Enhancing the Value of Indigo-Blue Dyes from Lonchocarpus Cyanescens Leaves

2013

English

The parameters for the extraction of an indigenous dyestuff from Lonchocarpus cyanescens leaves and its spectroscopic characterization are discussed. The extraction was achieved by cold maceration in alkaline Na2S2O4.solution. The IR spectra identified the presence of the following active functional groups; υ(O-H) and υ(C-O) stretching of primary and secondary alcohols as well as υ(N-H) and υ(C-N) stretching of an aromatic amine. These functional groups are similar to those associated with synthetic indigo dyes used in dyeing denim jeans. Refinement of the crude dyestuff is achieved by precipitation with acid leaving the noxious principles in solution. The variation of yield of dye with alkalinity is consistent with the dye existing as an insoluble ketal form in the leaves which is reduced with hydrosulfite to a sparingly soluble leuco form. This leuco form is converted to a more soluble salt species by addition of base.

Oduro, W.O.; Addo-Yobo, F.