Trapping of Dioxygen Dissolved in Water by Alkylhydroxylamines: A Comparison of Hydroquinone, Gallic Acid and Aminopheno
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ORIGINAL PAPER
Trapping of Dioxygen Dissolved in Water by Alkylhydroxylamines: A Comparison of Hydroquinone, Gallic Acid and Aminophenols as Organocatalysts Raphae¨l Lebeuf • Ve´ronique Nardello-Rataj Jean-Marie Aubry
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Published online: 18 May 2013 Ó Springer Science+Business Media New York 2013
Abstract One of the most usual methods used to deoxygenate water and prevent the corrosion of industrial boilers is based on the reduction of dioxygen in aqueous alkaline solution with an hydroxylamine in the presence of catalytic amounts of hydroquinone (H2Q). In order to improve the effectiveness and the ‘‘greenness’’ of this process, the influence of the nature of the hydroxylamine and of the catalyst has been investigated. With H2Q as a catalyst, the efficiency of various hydroxylamines was found to be in the following order: methylhydroxylamine[ dimethylhydroxylamine [ hydroxylamine [ tert-butylhydroxylamine [ diethylhydroxylamine (DEHA). To replace the potentially carcinogenic hydroquinone, a natural polyphenol, i.e. gallic acid, which was previously shown to be safer and more robust that H2Q to trap O2 in the presence of DEHA, was used. Methylhydroxylamine was still by far the most active partner, but DEHA was almost as efficient as the other hydroxylamines, free hydroxylamine being the least active oxygen scavenger. As only a catalytic amount of dioxygen scavenger is required in the presence of appropriate hydroxylamines, compounds having a bit more acute toxicity but higher reactivity than hydroquinone may also be alternative catalytic systems. Hence, five aminophenols, i.e. 4-aminophenol, 4-amino2,5-dichlorophenol, 5-amino-salicylic acid, 4-N-methylaminophenol and 4-N,N-dimethylaminophenol, were also investigated. Among them, 4-N-methylaminophenol was found to be the most efficient although much slower than H2Q.
R. Lebeuf V. Nardello-Rataj J.-M. Aubry (&) EA 4478 Chimie Mole´culaire et Formulation, Cite´ Scientifique, Universite´ Lille Nord de France, Universite´ Lille1 and ENSCL, BP 90108, 59652 Villeneuve d’Ascq Cedex, France e-mail: [email protected]
Keywords Oxygen scavengers Hydroxylamines Hydroquinone Gallic acid Aminophenols Boiler Deoxygenation
1 Introduction Corrosion of metallic surfaces due to dioxygen dissolved in water is an important industrial issue, in particular for boilers in which high temperatures and pressures are applied. Since oxygen free water limits such damages, dioxygen scavengers like polyphenols were employed as early as the 1910s [1], followed by other reductants like hydrazine and diethylhydroxylamine (DEHA) [2]. The latter is particularly attractive due to its low toxicity compared to hydrazine. However, DEHA alone reacts only slowly with 3O2 [3–5] and it requires a catalyst to react rapidly. Different efficient catalysts have been reported such as metallic salts [6–8] or polyphenols [9], hydroquinone being the most employed [10]. Actually, hydroquinone is oxidized by dioxygen in basic conditions to give benzoquinone, which can be reduced into hyd
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