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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.
In catalytic converters used on automobiles, the combustion of leaded gasoline produces elemental lead, lead(II) oxide, lead(II) chloride, and lead(II) bromide. Lead alloys with the metals present in the catalyst, while lead oxides and halides coat the catalyst's surfaces, reducing the converter's ability to reduce NOx emissions.
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 Mortreux system consists of molybdenum hexacarbonyl resorcinol catalyst system. The phenyl and p-methylphenyl substituents on the alkyne group are scrambled. Metal-catalyzed alkyne metathesis was first described in 1968 by Bailey, et al. The Bailey system utilized a mixture of tungsten and silicon oxides at temperatures as high as 450 °C.
Homogeneous catalysts are also used in asymmetric synthesis by the hydrogenation of prochiral substrates. An early demonstration of this approach was the Rh-catalyzed hydrogenation of enamides as precursors to the drug L-DOPA. [10] To achieve asymmetric reduction, these catalyst are made chiral by use of chiral diphosphine ligands. [11]
Phenylacetylene is a prototypical terminal acetylene, undergoing many reactions expected of that functional group. 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]
Drug withdrawal, drug withdrawal syndrome, or substance withdrawal syndrome [1] is the group of symptoms that occur upon the abrupt discontinuation or decrease in the intake of pharmaceutical or recreational drugs. In order for the symptoms of withdrawal to occur, one must have first developed a form of drug dependence.
Clomethiazole is particularly toxic and dangerous if overdosed and is potentially fatal. Alcohol multiplies the effect. As the drug can be fatal in high doses, prescribing clomethiazole outside of a controlled environment, for example a hospital, is not recommended, especially because there are much less toxic alternatives, such as diazepam.