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Search for "acidity" in Full Text gives 275 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.

New bio-nanocomposites based on iron oxides and polysaccharides applied to oxidation and alkylation reactions

  • Daily Rodríguez-Padrón,
  • Alina M. Balu,
  • Antonio A. Romero and
  • Rafael Luque

Beilstein J. Org. Chem. 2017, 13, 1982–1993, doi:10.3762/bjoc.13.194

Graphical Abstract
  • can be deduced from the intense and well-defined bands observed at 1449 and 1600 cm−1, which can be attributed to Lewis acid centers (Figure 4A). Additionally, in the spectrum of Fe2O3-PS4-MNP, having bands at 1440 and 1618 cm−1, indicates the peculiar Lewis acidity of this material (Figure 4B
  • ). Furthermore, in both materials, a band of lesser intensity can be seen around 1490 cm−1, which is due to the presence of both Brønsted and Lewis centers. These materials maintained a remarkable acidity, even at high temperatures (200 and 300 °C) with visible acid centers distinguishable from noise. This
  • behavior has a high value for acid-catalyzed processes such as alkylation. Furthermore, the Fe2O3-PS4 sample does not show appreciable acidity [43]. Pyridine (PY) and 2,6-dimethylpyridine (DMPY) titration The acidic properties of these materials have also been determined by the chromatographic method of
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Published 21 Sep 2017

Base-promoted isomerization of CF3-containing allylic alcohols to the corresponding saturated ketones under metal-free conditions

  • Yoko Hamada,
  • Tomoko Kawasaki-Takasuka and
  • Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 1507–1512, doi:10.3762/bjoc.13.149

Graphical Abstract
  • this interesting and efficient protocol, computation was performed [7] for obtaining the rough indication of the acidity of both protons Ha and Hb in 1F. Moreover, the corresponding allylic alcohols 2F as well as their non-fluorinated counterparts 1H and 2H were also employed for comparison whose
  • present instance to afford the desired compound 7a in 67% isolated yield (Table 2, entry 2). The result that the stronger tertiary amine DBU worked more effectively than Et3N was a clear support of our computation at least from a qualitative point of view which estimated the lower acidity of the allylic
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Published 01 Aug 2017

Towards open-ended evolution in self-replicating molecular systems

  • Herman Duim and
  • Sijbren Otto

Beilstein J. Org. Chem. 2017, 13, 1189–1203, doi:10.3762/bjoc.13.118

Graphical Abstract
  • -state. Instead, the environment may be continuously changing. Consider for instance changes in temperature, acidity, light intensity and humidity to which a system will inevitably be subjected. A replicator that is very well adapted to a certain environment, might not persist at a later time when the
  • interact with the evolutionary process. Can environmental conditions like acidity or temperature, for instance, be an incentive towards the development of novel functionalities in the replicators? And how is the notion of death introduced in an experiment in which the researcher does not actively intervene
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Published 21 Jun 2017

Transition-metal-free one-pot synthesis of alkynyl selenides from terminal alkynes under aerobic and sustainable conditions

  • Adrián A. Heredia and
  • Alicia B. Peñéñory

Beilstein J. Org. Chem. 2017, 13, 910–918, doi:10.3762/bjoc.13.92

Graphical Abstract
  • environment and moderate acidity of the methylene protons in benzyl selenocyanate (7h) or dibenzyl diselenide (8h) may afford intermediates prone to decomposition, directly affecting formation of 5h. Furthermore, the electronic and steric effects offered by different substituents on the aryl moieties attached
  • yield of product 5j to 52%. This is ascribed to a lower acidity of the acetylenic proton in 6c in relation to the unsubstituted alkyne 6a (Table 4, entry 3). For phenylethynyl derivatives substituted in para or ortho position by halides, the yields of the corresponding products 5k and 5l were 64% and 61
  • detected (Table 4, entry 6). This result indicates that although the acidity of acetylenic proton in 6f is higher than that for the unsubstituted one 6a, the resulting anion is highly stabilized by this group, thus reducing its nucleophilic character and being unreactive against di(n-octyl) diselenide (8a
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Published 16 May 2017

Metal-free hydroarylation of the side chain carbon–carbon double bond of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles in triflic acid

  • Anna S. Zalivatskaya,
  • Dmitry S. Ryabukhin,
  • Marina V. Tarasenko,
  • Alexander Yu. Ivanov,
  • Irina A. Boyarskaya,
  • Elena V. Grinenko,
  • Ludmila V. Osetrova,
  • Eugeniy R. Kofanov and
  • Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2017, 13, 883–894, doi:10.3762/bjoc.13.89

Graphical Abstract
  • room temperature (see Table 2, entries 16 and 28). Presumably, at higher temperatures the second protonation takes place at the C=C double bond giving rise to reactive dications D. The acidity of H2SO4, which is lower than that of FSO3H and TfOH, is not sufficient to promote this reaction. Thus, the
  • temperature (Table 2, entries 13, 16, 27, 28, and 30). Increasing the acidity of the reaction medium promotes the protonation of deactivated oxadiazoles. Thus, compound 1b in the system TfOH-SbF5 (20 mol %) reacted with benzene within 0.5 h at room temperature (Table 2, entry 9), but in less acidic neat TfOH
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Published 11 May 2017

New approach toward the synthesis of deuterated pyrazolo[1,5-a]pyridines and 1,2,4-triazolo[1,5-a]pyridines

  • Aleksey Yu. Vorob’ev,
  • Vyacheslav I. Supranovich,
  • Gennady I. Borodkin and
  • Vyacheslav G. Shubin

Beilstein J. Org. Chem. 2017, 13, 800–805, doi:10.3762/bjoc.13.80

Graphical Abstract
  • -methoxy-N-aminopyridinium cation possesses significantly lower acidity for both N–H and C–H hydrogens possibly due to the electron-donating effect of the methoxy group. These quantum chemical data together with Zoltewicz’s work [27] suggest 7-deuterium-labeled pyrazolo[1,5-a]pyridines could be obtained
  • a 93% DD for the methyl group after two runs in D2O. The 4-methoxy derivative 1c slowly underwent an H/D exchange at the 2-position of the pyridinium ring probably by reason of a lower acidity due to the electron-donating effect of the methoxy group. Thus, 5-methoxypyrazolopyridine 6 was obtained in
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Published 02 May 2017

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

  • Carmen Moreno-Marrodan,
  • Francesca Liguori and
  • Pierluigi Barbaro

Beilstein J. Org. Chem. 2017, 13, 734–754, doi:10.3762/bjoc.13.73

Graphical Abstract
  • support material, e.g., acid/base properties [184][185], morphology, grain size [186], porosity [187], strong metal–support interactions, swelling propensity [188]). In propyne hydrogenation, for instance, catalyst resistance was shown to decrease with increasing acidity of the support [189]. In order to
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Published 20 Apr 2017

Substitution of fluorine in M[C6F5BF3] with organolithium compounds: distinctions between O- and N-nucleophiles

  • Anton Yu. Shabalin,
  • Nicolay Yu. Adonin and
  • Vadim V. Bardin

Beilstein J. Org. Chem. 2017, 13, 703–713, doi:10.3762/bjoc.13.69

Graphical Abstract
  • ion pair (solution of Li[C6F5B(OMe)3] in CH2Cl2), such migration of −OMe and its subsequent elimination is hindered [42]. In the case of pentafluorophenyltrifluoroborates the similar conversion does not occur even with Li[C6F5BF3] in DME (contact ion pairs) due to the higher Lewis acidity of C6F5BF2
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Published 12 Apr 2017

Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

  • Abdusalom A. Suleymanov,
  • Dmitry V. Vasilyev,
  • Valentin V. Novikov,
  • Yulia V. Nelyubina and
  • Dmitry S. Perekalin

Beilstein J. Org. Chem. 2017, 13, 639–643, doi:10.3762/bjoc.13.62

Graphical Abstract
  • structure to that of 1a,b. We can speculate that COOEt groups of 1l formed a chelate complex with ZnI2 and therefore strongly diminished its Lewis acidity, which is necessary for catalyst activation. All the compounds obtained were characterized by 1H and 13C NMR spectroscopy as well as high-resolution mass
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Published 31 Mar 2017

Transition-metal-catalyzed synthesis of phenols and aryl thiols

  • Yajun Liu,
  • Shasha Liu and
  • Yan Xiao

Beilstein J. Org. Chem. 2017, 13, 589–611, doi:10.3762/bjoc.13.58

Graphical Abstract
  • chemical properties, such as acidity and nucleophilicity, and thus to some extent, the synthetic methods could be developed analogously to each other. In this context, it is valuable to compare their existing synthetic methods for better understanding, so as to inspire organic chemists to invent new
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Published 23 Mar 2017

Structure–efficiency relationships of cyclodextrin scavengers in the hydrolytic degradation of organophosphorus compounds

  • Sophie Letort,
  • Michaël Bosco,
  • Benedetta Cornelio,
  • Frédérique Brégier,
  • Sébastien Daulon,
  • Géraldine Gouhier and
  • François Estour

Beilstein J. Org. Chem. 2017, 13, 417–427, doi:10.3762/bjoc.13.45

Graphical Abstract
  • consisted first in the selective introduction of the imidazole substituent in position 2 in unit B of 6 by making use of the higher acidity of this hydroxy group compared to the OH groups in positions 3 and 6. As expected, the substitution reaction with the benzyl-like reactant 7 led to a higher yield than
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Published 06 Mar 2017

(Z)-Selective Takai olefination of salicylaldehydes

  • Stephen M. Geddis,
  • Caroline E. Hagerman,
  • Warren R. J. D. Galloway,
  • Hannah F. Sore,
  • Jonathan M. Goodman and
  • David R. Spring

Beilstein J. Org. Chem. 2017, 13, 323–328, doi:10.3762/bjoc.13.35

Graphical Abstract
  • acetylated (14) and the relevant proton is therefore absent. This implies that increased acidity is not the primary factor at play. Instead, based on the higher (Z)-selectivity observed whenever the electron-withdrawing group was closer to the aldehyde moiety (Table 2), we propose that it is withdrawal of
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Published 20 Feb 2017

Spectral and DFT studies of anion bound organic receptors: Time dependent studies and logic gate applications

  • Srikala Pangannaya,
  • Neethu Padinchare Purayil,
  • Shweta Dabhi,
  • Venu Mankad,
  • Prafulla K. Jha,
  • Satyam Shinde and
  • Darshak R. Trivedi

Beilstein J. Org. Chem. 2017, 13, 222–238, doi:10.3762/bjoc.13.25

Graphical Abstract
  • receptors for anions have been developed based on various modes of interactions such as hydrogen bond and electrostatic interactions which rely on directionality and distance-dependent nature, respectively. Hydrogen bond formation is further tuned by the acidity of protons by virtue of the presence of
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Published 06 Feb 2017

Interactions between photoacidic 3-hydroxynaphtho[1,2-b]quinolizinium and cucurbit[7]uril: Influence on acidity in the ground and excited state

  • Jonas Becher,
  • Daria V. Berdnikova,
  • Darinka Dzubiel,
  • Heiko Ihmels and
  • Phil M. Pithan

Beilstein J. Org. Chem. 2017, 13, 203–212, doi:10.3762/bjoc.13.23

Graphical Abstract
  • red-shifted absorption bands and causes a dual emisson, i.e., a combination of emission bands of the hydroxyquinolizinium and its deprotonated form. Whereas this compound is a weak acid in the ground state (pKa = 7.9), it has a strongly increased acidity in the excited state (pKa* = 0.4). As a result
  • acidity or basicity. In fact, it was shown that the pKa of organic acids and bases often shifts by orders of magnitude upon association with CB[n] [16][17][18][19][20][21][22][23][24], which may be used, e.g., to modify catalytic activity [6] or for sensing purposes [7]. Notably, the same effect was
  • observed for the excited-state proton transfer (ESPT) of so-called photoacids. The latter are weak acids in the ground state, whereas their acidity in the excited state increases significantly [25][26][27]. As the activity of photoacids is triggered by light, they have a great potential to be employed as
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Published 01 Feb 2017

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

  • Pavel Nagorny and
  • Zhankui Sun

Beilstein J. Org. Chem. 2016, 12, 2834–2848, doi:10.3762/bjoc.12.283

Graphical Abstract
  • substantial dipole moment (≈4.5 D) almost aligned with the C5–H bond and the relatively high acidity of this position (pKa(DMSO) = 27–28, for the 1H-tautomer). These heterocycles, which are easily available from 1,3-cycloaddition of alkynes and azides, can both form strong C–H bonds with hydrogen bond
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Published 23 Dec 2016

Copper-catalyzed asymmetric sp3 C–H arylation of tetrahydroisoquinoline mediated by a visible light photoredox catalyst

  • Pierre Querard,
  • Inna Perepichka,
  • Eli Zysman-Colman and
  • Chao-Jun Li

Beilstein J. Org. Chem. 2016, 12, 2636–2643, doi:10.3762/bjoc.12.260

Graphical Abstract
  • -arylated PyBox L2 gave very good er under our reaction conditions (Table 2, entry 2). It is noteworthy that the er observed was higher when copper(I) bromide was used as a co–catalyst, compared to copper(II) bromide (Table 2, entry 3), possibly due to the Lewis acidity difference of Cu(I) and Cu(II
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Published 06 Dec 2016

Construction of bis-, tris- and tetrahydrazones by addition of azoalkenes to amines and ammonia

  • Artem N. Semakin,
  • Aleksandr O. Kokuev,
  • Yulia V. Nelyubina,
  • Alexey Yu. Sukhorukov,
  • Petr A. Zhmurov,
  • Sema L. Ioffe and
  • Vladimir A. Tartakovsky

Beilstein J. Org. Chem. 2016, 12, 2471–2477, doi:10.3762/bjoc.12.241

Graphical Abstract
  • hydrazones with starting hydrazide [51]. The presence of acetic acid and mild reaction conditions (0 °C) was essential for the synthesis of hydrazones 1c and 1d (R1 = CH3, R2 = CH3 or (CH2)6CH3), probably because of the their enhanced NH-acidity. Reaction of α-halogen hydrazones 1 with benzylamine In our
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Published 21 Nov 2016

Et3B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

  • Ahlem Abidi,
  • Yosra Oueslati and
  • Farhat Rezgui

Beilstein J. Org. Chem. 2016, 12, 2402–2409, doi:10.3762/bjoc.12.234

Graphical Abstract
  • acidity is relatively higher, led to a mixture of the mono- and bis-alkylation products 3c and 4c in 45 and 23% yields, respectively (Table 2, entries 1–3). Under the same conditions, the allylation of a variety of β-keto esters and β-diketones (Table 2, entries 4–9), in DMF at 80 °C, selectively gave the
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Published 15 Nov 2016

Isosorbide and dimethyl carbonate: a green match

  • Fabio Aricò and
  • Pietro Tundo

Beilstein J. Org. Chem. 2016, 12, 2256–2266, doi:10.3762/bjoc.12.218

Graphical Abstract
  • bisphenol A in polycarbonate preparation. In this view, the main issue that limits the exploitation of this compound is its lower acidity. To overcome this problem, polycarbonates incorporating an isosorbide moiety have been synthesized via a chlorine-based approach, i.e., employing phosgene or its
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Published 26 Oct 2016

Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

  • Ángel Cantín,
  • M. Victoria Gomez and
  • Antonio de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188, doi:10.3762/bjoc.12.208

Graphical Abstract
  • 1.9 nm (ITQ-37) [36] have also been tested. These are aluminosilicogermanates that, as the previously tested Al-zeolites or the Al-MCM-41 material, present Brønsted acidity. Interestingly, the pore diameters of ITQ-33, and more so ITQ-37 are close to the pore of the mesoporous MCM-41 presented above
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Published 13 Oct 2016

Silica-supported sulfonic acids as recyclable catalyst for esterification of levulinic acid with stoichiometric amounts of alcohols

  • Raimondo Maggi,
  • N. Raveendran Shiju,
  • Veronica Santacroce,
  • Giovanni Maestri,
  • Franca Bigi and
  • Gadi Rothenberg

Beilstein J. Org. Chem. 2016, 12, 2173–2180, doi:10.3762/bjoc.12.207

Graphical Abstract
  • toluene (120 mL) and the resulting supported propylmercaptane has been oxidized to propanesulfonic acid by treatment with 30% aq H2O2 (100 mL; 1 mol) for 24 h under stirring at rt, adding a few drops of concentrated sulfuric acid after 12 h. Acidity has been measured via the titration method [35] (0.51
  • . Acidity has been measured via the titration method [35] (0.65 mmol H+/g). SiO2-(CH2)3-O-C6H4-SO3H: A mixture of amorphous silica gel (2.0 g) and bromopropyltrimethoxysilane (0.76 mL, 4.0 mmol) was refluxed in toluene (80 mL) under stirring for 24 hours. The resulting silica supported 3-bromopropane was
  • ). Acidity has been measured via titration method [35] (0.73 mmol H+/g). Esterification reaction Levulinic acid, pentanol and the heterogeneous catalyst were stirred for 24 hours in a batch reactor under air. The acid/alcohol ratio, the reaction temperature and the amount of the catalyst were modified as
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Published 12 Oct 2016

Superelectrophilic activation of 5-hydroxymethylfurfural and 2,5-diformylfuran: organic synthesis based on biomass-derived products

  • Dmitry S. Ryabukhin,
  • Dmitry N. Zakusilo,
  • Mikhail O. Kompanets,
  • Anton A.Tarakanov,
  • Irina A. Boyarskaya,
  • Tatiana O. Artamonova,
  • Mikhail A. Khohodorkovskiy,
  • Iosyp O. Opeida and
  • Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2016, 12, 2125–2135, doi:10.3762/bjoc.12.202

Graphical Abstract
  • strong Lewis acids (AlX3, X = Cl, Br) by their coordination with basic centers of organic compounds, or with acidic zeolites, possessing both Brønsted and Lewis acidity [33]. The main goal of this work was a study of reactions of 5-HMF and 2,5-DFF with arenes under electrophilic activation with Brønsted
  • products. It is interesting to note that compounds 4 were not observed in reactions with zeolite (Table 4, entries 3, 10, 14 and 17), most likely, due to lower acidity of the zeolite compared to TfOH and spatial restrictions in zeolite cages, diminishing the contact between protonated aldehyde groups and
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Published 05 Oct 2016

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

  • Maurizio Selva,
  • Alvise Perosa,
  • Sandro Guidi and
  • Lisa Cattelan

Beilstein J. Org. Chem. 2016, 12, 1911–1924, doi:10.3762/bjoc.12.181

Graphical Abstract
  • be recovered and reused to allow quantitative conversions even after several recycles. Moreover, the study highlighted that the catalytic activity increased with increasing acidity of the ILs and particularly with cations bearing SO3H anions (Scheme 5: ILs I, II, III, and IV). The same imidazolium
  • transesterification reaction of dimethyl carbonate with phenol to methyl phenyl carbonate (MPC) and diphenyl carbonate (DPhC), Deshmukh et al. studied dibutyltin oxide as a catalyst in conjunction with Brønsted and Lewis acidic ionic liquids [70]. The authors investigated the relative Lewis and Brønsted acidity of
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Published 26 Aug 2016

Dinuclear thiazolylidene copper complex as highly active catalyst for azid–alkyne cycloadditions

  • Anne L. Schöffler,
  • Ata Makarem,
  • Frank Rominger and
  • Bernd F. Straub

Beilstein J. Org. Chem. 2016, 12, 1566–1572, doi:10.3762/bjoc.12.151

Graphical Abstract
  • copper(I) acetate and sodium acetate as additional base in order to deprotonate the thiazolium salt 1b and to form the bisthiazolylidene copper(I) complex 2. Due to the relatively high acidity of the thiazolium precursor (pKa ≈ 18 [44]), a weak base such as sodium acetate yields small equilibrium
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Published 21 Jul 2016

Conjugate addition–enantioselective protonation reactions

  • James P. Phelan and
  • Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

Graphical Abstract
  • developed organocatalytic conjugate addition–enantioselective protonations of α,β-unsaturated imides using thiols. Thiols are attractive nucleophiles due to their acidity, which facilitates deprotonation by amine bases and also reduces undesired competitive deprotonation and epimerization of the enolizable
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Published 15 Jun 2016
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