Letter acids

Amine- and / or hydroxy-substituted naphthalene sulfonic acids are referred to as letter acids . They are important intermediates in dye chemistry . The name letter acid is derived from the fact that these acids are usually only named with a preceding letter, for example "H-acid". The letters were assigned historically and the choice of letter is not always comprehensible. Some acids are also labeled with the name of their discoverer (for example "Brönner acid") or bear the name of the company that first made this compound (for example "Cassella acid"); The last two types are also counted among the letter acids. The letter acids are used as diazo or coupling components in azo couplings or as substituents (for example to substitute a chlorine atom in cyanuric chloride ).

Naphthylamine sulfonic acids

One or more naphthylamine sulfonic acids are obtained from the naphthylamines α-naphthylamine and β-naphthylamine , depending on the reaction conditions, by sulfonation . More highly aminated compounds can be obtained by nitration and subsequent Béchamp reduction .

Naphthol sulfonic acids

One or more naphthol sulfonic acids are obtained from naphthols by sulfonation, depending on the reaction conditions. Aminated compounds can be obtained by nitration and subsequent Bechamp reduction.

Aminohydroxy naphthalene sulphonic acids

see aminohydroxynaphthalenesulfonic acids

nomenclature

The compounds have long been used as intermediates in the manufacture of azo dyes . Since the systematic names are confusing, most of them have been given trivial names. The salts of the sulphonic acids ( sulphonates ) are usually named after the "stem-trivial name": H- acid → H- salt , possibly also the cation ( sodium - H -salt). The trivial nomenclature is made even more confusing by the numbering of the substituents. Historically and for reasons of manufacturing technology, the carbon atom that carries the hydroxyl group and the one that carries the amino group is inconsistently given the locant 1 .

The trivial nomenclature was mainly created in the German-speaking area. In English , the translation is usually 1: 1 ( Brönner acid → Broenner's acid , also Brönner's acid ).

Examples

Letter acids of color chemistry (according to Römpp Lexikon Chemie )

Short name	Full name ( IUPAC )	CAS No .:	structure	Remarks
H-acid	4-amino-5-hydroxynaphthalene-2,7-disulfonic acid	90-20-0		very important as a coupling component for red (monoazo) and blue (bisazo) dyes
I-acid (name of I so-γ-acid)	7-amino-4-hydroxynaphthalene-2-sulfonic acid	87-02-5		very important as a coupling component for scarlet-red (monoazo) and red-brown (bisazo) dyes
γ-acid	6-amino-4-hydroxynaphthalene-2-sulfonic acid	90-51-7		important for red monoazo dyes which are lightfast as coupling components
K acid	4-amino-5-hydroxynaphthalene-1,7-disulfonic acid	130-23-4		as a coupling component for red, lightfast monoazo dyes
Tobias acid (also A acid)	2-aminonaphthalene-1-sulfonic acid	81-16-3		as a diazo component
Sulfo-Tobias acid	2-aminonaphthalene-1,5-disulfonic acid	117-62-4		as a diazo component
Broenner acid (also Brönner acid, Amino-Schäffer acid)	6-aminonaphthalene-2-sulfonic acid	93-00-5
Schäffer acid (α) (also α-Schäffer acid, tree acid)	1-hydroxynaphthalene-2-sulfonic acid	567-18-0
C acid (also Cassella acid)	3-aminonaphthalene-1,5-disulfonic acid	131-27-1		as a diazo and coupling component
Croceic acid (also Bayer acid, Rumpff acid)	7-hydroxynaphthalene-1-sulfonic acid	132-57-0
Neville Winther Acid	4-hydroxynaphthalene-1-sulfonic acid	84-87-7
L-acid (also azuric acid, oxylaurent acid)	5-hydroxynaphthalene-1-sulfonic acid	117-59-9
Schäffer acid (β)	6-hydroxynaphthalene-2-sulfonic acid	93-01-6
F acid (also Cassella acid)	7-hydroxynaphthalene-2-sulfonic acid	92-40-0
G acid	7-hydroxynaphthalene-1,3-disulfonic acid	118-32-1
δ acid (also CS acid, Schöllkopf acid, oxy-Chicago acid)	4-hydroxynaphthalene-1,5-disulfonic acid	117-56-6
D-acid (double name, see 81-05-0!)	4-hydroxynaphthalene-1,6-disulfonic acid	6361-37-1
ε-acid (also Andresen acid)	8-hydroxynaphthalene-1,6-disulfonic acid	117-43-1
R-acid	3-hydroxynaphthalene-2,7-disulfonic acid	148-75-4
RG acid (also GR acid)	4-hydroxynaphthalene-2,7-disulfonic acid	578-85-8
Boeniger acid (also 1,2,4 acid)	4-amino-3-hydroxynaphthalene-1-sulfonic acid	578-85-8
S acid (also Chicago S acid)	4-amino-5-hydroxynaphthalene-1-sulfonic acid	83-64-7
M acid	8-amino-4-hydroxynaphthalene-2-sulfonic acid	489-78-1
SS acid (also Chicago SS acid)	4-amino-5-hydroxynaphthalene-1,3-disulfonic acid	82-47-3
Sulfo-I-acid (also I-di-acid)	2-amino-5-hydroxynaphthalene-1,7-disulfonic acid	6535-70-2		as a coupling component
RR acid (also 2R acid, Columbia acid)	3-amino-5-hydroxynaphthalene-2,7-disulfonic acid	90-40-4
Naphthionic acid (also piria acid)	4-aminonaphthalene-1-sulfonic acid	84-86-6
Purpuric acid (also laurent acid)	5-aminonaphthalene-1-sulfonic acid	84-89-9
Dahl acid (also Dahl acid I, D acid (double name, see 6361-37-1!))	6-aminonaphthalene-1-sulfonic acid	81-05-0
Badische Acid (also Forsling Acid I)	7-aminonaphthalene-1-sulfonic acid	86-60-2
Peric acid (also Forsling acid I)	8-aminonaphthalene-1-sulfonic acid	82-75-7		as a coupling component
Cleve γ acid (also Cleve acid)	4-aminonaphthalene-2-sulfonic acid	134-54-3
Cleve-β-acid (also 1,6-Cleve-acid, μ-acid)	5-aminonaphthalene-2-sulfonic acid	119-79-9
Cassella F acid (also δ acid, F acid (double name, see 92-40-0!), Bayer acid (?))	7-aminonaphthalene-2-sulfonic acid	494-44-0
1,7 Cleve Acid	8-aminonaphthalene-2-sulfonic acid	119-28-8
Amino-I-acid (also Amino-J-acid)	6-aminonaphthalene-1,3-disulfonic acid	118-33-2
Amino-G acid	7-aminonaphthalene-1,3-disulfonic acid	86-65-7
Amino-S-acid (also disulfo-S-acid)	4-aminonaphthalene-1,5-disulfonic acid	117-55-5
Dahl acid III	4-aminonaphthalene-1,6-disulfonic acid	85-75-6
Amino-ε-acid	8-aminonaphthalene-1,6-disulfonic acid	129-91-9
Dahl acid II	4-aminonaphthalene-1,7-disulfonic acid	85-74-5
Alenic acid (also Freund's acid (1,3,7)) 1)	4-aminonaphthalene-2,6-disulfonic acid	6362-05-6
Kalle acid	1-aminonaphthalene-2,7-disulfonic acid	486-54-4
Amino-R acid	3-aminonaphthalene-2,7-disulfonic acid	92-28-4
Friend Acid (1,3,6) 1)	4-aminonaphthalene-2,7-disulfonic acid	6251-07-6
B acid (also melan acid)	8-aminonaphthalene-1,3,5-trisulfonic acid	17894-99-4
2R amino acid	7-aminonaphthalene-1,3,6-trisulfonic acid	118-03-6
T acid (also Koch acid, amino H acid)	8-aminonaphthalene-1,3,6-trisulfonic acid	117-42-0		not identical to 2,4,5-trichlorophenoxyacetic acid (also called T-acid )

¹⁾ named after Louis Freund.

swell

1. ↑ Entry on letter acids. In: Römpp Online . Georg Thieme Verlag, accessed on May 7, 2014.