NOVELTY - Chemical process of isolation of naphthalene sulfonic acid from fusion mass having salts of acid involves reacting fusion mass with acid, followed by isolation of product, recycle treatment, where impure mother liquor is treated for further recycling in reaction and isolation sequences carried out in steady state closed loop circuit inherently and intrinsically recycling at source level of all mother liquor generated, with cycles, where fresh water is added to make up for systemic losses such as by evaporation, where liquor is reaction medium, extraction medium and/or wash medium.    USE - As chemical process of isolation of a naphthalene sulfonic acid from fusion mass containing salts of the naphthalene sulfonic acid; and also for isolation of similar kind of sulfonic acid products like 1,8-dihydroxynaphthalene-4-sulfonic acid, 1-amino-8-naphthol-5,7-disulfonic acid, 1-amino-8-naphthol-2,4-disulfonic acid (Chicago Acid), 2-amino-8-naphthol-3,6-disulfonic acid (Gamma disulfonic acid), 2-amino-5-naphthol-7-sulfonic acid (J-acid), 2-naphthol-6-sulfonic acid (Schaffer Acid), 2-amino-5-naphthol-1,7-disulfonic acid (J-disulfonic acid), 2-phenyl amino-5-naphthol-7-sulfonic acid (Phenyl J-acid), 1-naphthylamine-8-sulfonic acid (Peri acid), 2-aminonaphthalene-4,8-disulfonic acid (C-acid), 1-amino-8-naphthol-4,6-disulfonic acid (K-acid), 1,8-dihydroxynaphthalene-3,6-disulfonic acid (Chromotropic acid), 1-naphthylamine-3,6,8-trisulfonic acid (Koch acid), 1-naphthylamine-6-sulfonic acid (Cleve Acid), 1-naphthylamine-7-sulfonic acid (Cleve acid), R-acid, G-acid, Amino G-acid, 2-amino-8-naphthol-6-sulfonic acid (Gamma Acid), 2-amino-5-naphthol-7-sulfonic acid (iso gamma acid), M-acid, 1-amino-8-naphthol-5-sulfonic acid, 1-naphthylamine-4,7-disulfonic acid and all similar naphthalene sulfonic acid and beta-naphthol derivatives having functional groups like Amino, Nitro, Halo, Hydroxy, Sulfonic, Carboxylic, Benzyl, phenyl, ketone, or aldehyde (claimed), where the sulfonic acid is used as intermediate for the production of dyes and pigments and in pharmaceuticals, agrochemicals, specialty chemicals, fine chemicals and explosives.    ADVANTAGE - The method forms the product in high overall yield and avoids use of large amounts of acids and bases. The method avoids generation of large quantities of acidic liquid waste which is difficult to recycle; does not require environmentally unsustainable reaction conditions in terms of pH, temperature, concentration, reaction agents and medium; and does not leave unsustainable impact on the environment, specifically on water bodies. The method has good conversion rate and good yield making the method economical and environmentally sustainable. The method avoids formation of organic and inorganic side products; avoids formation of large quantity of inorganic solid wastes that are contaminated with compounds like starting material, product and side products and does not cause serious pollution problem. The method is green, sustainable, economical, and does not cause harm to environment. The method allows green isolation of compound with inherent recycle of acidic mother liquor thereby avoiding drawbacks of the prior art methods. The method effectively uses commercially available customized formulations for isolation of compounds with inherent recycle of mother liquor and washings generated during process. The method provides environmentally friendly process that overcomes the problems of generation of large quantities of acidic waste resulting from conventional process; avoids the limitations encountered in the isolation of compounds from the alkali fusion mass; provides green process for isolation of compounds which are not only inexpensive in operation but also produces the product of high quality; provides improved process for producing compounds with recycle of acidic streams generated during isolation, separation and washing of product resulting in 0 liquid discharge. Since both the number and quantity of organic and inorganic impurities are comparatively less, the possibility of build of side products in acidic mother liquor during recycle is less due to use of proprietary formulation R-Cat-1 and R-Cat 2. This fact advantageously makes possible infinite number of acidic mother liquor recycles in the process. The product separation processes ensure that the solid spent formed in the process has surprisingly low levels of organic compounds and are thus green in nature. Consequently, the process does not require any liquid effluent treatment facility or elaborate solid waste disposal facility. The process is not constrained in respect of plant location, and it doesn't necessarily have to be carried out in industrial areas. The method is carried out at milder reaction conditions and at atmospheric pressure, which makes it safer. The use of the proprietary reaction formulations R-Cat 1 and R-Cat 2, or any other similar formulations makes it possible to recycle the acidic liquid streams completely. The inherent thermodynamic conditions defined in terms of pressure, temperature, pH, concentrations of reaction components, and various reaction agents is close to respective conditions occurring in the nature, thereby making the process benign and environmentally friendly. The process is carried out at such temperatures and pH values that it saves energy and therefore results in the process economy and also is greener since generation of energy mostly leads to lots of pollution.    DETAILED DESCRIPTION - A chemical process of isolation of a naphthalene sulfonic acid from fusion mass containing salts of the naphthalene sulfonic acid, which is a sustainable process involves a reaction sequence of reacting fusion mass with acid, followed by an isolation sequence, where isolation of the reaction product is completed, followed by a recycle treatment sequence, where the impure mother liquor is treated for further recycling in the reaction and isolation sequences, and further the reaction sequence and the isolation sequence are carried out in a steady state closed loop circuit capable of inherently and intrinsically recycling at source level of all mother liquor generated, with cycles, where fresh water is added only to make up for systemic losses such as by evaporation, where the mother liquor is any of the reaction medium, extraction medium, and/or wash medium, used in the process, as shown in Figure 4 of the specification.