Jonathan Alan Medlock

One Hundred Years of Vitamins—A Success Story of the Natural Sciences

The discovery of vitamins as essential factors in the diet was a scientific breakthrough that changed the world. Diseases such as scurvy, rickets, beriberi, and pellagra were recognized to be curable with an adequate diet. These diseases had been prevalent for thousands of years and had a dramatic impact on societies as well as on economic development. This Review highlights the key achievements in the development of industrial processes for the manufacture of eight of the 13 vitamins.

Effects of Ultrasound and Microwaves on Selective Reduction: Catalyst Preparation and Reactions

The reduction of organic compounds through catalytic hydrogenation is an important transformation in organic chemistry, especially in the synthesis of fine chemicals, natural products, and pharmaceuticals. This review mainly focuses on the selective reduction of substrates with multiple functional groups. Literature from the last two decades has proved the pivotal role that ultrasound and microwaves can play not only in the preparation of environmentally friendly, efficient catalysts but also in their use in catalytic reactions. Owing to the specific selective activation of the solid catalyst surface, dielectric heating and acoustic cavitation may dramatically enhance the reaction rate and selectivity. A thorough literature survey was the first step in the MAPSYN project (EU 7th Framework Program) and has the goal of the industrial demonstration of selective hydrogenations intensified by microwaves and ultrasound. Both techniques are irreplaceable tools in heterogeneous catalysis and can be expected to bring even greater success in the near future as processes are scaled up with suitable flow reactors equipped with on‐line analytical monitoring.

Ultrasound‐ and Microwave‐Assisted Preparation of Lead‐Free Palladium Catalysts: Effects on the Kinetics of Diphenylacetylene Semi‐Hydrogenation

The effect of environmentally benign enabling technologies such as ultrasound and microwaves on the preparation of the lead‐free Pd catalyst has been studied. A one‐pot method of the catalyst preparation using ultrasound‐assisted dispersion of palladium acetate in the presence of the surfactant/capping agent and boehmite support produced the catalyst containing Pd nanoparticles and reduced the number of pores larger than 4 nm in the boehmite support. This catalyst demonstrated higher activity and selectivity. The comparison of kinetic parameters for diphenylacetylene hydrogenation showed that the catalyst obtained by using the one‐pot method was seven times as active as a commercial Lindlar catalyst and selectivity towards Z‐stilbene was high. Our work also illustrated that highly selective Pd/boehmite catalysts can be prepared through ultrasound‐assisted dispersion and microwave‐assisted reduction in water under hydrogen pressure without any surfactant.

Hydrogenation in the Vitamins and Fine Chemicals Industry – An Overview

In the pharmaceutical and partly also in the fine chemicals industry many chemical conversions require stoichiometric amounts of reagents, and thus generate large amounts of waste [1, 2]. This is in contrast to the production of bulk chemicals which mostly relies on catalysis. This difference can be explained by the higher complexity of pharmaceuticals and fine chemicals which makes catalysis more demanding and process development more expensive.

Selective Hydrogenation of α,β-Unsaturated Aldehydes and Ketones by Air-Stable Ruthenium NNS Complexes

The selective hydrogenation of the carbonyl functionality of α,β-unsaturated aldehydes and ketones is catalysed by ruthenium dichloride complexes bearing a tridentate NNS ligand as well as triphenylphosphine. The tridentate ligand backbone is flexible, as evidenced by the equilibrium observed in solution between the cis- and trans-isomers of the dichloride precatalysts, as well as crystal structures of several of these complexes. The complexes are activated by base in the presence of hydrogen and readily hydrogenate carbonyl functionalities under mild conditions. Despite the activation by base, side reactions are negligible, even for aldehyde substrates, because of the low amount of base. Thus, the corresponding allylic alcohols can be isolated in very good yields on a 10-25 mmol scale. Turnover numbers up to 200 000 were achieved.

Hydrogenation of 2-methyl-3-butyn-2-ol over a Pd/ZnO catalyst: kinetic model and selectivity study

The three-phase hydrogenation of 2-methyl-3-butyn-2-ol has been studied over a Pd/ZnO catalyst. A Langmuir–Hinshelwood mechanism was applied assuming noncompetitive adsorption between hydrogen and organic molecules on the catalyst active sites. All experimental runs used for the modeling have been obtained in the intrinsic kinetic regime in order to exclude any mass transfer limitation. An optimization procedure allowed the estimation of the kinetic and adsorption parameters governing the process. The results revealed that the proposed model accurately describes the behavior of the system in the typical operating ranges of industrial reactors. The performance of the catalyst in terms of selectivity to 2-methyl-3-buten-2-ol and initial activity is found to be higher compared with that of a commercial Lindlar catalyst under the same operating conditions. The mathematical model, successfully validated, is able to accurately predict the selectivity of the process.

Ultrasonically improved semi-hydrogenation of alkynes to (Z-)alkenes over novel lead-free Pd/Boehmite catalysts.

This paper reports the application of ultrasound in the semi-hydrogenation of alkynes over two novel Pd/Boehmite catalysts. The semi-hydrogenations of phenylacetylene, diphenylacetylene and 2-butyne-1,4-diol have either been investigated in an ultrasonic bath under atmospheric hydrogen pressure, or in an ultrasonic horn reactor under 0.1-0.5MPa hydrogen pressure. Alkyne hydrogenation was suppressed by sonication under atmospheric hydrogen pressure, but promoted by sonication under 0.1MPa of hydrogen pressure. Sonication increased selectivity towards the semi-hydrogenated products in both cases. Catalyst loading, hydrogen pressure, temperature and the presence of quinoline, all impacted on hydrogenation rate, activity and selectivity to semi-hydrogenated products. Palladium leaching from the catalyst was evaluated in ethanol and hexane both under plain stirring and sonication.

Sonochemical preparation of alumina-spheres loaded with Pd nanoparticles for 2-butyne-1,4-diol semi-hydrogenation in a continuous flow microwave reactor

A novel protocol for microwave-assisted alkyne semi-hydrogenation under heterogeneous catalysis in a continuous flow reactor is reported herein. This challenging task has been accomplished using a multifaceted strategy which includes the ultrasound-assisted preparation of Pd nanoparticles (average O 3.0 ± 0.5 nm) that were synthesized on the μ-metric pores of sintered alumina spheres (O 0.8 mm) and a continuous flow reaction under H2 (flow rate 7.5 mL min−1) in a microwave reactor (counter-pressure 4.5 bar). The semi-hydrogenation of 2-butyne-1,4-diol in ethanol was chosen as a model reaction for the purposes of optimization. The high catalyst efficiency of the process, in spite of the low Pd loading (Pd content 111.15 mg kg−1 from ICP-MS), is due to the pivotal role of ultrasound in generating a regular distribution of Pd nanoparticles across the entire support surface. Ultrasound promotes the nucleation, rather than the growth, of crystalline Pd nanoparticles and does so within a particularly narrow Gaussian size distribution. High conversion (>90.5%) and selectivity to (Z)-2-butene-1,4-diol (95.20%) have been achieved at an alkyne solution flow rate of 10 mL min−1. The lead-free, alumina-stabilized Pd catalyst was fully characterized by TEM, HR-TEM, EDX, IR, XRPD and AAS. Highly dispersed Pd nanoparticles have proven themselves to be stable under the reaction conditions employed. The application of the method is subject to the dielectric properties of substrates and solvents, and is therefore hardly applicable to apolar alkynes. Considering the small volume of the reaction chamber, microwave-assisted flow hydrogenation has proven itself to be a safe procedure and one that is suitable for further scaling up to industrial application.

Correction: Hydrogenation of 2-methyl-3-butyn-2-ol over a Pd/ZnO catalyst: kinetic model and selectivity study

Correction for ‘Hydrogenation of 2-methyl-3-butyn-2-ol over a Pd/ZnO catalyst: kinetic model and selectivity study’ by S. Vernuccio et al., React. Chem. Eng., 2016, 1, 445–453.