Pd/CaCO

Substances that have been hydrogenated in slurry reactors include nitrobenzene with Pd-C, butynediol with Pd-CaCO,3, chlorobenzene with Pt-C, toluene with Raney Ni, and acetone with Raney Ni. 

The selecdve reducdon of4-nitrosteroid to the conespondmg aminosteroidhas been carried out by Pd/CaCO- and quinolme f5 mol wt%) under atmosphere fEq 6 56 This is the first... 

Dibromo-5,6,7,8-tetrafluoroquinoxaline (187) gave 5,6,7,8-tetrafluoroqui-noxaline (186) [H2, Pd/CaCOs (deactivated. Lindlar s catalyst), EtsN CH2CI2, 3 days 44%] or 5,6,7,8-tetrafluoro-l,2,3,4-tetrahydroquinoxaline (188) (H2, Pd/C, EtsN, CH2CI2, 2.5 days >95%) note the selective dehalogenation in both procedures. ... 

Triple bonds can be reduced, either by catalytic hydrogenation or by the other methods mentioned in the following two sections. The comparative reactivity of triple and double bonds depends on the catalyst. With most catalysts, (e.g., Pd) triple bonds are hydrogenated more easily, and therefore it is possible to add just 1 mol of hydrogen and reduce a triple bond to a double bond (usually a stereoselective syn addition) or to reduce a triple bond without affecting a double bond present in the same molecule. A particularly good catalyst for this purpose is the Lindlar catalyst (Pd-CaCOs—PbO). An alternative catalyst used for selective hydrogena-... 

Scheme 64, Reaction conditions i, PhCH=CH2, Pd(PPli3)4, CH3COOK ii, Phr==rT4 Pd(PPh3)4, CH3COOK iii, Hj/Pd-CaCO, iv, LiAlH4.

Scheme 8.5 i, nBuLi ii, Pd-CaCOs, quinoline iii, BU4NF, THF iv, UAIH4, diglyme v, amberlyst 15, MeOH vi, TsCI, pyridine vii, TSNH2, NBU4NI, NaOH, PhH-H20 viii, Na, naphthalene ix, 118, DPPA, DMF x, UAIH4, THF. 

MnCli-modified catalyst. The selectivity and reproducibility of Lindlar catalyst (Pd/CaCO,/PbO) can be improved by doping with various salts, such as CdCL, SnCL, NiCL, and particularly MnCL. A secondary poison such as quinoline is still essential for satisfactory selectivity. 

Hydrogen adds exclusively to the terminal triple bond of monosubstituted conjugated diynes but the initially formed enynes react rapidly with hydrogen, and even from the beginning, products of over-hydrogenation appear - . After the absorption of one mole of hydrogen by 1,3-pentadiyne in the presence of Pd(CaCOs), the product contains 67% l-penten-3-yne. No products have been detected which correspond to the initial addition of hydrogen to the internal triple bond. 

Substituted gibberellins, such as la- and ip-hydroxy GA5 and GA20 were prepared from a single enone precursor by 1,2-reduction with NaBH4 (Scheme 28). Conversely, catalytic hydrogenation of the same enone with 10% Pd/CaCOs in pyridine afforded the 1,4-reduction product, I-OXO-GA20. ... 

Catalyst poisoning by sulfur has discouraged development of procedures for cleavage of sulfides. Desulfurization of highly activated allylic methyl sulfides can be effected by addition of lead to the palla-dium(O) catalyst. In the presence of various tertiary amines satisfactory cleavage of several related allyl sulfides has been utilized (equation 12) using a modified Pd/CaCOs catalyst. 

---