Seliwanoff Test

7/29/2019 Seliwanoff Test

1/14


2/14

SELIWANOFF TEST

INTRODUCTION

PROCEDURE

RESULTS && DISCUSSIONAPPLICATIONS

FRAGMENTATION WITH STRONG ACID


3/14

INTRODUCTION

Many carbohydrates can be identified using condensation

reagents, which react with the carbohydrates to produce

highly colored products.Often the carbohydrate is initially dehydrated into smaller

saccharide units, using a dehydrating acid.

The smaller the units or molecules, formed will produce a

more highly colored complex with the condensation reagent,

as in Molisch's, Bial's andSel i w ano f f ' s t e s t s .


4/14

INTRODUCTION

A BIOCHEMICAL TEST TO IDENTIFY THE PRESENCE OF

KETONIC SUGARS IN SOLUTION.

F. F. SELIWANOFF

A FEW DROPS OF THE REAGENT, CONSISTING OF

RESORCINOL CRYSTALS DISSOLVED IN EQUAL AMOUNTS OF

WATER AND HYDROCHLORIC ACID, ARE HEATED WITH THE

TEST SOLUTION AND THE FORMATION OF A REDPRECIPITATE INDICATES A POSITIVE RESULT.


5/14

PROCEDURE

1. To 3 ml of Seliwanoff's reagent, Add 0.5 ml ofthe test solution heat the mixture in a boilingwater bath for 10-15 minutes.

2. Observe the production of a red color or abrownish-red precipitate and the rate of itsappearance.


6/14

PROCEDURE

CONDITIONS TO BE OBSERVED IN PERFORMING THETEST:

A. The concentration of HCl must not be more than 12 %

B. The reaction must be observed after not more

than 20-30 seconds of boiling

C. Glucose must not be present in amounts exceeding 2%


7/14

RESULTS &&DISCUSSION

PROPOSED RESULT :

A ketone hexose, also called a ketohexose, will form a

deep red color when reacted with Seliwanoff's reagent.

An aldehyde hexose, also called a aldohexose, will showa light pink color that takes a longer time to develop

when reacted with Seliwanoff's reagent.

Ke t o s e --> deh y d r a t i o n p r o d u c t - -> ch e r r y - r ed p r o du c t (w i t h i n 2 m i n u t e s )


8/14


Galactose (-) Dark Yellow(Original Color of Reagent)

Glucose (-) Dark Yellow(Original Color of Reagent)

Fructose (+) WINE REDMaltose (-) Dark Yellow

(Original Color of Reagent)Sucrose (+) PINKISH REDXylose (-) Dark Yellow

(Original Color of Reagent)


9/14



10/14


Used to distinguish between aldehyde and

ketone hexoses

Seliwanoff's test uses:

12% hydrochloric acid as the dehyd r at i n g ac i d

5% resorcinol as the con densa t i o n r eagen t


11/14


The acid hydrolysis of polysaccharides andoligosaccharides yields simpler sugars.

The dehydrated ketose then reacts withthe resorcinol to produce a deep cherry red color.

Aldoses may react slightly to produce a faint pinkcolor.

Fructose and sucrose are two common sugars whichgive a positive test.

Sucrose gives a positive test as it is a disaccharideconsisting of fructose and glucose.


12/14


T h e t e s t r e a g en t d e h y d r a t e s k e t o h e x o s e s

t o f o r m 5 -h y d r o x y m e t h y l f u r f u r a l .


13/14


Aldohexose reacts more slowly

to give 5-hydroxylmethylfurfural


14/14


(Aldohexoses)Once 5-hydroxylmethylfurfural is produced, it reacts withresorcinol to give a dark red condensation product.

Sucrose hydrolyzes to give fructose, which

eventually reacts to produce a dark red color.

Seliwanoff Test

Documents