Discuss the chemical reactions that occurred between glucose,
fructose, xylose and sucrose and the 4 reagents(Benedict,...
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Discuss the chemical reactions that occurred between glucose,fructose, xylose and sucrose and the 4 reagents(Benedict, Bial,Seilwanoff and Molisch) which have resulted in color changes.Describe how it occurs in full using the chemical makeup of thereagents.
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Bial’s reagent
Test for pentoses.components include orcinol,HCl,ferric
chloride.Pentoses react to form furfural ,which gives colored
substance.pentoses gives blue/green
Positive for pentose sugar -xylose
Benedict’s
-Free aldehyde or keto group in reducing sugars reduce cupric
hydroxide in alkaline medium to red colored cuprous oxide.All
monosaccarides are reducing .
Seilwanoff
Color reaction specific for ketoses.
Ketoses+conc HCl undergoes dehydration to yield
5-hydroxymethylfurfural derivatives that form deep red color
complex with resorcinol. Faster rxn than aldoses
Molisch
All pentose sugar and hexoses are dehydrated by conc. Sulphuric
acid to form furfural or hydroxymethylfurfural, respectively. These
products condense with α-naphthol to form purple colored
condensation product.
glucose
Negative -hexose
positive
negative
positive
fructose
Negative -hexose
positive
positive
positive
xylose
positive
Positive
negative
positive
sucrose
Negative-dimer of hexose
Negative-disaccharides
positive
positive
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