1,721,034 research outputs found
Electrochemical Methodologies for the Carboxylation Reactions in Organic Synthesis. An Alternative Re-use of Carbon Dioxide
No full textToday, the need to control carbon dioxide production and emission has become an important target
for both scientific and industrial world. To this purpose, the use of carbon dioxide as raw material and build-
ing block for the synthesis of complex molecules represents an efficient tool to its recycle and re-use. A great
effort has been made in order to reconvert carbon dioxide to valuable organic compounds and utilize it as a
source of carbon in organic synthesis. However, carbon dioxide is considered as an inert molecule and the electrochemical methodologies represent a valuable tool for its "activation" either in a direct or indirect way. In this re- view, the main electrochemical methodologies using carbon dioxide for the carboxylation of a large number of organic compounds appeared in the literature in the last decade, will be reported. In particular, the incorporation reaction of car- bon dioxide molecule in alkenes, carbonyl compounds, alcohols, epoxides, amines and halides yielding carboxylic acids, linear and cyclic carbamates and carbonates will be discussed. The electrochemical methods that utilize CO2 in carboxyla- tion reactions will be considered in detail, to provide a detailed picture of the state of the art
Electrochemical carboxylation of alcohols. Synthesis of organic carbonates
No full textSeveral methods for the synthesis of organic carbonates using electrochemical syntheses will be discussed. These methodologies avoid the use of toxic and harmful reagents such as phosgene, carbon monoxide and isocyanates. Carbon dioxide, a cheap, safe and abundant reagent is used as starting material. High to excellent yields of cyclic carbonates are obtained by reaction of alcohols bearing a leaving group in a or in13 position with tetraethylammonium carbonate (TEAC) or tetraethylammonium peroxocarbonate (TEAPC) respectively obtained by direct or indirect electrochemical reduction of carbon dioxide. Only moderate yields of linear carbonates are obtained from primary or secondary alcohols after addition of a suitable alkylating reagent. Alternatively, the use of electrogenerated base associated with carbon dioxide allows the conversion of primary alcohols in excellent yields and of secondary alcohols in moderate yields. In addition, the application o f the above reported methodologies allows the conversion of 1,2-diols into cyclic carbonates in moderate to good yields
Teytalkyl ammonium carbonates in organic synthesis
No full textTetraalkylammonium carbonates such as
tetraethylammonium carbonate (TEAC),
tetraethylammonium hydrogen carbonate (TEAHC),
tetrabutylammonium methyl and ethyl carbonate (TBAMC and TBAEC) are useful reagents in a wide number of organic reactions. They shown a double
reactivity and can be employed as well as carboxylating reagents or bases. According to these features tetraalkylammonium carbonates easily
perform conversion of alcohols and/or alkyl halides into carbonates, the conversion of amines into carbamates, the alkylation reaction of classes of compounds such as pyrroles and thiols and the synthesis of 2,4-oxazolidindiones starting from a- haloamides. These new methodologies offers safe and mild alternatives to the classical methods reported in literature, avoiding the use o f toxic and harmful reagents and/or harsh reaction conditions. All carbonates are, in fact, obtained starting from carbon dioxide through chemical or electrochemical methodologies
Mild Regioselective Catalytic Hydrogenation of α,β-Unsaturated Carbonyl Compounds with Lindlar Catalyst
No full textThe hydrogen-Lindlar catalyst system is effective for the highly regioselective reduction of alfa,beta-unsaturated carbonyl compounds to the corresponding alfa,beta-saturated compounds
A convenient method for the synthesis of carbamate esters from amines and tetraethylammonium hydrogen carbonate
No full textChiral Sulfoxides in Asymmetric Synthesis: Enantioselective Synthesis of the Lactonic Moiety of (+)-Compactin and (+)-Mevinolin. Application to a Compactin Analogue
No full textThe lactonic part of (+)-compactin and (+)-mevinolin as well as a compactin analogue were synthesized in an enantioselective way from a beta,delta-diketo sulfoxide easily obtained by the reaction of the trianion of methyl 3,5-dioxohexanoate with (-)-menthyl (S)-p-toluenesulfinate. The main reaction was the two-step stereoselective reduction of beta,delta-diketosulfoxide without any protective group
BMIm HCO3: an ionic liquid with carboxylating properties. Synthesis of carbamate esters from amines
No full text1-Butyl-3-methylimidazolium hydrogen carbonate (BMIm HCO3) was used as an ionic liquid with carboxylating properties able to convert, in the presence of an alkyl halide, amines into the corresponding carbamate esters. Moderate to good yields of carbamates were obtained according to the nature of the amine and the alkylating agent
Geographical discrimination and authentication of lentils (Lens culinaris Medik.) by ICP-OES elemental analysis and chemometrics
No full textGeographical classification and authentication of lentils (Lens culinaris Medik.) was attempted by discriminant
and modelling pattern-recognition methods applied to multi-elemental composition determined by means of
inductively coupled plasma optical emission spectrometry (ICP-OES). After microwave-assisted digestion, the
content of 15 elements was determined in 89 Italian lentil samples produced in three relatively close areas of the
Central Apennines (Castelluccio di Norcia, Colfiorito and Santo Stefano di Sessanio) and 20 samples imported
from Canada. Preliminary exploration of the ICP-OES data revealed a visible effect of the production year on the
mineral composition. A good geographical classification of the lentil samples was obtained by discriminant
approaches. Class models generated by Soft Independent Model Class Analogy presented high sensitivity (all the
calibration and external samples were correctly accepted by the target classes) and good specificity since most of
non-compliant samples were refused by each of the four modelled classes
Electrogenerated base-promoted synthesis of organic carbonates from alcohols and carbon dioxide
No full textElectrogenerated bases promote the reaction between primary alcohols and carbon dioxide to give organic carbonates in excellent yields. Secondary alcohols are converted in moderate yields, whereas tertiary alcohols and phenols are unreactive. 1,2-Diols give a mixture of both cyclic and linear di- and monocarbonates. These latter are intermediates in the reaction pathway leading to the cyclic derivatives
Electrogenerated cyanomethyl anion in organic synthesis
No full textSuitable electrochemical methodologies for the generation of cyanomethyl anion and some electrochemically induced cyanomethylation reactions of electrophilic substrates are described and discussed. In addition, the electrochemical syntheses of carbamates and chiral oxazolidin-2-ones (under mild conditions and avoiding the use of hazardous chemicals), via a new carboxylating reagent (CH2CN-/CO2), are reported in this article
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