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.

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. LXX. The deuteration of alkyl hydrogens in the short-chain alkylbenzenes using homogeneous platinum and heterogeneous platinum and nickel catalysts

1974 ◽  
Vol 27 (5) ◽  
pp. 1023 ◽  
Author(s):  
JL Garnett ◽  
RS Kenyon
Keyword(s):  
Theoretical Calculations ◽  
Acetic Acid Solution ◽  
Heterogeneous Systems ◽  
Nickel Catalysts ◽  
Deuterium Exchange ◽  
Short Chain ◽  
Side Chain ◽  
Exchange Reactions ◽  
Carbon 14

The mechanism of deuterium exchange in the short-chain alkylbenzenes has been studied using a homogeneous sodium tetrachloroplatinate catalyst in acetic acid solution. Carbon-14 labelled ethylbenzene has been synthesized and used to differentiate between previously proposed mechanisms. When deuteration of the side chain in ethylbenzene occurs, there is no scrambling of the α and β carbon atoms, thus eliminating the role of a symmetrically coordinated ethylene group previously proposed. This conclusion is confirmed by theoretical calculations of the exchange in ethylbenzene. The ethyl group in ethylbenzene derivatives deuterates with a low multiple character. These results from the homogeneous platinum system have been compared with corresponding data using heterogeneous platinum and nickel catalysts. Analogous intermediates are shown to be capable of existing in both homogeneous and heterogeneous systems, and are postulated to be general π-complexes for aromatic deuteration and π-allylic species for alkyl group exchange.

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.

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.

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