon changing the amine basicity. The microscopic rate constants (k(1) and k(2)/k(-)(1) ratio) associated with the S-O bond fission pathway support the proposed mechanism. The second-order rate constants for the S-O bond fission result in good linear Yukawa-Tsuno plots for the aminolyses of 2,4-dinitrophenyl X-substituted benzenesulfonates. However, the second-order rate constants for the C-O bond fission show no correlation with the electronic nature of the sulfonyl substituent X, indicating that the C-O bond fission proceeds through an S(N)Ar mechanism in which the leaving group departure occurs rapidly after the rate-determining step.     

Kinetic investigation of the reactions of S-4-nitrophenyl 4-substituted thiobenzoates with secondary alicyclic amines in aqueous ethanol

The reactions of S-4-nitrophenyl 4-X-substituted thiobenzoates (X = H, Cl, and NO(2): 1, 2, and 3, respectively) with a series of secondary alicyclic amines (SAA) were subjected to a kinetic investigation in 44 wt % ethanol-water, at 25.0 degrees C and an ionic strength of 0.2 M (KCl). The reactions were followed spectrophotometrically by monitoring the release of 4-nitrobenzenethiolate anion at 420-425 nm. Under excess amine, pseudo-first-order rate constants (k(obsd)) are obtained for all reactions. The plots of k(obsd) vs [SAA] at constant pH are linear with the slope (k(N)) independent of pH. The statistically corrected Br?nsted-type plots (log k(N)/q vs pK(a) + log p/q) for the reactions of 1 and 2 are nonlinear with slopes at high pK(a), beta(1) = 0.27 and 0.10, respectively, and slopes at low pK(a), beta(2) = 0.86 and 0.84, respectively. The Br?nsted curvature is centered at pK(a) (pK(a)(0)) 10.0 and 10.4, respectively. The reactions of SAA with 3 exhibit a linear Br?nsted-type plot of slope 0.81. These results are consistent with a stepwise mechanism, through a zwitterionic tetrahedral intermediate (T(+/-)). For the reactions of 1 and 2, there is a change in rate-determining step with amine basicity, from T(+/-) breakdown to products at low pK(a), to T(+/-) formation at high pK(a). For the reactions of 3, breakdown to products of T(+/-) is rate limiting for all the SAA series (pK(a)(0) > 11). The increasing pK(a)(0) value as the substituent in the acyl group becomes more electron withdrawing is attributed to an increasing nucleofugality of SAA from T(+/-). The greater pK(a)(0) value for the reactions of SAA with 1, relative to that found in the pyridinolysis of 2,4-dinitrophenyl benzoate (pK(a)(0) = 9.5), is explained by the greater nucleofugality from T(+/-) of the former amines, compared to isobasic pyridines, and the greater leaving ability from T(+/-) of 2,4-dinitrophenoxide relative to 4-nitrobenzenethiolate.     

The reaction of GeCl4 with primary and secondary phosphines

Reaction of GeCl4 and CyPH2 leads to a range of products from which crystals of [CyPH3]+[GeCl3]- have been obtained. The major intermediate in this reaction, Cy(H)PGeCl3, can be obtained as the dominant product only when an excess of GeCl4 is used in the preparation. Similarly, crystals of [Ph2PH2]+[GeCl3]- have been obtained from reaction of Ph2PH and GeCl4(1 : 1). The structures of both primary and secondary phosphonium cations are reported. Aerosol-assisted and low-pressure chemical vapour deposition experiments using Cy(H)PGeCl3 as precursor lead to the deposition of thin films containing both germanium and phosphorus, contaminated with large amounts of oxygen. GeP has been identified as components of the film from bandgap measurements.     

Phosphorus-containing trifluoromethylureas and their reaction with secondary amines

Conclusions O,O-Dialkyl-1-(3-dialkylaminofluoromethyleneureido)-1-methylalkylphosphonates were synthesized by the reaction of O,O-dialkyl-1-(3-trifluoromethylureido)-1-methylalkylphosphonates, obtained from the corresponding carbodiimides, with secondary amines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2618–2620, November, 1988.     

Effect of stoichiometry and diffusion on an epoxy/amine reaction mechanism

The bulk phase kinetics of an epoxy (DGEBA) /amine (DDS) thermoset have been studied using DSC, FTIR, and ¹³C-NMR. In the absence of catalyst, the reaction was found to involve a main exothermic reaction between epoxide and amine hydrogen and a side reaction between tertiary amine formed in the main reaction and epoxide. The main reaction was exothermic while the side reaction had no discernable exotherm. Etherification did not occur to any significant extent. Since only the main reaction is exothermic, DSC was very useful for studying the main reaction kinetics. FTIR was used for determining whether epoxide and amine hydrogen were consumed at different rates as a way of following the side reaction. An IR band previously unused by other investigators was used to monitor the amine hydrogen concentration. NMR confirmed the above mechanism by identifying the formation of a quaternary ammonium ion/alkoxide ion pair as a reaction product of tertiary amine and epoxide. This mechanism has been successfully fit to a rate law valid over the entire extent of reaction. The rate constant for the epoxy/amine addition reaction was found to depend on hydroxide concentration (extent), reaction temperature, and glass transition temperature and included contributions from uncatalyzed and autocatalyzed parts. The side reaction (quaternary ammonium ion formation) formed weak bonds which did not affect the overall system T_g. Both reactions were second order. The rate constants for the main reaction first increase with increasing extent due to autocatalysis by hydroxide before decreasing due to the diffusion limit caused by gelation and vitrification. © 1995 John Wiley & Sons, Inc.     

The relative reactivity of primary and secondary amine hydrogen atoms of aromatic amines with epichlorohydrin and N- and O-glycidyl compounds

The relative value of the rate constants for the reactions between the secondary and primary amine hydrogen atoms of 3-trifluoromethylaniline with epichlorohydrin, and of aniline with phenyl glycidyl ether and with some N-alkyl-N-glycidylanilines were determined by HPLC analysis. Values ranged from 0.14 to 0.24 and are in agreement with the findings of earlier workers for the reactions of aromatic amines with O-glycidyl compounds but in direct conflict with the claim of a recent publication. The value for the reaction between 3-trifluoromethylaniline and epichlorohydrin was unaffected by the nature of the catalyst, which covered a wide range of strengths and steric requirements.     

On the reaction of glycidol with a secondary amine

The attempt was made to prepare an ionene like base by reacting diethylamine (DEA) with glycidol (Gly). It turned out that the reaction proceeds via two steps witch differ significantly. When the rate of added DEA to Gly in bulk becomes 1 : 13 the temperature jumps up suddenly. The product proved to be a water soluble oligomer having a molecular weight of M_n > 465 g/mol, a nitrogen content of 1.06%, and pH 9.5. Based on the ¹³C NMR and IR spectra, schemes of polyreactions were proposed according to which amine groups containing moieties of low molecular weight are formed. These subsequently function as initiators of Gly homopolymerization according to a chain mechanism.