Narrow Results

The condensation of pyrrole and benzaldehyde has generally been carried out with trifluoroacetic acid (TFA)(20-50 mM), BF₃-etherate (1 mM), or more recently with BF₃-etherate in the presence of a salt. Differences in the reaction course with TFA or BF₃-etherate prompted studies of the combined use of BF₃-etherate and TFA. We found that the reaction of pyrrole + benzaldehyde (10 mM each) cocatalyzed by TFA (15 mM) and BF₃-etherate (0.3 mM) provided tetraphenylporphyrin (TPP) in yields of 50–55%, compared with 40% or 26%, respectively, from optimal catalysis by TFA (20 mM) or BF₃-etherate (1 mM) individually. Examination of the oligomer composition (LD-MS), yield of TPP (UV-vis), yield of N-confused TPP (HPLC), and level of unreacted aldehyde (TLC) in the cocatalytic reaction indicated a reaction course that contained features of those observed with each acid individually. Cocatalysis also was observed with methanol (50 mM) and BF₃-etherate (1.0 mM), which gave TPP in ~40% yield. The beneficial effect of an added salt in BF₃-etherate catalyzed reactions was reexamined by comparisons of reactions with NaCl/BF₃-etherate versus BF₃-etherate alone in terms of the oligomer composition, yield of TPP, yield of N-confused TPP, level of unreacted aldehyde, reversibility of the reaction, inactivation of the acid, and formation of TPP via intermediate oligomers. The studies strongly suggest that the presence of salt facilitates the addition of benzaldehyde to pyrrolic units (which is the limiting step with catalysis by BF₃-etherate alone), thereby affording better utilization of the aldehyde and a giving a commensurate increase in the yield of TPP.

Density functional theory has been used to study Rh(I)-catalyzed hydroacylation of ethene or ethyne. All the intermediates and the transition states were optimized completely at the B3LYP/6-311++G(d,p) level (LANL2DZ(d) for Rh, P). Calculation results confirm that Rh(I)-catalyzed hydroacylation of ethene is exothermic and the total released energy is -54 kJ/mol, and that Rh(I)-catalyzed hydroacylation of ethyne is also exothermic and the total released energy is -122 kJ/mol. In Rh(I)-catalyzed hydroacylation, ethene and ethyne have similar reactivity. Rh(I)-catalyzed oxidative addition of aldehyde is the rate-determinating step for the Rh(I)-catalyzed hydroacylation of ethene or ethyne. Hydrogen transfer reaction is prior to the C–C bond-forming reaction for Rh(I)-catalyzed hydroacylation of ethene. Thus hydrogen transfer reaction and the C–C bond-forming reaction may be co-existed for Rh(I)-catalyzed hydroacylation of ethyne. The effect of solvent in the hydroacylation of ethyne is greater than that in the hydroacylation of ethene.

A variety of aromatic and aliphatic aldehydes were oxidized to the corresponding carboxylic acids in the presence of platinum porphyrin, sunlight and air in acetonitrile solvent under mild conditions. Nitrobenzaldehydes were found to be very efficient ¹O₂ scavengers that quench the formation of acids from any aldehyde in the presence of free-base porphyrin sensitizers. However, nitrobenzaldehydes were converted to the corresponding acids in the presence of platinum porphyrins. The platinum porphyrins are very good and efficient catalysts for a wide range of applications in the aerobic conversion of aldehydes to acids.

Reactions of thiol with the C3-vinyl group of various chlorophyll (Chl) derivatives were examined. The reactions resemble thiol-olefin co-oxidation, except that the vinyl C=C double bond was cleaved to afford a formyl group without any transition metal catalyst, and that the simple anti-Markovnikov adduct of thiol to olefin was obtained as a minor product. Peripheral substituents of Chl derivatives little affected the reaction, while the central metal atom of the chlorin macrocycle influenced the composition of the products. Oxygen and acid dissolved in the reaction mixture can facilitate the oxidation. Sufficiently mild conditions in this regioselective oxidation at the C3¹-position are significant in bioorganic chemistry.

Today, fossil carbon provides us with fuels (energy), polymers (packaging, insulating and building materials, household utensils, glues, coatings, textiles, 3D-printing inks, furnitures, vehicle parts, toys, electronic and medical devices, etc.) and biologically active substances (drugs (Chapter 9), flavorings, fragrances, food additives, plant protection products, etc.). In this chapter we discover the modern materials of our civilization which are very often polymers derived from oil. They are referred to as “plastics” (annual world production: 380 × 10⁶ tons). Their production consumes 8% of the crude oil extracted (ca. 5 billion tons per year). An increasing part of the plastics originates from renewable resources (less than 10% today, see Section 11.10, bio-sourced plastics). Plastics make life easy for us, but at the underestimated cost of damage to our environment (Figure 8.1) and our health. They contaminate the hydrosphere and the agricultural soil. The atmosphere is also contaminated by microplastics…

The sun is the only source of renewable energy available to us, if geothermal energy is not taken into account. In the form of radiation (UV light, visible light, infrared light, Section 1.1) it sends us annually 178,000 terawatts (1 TW = 10¹² W; unit of power 1 W = 1 J s^–1 = 859.85 calories per hour), that is to say 15,000 times the energy consumed annually by humanity. Only 0.1% of the solar energy received by planet Earth is converted into plant biomass, i.e. 100 × 10⁹ tons per year which corresponds to ca. 180 × 10⁹ tons per year of CO₂ captured from the atmosphere. This CO₂ returns to the biosphere after the death of the plants. Consumption of fossil carbon emits ca. 35 × 10⁹ tons of CO₂ yearly. Biomass is the material produced by all living organisms (plants, animals, microorganisms, fungi)…

Syngas is a mixture of carbon monoxide (CO) and molecular hydrogen (H₂) that can be converted into a host of industrial feedstocks including fuels such as gasoline, fuel oil and kerosene. We examine what are the most abundant sources of these two gases and describe some important transformations that continue to fascinate scientists because, with a reactant as simple as CO, which contains only one carbon atom, catalysts allow to condense it with H₂ and to form C–C bonds even though all oligomers of the (CO)_n type (n = 2, 3, …) are kinetically and thermodynamically unstable. Let us recall here that thanks to photosynthesis, Nature builds C–C bonds (e.g. D-glucose) from CO₂ and H₂O and solar light! (Section 1.4.2, reaction (1.8), Figure 1.10)…

Knoevenagel condensation reaction is an important method for synthesis of carbon carbon double bond. It can directly synthesize a large number of useful compounds in industry, agriculture, pharmaceutical, biological sciences, Pharmaceuticals. The application of functional Ionic liquids provides a high efficient and environmental friendly approach for Knoevenagel condensation reaction. Ionic liquids as catalysts and solvents can promote reaction of a wide range of aldehydes and ketones with methylene compounds. In this paper. the progress in the use of functional ionic liquids for Knoevenagel reactions is reviewed.