Search results
Results from the WOW.Com Content Network
A Lindlar catalyst is a heterogeneous catalyst consisting of palladium deposited on calcium carbonate or barium sulfate then poisoned with various forms of lead or sulfur. It is used for the hydrogenation of alkynes to alkenes (i.e. without further reduction into alkanes). It is named after its inventor Herbert Lindlar, who discovered it in 1952.
The United States Drug Enforcement Administration (DEA) maintains lists regarding the classification of illicit drugs (see DEA Schedules).It also maintains List I of chemicals and List II of chemicals, which contain chemicals that are used to manufacture the controlled substances/illicit drugs.
Common catalysts used are tungsten and molybdenum sulfide. Adding cobalt and nickel [8] to either edges or partially incorporating them into the crystal lattice structure can improve the catalyst's efficiency. The synthesis of the catalyst creates a supported hybrid that prevents poisoning of the cobalt nuclei.
In many cases, highly empirical modifications involve selective "poisons". Thus, a carefully chosen catalyst can be used to hydrogenate some functional groups without affecting others, such as the hydrogenation of alkenes without touching aromatic rings, or the selective hydrogenation of alkynes to alkenes using Lindlar's catalyst.
Herbert Lindlar-Wilson (15 March 1909 – 27 June 2009), better known as Herbert Lindlar, was a British-Swiss chemist. He is known in particular through the development of his catalyst for hydrogenation , as the Lindlar catalyst bears his name.
The so-called "canopy catalysts" containing tripodal ligands are particularly active and easy to prepare. [7] [8] Thorough experimental and computational studies showed that metallatetrahedranes were isolable but dynamic species within the catalytic cycle. [9] Alkyne metathesis catalyst have also been developed using rhenium(V) complexes. [10]
To absorb hydrogen, the dehydrated form of LOHC (an unsaturated, mostly aromatic compound) reacts with the hydrogen in a hydrogenation reaction. The hydrogenation is an exothermic reaction and is carried out at elevated pressures (approx. 30-50 bar) and temperatures of approx. 150-200°C in the presence of a catalyst.
It undergoes semihydrogenation over Lindlar catalyst to give styrene. In the presence of base and copper(II) salts, it undergoes oxidative coupling to give diphenylbutadiyne. [6] In the presence of metal catalysts, it undergoes oligomerization, trimerization, and even polymerization. [7] [8]