Catalytic deuterium exchange reactions with organics. XXIII. Deformylation during the deuteration of aromatic α-hydroxy acids and related compounds

1966 ◽  
Vol 19 (2) ◽  
pp. 211 ◽  
Author(s):  
GE Calf ◽  
JL Garnett
Keyword(s):  
Carboxylic Acid ◽  
Heavy Water ◽  
Mandelic Acid ◽  
Hydroxy Acids ◽  
Exchange Reactions ◽  
Catalyst Activation ◽  
Π Complex ◽  
Complex Adsorption ◽  
Benzilic Acid ◽  
Related Compounds

The transition-metal catalysed exchange of aromatic a-hydroxy acids with heavy water has been studied. Benzilic acid and its 00'-dichloro- and pp'-dimethyl derivatives simultaneously deformylate with the formation of the corresponding diary1 ketones. Mandelic acid and derivatives are stable under these conditions and only deuterate, whereas 9-hydroxyfluorene-9-carboxylic acid decomposes quantitatively to 9-fluorenol and 9-fluorenone. Benzhydrol decomposes appreciably to benzophenone. The effect of catalyst (soluble Fe, Co, Ni, Ru, Rh, Pd, Ir, and Pt chlorides versus insoluble oxides) and the method of catalyst activation (hydrogen, sodium borohydride, and self-activation) on the exchange and deformylation reactions have been studied. The results are interpreted in terms of a mechanism based on π-complex adsorption.

Catalytic deuterium exchange reactions with organics. XL. Pyridine, the quinolines, azines, and aniline on unsupported Group VIII transition metals

1968 ◽  
Vol 21 (4) ◽  
pp. 961 ◽  
Author(s):  
GE Calf ◽  
JL Garnett ◽  
VA Pickles
Keyword(s):  
Charge Transfer ◽  
Transition Metals ◽  
Heavy Water ◽  
Heterocyclic Compounds ◽  
Group Viii ◽  
Borohydride Reduction ◽  
Exchange Reactions ◽  
Catalyst Activation ◽  
Π Complex ◽  
Sodium Borohydride Reduction

Pyridine, the quinolines, pyridazine, pyrimidine, pyrazine, s-triazine, and aniline have been exchanged with heavy water on the following Group VIII transition metals: Fe, Co, Ni, 0s. Ru, Rh, Pd, Ir, and Pt. Three types of catalyst activation have been used, including self-activation, hydrogen and sodium borohydride reduction of the inorganlo salts. Platinum is the most useful catalyst for general exchange whereas cobalt possesses valuable specificity for selective a exchange in a large number of the heterocyclic compounds. A kinetic study of the deuteration of pyridine on platinum has been performed. The exchange results have been rationalized in terms of charge-transfer adsorbed intermediates. E.s.r. has been used to support this conclusion for the interaction between pyridine and potassium chloropalladite. π-Complex mechanisms have been proposed to explain the observed deuteration behaviour.

Catalytic deuterium exchange reactions with organics. XIII. Characteristic reactions of the Group VIII transition metals

1965 ◽  
Vol 18 (7) ◽  
pp. 1003 ◽  
Author(s):  
JL Garnett ◽  
WA Sollich
Keyword(s):  
Transition Metal ◽  
Hydrogen Exchange ◽  
Deuterium Oxide ◽  
Metal Catalysts ◽  
Transition Metal Catalysts ◽  
Group Viii ◽  
Exchange Reactions ◽  
Substitution Mechanism ◽  
Π Complex ◽  
Complex Adsorption

Activation procedures and hydrogen exchange reactions with six Group VIII transition metal catalysts (Pt, Pd, Ru, Rh, Ir, Ni) are reported for three characteristic reaction systems: (i) deuterium oxide/benzene, (ii) deuterium oxide/naphthalene, and (iii) deuterium oxide/n-octane. Results of these exchange reactions indicate that both π-complex adsorption and the dissociative π-complex substitution mechanism previously established for platinum are applicable to other Group VIII transition metal catalysts. For general catalytic labelling with isotopic hydrogen, platinum was found to be the most efficient of the catalysts investigated.

Mechanism of Oxidative Decarboxylation of α-Hydroxy Acids by Bromine Water. Part I. Oxidation in Neutral and Alkaline Medium

1971 ◽  
Vol 49 (4) ◽  
pp. 649-653 ◽  
Author(s):  
Judith M. Pink ◽  
Ross Stewart
Keyword(s):  
Steady State ◽  
Kinetic Study ◽  
Oxidation Rate ◽  
Mandelic Acid ◽  
Oxidative Decarboxylation ◽  
Hydroxy Acids ◽  
Bromine Water ◽  
Benzilic Acid ◽  
Hydroxylic Proton ◽  
Good Agreement

A kinetic study of the oxidative decarboxylation of α-hydroxy acids by bromine water shows that above pH 6 Br2 is a much more significant oxidant for these compounds than is HOBr, and that OBr− is virtually inert. The rate law – d[oxidant]/dt = k[oxidant][substrate] is observed and the oxidation pattern differs from that of alcohols in that the α-hydrogen is not involved in the reaction.All the compounds studied (benzilic, mandelic, and 2-hydroxy-2-methylpropanoic acids) exhibit bell-shaped pH-rate profiles with maxima at about pH 8. A mechanism is proposed involving the attack of Br2 (or HOBr) at the carboxylate site concurrently with base-catalyzed loss of the hydroxylic proton. A steady state treatment based on this mechanism yields calculated rates in good agreement with the observed values. Furthermore, the same parameters predict the rates observed at lower pH in the presence of added excess bromide. The Br2 oxidation rate is greater than the HOBr rate by a factor of 60 for benzilic acid, 37 for 2-hydroxy-2-methylpropanoic acid, and 10 for mandelic acid.

Deuterium Exchange Reactions with Substituted Aromatics. II. The Monohalogenated Benzenes and Naphthalenes

1961 ◽  
Vol 14 (3) ◽  
pp. 441 ◽  
Author(s):  
JL Garnett ◽  
WA Sollich
Keyword(s):  
Complex Formation ◽  
Ionization Potential ◽  
Heavy Water ◽  
Product Formation ◽  
Ortho Position ◽  
Exchange Reactions ◽  
Naphthalene Derivatives ◽  
Aromatic Molecules ◽  
Π Complex ◽  
Benzene Series

The platinum-catalysed exchange between heavy water and the monohalogenated benzenes and naphthalenes has been studied at 130-180 �C. Rate of exchange is found to decrease with increasing size of halogen substituent. Naphthalene derivatives exchange more slowly than the corresponding members of the benzene series. Rate of exchange increases with increasing ionization potential. From this correlation it is postulated that chemisorption of aromatic molecules on active platinum occurs through π-complex formation. In the benzene series, exchange in the ortho-position is slower than in the meta- or para-positions which react at approximately the same speed. ortho-Exchange increases with increasing size of halogen substituent. This deuteration technique is applicable to tritium labelling especially for aromatics since radiochemical by-product formation is minimized.

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