Methoxide Ion In Methanol Research Articles

Kinetics and quantification of the electrophilic reactivities of substituted thiophenes and structure‐reactivity relationships

AbstractSecond‐order rate constants (k1) have been measured spectrophotometrically for reactions of 2‐methoxy‐3‐X‐5‐nitrothiophene 1a‐c (X = NO2, CN, and COCH3) with secondary cyclic amines (pyrrolidine 2a, piperidine 2b, and morpholine 2c) in CH3CN and 91:9 (v/v) CH3OH/CH3CN at 20°C. The experimental data show that the rate constants (k1) values exhibit good correlation with the parameters of nucphilicity (N) of the amines 2a‐c and are consistent with the Mayr's relationship log k (20°C) = s(E + N). We have shown that the electrophilicity parameters E derived for 1a–c and those reported previously for the thiophenes 1d‐g (X = SO2CH3, CO2CH3, CONH2, and H) are linearly related to the pKa values for their gem‐dimethoxy complexes in methanol. Using this correlation, we successfully evaluated the electrophilicity E values of 12 structurally diverse electrophiles in methanol for the first time. In addition, a satisfactory linear correlation (r2 = 0.9726) between the experimental (log kexp) and the calculated (log kcalcd) values for the σ‐complexation reactions of these 12 electrophiles with methoxide ion in methanol has been observed and discussed.

Nucleophilic Substitution Reactions of 2‐Methoxy‐3‐X‐5‐nitrothiophenes: Effect of Substituents and Structure–Reactivity Correlations

ABSTRACTA kinetic study is reported for reactions of 2‐methoxy‐3‐X‐5‐nitrothiophenes 1a–d (X = SO2CH3, CO2CH3, CONH2, H) with piperidine in different solvents at 20°C. It is shown that the reactions take place through a SNAr mechanism with the initial nucleophilic addition step being rate limiting. The satisfactory Hammett correlations (log k1 vs. σ) obtained in the present system confirms that a 3‐X substituent exerts an effect on the 2‐position of the same type as that exerted from the 5‐position. The second‐order rate constants associated with these reactions are employed to determine the electrophilicity parameters E of the thiophenes 1a–d according to the relationship log k (20°C) = s(E + N) (Angew. Chem., Int. Ed. Engl. 1994, 33, 938–957). The E values of 1a–d are found to cover a range from −21.33 to −17.18, going from 1d, the least reactive, to 1a, the most reactive thiophene. Interestingly, a linear correlation (r2 = 0.9910) between the electrophilicity parameters E determined in this work and the Hammett's σ constants values has been observed and discussed. On the other hand, we have found that the reported rate constants of some thiophenes 1 complexation by the methoxide ion in methanol are 3.5–73.5 times higher than predicted by Mayr's approach.

The Reversible Consecutive Mechanism for the Reaction of Trinitroanisole with Methoxide Ion

Although the competitive mechanism for Meisenheimer complex formation during the reaction of 2,4,6-trinitroanisole with methoxide ion in methanol is generally accepted, no kinetic evidence has been presented to rule out a reversible consecutive mechanism. Simulation of the competitive mechanism revealed that a fractional order in [MeO(-)] is predicted by the latter. Conventional pseudo-first-order analysis of the kinetics resulted in cleanly first-order in [MeO(-)], which rules out the competitive mechanism. The kinetic data are consistent with the reversible consecutive mechanism, which is proposed for this important reaction. An intermediate is required for this mechanism, and we propose that a dianion complex (III) is formed reversibly from the initial 1,3-σ complex (I). The trimethoxy complex (III), the (1)H NMR spectrum of which was observed earlier by Servis (Servis, K. L. J. Am. Chem. Soc. 1965, 87, 5495; 1967, 89, 1508), then eliminates methoxide ion reversibly to form the 1,1-σ complex product (II).

Photoinduced demethylation of 4-nitro-N,N-dimethylaniline.

The title compound (3) upon photoexcitation becomes demethylated by either an external acceptor in benzene or the methoxide ion in methanol. The triplet state of 4-nitroaniline (1), 4-nitro-N-methylaniline (2), 3 and the 3-nitro analogue (4) in solution at room temperature was characterized by time-resolved UV-vis spectroscopy. The triplet state of 3 in benzene reacts with other nitroarenes, such as nitrobenzene and nitronaphthalenes, by demethylation, yielding eventually 2 and further products. This quenching reaction is close to the diffusion-controlled limit. The conversion of 3 into 2 is accompanied by a permanent bleaching at 370-400 nm within 10 its and the quantum yield is up to 0.3, this being in agreement with the quantum yield of intersystem crossing. An intermediate with peaks at 420 and 700 nm is attributed to a C-centered radical: H2*C(CH3)N-C6H4-NO2, which is also involved with 3 in methanol in the presence of methoxide. The overall H-atom transfer takes place within a few micros. Another electron transfer reaction, involving the non-absorbing alpha-aminoethyl radical, occurs from triethylamine to the triplet state of 3. The observed transient with a maximum at 330 nm in benzene or acetonitrile is assigned to the conjugate acid of the radical anion of 3 which subsequently disproportionates in the ms range. The photochemical properties of 1-4 and the mechanisms of the demethylation and reduction reactions are discussed.

Proton transfer between carbon acids and methoxide: Studies in methanol, the gas phase and by ab initio MO calculations

AbstractA detailed mechanism that features hydrogen‐bonded carbanions as well as free carbanions is presented for hydrogen transfer between carbon acids and methoxide ion in methanol. This is refined for several compounds by measuring their gas phase acidities, ΔG kcal/mol: C6H5CH(CF3)2 [335.3]; p‐C6H4CHClCF3 [337.4]; 9‐phenylfluorene [335.6]; C6F5H [349.2]. Ab initio molecular orbital calculations are reported to evaluate the stability of possible intermediates along the reaction pathway from 2‐hydro‐2‐phenyl‐perfluoropropane and methoxide ion to the carbanion and methanol. The intermediate, {C6H5C(CF3)2}−. HOCH3, is 6.8 kcal/mol more stable than the separated species, {C6H5C(CF3)2}− and CH3OH, and 43.2 kcal/mol more stable than C6H5CH(CF3)2 and −OCH3.

A theoretical study of the structure, electronic properties, and reactivity of phenylcyanates

Calculations are reported on the structure and electronic properties of phenylcyanate and its 4-nitro and 4-amino derivatives using both the semi-empirical AM1 and PM3 methods and the ab initio 6–31G ∗∗ basis set. The calculated structures are compared with crystallographic data where available and their electronic properties with their expected reactivity. A study of the reactions of the phenylcyanates with methoxide ion in methanol using the AM1/COSMO method suggests that the rate-controlling step of the nucleophilic substitution reactions of the phenylcyanates is controlled by the addition of methoxide ion to the cyanato group to give a stable intermediate. Ring substituents exert little effect on this process, although, thermodynamically, the formation of the 4-nitrophenylcyanate intermediate is favoured over the others. The conversion of the intermediate into products is strongly affected by the nature of the ring substituents so that both the kinetics and thermodynamics of the subsequent displacement of the phenoxide ion is facilitated by the nitro group and retarded by the amino group.

Theoretical studies on the reactivity of phenylthiocyanates

Molecular orbital calculations are reported on the electronic structure of phenylthiocyanate and its 4-nitro and 4-amino derivatives using the semi-empirical AM1 and PM3 methods. The reactivity of these systems at the cyano carbon, sulfur atom and aryl carbon have been explored with the methoxide ion in methanol using the AM1/COSMO method. In terms of overall stability, attack at the aryl carbon with the displacement of the thiocyanate anion is the preferred process in all three cases followed by the alternative attack at the cyano carbon resulting in the displacement of the phenylthiolate anion: the corresponding attack at the sulfur atom with the displacement of the cyanide ion is strongly disfavoured. Kinetically, the reaction selectivity is highly dependent on the substituent present though all three molecules readily form reversible complexes at the sulfur atom. The activation energies suggest that 4-nitrophenylthiocyanate will react at both the aryl carbon or cyano carbon, but phenylthiocyanate and 4-aminophenylthiocyanate would be expected to react preferentially at the cyano carbon only.

Remarkable catalysis by strontium ion in SN2 and E2 reactions occurring in proximity to a crown ether structure

Strontium ion catalyses the reactions of the crown ether derivatives 1 and 2 with methoxide ion in methanol at 40 °C to yield the product of substitution 3 and elimination 4, respectively.

Elimination reactions of hydrazonium salts: experimental and theoretical evidence for a large stereoelectronic effect of nitrogen

Elimination of trimethylamine from hydrazonium salts is promoted by base (methoxide ion in methanol). The mechanism is characterized as E2 as shown by substituent effects (ρ=+2.57), Bronsted coefficients, a primary kinetic isotope effect (k H /k D =2.10), and solvent effects. Variation in the leaving group shows that N-N bond cleavage is less well advanced in the transition state than C-H bond breaking

Formation of 4,6-dinitro-2-nitrosoaniline by intramolecular redox reaction of esters and amides of 2-(2,4,6-trinitroaniline) carboxylic acids

The reaction of methyl and ethyl esters of N-(2,4,6-trinitrophenyl) glycine and N-(2,4,6-Trinitrophenyl)α-alanine (3a–d) with methoxide ion in methanol produces 4,6-dinitro-2-nitrosoaniline (4). N-(2,4,6-Trinitrophenyl) glycine methylamide (1d) gives, under the same conditions, the nitroso compound (4) in addition to 12% of the spiro adduct (2d). A reaction mechanism is suggested, and the influence of the side chain on the reaction kinetics has been studied.

The alkaline hydrolysis of 4-methoxycoumarin

The aqueous alkaline hydrolysis of 4-methoxycoumarin occurs in two stages. In the first, the lactone ring is opened at a rate directly proportional to the concentration of base. In the second, the methoxy group is replaced by an unusual route that depends upon the presence of an un ionised phenolic hydroxy group and is therefore inversely proportional to the concentration of base. Methanolysis by methoxide ion in methanol occurs primarily at position 4 and replaces the methoxy group before the ring is opened; the difference from the aqueous hydrolysis is ascribed to solvent effects.

Reactions of tetrafluoroethene oligomers. Part 4. Some reactions of the major hexamer oligomer with nucleophiles based on oxygen and sulphur

The major hexamer oligomer of tetrafluoroethene [perfluoro-2-(1-ethyl-1-methylpropyl)-3-methyl-pent-1-ene] (1) reacted with sodium hydroxide under vigorous conditions to afford perfluoro-[(1-ethyl-1-methylpropyl) (1-methylpropyl)]keten (3). Reaction of (1) with methoxide ion in methanol afforded 4-methoxycarbonyl-heneicosafluoro-3,5-dimethyl-5-ethyl-hept-3-ene (5) whereas reaction with methanol In the presence of triethylamine initially afforded (5), but on further reaction yielded (E, Z)-4H-heneicosafluoro-3,5-dimethyl-5-ethylhept-3-ene (4). Reaction of (1) with potassium-t-butoxide in t-butanol afforded (3) whilst with water/triethylamine (4) was obtained. With ethanethiol and sodium benzylthiolate, respectively, hexamer (1) gave ethyl and benzyl [tricosafluoro-3-ethyl-3-methyl-2-(1-methylpropyl)pent-1-enyl]sulphides (6) and (7). With aqueous potassium cyanide 1-cyanotricosafluoro-3-ethyl-3-methyl-2-(1-methylpropyl)pent-1-ene (8) was obtained.

Ionization of 9-cyanofluorene in Me2SO–water mixtures. The role of solvent reorientation in proton tranfers

Rate constants of the reversible deprotonation of 9-cyanofluorene by primary aliphatic amines were measured in 10%, 50%, and 90% aqueous Me2SO (v/v) by the stopped-flow method. Intrinsic rate constants defined as k0 = k1B/q = k−1BH+/p at ΔpK + log (p/q) = 0 were obtained from Brønsted plots. The values for log k0 are 3.60 ± 0.15 in 10%, 3.81 ± 0.10 in 50%, and 3.61 ± 0.05 in 90% Me2SO. The constancy of k0 with increasing Me2SO content of the solvent contrasts with results obtained by Ritchie (C. D. Ritchie, J. Am. Chem. Soc. 91, 6749 (1969)) who found that k0 for the ionization of 9-carbomethoxyfluorene by carboxylate ions in Me2SO is much higher than for the ionization of the same carbon acid by methoxide ion in methanol. Our findings suggest that it is mainly early desolvation of the oxyanions in the hydroxylic solvent which accounts for Ritchie's results.

Improved synthesis of anti-sesquinorbornene

Treatment of methyl hydrogen decahydro-1,4:5,8-exo,endo-dimethanonaphthalene-4a,8a-dicarboxylate with lead tetraacetate in benzene – acetic acid replaces the carboxyl group by an acetoxy group. Hydrolysis of this product with 25% sulfuric acid at 130 °C forms 8a-hydroxydecahydro-1,4:5,8-exo,endo-dimethanonaphthalene-4a-carboxylic acid 10. The reaction between 10 and benzenesulfonyl chloride in pyridine containing triethylamine at 95 °C produces anti-sesquinorbornene 1 in 34% yield. In the absence of triethylamine 1 is converted to the hydrochloride. The iodohydroperoxide of 1 is converted by silver acetate at 0 °C to the diketone in a luminescent reaction. The 1,2-dioxetane could not be isolated. Decahydro-1,4:5,8-exo,exo-dimethanonaphthalene-4a,8a-dicarboxylic anhydride is converted slowly by methoxide ion in methanol at 150 °C to the monomethyl ester which then undergoes demethylation. The isomeric exo,endo anhydride undergoes reaction readily with methoxide ion at 80 °C.

The stabilities of Meisenheimer complexes. Part 36. The reaction of 2,4,6-trinitrobenzyl chloride with sodium hydroxide in water

The reaction of 2,4,6-trinitrobenzyl chloride with dilute aqueous sodium hydroxide gives a σ-adduct by hydroxide ion attck at the 1-position. Kinetic and equilibrium data for this reaction are reported and are compared with those for the reaction with methoxide ions in methanol.

Quantum and statistical mechanical studies of liquids. 21. The nature of dilute solutions of sodium and methoxide ions in methanol

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTQuantum and statistical mechanical studies of liquids. 21. The nature of dilute solutions of sodium and methoxide ions in methanolWilliam L. Jorgensen, Bernard Bigot, and Jayaraman ChandrasekharCite this: J. Am. Chem. Soc. 1982, 104, 17, 4584–4591Publication Date (Print):August 1, 1982Publication History Published online1 May 2002Published inissue 1 August 1982https://doi.org/10.1021/ja00381a013RIGHTS & PERMISSIONSArticle Views202Altmetric-Citations43LEARN 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 (982 KB) Get e-Alerts Get e-Alerts

The reinvestigation of the kinetics of the reactions of fluorodi(4-nitrophenyl)ethanes with sodium methoxide in methanol

The procedure previously described for the preparation of 1-fluoro-2,2,-di(4-nitrophenyl)ethane actually yields 1,1,2-tri-(4-nitrophenyl)ethane. 1-Fluoro-2,2-di(4-nitrophenyl)ethane has been prepared and rate constants, isotope effects, and activation parameters for the β-elimination reaction with methoxide ion in methanol are reported. These parameters indicate a concerted E2 mechanism, with a fairly symmetrical transition state. The subsequent dimerization reaction of the olefin product to yield 1,1,3,3-tetra(4-nitrophenyl)butene-1 is described.The reaction of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane with methoxide ion in methanol has been reinvestigated and the reaction of the first product 1,1-difluoro-2,2-di(4-nitrophenyl)ethylene with excess methoxide, to give di(4-nitrophenyl)ketene dimethylacetal in a multistep reaction, is reported.

The stabilities of Meisenheimer complexes. Part 31. The reactions of 2,2′,4,4′,6,6′-hexanitrostilbene with alkoxides

1 H N.m.r. and visible spectral measurements indicate three types of 1 : 1 interaction of 2,2′,4,4′,6,6′-hexanitrostilbene with alkoxides. σ-Adducts are formed by attack at the 3- or 1-ring position, while the third interaction may involve attack at the olefinic double bond. A 1 : 2 adduct is produced by attack at the 1- and 1′-ring position. Kinetic and equilibrium results for reactions with methoxide ions in methanol and ethoxide ions in ethanol have been obtained and are compared with those for related compounds.

A kinetic study of the mechanisms of S NAr reactions of neutral and cationic metal-complexed halogenoarenes with methoxide ion

Rate studies have shown that the activation of halogenobenzenes towards nucleophilic attack by methoxide ion in methanol increases through the series of π-attached residues: (OC)3Cr chlorobenzene > chlorotoluene. Rates of reaction with methoxide are retarded in the presence of NaClO4 or LiCl, but accelerated when the methanol solvent is diluted with tetrahydrofuran or 1,4-dioxan. Fluorobenchrotrene (OC)3Cr(η6-PhCl) is slightly more reactive towards ethoxide in ethanol than towards methoxide in methanol. Evidence has been obtained that the cationic (halogenoarene)metal complexes readily form ion-pairs with methoxide, resulting in a reduction in their reactivity towards nucleophilic attack. Methoxide adds to [(π-methoxyarene)Mn(CO)3]+ complexes to give (η5-cyclohexadienyl) products which are reconverted into the cations by acid treatment.

Fluoride-catalyzed conversion of acylsilanes to aldehydes and ketones

Acylsilanes undergo efficient protodesilylation upon treatment with fluoride ion in moist DMSO, HMPT, or THF. The reaction is also catalyzed by methoxide ion in methanol or DMSO, but not by chloride ion or bromide ion. Fluoride-catalyzed desilylation in the presence of alkyl halides, aldehydes, or ketones results in modest yields of the corresponding alkylated products.