Search

Azo coupling of 6-amino-4-hydroxy-2-naphthalenesulfonic acid (γ-acid) with 2,4-dinitrobenzenediazonium ion in alkaline solution gave a mixture of aminoazo and hydroxyazo dyes. The use of dry diazonium salt, stabilised as o -benzenedisulfonimide derivative, afforded a higher quantity of desired hydroxyazo dye compared to use of diazonium salt prepared via nitrosylsulfuric acid. The addition of a highly acidic diazonium salt solution determines a local pH-value decreasing. In the mixing zones the acid-base equilibrium corresponds to the “microscopic”, lower pH-values and the aminoazo dye is formed. Only hydroxyazo dye was obtained when N -acetyl derivative of γ-acid was used as a coupling agent. In any case, the use of 2,4-dinitrobenzenediazonium o -benzenedisulfonimide allowed for an easier experimental procedure. 1 H NMR analysis, in particular 1 H– 1 H COSY and 1 H– 1 H NOESY techniques, elucidated the structure of dyes evidencing that coupling took place at the para-position to the hydroxy group in hydroxyazo dye and at usual ortho-position in aminoazo dye. Preliminary spectroscopic study showed that p -hydroxyazo dye gave change in colour in the physiological range of pH, an important requisite for its use in a sensor applicable for the monitoring of blood parameters.

A series of azo disperse dyes with variable hydrophobic chain length and hydrophilic (hydroxy or glucosyl group) head were synthesised. 1 H and 13 C NMR spectra indicated that the glucosyl moiety was linked to the azo structure with a β anomeric bond. The dyeing properties on polyamide fibres were assessed with dyeing isotherms and Linitest experiments. The positive effects of additives, as ternary systems (SDS, Brij 35 and octanol) or cyclodextrins, on the dyeing uniformity were shown by tristimulus colorimetry.

Novel azobenzene dyes containing a glucopyranoside moiety were applied to polyethylene terephtalate and cellulose diacetate fibres. Isothermal rate-of-dyeing curves at different temperatures, calculations of the apparent activation energies, light and dry heating colourfastness are reported for polyester. For the cellulose diacetate fibres, bath exhaustions at equilibrium are considered. The data suggest that while the hydrophilic β- d -glucopyranose ring decreases toxicity, it also reduces the substantivity towards hydrophobic fibres. The analogue with an acetylated β- d -glucopyranose ring has dyeing properties comparable to traditional disperse dyes, and, in effluent treatment, is easily converted by hydrolysis of acetate groups to a non-toxic dye.

The synthesis of a series of azo colorants from diazotised arylamines and 4(5)-cyano-5(4)-hydroxyimidazole is described. The dyes exhibit large bathochromic shifts of visible absorption maxima relative to analogous dyes derived from carbocyclic coupling components. Some preliminary spectra data are reported.

4- Tert-butyl-1-(4'-dimethylaminobenzylideneamino)pyridinium perchlorate (BDPP) is a novel dye showing unusual properties, viz. (i) it gives a yellow-green fluorescence which quenched on heating and in solution, and (ii) by heating at 180° or by simple squeezing, it is transformed into orange, non-fluorescent crystals (i.e. it is piezochromic). Surprisingly, among other 1- (benzylideneamino) pyridinium salts, BDPP was the only dye revealing the above properties.

A series of heter acyclic azo dyes derived from aminophenyl-benzothiazoles and substituted dialkylanilines was prepared and tested on polyamide and polyester. The overall properties were satisfactory and compared favourably with related dyes previously described. Several correlations between structure and physical, spectroscopic (VIS and NMR) and fastness properties were found. An investigation of the photofading of the dyes on substrates as a function of time, checked with colourimetric techniques, proved a close time-dependent feature for colour parameters.

Using 4-alkylamido-2-hydroxybenzoic acids containing alkyl chains in the range C 1 -C 15 as coupling components and diazotized aminophenyl-benzo(or pyrido)-X-azoles, a series of monoazo dyes was obtained. The dyes are suitable for application to polyamide fibres. Electronic absorption spectra of the amines and the dyes, dyeing properties and fastness data of the dyed fabrics, as well as their colour parameters, have been measured and discussed with respect to chemical structure and in comparison with previously described analogous compounds.

A series of monoazo dyes was obtained by coupling diazotized aminophenyl-X-azolo-pyridines to N,N-diethylaniline. The dyes showed a great versatility towards different substrates such as polyamide, polyester, cellulose acetate and, after quaternization, polyacrylonitrile. In addition to the evaluation of parameters such as physical and spectroscopic constants, fastnesses on dyed fabrics, colour assessment and their correlation with structure, the dyes were also used in investigating the reactivity of the hetaryls. 1 H NMR was used to clarify the structure of the cationic dyes which, in the case of the imidazo-[4,5-c] isomers, proved to be imidazolium salts rather than the pyridinium salts previously observed for dyes containing an X-azolopyridine moiety.