Carbenium Ion Intermediates Research Articles

ChemInform Abstract: ADDITIONS OF CHLOROSULFONYL ISOCYANATE TO 6‐SUBSTITUTED BENZONORBORNADIENES

AbstractDie 6‐substituierten Benzonorbornadiene (I) reagieren mit Chlorsulfonylisocyanat (II) zu den isomeren N‐Chlorsulfonyllactamen (III) und (IV); (I) mit R: ‐NO2 liefert mit (II) nur Spuren der entsprechenden Lactame (III) und (IV).

Additions of Chlorosulfonyl Isocyanate to 6‐Substituted Benzonorbornadienes

AbstractThe addition of chlorosulfonyl isocyanate (CSI) to 6‐substituted benzonorbornadienes gives pairs of isomeric syn and anti β‐lactam products. Previously published molecular orbital calculations indicate that the benzonorbornadiene π‐bond is not polarized. Relative rate data are inconsistent with either a concerted addition process or a process which proceeds by the direct formation of a carbenium ion intermediate. A mechanism proceeding through the initial formation of a benzonorbornadiene‐CSI π‐complex which decays to a carbenium ion in a product determining step is suggested.

Alkylaluminum halides : Lewis acid catalysts which are brønsted bases

Alkylaluminum halides react with Brønsted acids to liberate an alkane and generate a new Lewis acid. Using these reagents, Lewis acid catalyzed reactions can be run under aprotic conditions, even when acidic protons are produced in the reaction. The use of these reagents for Lewis acid catalyzed ene, Diels-Alder and cycloaddition reactions and Claisen rearrangements is described. These reagents are also useful initiators for cation-olefin addition reactions. In some cases the alkyl groups react as nucleophiles. While this is often undesirable, addition of an alkyl group to carbenium ion intermediates provides novel classes of compounds.

Mechanism of the oxidation of alkanes with nitronium tetrafluoroborate in acetonitrile. Evidence for a carbenium ion intermediate

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMechanism of the oxidation of alkanes with nitronium tetrafluoroborate in acetonitrile. Evidence for a carbenium ion intermediateRobert D. Bach, Joseph W. Holubka, Robert C. Badger, and Sundar J. RajanCite this: J. Am. Chem. Soc. 1979, 101, 15, 4416–4417Publication Date (Print):July 1, 1979Publication History Published online1 May 2002Published inissue 1 July 1979https://doi.org/10.1021/ja00509a081RIGHTS & PERMISSIONSArticle Views242Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (309 KB) Get e-Alerts Get e-Alerts

Ether cleavage of isomeric 2,3‐(dimethoxycarbonyl)‐7‐oxabicyclo[2.2.1]heptanes

AbstractThe ether cleavage of the three isomeric 2,3‐(dimethoxycarbonyl)‐7‐oxabicyclo[2.2.1]‐heptanes with acetic anhydride under influence of BF3 etherate or FeCl3 has been studied. A complex mixture of products was obtained, resulting from elimination, migration and substitution reactions. The results are interpreted in terms of reactions occurring via an acyloxonium ion and not via a ringopened carbenium ion intermediate.

Anisotropic properties of molybdenum disulfide single crystals in catalysis

When a wafer of molybdenum disulfide single crystal was mounted in a reactor with the basal plane of sulfur exposed and a similar wafer cut into small pieces was mounted in a twin reactor with a large edge surface area of coordinatively unsaturated molybdenum ions exposed, the cut, but not the uncut, catalyst was active for the cis-trans isomerization of 2-butene in the presence of hydrogen at 100/sup 0/C. The reaction induction period was characteristic of reactions that proceed via sec.-alkyl intermediates. The uncut and the cut catalysts were both active for the 2-methyl-1-butene double-bond migration, which indicated that this structure-insensitive reaction proceeds through carbenium ion intermediates in a reaction that is controlled by the proton activity or acidity of the sulfur layer.

Acidic Property and Catalytic Activity of Tungsten Oxide

Abstract A maximum activity of tungsten oxide for the isomerization of 1-butene was observed when the catalyst was evacuated at 600 °C, the ratio of cis-2-butene to trans-2-butene being 1.4. The activity was lost by the addition of NH3, but not affected by the addition of CO2 or H2O. The oxidation states of tungsten oxide treated with hydrogen at 550 and 650 °C were WO2.89 and WO2, respectively. The activity of WO2.89 for the double bond isomerization of 1-butene was almost the same as that of WO3 but the activity of WO2 for the double bond and skeletal isomerization of 1-butene and the dehydration of isopropanol was higher than that of WO3 or WO2.89· The coisomerization of cis-2-butene-d0/d8 revealed that the double bond isomerization of butenes proceeds by an intermolecular hydrogen transfer mechanism. When cis-2-butene-d8 was introduced to the catalyst on which cis-2-butene-d0 had been preadsorbed, the reactant and the product containing much of H were obtained, no d0-species being observed. It was concluded that the active sites for the isomerization of butenes are protons of polymerized butene formed by the adsorption on Lewis acid sites of tungsten oxide surface and the isomerization takes place via carbenium ion intermediates.

Surface property and catalytic activity of MgOTiO 2

The acid-base and reducing properties of MgOTiO 2 of various compositions—binary mixtures of a basic oxide (MgO) and an acidic oxide (TiO 2)—were studied and compared with their catalytic activities for the decomposition of diacetone alcohol, the dehydration of 4-methyl-2-pentanol, and the alkylation of phenol with methanol. The acidity of TiO 2 decreased upon addition of MgO, whereas the basicity of MgO was found to increase upon addition of 10 wt% TiO 2. The decomposition rate of diacetone alcohol was correlated well with the basicity of MgO-TiO 2 of different compositions, while the dehydration of 4-methyl-2-pentanol was correlated with the acidity. On the other hand, a maximum conversion of the alkylation was observed over MgOTiO 2 (weight ratio, 1:1) which has both basicity and acidity. No correlation was found between the reducing property and catalytic activity. The hydrogen exchange reaction of propylene with D 2O or D 2 over MgOTiO 2 (1:1) was shown by microwave spectroscopy to proceed via π-allyl carbanion or isopropyl carbenium ion intermediates, indicating that the active sites are basic and acidic, respectively.

Synthesis of 2‐amino‐5,6‐dihydro‐4H‐1,3‐thiazines and related compounds by acid catalyzed cyclization of allylic isothiuronium salts

AbstractSeveral allylic isothiuronium salts 6 have been shown to yield 4‐substituted 2‐amino‐5,6‐dihydro‐4H‐1,3‐thiazines (2; R3 = H) and the 2‐phenylimino compound 10 on exposure to trifluoroacetic acid or trifluoroacetic acid‐stannic chloride. The overall process constitutes a convenient transformation of readily available ketones or aldehydes 3 into the target hetero‐cycles. The scope and limitations of this approach are discussed in terms of carbenium ion intermediates (7). Whereas this method successfully led to the imidazo[2,l‐b][1,3]thiazine 13 (93% from 12), its application to the synthesis of 2‐amino‐2‐thiazolines (eg. 14→ 15) or imidazo‐[2,1‐b]thiazoles (eg. 16 → 17) was unsuccessful. The 2‐acetylimino derivatives 9 were found to be useful for purification of the 2‐aminothiazines.

Elektrochemische Synthesen, XI Die anodische Reaktion verzweigter Alkane / Electrochemical Syntheses, XI The Anodic Reaction of Branched Alkanes

Preparative electrochemical oxidation of branched alkanes in trifluoroacetic acid yields — as function of the applied potential — mono- or bifunctionalized derivatives. Esters with rearranged skeleton (hydride or methyl shift) suggest carbenium ion intermediates. These are generated by oxidative elimination of a proton or fragmentation. A method is described to measure small differences in reactivity of alkanes.

SOLVOLYSIS OF BUTATRIENYL HALIDES: EVIDENCE OF AN AMBIDENT VINYL CATION

Abstract The reactions of butatrienyl halides 4 and 5 in aqueous ethanol exclusively gave bis(benzofuranyl)acetylene 6. The first-order kinetics, the leaving group effect, kBr⁄kCl=52, and the Grunwald–Winstein’s m value of ca. 0.5 show that 4 and 5 are solvolyzed by an SN1 mechanism. The intermediate carbenium ion 7 is a new type of ambident vinyl cations.

ChemInform Abstract: ACETOLYSIS OF 4‐HOMOADAMANTYL TOSYLATE. MULTIPLE DEGENERATE REARRANGEMENTS AND MECHANISM

AbstractAus dem nach bekannten Methoden dargestellten Keton (I) wird durch Hydrierung mit LiAlH4 und Tosylierung die Titelverbindung (IIa) erhalten (Ausbeute 60%).

Remarkable behaviour in acid hydrolysis of the cycloadducts formed between allyl bromide and 1,2,4-trichloro-3,5,5-trimethoxycyclopentadiene

Two isomeric compounds ( 2a and 2b) are formed on addition of allyl bromide to 1,2,4-trichloro-3,5,5-trimethoxycyclopentadiene ( 1). The striking difference in behaviour of these two isomers on acid catalysed solvent addition can be explained by assuming a stabilization of the intermediate carbenium ion by the near endo-CH 2Br group in 2a. The stabilization of this cation from the endo-side forces subsequent nucleophiles to attack from the exo-direction, resulting in an overall cis-exo addition to 2a. trans-Additions on the contrary are observed for 2b. Screening by the bromomethyl grouping of the intermediate cation formed from 2a gives a satisfactory explanation for the formation of the observed reaction products and for the sigmatropic rearrangement observed in poorly nucleophilic media. The structures of parent compounds 2a and 2b are confirmed from the different reaction products. The structure 4a, as previously reported 4 to be formed under similar reaction circumstances, is revised and an alternative structure 4'a is proposed.

The nature of active sites on aluminum phosphate for the isomerization of butenes

The nature of active sites on aluminum phosphate for the isomerization of n-butenes was investigated by means of a tracer study which consisted of isomerization over deuterated catalyst and co-isomerization of light and perdeuterated butene. There exist three kinds of active sites, Brönsted acid sites, Lewis acid sites where intermolecular hydrogen transfer occurs (L-inter sites), and Lewis acid sites where intramolecular hydrogen transfer occurs (L-intra sites). Their contributions to n-butene isomerization, which were quite dependent on the thermal treatment of the catalyst, were calculated for different evacuation temperatures. At low evacuation temperature, Brönsted acid sites and L-inter sites are the main active sites, while L-intra sites become prominent at high evacuation temperature. L-intra sites are characteristically active for cis-trans rotation. The adsorption state of butene molecules was also examined. From the isotopic distributions of butene isomers, it was concluded that secondary butyl carbenium ion intermediates on Brönsted acid sites and L-inter sites were adsorbed weakly, and all bonds of the intermediates rotated freely. Over L-intra sites, the isomerization may be initiated by the abstraction of H − at the vinyl hydrogen of butene.

The rôle of carbocations in cationic polymerization (polycondensation) of π‐, σ‐, and n‐donor monomers

AbstractThe rôle of carbocations in cationic polymerizations is discussed, differentiating σ‐ (i.e. alkene and arene), π‐ (i.e. alkane) and n‐donor (i.e. ether, sulfide, nitrogen compound) monomers as the reactive nucleophiles. The mechanism of the initiation step in alkene polymerization is evaluated considering both protic (i.e. coinitiator containing) and aprotic systems. The aluminum bromide catalyzed polymerization of isobutylene, as an example, can involve besides the conjugate protic acid, bromoalanation intermediates in aprotic media, which, however, themselves rapidly can undergo elimination, forming HBr in the originally acid free system. The involvement of dialkylhalonium ions in alkyl halide solvent systems is also of substantial interest and may explain increasing deactivation in the order RI>RBr>RCl. Oxidative polycondensation of π‐donor arenes (such as benzene) and σ‐donor alkanes (such as methane) is discussed in the context of the general carbocation concept, involving trivalent carbenium ion intermediates in the former and pentacoordinated carbonium ions in the latter case, as the reactive alkylating agents responsible for the ionic propagation reactions. n‐Donor monomers, such as ethers, sulfides or miscellaneous nitrogen compounds, undergo polymerization via nucleophilic displacement reactions on the polarized carbocationic sites of intermediate alkylated or protonated onium ions.

Stereochemistry and mechanism of the prins reaction involving strong charge-delocalization in the intermediate carbenium ion

Stereochemistry and mechanism of the prins reaction involving strong charge-delocalization in the intermediate carbenium ion