Azo compounds, diazotization coupling reaction

lzThis problem is actually quite big.。。 I can only talk about it in general terms.

Belch.. Pigments can be understood as synthetic additives, and its use is to make our lives more "colorful", such as synthetic dyes for house decoration and food additives that make food more "beautiful" and so on.

In fact, the chemical composition of many pigments (dyes) is mostly azo compounds, because azo compounds have a special mechanism that makes them "color". Let me briefly explain the principle. Azo compounds are azo groups (i.e., "—n=n—").

A compound formed by linking two hydrocarbon groups, with the general formula r-nn-r, with parageometric and antigeometric isomers.

However, trans is more stable than cis, so the two isomers can be converted to each other under light or heating conditions. The conversion process requires the absorption of a specific wavelength of light (as the absorbed energy, i.e., the work done to overcome the "energy barrier" in the conversion process), so it appears as an inverse color that absorbs the light of that specific wavelength. Thus giving "color" to objects containing azo compounds.

The same... As for its harm to the human body, it is still a problem. Azo bond -n=n-, it is the color carrier of azo pigment, the chemical properties are generally more active, under the action of strong reducing agent, the azo bond nn is broken to form amine compounds, and finally 2 molecules of aromatic amine (pigments generally contain aromatic ring structure), and it is these aromatic rings (such as -naphthylamine, -naphthalene amine.

Carcinogenic activity...

I typed it out word by word... Simplify your question ... But in fact, there are many aspects that have an impact. I think when you study it in depth in the future, you should gradually understand ...

What the? I don't know the pigments! It's time for you to study hard! Let's recommend a good place to go! Check it out at the first broker network.

Diazotization coupling reaction is a characteristic reaction of the first amine group of aromatics. The first aromatic amine group undergoes diazotization reaction in the sodium nitrite-hydrochloric acid test solution to form diazonium salt, and then alkaline-naphthol is added to the coupling reaction to produce orange-red azo compound precipitation.

The reaction of aromatic primary amines and nitrous acid (under the strong acid medium state capital) to generate diazonium salts is called diazotization (generally carried out at low temperatures, the molar ratio of primary amines and acids is: 1: Qin Xiao, aryl primary amines are often weighed as diazo components, nitrous acid is diazotizing agent, because nitrite is unstable, sodium nitrite and hydrochloric acid or sulfuric acid are usually used to make the nitrite produced during the reaction immediately react with aryl primary amine to avoid the decomposition of nitrite acid, and diazotization reaction is generated after diazotization.

The mechanism of diazotization reaction is that the primary amine is first combined with the diazotization reagent, and then through a series of proton transfers, and finally the diazo salt is generated. The form of diazotization reagent is related to the inorganic acid used. When a weaker acid is used, nitrous acid is balanced with nitrous oxide in solution, and the effective diazotization reagent is nitrous oxide.

When a stronger acid is used, diazotization reagents are protonated nitrite and nitrosyl cations. Therefore, it is important to control the appropriate pH value in diazotization reactions. Aromatic primary amines are weakly alkaline and require a strong nitrosation reagent, so the reaction is usually carried out under strong acidity.

Diazotization reaction can be expressed by the reaction formula as:

ar-nh2+2hx+nano2=ar-n2x+nax+2h2o

Sequence cavity method

The shun method is to add an appropriate amount of water to the color base first, then add a specified amount of hydrochloric acid, and slowly add sodium nitrite under low temperature and continuous stirring to complete the diazotization reaction. Color-based red G, color-based orange GC and color-based purple sauce GBC can all use the shun method. The diazotization temperature is 5 10 and the time is about 10min, and the temperature is too high and the time is too short, and no good diazo results can be obtained.

In order to complete the diazotization reaction, it is necessary to place the color-based diazotization solution for about 15min, and add an appropriate amount of acetic acid and sodium acetate before use. Most primary aryl amines soluble in dilute inorganic acids are diazotized by this method.

Reverse law

Reverse diazotization is to mix the color base with sodium nitrite and an appropriate amount of cold water into a uniform paste and add ice to cool, and then slowly pour it into the continuously stirred ice hydrochloric acid solution to complete the reaction. Aminoaromatic sulfonic acid, which is difficult to dissolve in dilute acid, is diazotized by this method.

Hno5S method

The nitrosyl sulfuric acid method is used for diazotization of primary aryl amines (very weak alkaline) that are difficult to dissolve in dilute acids, that is, primary aromatic amines are first dissolved in concentrated sulfuric acid or glacial acetic acid, and then nitrosyl sulfuric acid solution is added to them.

Diazotization coupling reaction is the characteristic reaction of the first aromatic amine group, the first aromatic amine group undergoes diazotization reaction with sodium nitrite-hydrochloric acid test solution to generate diazo salt, and then alkaline-naphthol, the coupling reaction of silver orange is generated, and the orange-red azo compound precipitation is produced.

The diazotization reaction is carried out in a strong acid, which is actually nitrous acid acting on ammonium ions. Because nitrite is unstable, sodium nitrite and hydrochloric acid or sulfuric acid are usually used to make the nitrite produced by the reaction react with aryl primary amine immediately to avoid the decomposition of nitrite acid. In order for the reaction to proceed smoothly, the primary arylamine must first be converted into ammonium cation.

Aromatic amines are weakly alkaline, so diazotization is carried out in a strong acid mass permeation. Some aromatic amines are very weak in alkalinity and require special methods to diazotize.

Diazotization is an exothermic reaction, and diazo salt is unstable to heat, so it should be carried out in the case of cooling, generally cooled with an ice salt bath, and the addition rate of sodium nitrite is adjusted to maintain the reaction temperature around 0.

Because diazonium salts are unstable, their solutions are generally used, and they are used as they go. Solid diazo salts will occur when exposed to heat, vibration, and friction, and it is necessary to be cautious when using some solid diazonium salts with good stability.

Primary aromatic amines react with an acidic solution of sodium nitrite (to form nitrous acid) to generate diazo salts, which are then coupled with phenols to form azo compounds, which are the main reactions for the preparation of azo dyes, and can also be used for qualitative and quantitative analysis of organic structure.

Correct answer: c

Analysis: Diazotization-coupling reaction.

The coarse agent used for the coupling test is alkaline-naphthalene stool burning.

Some azo compounds can be used as acid-base indicators and metal indicators in analytical chemistry. Some azo compounds are easy to decompose when heated, release nitrogen, and produce free radicals, such as azodiisobutyronitrile AIBN, etc.: Therefore, it can be used as an initiator of polymerization reaction. Azo compounds.

Many azo compounds have carcinogenic effects, such as "cream yellow", which was once used for margarine coloring, can induce liver cancer, and is now banned. Methyl red, used as an indicator, can cause bladder and breast tumors.

It is the main component of important fine chemical products, such as dyes, drugs, pigments, indicators, analytical reagents, etc.