An Era Of Chemical Catalysis: A Theoretical And Experimental Perspective

Catalytic technologies have played a vital role in the economic development of the chemical industries in the 20th century. About 90% of the chemical processes worldwide are carried out with the help of catalysts. Different organic intermediates, necessary for the synthesis of dyes, plastics, pigments, crop-protection agents and drugs, rely only upon the use of catalysts. In this book, we will give a brief introduction on the application of chemical catalysis both from experimental and theoretical point of view.
Chapter 1 describes importance of silver catalysis in click reaction as a substitute to CuAAC. Click reaction in a broader sense specify a set of reactions that are fast, simple, easy to purify, versatile, regiospecific, and high yielding. Among various click reactions copper catalyzed azide-alkyne cycloaddition (CuAAC) is a prime example that allow access to 1,4-disubstituted-1,2,3-triazoles. However, Cu-free catalytic systems are drawing much more attention recently considering cytotoxic nature of copper based catalysts. Silver is a chemical element that belongs to 11th group of periodic table, has long been known to humans as a precious metal. The possibility of silver acting as a substitute to copper in AAC has been demonstrated by McNulty and coworkers using P,O-type silver complexes for the first time. After that many reports were made on Ag catalyzed azide-alkyne cycloaddition reaction.
Density Functional Theory based study has been carried out to investigate the effect of substituents attached to nitrogen atoms of N-heterocyclic carbenes and their different analogs on their ability to activate dihydrogen molecule in Chapter 2. Different electron donating and electron withdrawing substituents have been considered in this study. The activation barriers for the activation of dihydrogen is strongly dependent on the singlet-triplet energy gap of the carbene compound.
Chapter 3 give a brief idea of the different montmorillonite clay based catalysts and their application in dye degradation.. Use of natural dyes has been started with the starting of human civilization. Later synthetic dyes took the place of natural dyes and with the development of variety of industries use of synthetic dye also increased, in fact they have become indispensable chemicals. Unfortunately, most of them are toxic and due to the toxicity, carcinogenicity, and mutagenicity of synthetic dyes, they create a huge threat to human health as well as for animals. Due to the complex aromatic structures and high stability against light, temperature, water, etc, these synthetic organic dyes cannot be degraded by conventional water treatment process and they cause substantial water pollution as well as environment pollution. Therefore effective removal of toxic dyes is extremely important. In the recent years researchers proposed various methods involving biochemical, electrochemical, sonochemical and photochemical reactions etc. for these purpose. A number of catalysts have also been reported for effective removal of dyes from waste water. A considerable number of montmorillonite clay supported heterogeneous catalysts have also been found very effective for this purpose. Montmorillonite can be considered a potential adsorbent toward dyes. In pure form, montmorillonite shows a high ability to adsorb dye molecules via a cationic exchange and molecular sieve mechanism.
Chapter 4 discusses the recent developments in the area of cellulose-supported metal catalysts. Cellulose is one of the organic polymers distributed abundantly in nature. This material exhibits extraordinary properties of enhanced metal adsorption and drug loading. The surface of cellulose contains abundant hydroxyl groups which can be modified with functional groups such as –SO3H, -COOH, -NH2 etc. and this in turn improves the reusability of the material. Cellulose-supported metals have gained tremendous interest in recent years and have been extensively used as efficient catalytic systems for organic transformations, which includes, click reaction, alcohol oxidation, oxidative decarboxylation and coupling reactions.
In the chapter 5, the applications of doped-graphene in various chemical transformations have been highlighted. Theoretical studies and facts on doped-graphene have been given prime importance in the chapter. Chapter 6 describes the method of cascade synthesis of biologically important N-heterocycles using transition metal.
In chapter 7, synthesis of a few such hydrophilic complexes are discussed, particularly highlighting two Pd(II) and Fe(III) complexes which have been successfully applied as catalyst in aqueous Suzuki-Miyaura cross coupling and oxidation of alcohols respectively. Schiff bases are a class of organic compounds containing azomethine (–HC=N–) group which have extremely been studied because of their simple synthesis, high air stability, cost effectively of the precursors and wide applicability. They show characteristic coordination through nitrogen atoms with transition metals to form complexes, although other atoms viz. O, S, P sometimes may also act as additional donor sites along with nitrogen. Their electronic and steric properties could easily be tuned by proper selection of precursor materials. But majority of these Schiff base compounds are little soluble in water because of their hydrophobic framework, thereby limiting their use as catalysts in aqueous media. Therefore, designing of hydrophilic Schiff base catalysts by introducing functionalities like –SO3-, -COO etc. have been a fascinating area in catalysis during recent years.
The study on Chapter 8 will be helpful in understanding the tuning of hydrogen storage properties of materials and thus in designing suitable storage of hydrogen. Aluminium (Al) clusters are always been a site of attraction for designing hydrogen storing materials due to its light atomic weight and very high abundance on Earth’s crust. Moreover, the fcc structure of bulk Al can be depicted by one of its sub-nano form, such as Al6 cluster as it has a octahedral structure. Several theoretical studies on Al clusters already suggest that it can be effectively used for hydrogen storage. The dissociation mechanism of hydrogen molecule on the host material is also a key factor for designing a suitable storing system. In metal clusters the dissociation of hydrogen molecule can be tuned very constructively via doping or by varying the size of the host cluster.
Ionic Liquid (IL) based catalytic systems is presented in Chapter 9. Chapter 10 includes the description of catalyst in the synthesis of ynones. α, β-Acetylenic ketones or ynones have become extremely important in last few years because of their versatile applications in various fields such as click chemistry, pharmaceutical, organic synthesis and natural products etc. Ynones are the construction blocks of organic chemistry, used to prepare many biologically active compounds, heterocyclic components for synthesis of various reaction intermediates so forth.
Coumarins are one of the important classes of benzopyrones which strengthen their own realm among the usually encountered heterocycles in this present era owing to the possession of significant properties in pharmaceutical as well as industrial field. Chapter 11 describes the Pechmann Condensation in Task Specific Room Temperature Ionic Liquid to synthesis coumarin. Coumarin scaffold is found as an integral part of many anticoagulants, anti-HIV, anti-venom, antibiotic drugs. Ranging from food to cosmetics, its industrial uses extend to optical brighteners and laser dyes as well. Moreover, the property to act as fluorescent probe makes the coumarins attractive molecular scaffold among scientific community.
Chapter 11 describes development of various methods for Pechmann Condensation and impact of various acidic ILs as catalysts in coumarin synthesis that reduces the task of an acid catalyst as well as extra solvent and also meets the principles of green chemistry. Among various synthetic routes, Pechmann condensation is one of the most widely used synthetic methods towards coumarin synthesis where the desired product is obtained by the condensation of phenolic compounds with β-keto esters or carboxylic acids. The reaction is firmly catalyzed by acids under different reaction conditions. Recently, acid ionic liquids as catalyst for coumarin synthesis are becoming quite popular owing environment friendliness of these catalysts. Ionic liquids (ILs), salt of organic cation and inorganic/organic anion, are one of the best alternative solvents to the conventional ones which serve the reaction in a greener way which is very much important to meet the conditions for sustainable developments.