Deuterium Exchange Reactions with Substituted Aromatics. III. Heterocyclics and Polycyclic Hydrocarbons

1962 ◽  
Vol 15 (1) ◽  
pp. 56 ◽  
Author(s):  
JL Garnett ◽  
WA Sollich
Keyword(s):  
Adsorption Mechanism ◽  
Lone Pair ◽  
Deuterium Exchange ◽  
Catalyst Poisoning ◽  
Polycyclic Aromatics ◽  
Exchange Reactions ◽  
Aromatic Molecules ◽  
Π Complex ◽  
Additional Interaction ◽  
A Charge

Platinum-catalysed deuterium exchange reactions between heavy-water and polycyclic aromatics and heterocyclics have been investigated. The results confirm a charge-transfer-no-bond adsorption mechanism for catalytic chemisorption. Degree of catalyst poisoning increases with decreasing ionization potential for aromatic molecules of similar complexity, e.g., anthracene and phenanthrene. As the number of nodal planes in the bonding orbitals of the more complex polycyclic aromatics increases, a decrease is observed in catalyst poisoning. Exchange of pyridine is slower than benzene and this is attributed to an additional interaction of the pyridine molecule with the catalyst through its lone-pair of electrons. The reactivity of n-octane supports extension of the authors' π-complex chemisorption theory to molecules possessing only σ-electrons. Anisole, cyclohexane, nitrobenzene, cyclohexene, and phenyl cyanide exchange in an anomalous manner.

Deuterium-exchange Reactions with Substituted Aromatics. IV. The Poisoning Effect of Molecules Containing Nitrogen, Sulphur, or Arsenic

1963 ◽  
Vol 16 (4) ◽  
pp. 549 ◽  
Author(s):  
RA Ashby ◽  
JL Garnett
Keyword(s):  
Heavy Water ◽  
Aromatic Amines ◽  
Adsorption Mechanism ◽  
Specific Activity ◽  
High Specific Activity ◽  
Side Reactions ◽  
Exchange Reactions ◽  
Poisoning Effect ◽  
A Charge ◽  
Catalytic Exchange

The catalytic exchange properties of a number of organic compounds containing nitrogen, sulphur, or arsenic have been studied in the presence of benzene and heavy water. The results confirm a charge-transfer-no-bond adsorption mechanism previously proposed for the deuteration of aromatic polycyclic hydrocarbons. For aromatic nitrogen compounds an increase in ionization potential of substrate leads to an increase in deuterium incorporation and a decrease in catalyst poisoning. Some aromatic amines deuterate faster than expected by theory and this is attributed to rapid exchange of the amino hydrogens in heavy water with a consequential increase in D-H ratio at the catalyst; surface. Sulphur and arsenic, even in their saturated valency states, extensively poison benzene exchange as does triethylamine. p-Benzoquinone, 2,6-dichloroquinone, and NN-dimethyl benzylamine exhibit catalytic side reactions which poison benzene exchange. With tritium oxide, the technique is suitable for the synthesis of tritiated aromatic amines and heterocycles to high specific activity.

Catalytic deuterium exchange reactions with organics. XII. Further studies in platinum catalyst preparation-the process of self-activation

1965 ◽  
Vol 18 (7) ◽  
pp. 993 ◽  
Author(s):  
JL Garnett ◽  
WA Sollich
Keyword(s):  
Active Sites ◽  
Catalyst Deactivation ◽  
Platinum Catalyst ◽  
Platinum Oxide ◽  
Deuterium Exchange ◽  
Hydrogen Gas ◽  
Distribution Data ◽  
Exchange Reactions ◽  
Π Complex ◽  
Distribution Studies

A new process for the activation of platinum oxide, termed self-activation, is described. This procedure involves the reduction of platinic oxide with an organic compound such as benzene, naphthalene, or n-octane. The potential of the resulting catalyst in deuterium exchange reactions has been evaluated with three characteristic organic compounds, n-octane, naphthalene, and benzene. A comparison has been made in the properties of prereduced catalysts prepared by a self-activation procedure and catalysts activated conventionally with hydrogen gas. For high-temperature exchange reactions ( >90�), the former catalysts are to be preferred since higher final activities of up to 300% may be achieved. The kinetics of self-activation suggest that catalyst deactivation by reagents may be due to modification of active sites. With aromatic compounds, it is proposed that this deactivation occurs through a π-complex interaction. Isotope distribution studies in the labelled benzenes indicate that self-activated, prereduced catalysts, by comparison with hydrogen-activated catalysts, exhibit relatively low M values in relation to their activities. Distribution data are consistent with the explanation that catalyst deactivation by benzene is a process involving the generation of new types of active sites which are more numerous but of lower activity than the original sites. Attempts to stabilize prereduced catalysts by chemical methods were unsuccessful.

Catalytic deuterium exchange reactions with organics. LXXI. Homogeneous platinum catalysed deuteration of the long-chain alkylbenzenes. Relationship toalkane exchange

1974 ◽  
Vol 27 (5) ◽  
pp. 1033 ◽  
Author(s):  
JL Garnett ◽  
RS Kenyon
Keyword(s):  
Deuterium Exchange ◽  
Side Chain ◽  
Exchange Reactions ◽  
Degree Of Branching ◽  
Isotope Incorporation ◽  
Π Complex ◽  
Long Chain

The long-chain alkylbenzenes out to nonylbenzene have been exchanged with D2O in the presence of homogeneous platinum, deuteration occurring in both ring and side chain. ortho-Deactivation in the ring is observed, consistent with a mechanism involving a π-dissociative process. Total isotope incorporation in a particular compound decreases with increase in length and degree of branching of the side chain. In the side chain α and terminal positions deuterata predominantly, degree of isotope incorporation in these positions decreasing gradually down the series to nonylbenzene. For butylbenzene and higher homologues, deuteration of methylene positions is low. Orientation of isotope in the side chain of l',l?-dimethylpropylbenzene is unique and is used as a basis for a novel terminal abstraction π-complex (TAPC) mechanism proposed to explain terminal exchange in the alkylbenzenes. Concepts involving 'inner' and 'outer' π-complexes are shown to be of value in discussing mechanisms of exchange in other positions of these compounds. The data may be related to mechanisms for simple alkane exchange using this same catalyst.

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.

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.

Hydrogen-deuterium-exchange reactions of methoxide-methanol clusters

1990 ◽  
Vol 112 (19) ◽  
pp. 6832-6838 ◽  
Author(s):  
S. E. Barlow ◽  
Dang Thuy Thanh ◽  
Veronica M. Bierbaum
Keyword(s):  
Deuterium Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Exchange Reactions ◽  
Hydrogen Deuterium
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