Effect of steric hindrance on the rates and kinetic isotope effects of the reactions of 1-nitro-1-(4-nitrophenyl)alkanes with TBD and MTBD bases in THF

Galezowski, Wlodzimierz; Grzeskowiak, Iwona; Jarczewski, Arnold

doi:10.1039/a801482e

Cited by 24 publications

(6 citation statements)

References 11 publications

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“…The equilibrium constant, K, for the proton transfer reaction between NPNE and DBU was found to be 2060 M -1 (Table 8), while for the phosphazenes studied the equilibrium constants were too large to be [13,14]. Moreover, the large difference in entropy of activation can be seen between values obtained for the reaction of phosphazene with NPNE and MNPNE.…”

Section: Resultsmentioning

confidence: 78%

“…3 eludes a clear cut explanation of the problem. [14] Iwona Binkowska Włodzimierz Gałęzowski and Arnold Jarczewski…”

Section: Resultsmentioning

confidence: 99%

“…These results show that the steric factor and ordering effects in forming the transition state play an important role, confirmed by negative and relatively large entropies of activation: ∆S ‡ = -149.7, -176.5, -178.7, -227.8 J mol -1 K -1 . The reactions between nitroalkanes with different steric hindrance and classic nitrogenous bases such as amidines or guanidines in acetonitrile and tetrahydrofuran have been disscussed previously [12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

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Equilibrium and kinetic study of the proton transfer reactions between nitroalkanes and strong organic bases — phosphazenes in tetrahydrofuran solvent

2010

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Proton transfer reactions rates between carbon acids 1-nitro-1-(4-nitrophenyl)ethane (NPNE), 2-methyl-1-nitro-1-(4-nitrophenyl)propane (MNPNP)) and phosphazenes (BEMP, BTPP, P 1 -t-Oct) in tetrahydrofuran have been measured, and the activation parameters were determined. The results are compared with those previously obtained for P 1 -t-Bu phosphazene, guanidines and amidines.© Versita Sp. z o.o.

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Section: Resultsmentioning

confidence: 78%

“…3 eludes a clear cut explanation of the problem. [14] Iwona Binkowska Włodzimierz Gałęzowski and Arnold Jarczewski…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Equilibrium and kinetic study of the proton transfer reactions between nitroalkanes and strong organic bases — phosphazenes in tetrahydrofuran solvent

2010

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“…In previous kinetic and equilibrium experiments, uncomplicated C-acids, such as 3, were used (14). At that time, the large primary deuterium kinetic isotope effect (KIE) values were attributed to three factors: steric hindrance of the reacting base (15,16), symmetry of the transition state (9,13,17), and polarity of the solvent used (13,18,19). To find the factors influencing the values of KIE, the series of C-acids with increasing R substituent bulk, and hence increasing steric hindrance, were synthesized and used (2,13,16,19,20).…”

Section: Resultsmentioning

confidence: 99%

Potentiometric study of equilibrium acidities of some carbon acids in acetonitrile

Stanczyk-Dunaj¹,

Galezowski²,

Jarczewski³

2002

Can. J. Chem.

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The pK a values for 30 C-acids of the type CH·R 1 ·R 2 ·R 3 -where the R 1 , R 2 , and R 3 substituents are H, alkyl, and aryl, and the most common electron withdrawing groups used in studies of proton-transfer reaction -are given herein. The pK a values have been measured potentiometrically in acetonitrile, using a glass electrode. These values were determined in a buffer solution consisting of a C-acid and its tetrabutylammonium salt, at constant ionic strength (0.001 M), at 25°C. The measurements were done under nitrogen, to prevent oxidation of the anion. The influence of water within the sample of the tetrabutylammonium hydroxide base was negligible. The lowest pK a value of 19.1 was found for bis(4-nitrophenyl)cyanomethane, while the largest pK a s that could be measured were limited by the basicity of the hydroxide ion, and did not exceed 28. A satisfactory agreement between spectrophotometric and potentiometric acidities was achieved.

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“…[9,10] Considering that the pK a of a nitroalkane (AlkNO 2 ) in MeCN falls in the range 27-31, a base stronger than PS-TBD would be helpful to increase the efficiency of the addition of AlkNO 2 to an a,b-unsaturated ketone or ester, and to reduce the amount of catalyst needed. We focused our attention on PS-BEMP ( MeCN pK a is 27.63), [10] a member of the class of Schwesingers phosphazene bases, that have proved to be very strong and widely useful uncharged auxiliary bases.…”

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Polystyryl‐BEMP as an Efficient Recyclable Catalyst for the Nucleophilic Addition of Nitroalkanes to α,β‐Unsaturated Carbonyl Compounds under Solvent‐Free Conditions

et al. 2008

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2-tert-Butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine supported on polystyrene (PS-BEMP) is an efficient catalyst for the addition of nitroalkanes (1-1.5 equiv.) to a,b-unsaturated carbonyl compounds (1.0 equiv.) in the absence of a reaction medium (solvent-free conditions). The corresponding g-nitro carbonyl compounds have been isolated in excellent yields but the catalyst can be satisfactorily recovered and used for only 3 times due to the magnetic stirring which caused crunching of the catalyst beads thus hampering its complete recovery. To optimize the catalysts reuse and improve the environmental efficacy of solvent-free conditions, the first solvent-free cyclic continuous-flow reactor has been set up. This reactor has allowed the product to be isolated in an almost quantitative yield by using a very small amount of organic solvent, making the recovery and reuse of the catalyst efficient and reproducible.

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Effect of steric hindrance on the rates and kinetic isotope effects of the reactions of 1-nitro-1-(4-nitrophenyl)alkanes with TBD and MTBD bases in THF

Cited by 24 publications

References 11 publications

Equilibrium and kinetic study of the proton transfer reactions between nitroalkanes and strong organic bases — phosphazenes in tetrahydrofuran solvent

Equilibrium and kinetic study of the proton transfer reactions between nitroalkanes and strong organic bases — phosphazenes in tetrahydrofuran solvent

Potentiometric study of equilibrium acidities of some carbon acids in acetonitrile

Polystyryl‐BEMP as an Efficient Recyclable Catalyst for the Nucleophilic Addition of Nitroalkanes to α,β‐Unsaturated Carbonyl Compounds under Solvent‐Free Conditions

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