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Heading 2927 : Diazo-, azo- or azoxy-compounds.
These compounds, the most important of which belong to the aromatic series, are characterised by two nitrogen atoms linked by a double bond.(A) DIAZO-COMPOUNDS
This group of products includes : (1) Diazonium salts. These are products of general formula RN2+X- where R is an organic radical and X- is an anion, for example : (a) Benzenediazonium chloride. (b) Benzenediazonium tetrafluoroborate.
This heading covers diazonium salts, whether or not stabilised.
This heading also covers diazonium salts diluted to standard strengths (e.g., by the addition of a neutral salt such as sodium sulphate) for the production of azo dyes. (2) Compounds of general formula RN2 where R is an organic radical, for example : (a) Diazomethane. (b) Ethyl diazoacetate. (3) Compounds of general formula R1 - N = N - N where R1 and R2 are organic radicals and R3 is either an organic radical or hydrogen, for example : (a) Diazoaminobenzene. (b) N-Methyldiazoaminobenzene. (Here R1 = R2) (c) 3,3-Diphenyl-1-p-tolyltriazene. (B) AZO-COMPOUNDS
These are compounds containing the group R1 - N = N - R2, where R1 and R2 are organic radicals with one of their carbon atoms linked directly to one of the nitrogen atoms, for example: (1) Azobenzene. (2) Azotoluenes. (Here R1 = R2) (3) Azonaphthalenes. (4) 2,2'-Dimethyl-2,2'-azodipropionitrile. (5) Aminoazobenzenesulphonic acids. (6) p-Aminoazobenzene.
The radicals R1 and R2 may themselves contain further -N=N- groups (bisazo-, trisazo-, etc., compounds). (C) AZOXY-COMPOUNDS
These are compounds of the general formula R1-N2 O-R2 in which an oxygen atom is linked to one of the two nitrogen atoms and where R1 and R2 are generally aryl radicals.
Azoxy-compounds are generally pale yellow crystalline substances. They include : (1) Azoxybenzene. (2) Azoxytoluene. (3) p-Azoxyanisole. (4) p-Azoxyphenetole. (5) Azoxybenzoic acid. (6) Azoxycinnamic acid. (7) Azoxytoluidine. Diazo- and azo-compounds are the starting point in the formation of azo dyes. They give substitution derivatives which are also included here.
Organic colouring matters are excluded from this heading and are classified in Chapter 32.
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