scholarly journals HYDRODENITROGENATION OF 2-METHYL QUINOLINE - EFFECT OF STERIC HINDRANCE IN LIQUID PHASE CATALYTIC HYDROGENATION

2021 ◽  
Vol 72 (3) ◽  
pp. 58-70
Author(s):  
Shanmugam Palanisamy
Keyword(s):  
Liquid Phase ◽  
Steric Hindrance ◽  
Batch Reactor ◽  
Intermediate Formation ◽  
Quasi Equilibrium ◽  
Rate Limiting Step ◽  
Alpha Olefin ◽  
Amine Adsorption ◽  
Butyl Benzene ◽  
Rate Limiting

Hydrodenitrognation (HDN) of 2-methyl quinoline (quinaldine) and quinoline in liquid phase on S-NiMo/a-Al2O3 catalyst was carried out in a batch reactor at 3.0 - 10.0 MPa and 130 � 360oC in Poly alpha-olefin solvent. Hydrogenolysis and Hydrogenation results in formation of products such as 1,2,3,4-treta hydro Quinaldine (1-THQ), 5,6,7,8-terta hydro Quinaldine (5-THQ), Deca hydro Quinaldine (DHQ), Butyl cyclohexane (BCH), Butyl cyclo hexene (BCHE) and butyl benzene (BB). Under studied condition, amine rings of quinaldine was rapidly hydrogenated and it forms relevant quasi equilibrium with 1,2,3,4-treta hydro quinaldine (1-THQ), 5,6,7,8-terta hydro quinaldine(5-THQ) and Deca hydro quinaldine (DHQ). The quinaldine reaction path either 1-THQ or 5-THQ indicated dependent of temperature and independent of partial pressure. Over which amine adsorption on metal sites reduced due to steric hindrance of methyl-group adjacent to N-bonding and increases the rate of intermediate formation through benzene ring hydrogenation. Distinguished HDN hydrogenolysis mechanism of quinaldine and its intermediate compounds were studied and compared with quinoline HDN. Thus, 5-THQ to DHQ and C-N cleavage identified as rate limiting step through steric hindrance HDN mechanism.

Kinetics and mechanism of methanolysis of benzoyl derivatives of substituted phenylureas and phenylthioureas

1984 ◽  
Vol 49 (9) ◽  
pp. 2103-2110 ◽  
Author(s):  
Jaromír Kaválek ◽  
Said El Bahaie ◽  
Vojeslav Štěrba
Keyword(s):  
Nitrogen Atom ◽  
Steric Hindrance ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Kinetics And Mechanism ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Order Of Magnitude ◽  
Rate Limiting ◽  
Derivatives Of

The methanolysis rate constants and dissociation constants have been measured of benzoyl derivatives of substituted phenylureas and phenylthioureas. The dissociation constants of the thio derivatives are higher by 1 order of magnitude and the rate constants are higher by 2 orders of magnitude than the respective values of the oxygen analogues. Logarithms of the rate and dissociation constants have been correlated with the Hammet σ constant; the ρ constant of the methanolysis of the oxygen derivatives is almost 2x higher than that of the thio derivatives, which is explained by a change in the rate-limiting step. Methylation of the phenyl nitrogen atom increases the acidity by almost 2 orders of magnitude. This effect is due obviously to steric hindrance to the conjugation with the adjacent carbonyl or thiocarbonyl group.

Kinetics of Coupling of 4-Methoxybenzenediazonium Ion with 2,6-Dihydroxypyridine

1996 ◽  
Vol 61 (6) ◽  
pp. 951-956 ◽  
Author(s):  
Jaroslava Horáčková ◽  
Vojeslav Štěrba
Keyword(s):  
Methyl Ester ◽  
Steric Hindrance ◽  
Base Catalysis ◽  
Necessary Condition ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Reaction ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of reaction of 4-methoxybenzenediazonium ion (3) with 2,6-dihydroxypyridine (1) has been studied in methoxyacetate, acetate, and phosphate buffers. The rate-limiting step is the formation of the reaction intermediate and not the splitting off of the proton (which was detected in the cases of citrazinic acid and its methyl ester). Therefrom it follows that for 2,6-dihydroxypyridine derivatives the steric hindrance to the formation of the Wheland intermediate exerted by CO2- and CO2CH3 groups represents a necessary condition for the rate-limiting splitting off of the proton and, hence, for the existence of general base catalysis.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

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