Rapid furfural test

Molisch s test A general test for carbohydrates. The carbohydrate is dissolved in water, alcoholic 1-naphthol added, and concentrated sulphuric acid poured down the side of the tube. A deep violet ring is formed at the junction of the liquids. A modification, the rapid furfural test , is used to distinguish between glucose and fructose. A mixture of the sugar, 1-naphthol, and concentrated hydrochloric acid is boiled. With fructose and saccharides containing fructose a violet colour is produced immediately the solution boils. With glucose the appearance of the colour is slower. 

Rapid furfural test," Fructose gives an immediate violet coloration on boiling (see Test 4 for glucose). 

Rapid furfural test" A violet coloration is produced immediately on boiling (as for fructose). 

Rapid furfural test." The violet coloration is produced only after boiling for about 1 minute (as for glucose). 

Rapid furfural test." Violet coloration after about i minute s boiling, as for glucose and maltose. 

CA 31,2126(1937)(Rapid detn of acetone in w conducted by mixing 1 ml of soln to test with 1 ml of 0.2% furfural and 1 ml KOH soln. Treat in a similar manner 1 ml w contg 0.05% and 1 ml w contg 0.025% serving as standards. Compare the rates of pptn of sample with those of standards and calc concn of acet from the formula given in paper. The accuracy of the method is 5%) 12)Kirk Othmer, 1(1947),92(Analytical procedures and specs for acet) 13)T.G.Bonner, Anaiysr 72,434-39 (1947) 14) W.B.Huckabay et al, AnalChem 19,... 

Ketoses are dehydrated more rapidly than aldoses to give furfural derivatives that can be condensed with phenols. In the Seliwanoff test for ketoses, the aqueous carbohydrate sample is treated with 3 M hydrochloric acid containing resorcinol. A deep-red precipitate is formed, indicating the presence of ketose(s). The faster rate of dehydration of ketoses by HCl versus the dehydration of aldoses permits the specific detection of ketoses [10,11]. 

---