Hydrothermal stability of aromatic carboxylic acids

Dunn, Jennifer B.; Burns, Michael; Hunter, Shawn E.; Savage, Phillip E.

doi:10.1016/s0896-8446(02)00241-3

Cited by 69 publications

(57 citation statements)

References 35 publications

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“…The results are consistent with the reported thermal decarboxylation of terephthalic and isophthalic acid which gave yields of 10 ± 15% at 350 8C for 30 min but for trimellitic anhydride, complete degradation was observed. [23] Similarly it has been shown that o-phthalic acid thermally decarboxylates much easier than terephthalic and isophthalic acids. However, the relative importance of thermal and metal-catalysed decarboxylation, remains uncertain.…”

Section: Full Papersmentioning

confidence: 98%

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Is it Possible to Achieve Highly Selective Oxidations in Supercritical Water? Aerobic Oxidation of Methylaromatic Compounds

et al. 2004

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Abstract:We have demonstrated that different methylaromatic compounds [1,4-dimethylbenzene (p-xylene), 1,3-dimethylbenzene (m-xylene), 1,2-dimethylbenzene (o-xylene), 1,3,5-trimethylbenzene (mesitylene) and 1,2,4-trimethylbenzene (pseudocumene)] can be aerobically oxidized in supercritical water (scH 2 O) using manganese(II) bromide as catalyst to give corresponding carboxylic acids in the continuous mode over a sustained period of time in good yield. No partially oxidized intermediates (i.e., toluic acid and benzaldehydes) were detected for the dimethylbenzenes and mesitylene reactions. By fine tuning pressure and temperature, scH 2 O becomes a solvent with physical properties suitable for single-phase oxidation since both organic substrate and oxygen are soluble in scH 2 O. There is a strong structural similarity of metal/bromide coordination compounds in the active oxidation solvents (acetic acid and scH 2 O) which does not exist in the much less active H 2 O at lower temperatures. This may account for the successful catalysis of the reactions reported herein. Aromatic acids produced by the loss of one methyl group occurred in all of these reactions, i.e., 3 ± 6% benzoic acid formed during the oxidation of the dimethylbenzenes. Part of this loss is thought to be due to thermal decarboxylation. The thermal decarboxylation process is monitored via Raman spectroscopy.

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Section: Full Papersmentioning

confidence: 98%

“…The stability of the aromatic carboxylic acid in ncH 2 O and scH 2 O has received previous attention. [23] We have started to study such reactions using high temperature, high pressure Raman spectroscopy. We have demonstrated that phthalic acid 2a decarboxylates to benzoic acid 6 ( Figure 3) at high temperature and in the presence of NaOH.…”

Section: Full Papersmentioning

confidence: 99%

Is it Possible to Achieve Highly Selective Oxidations in Supercritical Water? Aerobic Oxidation of Methylaromatic Compounds

et al. 2004

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“…o-Xylene is also different from p-xylene in that the rates of thermal decarboxylation, Eq. (18), [33] and catalytic decarboxylation [27] are both faster for ophthalic acid than terephthalic acid.…”

Section: Resultsmentioning

confidence: 97%

“…The relative degrees of thermal decarboxylation are trimellitic acid @ o-phthalic acid > benzoic acid. [33] The product of thermal decarboxylation of o-phthalic acid is benzoic acid. Addition of ophthalic acid to the oxidation of o-xylene did not increase the selectivity to benzoic acid, as can be seen by comparing entry 1 with entries 5 and 6 in Table 2.…”

Section: à5mentioning

confidence: 99%

“…Other interpretations are also possible. The recation of thermal decarboxylation is acid catalysed, [33] so this rate [a] Selectivity for the identified aromatic compound calculated as the molar concentration of that compound relative to the total molar concentration of all identified aromatic compounds. [b] Recovered manganese as determined by atomic absorption.…”

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confidence: 99%

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Prevention of Manganese Precipitation during the Continuous Selective Partial Oxidation of Methyl Aromatics with Molecular Oxygen in Supercritical Water

et al. 2009

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Presented here is an investigation of the activity and recovery of the homogeneous manganese/bromide catalyst during the continuous flow oxidation of o-xylene, as model substrate, with molecular oxygen (O 2 ) in supercritical water (scH 2 O). Two strategies are discussed for preventing catalyst precipitation, mainly in the form of oxides such as manganese(IV) oxide, The first strategy involves varying the manganese:bromide ratio using either manganese(II) acetate or manganese(II) bromide in the presence of hydrobromic and other acids. The results show that the effect of acidity and bromide concentration plays an important role in preventing the manganese/bromide catalyst from precipitating. The second strategy uses aromatic carboxylic acids in combination with the manganese/bromide catalyst, particularly benzoic acid, which improves the catalyst recovery dramatically over a certain range of acid concentrations. Our studies show how the presence of an organic acid and/or its precursors is important in stabilising the catalyst. Our results are rationalised on the basis of a tentative reaction mechanism.

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Water Under Extreme Conditions for Green Chemistry

Savage

Rebacz

2010

Handbook of Green Chemistry

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The sections in this article are Introduction Background Properties of HTW Process Engineering Considerations Theoretical, Computational, and Experimental Methods Classical Theory Molecular and Computational Modeling Experimental Methods p H Effects Recent Progress in HTW Synthesis Hydrogenation C  C Bond Formation Friedel–Crafts Alkylation Heck Coupling Nazarov Cyclization Condensation Hydrolysis Rearrangements Hydration/Dehydration Elimination Partial Oxidation to Form Carboxylic Acids C  C Bond Cleavage H – D Exchange Amidation Acknowledgments

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Hydrothermal stability of aromatic carboxylic acids

Cited by 69 publications

References 35 publications

Is it Possible to Achieve Highly Selective Oxidations in Supercritical Water? Aerobic Oxidation of Methylaromatic Compounds

Is it Possible to Achieve Highly Selective Oxidations in Supercritical Water? Aerobic Oxidation of Methylaromatic Compounds

Prevention of Manganese Precipitation during the Continuous Selective Partial Oxidation of Methyl Aromatics with Molecular Oxygen in Supercritical Water

Water Under Extreme Conditions for Green Chemistry

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