Rosenmund Reduction Mechanism

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Karl Wilhelm Rosenmund 

CBSE Class 12 Chemistry syllabus includes many name reactions, Rosenmund Reaction is one of them. It is an important reaction. It involves the hydrogenation of acyl chloride. Rosennmund reduction reaction was given by Karl Rosenmund in 1918, so the reaction is named after him. As the name suggests, it involves reduction of acyl chloride by addition of hydrogen atom. Palladium on barium sulphate surface is used as catalyst in rosenmund reduction reaction. Which is also known as rosenmund catalyst. 

Rosenmund Reduction Reaction 

In Rosenmund Reaction, acyl chloride is hydrogenated to get reduced into aldehyde and palladium-barium sulphate is used as catalyst. It is a reduction reaction involves addition of hydrogen. 

Rosenmund Reaction can be written as follows –

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Acyl Chloride                                                                                      Alkyl Aldehyde 

R can be an alkyl or aryl group in the above reaction. 

Examples of Rosenmund Reduction Reaction – 

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Rosenmund Catalyst 

As we have discussed above, Palladium on barium sulphate is called rosenmund catalyst. Use of palladium induces the reduction process while use of barium sulphate reduces the activity of palladium as barium sulphate has low surface area, thus prevents the over reduction. Over reduction should be stopped for the desired product which is aldehyde in this reaction. If over reduction takes place, then aldehyde converts into alcohol which would the react with remaining acyl chloride and form ester. To prevent further hydrogenation, catalyst is mixed with poison. 

Rosenmund catalyst is prepared by reduction of palladium (II) chloride solution in the presence of barium sulphate. 

Rosenmund Reduction Reaction Mechanism 

1. Preparation of Acyl Chloride From an Acid –

(Image to be added soon) SOCl2 or PCl3or PCl5    (Image to be added soon)

Carboxylic Acid                Acyl Chloride 

2. Preparation of Aldehyde – 

We use a poisoned rosenmund catalyst to get the desired product which is aldehyde. So, we use palladium with barium sulphate. 

(Image to be added soon)         Pd-BaSO4 (partial hydrogenation)        (Image to be added soon) + HCl   

If we don’t use poisoned palladium then reaction will take place as follows – 

(Image to be added soon) Pd(non poisoned catalyst)  (Image to be added soon)        Pd  (Image to be added soon)                                                                                                          (Image to be added soon)

In this condition we get ester in place of aldehyde. 

Applications of Rosenmund Reduction Reaction          

1.Rosenmund reduction reaction is used for the production of aldehydes.     

2. It is used for the production of saturated fatty aldehydes. 

3. It is used for the production of alkyl or aryl aldehydes. 

Limitation of Rosenmund Reaction 

We can prepare many aldehydes by Rosenmund Reduction Reactions but formaldehydes cannot be prepared. As formyl chloride is unstable at room temperature. 

Rosenmund reduction reaction is one of the important name reactions of CBSE Class 12 Chemistry for your final board examinations. You need to practice twice all the name reactions to score high marks in the examination. We at Vedantu have provided “Important Chemical Reactions of Class 12 Chemistry” page also for you so that you can score maximum. You can also find similar articles on other name reactions such as diazotization reaction, hofmann elimination reaction, Friedel crafts reaction etc. at Vedantu.