HOMOGENEOUS CATALYTC REACTIONS.pptx

Catalysis and its Types
Homogeneous Catalysis
Advantages of Homogeneous Catalysis
History of Homogeneous Catalytic Reactions
Examples of Homogeneous Catalytic Reactions

1. SUBMITTED BY HAMYAL AWAIS MPHIL CHEMICAL ENGINEERING SCME, NUST

2. HOMOGENEOUS CATALYTC REACTIONS

3. “Catalysis is the key process to accelerate the  rate of a  chemical reaction  in the presence of a   catalyst” CATALYST A catalyst is a chemical substance that accelerates the rate of a chemical reaction by providing a new path with a low activation energy and is not chemically consumed and can be regenerated at the end of the reaction. TYPES OF CATALYSIS Catalysis can be divided into following two types Homogeneous Catalysis Heterogeneous Catalysis CATALYSIS https://www.energy.gov/science/doe-explainscatalysts#:~: text=Catalysis%20is%20the%20process%20of,the%20atoms%20into%20new%20molecules.V

4. The word homogeneous divides into two categories “ Homo ” mean “ Same ” & “ Geneous ” means “ Phase ” FEATURES In the homogeneous catalytic process: The reactants involved in the chemical reaction are in same phase with the catalyst used The catalyst is distributed evenly with the reactants The reaction proceeds with the decrease in activation energy The reaction continues with the formation of intermediate molecules Multiple steps are usually involved in the catalytic process HOMOGENEOUS CATALYSIS https://en.wikipedia.org/wiki/Homogeneous_catalysis

5. HOMOGENEOUS VS HETEROGENEOUS CATALYSIS HOMOGENEOUS HETROGENEOUS https://www.chemguide.co.uk/physical/catalysis/introduction.html

6. HISTORICAL BACKGROUND of HOMOGENEOUS CATALYSIS Wisniak , J. (2010). The history of catalysis. From the beginning to Nobel Prizes.  Educación química ,  21 (1), 60-69.

7. L ess time is required Economic and easy avalibility High yield is obtained Less conditions are required to fulfil Catalysts are more active and selective Pore diffusion limitations are not present as catalysts are equally dispersed in the mixture Acidic catalysts are not affected by the content or vice versa Chemistry and mechanism of reaction can be studied more effeciently Not efficient way is present to separate the reaction mixture Large amount of water is required for the reaction Bas ic catalysts are affected by the content Bulk phase mass transfer limitations are present ADVANTAGES DISADVANTAGES https://www.researchgate.net/figure/Advantages-and-disadvantages-of-homogeneous-and-heterogeneous-catalysts-in-biodiesel_tbl2_337389292

8. The mechanism of homogeneous catalysis involves a series of following steps through which a catalyst facilitates a chemical reaction between reactants. STEP I CATALYST-SUBSTRATE INTERACTION The catalytic reaction begins when the catalyst interacts with the reactants to form an intermediate complex . The binding usually occurs through coordination bonds, where catalyst is used as a coordination center . STEP II REACTION INTERMEDIATES FORMATION The crucial step in the catalytic process is the transformation of catalyst-reactant complex into reactive intermediates . The reactivity of these intermediates is different than original reactant molecules, which allows the occurrence of desired chemical transformation. STEP III CATALYTIC CYCLE This step includes different steps that facilitates the conversion of reactants into desired products ; such as substrate binding, activation, reaction process, and release of product. MECHANISM of homogeneous catalysis

9. STEP IV REACTION FACILITATION The catalysts accelerates the chemical reaction by providing an alternate pathway that helps to stabilize the transition states by lowering the energy of activation. STEP V CATALYST REGENERATION In the final step of catalytic process, after facilitating the reaction, the catalyst is regenerated. STEP VI MULTIPLE TURNOVERS The catalyst can efficiently facilitates the conversion of multiple sets of reactants into products , therefore can repeatedly catalyzed same reaction without being consumed. MECHANISM of homogeneous catalysis https://chem.libretexts.org/Courses/University_of_Kentucky/UK%3A_CHE_103Chemistry_for_Allied_Health_%28Soult%29/Chapters/Chapter_11%3A_Properties_of_Reactions/11.6%3A_Rates_of_Reactions

10. Exothermic Reaction Endothermic Reaction https://chem.libretexts.org/Courses/University_of_Kentucky/UK%3A_CHE_103Chemistry_for_Allied_Health_%28Soult%29/Chapters/Chapter_11%3A_Properties_of_Reactions/11.6%3A_Rates_of_Reactions

11. Acid-Base Catalysis Transition Metal Complexes Organocatalysis Photocatalysis Enzymatic Catalysis Metathesis Catalysis TYPES of homogeneous catalysis

12. In acid catalysis, An acid catalyst donates proton(s) (H+) to the reactant molecules to facilitate the catalytic reaction. An electrophilic specie is formed. A stable carbocation intermediate is formed. EXAMPLES Hydrolysis of Ester or Amines Formation of Sulphur dioxide Formation of Ethyl acetate ACID catalysis

13. Acid catalyzed hydrolysis reactions involves the cleavage of chemical bonds by the addition of water molecule . In the hydrolysis of an ester, the (-OR) group of the ester is replaced by the hydroxyl (-OH) group from water , which results in the formation of a carboxylic acid and an alcohol .   CATALYSTS : Mineral acid e.g. dilute sulphuric acid (H 2 SO 4 ) or dilute hydrochloric acid ( HCl ) MECHANISM : S tep 1 : The acid catalyst protonated the oxygen atom present on the carbonyl group. The positively charged oxygen increases the electrophilicity of the carbonyl carbon. S tep 2 : The water molecule attacks the electrophilic carbon of carbonyl group Step 3 : A tetrahedral intermediate is formed. Step 4 : The acid causes the protonation of -OR group which causes its detachment. Step 5 : A molecule of carboxylic acid is generated . https://psiberg.com/hydrolysis-of-esters/ HYDROLYSIS OF ESTER

14. In base catalysis, A base catalyst donates proton(s) (H+) to the reactant molecules to facilitate the catalytic reaction. An nucleophilic specie is formed. A stable carbanion intermediate is formed. EXAMPLE Hydrolysis of Ester (Saponification) BASE catalysis

15. SAPONIFICATION Base catalyzed hydrolysis reactions involves the cleavage of chemical bonds by the addition of water molecule . In the saponification process, the (-OR) group of the ester is replaced by the hydroxyl (-OH) group from water, which results in the formation of a carboxylate ion and an alcohol.   CATALYSTS : S trong alkali such as sodium hydroxide ( NaOH )   MECHANISM S tep 1 : T he hydroxide ion acts as a nucleophile and attacks the electrophilic carbonyl carbon to form a tetrahedral intermediate . Step 2 : The oxygen atom removes a -OR group and forms a double bond which causes the formation of carboxylic acid. Step 3 : The alkoxide ion cleaves the p roton by breaking acyl –oxygen bond to form a carboxylate ion and an alcohol molecule. https ://psiberg.com/hydrolysis-of-esters/

16. Conversion of unsaturated compounds (e.g. alkenes, alkynes or olefins) into saturated compounds (e.g. alkanes) by the addition of hydrogen gas under the influence of transition metals catalysts. It reduces the unsaturation by converting the double or triple bonds into single bond of saturated compounds SUBSTRATE : alkenes, alkynes PRODUCT : alkanes CATALYST : Nickel, Palladium, Platinum, Wilkinson's catalyst, Chlorotris -( triphenylphosphine ) rhodium, [(Ph3P)3RhCl ] USE : Using this process, vegetable oils are converted into solid fats (ghee) EXAMPLES : Hydrogenation of Alkenes Hydrogenation of Alkynes Hydroformylation Reaction HYDROGENATION REACTIONS

17. HYDROGENATION OF ALKENES The double bond in alkenes is converted in single bond of alkanes by the addition of hydrogen in the presence of Pd catalyst The mechanism of hydrogenation reaction is shown below

18. HYDROGENATION OF VARIOUS HYDROCARBONS

19. The hydroformylation process, also known as oxo -reaction , was developed by O. Roelen . In the hydroformylation process, branched or linear aldehyde molecules are synthesized in the industries by the addition of a hydrogen atom and a formyl group in alkenes. CATALYSTS : tris rhodium carbonyl hydride & cobalt tetra carbonyl hydride hydroformylation REACTION https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Inorganic_Chemistry_(LibreTexts)/14%3A_Organometallic_Reactions_and_Catalysis/14.03%3A_Organometallic_Catalysts/14.3.02%3A_Hydroformylation

20. MECHANISM Step 1 : The pre-catalyst Co 2 (CO) 8  in converted into actual catalyst HCo (CO) 4 in the presence of H 2 . Then a molecule of CO is removed from catalyst to give the 16-electronmolecule . Step 2 : The alkenes bind with resultant molecule to form an molecule containing18-electrons Step 3 : The olefin molecule is inserted to form alkyl tricarbonyl . Step 4 : Another molecule of CO is added from catalyst to form alkyl tetracarbonyl . Step 5 : The alkenes bind with resultant molecule to form an molecule containing18-electrons Step 6 : Another molecule of CO is added to form an acyl molecue containing16-electrons Step 7 : A molecule of hydrogen is added to form a di hydrido complex Step 8 : In the end, a molecule of aldehyde is released by reductive elimination process. https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Inorganic_Chemistry_(LibreTexts)/14%3A_Organometallic_Reactions_and_Catalysis/14.03%3A_Organometallic_Catalysts/14.3.02%3A_Hydroformylation

21. Hydrosilylation or hydrosilation is a catalytic process in which organsilanes and organosilicones ( alkyl silanes , vinyl silanes and silyl ethers) are synthesized by the addition of a H-Si in a bond such as carbon-carbon, carbon-oxygen, carbon-nitrogen, nitrogen-nitrogen and nitrogen-oxygen present in unsaturated compounds ( alkenes, alkynes, aldehydes  and  ketones) through transition metal catalyst, Lewis acid , or radical . CATALYST : Speier's catalyst (H 2 PtCl 6 ), Karstedt's catalyst, Wilkinson's catalyst MECHANISM A most recognized mechanism for metal catalyzed hydrosilylation reaction is Chalk- Harrod mechanism . There are various modifications to this mechanism. Step 1 : The Si-H bond is added to metal catalyst by the process of oxidation. Step 2 : After that the alkene molecules a re inserted . Step 3 : The hydrogen atom is added to the alkene molecule through beta-insertion process . Step 4 : The adduct is obtained by the reduction of alkylsilyl Pd (II) complex and the metal catalyst returns to its original oxidation state . Hydrosilylation REACTION , https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_%28Inorganic_Chemistry%29/Catalysis/Catalyst_Examples/Hydrosilylation

22. The hydrocyanation process was developed by Arthur and Pratt in 1954 . It is an industrial catalytic process for the conversion of  unsaturated hydrocarbons (e.g. linear alkenes and alkynes)  to  nitriles by the addition of hydrogen cyanide (HCN) to the metal complexes . SUBSTRATE : alkenes PRODUCT : nitriles CATALYST :  copper, palladium ,   nickel,   phosphite  (P(OR) 3 ) complexes of nickel, c hiral ,  chelating aryl diphosphite complexes, Lewis acids such as B(C 6 H 5 ) 3 , triphenylboron EXAMPLES : Hydrocyanation REACTION Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann , M.  Advanced Inorganic Chemistry ; John Wiley & Sons: New York, 1999; pp. 244-6, 440, 1247-9

23. Following is the mechanism of industrial process for catalytic hydrocyanation of butadiene to  adiponitrile , which was developed by   W. C . Drinkard . MECHANISM Step 1 : First Hydrocyanation B utadiene is transformed into a mixture of 2-methyl-3-butenenitrile (2M3BM) and 3-pentenenitrile (3PN) Step 2 : Isomerization 2M3BM (unwanted product) is converted to 3PN Step 3 : Second Hydrocyanation 3PN is converted into   adiponitrile using a Lewis acid such as aluminium trichloride as a catalyst https://www.sciencedirect.com/science/article/abs/pii/B9780080951676005176

24. ADVANTAGES T he   nitriles obtained as a result of hydrocyanation can be converted into a variety of industrially useful products which includes amines, amides, carboxylic acids, esters. Adiponitrile serves as a precursor of hexamethylenediamine which is used in the synthesis of a variety of Nylon https://www.sciencedirect.com/science/article/abs/pii/B9780080951676005176

25. OXIDATION OF SULPHUR DIOXIDE The formation of sulphur trioxide is an example of gas phase homogeneous catalyzed reaction. In the lead chamber process, during the manufacturing process of sulphuric acid (H 2 SO 4 ), nitric oxide (NO) acts as a catalyst in the oxidation s ulphur dioxide (SO 2 ) to sulphur trioxide ( SO 3 ). DECOMPOSITION OF ACETALDEHYDE The formation of sulphur trioxide is an example of gas phase homogeneous catalyzed reaction. During the normal decomposition of acetaldehyde (R-COH) into methane (CH 4 ) and carbon monoxide (CO) , iodine vapors are used as a catalyst . https://www.sciencedirect.com/science/article/abs/pii/S0010218073800628 https ://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1930.0096

26. OXIDATION OF CARBON MONOXIDE The degradation of two environmentally hazardous gases, CO and N 2 O , can be done through the oxidation of CO by N 2 O in the presence of ruthenium hydride ((PNN)Ru–H) pincer complex under mild conditions. During this reaction, an O-atom is transferred from N 2 O to Ru–H bond to form a Ru–OH intermediate, followed by intramolecular attack of hydroxyl ion on the adjacent CO molecule, synthesizing two non hazardous gases, carbon dioxide (CO 2 ) and nitrogen ( N 2 ). FORMATION OF ETHYL ACETATE The synthesis of ethyl acetate is an example of liquid phase homogeneous catalytic reaction . During this reaction, ethanol and acetic acid react with each other in the presence of H 2 SO 4 . https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6502446/

27. CONCLUSION & FUTURE PERSPECTIVE Homogeneous catalysis is a catalytic driven approach that plays pivotal role in modern chemistry, enabling more efficient and selective chemical processes. By harnessing the powerful, well-designed catalysts, we can achieve more efficient and environmental friendly chemical transformations both in industries and laboratory research as well as address pressing global challenges. Continued research will pave the way to greener and more sustainable chemical processes .

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