Absolute Rate Constants for Reactions of Tributylstannyl Radicals with Bromoalkanes, Episulfides, and alpha-Halomethyl-Episulfides, -Cyclopropanes, and -Oxiranes: New Rate Expressions for Sulfur and Bromine Atom Abstraction

Journal Article · Fri Feb 20 04:00:00 EST 2004 · Journal of Organic Chemistry, 69(4):1020-1027

DOI:https://doi.org/10.1021/jo035467h· OSTI ID:15007496

Franz, James A; Shaw, Wendy J; Lamb, Claude N; Autrey, Thomas; Kolwaite, Douglas S; Camaioni, Donald M; Alnajjar, Mikhail S

Arrhenius rate expressions were determined for the abstraction of bromine atom from 2-phenethyl bromide by tri-n-butylstannyl radical (Bu3Sn) in benzene using transient absorption spectroscopy, (log(kabs,Br/M-1 s-1) ) (9.21 ( 0.20) - (2.23 ( 0.28)/, ) 2.3RT kcal/mol, errors are 2) and for the abstraction of sulfur atom from propylene sulfide to form propylene, (log(ks/M-1 s-1) ) (8.75 (0.91) - (2.35 (1.33)/). Rate constants for reactions of organic bromides, RBr, with Bu3Sn were found to vary as R ) benzyl (15.6) > thiiranylmethyl (6.2) > oxiranylmethyl (3.1) > cyclopropylmethyl (1.3) > (2-phenethyl (1.0), with kabs,Br ) 6.8* 107 M-1 s-1 at 353 K for 2-phenethyl bromide.Bromine abstraction from R bromomethylthiirane is about 7-fold faster than sulfur atom abstraction and is comparable to the reactivity of a secondary alkyl bromide. The potential surface for the vinylthiomethyl f allylthiyl radical rearrangement at UB3LYP/6-31G(d) and UB3LYP/6-311+G- (2d,2p) levels of theory suggests that the thiiranylmethyl radical is produced about 9 kcal/mol above the allylthiyl radical on the rearrangement surface, consistent with the observed enhancement of the Br atom abstraction from the thiirane and with synchronous C-S bond scission of the thiirane ring. The selectivities reported in this work for S vs Cl and Br abstraction provide applications for radical-based synthesis and new competition basis rate expressions for trialkylstannyl radicals.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 15007496
• Report Number(s): PNNL-SA-41000; KC0302010
• Journal Information: Journal of Organic Chemistry, 69(4):1020-1027, Journal Name: Journal of Organic Chemistry, 69(4):1020-1027
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY