Amines chemical elucidation

Another alkaloid with the oxazolidine system is samandaridine (XVII), C21H31NO3, also a secondary amine. Chemical reactions (9) and IR-spectra indicate that it possesses a five-membered lactone ring. Its structure was also elucidated by X-ray analysis. Samandaridine hydrobromide crystallizes from methanol in monoclinic prisms its space group is C2 with four molecules in the unit cell. The cell constants are a = 14.50 A, b = 6.15 A, c = 22.52 A, = 94° (10). 

Both CIDNP and ESR techniques were used to study the mechanism for the photoreduction of 4-cyano-l-nitrobenzene in 2-propanol5. Evidence was obtained for hydrogen abstractions by triplet excited nitrobenzene moieties and for the existence of ArNHO, Ai N( )211 and hydroxyl amines. Time-resolved ESR experiments have also been carried out to elucidate the initial process in the photochemical reduction of aromatic nitro compounds6. CIDEP (chemically induced dynamic electron polarization) effects were observed for nitrobenzene anion radicals in the presence of triethylamine and the triplet mechanism was confirmed. 

Microwave-assisted synthesis is attractive to researchers for many reasons, including speed, yields, and the potential for reduced solvent use. Raman monitoring offers a convenient way to elucidate the chemical mechanism while instantly, continuously monitoring reaction kinetics. This enables rapid, data-driven process optimizations without concerns about safely and accurately sampling out of a microwave vessel stopped mid-reaction. Pivonka and Empheld of AstraZeneca Pharmaceuticals describe the continuous acquisition of Raman spectra of an amine or Knoevenagel coupling reaction in a sealed microwave reaction vessel at elevated temperatures and pressures [134]. 

Since the late 1950s PMR spectroscopy has contributed immensely to many areas of the chemistry of alkaloids (7). With the advent of Fourier transform spectrometers CMR has rapidly approached the level of PMR in its application to problems of structural elucidation and stereochemistry. In the case of the alkaloids many classes of the isoquinoline family have been studied. These alkaloids are of particular interest not only because of their widespread occurrence in nature but also because of their pharmacological activity (2-5). Wenkert et al. (6) were the first to review progress in this area. More recently, Shamma and Hindenlang (7) have made an extensive compilation of chemical shift data on amines and alkaloids that includes many... 

Microderivatization or chemical modification of analytical samples can be useful in enhancing the ion response, and hence the LC-MS sensitivity, for any particular analyte. In the case of alkaloids, which are already capable of ready ionization, chemical modification can be more valuable in elucidating structures by providing tandem MS evidence for positions of substitution in the parent molecule. Such derivatization or chemical modification for HPLC-MS can include H/D exchange by using deuterated mobile phases, Jones oxidation of aliphatic hydroxyls, selective acetylation of hydroxyl and amine groups, and N-oxide reduction [19,20]. 

Optical detection of intermediates produced in the reactions of triplet carbonyl compounds with electron donors has some obvious limitations. However, the technique of CIDNP is proving particularly effective at elucidating the reaction pathways in these systems. The outstanding work of Hendriks et al. (1979) illustrates the power of the technique. Not only was the role of radical ions in the reactions of alkyl aryl ketones with aromatic amines defined but the rate constants for many of the processes determined. The technique has been used to show that trifluoracetyl benzene reacts with electron donors such as 1,4-diazabicyclo[2.2.2]octane and 1,4-dimethoxy-benzene by an electron-transfer process (Thomas et al., 1977 Schilling et al., 1977). Chemically induced dynamic electron polarisation (CIDEP) has been... 

The sensitivity of Si chemical shifts to structural changes and the technique of silylating compounds for more favourable analysis or synthesis have been combined by several researchers to produce a powerful structure elucidation technique for monofunctional or polyfunctional compounds. (135-141) Specifically, the trimethylsilyl derivatives of imidophosphoryl compounds, (141) sugars, (138-140) steroids, (140) amines, amides, and urethanes, (135,136) and amino-, hydroxy-, and mercaptocarboxylic acids (137) have all been studied within the past three years. 

In general, the mechanisms which have been discussed form the basis of most polymerizations of NCAs. Clearly, they often may lead to very complex kinetic behaviour, particularly since primary and secondary amines can initiate either by direct nucleophilic attack or by proton abstraction. The elucidation of the various chemical steps, their consequences and their relative importance in specific instances have been based on extensive chemical and kinetic data which we present below. Alternative mechanisms for the polymerization of NCAs have been proposed, but have in the main been rejected because they are not consistent with some of the experimental observations. The reader is referred to the extensive... 

SERS has also been shown to be a useful analytical tool in the elucidation of reaction mechanisms in heterogeneous catalysis (e.g., dehydroamination reactions on copper surfaces). The adsorption and desorption of amines were investigated on copper foils which were roughened by chemical etching and exhibited strong surface enhancement. Enhanced Raman spectra were obtained for adsorbed m-toluidine on copper with submonolayer sensitivity. The mechanism of adsorption is thought to be via the nitrogen lone pair without N-H bond dissociation. 

To date, four main types of catalytic activity have been reported in detail for thermal polyamino acids. These are (with the most studied substrates in parentheses) hydrolyses (p-nitrophenyl acetate, p-nitro-phenyl phosphate, ATP), decarboxylations (OAA, glucuronic acid, pyruvic acid), and aminations (a-ketoglutaric acid, OAA, pyruvic acid, phenylpyruvic acid). The fourth type is a deamination reaction yielding a-ketoglutaric acid (51). For some of the actions of the thermal polymers the products are identified quantitatively, and the kinds of amino acid side chain necessary for activity in the polymer elucidated. In others, products have yet to be fully identified. The activities of thermal polyamino acids are manifest on substrates which range from chemically labile to relatively stable. 

Carbothialdine" i.e. 4,6-dimethylperhydro-l,3,5-thiadiazine-2-thione, the reaction product of acetaldehyde with ammonia and carbon disulfide, has been known a long time (260, 288). Various structures have been proposed for it (83, 143, 164, 234). It was also known that this product may be obtained from acetaldehyde and ammonium dithiocarbamate and that two moles of aldehyde are necessary for the reaction. The reaction products of other aldehydes and amines had also been investigated with a view to elucidating their structure (31, 108). However, Ainley and co-workers (1) in 1944 were the first to determine the structure with certainty. The instability of "carbothialdines made it difficult to determine their structure by chemical means. It was by comparison of its U.V. spectrum with that of similar compounds such as (CCII) that the formula of perhydro-l,3,5-thiadiazine-2-thione (CCIV) was established, which accounts quite well for its properties. It is accepted... 

Figure 10.1 Chemical structures of dC-modified aromatic amine and B[o]P adducts whose solution DNA structures have been elucidated, (a) AF, 2-aminofluorene FAF, 7-fluoro-2-aminofluorene AAF, 2-acetylaminofluorene FAAF, 7-fluoro-2-acetylaminofluorene. (b) IQ, 2-amino-3-methylimidazo[4,5-/ quinoline PhIP,...

Toxic and physiological impacts of polymer stabilizers have been carefully elucidated. Pharmaco-kinetic models for determining the chemical dose delivery to die target tissue were examined and doses responsible for allergies, acute and chronic toxicities were defined [306], Information on potential irritant effects, dermatitis, mutagenicity or carcinogenicity due to amines is of prime importance. It has been estimated that about 75-80% of all human cancers are environmentally induced (30-40% of them by contaminated diet [308]). 

In most equilibrium-based analytical methods, the success or failure of a determination is not affected by the reaction mechanism, provided that the reaction is either quantitative or the measured parameter at equilibrium is linearly proportional to the initial concentration of the species of interest. This is not the case in reaction-rate methods. Any development of a kinetic method should include, if possible, a complete study of the reaction mechanisms involved in the procedure. (Unfortunately, some reactions, such as catalytic reactions, are so complicated that complete elucidation of the mechanism is impossible.) It should also include a detailed study of the effects of typical sample-matrix components, which can act as catalysts, induce side-reactions, alter the activity of the reactants, and so on. The rates and rate constants for chemical reactions are very sensitive to low concentrations of such spectator species hence, samples containing the same true initial composition of the species of interest but coming from different sources can very often give quite different apparent concentrations. Unless the experimenter is aware of the total reaction mechanism and of all possible factors that can affect either the activation energy or the reaction path, erroneous analytical results can be obtained. A detailed investigation of the simultaneous, in situ, analysis of binary amine mixtures illustrates this point. (Most systems, by the way, are less error-prone than this one.) The rate constants for the reaction of many individual organic amines with methyl iodide in acetone solvent... 

The metabolism of MBOCA was also investigated in vitro by incubating human and rat liver microsomes with C-MBOCA. The formation of metabolites was quantified using appropriate chemically synthesized standards (Morton et al. 1988). The rate of N-hydroxylation of MBOCA, an obligatory step in metabolic activation of aromatic amines, was higher in rat than in human microsomes (Morton et al. 1988). Rat liver microsomes were also found to be more efficient in o-hydroxy-MBOCA formation when compared with human microsomes (see Figure 2-2). The same in vitro microsomal system was used to elucidate the role of hepatic cytochrome P-450 monooxygenases in metabolic oxidation and detoxification of MBOCA (Butler et al. 1989). The... 

To decipher this complexity, electrochemistry at the polarized liquid-liquid interface developed over the past two decades has been proven to be a powerful tool, as shown in elucidation of the mechanism of ion-pair extraction [1 ] and the response of ion-selective electrodes of liquid-membrane type to different types of ions [5 7]. Along this line, several attempts have been made to use polarized liquid liquid interfaces for studying two-phase Sn2 reactions [8-10], two-phase azo-coupling [11], and interfacial polymerizations [12]. Recently, kinetic aspects of complexation reactions in facilitated ion transfer with iono-phores and the rate of protonation of amines have been treated quantitatively [13-16]. Their theoretical framework, which was adapted from the theories of kinetic currents in polaro-graphy, can be directly applicable to analyze quantitatively the chemical reactions in the two-phase systems. In what follows is the introduction to recent advances in electrochemical studies of the chemical reactions at polarized liquid liquid interfaces, mainly focusing on... 

An alternate chemical mechanism for the HjS transport data Is that the HS species Is the complex. Formed by reaction with the amine, HS could diffuse to the sweep side of the membrane where reaction with the EDA species could produce HaS and EDA. However, this explanation appears to be Inconsistent with results using TMEDA as a carrier. If HS Is the carrier species, then similar results might be expected for membranes Incorporating either EDA and TMEDA carriers. However, the HaS facilitation factor for the EDA lEM Is 8.2 times larger than F for the TMEDA lEM. More research would help elucidate the chemical mechanism of HjS facilitated transport In lonomers. 

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