 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. We have been discussing a very interesting reaction, which is Reppe chemistry with regard to this particular topic. Now, Reppe chemistry stands very relevant in today's context and we are going to be looking at the development in the overall scheme of the developments that happened in Transition Metal Organometallic Chemistry. In this context, in today's lecture, we are going to take a look at the chronological sequence, in which the Reppe chemistry evolved under conditions and requirement that was the need for the day. Now, what we had seen in the earlier class is the fact that this Reppe chemistry allows access to a large number of functionalised chemical feedstocks or compounds all originating from acetylene chemistry. And it was as if the acetylene serves as a feedstock for various different functionalised chemistry. And today, we are going to see this development in the light of the overall development of Transition Metal Organometallics in the scheme of things and we are going to see how the need of the day resulted in the development of Reppe chemistry. Much of the research that goes on in the present day as well as it was relevant in earlier times depends on the need of the day and is guided by the economics and the need of the time. And hence, in current context, for example, the much of the research is about developing renewable source of energy. This involved looking into options like solar, wind, water, biomass, so on and so forth. The reason for more need for the development of renewable source of energy arises from the fact that these are clean energy, that means no carbon footprint or no carbon dioxide and so on and so forth. So, these are the reasons which allow us to focus more on renewable energy. The other reason to have this emphasis on renewable energy arises from the fact that depletion of the carbon footprint from the face of the earth in terms of the so-called non-renewable energy like petrochol and petroleum of fossil fuel. So, the way the focus has been on renewable energy in the current century, things were however different if we go back just about 100 years or so. For example, around 1900 till around 1950s, the focus of the energy source had been primarily on non-renewable energy. And these involved fossil fuels, which would include sources like coal, natural gas, crude oil. Now chronologically, if one were to look at that these emphasis of energy from these sources had been in the order shown here that petroleum as well as the natural gas crude oil sources were probed mainly in 1950s whereas the one those of coal or coal-driven energy sources were more in vogue even before that that is in 1800s or 1900s. Now to see the connection with respect to acetylene is that from the coal is a major source for production of acetylene and whereas from natural gas or from petrochemical industry what people get is ethylene or propylene. Now the way in current times the focus had been on generating energy from renewable sources about 100 years or so back the focus had been on gathering energy from non-renewable sources which were for example from that of coal or from that of acetylene or to be more accurate that in early 1900s or so the focus had been on getting it from acetylene which is a product from from the coal whereas maybe about three or four decades later in 1950s the focus shifted from on to acetylene to more economically feasible source like ethylene and propene. Now the whole gamut of rapid chemistry starts from here that we talk about it is about utilizing acetylene. Now rapid chemistry as we have seen in our previous discussion that acetylene could be converted to large number of functionalized products and that had solely been because of the efforts of Walter Rappey who found out how to deal with acetylene and to elaborate further on that for example one can convert acetylene to acetyldehyde which is a useful intermediate aldehyde are useful intermediate for other functionalized chemicals functionalized feedstock and the conversion of ethylene to acetylene can be achieved by treatment with water in presence of sulfuric acid and mercury sulphate and these had been one of the major exploits of acetylene so that one can see the need for developing acetylene as a feedstock for carrying out chemical reaction however and that had been the reason that has led to the development of rapid chemistry however with time the focus shifted from acetylene to ethylene which was more easier and more cheaply obtained from natural grass and crude oil and then that had led to sort of exploring the possibility of using ethylene to for making acetyldehyde so that again the useful intermediate for accessing other functionalized feedstock could be gained and for this also resulted in a very important process which is called Wacker oxidation so Wacker oxidation involves reaction of ethylene in presence of palladium by chloride catalyst and copper chloride catalyst which results in formation of the acetylides and this process this process from obtaining acetyldehyde from ethylene become more prevalent in 1950s and overtook the production from that from acetylene which were more prevalent in 1920s so what we see is that the shift of sort of technology for obtaining functionalized feedstock moving on from acetylene to ethylene now these were the stories which were more invoke about 50 or 60 years back whereas now we move on to more unconventional but more permanent solutions that is exploring energy from renewable sources like solar, wind, water, biomass so on and so forth and the primary reason is that at some point or other the whole of these non-renewable sources would get depleted from the face of the earth and then our energy requirement has to be made from those sources available from the renewable energy now even under the current scenario there is a larger argument still prevalent in favor of developing this rapid chemistry which sort of makes a comparative estimates of how long this fossil fuel like coal or natural gas or crude oil would last on earth and based on the estimate it is still suggested that probably the natural reserve of coal will outlive that of petroleum products and hence we still would require to focus on getting energy some amount of energy using the rapid chemistry and this brings us to the relevance of rapid chemistry in today's context even though both coal and natural gas crude petroleum at some point or other would get exhausted but coal reserve would outlast or outlive the natural gas and the crude oil reserve and hence the energy potential arising from coal should also be exploit even under today's context when the focus is shifting towards more renewable energy. Now another point to mention over here is that in this world where everything is still yet to be standardized or people do not have a standardized opinion on several issues there are countries pursuing each of these technologies depending on their results for example China China has a large coal reserve and China still explodes the potential of acetylene as a feedstock now with these being the scenario there is a lot of thrust in looking into the acetylene chemistry and as far as the chemical nature as the chemical intuition is concerned acetylene has higher reactivity more reactive than ethylene and hence would require less step in reacting or in reactions to reach the intermediates than what one would require from that of acetylene. Another last but not the least but important argument however in favor of non renewable energy is that unlike renewable energy for example like that of the solar energy there is depending on the strength of the wind there is a huge fluctuation in the power that is generated arising out of this wind whereas in contrast to that energy from non renewable sources like coal provides a steady supply of energy in terms of the electrical power that is generated and hence there is still demand as well as argument in favor of exploring the non renewable energy sources as an option for making our energy needs now with these background I think now you would have a understanding of the reason as to why repeat chemistry which was developed so early on in 1900s is still relevant in today's context and that those reactions has led to so many different products because of its various chemical exploits and that had been carried out by very dedicated scientists for example in the form of repeat who has developed this chemistry and the name suggest so now with that I think I have provided you a picture of how relevant is acetylene and conversion of acetylene to other feedstock and the challenges involved in this which was the need of the day in early 1900s when the energy options were from non renewable sources were explored and even now about 100 or more years later the repeat chemistry is still of relevance because of reasons just mentioned now now with these we come back to the central of rapid reaction which is acetylene and then we are going to sort of look into the utility of acetylene apart from what I have been just talking about on repeat kind of conversion in our daily need now acetylene as I mentioned apart from the repeat chemistry has been long used for welding purposes and the first use of acetylene in welding is noted as early as 1906 and the reason being the applications of acetylene in welding is because this is the strongest safest and simplest safest and simplest to use as a fuel gas now why is it so useful because it gives a temperature of around around 3000 degree centigrade when mixed with oxygen in 1 is to 1.1 ratio so these by and large is a very important aspect that you can reach a temperature of about 3000 degree centigrade now if you compare this temperature this is almost about half the temperature of that in sun maybe 6000 or 7000 degree centigrade so if this is very high a temperature in which most of the metals would melt so application wise this temperature is by far the highest or the hottest of all fuel gases hottest of all fuel gases and hence it can easily melt all of them and hence it is not a surprise that acetylene is found extensive application in welding purpose now it has a specific gravity of about 0.9 relative to 1 for air so that means acetylene is lighter and hence would move up if unused so it is not going to sort of you know sink or stay low if there is any unused acetylene is there so in that way it is kind of very safe to use and also the oxygen ratio that it requires is very less which is about 1 is to 1 many other fuel gases for example ethylene or propylene would require more amount of oxygen to burn than what acetylene would and because of this reason because of its light nature because of its low oxygen consumption ratio and because of the very high temperature that it can attain when burning with oxygen acetylene is the best safest strongest and simplest fuel gas to use and has found applications in various welding type applications so apart from conversion of acetylene to feedstock acetylene has also a tremendous application in welding industry lastly it has also a smell of that of garlic so if there is any leak or anything that can also be easily detected garlic like order and all of these provided overview of as to why acetylene was important in context of application as early as beginning of 1900 and why so much research activities were centered around acetylene which has led to the development of rapid chemistry which we are talking about with these you know we are going to be a looking into some more reactions some of the reactions relevant to rapid chemistry as we go on for example the reaction of acetylene with alcohols results in formation of methyl vinyl ether so this is a reaction when vinyl functional group is formed and is a part of the reaction called a venylation similarly another example of venylation involves reaction with cyanides this involves a catalyst which gives acrylonitrile now these kind of intermediates are very important as intermediates or monomers for various polymerization reactions including polymerization to produce functionalized polyethylene where they have this functional moiety cyanide attached to the polyolefin so these intermediates have a lot of put application as monomer for various polymerization reaction so with these we come to the end of today's lecture on rapid reaction in which we have looked into the perspective of the development of rapid reaction in the context of the energy need as a function of time and what we had seen that with the passage of time from 1800 to 1900 to the present scenario the demand for energy have been made from non-renewable sources to that of the renewable or more technologically cleaner sources of energy and this has led to a shift in the energy sources on moving from coal fossil fuel particularly from coal to natural gas and crude oil in 1950s which was that time invoked because of the olefin polymerization discovery and because of the petrochemical developments at that point of time to the current scenario of clean technology involving solar, wind, biomass, water so on and so forth. The acetylene had been produced largely from coal and hence the conversion of acetylene to other feedstock has been explored and successfully demonstrated by Repi through his wonderful set of reaction as well as the development of being able to handle acetylene in higher pressure but unfortunately in 1950s with economics taking over the ethylene and propylene obtained from crude oil and natural oil were much cheaper and hence the development of ethylene chemistry particularly from ethylene to that of acetyldehyde using vachiar oxidation took over as opposed to the conversion of acetylene to acetyldehyde using mercury and sulfuric acid in water which was sort of taken over by vachiar oxidation where one could convert ethylene to acetyldehyde and which could then finally be used for synthesizing or accessing other functionalized chemical feedstocks that eventually gain ground however given the fact that the cold reserve on fossil fuel is going to outlast the oil reserve or the natural oil and crude oil so still even after 100 years so there are important arguments in favor of developing the acetylene chemistry as has been initiated by Repi in this context we have also looked at two venylation reactions particularly the reactions of alcohol with acetylene in potassium hydroxide and that of hydrogen cyanide with acetylene presence of a catalyst give acrylonitrile with these we come to an end of today's class and we are going to look into some more reactions on Repi in the subsequent lecture that we are going to be taken up in the next class so till then goodbye and thank you