 Welcome to this course on transition organometallics in catalysis and biology. We have been discussing about a very important reaction, which is called RAPAE synthesis, particularly that involves conversion of acetylene to various chemical functionalized feed stocks and was developed in early 1900 by Walter RAPAE. In the last lecture, we have looked into the context in which the RAPAE chemistry was developed and based on the need of the hour of looking for the application or utility of acetylene, which was produced from the coal as its major source, the RAPAE reaction became relevant. A great deal of developments in RAPAE chemistry had been performed or obtained under industrial conditions and that is why the RAPAE synthesis can be called as a gift of industry to the field of organometallic chemistry. Now this discussion that I have covered in the last lecture as well as part of what I will be covering now has been nicely reviewed in American Chemical Society ACS review article, which I am going to give the reference today for people to look up. The title is Catalytic reactions of acetylene feed stock for the chemical industry revisited. The reference is Chemical review 2014 114 1671 to 1782. This is a nice review, which discusses the importance of RAPAE chemistry not only at the time when it was developed, even the relevance of the development of RAPAE chemistry even under today's context. This is a beautiful review through which I have also covered in the last lecture and part of the present lecture and would request all the viewers of this course to look up if they want to read about the developments of RAPAE chemistry in much more details. Now what we had earlier also discussed that RAPAE chemistry involves a set of large number of reactions and the most common or the most important type of RAPAE reactions are vinylation reactions and what we had seen that in these vinylation reactions acetylene is converted to various vinyl derivatives and in our previous class we have discussed about how acetylene is converted to vinyl alcohol by reaction in presence of a base like potassium hydroxide as well as another example of vinylation which we had read about or spoken about in the last class was about reaction of acetylene with hydrogen cyanide Hc and in presence of catalyst giving a cryonitrile for the vinylation reaction. Another example of vinylation reaction which we are going to be taking up today is the reaction with HCl and this is called vinyl chloride. Now if you remember as I had said in my earlier class that there was a parallel development about accessing all of these products which were obtained through RAPAE using other methods particularly from that of the feedstocks from natural gas and crude oil which is ethylene. For example I had spoken about how focus of the industry shifted on conversion of acetylene to acetaldehyde in presence of water by reaction of water with acetylene in presence of acid and mercury plus to that of conversion of ethylene to acetaldehyde the same product acetaldehyde one obtained from acetaldehyde in rapid type chemistry the other obtained through Wacker oxidation which also is the industrial process developed for consumption or utilization of ethylene which are obtained as a product in petrochemical industry from natural oil and crude oil. Similar to the development for acetaldehyde which could also be obtained from acetylene and ethylene similar development also has been obtained from ethylene for the current purpose and the corresponding development is in presence of chlorine and oxygen it gives so this as I said is an interesting development whereby one could see that the same product was obtained from two different substrates one from acetaldehyde and another from ethylene as the time progressed and the focus shifted from utilizing ethylene source to that of utilizing olefin ethylene source to that of using acetylene source the focus shifted as a result the technology shifted the reaction shifted however the product obtained from both of these reactions remains the same. So this is a beautiful example where one can see that how chemistry accommodates different transformation from different sources to give the same product as per the need and the demand of the time. So this is a beautiful example another example we had also seen similarly acetaldehyde could be obtained from acetylene as well as could be obtained from ethylene and both have been developed technologically for large scale industrial productions. So we are continuing further on these vinylation reactions we are going to take up the reaction with carboxylic acids and the interesting thing about is that this also requires a metal catalyst and if ruthenium is used as the catalyst then the reaction proceeds at much milder conditions and with high selectivity ruthenium is used the reaction proceeds under milder conditions with high regioselectivity I will explain this with this example R1 COOH reacting with R2 CH it is a terminal acetylene in presence of ruthenium as a catalyst more milder conditions about 60 to 80 degree centigrade resulting in two product R1 O R2 plus R1 R2. So one can see that two different kinds of olefinic bonds are here where O and R2 are trans we designate these as A and B and with ruthenium being the catalyst the selectivity is primarily A and which is formed about 93 to 99 percent. So what we see is that ruthenium brings in great amount of selectivity in the formation of these two compounds and also ruthenium brings in these milder reaction conditions in which this reaction proceeds. So we are going to move on to see another very interesting synthesis of acrylic acid using the RAPI method and this involves hydrocarboxylation. What is the meaning of hydrocarboxylation? It means that simultaneous addition of Hx as well as CO and this is given by the reaction in presence of catalyst to give this acrylic acid. Now as mentioned earlier in case of vinyl cyanide as vinyl chloride, acrylic acid 2 is an important monomer for variety of polymerization processes and hence is of great demand in the industry. Here one can see the best catalyst user homoleptic as well as heterolative iron carbonyl complexes. So like metal carbonyl complexes like cobalt tetra carbonyl hydride nickel tetra carbonyl or iron pentacarbonyl are extremely good catalyst for these synthesis. Now one should or may argue that how come these are behaving as a catalyst because all of these complexes are both electronically saturated as well as co-ordinatively saturated. Now we had an elaborate discussion on electronic saturation and co-ordinate saturation in our previous course where we said that prerequisite for behaving as a catalyst is the requirement of electronic unsaturation as well as co-ordinate unsaturation. Now if one were to look at all of these complexes one would see that they have 18 valence electron counts and also have about 4 or 5 coordination number. So what does that mean tell us that these are not the real catalyst but most likely are the precatalyst for the reaction. What is it mean is that they lose carbon monoxide one or two of them to become electronically as well as co-ordinatively unsaturated when they participate in the catalytic cycle as the active catalytic species for carrying out this transformation. So we see that these complexes metal carbonyl complexes like cobalt hydride tetra carbonyl, nickel tetra carbonyl and iron pentacarbonyl are very good catalyst for converting acetylene to acrylic acids and using these methods acrylates can also be made from acetylene, CO and alcohol using this method acrylates can be obtained from acetylene, CO and alcohol. So what it says that this method is very common a generic one where one can replace water with alcohol and in presence of forming acrylic acid one can also form acrylates acrylic ester using the same method. So these further highlights the versatility of this transformation that we just spoke about. Now we would like to give an example of how this reaction proceeds in terms of the catalytic cycle. As mentioned earlier that nickel tetra carbonyl is both electronically as well as co-ordinatively saturated because it has 18 valence electrons. So when it reacts with Hx let us say for this hydrocarboxylation prior to that it loses 2 CO and Hx undergoes oxidative addition to give 8 ni CO2x. So as is common for oxidative addition one can see that the oxidant state of nickel has gone from nickel 0 to nickel 2 by the addition of these Hx. Now once this is formed then the acetylene reaction takes place with this species and the nickel hydride at across the acetylene giving this vinyl bound nickel species which is drawn over here. Now once this is formed one of the CO which is liberated comes in and undergoes an insertion into the nickel carbonyl bond. This is what is called migratory insertion to give this compound and then subsequent reaction with alcohol gives the vinyl ester would give back the initial starting catalyst that one started off with. This is a good monomer for acrylic acid or polyacrylate. So this is a polymer polyacrylate and they can be obtained by polymerizing this monomer or acrylate esters. What we see is here is a nice demonstration of hydrocarboxylation which had resulted in production of acrylic esters and they are important feedstock for polyacrylates or the polymer. These again highlights the importance of lepe chemistry in terms of producing this important monomer through a large scale industrial process and by which also utilizing acetylene as one of the sources of feedstock from to produce the monomer acrylates and then they are also used for another industrial process of polymerization giving polyacrylates. With that we had come into discussing the end of the vinylation reactions that are used for making the vinyl derivatives which can be halide, ester, acid and the cyanides from acetylene feedstock. Then we move on to another interesting topic which is in lepe reaction or lepe chemistry another set of reaction which are called ethyl ethyylation reactions. This reaction involves addition of acetylene and its removable protons carbonyl group and these are similar to one-two addition and employs copper for this chemistry. So, you have to see to water 80 to 100 degree centigrade 2 to 6 bar pressure produces CH2OH that reacts with aldehyde to give CH2OH and that in presence of hydrogen and raninical produces 1,4 butane diol. So, these are important demonstration of how acetylene can be used to convert, can be used to undergo this ethylene reaction like this acetylide CH adding across this CO group and giving CH2OH and then another reaction over at that other end to giving 2 CH2OH and that under reduction giving this 1,4 butane diol. So, in the current examples the addition of the addition of alkenyl CH across one CO group as well as the second CH across the second CO group resulting in CH2OH, CH2OH which under reduction give important intermediate 1,4 butane diol. So, with these we come to an end of today's lecture in this we have looked into the various types of reactions of lepe chemistry particularly with regard to the vinylization reactions in which the acetylene moiety has been reacted with various kinds of reagent like HCl, HCl, Acid esters to give various kinds of vinyl acid cyanide esters acrylates. We have also looked into the mechanism in which how acrylates esters were obtained from reaction of acetylene carbon monoxide and Hx. These are called hydrocarboxylation reaction and then with that we had come to an end of vinylation reactions and then in the end we have looked into another new type of reaction of lepe chemistry which are called ethylenation reaction that involves the reaction of acetylene with the carbonyl group and which also resulted finally to the conversion of 1,4 propane diol. So, with these we come to our current discussion on lepe chemistry in today's class. We are going to be looking into some more important applications of lepe reaction, lepe chemistry as we take up in the next class. I hope you have enjoyed the content which has been discussed today in this with regard to lepe chemistry. We look forward to some more exciting reactions and developments on lepe reactions as we cover the topic in bit more detail in the next class. Till then, goodbye and see you in the next class.