Patent GB-874209-A (GB)
Title: Improvements relating to the production of benzimidazolylidene compounds and the resulting products
IPC: C07D235/20
Filed: 1957-12-20
Abstract: Benzimidazolylidene compounds are prepared by condensing a benzimidazole-2-aldehyde, unsubstituted in the benzene ring, with an organic compound containing an activated methyl or methylene group and having the general formula X-CH2-Y as hereinafter defined, if necessary in the presence of an acid or basic condensation catalyst, with splitting off of water.  The organic compounds containing an activated methyl or methylene group are those in which X represents an electrophilic group such as a carbonyl, carboxyl, carboxylic ester, carboxylic amide, cyano, nitro or organic ammonium group, an aromatic-heterocyclic containing tertiary nitrogen, or a negatively substituted-aromatic isocyclic radical, and Y represents hydrogen, an inert organic group or an electrophilic group.  Specified compounds include acetophenone, phenylacetic acid, benzyl cyanide, cyano acetic esters and amides, open and cyclic 1:3-diketones, malonic esters and amides including cyclic amides such as 1:3-diketo pyrazolidines, acyl acetic esters and amides including cyclic amides such as the 5-pyrazolones, heterocyclic compounds containing an activated methyl group in the o- or p-position to a tertiary N atom, preferably in the form of a cyclammonium salt form, such as methylsubstituted pyridines, pyrimidines, pyridazine, pyrazine, azophenanthrene, quinolines, benzthiazoles, benzoxazoles and benzimidazoles, and 4-nitro-1-methyl benzenes having a negative group in the 2-position, e.g. an alkyl sulphonyl, sulphonic acid ester, sulphonamide or cyano group. The benzimidazole-2-aldehydes may be 1-substituted by, for example, lower alkyl groups such as inter alia methyl, butyl, cyano-, hydroxy- or ethoxy-ethyl groups.  The condensation is effected under the usual conditions for the condensation of an aldehyde with an active-methyl or -methylene compound.  Suitable catalysts are nitrogen bases, caustic alkalies, alkali metal alcoholates, zinc chloride, boric acid, fluoboric acid, sulphuric acid and hydrogen chloride.  In some cases a reactant serves as catalyst (of Examples 9, 10 and 14).  The water formed may be removed by an entrainer or a fatty acid anhydride.  The products obtained from the heterocyclic compounds containing an activated methyl group are optical brightening agents.  The compounds obtained from the 4-nitro-1-methyl benzenes may be converted into brightening agents by reducing the nitro-group and then reacting the amino group with an acylating agent, potassium cyanate or a cyanuric halide.  The compounds prepared from araliphatic ketones may be reacted with aryl hydrazines to give fluorescent 1:3-diaryl-5-benzimidazolyl-pyrazolines.  In the examples, benzimidazole-2-aldehyde is condensed with (1) 2-methyl sulphonyl-4-nitro toluene, the product being reduced to the amino-compound which is reacted with acetic anhydride or potassium cyanate, (4) acetophenone, (5) 1:2-dimethyl benzimidazole, (6) 1-ethyl-2-methyl benzimidazole or (12) 1-b -hydroxy ethyl-2-methyl benzimidazole; 1-methyl benzimidazole-2-aldehyde is condensed with (2) 4-nitro-2-methyl sulphonyl toluene, the product being reduced to the corresponding amino compound which is reacted with acetic anhydride, potassium cyanate or diglycollic acid anhydride, (3) the phenyl ester of 4-nitro toluene-2-sulphonic acid, the product being saponified and reduced to convert the nitro-group to -NH2 which is then acylated, (5) 2-methyl benzimidazole, (6) 1:2-dimethyl benzimidazole, (7) 2:5-dimethyl benzoxazole yield a product existing in cis- and trans-forms which are separated, the cis-form being converted into the optical brightening trans-form on heating, (8) quinaldine, (9) 1:2-dimethyl quinolinium iodide, (10) 2 : 3 - dimethyl - benzthiazolium iodide, (12) 1-b -hydroxy ethyl -2-methyl benzimidazole and (14) 1-ethyl-2-methyl benzimidazole, part being in hydrochloride form as catalyst; (11) 1-ethyl benzimidazole-2-aldehyde is condensed with 1:2-dimethyl benzimidazole and (13) 1-phenyl benzimidazole is condensed with 1:2-dimethyl or 2-methyl benzimidazole.  Other 2-methyl benzimidazole reactants are specified containing chlorine in the benzene ring.  Benzimidazole-2-aldehyde reactants are prepared by reacting suitable 1:2-diamino benzenes with glyoxylic acid alkyl ester dialkyl acetals and then saponifying the acetal group or by condensing the diamino benzenes or their hydrohalic salts with dichloro- or dibromo-acetic acid and saponifying the resulting 2-dihalo benzimidazole.ALSO:Optical brightening and sometimes dyeing of such materials as wool, fibres of cellulose, polyacrylonitriles, polyesters and polyamides, and cotton and nylon fabrics is effected by means of benzimidazolyl compounds prepared by condensing a benzimidazole- 2-aldehyde, unsubstituted in the benzene ring, with an organic compound containing an activated methyl or methylene group which is (1) a heterocyclic compound having a methyl group in the o-or p-position to a tertiary nitrogen atom in the ring, this nitrogen preferably being in the form of a cyclammonium salt, such as a methyl substituted pyridine, pyrimidine, pyradazine, pyrazine, quinoline, azophenanthrene, benzoxazole, benzthiazole or benzimidazole, (2) an araliphatic ketone, the product then being condensed with an aryl hydrazine to yield a fluorescent 1 : 3-diaryl- 5-benzimidazolyl-pyrazoline, or (3) a nitro-toluene having an activating negative substituent such as an alkyl sulphonyl, sulphonic acid ester, sulphonamide or cyano group, the resulting nitro styryl-benzimidazole product being converted into the desired brightening agent by reduction of the nitro-group to the amino-group followed by reaction of the latter with an acylating agent, e.g. acetic anhydride or diglycolic acid anhydride, or with a cyanuric halide or potassium cyanate.  The condensation of the benzimidazole- 2-aldehyde is effected with splitting-out of water, if necessary with the aid of a basic or acidic condensation catalyst.  The aldehyde may be substituted in the 1-position by, for example, a lower alkyl, hydroxyethyl, methoxy- or ethoxy ethyl, cyanoethyl or hydroxypropyl group.  Numerous examples of the brightening agents are given.  The compounds prepared from 1-methylbenzimidazole- 2-aldehyde and 1 : 2-dimethyl-quinolinium iodide and 2 : 3-dimethyl-benzthiazolium iodide dye cellulose and polyacrylonitrile fibres a fluorescent yellow colour.