Catalytic effect of molybdenum oxo-species on reduction of allyl alcohol at a Pt electrode in strongly acidic solutions

2012 ◽  
Vol 63 ◽  
pp. 89-99 ◽  
Author(s):  
Maria Bełtowska-Brzezinska ◽  
Tomasz Węsierski ◽  
Teresa Łuczak ◽  
Józef Camra
Keyword(s):  
Allyl Alcohol ◽  
Catalytic Effect ◽  
Pt Electrode ◽  
Acidic Solutions

STUDIES ON LIGNIN AND RELATED COMPOUNDS: VI. THE MECHANISM OF AQUEOUS HALOGENATION

1931 ◽  
Vol 4 (2) ◽  
pp. 119-133 ◽  
Author(s):  
K. Austin Taylor ◽  
O. Maass ◽  
Harold Hibbert
Keyword(s):  
Hydrochloric Acid ◽  
Allyl Alcohol ◽  
Hydrobromic Acid ◽  
Catalytic Effect ◽  
Hypochlorous Acid ◽  
The Real ◽  
Unsaturated Compounds ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Chlorine Ions

The rates of addition of hypochlorous and hypobromous acids to several unsaturated compounds, under the influence of various catalysts, have been studied.The addition of hypochlorous acid to allyl alcohol and dipropenyl glycol is catalysed by both hydrogen and chlorine ions, the catalytic effects of these ions, mole for mole, being equal. The effect of hydrogen and chlorine ions, when added together as hydrochloric acid, is not the sum of their separate effects but is proportional to their product, indicating undissociated hydrochloric acid as the real catalyst. The catalytic effect of varying amounts of added hydrochloric acid is approximately proportional to the square of the amount added, again indicating undissociated hydrochloric acid as the real catalyst.The addition of hypobromous acid to allyl alcohol is catalysed by hydrochloric and hydrobromic acids to about the same degree. This catalysis of hypobromous acid addition by hydrochloric acid provides further support for the hypothesis of undissociated hydrochloric acid as the real catalyst in the addition of hypochlorous acid.This catalytic effect of undissociated halogen acid on the addition of hypohalous acids is put forward as an explanation of the greater rates of addition of hypochlorous and hypobromous acids from chlorine and bromine water as compared with solutions of hypochlorous and hypobromous acids.The addition of hypobromous acid to fumaric acid is not catalysed by hydrobromic acid but, on the other hand, is considerably decreased. It is catalysed, however, by hydrochloric acid, although not nearly to the same degree as the addition to allyl alcohol. This difference in behavior between fumaric acid and allyl alcohol shows the necessity for studying the effect of hydrochloric and hydrobromic acids on the rate of addition of hypobromous acid to a wide variety of unsaturated compounds, before any general theory of aqueous halogenation applicable to all types of unsaturated compounds can be put forward. The possible influence of conjugation has, however, been pointed out.An attempt has been made to apply the theory of hypohalous acid addition catalysed by undissociated halogen acid to the aqueous halogenation of phenols. The reaction between hypobromous acid and m-nitrophenol has been shown to be catalysed by hydrochloric acid although not to the same extent as by hydrobromic acid. This indicates hypobromous acid addition, catalysed by undissociated hydrobromic acid, as one of the mechanisms involved in the aqueous bromination of phenols.It has been pointed out that a similar mechanism cannot be the fastest one in the aqueous chlorination of phenols, since it is in disagreement with kinetic data of Soper and Smith (21), showing chlorine to react faster than hypochlorous acid with phenols.It has been shown that resorcinol and phloroglucinol do not fall under the general classification proposed by Soper and Smith for phenols. Even here, however, the main reaction between chlorine water and the phenol seems to involve chlorine rather than hypochlorous acid.It has been suggested that several parallel mechanisms may be involved in the aqueous halogenation of phenols and the necessity for further work in this field has been emphasized.

Zur Frage der Bildung von Dimethylnitrosamin aus Tetracyclin-Derivaten bei der Nitrosierung in saurer Lösung / On the Problem of Dim ethylnitrosamine Form ation from Tetracycline-Derivatives by Nitrosation Reaction in Acidic Medium

1977 ◽  
Vol 32 (9-10) ◽  
pp. 696-702 ◽  
Author(s):  
Harald Röper ◽  
Kurt Heyns
Keyword(s):  
Liquid Chromatography ◽  
Sodium Nitrite ◽  
Acidic Medium ◽  
Catalytic Effect ◽  
Sodium Thiocyanate ◽  
Gas Liquid Chromatography ◽  
Hydrogen Bridge ◽  
Liquid Chromatography Mass Spectrometry ◽  
Acidic Solutions ◽  
Buffer Solutions

Abstract The hydrochlorides from tetracycline and six tetracycline derivatives *-7-dimethylamino-6-des-methyl-6-desoxytetracycline [minocycline], 7-chlorotetracycline [chlorotetracycline], 7-chloro-anhy-drotetracycline [anhydrochlorotetracycline, 7-chloro-6-desmethyltetracycline [demethylchlorotetra- cycline], 5-hydroxytetracycline [oxytetracycline] and 6-desoxy-5-hydroxytetracycline [doxycycline] - were reacted with different amounts of sodium nitrite at 37 °C for two hours in aqueous buffer solutions at pH 2 and 4.Dimethylnitrosamine formation was confirmed by gas-liquid chromatography and by combined gas-liquid chromatography/mass-spectrometry from minocycline, doxycycline, oxytetracycline and an- hydrochlorotetracycline.Dimethylnitrosamine formation from minocycline and doxycycline was blocked by ascorbic acid. The catalytic effect of sodium thiocyanate for the dimethylnitrosamine formation from minocycline and nitrite was investigated.The different reactivity of the investigated tetracycline derivatives towards nitrite in acidic solutions is discussed by stereochemical considerations in connection with the formation of hydrogen bridge linkages. This hypothesis was confirmed by dimethylnitrosamine formation from anhydro-chlorotetracycline and sodium nitrite at pH 2.

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