1. Field of the Invention
The present invention relates to a monoazo compound used to color petroleum products and hydrocarbon solvents and for other purposes, and a dense solution of said monoazo compound in a hydrocarbon solvent.
2. Description of the Prior Art
As coloring agents for synthetic resins, lacquers, natural and synthetic waxes, solid paraffins, etc., various monoazo oil-soluble dyes listed in the Color Index (e.g., C.I. Solvent Colors: YELLOW 2, 7, 9, 10, 11, 12, 14, 16, 18, 56, 58; ORANGE 2, 7; RED 2, 24) are known.
Industrial organic solvents and petroleum products such as gasoline, lamp oil and light oil are colored for the purpose of their identification. For example, fuel oil is colored with an oil-soluble dye with improved solubility in hydrocarbon organic solvents. In this case, the oil-soluble dye is usually used as a solution of the maximum possible concentration in the hydrocarbon organic solvent.
Proposals concerning oil-soluble azo dyes for these uses are disclosed in the specification for British Patent No. 1142239, Japanese Patent Examined Publication Nos. 17390/1981 and 36940/1982 and Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 2525/1971, 94029/1975, 99959/1980 and 187456/1983.
For example, the specification for British Patent No. 1142239 describes a monoazo dye synthesized from m-toluidine and N,N-diethylaniline or N,N-dipropylaniline, and a dense solution thereof used to color petroleum and for other purposes.
Also, Japanese Patent O.P.I. Publication No. 2525/1971 describes that the dense solution prepared by dissolving a monoazo dye represented by the following formula: ##STR2## in an aromatic hydrocarbon solvent such as xylene is capable of imparting a bluish red color on petroleum products.
Japanese Patent O.P.I. Publication No. 99959/1980 discloses a monoazo dye capable of forming a salt with aliphatic amine obtained by reaction of an aniline substituted by a long-chain alkyl having 8 to 18 carbon atoms and a pyrazolone derivative having a carboxyl group or .beta.-naphthol.
Japanese Patent O.P.I. Publication No. 94029/1975 discloses a monoazo dye obtained by reaction with, for example, a alkylamino-substituted .beta.-naphthol derivative having 4 to 21 carbon atoms as a coupling component, stating that this red dye dissolves well or limitlessly in aromatic and aliphatic substances, and that it can be used to color automobile fuels, varnish, wax and fat.
The above-mentioned oil-soluble dyes listed in the Color Index have any one or more of the following drawbacks:
1) Solubility in hydrocarbon solvents, particularly paraffin solvents, is low. The saturation concentration of this kind of conventional oil-soluble dyes in paraffin solvents at normal temperature does not exceed 15% by weight. For example, the saturation concentration in hexane at normal temperature is not higher than 5% by weight.
2) Coloring power for petroleum products such as fuel oil is weak. Colored fuel oil should make it possible to distinguish between petroleum products to be taxed by coloring with coloring agents of concentrations of the order of some dozens of ppm.
3) Because of high crystallinity and high intermolecular aggregating force, the oil-soluble dye is easy to extract from the colored system. A countermeasure is therefore necessary against tax evasion by discoloring the petroleum products to be taxed.
4) In the case of dyes of long-chain alkyl-substituted structure, the high molecular weight lowers the coloring density per unit part by weight.
Also, the dye described in Japanese Patent O.P.I. Publication No. 99959/1980 poses a problem in coloring power, whose solubility in ligroine or kerosine is 0.5 to 1.5 g/10 cc.
The object of the present invention is to provide a monoazo compound which is excellent in compatibility with, solubility in and coloring power for almost all water-immiscible organic liquids, such as various hydrocarbon solvents, petroleum solvents, fuel oils, lubricating oils, plastics and hydrophobic synthetic fibers, and which is suitable for use to color molten plastics and dope dyeings and to color thermal transfer ink because of the low melting point, and a dense solution thereof which is free of the problems of powder formation and dust scattering because of the liquid form, which can easily be prepared by simple dissolution operation, which quickly and uniformly diffuses and dissolves in coloring subjects such as petroleum products, and which is capable of coloring fuel oil etc. to a desired distinguishable color density in small amounts.