5972-03-2Relevant academic research and scientific papers
Synthesis, Structure, and Thermolysis Mechanism of S-Alkoxythiazynes
Yoshimura, Toshiaki,Ohkubo, Masanori,Fujii, Takayoshi,Kita, Hiroshi,Wakai, Youko,Ono, Shin,Morita, Hiroyuki,Shimasaki, Choichiro,Horn, Ernst
, p. 1629 - 1637 (2007/10/03)
S-Alkoxy-S,S-diarylthiazynes were prepared by two methods: the alkaline hydrolysis of S,S-diaryl-N-halosulfilimines in aqueous alcohols and the reaction of S,S-diaryl-S-fluorothiazynes with sodium alkoxides. The structure of S,S-diphenyl-S-propoxythiazyne was determined by an X-ray crystallographic analysis, which showed a short SN bond length of 1.441(3) A. The thermolysis of S-alkoxythiazynes gave elimination products, which were identified as the corresponding carbonyl compounds and N-unsubstituted S,S-diarylsulfilimines. Kinetic experiments for the thermolysis of the S-alkoxy-S,S-diarylthiazynes were carried out. The first-order kinetic behavior, a large kinetic isotope effect (kHkD = 6.1 ) using S,S-diphenyl-S-[1,1-2H2]propoxythiazyne, a negative activation entropy (ΔS? = -30 J K-1mol-1), and a negative Hammett ρ-value (ρ= -0.35) on the phenyl group were obtained, suggesting that the reaction proceeds via a concerted five-membered cyclic transition state. A deviation from the ideal concerted transition state is discussed in comparison with that for sulfoxides.
Surface-Mediated Isomerization and Oxidation of Allyl Alcohol on Cu(110)
Brainard, Robert L.,Peterson, Cynthia G.,Madix, Robert J.
, p. 4553 - 4561 (2007/10/02)
Allyl alcohol reacts with clean and oxygen-covered Cu(110) surfaces to produce propanal, acrolein, n-propyl alcohol, and hydrogen under ultrahigh-vacuum conditions.Very small amounts of propylene and water are also formed.This pattern of reactivity contrasts sharply to the selective oxidation to acrolein observed on Ag(110).On the clean Cu(110) surface allyl alcohol undergoes O-H cleavage to form the surface alkoxide CH2=CHCH2O(a) and H(a).The results suggest that the olefin in this species undergoes partial hydrogenation to the surface-bound oxametallacycles (-CH2CH2CH2O-)(a) and (-CH-(CH3)CH2O-)(a) and complete hydrogenation to CH3CH2CH2O(a).Propanal forms at 320 K via further reaction of these oxametallacycles.Evidence for a ?-bonded allyl oxide CH2=CHCH2O(a), which is more stable than n-propoxide (CH3CH2CH2O(a)) toward β-hydride elimination, is presented.This allyl oxide decomposes at 370 K to form acrolein.The interaction of the double bond with the surface apparently restricts the interaction of the β-C-H bond with the surface and increases the stability of this species.Propanal, acrolein and H2 are formed at 435 K by a process thought to involve the thermal decomposition of (-CH2CH2CH2O-)(a) by a β-hydride elimination pathway.This dehydrogenation pathway exhibits an activation energy 8 kcal/mol greater than for acyclic alkoxides.The conversion of allyl alcohol to propanal and propyl alcohol obviously involves the hydrogenation of the double bond which, by comparison, does not occur for propylene coadsorbed with hydrogen under similar conditions on this surface.Clearly, the hydroxyl group in allyl alcohol facilitates the hydrogenation of its olefin group by tethering the doublebond to the surface at temperatures higher than the normal desorption temperature of olefins.
