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Industrial Dyes (Chemistry Properties Applications) (itocagawoler.gatile…
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Dyes in modern organic chemistry
We are selling reactive dyes in bangladesh. I wai your comments. Suresh Saranya. Priyanka Singh. Choudhary Arbendra , EEE at student. Show More. No Downloads. Views Total views. Actions Shares. Embeds 0 No embeds. All three methods are also applied to halogenated nitro compounds, and can thus contribute to AOX loads in waste water streams. Figure 5 shows a typical sequence of operations for the reduction of aromatic nitro compounds, possible input materials and associated waste streams.
The work-up depends on the properties of the amine obtained. Common methods are:. Figure 5: Typical sequence of operations for the reduction of an aromatic nitro compound. The scale and growth of the dyes industry is linked to that of the textile industry. World textile production has grown steadily to an estimated 35 million tonnes in The two most important textile fibres are cotton and polyester.
Consequently, dye manufacturers tend to concentrate their efforts on producing dyes for these two fibres. The estimated world production of dyes and pigments in was 1 million tonnes. The rapid growth in the high tech uses of dyes, particularly in ink-jet printing, is beginning to make an impact.
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Although the volumes in this area remain small in comparison to dyes for traditional applications, the value will be significant because of the much higher price. This decline is coupled with an increase of production in commodity dyestuffs in lower cost countries such as India, Taiwan and China.
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The world output of organic dyes is estimated to be tonnes per year [6, Ullmann, ]. Jump to: navigation , search. Pigments Pigments are defined as colouring agents that are practically insoluble in the application medium, whereas dyes are colouring agents that are soluble in the application medium. Heavily halogenated aromatic hydrocarbons Especially as a result of the environmental persistence of the heavily chlorinated benzenes, toluenes and biphenyls, in recent years drastic measures have been applied to this range of chemicals, such as prohibitions, and restrictions on their production and use, and legislation regulating waste disposal.
Possible side reactions of the chlorination process can result in the formation of polychlorinated biphenyls or hexachlorobenzene. Chemical reaction These chemicals are of major relevance on an industrial scale in substitutions of the aromatic nucleus and in the substitution of aliphates.
Lewis acids such as FeCl3, AlCl3 …. A wide range of organic and aqueous solvents are currently in use, and especially tetrachloromethane, tetrachloroethane, dichlorobenzene and trichlorobenzene are recommended for halogenations.
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Methanol is the solvent of choice since the resulting methyl bromide can be widely marketed as a fumigant. Operations Figure 1 shows a typical sequence of operations for the halogenation to distillable products. Figure 2 shows a typical sequence of operations for the halogenation precipitation of the product. The reactor material depends on the reactants and the chosen reaction mechanism. The exothermic reaction is controlled by the rate of halogen addition, which is dependent on the refrigeration capacity of the reactor cooling system.
The choice of temperature profile is based on the reactivity of the aromatic. On completion of the reaction, degassing is carried out with nitrogen. The product is distilled or precipitated e. Most side chain chlorinations are carried out continuously or discontinuously in bubble column reactors of enamel or glass, e. The reaction is stopped by the introduction of N2. N-acylation N-acylation is a widely spread reaction for the protection of anilinic amino groups before chlorinations, nitrations or sulphonations are carried out.
Chemical reaction The most important N-acylation agents are: acetic acid acetic anhydride, other carboxylic anhydrides diketene acetoacetic ester acetic chloride, other acyl halides N-carboxy anhydrides. HX may be, e. Operations Figure 3 shows a typical sequence of operations for N-acylations and the typical waste streams. Amine and an equimolar amount of an acylation agent are typically dissolved in H2O or diluted acetic acid for acetoacetic ester, xylene is often used and heated. Reaction water or acetic acid or ethanol and solvent are distilled off and the product is obtained directly or following crystallisation occasionally by salting out and filtration.
Chemical reaction Nitration is the irreversible introduction of one or more nitro groups into an aromatic system by electrophilic substitution of a hydrogen atom. Nitration is normally carried out in a liquid phase reaction with a mixture of nitric and sulphuric acids mixed acid and occasionally with nitric acid. The strength of the mixed acid and the temperature can be varied to maximise the formation of the required isomer.
Stronger mixed acid and higher temperature lead to oxidative side reactions. An important side reaction leads to phenolic by-products. Operations Figure 4 shows a typical sequence of operations for the nitration of aromatic compounds, possible input materials and associated waste streams. The reaction is carried out in cast iron, stainless steel or enamel-lined mild steel reactors. The substrate is dissolved in the sulphuric acid phase and the mixed acid is subsequently added.
On completion of the reaction, the batch is transferred into water to give a two phase mixture of diluted acid and an organic product phase. After phase separation, liquid products are purified by distillation. The remaining acid phase can be extracted with the feed material in order to recover organic compounds. The crude nitroaromatic is washed with water and diluted NaOH to remove the acids and phenolic by-products.
The Chemistry of Synthetic Dyes V8
Depending on the quality requirements, a recrystallisation from water or organic solvent may be necessary. Isomer separation is carried out within the crystallisation, washing or distillation steps. To reduce these hazards, the concentration of nitro compound, the amount and partial pressure of the hydrogen, the temperature, and the activity of the catalyst, are controlled. Most aromatic nitro compounds are hydrogenated in the liquid phase.
In this case, the pressure and temperature can be changed independently. The preferred solvents are methanol and 2-propanol; and also dioxane, tetrahydrofuran, and N-methylpyrrolidone are used.
In the hydrogenation with a water immiscible solvent, such as toluene, the water must be removed, as in solvent-free hydrogenation, in order to maintain the activity of the catalyst.
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