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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.
2-Butyne (dimethylacetylene, crotonylene or but-2-yne) is an alkyne with chemical formula CH 3 C≡CCH 3. Produced artificially, it is a colorless, volatile, pungent liquid at standard temperature and pressure .
An important driving force for this type of reaction is the expulsion of small gaseous molecules such as acetylene or but-2-yne. The same two-step procedure was used in the synthesis of the naturally occurring cyclophane turriane. Trisamidomolybdenum(VI) alkylidyne complexes catalyze alkyne metathesis. [12]
If the catalyst and reaction conditions are indicative of low effectiveness, selective poisoning may be observed, where poisoning of only a small fraction of the catalyst's surface gives a disproportionately large drop in activity. [4] If η is the effectiveness factor of the poisoned surface and h p is the Thiele modulus for the poisoned case:
Steps in the hydrogenation of a C=C double bond at a catalyst surface, for example Ni or Pt : (1) The reactants are adsorbed on the catalyst surface and H 2 dissociates. (2) An H atom bonds to one C atom. The other C atom is still attached to the surface. (3) A second C atom bonds to an H atom. The molecule leaves the surface.
The C≡C bond distance of 118 picometers (for C 2 H 2) is much shorter than the C=C distance in alkenes (132 pm, for C 2 H 4) or the C–C bond in alkanes (153 pm). [ 3 ] Illustrative alkynes: a , acetylene, b , two depictions of propyne, c , 1-butyne, d , 2-butyne , e , the naturally occurring 1-phenylhepta-1,3,5-triyne, and f , the strained ...
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]
Hydrogenation of imines is complicated by both syn/anti isomerization and tautomerization to enamines, which may be hydrogenated with low enantioselectivity in the presence of a chiral catalyst. [3] Additionally, the substituent attached to nitrogen affects both the reactivity and spatial properties of the imine, complicating the development of ...