 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. Continuing in our discussion in the previous class, where we are talking about applications of Transition Metal Organometallics in catalysis, particularly in the areas of homogeneous as well as heterogeneous catalysis, we had observed that these applications had been developed not only in the laboratories of the academia, but many have also been parallelly developed in the laboratories of industry. One thing about this field of Transition Metal Organometallics is that this is a special bond that academia shares with industry and parallelly the development of the field has been attained in both of these platforms. With that in mind, we are going to continue the discussion further and take up some more examples which have been developed in industry, which is not so common in other fields where most of the developments or new ideas are developed in industry. Today, I am going to talk about another such important development, which has primarily or exclusively been done in the industry in the form of repa synthesis. Now, there are several reactions, which have been developed at the industry like this hydroformylation, the water gas shift reactions, and so on and so forth, which has went on to become a big development in the industrial world, olefin polymerization, metathesis polymerization to some extent, so there has been a lot of contribution from the industry in the development of a particular area, and here is another important such discovery that we are going to be taking up in today's lecture, and this is on repa synthesis. Repa synthesis or repa chemistry refers to conversion of acetylene to a different form of compounds, functionalized versions of acetylene, which has been carried out by Walter Repa in an industrial setting. Now, one of the major challenges about acetylene or conversion of acetylene to other functional compounds is the fact that acetylene is highly explosive and is extremely difficult to handle, and that the reason being acetylene in presence of oxygen is used for welding purpose, and they form a fuel gas, which can be ignited very easily and is used and also a lot of heat is generated and is a perfect gas for carrying out all the welding type applications, and hence because of this explosive and flammable nature of acetylene in presence of air, any reaction or industrial scale utility of conversion of acetylene to other chemicals became a primary challenge, and more so this was more difficult and more formidable a challenge about 100 years back when the understanding as well as handling ability of organometallic compounds were even not as developed as it is today. So, Repa was a chemist at BASF Germany, so most of the chemistry of Repa synthesis that I would be talking about today had been developed about 100 years back in an industrial setting in Germany. The goal of this Repa was in being able to handle acetylene under safe conditions, and so far most of the time people were using acetylene in small scale under low pressure, even though there were explosions, and that time in acetylene chemistry explosions was quite common, and to take up this challenge what Repa did is Repa successfully studied the decomposition of acetylene in ignition experiments. So, this is something that he took up in order to understand, in order to overcome the difficulty associated with handling of acetylene, what he studied is the reactivity of acetylene under ignition conditions, and then designed a special test tube called Repa glasses, which are stainless steel spheres with screw caps, and that allowed high pressure experiments with acetylene that could be carried out, and finally he succeeded in handling acetylene at a very high pressure of about 200 atmospheres. So, this is a very important contribution of Repa that led to the subsequent development of Repa chemistry. Now, the primary source of acetylene is from coal, not like other alkenes or alkynes which comes from natural grass and crude oil. Acetylene is exclusively obtained from coal, so the source of acetylene is different from that of the crude oil, but however like alkenes and alkynes, acetylene also can be used for fuel as well as because of its unsaturation can also be used for conversion to other chemical. Now, one thing at this juncture I should note that these utility of acetylene or other alkenes or alkynes for as fuel for energy purpose is still something which in the present day is becoming obsolete as these are sources of energy from non-renewable resources, and finally at some point our earth is going to be depleted of all of these natural resources from where energy could be made, and hence right now the focus is more on developing energy as a source from renewable resources which are going to be lasting even forever as compared to that from the natural non-renewable resources. However, one should also understand that the time when this chemistry of Repa was developed that was about 100 years back or so when the perspective was different and hence so much of discrimination as to what is the source of energy, it was not as stringent as it is today, and that time there was a significant interest in developing energy from non-renewable sources like crude oil or from coal, so Repa let me give a big background historical background, so Repa's interest in acetylene started in 1928 in BSF and where he actually found a convenient method for handling acetylene because the accidents and the explosions were quite common at that point of time, and what this allowed was that it opened door to a large number of interrelated reactions, and all of them finally consolidated wise was termed as Repa chemistry, so Repa chemistry refers to a large number of compounds under different conditions which could all be obtained from the source apparent source of acetylene, and all of it together is what is known as the Repa synthesis or Repa chemistry, and of the several processes that were part of the Repa chemistry, the most important one is this discovery in 1939 of polyvinyl pylolidone or PVP which is a significant derivative in acetylene chemistry and has been synthesized using Repa method, so what this Repa synthesis did was opened door to a large number of rich chemistry many of which had industrial importance and hence was extremely useful for carrying out these reactions, so now let us just take a look at some of the interesting conversions which fall in the gamete of Repa synthesis, so for example reaction of acetylene with HCl and catalyst would give vinyl chloride, similarly the reaction with HCl and catalyst nickel phosphide whole 4 would give vinyl cyanide with carbon monoxide water in presence of iron catalyst FeCO5 would give this phenol with alkoxy group in the paraposition with ketone will give propazyl alcohol and then with hydrogen palladium catalyst will give allylic alcohol the reaction of acetylene with formaldehyde amine in presence of copper catalyst copper to Cu2 copper carbide would give this acetylene with N2 amine again with carbon monoxide water catalyst nickel bromide and copper iodide would give CH2CHCO2H with formaldehyde water and Cu2C2 copper iodide would give the reduced product when hydrogenated with carbon monoxide nickel catalyst and hydrogen would give the alcohol. So, what is amazing about this is that so many a different chemistry or so many different product is emerging out from this simple acetylene. So, as if acetylene has given away are open doors to the formation of so many different compounds starting from the same acetylide source. Another interesting thing to note is that all of these chemistry is catalyzed by transition metals and there are different metals for example that ranges from iron to mercury to nickel to palladium to copper nickel copper. So, what we see is that there are transition metals which are playing an important role in expanding this chemistry of acetylene to different specialty chemicals. So, obviously the role of metal which gives a flavor of organometallic chemistry and these have been catalyzed by various transition metals like iron, nickel, copper that successfully carry out or participate in this whole range of catalysis and all of these have been achieved using this acetylene which is explosive in nature. Now, we are going to look at another interesting correlation apart from the role of metals that we had observed which is the type of reactions that is mainly observed over here. Actually, repi chemistry has four types of reactions, mainly starting with vinylization. I will discuss in more details of reaction. One is vinylization of alcohol. So, what are vinylization reactions? The formations of vinyl chloride or vinyl cyanide or acid, these are examples of vinylization reactions. The second type of compound are reactions that are observed are ethylenation, catalytic y catalytic ethylenation of aldehydes or ketones. The example of these are the formation of these where the acetylene moiety is making alkenyl derivative. The third type of reactions are reactions with carbon monoxide, CO reactions, and they are part of the formations of products like these where the CO is forming. The fourth type of reactions are cyclo oligomerization. This also is an example of cyclo oligomerization reactions where like benzene moiety has been formed from this acetylene. There are more examples of cyclo oligomerization reactions whereby benzene derivatives can be synthesized from this acetylene. So, what we see is if you step back and look at the different utility that has emerged from lepy reaction is that tremendous amount of different functionalized chemicals which can be obtained through functionalization of acetylene have been achieved through rapid synthesis. The primary difficulty in carrying out this reaction had been unable to handle acetylene safely because acetylene is highly explosive and in presence of oxygen forms of fuel gas which we all of us know is extensively used as welding gas. So, being able to handle acetylene safely is the primary challenge which had been overcome by lepy and then having done that it opened over to a wide variety of different chemical reactions with different functionalized specialty chemicals that can be converted or obtained from acetylene. What is more important, we have seen that all of these require some sort of metal catalyst and they are where the organometallic chemistry comes into play and the metal catalysts that are used in repress synthesis are extremely important ones like iron, nickel, copper these are first flow transition metals very economic chip and they are the ones which carry out all these transitions. Secondly, if one sees that these are all organometallic catalysts also if one step backs and sees the type of compounds reactivity which has been obtained out of acetylene one can see that there are four types of reaction first is vinylization where you make the vinyl derivative from acetylides second is catalytic ethylization of aldehydes or ketone which is shown over here third is carbon monoxide reactions two three examples of the same is shown and last but not the least but very important outcome of lepy synthesis is cyclo-autogomerization where one can form benzene derivatives or even higher cyclo-octatetraene derivatives from acetylene through these oligocyclomerization reactions. So, I think this picture gives a capability or and capacity of rapid reaction and how this had been very important in making different chemicals about a century back and all how all of these were developed in industry about a century back. However, having said that the bottom line however is that acetylene is obtained from coal and again the coal is a non-renewable resource and in today's context at some point rather we have to move beyond non-renewable source of energy and hence we have to go beyond looking for alternatives for carrying out these reactions. But having said that these presents an exciting domain of chemistry exciting domain of organometallic compounds the utility of organometallic compounds in carrying out these synthesis in being able to convert acetylene to different chemicals and then use it for industrial good. So, with these I come to an end of today's lecture where we have looked at and important applications of organometallic compound particularly with respect to this repi chemistry which was solely developed in industry about a century back whereby acetylene was converted into several different important chemicals. So, the repi chemistry is important as mentioned earlier not only from the perspective of being able to convert acetylene to different feed stocks but also from the perspective of the fact that this has been an industrial contribution to the field of organometallic chemistry which also says highlights the importance of organometallic chemistry in the area of catalytic utility. So, in this particular reaction we have looked at today how repi was successful in designing repi glasses or the containers which can handle acetylene at very high pressure and overcome the challenge of explosion as well as ignition of handling acetylene and he did so by studying the ignition of acetylene under different conditions so as to come up with the solution to be able to handle acetylene at very high pressure. Now, the outcome of such a diligent study is open for all to see and here in this slide as has been rightly shown that acetylene can be converted to different feed stock using transition metal catalyst and all of these we have also observed in this lecture can be grouped into four kinds of reaction primarily namely the venylation of acetylene and then catalytic alkylation of aldehydes and ketones this is just an addition reaction venylation also is an addition reaction then cyclo oligomerization reaction and the reactions with carbon monoxide. So, we are going to take up these interesting examples in more details as we go through these applications of repi chemistry and their usage in industrial world in terms of developing some of the large scale industrial processes which has come out of the application of repi synthesis. So, more of these and some more developments of repi chemistry as we take up the topic in the lecture till then goodbye and I look forward to being you in the next lecture where we take up repi synthesis in a lot more details. Thank you.