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  • 1
    Electronic Resource
    Electronic Resource
    NMR Observation of the Koch Reaction in Zeolite H-ZSM-5 under Mild Conditions (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 3615-3616 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00117a032
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  • 2
    Electronic Resource
    Electronic Resource
    In situ 1H MAS NMR studies of the H/D exchange of deuterated propane adsorbed on zeolite H‐ZSM‐5 (1998)
    Springer
    Catalysis letters 54 (1998), S. 1-4 
    Details
    ISSN: 1572-879X
    Keywords: hydrogen exchange ; zeolite H‐ZSM‐5 ; propane ; in situ 1H MAS NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The hydrogen exchange in the propane‐d 8 loaded zeolite H‐ZSM‐5 was monitored by in situ 1H MAS NMR spectroscopy within the temperature range 457–543 K. Measurements of the H/D exchange between the acidic hydroxyl groups of the zeolite and the adsorbed deuterated propane molecules show that both methyl and methylene groups of alkane are involved in the exchange. The comparison of the experimentally obtained apparent activation energies for the exchange in methyl groups (108 ± 7 kJ mol-1) and methylene groups (117 ± 7 kJ mol-1) with theoretical values for methane and ethane supports the assumption that the H/D exchange for methyl and methylene groups takes place via a pentavalent transition state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019067603317
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  • 3
    Electronic Resource
    Electronic Resource
    Carbenium ion properties of octene-1 adsorbed on zeolite H-ZSM-5 (1994)
    Springer
    Catalysis letters 24 (1994), S. 271-284 
    Details
    ISSN: 1572-879X
    Keywords: Octene-1 ; H-ZSM-5 zeolite ; 13C carbon scrambling ; carbenium ion ; 13C CP/MAS NMR ; 2H NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It is shown that octene-1 adsorbed on zeolite H-ZSM-5 at ambient temperature exhibits carbenium ion properties. Namely: (1) According to2H NMR, the proton of the acidic ≡Al-OH-Si≡ group of the zeolite is transferred into the CH2= group of the octene-1 molecule. (2) According to13C NMR the13C label inserted into the terminal CH2= group of the octene-1 molecule is scrambled over its hydrocarbon skeleton. Thermodynamic and kinetic parameters for carbon scrambling are measured within the temperature range 290–343 K. The zeolite framework is shown to favour the formation of the linear rather than branched carbeniumion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811800
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  • 4
    Electronic Resource
    Electronic Resource
    13C solid state NMR evidence for the existence of isobutyl carbenium ion in the reaction of isobutyl alcohol dehydration in H-ZSM-5 zeolite (1993)
    Springer
    Catalysis letters 19 (1993), S. 153-158 
    Details
    ISSN: 1572-879X
    Keywords: Isobutyl carbenium ion ; carbon scrambling ; H-ZSM-5 zeolite ; 2DJ-resolved13C solid state NMR ; dehydration of isobutyl alcohol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using two-dimensionalJ-resolved and CP/MAS13C NMR, the pathway for the transfer of the13C label from the CH2 group of isobutyl alcohol into the hydrocarbon skeleton of butene oligomers has been elucidated in the course of isobutyl alcohol dehydration inside H-ZSM-5 zeolite. First, the label is transferred selectively into the CH2 group of the isobutyl silyl ether reaction intermediate (IBSE), and then into the CH and CH3 groups of the isobutyl fragment (-CH2CH(CH3)2) of IBSE and/or butene oligomers. Finally, it is scrambled over the carbon skeleton of the oligomers. The obtained data suggest that isobutyl carbenium ion is formed as a reaction intermediate or transition state during the transformation of isobutyl silyl ether into butene oligomers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00771750
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  • 5
    Electronic Resource
    Electronic Resource
    13C CP/MAS NMR study of isobutyl alcohol dehydration on H-ZSM-5 zeolite. Evidence for the formation of stable isobutyl silyl ether intermediate (1992)
    Springer
    Catalysis letters 13 (1992), S. 395-405 
    Details
    ISSN: 1572-879X
    Keywords: Isobutyl alcohol ; dehydration ; H-ZSM-5 zeolite ; isobutyl silyl ether ; di-isobutyl ether ; carbenium ion ; 13C CP/MAS NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dehydration of isobutyl alcohol selectively labelled with a13C nucleus in the CH2 group (i-BuOH[1−13C]) has been studied on H-ZSM-5 zeolite within the temperature range 296–448 K using13C CP/MAS NMR. The formation of the isobutyl silyl ether intermediate (IBSE) has been detected. It is stable below 398 K. Within the temperature range 398–423 K IBSE decomposes gradually to produce first a butene dimer, probably 2,5-dimethyl-l-hexene and then other butene dimers and oligomers. AtT 〉 423 K scrambling of the selectively labelled carbon of the initial dimeric product over various positions in the carbon skeleton of the final dimers (oligomers) is observed. This is explained in terms of the formation of carbenium ion as the reaction intermediate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00765043
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  • 6
    Electronic Resource
    Electronic Resource
    13C CP/MAS and2H NMR study of tert-butyl alcohol dehydration on H-ZSM-5 zeolite. Evidence for the formation of tert-butyl cation and tert-butyl silyl ether intermediates (1992)
    Springer
    Catalysis letters 13 (1992), S. 407-422 
    Details
    ISSN: 1572-879X
    Keywords: tert-butyl alcohol ; dehydration ; H-ZSM-5 zeolite ; tert-butyl cation ; tert-butyl silyl ether ; mechanism of reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The dehydration reaction of tert-butyl alcohol, selectively labelled with13C in CH3 or C-O groups (t-BuOH[2−13C2] andt−BuOH[1-13C]), as well as selectively deuterated in methyl groups (t-BuOH[2-2H9]), was studied on H-ZSM-5 zeolite simultaneously with13 C CP/MAS and2H solid state NMR. When adsorbed and dehydrated on zeolite at 296 K,t-BuOH[2−13C1] andt-BuOH[1−13C] give rise to identical13C CP/MAS NMR spectra of oligomeric aliphatic products. This is explained in terms of the fast isomerization of the tert-butyl hydrocarbon skeleton via the formation of tert-butyl cation as the key reaction intermediate. An alkoxide species, most probably tert-butyl silyl ether (t-BuSE), was also detected as the “side” reaction intermediate. This intermediate was stable within the temperature range 296–373 K and decomposed at 448 K to produce additional amounts of final reaction products, i.e. butene oligomers. NMR data point to the existence of equilibria between the initial tert-butyl alcohol, tert-butyl cation and butene that is formed from the intermediate carbocation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00765044
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  • 7
    Electronic Resource
    Electronic Resource
    In Situ 13C Solid-State NMR and Ex Situ GC-MS Analysis of the Products of tert-Butyl Alcohol Dehydration on H-ZSM-5 Zeolite Catalyst (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 157-167 
    Details
    ISSN: 0947-6539
    Keywords: alcohols ; cracking ; dehydrations ; isomerizations ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrocarbon products that are formed upon dehydration at 296-673 K of tert-butyl alcohol (tBuOH), adsorbed on H-ZSM-5 zeolite in concentrations equal to that to active Al—OH—Si sites in the catalyst, have been analyzed by 13C solid-state MAS NMR and GC-MS. To facilitate 13C NMR analysis, the alcohol selectively labeled with 13C isotope in the COH group was used. It was found that tBuOH transforms to the adsorbed C8 butene dimers plus a trace amount of alkanes at 296 K. Butene dimers exist inside H—ZSM-5 pores in the form of interconverting adsorbed octene, octyl silyl ether, and octyl carbenium ion; octyl silyl ether is the main adsorption state. Fluxionality of the carbenium ion form provides a pathway for isomerization of the highly branched hydrocarbon skeleton of the intial alcohol to the predominantly linear one in the adsorbed butene dimer. The driving force for the isomerization into the linear structure is the shape selectivity induced by the small size of the zeolite channels. At 373 K the adsorbed butene dimers further crack into species that contain an average of about 6.5 carbon atoms, in addition to further alkanes. At 448 K the adsorbed C3-C7+ paraffins become the predominant hydrocarbon products observed with both in situ 13C NMR and ex situ GC-MS. Simultaneously, a mixture of adsorbed polyenes is formed. According to 13C CP/MAS NMR, polyenes exist in the zeolite pores in the form of rather stable cyclopentenyl cations. At 573-673 K adsorbed cyclopentenyl cations further transform into a mixture of condensed and simple aromatics and then into xylenes and toluene. Simultaneously, paraffins crack further to give mainly C3-C4 paraffinic species at 573 K and propane at 673 K.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020207
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  • 8
    Electronic Resource
    Electronic Resource
    Interaction of Acetonitrile with Olefins and Alcohols in Zeolite H-ZSM-5: In situ Solid-state NMR Characterization of the Reaction ProductsDedicated to the Memory of Professor K. I. Zamaraev (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 47-56 
    Details
    ISSN: 0947-6539
    Keywords: alcohols ; nitriles ; NMR spectroscopy ; olefins ; zeolites ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction products and intermediates from the interaction of acetonitrile with olefins (oct-1-ene) or alcohols (tert-butyl alcohol) in zeolite H-ZSM-5 at 296 K have been characterized with 13C and 15N solid-state NMR. It has been shown that coadsorption of acetonitrile and olefin on H-ZSM-5 gives rise to the intermediate N-alkylnitrilium cation represents a persistent species inside a zeolite under anhydrous conditions. Upon admittance of water to the pores of the zeolite, the N-alkylnitrilium cation slowly converts into N-alkylamide in accordance with the classic Ritter reaction. In the case of acetonitrile and alcohol, just after coadsorption both the intermediate N-alkylnitrilium cation and the final N-alkyl-amide are identified simultaneously; the former slowly disappears over a few days. Thus, 1) it has been shown that the Ritter reaction can occur not only in liquid acidic media but also on a solid acid catalyst, zeolite H-ZSM-5; 2) N-alkylnitrilium cations have been detected and characterized with solid-state NMR as persistent intermediates in the Ritter reaction for the first time while the reaction proceeds.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030109
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  • 9
    Electronic Resource
    Electronic Resource
    Spin delocalization from paramagnetic metal complexes [Cr(acac)3 and Fe(acac)3] to saturated hydrocarbons in CHCl3 and CCl4 solutions (1986)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 705-708 
    Details
    ISSN: 0749-1581
    Keywords: Paramagnetic 13C NMR shifts ; Cr(acac)3 ; Fe(acac)3 ; saturated hydrocarbons ; hex-1-ene ; contact charge transfer ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Paramagnetic 13C NMR shifts induced by tris(acetylacetonato)chromium(III) [Cr(acac)3] and tris(acetylacetonato)iron(III) [Fe(acac)3] in various saturated hydrocarbons were determined for the first time using a special technique.The observed shifts, Δδspec, are the result of partial delocalization of unpaired electrons from the paramagnetic complexes on the alkanes. The value of Δδspec depends strongly on the position of a carbon atom in the hydrocarbon molecule, and tends to decrease on passing from primary to quaternary carbon atoms. The observed spin transfer seems to reflect the ‘contact charge transfer.’ The Δδspec shifts in the unsaturated hex-1-ene only slightly exceed those in alkanes.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260240815
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  • 10
    Electronic Resource
    Electronic Resource
    Deuterium solid-state NMR study of the molecular mobility and dehydration of tert-butyl alcohol on zeolite H-ZSM-5 (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 16-23 
    Details
    ISSN: 0749-1581
    Keywords: tert-Butyl alcohol ; Dehydration ; H-ZSM-5 zeolite ; 2H NMR ; Molecular mobility ; Diffusion ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular mobility and dehydration reaction of tert-butyl alcohol, selectively deuteriated in the methyl groups (t-BuOH[2 - 2H9], dTBA), absorbed on H-ZSM-5 zeolite was studied using 2H NMR spectroscopy. At 173-298 K two modes of fast anisotropic motion were observed for the adsorbed alcohol: rotation of CD3 groups around the C—C bonds and rotation of the entire (CD3)3C fragment around the C—O bond. The influence of the walls of the H-ZSM-5 channels on the geometry of adsorbed dTBA is small, the increase in the CD3—C—O angle not exceeding 2.7 ± 1.2° compared with the same angle in solid dTBA. This is explained by location of the alcohol molecules at channel intersections of the zeolite, whose dimensions exceed those of the dTBA molecule. The lifetime of the dTBA molecule at these adsorption sites exceeds 1 × 10-5 s. The observed reaction products are deuteriated water with an unusual 2H NMR lineshape and two types of butene oligomers: less mobile species with the lineshape typical of solid-state 2H NMR and more mobile species with a liquid-like lineshape. The number of more mobile species increases with increase in temperature. In addition, 2H NMR indicates the presence of tert-butyl groups in the reaction products. For oligomers with a liquid-like lineshape, the diffusion coefficient D is 3 × 10-13 m2 s-1 at 373 K, whereas for oligomers with a solid-like lineshape D ≪ 5 × 10-14 m2 s-1 at 173-373 K. The diffusion coefficient for the t-BuOH molecule was estimated as D ≪ 2 × 10-14 m2 s-1 within the temperature range 173-296 K.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260320105
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