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what are the steps for the convertion of 2,4 dinitro phenyl hydrazine to propane?

what are the steps for the convertion of 2,4 dinitro phenyl hydrazine to propane?

Grade:12th pass

1 Answers

dolly bhatia
54 Points
5 years ago
A solution of 2,4-dinitrophenylhydrazine is added to test tubes containing 2-propanol, an alcohol; 2-propanone (acetone), a ketone and propionic acid-a carboxylic acid. 2,4-dinitrophenylhydrazine only reacts with carbonyl group of 2-propanone, forming orange precipitate.
 
 
Another test can distinguish between aldehydes and ketones. Silver Mirror Tollens Test for aldehydes:
Tollens reagent is an aqueous solution of silver nitrate, sodium hydroxide and a little ammonia. If an aldehyde, in this case, glucose is added to solution, silver ion is reduced by aldehyde and aldehyde is oxidized into a carboxylic acid. This produces silver metal, which coats flask and creates the mirror. Similar reaction does not occur for ketones, so only aldehydes produce the silver mirror. Equation for the reaction is:
 
 
Endings al and one signify aldehyde and ketone. General formula for an aldehyde is R-CHO while for a ketone, it is R-COR’. Every ketone is isomeric with at least one aldehyde. Acetone has same molecular formula ((C3H6O) as propanal.
Aldehyde and ketone molecules cannot hydrogen bond among themselves for same reason that ethers cannot – they do not contain hydrogens attached to highly electronegative atoms. Carbonyl group is polar, however, since difference between electronegativities of carbon (2.5) and oxygen (3.5) is rather large and there are no other dipoles in an aldehyde or ketone molecule to cancel effect of C=O.
Thus, boiling points of aldehydes  and ketones are intermediate between those of alkanes on the one hand and alcohols on the other hand. Acetaldehyde, CH3CH2CHO, boils at 20.8 degrees centigrade midway between propane (-42°C) and ethanol (78.5°C). boiling points of propanal and acetone are compared with other organic compounds which shows same trend.
2,4-dinitrophenylhydrazine (Brady’s reagent) is an important reagent related to hydrazine. Most aldehydes and ketones react readily with this reagent to give yellow orange and red precipitates of 2,4-dinitrophenylhydrazones. Unconjugated aldehydes and ketones give precipitates toward yellow while conjugated compound tend to be deeper red colour. Conversion of aldehydes and ketones into hydrazine is an example of addition-elimination reaction occurring at unsaturated carbonyl group.
1. Preparation: 4g of 2,4-dinitrophenylhydrazine is dissolved in 8ml of concentrated H2SO4. Mixture is cooled and added with 90 ml of methanol and 10 ml of water.
2. To 1 ml of acetaldehyde, benzaldehyde, acetophenone, 3-pentanone, isopropyl alcohol and 1-propanol in separate dry test tube, 2 ml of Brady’s reagent is added and is shaken vigorously. Crystalline precipitate indicates presence of a carbonyl compound.
3. Step 2 is repeated with unknown A, B and C and observations are made.             
 

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