Palladium - barium sulphate catalyst

The palladium - barium sulphate catalyst Is prepared by treating a suspension of20g. of barium sulphate (which has been precipitated in hot solution) in 400 ml. of hot water with a solution of I - 7 g. of palladium chloride (equivalent to I - 0 g. of palladium) in 50 ml. of water and with I - 5 ml. of 40 per cent, formaldehyde solution. The mixture is rendered faintly alkaline to litmus by the addition of sodium hydroxide solution and then boiled for a short time. When the supernatant liquid is clear, the grey precipitate is filtered oS, and wa.shed with hot water until the... 

For use in the Rosenmund reduction (Expt 6.120) the catalyst is moderated by the addition of the appropriate quantity of a quinoline-sulphur poison prepared in the following manner. Heat under reflux 1 g of sulphur with 6g of quinoline for 5 hours and dilute the resulting brown liquid to 70 ml with xylene which has been purified by distillation over anhydrous aluminium chloride. Thiourea (about 20% by weight of the palladium-barium sulphate catalyst) may also be used as a catalyst poison. 

Fit a 250-ml three-necked flask with a reflux condenser, a high-speed sealed stirrer (1) and a gas inlet tube extending to a point just above the bottom of the stirrer. Place 28.5 g (0.15 mol) of 2-naphthoyl chloride (Expt 6.161), 100 ml of sodium-dried xylene, 3 g of palladium-barium sulphate catalyst and 0.3 ml of the stock poison solution (Section 4.2.54, p. 452) in the flask. Connect the top of the condenser by a rubber tube to a 6-mm glass tube extending to the bottom of a 250-ml conical flask containing 200 ml of distilled water and a few drops of phenolphthalein indicator arrange a burette charged with c. 1m sodium hydroxide solution (prepared from the pure solid) for delivery into the flask. The apparatus must be sited in the fume cupboard. 

It has been stated that thiourea (about 20 per cent, of the weight of the palladium - barium sulphate) may also be used as a catalyst poison. 

The title compounds LTB4, 21 (Z) and 22 (Z), have been synthesized23 by stereoselective reduction with deuterium gas of a 1 1 mixture of the suitable diacetylenic precursors 23 and 24 using Lindlar catalyst or palladium on barium sulphate catalyst (equation 10). Leukotriene B4, a 5-lipoxygenase metabolite of arachidonic acid, playing... 

D, Palladium on barium sulphate catalyst (5 per cent. Pd). (4) Prepare a solution of 4-1 g. of anhydrous palladium chloride (1) in 10 ml. of concentrated hydrochloric acid and 25 ml. of water (as in A). Add all at once 60 ml. of 6.sulphuric acid to a rapidly stirred, hot (80°) solution of 63-1 g. of A.R. crystallised barium hydroxide in 600 ml. of water contained in a 2-litre beaker. Add more 6.sulphuric acid to render the suspension just acid to litmus (5). Introduce the palladium chloride solution and 4 ml. of 37 per cent, formaldehyde solution into the hot mechanically-stirred suspension of barium sulphate. Render the suspension slightly alkaline with 30 per cent, sodium hydroxide solution, continue the stirring for 5 minutes longer, and allow the catalyst to settle. Decant the clear supernatant liquid, replace it by water and resuspend the catalyst. Wash the catalyst by decantation 8-10 times and then collect it on a medium - porosity sintered glass funnel, wash it with five 25 ml. portions of water and suck as dry as possible. Dry the funnel and contents at 80°, powder the catalyst (48 g.), and store it in a tightly-stoppered bottle. 

Rosenmund reduction The reduction of an acyl chloride to an aldehyde by hydrogenation using a palladium on barium sulphate catalyst. 

From acid chlorides by selective hydrogenation in the presence of a catalyst (palladium deposited upon a carrier, which is usually barium sulphate but is... 

The palladium may be recovered by heating the spent catalyst to redness in order to remove organic impurities this treatment may reduce some of the barium sulphate to barium sulphide, which acts as a catalytic poison. The palladium is then dissolved out with aqua regia and the solution evaporated the residue is dissolved in hot water and hydrochloric acid to form palladium chloride. 

Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund reduction. 

Preparation of cis-alkenes Lindlar s catalyst, which is also known as poisoned catalyst, consists of barium sulphate, palladium and quinoline, and is used in selective and partial hydrogenation of alkynes to produce c/s-alkenes. Hydrogen atoms are delivered simultaneously to the same side of the alkyne, resulting in syn addition (cw-alkenes). Thus, the syn addition of alkyne follows same procedure as the catalytic hydrogenation of alkyne. 

Platinum in a finely divided form is obtained by the in situ reduction of hydrated platinum dioxide (Adams catalyst) finely divided platinum may also be used supported on an inert carrier such as decolourising carbon. Finely divided palladium prepared by reduction of the chloride is usually referred to as palladium black. More active catalysts are obtained however when the palladium is deposited on decolourising carbon, barium or calcium carbonate, or barium sulphate. Finely divided ruthenium and rhodium, usually supported on decolourising carbon or alumina, may with advantage be used in place of platinum or palladium for some hydrogenation reactions. 

Where it is advantageous to maintain the neutrality of the hydrogenation mixture, palladium on barium carbonate catalyst is recommended. For the preparation of this catalyst the experimental details noted above for the barium sulphate based catalyst are used, but the barium hydroxide and sulphuric acid are replaced by 46.5 g of precipitated barium carbonate and the volume of hydrochloric acid is reduced to 4.1 ml. 

With most hydrogenation catalysts of the platinum and nickel groups (Sections 4.2.61, p. 459 and 4.2.50, p. 450), a mixture of products is obtained even if an attempt is made to stop the reaction at the half-way stage. An alkene may only be obtained in good yield if particular attention is paid to the selection of a deactivated hydrogenation catalyst. An early, highly effective formulation of a deactivated palladium catalyst is Lindlar s catalyst (Section 4.2.54, p. 453), but palladium-on-barium sulphate in the presence of quinoline, or palladium-on-calcium carbonate, is also recommended. In these cases it is advisable to... 

Acid chlorides can be selectively hydrogenated in the presence of a catalyst (palladium deposited on a carrier, which is usually barium sulphate but is occasionally charcoal). The reaction, which involves the hydrogenolysis of the carbon-halogen bond, is known as the Rosenmund reduction and has been widely used for the synthesis of aromatic and heterocyclic aldehydes. 

---