IDENTIFICATION OF REDUCING SUGARS BY PREPARING OSAZONE

 

IDENTIFICATION OF REDUCING SUGARS BY PREPARING OSAZONE

 

                All carbohydrates contain either aldehyde or a ketonic group. This group can react with phenlyhydrazine to form solid derivatives. These solid dervatives have characteristic crystalline forms which can be easily identified under the microscope. These derivatives are called osazones etc. The important feature about these osazones is that different sugar give osazones with different crystalline forms.

 

                Only reducing sugars form osazones because they have free aldehyde or ketonic group. Sucrose which is a non reducing sugar has no free aldehyde or ketonic group, and does not form an osazone.

 

                Hexoses which differ only in carbon atoms 1 & 2 in their structure give the same osazone, Glucose, Fructose & mannose form identical osazones.

 

Procedure for Osazone Formation:

Note: Since osazone formation takes time this expt. should be started as early as possible in the work period, so before doing anything else start to boil some water in a large beaker or in a water bath.

 

                Take 3 ml of 1% solution of glucose, lactose and maltose in different test tubes and label them as G; L and M. To each test tube add 10 drops of glacial acetic acid and add one measure of phenylhydrazine hydrochloride followed by twice the amount of sodium apetate. Mix well and place in a boiling water bath for 30 minutes. If any crystals are formed remove the tube and study the shape of the crystals under the microscope.

 

                If no crystals are formed, after 30 minutes, remove the flame and allow the tubes to cool in the hot water itself.

 

                Glucose & fructose osazones separate at boiling temperature but maltose and lactose osazones separate only on cooling.

 

                Draw the figures of these Osazones.