Benzotriazole (BTA), a vital fine chemical, has extensive applications as a corrosion inhibitor for copper alloys, an antirust agent for metals, and an intermediate in organic synthesis. It serves critical roles in coatings, lubricants, synthetic dyes, detergents, UV stabilizers, and growth regulators, driving demand across industries like automotive, metallurgy, and chemicals. With rapid economic growth, cost-effective BTA production has become essential, yet traditional methods face significant hurdles, including high operational expenses and safety risks.

Existing synthesis routes, such as the ortho-phenylenediamine approach (from J. Chem. Soc., 1926), ortho-nitrohydrazine methods (Chemical World, 1998), or ortho-nitrochlorobenzene-based processes (as in DE3117985), rely heavily on costly or scarce raw materials. These techniques often occur under extreme temperatures, require large hydrazine hydrate inputs, and pose explosion threats during solvent recovery. For instance, prior art involving solvents like n-heptanol or polyethylene glycol improves yield but amplifies costs and complexity, limiting scalability and safety. As research highlights (Fine Chemicals, 2006; Chemical Technology Development, 2010), such inefficiencies spur the need for innovation.

The novel synthesis process addresses these challenges through a streamlined, two-step method: First, converting ortho-nitrochlorobenzene to 1-hydroxybenzotriazole (HBTA) with hydrazine hydrate in a DMSO medium, then reducing HBTA to pure BTA using iron powder. Key steps include heating the mixture at 115°C for reflux, followed by hydrazine release via sodium hydroxide, and vacuum distillation for solvent recovery. A final salt crystallization step ensures high-purity output. This design minimizes hazards while optimizing resource use for industrial adaptation.

Critical innovations center on DMSO as a homogeneous solvent, which enables efficient reactions at lower hydrazine ratios. Preferentially, a 1:1 DMSO-to-ortho-nitrochlorobenzene mass ratio and a 3.5-4:1 hydrazine molar ratio reduce chemical consumption by over 30% versus older systems. Additionally, the process facilitates near-complete recovery of DMSO and hydrazine under controlled vacuum conditions (10-20 kPa), cutting costs and mitigating explosion risks. As experiments confirm, yields reach up to 91% with 99% purity, outperforming alternatives that peak at 84%.

Implementation details, demonstrated in multiple examples, show consistent results. In one optimized trial (similar to Example 5), combining 158g ortho-nitrochlorobenzene, 158g DMSO, and 160g 80% hydrazine hydrate at 115°C yields HBTA. After pH adjustment to 3.5 with hydrochloric acid and filtration, HBTA is reduced with iron powder and sodium chloride for BTA crystallization at -5°C. This achieves 86% yield at 98.8% purity, with HPLC validation. Efficiency escalates when scaling inputs, as seen in trials (e.g., Example 8) that delivered 91% yield through adjusted reductant ratios.

Compared to non-optimal runs—such as reduced DMSO cases yielding 59% (Example 7)—the protocol proves that precise DMSO utilization is paramount for maximizing output. The homogeneous nature of DMSO not only accelerates kinetics but also slashes energy inputs by 20%. Recapture methods via distillation in the 135-140°C range further enhance sustainability, allowing solvent reuse in subsequent batches. Overall, this synthesis revolutionizes BTA manufacturing by boosting productivity, slashing expenses by an estimated 40%, and elevating safety standards in chemical plants, thereby supporting global industrial expansion with reliable, eco-friendlier outputs.