Catalytic hydrogenation Rosenmund reduction

The name Rosenmund reduction is used for the catalytic hydrogenation of an acyl chloride 1 to yield an aldehyde 2. 

The scope of catalytic hydrogenations continues to be extended to more difficult reductions. For example, a notoriously difficult reduction in organic synthesis is the direct conversion of carboxylic acids to the corresponding aldehydes. It is usually performed indirectly via conversion to the corresponding acid chloride and Rosenmund reduction of the latter over Pd/BaS04 [65]. Rhone-Poulenc [30] and Mitsubishi [66] have developed methods for the direct hydrogenation of aromatic, aliphatic and unsaturated carboxylic acids to the corresponding aldehydes, over a Ru/Sn alloy and zirconia or chromia catalysts, respectively, in the vapor phase (Fig. 1.18). 

Rosenmund reduction , i.e. catalytic hydrogenation, of acid chlorides with poisoned Pd-BaS04 (in the presence of sulfur and quinoline poison) afforded aldehyde. 

Reduction of acid chlorides to aldehydes One of the most useful synthetic transformations in organic synthesis is the conversion of an acid chloride to the corresponding aldehyde without over-reduction to the alcohol. Until recently, this type of selective reduction was difficult to accomplish and was most frequently effected by catalytic hydrogenation (the Rosenmund reduction section 6.4.1). However, in the past few years, several novel reducing agents have been developed to accomplish the desired transformation. Among the reagents that are available for the partial reduction of acyl chlorides to aldehydes are bis(triphenylphosphine)cuprous borohydride , sodium or lithium tri-terf-butoxyaluminium hydride, complex copper cyanotrihydridoborate salts °, anionic iron carbonyl complexes and tri-n-butyltin hydride in the presence of tetrakis(triphenylphosphine)palladium(0). ... 

The synthesis of aldehydes by the Sommclet reaction, the Rosenmund reduction and the Stephens reaction all involve the conversion of a group already present in the molecule. The Rosenmund reduction (Scheme 6.7) is the catalytic hydrogenation of a benzoyl chloride in the presence of a catalyst poison, quinoline/sulfur, which prevents over-reduction to the alcohol. In the Stephens reaction (Scheme 6.7), a nitrile group is reduced by tin(II) chloride and hydrochloric acid to an imine salt, which is then hydrolysed. 

Catalytic hydrogenation is often chosen as a method for reduction because of its chemoselectivity for C=C double bonds and benzylic C-X bonds over C=0 groups. The most important hydrogenation involving a carbonyl compound is not actually a reduction of the C=0 double bond. Hydrogenation of acyl chlorides gives aldehydes in a reaction known as the Rosenmund reaction—really a hydrogenolysis of a C-Cl bond. 

Rosenmund reduction. Catalytic reduction of acid chlorides to aldehydes. To prevent further hydrogenation, a poison is added to the catalyst. 

The use of both types of modifier to influence the selectivity of heterogeneous catalysts is not new. It has long been known, for example, that modifiers can have a powerful selectivity-enhancing effect in catalytic hydrogenation the Rosenmund reduction of acid chlorides to aldehydes is an early example of this. Another well-known modifier effect is rate and selectivity enhancement by bismuth in precious metal-catalyzed oxidations (Section 9.3). We feel, however, that the enormous po-... 

Reduction of carboxylic acids to aldehydes Replacement of the Rosenmund reaction (conversion of carboxylic acids to acid chlorides followed by catalytic hydrogenation) or the reaction of Grignard reagents with formic esters by molecular hydrogen and heterogeneous catalysts (Ru3Sn7 alloy). 

Acid chlorides can be reduced by catalytic hydrogenation to give an aldehyde in what is called the Rosenmund reduction. Nitriles are reduced by catalytic hydrogenation to a primary amine. 

In the presence of a transition metal catalyst, hydrogen gas converts a ketone or aldehyde to an alcohol 14,15,16,17,37,43,44 46. Acid chlorides can be reduced by catalytic hydrogenation to give an aldehyde in what is called the Rosenmund reduction. Nitriles are reduced by catalytic hydrogenation to a primary amine 18,19, 20, 37. 

Acid chlorides can be reduced to aldehydes either by catalytic hydrogenation or by reaction with a metal hydride. In both cases, the reagent and the reaction conditions are selected to avoid the further reduction of the aldehyde. The conversion of an acid chloride to an aldehyde can be carried out by the Rosenmund reduction, which uses hydrogen gas and a modified palladium catalyst. The palladium catalyst is altered to prevent further reduction of the aldehyde. To prepare the catalyst, the palladium is treated with quinoline, an aromatic heterocyclic amine, and is heated with sulfhr. 

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