Mono- and dipotassium salts of azo compounds

Details Mono- and dipotassium salts of azo compounds Mono- and dipotassium salts of azo compounds

2000-09-19

2001-08-28

Powers, Fiona T. (Department: 1626)

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

Organic compounds

Azo

C534S602000, C534S707000, C534S737000, C534S767000, C008S685000, C008S919000, C106S480000, C106S496000, C524S190000

Reexamination Certificate

active

06281338

ABSTRACT:

The invention relates to the mono and dipotassium salts of azo compounds of the formula (I) and to their hydrates, processes for their preparation, their use for preparing metal complexes, substrates containing the thus obtainable metal complexes and potassium metal complexes which contain at least one guest compound.
The use of azobarbituric acid and its metal salts, especially those of polyvalent metals, as pigments is described in DE-A-2 064 093.A suitable method for preparing the salts of polyvalent metals is said to be the reaction of barbituric acid with an azo group transfer agent, for example benzenesulphonyl azide, in an alkaline medium by the method of Regnitz (Angewandte Chemie, 79, 786 (1967)) in the presence of appropriate metal salts or the reaction of azobarbituric acid with salts of polyvalent metals.
EP-A-297 397 utilizes azidoformamidinium salts as azo group transfer agents for preparing diazo compounds of &agr;,&ggr;-diketones, for example barbituric acid. It also describes the preparation of the corresponding azo compounds, for example azobarbituric acid, by coupling the thusly prepared diazobarbituric acid with barbituric acid in a sodium-alkaline medium.
EP-A-73 463 discloses intercalation compounds of the metal salts of azo derivatives of certain &agr;,&ggr;-diketones, including of barbituric acid, and their use as pigments. The method disclosed for preparing the azobarbituric acid comprises the reaction of barbituric acid with an azo group transfer agent in a neutral or alkaline medium by the Regnitz method (see above) with or without isolation of the diazobarbituric acid intermediate. However, the only azo group transfer agent used is sodium nitrite, so that the azobarbituric acid is obtained as sodium salt. The sodium azobarbiturate prepared by the syntheses described in the literature contains appreciable amounts of up to 15 mol % of unconverted diazobarbituric acid as included impurity. In the course of the subsequent reaction with other metal salts, especially with nickel salts (preparation of C.I. Pigment Yellow 150), and intercalation, the diazobarbituric acid likewise leads to unwanted byproducts, which lead to impure pigments.
It has now been found that, surprisingly, the mono- and dipotassium salts conforming to the formula (I) or one of its tautomeric structures
where
R and R′ are independently OH, NH
2
, NH—CN, acylamino or arylamino and
R
1
and R
1′
are independently —OH or —NH
2
,
and also their hydrates do not have these disadvantages. The salts of the invention preferably contain only negligible quantities, if any, of diazobarbituric acid.
Aryl substituents in the formula (I) are preferably phenyl or naphthyl, which may each be substituted for example by halogen such as F, Cl, Br, —OH, C
1
-C
6
-alkyl, C
1
-C
6
—alkoxy, —NH
2
,—NO
2
and —CN.
Acyl substituents in the formula (I) are preferably (C
1
-C
6
-alkyl)-carbonyl, phenylcarbonyl, C
1
-C
6
-alkylsulphonyl, phenylsulphonyl, optionally C
1
-C
6
-alkyl-,phenyl- and naphthyl-substituted carbamoyl, optionally C
1
-C
6
-alkyl-, phenyl- and naphthyl-substituted sulphamoyl or optionally C
1
-—C
6
-alkyl-, phenyl-naphthyl-substituted guanyl, where the alkyl radicals mentioned may be substituted for example by halogen such as Cl, Br, F, —OH, —CN, —NH
2
or C
1
-C
6
-alkoxy and the phenyl and naphthyl radicals mentioned may be substituted for example by halogen such as F, Cl, Br, —OH, C
1
-C
6
-alkyl, C
1
-C
6
-alkoxy, —NH
2
, —NO
2
and —CN.
Very particularly preferred potassium salts according to the invention are those of azo compounds of the formula (I) which in the form of their free acid conform to one of its tautomeric structures of the formula (II)
where
R and R′ are independently OH and NHCN.
Preference is given here in particular to those novel potassium salts of azo compounds of the formula (II) which in the form of their free acid correspond to one of the tautomeric structures of the formulae (IIa to IIc)
Particular preference is given to the mono- or dipotassium salt of the azobarbituric acid of the formula (IIa)
or its hydrates. These preferably contain only negligible amounts, if any, of diazobarbituric acid and thus do not have the above disadvantages.
It is likewise a surprise that the mono- and dipotassium salts of the formula (I), but especially the monopotassium salt of the azobarbituric acid of the formula (IIa), are also significantly more suitable for the synthesis of the corresponding metal complexes of azobarbituric acid and its intercalation compounds, for example C.I. Pigment Yellow 150,than the customarily employed sodium salt, since the process is much more rapid.
A further advantage of the mono- or dipotassium salts according to the invention is that the customary synthesis conditions will always provide reproducible product qualities, whereas this is not the case with the corresponding sodium salts. Since the quality of the reactants affects the quality of the resulting pigments as a result of reaction with the corresponding metal salts, the potassium salts according to the invention also directly affect the resulting pigments. The mono- or dipotassium salts according to the invention are therefore particularly advantageous, as compared with the sodium salts customarily used, for preparing the metal complexes of azo compounds, especially of azobarbituric acid and its intercalation compounds. The potassium salts of the invention may also be present as hydrates, that is to say they may host water of crystallization in their crystallized form. The monopotassium salts of the invention preferably contain approximately 0.5 to 1 mol equivalent of water of crystallization.
Particular preference is given to monopotassium salts of azobarbituric acid of the formula (IIa) as monohydrate.
The particularly preferred monohydrate detaches one mole equivalent of water of crystallization at 135° C.±10° C. when subjected to the conditions of differential scanning calorimetry (DSC) with a heating rate of 10 K/min.
The similarly preferred monohydrate of azobarbituric acid detaches one mole equivalent of water of crystallization at 230° C.±10° C. when subjected to the conditions of differential scanning calorimetry (DSC) with a heating rate of 10 K/min.
For simplicity, the monohydrate which loses its water of crystallization at about 135° C. will hereinafter be designated the &agr;-form and the monohydrate which loses its water of crystallization at about 230° C. as the &bgr;-form. The X-ray diffraction spectra of the two hydrate forms do not differ.
The similarly preferred monopotassium salt of azobarbituric acid detaches 0.4 to 0.6, especially 0.5,mol equivalent of water of crystallization at 195° C. +10°C. when subjected to the conditions of DSC with a heating rate of 10 K/min.
The invention further provides a process for preparing the inventive mono- or dipotassium salts of the azo compounds of the formula (I), characterized in that the diazo compound of the formula (Va) or (Vb)
where R, R
1
, R′ and R
1
′ are each as defined above,
in the form of its free acid is coupled in the presence of alkaline potassium salts with barbituric acid or its derivatives of the formula (IVa) and/or (IVb)
In a particularly preferred embodiment, the diazobarbituric acid compound of the formula (Va) or (Vb) is obtained by converting its sodium salt to the acid at a pH of less than 1.5 and isolating the acid.
The invention further provides a process for preparing the inventive mono- or dipotassium compounds, which is characterized in that barbituric acid derivatives of the formula (IVa) and/or (IVb)
where R, R′, R
1
and R
1
′ are each as defined above, are reacted with azo group transfer agents and the resulting diazobarbituric acid derivative is coupled onto barbituric acid compounds of the formula (IVa) or (IVb) in the presence of alkaline potassium compounds.
In a particularly preferred embodiment, the azo group transfer agent is prepared in the presence of potassium compounds, especially potassium nitrite, as sole alkali sour

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