Process for the preparation of aqueous diazonium salt solutions

Details Process for the preparation of aqueous diazonium salt solutions Process for the preparation of aqueous diazonium salt solutions

2000-05-02

2001-03-27

Powers, Fiona T. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Diazo or diazonium

Reexamination Certificate

active

06207809

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a novel process for the preparation of aqueous diazonium salt solutions. Aqueous diazonium salt solutions are used, for example, for the preparation of azo compounds, in particular of dyes and pigments. In the literature only a few methods for the preparation of aqueous diazonium salt solutions, starting from aromatic nitro compounds, are described, and even these have only been developed for the synthesis of small amounts for scientific purposes.
Usually, the aromatic nitro compound is firstly reduced to give the corresponding aromatic amine which, following work-up and isolation, is reacted in a second, separate step with an alkaline earth metal nitrite to give the desired diazonium salt. Here, the reduction is usually carried out as a catalytic hydrogenation using a suitable catalyst. The solvents normally used are organic solvents, in particular low molecular weight alcohols, such as methanol, ethanol or propanol, and also corresponding esters, such as, for example, ethyl acetate. After the aromatic amine formed in the process has been isolated, it is reacted in aqueous solution with nitrite to give the corresponding diazonium salt.
A procedure of this type is described in U.S. Pat. No. 5,051,131. Here, aromatic nitro compounds prepared by reacting nitrobenzoyl chloride derivatives and nitrobenzenesulfonyl chloride derivatives with aliphatic bisamines are reduced in ethanolic solution using a palladium catalyst to give the corresponding aromatic amine, and the latter is isolated from the solution. In the next step, the isolated amine is reacted in aqueous acetic acid solution with sodium nitrite to give the desired diazonium salt solution. A disadvantage of this procedure is the use of different solvents in the two reaction stages since, following the first stage, the organic solvent used has to be removed in a separate step and is formed as a waste product.
Because of the combustibility and possible formation of ignitable solvent vapor/air mixtures, this step is complex on an industrial scale and is also unacceptable from a safety viewpoint.
SUMMARY OF THE INVENTION
The object of this invention is to find a simple process for the preparation of aqueous solutions of diazonium salts of the formula (1), starting from aromatic nitro compounds of the formula (2). In addition, the process according to the invention should avoid solvents which are unacceptable in terms of safety, and the resulting products should be produced in high yield with minimum amounts of waste.
Surprisingly, we have found that if the aromatic nitro compound of the formula (2) is converted into a water-soluble salt or is in the form of such, it can be reduced in aqueous solution to a salt of the aqueous aromatic amine of the formula (3) which, optionally following removal of the catalyst, can be converted directly using a diazotization reagent, such as, for example, a nitrite, into the desired aqueous diazonium salt solution, without the need to change the solvent.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides a process for the preparation of aqueous solutions of diazonium salts of the formula (1)
in which some or all of the amino groups are in protonated form,
R
1
, R
2
, R
3
and R
4
, independently of one another, are hydrogen, a C
1
-C
16
-alkyl, C
3
-C
7
-cycloalkyl, C
2
-C
16
-alkenyl, aryl or a 5- to 6-membered aliphatic or aromatic heterocycle, which are optionally substituted by one or more, for example 1, 2, or 3, C
1
-C
4
alkyl radicals, halogen atoms or groups of the formula ═O, —OR′, —NR′R″, —SR′, —COR′, —COOR′, —CONR′R″, —NR′CONR″R′″ or —SO
2
NR′R″, where R′, R″, R′″ are hydrogen or a C
1
-C
10
-alkyl, C
3
-C
7
-cycloalkyl, C
2
-C
16
-alkenyl, aryl or a 5- to 6-membered aliphatic or aromatic heterocycle, or where R′ and R″, or R″ and R′″, or R
3
and R
4
together with the adjacent N atom form a 5- or 6-membered aliphatic or aromatic heterocycle, and
R
1
and R
2
can additionally be halogen or groups of the formula —OR′, —NR′R″R′″, —SR′, —COR′, —COOR′, —CONR′R″, —SO
3
H, —PO
4
H
2
, —NR′CONR″R′″ or —SO
2
NR′R″;
A, A′ and A″, independently of one another, are a divalent group of the formula —O—, —NR′—, —S—, —CO—, —COO—, —CONR′—, —NR′CONR″— or —SO
2
NR′—;
B, B′ and B″, independently of one another, are a substituted or unsubstituted C
1
-C
14
-alkylene, C
3
-C
7
-cycloalkylene, C
2
-C
14
-alkenylene, arylene or heteroarylene radical,
or B, B′ or B″ form, together with R
3
and/or R
4
and the adjacent N atom a 5- to 7-membered heterocycle;
Y
−
is F
−
, Cl
−
, Br
−
, HSO
4
−
, ½SO
4
2−
, H
2
PO
4
−
, ½HPO
4
2−
, ⅓PO
4
3−
, an anion of a pyro-, meta- or poly-phosphoric acid, BF
4
−
, PF
6
−
, HCO
3
−
, ½CO
3
2−
, NO
2
−
, NO
3
−
, formate, acetate, propionate, R″″SO
4
−
, R″″SO
3
−
or R″″COO
−
, where R″″ is a substituted or unsubstituted C
1
-C
21
-alkyl or aryl radical, preferably C
1
-C
10
-alkyl, naphthyl or phenyl;
k, l and m, independently of one another, are the number 0, 1, 2 or 3;
n, o and p, independently of one another, are the numbers 0 or 1;
x is an integer from 1 to 3; and
y and z are each an integer from 1 to 4, where the sum x+y+z is 3 to 5, which comprises
reacting an aqueous solution of a water-soluble salt of the aromatic nitro compound of the formula (2),
 with hydrogen and in the presence of a catalyst which catalyzes the reduction of aromatic nitro groups to amino groups, and diazotizing the aromatic amine formed in the process in the aqueous solution with a diazotization reagent to give the diazonium salt.
In the above definitions, aryl is preferably phenyl or naphthyl. Preference is given to compounds of the formula (1) and (2) in which A, A′ and A′ are —O—, —NR′—, —CONR′ or —SO
2
NR′—.
Also preferred are compounds of the formula (1) and (2) in which B, B′ and B″ are C
2
-C
6
-alkylene, C
6
-C
10
-arylene, benzylene or pyridylene which are unsubstituted or substituted by 1 to 4 radicals from the group consisting of C
1
-C
4
-alkyl, C
1
-C
4
-alkoxy, OH, NH
2
, NH(C
1
-C
4
-alkyl), NH(C
1
-C
4
-alkyl)
2
, COOH, CONH
2
, CONH(C
1
-C
4
-alkyl), CON(C
1
-C
4
-alkyl)
2
, F and Cl, or together with R
3
and/or R
4
form a heterocycle from the group consisting of pyrrolidine, piperidine, piperazine and morpholine which is optionally substituted by 1 to 6 radicals from the group consisting of C
1
-C
4
-alkyl, C
1
-C
4
-alkoxy, OH, NH
2
, NH(C
1
-C
4
-alkyl), NH(C
1
-C
4
-alkyl)
2
, COOH, CONH
2
, CONH(C
1
-C
4
-alkyl), CON(C
1
-C
4
-alkyl)
2
, F and Cl.
Also preferred are compounds of the formula (1) and (2) in which R
1
and R
2
are C
1
-C
6
-alkyl, C
5
-C
6
-cycloalkyl, C
2
-C
6
-alkenyl, C
6
-C
10
-aryl or pyridinyl which are optionally substituted by 1 to 3 radicals from the group consisting of fluorine, chlorine, bromine, C
1
-C
4
-alkoxy, NH
2
, N(C
1
-C
4
-alkyl)
2
, NH(C
1
-C
4
-alkyl), COH, CO(C
1
-C
4
-alkyl), COOH, —COO(C
1
-C
4
-alkyl), CONH
2
, CONH(C
1
-C
4
-alkyl), CON(C
1
-C
4
-alkyl)
2
, SO
2
NH
2
, SO
2
NH(C
1
-C
4
-alkyl), SO
2
N(C
1
-C
4
-alkyl)
2
and SO
3
H; or hydrogen, fluorine, chlorine, bromine, C
1
-C
4
-alkoxy, NH
2
, NH(C
1
-C
4
-alkyl), N(C
1
-C
4
-alkyl)
2
, S(C
1
-C
4
-alkyl), CO(C
1
-C
4
-alkyl), COOH, COO(C
1
-C
4
-alkyl), CONH
2
, CONH(C
1
-C
4
-alkyl), CON(C
1
-C
4
-alkyl)
2
, SO
3
H, SO
2
NH
2
, SO
2
NH(C
1
-C
4
-alkyl) or SO
2
N(C
1
-C
4
-alkyl)
2
.
Also preferred are compounds of the formula (1) and (2) in which R
3
and R
4
are C
1
-C
6
-alkyl, C
5
-C
6
-cycloalkyl, C
2
-C
6
-alkenyl, C
6
-C
10
-aryl or pyridinyl which are op

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