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Another dye, para red, is an azo-dye.

Thename 'direct dye' alludes to the fact that these dyes do not require any form of'fixing'. Theyare almost always azo dyes, with some similarities to acid dyes. They alsohave sulphonate functionality, but in this case, it is only to improvesolubility, as the negative charges on dye and fibre will repel each other. Their flat shape and their length enable themto lie along-side cellulose fibres and maximise the Van-der-Waals, dipole andhydrogen bonds. Below is a diagram of a typical direct dye. Notethat the sulphonate groups are spread evenly along the molecule on the oppositeside to the hydrogen bonding -OH groups, to minimise any repulsive effects2.

Wash fastness may be improved, though, by the application of , which contain -NH2 functional groups as wellas sulphonate groups. In this process, the dyed fabric is treated withsodium nitrite, which causes the dye to be converted to a diazo salt. Itis then treated with a coupling compound such as 2-napthol. The resultantlarger azo molecule now has more affinity for the fibres, and is less soluble2.

Living Radical Polymerization as a Tool for the Synthesis of Polymer-Protein/Peptide Bioconjugates.
Photo provided by Flickr

The Synthesis of Azo Dyes - University of New …

One-Pot Procedure for Diazo Transfer and Azide-Alkyne Cycloaddition: Triazole Linkages from Amines.
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Tautomeric forms can be identified form their characteristicspectra. Ketohydrazones are normally bathochromic compared to theircounterpart hydroxyazo forms. Ketohydrazones also have higher molarextinction co-efficients. However, not all azo dyes show tautomerism, andsome tautomeric forms are more stable than others2.

What is understood is the space of the hydroxyl groups of the cotton matches fairly well the space needed for the diazo- dye to directly dye with hydrogen bonds.

CHEM 322: Azo Dyes: Combinatorial Synthesis of Dyes

Purpose: to identify the best fabric to accept a dye and which dye is most successful
Project took place
3/18/13 Dye Lab By Jason Graham Partnered with Nicole Cahours, Jordan Fundaro, and Ben Kruse O Polyester
(Dacron 54) Polyacrylic
(Orlon 75) Conclusion Congo Red Para Red Indigo Malachite Green Methyle Orange Eosin Alizarin Undyed
Ingrain Azo Disperse Unmordanted Alum Mord.

M., Synthesis of bio-inspired hybrid polymers using peptide synthesis and protein engineering.
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In the USA, thiourea is used in animal hide glue, which contains thiourea at a concentration of 10–20% as a liquefying agent. Reports indicate its use in the production of flame retardant resins and as a vulcanization accelerator (NTP, 2000). In Germany, thiourea is not used in the leaching of ore mines and not processed to thiourea dioxide. Instead, the following use pattern is reported (BUA, 1995): auxiliary agent in diazo paper (light-sensitive photocopy paper) and almost all other types of copy paper (19%); metal cleaning, including silver polish (4%); precipitation of heavy metals (3%); additive in slurry explosives (3%); electroplating/electroforming (1%); corrosion inhibitor (1%); processing to organic intermediates (41%); mercaptosilanes (6.5%); vulcanization accelerators (0.5%); resin modification (4.5%); and chemicals industry and miscellaneous (16.5%) (BUA, 1995). In Japan, thiourea is added to fertilizers to inhibit the nitrification process (Hashimoto, 1979; Kubota & Asami, 1985). Data on the quantities used are not available.

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Synthesis of Red 13 Diazo Dye Introduction

Azo compound synthesis - Organic Chemistry Portal

The channels of AGS was clogged by azo dyes, which was evidenced by the hard release of aromatic amines in EPSs as well as decreased porosity of AGS and scanning electron microscope images.

TiO2-assisted photocatalytic degradation of azo dyes …

The spatial distribution of extracellular polymeric substance in the anaerobic granular sludge (AGS) showed that the high biological toxicity of azo dyes was mainly attributed to enrichment effect in tightly bound-EPS (TB-EPS).

Biosynthesis of Autoinducer-2 as the Possible Mechanism …

The acute toxicity of thiourea varies with the species, strain, and age of the animals exposed to the chemical and with the iodine content of their diet. Oral LD50s are about 1000 mg/kg body weight for mice, 125–1930 mg/kg body weight for rats, depending on the strain, and 10 000 mg/kg body weight for rabbits. The intraperitoneal LD50 for the rat ranges between 4 and 1340 mg/kg body weight, according to the strain. Death at these doses is due to lung oedema, and the survivors exhibit pleural effusion. Accordingly, thiourea at doses between 10 and 500 mg/kg body weight has been employed in experimental animal studies as a model agent for the elicitation of lung oedema and pleural effusion. The pathological effects are prevented by pretreatment of the animals with cysteine or glutathione, which reduces the irreversible binding of radioactivity to lung proteins after administration of [14C]thiourea. Toxic doses of thiourea also resulted in hyperglycaemia, glucosuria, polyuria, and a reduction in the liver glycogen level in rats (MAK, 1988).

specific mechanism of Williamson Ether Synthesis

In this study, the real textile wastewater with alternative concentrations of azo dyes (0–600 mg/L) were used to operate a lab-scale high-rate anaerobic methanogenic bioreactor for 127 days, and 50 μM anthraquinone-2-sulfonate (AQS) as RM was added at the last period of operation.


Filament acetate (Modified cotton)

Polysaccharide (Bleached cotton)

Polyamide (Nylon 6.6)

Polyester (Dacron 54)

Polyacrylic (Orlon 75)

Protein (Wool) Filament acetate


Polyamide (Nylon 6.6)

Polyester (Dacron 54)

Polyacrylic (Orlon 75)

Protein (Wool) Protein
(wool) Though not fully understood, diazo dyes, such as Congo red, are direct dyes for cotton.

compounds- a coupling component and a diazo ..

B., Synthesis of azide-alkyne fragments for click' chemical applications; formation of oligomers from orthogonally protected trialkylsilyl-propargyl azides and propargyl alcohols.

be reached by consuming azo dye coloured food

This involves the removal of a hydrogen from one part of themolecule, and the addition of a hydrogen to a different part of themolecule. This is common when there is an -OH group ortho or para to theazo group:

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