Лако-красочные материалы — производство

Cationic dyes were used initially for dyeing of silk, leather, paper, and cotton mordanted with tannin, as well as for the production of ink and copying paper in the office supplies industry. Their high brilliance and color strength partly com­pensated for their poor lightfastness on these materials. With the development of synthetic fibers their most […]

In contrast to dyes with delocalized charge, in which the charge is an essential part of the chromophore, in dyes with localized charge the charged atom in most cases is isolated from the chromophore by a nonconjugated group. Therefore, any chromophore can be used, and this chromophore is not or only slightly influ­enced by the […]

This chapter gives a short survey on cationic dyes and shows typical representa­tives of each class of cationic dyes. In general, the dyes are classified according to their chemical structure. 2.4.3.1 Dyes with Delocalized Charge Cationic dyes with delocalized charge are classified with the methine dyes (see Section 2.6). They may be viewed as vinylogous […]

Cationic functionality is found in various types of dyes, mainly in cationic azo dyes (Section 3.7) and methine dyes (Section 3.8), but also in anthraquinone (Section 3.4), di — and triarylcarbenium (Section 2.6), phthalocyanine dyes (Section 2.7), and in various polycarbocyclic and solvent dyes (Section 3.10).

2.4.1 Introduction Cationic dyes carry a positive charge in their molecule. The salt-forming counter­ion is in most cases the colorless anion of a low molecular mass inorganic or organic acid. Many of these dyes can be converted into water-insoluble dye bases by addition of alkali. For this reason, they were formerly called basic dyes; al­though […]

Indigo is readily reduced to leuco forms [cf., tetramethyl leucoindigo (8)] and oxi­dized to dehydroindigo (9). These reactions strongly influence the cross-conju­gated system, and pronounced hypsochromic shifts of the long-wave absorption band in the UV/Vis spectrum have been measured [9]. The low frequency of the CO band in the IR spectrum of indigo at 1626 […]

PPP calculations by Klessinger showed that the first excited state of indigo is more polar than the ground state, so that positive solvatochromism might be expected. This was in fact observed by Reichardt (see Table 2.1) [8]. Table 2.1 Absorption maximum of indigo in various media Medium Steam CCl4 Xylene Ethanol DMSO Solid (KBr) ^max […]

The question of the contribution of the benzene rings to the indigo chromogen led to a search for the basic chromophore. Consecutively removing parts of the mesomeric system leaves a cross-conjugated structure 7 that, as the basic chromo­phore, still exhibits the typical deep color and redox properties of indigo. A Pariser-Parr-Pople (PPP) calculation indicates that […]

2.3.3.1 Color One of the main fascinations of indigo is that such a small molecule should be blue. The reason for indigo’s deep blue color was long unknown. Normally, exten­sive conjugation (e. g., phthalocyanines) and/or several powerful donor and accep­tor groups (e. g., azo and anthraquinone dyes) are required to produce blue dyes. Only with […]

In most indigo syntheses the indole structure is built up by ring closure of appro­priate benzene derivatives by C-N or C-C bond formation. Examples of C-N bond formation include von Baeyer’s 1878 synthesis from phenylacetic acid (3) via oxindole (4). 3 Oxindole (4) In the Heumann I synthesis, which is the basis of modern synthetic […]