Hydroxynaphthoate salt

The BON or BONA Reds and Maroons derive their name from /(-hydroxynaphthoic acid, also known as 3-hydroxy-2-naphthoic acid. BON is used as a general coupling component for the entire group with various dia/oi.i/ed airlines containing salt-forming groups. 

High molecular weight quaternary salts such as bephenium hydroxynaphthoate (XXI) and pyrvinium embonate (XXII), being quaternary, have low lipid solubility but also have... 

This important development was soon followed by the appearance of many other substances based upon /5-hydroxynaphthoic acid anilide which were capable of coupling with diazonium salts, of which a few examples are ... 

The very heavy shades such as blacks and navies cannot be dyed by conventional methods on polyester fibres, even with the help of carriers. Since the difficulty is the slow diffusion of the larger dyestuff molecules into the closely packed crystalline structure of the fibre, the obvious approach is to present simple molecules and cause them to combine to form a coloured pigment after they have entered. Brenthols and Naphthol AS products are not adsorbed by polyesters from aqueous solutions of their sodium salts. A limited measure of success was achieved by immersing the goods in a suspension of naphthoic acid anilide derivatives and then coupling with a diazotized base. The results were more successful, however, when coupling components with smaller molecules were used and a- and /3-naphthoIs, applied from suspension, were satisfactory but jS-hydroxynaphthoic acid proved to be the most suitable. 

Usually salt formation is carried out to increase the solubility of the base, however, salts with lower solubilities are sometimes prepared to, e.g., mask taste, provide slower dissolution and increase chemical stability. An example of salt formation to decrease dissolution rate is described by Benjamin and Lin (1985), who prepared a range of salts of an experimental antihypertensive as shown in Table 3.10. The solubilities and intrinsic dissolution rates (IDR) of the prepared salts of this compound are also shown in Table 3.10. These in vitro tests showed that there were significant differences in the dissolution rate when the experiments were performed in water and buffer. However, the difference in the IDRs of the salts was similar in 0.1 M HC1. Hence, it was recommended that ebonate, 3-hydroxynaphthoate or napsylate salts should be formulated as enteric-coated dosage forms. This would avoid dissolution in the stomach acid, which could cause local GI irritation, and would still provide release of the compound. 

In some cases it is possible to directly polycondense acid and phenols evolving water at about 300 C [41]. This process works well when catalysed with compoimds of group IV or V metals tin salts are preferred, especially dialkyl tin dialkanoates or oxides. The process is not really suitable if p-hydroxybenzoic acid is involved because this can imdergo decarboxylation at >200 "C. The polymerisation is not affected because the phenol formed volatilises at the high temperatures involved, but the resultant polyester will contain less than the anticipated mole ratio of hydroxybenzoate-derived units. Hydroxynaphthoic acid does not suffer from this problem, and direct esterification processes may be used if non-benzoate copolymers are required [42]. 

Ghlorosulfonic acid added drop wise with stirring and ice-cooling during 10 min. to phenol in dimethylaniline-chloroform, after an additional 5 min. warmed 0.5 hr. at 40-50°, and the product isolated as the K-salt potassium phenyl sulfate. Y 85-90%. F. e., mostly with 2-hydroxynaphthoic arylamides, s. W. Hartrodt and H. Woohsmann, J. pr. 27, 99 (1965). 

---