273
15
15.5 Other Natural Dyes
In addition to the natural dyes Tyrian purple,
alizarin and indigo presented so far, there are
several dozen other plant dyes that have had or
still have significance in dyeing and other applications in the past. These include many flavones
and flavonoids, naphthoquinones and anthraquinones, such as red carmine from scale insects.
Alkaloids and corticoids, anthocyans and depsides as well as derivatives of chlorophyll are also
important. Another significant group of natural
dyes are carotenes, the most important of which -
β, β-carotene - turns carrots orange. Carotenes of
natural or synthetic origin are therefore used as
food colorants, e.g. in margarine. From a chemical perspective, these are tetraterpenes that have
a long, unsaturated carbon chain in which the
nine double bonds are conjugated (7 Sect. 12.3).
Further descriptions of these natural dyes,
some of which have very complex molecular structures, would go beyond the scope of this text book.
We refer here to the good books of H. Schweppe,
which are listed in the literature references.
market in 1897 after 17 years of development.
The process used today for indigo synthesis,
which has been further improved since then, is
shown in . Fig. 15.10:
5 Aniline is converted with formaldehyde
and hydrocyanic acid into phenylglycinnitrile.
5 This is hydrolyzed with sodium hydroxide
solution to form the sodium salt of phenylglycine.
5 Phenylglycine is converted in a salt melt
with sodium amide into sodium
indoxylate.
5 This is finally converted into indigo in an
oxidative hydrolysis with a total yield
of 84%.
Nowadays, the synthesis of indigo is only carried out at a few sites, e.g. in China, Brazil and
Europe only at a single plant operated by DyStar
(a joint venture of BASF, Bayer, Mitsubishi and
Hoechst) in Ludwigshafen. Natural indigo was
almost completely replaced by synthetic indigo
before the First World War.
NH 2
+ CH 2 O
+ HCN
N
H
CN
N
H
COONa
N
ONa
Na
+ NaOH
- NH 3
NaNH 2
H 2 O, O 2
N
H
O
H
N
O
Indigo
Aniline
Phenylglycinnitrile
Sodium N-phenylglycinate
Sodium indoxylate
. Fig. 15.10 The current synthesis of indigo
15.4 · Indigo, the “King of Dyes”
15
15.5 Other Natural Dyes
In addition to the natural dyes Tyrian purple,
alizarin and indigo presented so far, there are
several dozen other plant dyes that have had or
still have significance in dyeing and other applications in the past. These include many flavones
and flavonoids, naphthoquinones and anthraquinones, such as red carmine from scale insects.
Alkaloids and corticoids, anthocyans and depsides as well as derivatives of chlorophyll are also
important. Another significant group of natural
dyes are carotenes, the most important of which -
β, β-carotene - turns carrots orange. Carotenes of
natural or synthetic origin are therefore used as
food colorants, e.g. in margarine. From a chemical perspective, these are tetraterpenes that have
a long, unsaturated carbon chain in which the
nine double bonds are conjugated (7 Sect. 12.3).
Further descriptions of these natural dyes,
some of which have very complex molecular structures, would go beyond the scope of this text book.
We refer here to the good books of H. Schweppe,
which are listed in the literature references.
market in 1897 after 17 years of development.
The process used today for indigo synthesis,
which has been further improved since then, is
shown in . Fig. 15.10:
5 Aniline is converted with formaldehyde
and hydrocyanic acid into phenylglycinnitrile.
5 This is hydrolyzed with sodium hydroxide
solution to form the sodium salt of phenylglycine.
5 Phenylglycine is converted in a salt melt
with sodium amide into sodium
indoxylate.
5 This is finally converted into indigo in an
oxidative hydrolysis with a total yield
of 84%.
Nowadays, the synthesis of indigo is only carried out at a few sites, e.g. in China, Brazil and
Europe only at a single plant operated by DyStar
(a joint venture of BASF, Bayer, Mitsubishi and
Hoechst) in Ludwigshafen. Natural indigo was
almost completely replaced by synthetic indigo
before the First World War.
NH 2
+ CH 2 O
+ HCN
N
H
CN
N
H
COONa
N
ONa
Na
+ NaOH
- NH 3
NaNH 2
H 2 O, O 2
N
H
O
H
N
O
Indigo
Aniline
Phenylglycinnitrile
Sodium N-phenylglycinate
Sodium indoxylate
. Fig. 15.10 The current synthesis of indigo
15.4 · Indigo, the “King of Dyes”