LUKOSE MATHEW and JOHN WARKENTIN. Can. J. Chem. 66, l l (1988).The radical chain decomposition of cyclopropylmethyl (I-hydroxy-1-mcthylethy1)-diazcnc ((CH3)2C(OH)N=NCHI--<1 1) at 253-341 K in hexafluorobenzene or in dichloromethane solution containing brornotrichloromethane affords cyclopropylmethyl bromide, 4-bromo-I-butene, I-bromo-5,5,5-trichloro-2-pentene, and 3,5-dibromo-I, I, I-trichloropcntane from the cyclopropylmethyl portion of 1. Other major products are nitrogen, acetone, and chloroform. The rate constant for formation of cyclopropylmethyl bromide by attack of cyclopropylmethyl free radicals from 1 at bromine of BrCCI, (kyy) was calculated from the product composition using the known rate constant for rearrangement of cyclopropylmethyl radicals to 3-buten-I-yl radicals. At 25"C, kTF = 6.5 X lo8 M-I s-I and the temperature dependence is given by log (ksm/M-I s-) = ( 10.6 5 0.3) -(2.4 C 0.4)/0, where 0 = 2.3R~kcal/mol-l. Non-chain decompositionof (CH3),C(OH)N=N-R(2, R = Bu, and3, R = Ph) in the presence of excess 1 ,I ,3,3-tetramethylisoindolin-2-yloxyl (4) and bromotrichloromethane afforded BuBr and PhBr, respectively, in yields determined by the relative concentrations of 4 and BrCCI3. Rate constants for coupling ( k c ) of Bu. and Ph. with 4 were assumed to be proportional to rate constants for diffusion controlled reactions, kd, which were estimated from measured viscosities. Values of k ! : and k; : , calculated from kc and product yields for reactions at 80°C, are 0.26 X lo9 and 1.55 X lo9 M-' s-l, respectively. The relative radical reactivities toward BrCC13 at 80°C are Ph, 6; cpm, 5; Bu, 1.LUKOSE MATHEW et JOHN WARKENTIN. Can. J. Chem. 66, 1 1 (1988).La dCcomposition radicalaire en chaine du cyclopropylmCthy1 (hydroxy-l methyl-1 Cthyl) diazkne ((CH3)2C(OH)N= NCH2CH(CH2),, I), a des tempkratures allant de 253 2 341 K, dans des solutions d'hexafluorobenzkne ou de dichloromCthane contenant du bromotrichloromtthane, conduit au bromure de cyclopropylmCthyle, au bromo-4 butkne-I, au bromo-l trichloro-5,5,5 pentkne-2 et au dibromo-3,5 trichloro-l ,I , l pentane qui dtrivent tous de la portion cyclopropylmCthyle du compost 1. Les autres produits importants sont l'azote, I'acCtone et le chloroforme. On a calculi2 la constante de vitesse pour la formation du bromure de cyclopropylmtthyle par attaque des radicaux libres cyclopropylmCthyles, provenant du compost 1, au niveau du brome du BrCC13 (kTF); pour ce faire, on afait appel a lacomposition des produits-et on a utilisC la constante de vitesse connue pour la transposition des radicaux cyclopropylmCthyles en radicaux butkne-3 yles. A 25"C, kgm = 6.5 X lo8 M-' s-I et lavariation avec la tempkratureest donnte parl'iquation suivante : log (kxm/M-I s-I) = (10,6 C 0,3) -(2,4 -C 0,4)/0, dans laquelle 0 = 2,3R~kcal/rnol-'. Les dCcompositions des composCs (CH3)?C(OH)N=N-R (2, R = Bu, et 3, R = Ph) par un processus qui n'implique pas de chaines, en presence d'un excks de tCtramCthyl-1,1,3,3 isoindolinyl-2 oxyl (4) et de bromotrichloromCthane, fournissent respect...
a-Hydroperoxyalkyl diazenes (Me2C(OOH)N=NR, 1, R = CH2CF3, CH2CH20Me, CH(Me)2, CMe3, CH2Ph, Ph, CH2CH20Ph, and c-C3HSCD2) decompose in benzene, at 50°C or less, by a mechanism involving free radical (Re) intermediates. The radicals were trapped with 1-methyl-4-nitroso-3,5-diphenylpyrazole, 2, to afford spin adducts (nitroxyls) that were observed by ESR spectroscopy. When the solvent was ethyl vinyl ether, radicals from 1 (R = CH2CH20Ph) were trapped by the solvent and the adduct radicals so formed were spin trapped by 2. These observations support free radical mechanisms for thermolysis of 1 and for the hydroxyalkylations that occur when 1 are decomposed in solutions containing en01 ethers or other unsaturated substrates. The ring-opening of cyclopropylmethyl radicals (cpm) to 3-butenyl radicals was used to estimate the rate constant for radical trapping by 2. For cpm the rate constant is given by log kcPm = (10.7 =t 0.4) -(3.9 =t 0.5)/9 where 9 = 2.3 RT kcal mol-'. At 25"C, the spin trapping rate constant has the value 6.9 x lo7 M-' s-l. Les a-hydropCroxyalkyldiazbnes (Me2C(OOH)N=NR, 1, R = CH2CF3, CH2CH20Me, CH(Me)2, CMe3, CH2Ph, Ph, CH2CH20Ph et c-C3HSCD2) se dCcomposent dans le benzbne B une tempCrature Cgale ou infkrieure B 50°C selon un mkcanisme impliquant des radicaux libres (Re) intermediaires. On a piCgC les radicaux libres avec le rnCthyl-1-nitroso-4-diphCnyl-3,5-pyrazole, 2, pour obtenir des adduits de spin (nitroxyles) que l'on a observis par spectroscopie de ESR. L'tther ethylvinylique utilisC comme solvant piege les radicaux provenant du composC 1 (R = CH2CH20Ph) et les adduits radicalaires ainsi formCs sont captCs par le composC 2. Ces observations tendent ti prouver que la thermolyse du compost 1 et l'hydroxyalkylation, qui se produit lorsque le compost 1 se dCcompose dans des solutions contenant des Cthers Cnoliques ou d'autres substrats insaturis, impliquent un mecanisme radicalaire. On s'est bas6 sur l'ouverture du cycle des radicaux cyclopropylmtthyles (cpm) qui conduit aux radicaux butCnyl-3 pour Cvaluer la constante de vitesse de la capture des radicaux par le compost 2. Pour le cpm, la constante de vitesse est donnCe par la rklation : log kcpm = (10,7 =t 0,4) -(3,9 =t 0,5)/9 ou 9 = 2,3 RT kcal mol-I. On Cvalue la constante de capture de spin B 6,9 x lo7 M-I s-' 2 25°C.
Rate constants for induced decomposition of 5-hexenyl(1 -hydroperoxy -1 -methylethyl) diazene ((CH3)2C(OOH)N=N-(CH2),CH=CH2, 2) have been estimated. Thermolysis of 2 at 50°C affords 5-hexenyl radicals which abstract the hydroxyl group from 2 in competition with cyclization of 5-hexenyl to cyclopentylmethyl radicals. The known rate constant (kc) for that cyclization was used to clock the bimolecular hydroxyl abstraction process. For reaction in hexafluorobenzene at 50°C, the rate constant for abstraction of hydroxyl from 2 (koH) was found to be dependent on the concentration of 2. For example, at [2] = 0.4 M, koH = 3.2 X lo6 M-I S K I whereas, at [2] = 0.10 M, koH = 1.8 X lo7 M-I s-l. The concentration dependence of koH is attributed to the effects of intermolecular hydrogen bonding and the large absolute values of koH are ascribed to concerted induced decomposition, the 0-0 bond being broken in concert with scission of the nearest C-N bond of the azo function. The relevance of the results, to synthetic application of a-hydroperoxyalkyl diazenes in hydroxyalkylation reactions, is discussed.CHANDRA LAKHANI, LUKOSE MATHEW et JOHN WARKENTIN. Can. J. Chem. 65, 1748Chem. 65, (1987.On a CvaluC les constantes de vitesse pour la dCcomposition induite de I'hextne-5 yl (hydroperoxy-1 methyl-1 Cthyl) diazkne ((CH3)2C(OOH)N=N(CH2)4CH=CH2, (2). La thermolyse du composC 2, 50°C, conduit a des radicaux hexkne-5 yles qui enlkvent le groupernent hydroxyle du compose 2; cette rCaction est en compttition avec la cyclisation de I'hexkne-5 yle en radical cyclopentylmCthyle. On a utilist la constante de vitesse (kc) de cyclisation qui est connue comme chronomktre pour mesurer la vitesse du processus d'enltvement bimoltculaire de I'hydroxyle. Dans le cas de la reaction dans I'hexafluorobenzkne, a 50°C, on a trouvk que la constante de vitesse pour I'enlkvement de I'hydroxyle du composC 2 (kOH) depend de la [Traduit par la revue]
. J. Chem. 65, 31 1 (1987).Cyclization of the 5-hexenyl free radical to the cyclopentylmethyl free radical was used to clock chlorine atom abstraction by 5-hexenyl from carbon tetrachloride in solution. The source of 5-hexenyl radicals was 5-hexenyl[I-hydroxy-1-methylethylldiazene ((CH3)2C(OH)N=N(CH2)4CH=CH2), which decomposes thermally in CC14 by a radical chain mechanism to afford chloroform, acetone, nitrogen, 6-chloro-1-hexene, cyclopentylchloromethane, I-hexene, and methylcyclopentane as primary products. 6-Chloro-I-hexene is converted, in part, to a secondary product, 1,1,1,3,7-pentachloroheptane, by radical chain addition of CC14 to the double bond. The rate constant for chlorine atom abstraction, kc,, was calculated from the product composition and the known rate constant for cyclization of the 5-hexenyl radical. On utilid la cyclisation du radical libre hexkne-5 yle en cyclopentylmtthyle pour mesurer le temps qu'il faut au radical hexhe-5 yle pour enlever un atome de chlore du tttrachlorure de carbone en solution. On a utilisC I'hexkne-5 yl[hydroxy-1 mtthyl-1 tthylldiaztne ((CH3)2C(OH)N=N(CH2)4CH=CH2) cornme source de radicaux hexene-5 yles qui se dtcomposent thermiquement en solution dans le CC14 par un mtcanisme radicalaire en chaine pour donner du chloroforme, de I'acCtone, de l'azote, du chloro-6 hexene-1, du cyclopentylchloromtthane, de I'hexene-1 et du mCthylcyclopentane comme produits primaires. Le chloro-6 hextne-1 se transforme, en partie, en un produit secondaire, le pentachloro-1 , 1 , l,3,7 heptane, par une addition radicalaire en chaine du CC14 la double liaison. On a calculC la constante de vitesse pour la rtaction d'abstraction de l'atome de chlore, kcl, en se basant sur la composition des produits et sur la constante de vitesse connue pour la cyclisation du radical hextne-5 yle. A des temptratures allant de 274 a 353 K , la valeur de kcl est exprimee par ]'equation log (kcl/M-' s-') = (8,4 * 0,3) -(6,2 * 0,4)/0 dans laquelle 0 = 2,3RT kcal mol-'; ceci conduitaune valeur de kF;C = 7,2 X lo3 M-I S-I . Cette valeur est beaucoup plus faible que les tvaluations qui ont t t t rapporttes rtcemment pour d'autres radicaux alkyles primaires.[Traduit par la revue] Introduction Rate constants for abstraction of a chlorine atom from CC14 by carbon centered free radicals are of considerable current interest. The reaction is a potential kinetic standard for determination of a variety of other free radical reaction rate constants by the competition method. Two groups (1, 2) have recently pointed to the need for reliable values of kcl for solution work with alkyl radicals. There are two problems with literature values for kc,. First, the numbers from solution work with similar or identical alkyl radicals in different laboratories are widely scattered and, second, the numbers from gas phase studies are considerably smaller than most of the lowest values
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.