AROMATIC SUBSTITUTION: PART I. THE REACTION OF PHENYLLITHIUM WITH 3-ALKYLPYRIDINES. STERIC EFFECT AND QUANTITATIVE ANALYSIS OF ISOMER RATIOS

1962 ◽  
Vol 40 (2) ◽  
pp. 213-219 ◽  
Author(s):  
R. A. Abramovitch ◽  
Choo-Seng Giam
Keyword(s):  
Quantitative Analysis ◽  
Vapor Phase ◽  
Alkyl Group ◽  
Steric Effect ◽  
Main Product ◽  
Methyl Ethyl ◽  
Aromatic Substitution

No 4-phenylpyridine is formed in the reaction of phenyllithium with pyridine. When phenyllithium reacts with a 3-alkylpyridine the main product is the 3-alkyl-2-phenylpyridine if the alkyl group is methyl, ethyl, or isopropyl, but it is the 5-alkyl-2-phenylpyridine when the substituent is t-butyl. Methods are described for the separation and quantitative analysis of mixtures of 3-alkyl- and 5-alkyl-2-phenylpyridines using vapor phase chromatography. The results are discussed briefly and possible explanations of the observed orientations are mentioned.

ARYLPYRIDINES: PART I. ORIENTATION IN THE REACTION OF PHENYLLITHIUM WITH SOME 3-SUBSTITUTED PYRIDINES

1960 ◽  
Vol 38 (6) ◽  
pp. 761-771 ◽  
Author(s):  
R. A. Abramovitch ◽  
Giam Choo Seng ◽  
A. D. Notation
Keyword(s):  
Quantitative Analysis ◽  
Vapor Phase ◽  
Steric Effect ◽  
Main Product ◽  
Phenyl Substituent ◽  
First Case ◽  
Substituted Pyridines ◽  
Crude Mixture ◽  
Nucleophilic Reagents

The orientation of the entering phenyl substituent in the addition of phenyllithium to 3-picoline and nicotine has been studied. In the first case the main product was 3-methyl-2-phenylpyridine together with a small amount of 5-methyl-2-phenylpyridine; the ratio of the isomers being 19:1. The structure of the isomers was established by oxidation to the corresponding phenylnicotinic acids, by infrared and n.m.r. spectroscopy. Quantitative analysis of the crude mixture of isomers was effected by vapor phase chromatography. Phenylation of nicotine gave 2-phenyl- and 6-phenyl-nicotine in the ratio of 1:1. Separation of the isomers was effected by preparative vapor phase chromatography and their orientation established as above. Evidence that the 3-substituent exerts an appreciable steric effect in the end product of the addition is presented. The results are taken to mean that addition of phenyllithium, and probably of other nucleophilic reagents, to 3-substituted pyridines occurs preferentially at the 2-position but the 3-substituent, if sufficiently bulky, may exert a steric effect resulting in appreciable addition at the 6-position also.

The Influence of the 2-Alkoxy Group and of C-5 Substituents on the Direction of Reductive Cleavage of 2-Alkoxytetrahydrofurans by AlH2Cl in Ether Solution

1972 ◽  
Vol 50 (10) ◽  
pp. 1502-1512 ◽  
Author(s):  
P. C. Loewen ◽  
Miss L. P. Makhubu ◽  
R. K. Brown
Keyword(s):  
Transition State ◽  
Alkyl Group ◽  
Steric Effect ◽  
Bond Cleavage ◽  
Alkoxy Group ◽  
Ring Cleavage ◽  
Relative Ease ◽  
Ether Solution ◽  
A Minor ◽  
Minor Extent

The AlH2Cl hydrogenolysis of ether solutions of 2-alkoxytetrahydrofurans in which the alkoxy group is either CH3O, C2H5O, i-C3H7O, or t-C4H9O, gives only those products resulting from ring C—O bond cleavage. However, substituents at C-5 of 2-methoxytetrahydrofuran exert a strong effect on the ratio of ring to exo C—O bond cleavage. Thus, alkyl (electron donor) groups at C-5 promote an increase in the amount of exo cleavage, the proportion increasing from 62.5 to 100% as the C-5 alkyl group is changed from CH3 to t-C4H9. In contrast, electron withdrawing substituents, CH3OCH2— and C6H5, at C-5 favor ring cleavage to the extent of 93 and 84% respectively.The results are interpreted in terms of the influence that these substituents exert through their electronic properties on the relative ease of attainment of the transition state leading to either ring C—O or exo C—O bond cleavage. However, evidence is provided to show that the bulk steric effect of these substituents also controls, though to a minor extent, the proportion of ring to exo cleavage.

Quantitative Analysis of Trace Metals in Silicon Nitride Films by a Vapor Phase Decomposition/Solution Collection Approach

2000 ◽  
Vol 147 (4) ◽  
pp. 1499 ◽  
Author(s):  
G. Vereecke ◽  
M. Schaekers ◽  
K. Verstraete ◽  
S. Arnauts ◽  
M. M. Heyns ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Silicon Nitride ◽  
Trace Metals ◽  
Vapor Phase ◽  
Phase Decomposition ◽  
Silicon Nitride Films

scholarly journals Metals on ZrO2: Catalysts for the Aldol Condensation of Methyl Ethyl Ketone (MEK) to C8 Ketones

Catalysts ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 622 ◽  
Author(s):  
Zahraa Al-Auda ◽  
Hayder Al-Atabi ◽  
Keith Hohn
Keyword(s):  
Methyl Ethyl Ketone ◽  
Main Product ◽  
Aldol Condensation ◽  
Fixed Bed ◽  
Hydrogenation Reaction ◽  
Fixed Bed Reactor ◽  
Molar Ratio ◽  
Phase Reaction ◽  
Methyl Ethyl ◽  
One Step

Methyl ethyl ketone (MEK) was converted to heavier ketones in one step, using a multi-functional catalyst having both aldol condensation (aldolization and dehydration) and hydrogenation properties. 15% Cu supported zirconia (ZrO2) was investigated in the catalytic gas phase reaction of MEK in a fixed bed reactor. The results showed that the main product was 5-methyl-3-heptanone (C8 ketone), with side products including 5-methyl-3-heptanol, 2-butanol, and other heavy products (C12 and up). The effects of various reaction parameters, like temperature and molar ratio of reactants (H2/MEK), on the overall product selectivity were studied. It was found that with increasing the temperature of the reaction, the selectivity to the C8 ketone increased, while selectivity to the 2-butanol decreased. Also, hydrogen pressure played a significant role in the selectivity of the products. It was observed that with increasing the H2/MEK molar ratio, the 2-butanol selectivity increased because of the hydrogenation reaction, while decreasing this ratio led to increasing the aldol condensation products. In addition, it was noted that both the conversion and selectivity to the main product increased using a low loading percentage of copper, 1% Cu–ZrO2. The highest selectivity of 5-methyl-3-heptanone reached ~64%, and was obtained at a temperature of around 180 °C and a molar ratio of H2/MEK equal to 2. Other metals (Ni, Pd, and Pt) that were supported on ZrO2 also produced 5-methyl-3-heptanone as the main product, with slight differences in selectivity, suggesting that a hydrogenation catalyst is important for producing the C8 ketone, but that the exact identity of the metal is less important.

Kinetics and Mechanism of Acid Catalyzed Decomposition of 1-Phenyl-3,3-dialkyltriazenes

1994 ◽  
Vol 59 (2) ◽  
pp. 401-411 ◽  
Author(s):  
Miroslav Ludwig ◽  
Pavla Valášková ◽  
Oldřich Pytela
Keyword(s):  
Rate Constants ◽  
Steric Effect ◽  
Aqueous Ethanol ◽  
Pivalic Acid ◽  
Decomposition Kinetics ◽  
Methyl Ethyl ◽  
Rate Determining Step ◽  
Alkyl Groups ◽  
Acid Catalyzed ◽  
Catalytic Rate

Five model 1-phenyl-3,3-dialkyltriazenes (methyl, ethyl, 2-propyl, butyl, cyclohexyl) have been synthesized and their acid-catalyzed decomposition kinetics have been investigated spectrophotometrically in aqueous ethanol (40 vol.%) with pivalic acid as the catalyst. The results show that the rate-determining step is catalyzed by the proton. The decrease in the observed rate constant at higher concentrations of pivalic acid is explained by the formation of an unreactive complex of the nondissociated acid and respective triazene. The steric effect of alkyl groups on the catalytic rate constants is discussed.

Chemoselective intramolecular annulation of 3-alkylindolines into dihydro or tetrahydrofuro[2,3-b]indoles

1997 ◽  
Vol 75 (7) ◽  
pp. 959-964 ◽  
Author(s):  
Oscar R. Suárez-Castillo ◽  
Manuel García-Velgara ◽  
Martha S. Morales-Ríos ◽  
Pedro Joseph-Nathan
Keyword(s):  
Alkyl Group ◽  
Grignard Reagent ◽  
Steric Effect ◽  
Aprotic Solvent ◽  
Protic Solvent ◽  
Ring Transformation

3-Alkyl-2-hydroxyindolines, conveniently prepared from 2-hydroxyindolenines and a Grignard reagent, cyclize in the aprotic solvent tetrahydrofuran to afford tetrahydro-3-cyano-2-oxofuro[2,3-b]indoles, while in the protic solvent methanol the chemoselectivity changed to give dihydro-2-amino-3-carbomethoxyfuro[2,3-b]indoles. The steric effect of the alkyl group on the reactivity of 3-alkyl-2-hydroxyindolines is discussed for both processes. The ring transformation of tetrahydro-3-cyano-2-oxofuro[2,3-b]indoles into dihydro-2-amino-3-carbomethoxyfuro[2,3-b]indoles via γ-lactone imines is also discussed. Keywords: furo[2,3-b]indoles, α-cyano-γ-lactones, chemoselectivity, ring transformation, β-enamino esters.

Infrared Study of Alkyl Isothiocyanates in Carbon Tetrachloride and/or Chloroform Solutions

1993 ◽  
Vol 47 (6) ◽  
pp. 677-686 ◽  
Author(s):  
R. A. Nyquist ◽  
C. W. Puehl
Keyword(s):  
Carbon Tetrachloride ◽  
Alkyl Group ◽  
High Frequency ◽  
Fermi Resonance ◽  
Methyl Ethyl ◽  
Infrared Study ◽  
Tert Butyl ◽  
Electron Donation ◽  
Hydrogen Bonded

The νasym.NCS frequencies for alkyl isothiocyanates occur at higher frequency in CHCl3 or CDCl3 solution than in CCl4 solution. The νasym.NCS mode increases in frequency as the mole % CHCl3/CCl4 increases. The νasym.NCS mode for butyl isothiocyanate occurs at an exceptionally high frequency, and this result is explained in terms of the formation of a pseudo-six-membered intramolecularly hydrogen-bonded ring. The νasym.NCS modes for the alkyl isothiocyanates are corrected for Fermi resonance (FR), with the exception of the propyl analog. The propyl analog appears to have three other modes in FR with νasym.NCS, and an equation has not yet been developed to correct for FR in this case. The unperturbed νasym.NCS frequencies for alkyl isothiocyanates decrease in the alkyl order: methyl, butyl, ethyl, and tert-butyl. The decrease in frequency of νasym.NCS in the order methyl, ethyl, and tert-butyl isothiocyanate is attributed to weakening of the N=C=S bonds due to σ electron donation of each alkyl group. In the case of the butyl analog, the σ electron donation is partially compensated for by the postulated existence of a pseudo-six-membered hydrogen-bonded ring.

scholarly journals Reactions of Thiyl Radicals. VIII. Photolysis of Methyl Ethyl Sulfide Vapor

1972 ◽  
Vol 50 (11) ◽  
pp. 1734-1742 ◽  
Author(s):  
D. R. Tycholiz ◽  
A. R. Knight
Keyword(s):  
Absorption Spectrum ◽  
Mass Balance ◽  
Vapor Phase ◽  
Exposure Time ◽  
Quantum Yields ◽  
Methyl Ethyl ◽  
Chemical Decomposition ◽  
Thiyl Radicals ◽  
A Value ◽  
Single Substrate

Methyl ethyl sulfide has been photolyzed in the vapor phase with wavelengths between 2000 and 2350 Å and the effects of pressure, temperature, and exposure time investigated. The vapor phase absorption spectrum of the sulfide has been determined and the variation in the nature and rates of formation of products in the presence of CO2, CF4, propylene, and 2-pentene measured. Quantum yields of products from the decomposition of the pure substrate were determined at 2288 Å.The products of the reaction are, in order of decreasing importance, C2H6, CH3SSC2H5, C2H5SSC2H5, CH4, CH3SCH3, C2H5SC2H5, C3H8, C2H4, CH3SSCH3, C4H10, C2H5SH, and CH3SH. A carbon/sulfur mass balance is obtained at all substrate pressures at 25 °C, and at the single substrate pressure examined at 120 °C. In the presence of propylene four additional products, n-C5H12, CH3S(CH2)2CH3, (CH3CH2CH2)2S, and CH2=CH—CH2SC2H5, were found.Only a small fraction of photochemically excited methyl ethyl sulfide molecules undergoes chemical decomposition. The two primary processes[Formula: see text]and subsequent reactions of the radicals so formed account for the observed products. R3a/R3b has a value of 1.32 at 25 °C.

Thermolysis of 2-acyloxy-Δ3-1,3,4-oxadiazolines. Evidence for a preferred sense of cycloreversion to carbonyl ylides and for fast 1,4-sigmatropic ylide rearrangement

1989 ◽  
Vol 67 (11) ◽  
pp. 1753-1759 ◽  
Author(s):  
Michael W. Majchrzak ◽  
John Warkentin
Keyword(s):  
Alkyl Group ◽  
Steric Effect ◽  
Benzene Solution ◽  
Sigmatropic Rearrangement ◽  
Acetoxy Group ◽  
High Yield ◽  
Enol Ethers ◽  
Carbonyl Ylide

Thermolysis of 2-acyloxy-2,5,5-trialkyl-Δ3-1,3,4-oxadiazolines in benzene solution at 80 °C furnishes acyloxy-substituted enol ethers (hemiacylals) in high yield. Mixtures of cis:trans isomers of such oxadiazolines afford mixtures of isomeric hemiacylals in nearly the same ratio. Those and other results are rationalized in terms of cycloreversion of the oxadiazolines to carbonyl ylides that are not equilibrated during their lifetimes and undergo primarily 1,4-sigmatropic H-migration. Some fragmentation of the ylides to anhydrides and carbenes was also observed. A consistent mechanistic account includes concerted suprafacial (4π + 2π) cycloreversion in the sense that places a large ylide substituent at C-1 or at C-3, preferentially exo. A smaller preference for the cycloreversion that places the acetoxy group at C-1 in the endo position, when the steric effect of the alkyl group at C-1 is small, can be inferred. The possibility that the overall 1,4-H shift is the result of sequential 1,7-antarafacial and 1,4-suprafacial shifts, in some cases, is considered. Keywords: carbonyl ylide; 1,4-sigmatropic rearrangement; cycloreversion, thermal, of oxadiazolines; ylide, carbonyl; oxadiazoline, thermolysis of.

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