Hydrogenation Reactions

There are two main types of hydrogenation reactions:

Single bonds form by adding hydrogen atoms to an organic compound with double or triple-bond functionality. Examples of hydrogenation reaction products that form in a single step include:

• C—C single bonds from alkenes and alkynes
• C—O bonds from ketones, aldehydes, or esters
• C—N bonds (amines) from imines or nitriles 

Metal catalysts are often used in hydrogenation reactions to reduce the high energy barrier of the transformation and are often referred to as a catalytic hydrogenation. For example, alkenes and alkynes require a nickel, palladium, or platinum catalyst to transform into alkanes. Hydrogenation reactions can be homogenous or heterogeneous when using metals adsorbed on various substrates. For example, to achieve homogeneous asymmetric hydrogenation, specific ligands are coordinated with rhodium and iridium metal catalysts.

In all cases, the choice of the catalyst greatly influences a hydrogenation reaction. Factors of the catalyst that impact the hydrogenation reaction include the catalyst concentration, solvent, substrate purity, temperature, and pressure. 

Data-rich experimentation brings the maximum amount of information, resulting in fewer experiments. This efficiency helps identify the relationships between a wide range of reaction parameters and leads to greater process understanding. 

Reaction calorimetry used in conjunction with in-situ process analytical technology (PAT) helps identify the optimal operating conditions of a chemical process by combining knowledge of kinetic and thermodynamic parameters. 

Delgado, J., Salcedo, W. N. V., Devouge-Boyer, C., Hebert, J., Legros, J., Renou, B., Held, C., Grenman, H., & Leveneur, S. (2023). Reaction enthalpies for the hydrogenation of alkyl levulinates and levulinic acid on Ru/C– influence of experimental conditions and alkyl chain length. Chemical Engineering Research & Design, 171, 289–298. https://doi.org/10.1016/j.psep.2023.01.025

This example presents a study on how to optimize catalysts for batch hydrogenation reactions using automated high-throughput experimentation. The authors describe how they used a combination of ReactIR™ in-situ FTIR spectroscopy and RC1 high-pressure reaction calorimeter to monitor and control the hydrogenation process and perform in-situ measurements of reaction kinetics and product formation.

The study showed that the automated high-throughput experimentation approach with METTLER TOLEDO instruments can significantly improve the efficiency and accuracy of catalyst optimization for batch hydrogenation reactions. The authors noted that the use of ReactIR and RC1 reactor control unit enabled real-time monitoring of the reaction, which facilitated the identification of optimal catalyst conditions based on reaction kinetics and product formation. The use of FTIR and reaction calorimetry instruments for optimizing hydrogenation processes and catalysts led to faster and more efficient reaction optimization in batch hydrogenation.

Baimuratova, R. K., Andreeva, A. V., Uflyand, I. E., Shilov, G. V., Bukharbayeva, F. U., Zharmagambetova, A. K., & Dzhardimalieva, G. I. (2022). Synthesis and Catalytic Activity in the Hydrogenation Reaction of Palladium-Doped Metal-Organic Frameworks Based on Oxo-Centered Zirconium Complexes. Journal of Composites Science, 6(10), 299. https://doi.org/10.3390/jcs6100299

The authors describe the use of METTLER TOLEDO instruments such as the EasyMax automated reactor system and in-situ FTIR probe for real-time monitoring of hydrogenation reactions. They also discuss the integration of a robotic platform to automate the process of reaction screening, allowing for high-throughput optimization of reaction conditions.

Automated platforms help reduce the time and resources required for optimizing hydrogenation reactions, as well as improving the efficiency and accuracy of the process. The use of in-situ FTIR spectroscopy instruments in combination with the automated platform provides a reliable and efficient method for screening and developing hydrogenation reactions.

Zhang, Y., Yuan, M., Liu, W., Xie, J., & Zhou, Q. (2018). Iridium-Catalyzed asymmetric transfer hydrogenation of alkynyl ketones using sodium formate and ethanol as hydrogen sources. Organic Letters, 20(15), 4486–4489. https://doi.org/10.1021/acs.orglett.8b01787

This example describes a new method for the asymmetric transfer hydrogenation of alkynyl ketones using iridium catalysts. The authors discuss the use ReactIR spectrometer to monitor the progress of the reaction in real time, allowing them to optimize the reaction conditions and monitor the reaction intermediates. The use of EasyMax™ reactor system for the reaction setup allowed for precise control of the reaction parameters such as temperature and stirring speed.

The combination of the in-situ reaction monitoring instruments with the iridium catalyst system enabled the researchers to perform the reaction with high reproducibility and accuracy. This approach could be extended to other catalytic reactions, allowing for more efficient and accurate reaction optimization and analysis. 

There are several risks associated with hydrogenation reactions, including:

• Explosion hazard: Hydrogen gas is highly flammable and can cause explosions if it accumulates in confined spaces.
• Fire hazard: Hydrogenation reactions can generate heat, which can cause fires if not properly controlled.
• Toxicity: Some hydrogenation catalysts, such as nickel, can be toxic if inhaled or ingested.
• Environmental impact: Hydrogenation reactions can produce waste products that can harm the environment if not properly disposed of.
• Health risks: Certain hydrogenated products, such as hydrogenated vegetable oils, have been linked to an increased risk of heart disease.
• Safety risks: Hydrogenation reactions can be exothermic and generate heat during the process, which can cause thermal runaway if not properly controlled.
• Handling of the reagents: Catalysts and intermediates must be handled carefully as they can be corrosive, toxic, flammable, and reactive. It is important to note that these risks can be mitigated by following proper safety protocols and using appropriate equipment and materials.

Hydrogenation reactions can have potential environmental impacts due to the use of catalysts and solvents, which can generate waste and potentially harm the environment. To alleviate these potential environmental impacts, scientists are now utilizing chemical reaction modeling and simulation software to reduce the use of hazardous materials. By using computer simulations, engineers can predict the outcome of the reaction and optimize the conditions to minimize waste and reduce the use of harmful chemicals.

Additionally, reaction modeling can be used to identify alternative, more environmentally friendly catalysts, and solvents, which can further reduce the impact of the reaction on the environment. By using chemical reaction modeling to design and optimize hydrogenation reactions, it is possible to minimize waste and reduce the environmental impact while maintaining or improving the efficiency and cost of the reaction.

Hydrogenation catalyst screening is a crucial step in the development of a successful hydrogenation reaction. It involves evaluating various catalysts to determine the most efficient and effective one for a specific reaction. During the screening process, factors such as the rate of reaction, selectivity, and stability of the catalyst are considered to select the best one.

The screening process typically involves conducting a series of experiments with different catalysts, evaluating the results, and making comparisons to determine the most suitable catalyst. In addition to traditional catalysts like nickel and palladium, other catalysts such as rhodium, iridium, and ruthenium can also be evaluated. The outcome of the hydrogenation catalyst screening process is important because it directly impacts the efficiency, cost, and overall success of the hydrogenation reaction. 

Another challenge with hydrogenation reactions is achieving the desired degree of selectivity, or the ability to selectively hydrogenate certain bonds or molecular functional groups while leaving others unreacted. This can be difficult, especially when the molecule contains multiple bonds or functional groups that can be hydrogenated.

In-situ FTIR spectroscopy is an analytical technique that provides instantaneous information and enables actionable decisions to be made in real time. FTIR probe technology, such as ReactIR, is impervious to solid particles, gases, and most reaction conditions, and offers advantages over alternative offline analytical methods with the ability to:

• Investigate homogeneous and heterogeneous hydrogenations under actual reaction conditions, including at elevated pressure and temperature
• Identify, track, and measure reactants, reagents, products, reaction intermediates, and byproducts produced in hydrogenations
• Rapidly acquire data-rich information for determining reaction kinetics and understanding reaction mechanisms and pathways
• Test and develop ideal hydrogenation conditions for optimizing end-product yield and minimizing side products
• Quickly screen catalysts and conditions for specific hydrogenation reactions
• Eliminate the introduction of air, moisture, or disturbing reaction equilibria resulting from sample extraction 

Another challenge with hydrogenation reactions is catalyst deactivation or the loss of catalytic activity over time. This can be caused by various factors, such as the poisoning of the catalyst by impurities in the reactants or by-products, or by sintering (the formation of a solid mass) of the catalyst. The use of a probe-based automated sampling system provides representative reaction samples over extended periods, even under pressure. 

Hydrogenation reactions are typically carried out under high pressure, which can be dangerous and cause equipment to fail, potentially leading to accidents and injuries. As such, it is important to carefully control the pressure during the reaction to ensure that it remains within a safe and consistent range.

Appropriate safety measures should be in place to protect workers and equipment. This includes the use of pressure-rated equipment, such as reactors and piping, as well as safety devices like pressure relief valves and pressure gauges.

Hydrogenation reactions are exothermic, meaning that they release heat. Managing the heat of reaction can be challenging, as excessive heat can cause problems such as thermal runaway (a rapid increase in temperature) or decomposition of the reactants.

Reaction calorimetry is used to identify thermodynamic and kinetic parameters, which are crucial for the design and optimization of chemical processes and safety evaluations.

High-accuracy calorimetric measurements under pressure are essential for trustworthy and reliable data for process safety evaluations. 

Inaccurate calorimetry results might lead to:

• Lack of understanding of accurate thermochemistry data
• Risk of accidents and personnel injuries
• No trust in data - plant cannot run in an optimal way
• Environmental consequences
• Monetary and reputation loss