Substituent effects in the pyrolysis of aryl n-propyl sulfoxides

Emerson, David R.; Korniski, Thomas J.

doi:10.1021/jo01264a076

Cited by 46 publications

(31 citation statements)

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“…Thus the accessability of a proton on the fl-carbon to the sulfoxide group is the limiting factor rather than the stereochemistry of the sulfoxide group, i.e., whether it is axial or equatorial. This is in accord with a concerted process for the syn fl-elimination of the type shown in Scheme 4 which has been proposed [13].…”

Section: Resultssupporting

confidence: 87%

Cyclophane bis(sulfoxides) a thermal analysis study

Hill

Jessup

Reiss

1981

Journal of Thermal Analysis

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Section: Resultssupporting

confidence: 87%

Cyclophane bis(sulfoxides) a thermal analysis study

Hill

Jessup

Reiss

1981

Journal of Thermal Analysis

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“…Likely, a partial positive charge develops at the α-carbon atom in the E1-like transition state, while a partial negative charge develops at the β-carbon atom in the carbanion-like transition state, although the development of any charge is small because of the concerted nature of the cyclic transition state. The present positive Hammett ρ-values for X-substituents are consistent with an E1-like mechanism and are larger than that for the pyrolysis of substituted phenyl propyl sulfoxides (ρ = 0.51), 9 threo-1-phenylethyl substituted phenyl sulfoxides (ρ = 0.60∼0.64), 12 and t-butyl substituted phenyl sulfoxides (ρ = 0.695). 8 These pyrolyses proceed via an E1-like mechanism.…”

Section: Discussionsupporting

confidence: 64%

“…Both values are a little larger than those of aryl α-methylbenzyl sulfoxides (ρ = 0.60) 12 and aryl propyl sulfoxides (ρ = 0.51). 9 These results for kinetic isotope effect and substituent effect reveal that both the C S bond cleavage and the proton transfer are important in the transition state, namely the reaction proceeds via a concerted process and the positive ρ-values suggest that the reaction of 2a and 2b proceeds via a mechanism deviated to E1-like.…”

Section: Kineticsmentioning

confidence: 82%

“…[2][3][4][5][6][7][8] Kinetic investigations for the Ei reaction of the sulfoxides have revealed that both C S bond fission and β-proton transfer are important, and thus a concerted mechanism has been suggested from the observations of positive Hammett ρ-values 8,9 for the substituent effect on the S-phenyl group and large deuterium kinetic isotope effects on β-position. 10,11 However, we recently demonstrated that the transition state is variable depending on the substituent on the α-or β-position of the sulfoxides.…”

Section: Introductionmentioning

confidence: 99%

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Pyrolysis of α- and β-Heteroatoms Substituted Ethyl Phenyl Sulfoxides

Yoshimura

Sakae

Yoshizawa

et al. 2010

Phosphorus, Sulfur, and Silicon and the Related Elements

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A study on the mechanism of the thermal decomposition of α-and β-heteroatoms substituted ethyl phenyl sulfoxides was carried out using 1-chloroethyl phenyl sulfoxide (1); two diastereomeric 1-acetoxyethyl (substituted phenyl) sulfoxides (2a) and (2b); and 2-chloroethyl phenyl, 2-bromoethyl phenyl, and 2-methoxyethyl phenyl sulfoxides (3, 4, 5). The rate of pyrolysis of 1 was 4.8 times faster at 160 • C than that of ethyl phenyl sulfoxide used as a reference, while those of 2a and 2b were 107 and 155 times faster, respectively. The results indicate that the lone pair of electrons on the α-heteroatoms has a larger rate acceleration effect than the electronegativity of them. The substituent effects of the phenyl group of 2a and 2b gave positive Hammett ρ-values (ρ a = 0.76 and ρ b = 0.80 vs. σ ). Activation parameters for 2a and 2b are as follows: 2a, H ‡ = 112 kJmol −1 , S ‡ = −20 JK −1 mol −1 ; 2b, H ‡ = 107 kJmol −1 , S ‡ = −29 JK-1mol −1 .Large deuterium kinetic isotope effects for 1-acetoxyethyl-2,2,2-d 3 phenyl sulfoxides (2ad and 2bd) were observed (k H /k D = 3.5 ∼ 4.1). These results suggest that the pyrolysis of α-heteroatom substituted ethyl phenyl sulfoxides proceeds via a five-membered transition state deviated to E1-like in character. On the other hand, from the results of kinetics for the pyrolysis of 3, 4, and 5, no effect by the β-halogen atoms or some deceleration effect by the β-methoxy group was observed. Thus the reaction seems to proceed via an E1-like mechanism.

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“…Evidence available when this work was begun (9)(10)(11)(12), and added to subsequently (13)(14)(15), strongly indicates that the thermolysis of simple alkyl (or aryl alkyl) sulfoxides with at least one P-hydrogen atom leads to the olefin and the sulfenic acid via a cyclic concerted process in which the sulfoxide oxygen acts as the proton-abstracting agent. Reactions 4 + 5 c 6 in Scheme 2 illustrate the specific example of the sulfoxide thermolysis corresponding to the general system in Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

Axial:Equatorial Rate Ratios. 1. Eliminations Leading to the Exocyclic Methylene Group

King¹,

Coppen²

1971

Can. J. Chem.

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Phenyl cis-4-t-butylcyclohexanemethyl sulfoxide (4) thermolyzes to 1-t-butyl-4-methylenecyclohexane (5) at 116 and 130" about five to six times faster than its irans (equatorial) epimer 6. cis-4-t-Butylcyclohexanemethyl bromide (7) undergoes elimination with potassium t-butoxide in t-butyl alcohol at 100' about nine times faster than its trans (equatorial) epimer 8. The rate difference found for the sulfoxides 4 and 6 is the first clear demonstration of steric acceleration (without any contribution from any reagent repulsion effect) in the formation of an exocyclic carbon-carbon double bond in a simple anchored cyclohexane system. The faster elimination from 7 (us. 8) is ascribed primarily to steric acceleration; the experiment neither requires nor excludes the influence of non-bonding repulsions between the substrate and the attacking base.Le phenyl t-butyl-4 cis cyclohexanemethyl sulfoxyde (4) se transforme par thermolyse a 116 et 130' en t-butyl-1 methylene-4 cyclohexane (5); la vitesse est de cinq a six fois plus grande que pour 1'6pimkre (equatorial) trans 6. Le t-butyl-4 bromomethyl-1 cyclohexane (7) subit une reaction d'elimination sous I'action du t-butoxyde de potassium dans I'alcool t-butylique a 100" et la vitesse est de neuf fois plus grande que pour l'epimere (equatorial) trans 8. La difference de vitesse trouvee pour les sulfoxydes 4 et 6 constitue la premiere preuve d'dne acceleration sterique (sans aucune contribution d'effets de rkpulsion du reactif) dans la formation d'une double liaison carbone-carbone exocyclique appartenant a un systkme cyclohexanique rigide. L'klimination plus rapide dans 7 (us. 8) est due principalement a une acceleration stkrique; les resultats obtenus n'impliquent et n'excluent pas I'influence des rCpulsions de non-liaison entre le substrat et la base qui vient d'attaquer.

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Substituent effects in the pyrolysis of aryl n-propyl sulfoxides

Cited by 46 publications

References 1 publication

Cyclophane bis(sulfoxides) a thermal analysis study

Cyclophane bis(sulfoxides) a thermal analysis study

Pyrolysis of α- and β-Heteroatoms Substituted Ethyl Phenyl Sulfoxides

Axial:Equatorial Rate Ratios. 1. Eliminations Leading to the Exocyclic Methylene Group

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