Deuterium Isotope Effects on the Air Oxidation of Cumene

Boozer, Charles E.; Ponder, B. W.; Trisler, John C.; Wightman, C. E.

doi:10.1021/ja01588a062

Cited by 18 publications

(7 citation statements)

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“…7). These isotope effects are in fair agreement n-it11 the values obtained by Boozer et al (14) from the oxidation of curnene and CGI-IjC (CD3) 2H, i.e., rateII/rate, = 0.88. This deuteriuru (10) and Vzclrzitinskzz (12) For personal use only.…”

Section: Uni?zhibited Oxidation Of A-methylstyrenesupporting

confidence: 89%

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: III. Α-Methylstyrene, Β-Methylstyrene, AND INDENE

Howard¹,

Ingold²

1966

Can. J. Chem.

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Absolute rate constants for the copolymerization of a-methylstyrene and oxygen have been measured from 13 to 50 OC. The propagation and termination rate constants can be represented by k, = (6.6 Z+Z 0.7) X lo6 exp (-(8 070 + 800)lRT) 1 mole-' s-I kt = (1.6 =t 0.7) X lo8 exp (-(3 700 ZI Z 1 GOO)/RT) 1 m~l e -~s -] . Experiments with 2.6-di-t-butyl-4-methylphenol a t 65 "C have shown that C G H~C ( C H~) : C H~ and C O H~C ( C D~) : C D~ have the same propagation rate constant but that cham termlnatlon involves a deuterium isotope effect ( k t ) n / ( k t )~ = 1.5.Absolute rate constants for the copolymerization of oxygen with a-methylstyrene and with indene at 30 "C showed that a significant fraction of the oxidation chains were terminated by a lcinetically first order process (rate constant k,). The rate constants for 8-methylstyrene and indene a t 30 "C are k, = 51 and 142 1 mole-Is-', k t = 1.6 X lo7 and 2.5 X 107 1 mole-1s-1, and k, = 0.61 and 1.2 s-l, respectively. The propagation rate constant for indene can be separated into a rate constant for the copolymerization with oxygen (kndd = 128 I mole-' s-l) and a rate constant for hydrogen atom abstraction (k,b,t, = 14 1 mole-' s-I). In the presence of heavy water the first order process for indene had a deuterium isotope effect (k,)/(k,)~?o = 3. IXTRODUCTIONThe effects of temperature and solvents on the absolute rate constants for the autoxidation of styrene, i.e., for its copolylnerization with oxygen, were described in the first paper in this series (1). The second paper gave the absolute rate constants for four deuteriunl-labelled styrenes and a nurtlber of ring-substituted styrenes (2). The present paper extends this xvork t o a-and P-methylstyrene and indene. Both a-methylstyrene and iridelie have been shown to copolylnerize with oxygen in tllermally initiated oxidations (3, 4). a-PIethylstyrene is of particular interest since it yields a tertiary peroxy radical. The mechanis~n of chain termination for con-lpounds giving tertiary peroxy radicals has beell under very active study in the past 2 or 3 years (5-9) but absolute rate constants have been lneasured in only a few cases, i.e., for chain propagation (k,) and chain termination ( k t ) in the autoxidation of culnene (9-12) and 2,4,6-trimethyl heptane (13) and for the mutual destruction of t-butylperoxy radicals derived from t-butylhydroperoxide (9). a-A,leth>,lstyrene is also interesting in that the rate of the a,al-azo-bis-isobutyronitrile (AIBN) therlnally initiated oxidation has been reported to increase very noticeably as the oxygen pressure is increased, e.g., the rate a t 50' with 0.01 mole/l AIBN is 0.076, 0.12, and 0.13 mole 1-I h-I a t 100, 750, and 3 200 n~m oxygen pressure, respectively (3). This variation in the rate with the oxygen pressure has been attributed to a contribution from crossed chain termination, involving aralkyl (R') and aralliylperoxy (RO;) radicals, to the overall rate of chain terlnination a t oxygen pressures below 3 200 mm (3). This paper describes the effects o...

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Section: Uni?zhibited Oxidation Of A-methylstyrenesupporting

confidence: 89%

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: III. Α-Methylstyrene, Β-Methylstyrene, AND INDENE

Howard¹,

Ingold²

1966

Can. J. Chem.

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“…Russell (14) calculated the true primary isotope effect for hydrogen abstraction, (kpcc)/(lcpc9,D, to be 5.5 at 60" using cumene-a-d containing 58.4% deuterium. Boozer et al (15) compared cumene with two samples of P-deutero-cumene containing 1.4 and 3.0 atoms of deuterium per molecule.The secondary isotope effect for propagation was measured by addingp-nitrophenol or 2,4-dichlorophenol to inhibit the normal termination process. Values of (kPCC)/(kpC9, ,,-, in the range 1.05-1.27 were obtained at 65".…”

Section: Resultsmentioning

confidence: 99%

Absolute rate constants for hydrocarbon oxidation. VIII. The reactions of cumylperoxy radicals

Howard¹,

Ingold²,

Symonds³

1968

Can. J. Chem.

104

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Absolute rate constants have been measured for the reactions of cumylperoxy radicals with a number of hydrocarbons. The cumylperoxy radicals were produced from cumene hydroperoxide. Sufficient hydroperoxide was present to ensure that only cumylperoxy radicals were involved in the rate-determining propagation reaction.Primary and secondary deuterium isotope effects have been measured for propagation and termination in the oxidation of cumene. The rate of hydrogen atom abstraction from ring-substituted cumenes by cumylperoxy radicals can be correlated by the Hammett equation using o* substituent constants, p = -0.29. Primary and secondary peroxy radicals are about 3-5 times more reactive in hydrogen abstraction than tertiary peroxy radicals.

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“…Russell, 17 Walling 16 and Boozer et al 31 have reported the formation of α-methylstyrene in the autoxidation of cumene and have suggested that it arises from cumylperoxyl radicals. Although no mechanisms were proposed, a plausible route is shown in Scheme 4.…”

Section: Oxidation Of Cumene and Tert-butylbenzenementioning

confidence: 99%

The oxidation of ethylbenzene and other alkylaromatics by dioxygen catalysed by iron(III) tetrakis(pentafluorophenyl)porphyrin and related iron porphyrins

Evans

Smith

2000

J. Chem. Soc., Perkin Trans. 2

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The oxidation of ethylbenzene with dioxygen catalysed by iron() porphyrins in a solvent free system has been studied over the temperature range 30-110 ЊC. The time dependence of the formation of the three main products, 1-phenylethanol, acetophenone and 1-phenylethyl hydroperoxide, and the fate of the iron porphyrin are interpreted in terms of a free radical autoxidation mechanism. The yields of the oxidation products are determined by the rate of reaction and by the lifetime of the catalyst. Catalyst degradation is shown to involve reaction of the porphyrin ligand with 1-phenylethoxyl and 1-phenylethylperoxyl radicals. The disadvantages of increased induction periods and longer reaction times of the oxidations observed at lower reaction temperatures are counter balanced by increased catalyst turnovers. Less extensive studies on the oxidations of toluene, cumene, (2-methylpropyl)benzene and tert-butylbenzene support the overall mechanism proposed for ethylbenzene.A comparative study using the catalysts iron() 2, 3,7,8,12,13,17,18-octachloro-5,10,15,20-tetrakis-(2,6-dichlorophenyl)porphyrin and iron() tetrakis(pentafluorophenyl)porphyrin and five of its derivatives reveals that halogenation of the β-pyrrole positions markedly increases the activity of the catalysts but not the stability of the porphyrin towards degradation. The highest yields were obtained with the µ-oxodimer of iron() tetrakis(pentafluorophenyl)porphyrin and iron() tetrakis(4-dimethylamino-2,3,5,6-tetrafluorophenyl)porphyrin.

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Deuterium Isotope Effects on the Air Oxidation of Cumene

Cited by 18 publications

References 0 publications

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: III. Α-Methylstyrene, Β-Methylstyrene, AND INDENE

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: III. Α-Methylstyrene, Β-Methylstyrene, AND INDENE

Absolute rate constants for hydrocarbon oxidation. VIII. The reactions of cumylperoxy radicals

The oxidation of ethylbenzene and other alkylaromatics by dioxygen catalysed by iron(III) tetrakis(pentafluorophenyl)porphyrin and related iron porphyrins

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