Lindlar catalyst preparation

The product i n this case is a cis-disubstituted alkene, so the fi rst question is, " What is an immediate precursor of a cis-disubstituted alkene " We know that an alkene can be prepared from an alkyne by reduction and that the right choice of experimental conditions will allow us to prepare either a trans-disubstituted alkene (using lithium in liquid ammonia) ora cis-disubstituted alkene (using catalytic hydrogenation over the Lindlar catalyst). Thus, reduction of 2-hexyne by catalytic hydrogenation using the Lindlar catalyst should yield cis-2-hexene. 

The used Pd/ACF catalyst shows a higher selectivity than the fresh Lindlar catalyst, for example, 94 1% versus 89 + 2%, respectively, at 90% conversion. The higher yield of 1-hexene is 87 + 2% with the used catalyst versus 82 + 3% of the Lindlar in a 1.3-fold shorter reaction time. Higher catalyst activity and selectivity is attributed to Pd size and monodispersity. Alkynes hydrogenation is structure-sensitive. The highest catalytic activity and alkene selectivity are observed with Pd dispersions <20% [26]. This indicates the importance of the Pd size control during the catalyst preparation. This can be achieved via the modified ME technique. 

Warren and associates (18) have prepared a glycosyl azide derivative (15) of a heptasaccharide. This glycosyl azide was obtained from O-a-D-manno-pyranosyl-( 1 — 6)-0-[a-D-mannopyranosyl-( 1 — 3)-(9-a-D-mannopyrano syl-(l— 6)-0-a-D - mannopyranosyl - (1 — 3)] - O-fi- d - mannopyranosyl -(1 — 4) - O - (2 - acetamido - 2 - deoxy-/ -d-glucopyranosyl) - (1 — 4) - 2 -acetamido-2-deoxy-D-glucopyranose (12) by treatment of its peracetylated derivative 13 with trimethylsilyl trifuoromethanesulfonate, followed by reaction of the intermediary oxazoline 14 with trimethylsilyl azide. Reduction of the glycosyl azide 15 in the presence of Lindlar catalyst gave the glycosyla-mine derivative 16. The condensation of 16 with 1-tert-butyl N-(9-fluoren-... 

The compound of formula (5) is next subjected to selective hydrogenation to convert the acetylenic bond to an ethylenic bond. This can be readily accomplished by a number of different catalysts, such as a nickel catalyst prepared from a nickel salt and NaBFi4, Lindlar catalyst, or 5% palladium on barium sulfate in the presence of qunioline. The reaction was run at one atmosphere. Analyses by nuclear magnetic resonance and vapor phase chromatography showed the correct structure in good quantity. The product obtained was 3,7,ll,15-tetramethylhexadeca-2,5-dien-l-acetate (6), a C2o dienolacetate. 

Bombykol was for the first time prepared by Butenandt using the Wittig reaction of 2-hexynylidene-triphenylphosphorane with 9-formylnonanoic ester. The resulting (Z)- resp. ( )-10-hexadecen-12-ynoic acid esters were resolved by urea, the ( )-isomer hydrogenized with Lindlar catalyst and reduced with lithium aluminium hydride. Further purification via the urea inclusion compound and low-temperature crystallization gave (10F,12Z)-10,12-hexadecadien- l-ol 186,187). 

Palladium metal is too active a catalyst to allow the hydrogenation of an alkyne to stop after one equivalent of H2. To prepare a cis alkene from an alkyne and H2, a less active Pd catalyst is used— Pd adsorbed onto CaC03 with added lead(II) acetate and quinoline. This catalyst is called the Lindlar catalyst after the chemist who first prepared it. Compared to Pd metal, the Lindlar catalyst is deactivated or poisoned. ... 

The reactions involving the generation of acetylenic bonds or extension of unsaturated bonds are extremely useful in chemical synthesis of unsaturated alcohols, carboxylic acids, and poly-yne acetals [Eq. (47) 125]. For the preparation of essential fatty acids, extension of propargyl units, followed by hydrogenation in the presence of Lindlar catalyst, will result in the efficient formation of ail c/x-type fatty acids [Eqs. (48) and (49) 126,127]. 

W. Kitdiing, Z, Rappoport, S. Winstein, and W. G. Young,v4m. Soc., 88,2054 (1966) Palladium catalysts, see also Lindlar catalyst. Engelhard Industries supplies 5% palladium catalyst on C, Al, AljOa, BaCOa, BaS04, or CaCOj also pelleted, granular catalysts, and unsupported palladium oxide and palladium black. MacKay supplies 10% Pd-C catalyst Mozingo describes the preparation of four catalysts ... 

Reaction of 2-chloro-l,l-dicyclopropylethene (35, prepared from dicyclopropyl ketone by chloroolefination) with butyllithium in tetrahydrofuran between — 110°C and + 20 °C affords dicyclopropylethyne (36) in 83% yield together with some 1,1-dicyclopropylhex-l-ene (37,10% yield). Hydrogenation of 36 over a Lindlar catalyst proceeded almost quantitatively and stereospecifically to give (Z)-l,2-dicyclopropylethene (38). 

The first racemic synthesis of fosfomycin is based on the epoxidation of ( ) (Z)-l-propenylphosphonic acid (Scheme 4.24). The reaction was effectively achieved using an excess of H2O2 (30% solution) at 60°C in the presence of Na2WO4 as catalyst (2%) at pH 5.5. The (Z)-l-prope-nylphosphonic acid was prepared by stereospecific hydrogenation, with Lindlar catalyst, of dibutyl 1-propynylphosphonate into dibutyl (Z)-l -propenylphosphonate, followed by hydrolysis of the ester functions with concentrated HCl. The resolution of the racemic ( ) (Z)-l,2-epoxypropylphosphonic acid to fosfomycin was accomplished by way of optically active amines, a-phenylethylamine, or quinine. ... 

Methylhept-2-en-6-one, usually referred to simply as methylhep-tenone, is a useful synthon for the total synthesis of terpenes. One early synthesis of this intermediate employed the Carroll reaction, the substrate for which is prepared by the addition of acetylene to acetone and subsequent partial hydrogenation to 2-methylbut-3-en-2-ol, as shown in Scheme 4.5. Addition of acetylene to methylheptenone gives dehydrolinalool, which can be hydrogenated to linalool using a Lindlar catalyst. 

Controlled hydrogenation, in a study of the controlled hydrogenation of acetylenes to r/.s-olcfins. Cram and Allinger38 found palladium on barium sulfate with a trace of pure quinoline (synthetic) to be superior to the Lindlar catalyst in reproducibility and ease of preparation (a sample of quinoline from coal tar was found to be unsuitable for this purpose). In one example 19.2 g of dimethyl 5-decynedioate (1) was hydrogenated with use of 0.4 g. of 5% palladium on barium sulfate and 0.4 g. of synthetic quinoline in 100 ml. of methanol. The mildly exothermal reaction ceased abruptly after 20 min., with absorption of exactly one equivalent of hydrogen. 

Alkenes can also be prepared using the Wittig reaction (see Section 8.3.4.3), and Z-alkenes can be prepared by the hydrogenation of alkynes in the presence of a Lindlar catalyst (see Section 6.3.2.4). 

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