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.

HCN elimination from vinyl cyanide: product energy partitioning, the role of hydrogen–deuterium exchange reactions and a new pathway

2015 ◽  
Vol 17 (10) ◽  
pp. 6948-6955 ◽  
Author(s):  
Saulo A. Vázquez ◽  
Emilio Martínez-Núñez
Keyword(s):  
Deuterium Exchange ◽  
Energy Partitioning ◽  
Hydrogen Deuterium Exchange ◽  
Schematic Diagram ◽  
Exchange Reactions ◽  
Hydrogen Deuterium

A schematic diagram of HCN elimination channels from vinyl cyanide including a new CCdiss pathway.

HYDROGEN EXCHANGE REACTIONS OF PHENOL ETHERS IN ACETIC ACID SOLUTION. PROMOTIVE AND INHIBITORY EFFECTS OF STERIC ORIGIN

1949 ◽  
Vol 27b (4) ◽  
pp. 398-407 ◽  
Author(s):  
Weldon G. Brown ◽  
Kenneth E. Wilzbach ◽  
Wilbert H. Urry
Keyword(s):  
Acetic Acid ◽  
Sulphuric Acid ◽  
Hydrogen Exchange ◽  
Acetic Acid Solution ◽  
Side Reactions ◽  
Exchange Reactions ◽  
Inhibitory Effects ◽  
Hydrogen Deuterium ◽  
Iodide Solution

As a means of avoiding side reactions which were encountered in earlier studies of hydrogen-deuterium exchange of phenol ethers with ethanol-sulphuric acid mixtures, a new procedure has been devised for the study of exchange reactions in acetic acid. The analysis for deuterium in the carboxyl group of acetic acid is performed by adding methyl magnesium iodide solution to the solution of phenol ether in acetic acid, combustion of the methane so produced, and finally, by determining the density of the water formed in the combustion. As compared with the former procedure, which required fractionation of the reaction mixture to recover the pure constituents, advantages in convenience and accuracy are claimed. Results are reported for the following ethers, reacting at 90 °C. in the presence of trace quantities of sulphuric acid: anisole, o-methylanisole, m-methylanisole, 3,5-dimethylanisole, 2-methylcoumarane, veratrole, di-isobutyl catechol ether, and the cyclic mono- (di-, tri-, and tetra) methylene ethers of catechol. The observed variations in rates are interpreted in part according to whether the conditions imposed by structural alterations favor or constrain the formation of an intermediate cation for which a quinoidal configuration of bonds is required. The role of steric factors is most strikingly demonstrated in the series of cyclic ethers of catechol, constraint being evident at a critical ring size (7-membered ring) and largely absent for either smaller or larger rings.

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.

scholarly journals F/OH ratio in a rare fluorine-poor blue topaz from Padre Paraíso (Minas Gerais, Brazil) to unravel topaz’s ambient of formation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
N. Precisvalle ◽  
A. Martucci ◽  
L. Gigli ◽  
J. R. Plaisier ◽  
T. C. Hansen ◽  
...  
Keyword(s):  
Supercritical Fluids ◽  
Fluorine Content ◽  
Minas Gerais ◽  
Hydroxyl Groups ◽  
Exchange Reactions ◽  
Silicate System ◽  
Mullite Phase ◽  
Anomalous Water

AbstractTopaz [Al2SiO4(F,OH)2] is one of the main fluorine-bearing silicates occurring in environments where variably acidic (F)/aqueous (OH) fluids saturate the silicate system. In this work we fully characterized blue topaz from Padre Paraíso (Minas Gerais, Brazil) by means of in situ synchrotron X-Ray and neutron powder diffraction measurements (temperature range 298–1273 K) combined with EDS microanalyses. Understanding the role of OH/F substitution in topaz is important in order to determine the hydrophilicity and the exchange reactions of fluorine by hydroxyl groups, and ultimately to characterize the environmental redox conditions (H2O/F) required for mineral formation. The fluorine content estimated from neutron diffraction data is ~ 1.03 a.f.u (10.34 wt%), in agreement with the chemical data (on average 10.0 wt%). The XOH [OH/(OH + F)] (0.484) is close to the maximum XOH value (0.5), and represents the OH- richest topaz composition so far analysed in the Minas Gerais district. Topaz crystallinity and fluorine content sharply decrease at 1170 K, while mullite phase starts growing. On the basis of this behaviour, we suggest that this temperature may represent the potential initial topaz’s crystallization temperature from supercritical fluids in a pegmatite system. The log(fH2O/fHF)fluid (1.27 (0.06)) is coherent with the fluorine activity calculated for hydrothermal fluids (pegmatitic stage) in equilibrium with the forming mineral (log(fH2O/fHF)fluid = 1.2–6.5) and clearly different from pure magmatic (granitic) residual melts [log(fH2O/fHF)fluid < 1]. The modelled H2O saturated fluids with the F content not exceeding 1 wt% may represent an anomalous water-dominant / fluorine-poor pegmatite lens of the Padre Paraíso Pegmatite Field.

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