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Reaction of glucose with 2,4-dinitrophenylhydrazine (DNPH)
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Kaori Kitao
Reaction of glucose with 2,4-dinitrophenylhydrazine (DNPH)
The test is based on imine formation. The formation of imine from carbonyl compound occurs in equilibriumergo the principle of Le Chatelier is applicable to the test. According to this principle the increase of the concentration of at least one of the products results in the decrease of degree of conversion of the reactant.
I guess that you are trying to perform the test in aqueous solution, because glucose has poor solubility in ethanol. The second product of the conversion of carbonyl to imine is water. So, performing the reaction in the tremendous excess of water, you are in fact pushing the degree of conversion toward zero in accordance with the principle of Le Chatelier.
That's why the expected precipitate is not formed.
The test is based on imine formation. The formation of imine from carbonyl compound occurs in equilibriumergo the principle of Le Chatelier is applicable to the test. According to this principle the increase of the concentration of at least one of the products results in the decrease of degree of conversion of the reactant.
I guess that you are trying to perform the test in aqueous solution, because glucose has poor solubility in ethanol. The second product of the conversion of carbonyl to imine is water. So, performing the reaction in the tremendous excess of water, you are in fact pushing the degree of conversion toward zero in accordance with the principle of Le Chatelier.
That's why the expected precipitate is not formed.
Imine and eanmine formation is reversible but the formation of DNPs, phenyl hydrazones, osazones, oximes and semicarbazides are not reversible under the mild conditions applied to imines and enamines. The latter group is used as derivatizing agents and are stable. These derivatizing agents all have N-N or N-O bonds. Was the DNP derivatization done under the same conditions applied to phenylhydrazone formation of glucose?More
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That is because when glucose reacts with 2,4-dinitrophenylhydrazine, instead of corresponding imine, amine analogue of acetal is preferred - ring gets closed and forms colourless DNPH substituted glucose.
Due to the two strongly electron withdrawing nitro groups on the aromatic ring, the electron cloud moves forward to the chain of hydrazine, so it prefers the ring closure. There is no imine that can be detected, and it will not give a positive test.
That is because when glucose reacts with 2,4-dinitrophenylhydrazine, instead of corresponding imine, amine analogue of acetal is preferred - ring gets closed and forms colourless DNPH substituted glucose.
Due to the two strongly electron withdrawing nitro groups on the aromatic ring, the electron cloud moves forward to the chain of hydrazine, so it prefers the ring closure. There is no imine that can be detected, and it will not give a positive test.
The test is based on imine formation. The formation of imine from carbonyl compound occurs in equilibrium ergo the principle of Le Chatelier is applicable to the test. According to this principle the increase of the concentration of at least one of the products results in the decrease of degree of conversion of the reactant.
I guess that you are trying to perform the test in aqueous solution, because glucose has poor solubility in ethanol. The second product of the conversion of carbonyl to imine is water. So, performing the reaction in the tremendous excess of water, you are in fact pushing the degree of conversion toward zero in accordance with the principle of Le Chatelier.
That's why the expected precipitate is not formed.
The test is based on imine formation. The formation of imine from carbonyl compound occurs in equilibrium ergo the principle of Le Chatelier is applicable to the test. According to this principle the increase of the concentration of at least one of the products results in the decrease of degree of conversion of the reactant.
I guess that you are trying to perform the test in aqueous solution, because glucose has poor solubility in ethanol. The second product of the conversion of carbonyl to imine is water. So, performing the reaction in the tremendous excess of water, you are in fact pushing the degree of conversion toward zero in accordance with the principle of Le Chatelier.
That's why the expected precipitate is not formed.
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That is because when glucose reacts with 2,4-dinitrophenylhydrazine, instead of corresponding imine, amine analogue of acetal is preferred - ring gets closed and forms colourless DNPH substituted glucose.
Due to the two strongly electron withdrawing nitro groups on the aromatic ring, the electron cloud moves forward to the chain of hydrazine, so it prefers the ring closure. There is no imine that can be detected, and it will not give a positive test.
That is because when glucose reacts with 2,4-dinitrophenylhydrazine, instead of corresponding imine, amine analogue of acetal is preferred - ring gets closed and forms colourless DNPH substituted glucose.
Due to the two strongly electron withdrawing nitro groups on the aromatic ring, the electron cloud moves forward to the chain of hydrazine, so it prefers the ring closure. There is no imine that can be detected, and it will not give a positive test.
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