GB408273A - Manufacture of carbocyanine dyes - Google Patents

Abstract

Carbocyanine dyes.--By condensing an alkyl quaternary salt of a 2-methylthiazole with an ester of an orthoaliphatic carboxylic acid other than orthoformic acid, thiazolocarbocyanines substituted on the central carbon of the trimethine chain by an alkyl residue, are obtained. By using an orthoformic ester in this reaction and working under certain conditions a neothiazolocarbocyanine dye may be obtained; this product appears to be a thiazolocarbocyanine dye substituted at the central carbon atom of the trimethine chain by a further quaternary alkylthiazyl-vinyl group (structural formul are given). An excess of the orthoformic ester and the use of a quaternary salt of the 2-methylthiazole formed from a dialkylsulphate or an alkyl-p-toluenesulphonate gives a preponderating yield of the neothiazolo dye admixed with the normal thiazolocarbocyanine dye; where separation is required this is effected by the use of suitable organic solvents followed by crystallization therefom. In examples: (1) 2 - methylthiazolemethyl - or ethyl-p-toluenesulphonate is refluxed in pyridine with triethyl orthoformate and the product treated with excess potassium iodide; extraction with acetone or acetone-methylalcohol removes the normal dye and the neothiazolo dye can be crystallized from the residue taken up in methyl alcohol; (2) 2.4-dimethylthiazole methyl-p-toluenesulphonate on similar treatment and separation yields a neothiazolo dye; using the quaternary salt formed from dimethylsulphate in this reaction, the normal dye is extracted with methyl alcohol and the neothiazolo dye recrystallized from the same solvent; using the quaternary salt formed from ethyl-p-toluenesulphonate in this reaction, the product is boiled in methyl alcohol, cooled to crystallize out the less soluble normal dye and the mother liquor further concentrated to yield the neothiazolo dye; (3) 2-methyl-4-phenylthiazole methyl and ethyl-p-toluenesulphonates on similar treatment and separation treatments to those above yield neothiazolo dyes; (4) 4 - phenyl - 2 - methylthiazole methyl - p - toluenesulphonate is boiled in pyridine with trimethyl orthoacetate and the product precipitated with potassium iodide to give 4 : 4<1> - diphenyl - 3 . 3<1> . 7<1> - trimethylthiazolocarbocyanine iodide; using instead of the orthoacetate trimethyl orthopropionate the corresponding 7-ethyl substituted dye is obtained. Specifications 232,740, [Class 2 (iii)], and 378,870 are referred to.