Continuous-flow-enabled intensification in nitration processes: a review of technological developments and practical applications over the past decade

• Feng Zhou,
• Chuansong Duanmu,
• Yanxing Li,
• Jin Li,
• Haiqing Xu,
• Pan Wang and
• Kai Zhu

Beilstein J. Org. Chem. 2025, 21, 1678–1699, doi:10.3762/bjoc.21.132

• acid/mixed acid is presented in Scheme 1. It has been proven that a homogeneous nitration reaction is a second-order reaction. Table 3 establishes a fundamental kinetics framework for quantifying this reaction. The apparent kinetics model centers on the observed second-order rate constant kobs derived

• equals . Next, the observed rate constant based on SM and HNO3, kobs, can be calculated from the slope. Then, the apparent activation energy Ea for the nitration between HNO3 with SM molecules and the pre-exponential factor A can be obtained according to the Arrhenius equation. For example, Zhang et al

• achieve apparent reaction kinetic rate constant and intrinsic kinetic parameters [22][24][50][60][61]. Reaction kinetics in liquid–liquid biphasic systems: The kinetics analysis of nitration reactions in liquid–liquid biphasic systems presents unique challenges due to interfacial mass transfer limitations

pH-Controlled isomerization kinetics of ortho-disubstituted benzamidines: E/Z isomerism and axial chirality

• Ryota Kimura,
• Satoshi Ichikawa and
• Akira Katsuyama

Beilstein J. Org. Chem. 2025, 21, 1568–1576, doi:10.3762/bjoc.21.120

• the obtained data points yielded an apparent first-order rate constant (k) of 8.3 × 10−7·s−1 at pH 4.6, 4.8 × 10−6·s−1 at pH 5.5, and 6.0 × 10−5·s−1 at pH 6.5. These results indicate that isomerization was suppressed as pH decreased, as expected. Plotting log(k) versus pH showed a linear relationship

• property of each substituent, which is represented as the Hammett substituent constant [28], on the rate constant at different pH. Consistent with the results for amidine 2, amidines 3–7 showed smaller rate constants at more acidic pH, suggesting that isomerization of the molecular form species was also

• isomerization rate constant and pH. The result indicates that C–N rotation from the molecular form of amidine was dominant in the observed isomerization. a) Correlation between isomerization rate constant and electronic effects of the substituents. b) Possible protonated states of compound 7. Analysis of the

Enhancing chemical synthesis planning: automated quantum mechanics-based regioselectivity prediction for C–H activation with directing groups

• Julius Seumer,
• Nicolai Ree and
• Jan H. Jensen

Beilstein J. Org. Chem. 2025, 21, 1171–1182, doi:10.3762/bjoc.21.94

• rate constant of the reaction leading to the other regioisomer at the reaction temperature of 90 °C. Experimentally, it is observed that the regioselective C–H activation happens on the more electron-rich aromatic ring with the methoxy substituent as opposed to the one with the alkoxycarbonyl group

Computational design for enantioselective CO₂ capture: asymmetric frustrated Lewis pairs in epoxide transformations

• Maxime Ferrer,
• Iñigo Iribarren,
• Tim Renningholtz,
• Ibon Alkorta and
• Cristina Trujillo

Beilstein J. Org. Chem. 2024, 20, 2668–2681, doi:10.3762/bjoc.20.224

• free energy correction at double-zeta. The kinetics of some reactions were calculated, applying the transition state theory [40]. Within this theory, the rate constant of an elementary reaction with the free energy barrier ΔG‡ is given by Equation 1, where k is the rate constant in s−1, kB is the

• Boltzmann constant, T is the temperature in Kelvin, h is the Planck constant, and R is the gas constant. The enantiomeric excess (%ee) was calculated using Equation 2 [41]. kfav stands for the kinetic rate constant of the most favourable process, and kdefav stands for the rate constant of the less

• favourable process. During the study, it will be observed that several transition states (TSs) can lead to the same product. As there is no possible interconversion between the reactant states, the different reactions will be considered independent, and it will be necessary to use an effective rate constant

Homogeneous continuous flow nitration of O-methylisouronium sulfate and its optimization by kinetic modeling

• Jiapeng Guo,
• Weike Su and
• An Su

Beilstein J. Org. Chem. 2024, 20, 2408–2420, doi:10.3762/bjoc.20.205

• approach allowed for the assumption that the concentration of HNO3 remained constant throughout the reaction, enabling the conversion of the rate constant to Kβ (Equation 1). The relationship between reaction time and the conversion of IO was analyzed according to the first-order (Equation 2) and second

• concentrations. Determining the intrinsic reaction kinetics Given the strong correlation between the observed HNO3-based reaction rate constant and the H2SO4 mass fraction, intrinsic reaction constants independent of H2SO4 concentrations were determined to study the intrinsic kinetics of the reaction. Previous

• research has established that the relationship between the apparent and intrinsic kinetics of nitrification can be described by Equation 9 [17][19]. where k0 is the intrinsic rate constant only based on NO2+ and independent of sulfuric acid concentration [34], n is a thermodynamic parameter related to the

Metal-free double azide addition to strained alkynes of an octadehydrodibenzo[12]annulene derivative with electron-withdrawing substituents

• Naoki Takeda,
• Shuichi Akasaka,
• Susumu Kawauchi and
• Tsuyoshi Michinobu

Beilstein J. Org. Chem. 2024, 20, 2234–2241, doi:10.3762/bjoc.20.191

• indicates that the formed double azide adduct is 6a, which is consistent with our previous report [18]. The double azide addition was further investigated by changing the reaction temperature. The rate constant was determined by the temperature-dependent 1H NMR spectra in CDCl3. The reaction kinetics

A fiber-optic spectroscopic setup for isomerization quantum yield determination

• Anouk Volker,
• Jorn D. Steen and
• Stefano Crespi

Beilstein J. Org. Chem. 2024, 20, 1684–1692, doi:10.3762/bjoc.20.150

• photon flux was calculated from the weighted mean of the power measured; molar absorptivities, εA and εB, as well as the thermal rate constant, kB→A, were taken from the most recent study reporting these values [17]. The initial spectrum was confirmed to contain 100% trans-azobenzene by comparison with

• volume of the sample. When the cis-isomer absorbs at the same wavelength, the reverse reaction will happen photochemically as well, as described by the second term. The last term describes the thermal reaction converting cis-azobenzene into the stable trans-azobenzene. For the selected example, the rate

• constant for the thermal back isomerization is 7.2∙10−7 s−1 at 20 °C [24]. This value is generally disregarded for routine experiments where the isomerization happens in the minute timescale, however we explicitly included it in our quantum yield determination for better accuracy. Using the Beer–Lambert

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• -excited state lifetime), the quenching rate constant is roughly four orders of magnitude lower than singlet quenching (kq ≈ 105 M−1 s−1). This is in good agreement with the reported high triplet energy of 4CP [75] at 3.08 eV compared to 2.32 eV of 3Aza-H and the lower reduction potential provided by the

• faster and reaches the baseline after only 10 µs (Figure 3B). Kinetic measurements yielded a rate constant as high as ≈109 M−1 s−1 for the reaction between Aza-H•+ and TsNa (Figure 3B, inset), which implies that potential side reactions cannot compete. The TA spectra clearly reach baseline level after

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• reaction, the protonation of the alkene is the rate-determining step. This process can be viewed as the reaction between a nucleophile (alkene) and an electrophile (proton). According to the Mayr–Patz equation log(k) = s(N + E), the second order reaction rate constant k at 20 °C for a reaction is related

Regioselective quinazoline C2 modifications through the azide–tetrazole tautomeric equilibrium

• Dāgs Dāvis Līpiņš,
• Andris Jeminejs,
• Una Ušacka,
• Anatoly Mishnev,
• Māris Turks and
• Irina Novosjolova

Beilstein J. Org. Chem. 2024, 20, 675–683, doi:10.3762/bjoc.20.61

• reactivity in the SNAr reactions in comparison to polar solvents such as DMSO and DMF. This is explained by solvent hydrogen bond acidity and basicity descriptors α and β, for example, α(DMSO) = 0, β(DMSO) = 0.88, α(MeOH) = 0.43, β(MeOH) = 0.47. The rate constant of the SNAr process escalates with an

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

• Ruichen Lan,
• Brock Yager,
• Yoonsun Jee,
• Cynthia S. Day and
• Amanda C. Jones

Beilstein J. Org. Chem. 2024, 20, 479–496, doi:10.3762/bjoc.20.43

• , and benzamide 1c (Table 4). Under standard conditions (2.5 mol % [JPhosAu(NCCH3)]SbF6, 0.05 M alkene in DCM) benzamide and carbamate hydroamination were too slow to measure, so the reactions were done with 55 μL MeOH promoter but still only an estimated rate constant was obtained for 1c (14

Optimizing reaction conditions for the light-driven hydrogen evolution in a loop photoreactor

• Pengcheng Li,
• Daniel Kowalczyk,
• Johannes Liessem,
• Mohamed M. Elnagar,
• Dariusz Mitoraj,
• Radim Beranek and
• Dirk Ziegenbalg

Beilstein J. Org. Chem. 2024, 20, 74–91, doi:10.3762/bjoc.20.9

• and reaction rate [42], which was used in this work to fit the experiment results (see Equation 4). where is the average (observed) reaction rate, k* is the kinetic rate constant, θ is the surface coverage of the photocatalyst, α is the optical density, ϕ is the quantum yield, qp is the volumetric

Using the phospha-Michael reaction for making phosphonium phenolate zwitterions

• Matthias R. Steiner,
• Max Schmallegger,
• Larissa Donner,
• Johann A. Hlina,
• Christoph Marschner,
• Judith Baumgartner and
• Christian Slugovc

Beilstein J. Org. Chem. 2024, 20, 41–51, doi:10.3762/bjoc.20.6

• , methanol has a detrimental effect on the reaction velocity as the rate constant (kMeOH = 1.2 mM−1 s−1) is almost halved compared to chloroform. The strong Michael acceptor acrylonitrile reacts only very slowly in chloroform (kCHCl3 = 5.6 × 10−3 mM−1 s−1). In methanol, 2a is formed with a similar rate

• constant (kMeOH = 2.1 mM−1 s−1) as 2b, the product of the poor Michael acceptor acrylamide in CHCl3. The results show no correlation of the rate constant with the electrophilicity parameter of the Michael acceptors. The low rate constant for the acrylonitrile reaction in chloroform suggests that the

Beyond n-dopants for organic semiconductors: use of bibenzo[d]imidazoles in UV-promoted dehalogenation reactions of organic halides

• Kan Tang,
• Megan R. Brown,
• Chad Risko,
• Melissa K. Gish,
• Garry Rumbles,
• Phuc H. Pham,
• Oana R. Luca,
• Stephen Barlow and
• Seth R. Marder

Beilstein J. Org. Chem. 2023, 19, 1912–1922, doi:10.3762/bjoc.19.142

• competitive. In the case of (Cyc-DMBI)2, the second-order rate constant, kET, is estimated as 6.0 × 10−3 M−1 s−1, whereas for (N-DMBI)2, kcl = 4.7 × 10−5 s−1 and kET = 1.0 × 10−2 M−1s−1. The difference in kET values is qualitatively consistent with the peak oxidation potentials, Epa(D2•+/D2), of the two

• dimers; values of −0.06 and −0.13 V vs FeCp2+/0 are found for (Cyc-DMBI)2 and (N-DMBI)2, respectively [18][44], indicating that ET from the former to benzyl bromide is more endergonic than from the latter. The rate constant for (Cyc-DMBI)2-to-BnBr ET is also much smaller than that previously determined

A deep-red fluorophore based on naphthothiadiazole as emitter with hybridized local and charge transfer and ambipolar transporting properties for electroluminescent devices

• Suangsiri Arunlimsawat,
• Patteera Funchien,
• Pongsakorn Chasing,
• Atthapon Saenubol,
• Taweesak Sudyoadsuk and
• Vinich Promarak

Beilstein J. Org. Chem. 2023, 19, 1664–1676, doi:10.3762/bjoc.19.122

• simple mix-up of the two states [56]. Furthermore, to further understand the PLQY of the molecule in solution and thin film, the radiative rate constant (kr) and non-radiative rate constant (knr) were calculated from the PLQY values and PL lifetimes (τ) according to Equation 1 and Equation 2. As can be

Benzoimidazolium-derived dimeric and hydride n-dopants for organic electron-transport materials: impact of substitution on structures, electrochemistry, and reactivity

• Swagat K. Mohapatra,
• Khaled Al Kurdi,
• Samik Jhulki,
• Georgii Bogdanov,
• John Bacsa,
• Maxwell Conte,
• Tatiana V. Timofeeva,
• Seth R. Marder and
• Stephen Barlow

Beilstein J. Org. Chem. 2023, 19, 1651–1663, doi:10.3762/bjoc.19.121

• V) and VII•– to VII2– (−1.93 V); since the cleavage is rate determining, VII will be converted to VII•– and then, when excess dimer is used, to VII2– with a comparable rate constant. Indeed spectra obtained at long-reaction times (see Supporting Information File 1, Figure S7) are similar to those

Radical chemistry in polymer science: an overview and recent advances

• Zixiao Wang,
• Feichen Cui,
• Yang Sui and
• Jiajun Yan

Beilstein J. Org. Chem. 2023, 19, 1580–1603, doi:10.3762/bjoc.19.116

• can decompose to produce a stoichiometric pair of the primary initiating radical and a nitroxide radical, thus combining the roles of a conventional initiator and a control agent. The mechanism is shown in Scheme 4 [35]. Due to the steric effect of TEMPO, the dissociation rate constant, kd, of the

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• a two-photon process. DBU was found to quench the steady-state fluorescence of *PC1 with a quenching rate constant two orders of magnitude smaller than the diffusion rate constant in DMSO at 298 K and one order of magnitude greater under the borylation reaction conditions (i.e., 0.20 M DBU) than the

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• . The ultrafast pump-probe technique was used to determine the photoinduced charge separation in zinc porphyrin 96 and the rate constant was found on the order of 1010 s−1, clearly showing ultrafast electron-transfer between graphene and porphyrin units. Hence, these hybrids could be useful for light

Experimental and theoretical studies on the synthesis of 1,4,5-trisubstituted pyrrolidine-2,3-diones

• Nguyen Tran Nguyen,
• Vo Viet Dai,
• Nguyen Ngoc Tri,
• Luc Van Meervelt,
• Nguyen Tien Trung and
• Wim Dehaen

Beilstein J. Org. Chem. 2022, 18, 1140–1153, doi:10.3762/bjoc.18.118

• /bjoc.18.118 Abstract Substituted 4-acetyl-3-hydroxy-3-pyrroline-2-ones have been prepared via three-component reactions and the tautomerism of these 3-pyrroline-2-ones is due to the slight difference of energy, and the significantly large rate constant of transformation between two tautomers. 1,4,5

• ···O intramolecular hydrogen bond (distance ca. 1.7–1.8 Å) (cf. Figures 4–6). The isomerization of 4a/4a’ is extremely fast due to the high rate constant of about 1012 s−1 at 298 K, calculated by the transitional state theory method and quantum tunneling effect [47]. It is thus impossible to

• IS8 can be omitted because it is so fast with a small activation energy of 2.1 kcal·mol−1), the formation of product 10ab is superior as compared to its isomer. In terms of the value of the rate constant k, the direction of 10ab formation is in the range of 103–106 times faster than 10ab-v2. The

Synthesis, optical and electrochemical properties of (D–π)₂-type and (D–π)₂Ph-type fluorescent dyes

• Kosuke Takemura,
• Kazuki Ohira,
• Taiki Higashino,
• Keiichi Imato and
• Yousuke Ooyama

Beilstein J. Org. Chem. 2022, 18, 1047–1054, doi:10.3762/bjoc.18.106

• -resolved fluorescence spectroscopy of the two dyes revealed that the fluorescence lifetimes (τfl) are 0.62 ns for OTK-2 and 0.66 ns for OTT-2, indicating that there is a little difference in the τfl values of the two dyes. The radiative rate constant (kr = 6.2 × 108 s−1) for OTT-2 is slightly larger than

• that (5.8 × 108 s−1) for OTK-2. However, the nonradiative rate constant (knr = 8.9 × 108 s−1) of OTT-2 is smaller than that (1.0 × 109 s−1) for OTK-2. As the result, the ratio of nonradiative constant to radiative constant (knr/kr = 1.4) for OTT-2 is smaller than that (1.7) for OTK-2, suggesting that

Site-selective reactions mediated by molecular containers

• Rui Wang and
• Yang Yu

Beilstein J. Org. Chem. 2022, 18, 309–324, doi:10.3762/bjoc.18.35

• ester group in turn to the aqueous solution. Addition of base would result in the hydrolysis of one ester group to the corresponding carboxylic acid. Product distributions indicated a two- to four-fold relative decrease in the hydrolysis rate constant of the second ester caused by the confined space in

A photochemical C=C cleavage process: toward access to backbone N-formyl peptides

• Haopei Wang and
• Zachary T. Ball

Beilstein J. Org. Chem. 2021, 17, 2932–2938, doi:10.3762/bjoc.17.202

• 1 in acetone. Preparation and hydrolysis kinetics (inset) of N-formyl product 11. Dashed line: first-order decay fit used in calculating the rate constant. Proposed mechanism for the formation of aldehyde 3 and N-formyl product 8. Supporting Information Supporting Information File 280: Experimental

Kinetics of enzyme-catalysed desymmetrisation of prochiral substrates: product enantiomeric excess is not always constant

• Peter J. Halling

Beilstein J. Org. Chem. 2021, 17, 873–884, doi:10.3762/bjoc.17.73

• elementary rate constants by the same factor will not change the shape of the progress of product formation and enantiomeric excess, just the timescale over which this occurs. Hence one elementary rate constant may be set to an arbitrary value, with others effectively expressed as a multiplier times this

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• due to the reduced electrostatic repulsion between the carboxylate groups of AC and the cationic ammonium groups of WP6. Although the selectivity is enhanced, the reaction rate constant of AC with WP6 is 4 times slower compared to that without any host molecule, which may be due to the mismatching