Azo Compounds. XV. Biradical Sources. The Synthesis and Decomposition of Large Membered Ring Azo Compounds<sup>1</sup>

Overberger, C. G.; Lapkin, M.

doi:10.1021/ja01622a063

Cited by 30 publications

(9 citation statements)

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“…Commonly, oxidation of the hydrazine, as the initial urazole hydrolysis product, to the azoalkane can be effected in-situ by carrying out the hydrolysis under air. 47 To prepare azoalkane 4, however, we found a cleaner reaction when we separated the hydrolysis step from the oxidation by carrying it out under inert atmosphere. In addition, the hydrolysis time needed to be prolonged significantly (2 days) to affect higher conversion in larger scales.…”

Section: Synthesismentioning

confidence: 99%

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Hennig¹,

Schwarzlose²,

Nau³

2007

Arkivoc

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Two novel derivatives of 2,3-diazabicyclo[2.2.2]oct-2-ene were synthesized, carrying a carboxyl (4) and a methylcarboxyl (5) substituent at the bridgehead position. The photodecomposition quantum yields (51% for 4 and 2.9% for 5) and fluorescence lifetimes (29 ns for 4 and 345 ns for 5) in water were determined. The higher photoreactivity and fluorescence quenching for 4 was attributed to its higher propensity to undergo photochemical elimination of nitrogen as a consequence of the presence of the radical-stabilizing carboxyl group in the α-position. The absolute photodecomposition rate constants of 4 became faster upon protonation (e.g., at pH 2), which contrasted anticipated substituent effects on the C-N bonds strengths. ) which was attributed to reduced Coulomb attractions as a consequence of the 1,3-alternate conformation which this host adopts in water. The binding constants towards β-cyclodextrin were also low at pH 7.0 (< 120 M -1 ), which was attributed to the low hydrophobicity of the anionic form of the guests; in line with this interpretation, the binding constants with β-cyclodextrin increased at pH 2.0, by about one order of magnitude.

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Section: Synthesismentioning

confidence: 99%

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Hennig¹,

Schwarzlose²,

Nau³

2007

Arkivoc

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“…Flash column chromatography with 2 % ethyl acetate/98% heptane (v/v) yielded 2.5 g (63%) of XV as a clear colorless oil GR/ = 0.33). NMR (CDCI3): 2.22 (m, 2 ), 1.75 (m, 4 ), 1.55 (m, 4 ), 1.40 (m, 2 ), 1.32 (s, 6 ), 1.25 (m, 2 ), acetate/98 % heptane (v/v) yielded 3.24 g (79 %) of XVI as a clear colorless oil which existed as a mixture of isomers (Rf = 0.33).…”

Section: Scheme III Initiation Of Styrene Polymerization With a Capto...mentioning

confidence: 99%

Cycloalkane perketal initiators for styrene polymerization. 3. Decomposition chemistry of spiroperketals

Dais¹,

Drumright²,

Ellington³

et al. 1993

Macromolecules

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Initiators that form diradicals are of interest due to their potential for increasing polymerization rate. Spiroperketals made from 2,5-dihydroperoxy-2,5-dimethylhexane and cyclic ketones theoretically can form two diradical fragments during decomposition. However, thermolyses in ethylbenzene and styrene showed that they mainly undergo in-cage decomposition, resulting in poor performance as both hydrogen atom abstractors and polymerization initiators.Recently, we reported the decomposition chemistry of 1,l-bis(tert-buty1peroxy)cyclohexane (11.l The decomposition chemistry of I involves three pathways (Scheme I). The use of difunctional peroxides as initiators for styrene polymerization leads to the formation of high molecular weight polystyrene a t faster rates than achievable using monoperoxides. This rate increase is generally viewed to arise from diradical fragments (11). However, for every diradical fragment formed, there are two tertbutylperoxy monoradicals also formed, which attenuates the polymerization rate actually gained by the use of typical difunctional initiators. A class of peroxides that should theoretically form only diradicals are cyclic peroxides. However, anomalous results have been reported. For example, cyclic peroxides 111-V decompose without initiating polymerization of styrene.2 U I11 IV VThe earliest work3 aimed at forming diradicals for styrene polymerization was performed in an effort to test the Flory diradical mechanism (Scheme IIIs4 However, earlyon, there was controversy over the ability of diradical initiation to produce higher molecular weight polymer^.^*^ Later w~r k ,~,~ however, showed successes in producing higher molecular weight vinyl polymers using biradical initiators. For example, when comparing the monoradical initiator VI and the diradical initiator VII, Borsig et found (polymerization of methyl methacrylate at 60 "C) that significantly higher molecular weight was formed at the same monomer conversion using the diradical initiator. However, these data are complicated by the fact that at the same molar initiator concentration, the polymerization rate was slower for VII. The difference in initiating efficiency of the two initiators was explained in terms of cage reactions. The monoradicals formed from initiator VI diffuse quite efficiently from the cage and react with monomer. The diradicals, on the other hand, are in a permanent cage in that they cannot diffuse away from each other. Therefore, significantly disproportionation of the diradical (VIII) takes place to compete with initiation.

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“…(9) showed that the photochemical breakdown of a cyclic disulphide in styrene gave verllittle high molecular weight polystyrene, in contrast with tlie result obtained using a linear disulphide. Overberger and Lapltiii (6) observed that the thermal decoinpositioll of a 21-membered ring azo compound in styrene gave a relatively low yield of high polymer, and Cohen et al (10) observed that a 6-membered ring azo compound behaved iii a similar manner.…”

Section: T H E Peroxides a S Initiators For Tlre Polymerization Of Stmentioning

confidence: 99%

The Preparation of Cyclic Peroxides and Their Decomposition in Solution

Russell¹

1960

Can. J. Chem.

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The cyclic dimers of sebacyl, dodecanedioyl, and tetradecanedioyl peroxide have been prepared, together with high yields of the corresponding high molec~llar weight polylneric peroxides. The decomposition of these peroxides in styrene and benzene solution has been studied. The results show that if diradicals are formed in the breal;down of the cyclic peroxides, they undergo self-terrilination before reacting with a significant number of styrene molecules. In the presence of low concentrations of 1,l-diphenpl-2-picrylhydrazyl (DPPH) in benzene solution, self-termination of diradicals is preferred to reaction with the hydrazyl. INTRODUCTIONThe main objective of this investigation was to study the reactions of diradicals obtained by the thermal breakdow~l of cyclic peroxides. Previous worli (1, 2) has shown that phthalyl peroxide may be readily prepared by the reaction of phthalyl chloride with sodium peroxide, but that its decoinpositioil in solution may be complex (2, 3). I t was thus not possible to reach firill coi1clusions concerlling the reactions of diradicals froin studies involving this arolnatic peroxide. Some cyclic aliphatic peroxides have now beell prepared using the saine experimental method. Attelnpts were made to isolate succinyl, adipyl, suberyl, azelayl, sebacyl, dodecanedioyl, and tetradecanedioyl peroxides, but lonr molecular weight cyclic peroxides were only obtained in the last three cases. Polymeric peroxides of high molecular weight were always obtained as the major reaction products.The decomposition of the cyclic and linear peroxides in benzene solutioil was studied by direct analysis in order to show that there is no fuildainelltal difference in the primary step of the brealidown. Measurements were made of the rate of polymerization of styrene using the various peroxides as initiators to determine to what extent the radical intermediates gronr to give high molecular weight polystyrene. The decomposition of the peroxides in benzene solutions of 1,l-diphenyl-2-picrylhydrazyl (DPPI-I) was studied t o give infor~nation concerning the reactions of the radical intermediates with DPPI-I. E X P E R I M E N T A L IllaterialsChloroform was treated 1~4th co~lcentrated sulphuric acid t o remove alcohol and was washed twice with distilled water. Reagent grade (Fisher) benzene was used for the kinetic studies. Styrene was distilled a t 15 mm pressure and subjected to two bulb-to-bulb distillations on the high vacuum line. D P P H was prepared by the method of Goldschinidt and Renn (4); it was heated in vacua t o 90" for 1 hour to relnove complexed solvent.Succinyl, adipyl, sebacyl, and hexanoyl chloricles were East~nall I

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Azo Compounds. XV. Biradical Sources. The Synthesis and Decomposition of Large Membered Ring Azo Compounds¹

Cited by 30 publications

References 1 publication

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Cycloalkane perketal initiators for styrene polymerization. 3. Decomposition chemistry of spiroperketals

The Preparation of Cyclic Peroxides and Their Decomposition in Solution

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Azo Compounds. XV. Biradical Sources. The Synthesis and Decomposition of Large Membered Ring Azo Compounds1

Cited by 30 publications

References 1 publication

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Cycloalkane perketal initiators for styrene polymerization. 3. Decomposition chemistry of spiroperketals

The Preparation of Cyclic Peroxides and Their Decomposition in Solution

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Azo Compounds. XV. Biradical Sources. The Synthesis and Decomposition of Large Membered Ring Azo Compounds¹