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A Study of Certain Natural Dyes II‐The Structure of the Metallic Lakes of the Brazilwood and Logwood Colouring Matters
Author(s) -
Arshid F. M.,
Connelly R. F.,
Desai J. N.,
Fulton R. G.,
Giles C. H.,
Kefalas J. C.
Publication year - 1954
Publication title -
journal of the society of dyers and colourists
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.297
H-Index - 49
eISSN - 1478-4408
pISSN - 0037-9859
DOI - 10.1111/j.1478-4408.1954.tb02044.x
Subject(s) - chemistry , metal , cationic polymerization , salt (chemistry) , mordant , chromate conversion coating , chromium , condensation , precipitation , ionic bonding , inorganic chemistry , organic chemistry , ion , dyeing , physics , meteorology , thermodynamics
The lake‐forming reactions of the oxidised and reduced forms of the logwood and brazilwood colouring matters with the more important mordanting metals have been investigated. The oxidised forms appear to be the lake‐forming species, the o ‐hydroxyquinone system of the molecule chelating with the mordanting metal atom; the leuco forms must first be oxidised by air or the mordanting salt before lake formation can take place. When a chromate or a dichromate is used as mordant, this is first reduced to the chromic cation, at the expense of the total destruction of some of the colouring matter, before lake formation occurs. The logwood colouring matter, when treated with a chromium salt in solution or on the fibre, forms a deep blue 2: 1 (dye: metal) complex, which is preceded by a transient purple 1: 1 complex. Aluminium, cobalt, and (ferric) iron also form 2: 1 complexes, and copper appears to form a 1: 1 complex. The lakes formed in substance are amorphous, infusible, and almost insoluble in all solvents. Exact characterisation of these bodies, which appear to be mixtures, is not practicable, but by a consideration of probable reaction sequences, in conjunction with the elementary analyses, a series of formulæ have been drawn up which are believed to represent their most probable constitutions. The development of insolubility is believed to be due to one or more of the following effects‐ mutual precipitation of cationic or anionic lakes by complex anions or cations respectively, formation of non‐ionic lakes, and the form of condensation polymerisation known as “olation“. It is suggested that similar changes occur in the fibre during the normal mordanting and dyeing processes, and that parallel reaction sequences may take place in dyeing other forms of mordant dye. The deep blue‐black logwood lake on the fibre is believed to be a mixture of an anionic complex, e.g. [hnCr(OH) 2 hn]‐ [Cr(OH) 2 H 2 O) 4 + , 4H 2 O with the derived olated body‐The iron lake is probably similar in constitution. In addition to the action of the chelating groups, the phenolic groups not in the quinonoid nucleus of the colouring matter molecule appear to take part also in salt formation with cobalt or copper, but not with chromium or iron.