Azo compounds are AZO, azo group - N=N - compounds formed by connecting two hydrocarbon groups, with the general formula R-N=N-R '.The azo group can absorb visible light of a certain wavelength and is a chromophore.azo dyeIt has the most varieties and the widest applicationSynthetic dyes, can be used for fiber, paper, ink, leather, plasticColour photographyColouring of materials and food.Some azo compounds can be used as acids and bases in analytical chemistryindicatorandMetal indicator。Some azo compounds are easy to decompose and releasenitrogen, and generateFree radical, such asAzodiisobutyronitrileAIBN, etc.: so it can be used aspolymerizationOfInitiator。[1]
It is a chromophore in organic chemistry and can be used as a synthetic dye, an indicator in analytical chemistry and an initiator in polymer chemistry
Azo compounds have cis and transGeometric isomer(SeeGeometric isomerism)。The trans form is more stable than the cis form.The two isomers can be converted to each other under light or heating conditions: azo compounds are mainly converted byDiazonium saltOfcoupling reactionFor example, hydrogenated azo compounds and aromatic amines can be oxidized to corresponding azo compounds in the presence of oxidants;Oxidized azo compounds andNitro compoundstayreducing agentIn the presence of, it can also be reduced to azo compounds.[1]
Azo compound
Aromatic azo
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characteristic
The conjugated system of aromatic azo compounds is further increased, and has higherchemical stabilityAnd thermal stability, good optical properties and solubility.Aromatic azo compounds usually exist in a relatively stable trans structure. Under the irradiation of appropriate wavelength of ultraviolet light, the trans structure will gradually transform into a cis structure. Under the irradiation of visible light, the cis structure can be restored to a trans structure.These characteristics make aromatic azo compounds, as an important intermediate of compounds, widely used inOrganic dye, biomedicinefood additives, free radical elicitors, liquid crystal materials, nonlinear optical materials and many other fields.[2]
synthesis
Therefore, the efficient synthesis of aromatic azo compounds has attracted much attention for a long time.The synthetic methods of azobenzene compounds reported in the literature mainly include diazo coupling method, nitro reduction method, arylhydrazine oxidation method and aromatic amine oxidation method.Among them, the aromatic amine oxidation method has a broader application prospect because of its wide source of raw materials, simple reaction operation, mild reaction conditions, etc.For example, Cu (I), Cu (II), Ag nanoparticles and Au nanoparticles have been reported in the oxidation of aromatic amines to synthesize azobenzene compounds.However, these methods require pretreatment of the catalyst or the participation of oxygen, and the raw materials are expensive.[2]
Research progress
School of Chemistry, Chemical Engineering and Biological Engineering, Donghua UniversityAn Yulong et al. investigated silver carbonate as catalyst and oxidantPotassium tert butanolUnder the assistance of, the heating reaction in chlorobenzene has been carried out to synthesize aromatic azo compounds with good reaction activity, which provides a simple and effective method for the synthesis of azobenzene compounds.The specific steps are as follows: Unless otherwise specified, all reactions are carried out in an open environment.Add 1 mmol of aromatic amine, 2 mmol of silver carbonate, 2 mmol of potassium tert butanol and 5 mL of chlorobenzene into the reaction flask in turn, heat them to 120 ℃ and stir them for 3h (monitor the progress of the reaction through TLC).After the reaction, cool to room temperature, evaporate the solvent under reduced pressure, add 50 mL of ethyl acetate and 20 mL of water, fully shake, and separate the organic layer. Extract the water layer with ethyl acetate 3 times, 10 mL each time.Combine the organic layers, dry the anhydrous sodium sulfate, and perform column chromatography (silica gel column 100-200 mesh, petroleum ether as eluent) to obtain azobenzene compounds.[2]
Hazards and limitations
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Many azo compounds have carcinogenic effects. For example, the cream yellow used for margarine coloring can induce liver cancer, which is prohibited;AsindicatorOfMethyl redCan cause bladder andBreast tumor。Although some azo compounds are not carcinogenic, their toxicity isNitro compoundSimilar to aromatic amine.In order to protect human health and provide consumer safety, the Netherlands, Austria and Germany have successively adopted mandatory rules to prohibit the use of colorants containing azo in consumer goods.On September 11, 2002 and January 6, 2003, the European Parliament and the European Commission also issued the 2002/61/EC and 2003/3/EC Directives, which restrict the use of carcinogenic azo colorants in certain textiles and leather products, and prohibit the sale of goods colored with restricted azo colorants.
Directives 2002/61/EC and 2003/3/EC were gradually incorporated into national laws and came into force on September 11, 2003 and June 30, 2004 respectively.Among 22 aromatic amines, the content of azo colorant (aromatic amine) in one or more aromatic amines shall be less than 30mg/kg.In addition, the content of blue color additive with index number 611-070-00-2 in any product shall be limited to 1000mg/kg.
AZO FREE azo control has become the most important quality monitoring project in the international textile and clothing tradeEcological textilesOne of the most basic quality indicators.The decree issued by the German government in 1994 stipulates that all leather and textiles entering Germany must undergo AZO testing, and then some EU countries followed suit.Twenty four carcinogenic aromatic amine dyes banned by the EU include:
