684-93-5Relevant articles and documents
The nitrosation of N-alkylureas: Evidence for a proton transfer mechanism
Casado, Iulio,Gonzalez-Alatorre, Guillermo,Izquierdo, Carmen,Brunner, Christian
, p. 307 - 313 (1996)
The kinetics of the nitrosation of methyl, ethyl, propyl, butyl, and allyl urea were studied by conventional and stopped-flow spectrophotometry in the presence or absence of acetate or mono-, di-, or trichloroacetate anions In the presence of a large excess of urea, the observed rate equation was chemical equations presented where Ka is the acidity constant of nitrous acid and KR that of the carboxylic acid The ureas exhibited the reactivity order methylurea ? (ethylurea ≈ propylurea ≈ butylureal ? allylurea. Experiments in D2O afforded values of kH2O/kD2O in general agreement with the values 4.1-5 5 predicted by a semiclassical transition state theory of kinetic isotope effects [i.e., kH2O/kD2O = exp(0.130hv/kT)]where v is the frequency of R3N - H stretching (2700-2250 cm-1) in the protonated urea. This result, the observed catalysis by carboxylate ions and the value of the Bronsted parameter β(0.45) show the rate-controlling step of these reactions to be the transfer of a proton from the protonated N-alkyl-N-nitrosourea to the solvent or to the organic anion. if present. The observed order of substrate reactivities is explicable in terms of the capacity of the protonated N-alkyl-N-nitrosourea for forming a hydrogen bond with the water molecule to which the proton will be transferred, and the degree to which the formation of such bonds is hindered by the hydrophobic alkyl chain of the nitrosourea.
REACTION MECHANISM OF THE NISTOSATION OF UREAS.
Casado,Castro,Mosquera,Rodriguez Preito,Vazquez Tato
, p. 1211 - 1216 (1983)
The nitrosation of methylurea has been studied under catalysis by acetate and mono-, di- and trichloroacetate buffers. The catalysis observed has been found to be due to the organic anions, and Bronsted relation is obeyed with beta equals 0. 24. The experimental results have been interpreted in terms of a reaction mechanism which features the rapid formation of an intermediate, MeNH(NO)CONH//2, when the methylurea is nitrosated. The rate controlling step is the transfer of a proton from this intermediate to the solvent or to a basic catalyst (the nitrite ion or the organic anion). That it is this step that controls the overall rate of reaction is supported by the isotopic effect (k//H/k//D equals 3. 5) observed on carrying out kinetic measurements in D//2O.
Heard et al.
, p. 4985 (1951)
Kinetic study of the nitrosation of N-alkylureas in dioxane-acetic acid mixtures
Alatorre,Zapiain,Quintana,Martinez
, p. 145 - 150 (1998)
The rate constants were determined for the nitrosation reactions of the following substrates: Methyl (MU), Ethyl (EU), Propyl (PU)Butyl (BU), and Allylurea (AU). The rate equation found at a constant pH was: v = k[HNO2] [Urea]. The reactions were carried out in predominantly organic media(dioxane-acetic acid-water) with differing polarities. The proposed reaction mechanism involves the proton transfer from the protonated N-alkyl-N-nitrosourea to the acetate anion. As the polarity of the medium decreased, an approximation of the rate constants of the nitrosation of the different substrates was observed. This approximation can be interpreted as a function of the impediment generated by the R alkyl radical in the rate controlling step. Accordingly, the substrate reactivity will be associated with the ease in which the protonated N-alkyl-N nitrosurea can transfer the proton to the acetate anion. The results achieved in this study are in accordance with there activities observed in the nitrosation of these substrates in aqueous media MU ? (EU ≈ PU ≈ BU) > AU.
Regioselective Synthesis of [6,6]-Open and [5,6]-Closed C70(CF3)8[CH2] Methanofullerenes with Rapid [6,6]-to-[5,6] Phototransformation
Semivrazhskaya, Olesya O.,Belov, Nikita M.,Rybalchenko, Alexey V.,Markov, Vitaliy Yu.,Ioffe, Ilya N.,Lukonina, Natalia S.,Troyanov, Sergey I.,Kemnitz, Erhard,Goryunkov, Alexey A.
, p. 750 - 758 (2018)
Fullerene derivatives with >CH2 addends in [6,6]-open or [5,6]-closed configuration are uncommon of fullerene derivatives, but they are readily accessible via treatment of Cs-C70(CF3)8 with diazomethane followed by thermolysis or photolysis. Both thermodynamic and kinetic factors favor regioselective addition of diazomethane at the near-equatorial [5,6]-double bond of Cs-C70(CF3)8 to give a thermally labile pyrazoline intermediate. Thermal extrusion of N2 from the latter is a kinetically controlled process with orbital symmetry controlled Woodward–Hoffmann-allowed mechanism. It quantitatively yields the less thermodynamically favorable [6,6]-open isomer of C70(CF3)8[CH2] homofullerene, but the latter turns out to be capable of unexpectedly rapid quantitative phototransformation into the thermodynamically preferable [5,6]-closed methanofullerene isomer. The transformation involves the manifold of the triplet states that facilitate the required cleavage of the Ccage–CH2 bonds.
Noncanonical RNA Nucleosides as Molecular Fossils of an Early Earth—Generation by Prebiotic Methylations and Carbamoylations
Schneider, Christina,Becker, Sidney,Okamura, Hidenori,Crisp, Antony,Amatov, Tynchtyk,Stadlmeier, Michael,Carell, Thomas
supporting information, p. 5943 - 5946 (2018/04/30)
The RNA-world hypothesis assumes that life on Earth started with small RNA molecules that catalyzed their own formation. Vital to this hypothesis is the need for prebiotic routes towards RNA. Contemporary RNA, however, is not only constructed from the four canonical nucleobases (A, C, G, and U), it also contains many chemically modified (noncanonical) bases. A still open question is whether these noncanonical bases were formed in parallel to the canonical bases (chemical origin) or later, when life demanded higher functional diversity (biological origin). Here we show that isocyanates in combination with sodium nitrite establish methylating and carbamoylating reactivity compatible with early Earth conditions. These reactions lead to the formation of methylated and amino acid modified nucleosides that are still extant. Our data provide a plausible scenario for the chemical origin of certain noncanonical bases, which suggests that they are fossils of an early Earth.
