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Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

Which is thermodynamically more

stable, chair or boat form?

Identification tests for carbohydrates

1) Molisch’s test: (See latter).

All carbohydrate gives purple color when treated with -naphthol

and conc. sulfuric acid. The color appears as a ring at the interface between the

aqueous solution of soluble carbohydrate “upper layer” and conc. sulfuric acid

“lower layer”. If H 2SO 4 is gently added with an insoluble carbohydrate such as

cellulose the color will not appear until the acid layer is shaken to bring it in

contact with the material.

2) Fehling’s solution: (See latter).

A mixture of equal parts of Fehling’s solution (No. 1 and 2) is added

drop-wise to a heated solution of the carbohydrate. Reduction takes place near

the boiling point and indicated by a brick-red precipitate of Cu2O. The reaction

is positive in certain cases:

• All Monosaccharide.

• Many reducing disaccharides, e.g., lactose, maltose, cellobiose

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