Antioxidants and stabilizers. LII. Sensitized photooxidation of 2,6‐di‐tert‐butyl‐4‐methylphenol

Taimr, L.; Pospı́šil, J.

doi:10.1002/apmc.1974.050390116

“…The reaction products are known to be the relatively unstable cyclohexadienone hydroperoxide intermediates (14-16), leading to demethoxylation, ring-opening, and side-chain elimination reactions (Schemes 5 and 6). In fact, such species have been detected, isolated, and quantified as photochemical transformation products of commercial antioxidants (26)(27)(28). The demethylation and ring-opening reactions give rise to catechols and various mono and dicarboxylic acids, such as maleic and muconic acids (Scheme 6), while the side-chain elimination reactions cause the formation of other organic acids and para-quinones, thus depolymerizing lignin.…”

Section: The Reactivity Of Guaiacyl Phenolic Units With Oxygenmentioning

confidence: 99%

Fundamentals of o×ygen delignification. Part II. Functional group formation/elimination in residual kraft lignin

Asgari¹,

1998

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The complex interaction of softwood residual kraft lignin with oxygen at elevated temperatures, pressures, and pH's was investigated by isolating and systematically oxidizing the lignin, as a function of time and temperature. The isolation of the oxidized lignin was carried out using a multistep procedure developed specifically to recover all species. Detailed quantitative 31 P NMR measurements provided, for the first time, three-dimensional plots describing the formation and (or) elimination of the various functional groups. Oxidative demethoxylation reactions were found to induce the formation of catechols, which are, most likely, reactive intermediates of the oxidation. The rate of carboxylic acid formation and guaiacyl phenol elimination was found to follow two distinct phases: a rapid initial phase followed by a slower phase. More specifically, the rate of carboxylic acid group formation was found to dramatically increase as the reaction temperature increased, analogous to the profiles obtained for the elimination of guaiacyl phenolic units. At reaction temperatures typical of conventional commercial oxygen delignification installations (80-100°C), only minor oxidation was found to occur within the lignin. At these temperatures, increasing the reaction time did not significantly aid the formation of carboxylic acid groups on lignin despite the idealized twophase homogeneous conditions. The technological ramifications of these data imply that a three-phase oxygen delignification system, operating at temperatures below 100°C, causes only minor oxidative changes to the structure of the lignin in the fibre. It was also possible to isolate the effect of alkali and temperature on the structure of residual kraft lignin through experiments in which pressurized oxygen was replaced by nitrogen. These data revealed a concealed set of alkali-induced condensation and fragmentation reactions.

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“…The reaction products are known to be the relatively unstable cyclohexadienone hydroperoxide intermediates (14)(15)(16), leading to demethoxylation, ring-opening, and side-chain elimination reactions (Schemes 5 and 6). In fact, such species have been detected, isolated, and quantified as photochemical transformation products of commercial antioxidants (26)(27)(28). The demethylation and ring-opening reactions give rise to catechols and various mono and dicarboxylic acids, such as maleic and muconic acids (Scheme 6), while the side-chain elimination reactions cause the formation of other organic acids and para-quinones, thus depolymerizing lignin.…”

Section: The Reactivity Of Guaiacyl Phenolic Units With Oxygenmentioning

confidence: 99%

Article

Asgari¹,

1998

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The complex interaction of softwood residual kraft lignin with oxygen at elevated temperatures, pressures, and pH's was investigated by isolating and systematically oxidizing the lignin, as a function of time and temperature. The isolation of the oxidized lignin was carried out using a multistep procedure developed specifically to recover all species. Detailed quantitative 31 P NMR measurements provided, for the first time, three-dimensional plots describing the formation and (or) elimination of the various functional groups. Oxidative demethoxylation reactions were found to induce the formation of catechols, which are, most likely, reactive intermediates of the oxidation. The rate of carboxylic acid formation and guaiacyl phenol elimination was found to follow two distinct phases: a rapid initial phase followed by a slower phase. More specifically, the rate of carboxylic acid group formation was found to dramatically increase as the reaction temperature increased, analogous to the profiles obtained for the elimination of guaiacyl phenolic units. At reaction temperatures typical of conventional commercial oxygen delignification installations (80-100°C), only minor oxidation was found to occur within the lignin. At these temperatures, increasing the reaction time did not significantly aid the formation of carboxylic acid groups on lignin despite the idealized twophase homogeneous conditions. The technological ramifications of these data imply that a three-phase oxygen delignification system, operating at temperatures below 100°C, causes only minor oxidative changes to the structure of the lignin in the fibre. It was also possible to isolate the effect of alkali and temperature on the structure of residual kraft lignin through experiments in which pressurized oxygen was replaced by nitrogen. These data revealed a concealed set of alkali-induced condensation and fragmentation reactions.Résumé : En procédant à son isolement et son oxydation systématique en fonction du temps et de la pression, on a étudié l'interaction complexe de la lignine kraft résiduelle de bois mou avec l'oxygène à des températures, pressions et pH élevés. On a réalisé l'isolation de la lignine oxydée en appliquant une méthode en plusieurs étapes développées spécifiquement pour récupérer toutes les espèces. Des mesures quantitatives détaillées de RMN du 31 P ont permis d'obtenir pour la première fois des courbes tridimensionnelles décrivant la formation et (ou) l'élimination de divers groupes fonctionnels. On a trouvé que les réactions de déméthoxylation oxydante induisent la formation de catéchols qui sont vraisemblablement des intermédiaires réactifs dans l'oxydation. On a trouvé que la vitesse de formation de l'acide carboxylique et d'élimination de guaïacol phénolique suit deux phases distinctes : une phase initiale rapide suivie d'une phase plus lente. D'une façon plus spécifique, on a trouvé que la vitesse de formation d'acide carboxylique augmente d'une façon dramatique lorsqu'on élève la température; on a obtenu des profils analogues pour...

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“…Thus, the formation of the starting bisphenol I1 was proved in all three cases and corresponds to the behavior of 2,6-ditert-butyl-4-methyl-4hydroperoxy-2,5-cyclohexadiene-l-one. 2 Consequently the reaction investigated in this work has a rather general character and can become important in the investigation of the stabilization of polymers, since it leads to the regeneration of the antioxidant.…”

Section: Ch3 C H 2 Chmentioning

confidence: 99%

Antioxidants and stabilizers. LXIII. Sensitized photooxidation of 2,2′‐methylenebis(4‐methyl‐6‐tert‐butylphenol)

Taimr

¹

,

Pospı́šil

²

1976

J. polym. sci., C Polym. symp.

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SUMMARY:In connection with a complex investigation of the transformations of stabilizers during the ageing of polymers, the photooxidation of 2,6-di-tert-butyl-4-methylphenol (IV) sensitized with methylene blue in methanol was investigated. If the reaction takes place in a dilute solution, phenol(1V) is oxidized with singlet oxygen forming 2,6-di-tert-butyl-4-methyl-4-hydroperoxy-2,5-cyclohexadiene-l -one (V). In a concentrated solution phenol (IV) is attacked by an excited sensitizer which gives rise to a corresponding aryloxy radical; transformations of the latter yield 2,6-di-tert-butyl-4-methoxymethylphenol (VI). The further reaction of phenol (IV) is slower, but similar to phenol (IV): by a reaction with singlet oxygen 2,6-di-tert-butyl-4-methoxymethyI-4-hydroperoxy-2,5-cyclohexadiene-1-one (VIII) is formed, while a reaction with the excited sensitizer again gives rise to the corresponding aryloxyl. Transformations of the latter produce 3.5-di-tert-butyl-4-hydroxybenzaldehyde (X). Under oxidizihg conditions the compounds (VIII) and (X) undergo further transformation to yield 2,6-di-tert-butyl-1.4-benzoquinone (IX). ZUSAMM ENFASSU NG :Die mittels Methylenblau sensibilisierte Photooxidation von 2,6-Di-tert-butyl-4-methylphenol (IV) in Methanol wurde im Zusammenhang mit dem Studium der Umwandlungen von Stabilisatoren wihrend der Alterung von Polymeren studiert. Wahrend der Reaktion in verdiinnter Losung wurde das Phenol (IV) mit Singulett-Sauerstoff zu 2.6-Ditert-butyl-4-methyl-4-hydroperoxy-2,5-cyclohexadien-1 -on (V) oxidiert. In konzentrierter Losung wurde das Phenol (IV) durch angersgten Sensibilisator angegriffen: dadurch entstand zuerst das entsprechende Aryloxyl, dessen weitere Umwandlung zu 2,6-Di-tertbutyl-4-methoxymethylphenol (VI) fuhrte. Das Phenol (VI) reagierte weit langsamer, aber analog dem Phenol (IV), d. h. durch Reaktion mit Singulett-Sauerstoff entstand 2,6-Di-tert-butyl-4-methoxymethyl-4-hydroperoxy-2,5-~y~lohexadien-l-on (VIII). Ebenso entstand ein Aryloxyl durch Reaktion mit dem angeregten Sensibilisator; weitere Umwandlungen fuhrten zum 3,5-Di-tert-butyl4-hydroxybenzaldehyd (X). Die Verbindungen (VIII) und (X) reagierten weiter zum 2,6-Di-tert-butyl-l,4-benzochinon (IX).

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Antioxidants and stabilizers. LII. Sensitized photooxidation of 2,6‐di‐tert‐butyl‐4‐methylphenol

Cited by 23 publications

References 19 publications

Fundamentals of o×ygen delignification. Part II. Functional group formation/elimination in residual kraft lignin

Fundamentals of o×ygen delignification. Part II. Functional group formation/elimination in residual kraft lignin

Article

Antioxidants and stabilizers. LXIII. Sensitized photooxidation of 2,2′‐methylenebis(4‐methyl‐6‐tert‐butylphenol)

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