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Pantoprazole Protonix / Pantoloc / Controloc

A proton pump inhibitor for ulcers, reflux and erosive oesophagitis, sold as the sodium sesquihydrate salt. It is one of the most widely consumed generic medicines in the world, which is why its manufacturing cost has been worked over so thoroughly.

  • Proton pump inhibitor (H⁺/K⁺-ATPase)
  • FDA 2000
  • C16H15F2N3O4S · 383.37 g/mol
  • CAS 102625-70-7

Coupling and oxidation in water

3 stages · 85% isolated yield

The hard part of making any prazole is the oxidation: the sulfide has to become the sulfoxide and stop there, because over-oxidation gives the sulfone, which is so similar to the product that separating the two needs preparative chromatography at plant scale. The usual answers are an expensive peracid at low temperature, or peroxide with a tungstate or molybdate catalyst over one to two days. This process instead uses household-strength sodium hypochlorite as the oxidant, and runs both the coupling and the oxidation in water with no organic solvent at all. Hypochlorite oxidises a thioether far faster than peroxide does, so the control comes not from the oxidant being slow but from dosing it in over two to three hours at 0–5 °C against a 1.05-fold excess of sulfide: the oxidant is consumed as it arrives and never accumulates, which is what keeps the sulfone down at 0.02%. Neither intermediate is isolated or dried, which removes the slow drying of a low-melting sulfide from the critical path.

Scale: 100 g of the benzimidazole per batch in a 3 L flask, giving 170 g of the API

5-(Difluoromethoxy)-2-mercapto-1H-benzimidazole no public CAS
+
2-(Chloromethyl)-3,4-dimethoxypyridine hydrochloride no public CAS
Step 1 99.8% isolated
NaOH (2 equiv), water, no organic solvent
10 volumes of water, 25–30 °C, 3 h
the two halves are joined in water alone · the volume of water decides the outcome: at 5 volumes the mixture is too thick to stir properly and the yield falls to 94%, at 10 volumes it reaches 99.8% · filtered off and carried forward as a wet cake, never dried
Pantoprazole sulfide, taken on as a wet cake no public CAS
Pantoprazole sulfide, taken on as a wet cake no public CAS
Step 2 98.3% conversion
NaOCl (1.05 equiv, 9% solution), NaOH (1.5 equiv)
water, 0–5 °C, oxidant added over 2–3 h
sulfide to sulfoxide, and no further · three numbers matter and the paper measures all of them: 1.05 equivalents of hypochlorite (1.2 pushes the sulfone to 0.10%), 0–5 °C (5–10 °C pushes it to 0.46%), and slow addition so the oxidant is never in excess · the leftover hypochlorite is destroyed with sodium metabisulfite, then the free base is taken into dichloromethane at pH 7.5–8.0
Pantoprazole free base
Pantoprazole free base
Step 3 85% overall, 99.92% pure
NaOH (1 equiv), acetonitrile, seeded
20–25 °C, then 0–5 °C for 3 h
the salt, and which crystal form it comes out as · acetonitrile gives the sesquihydrate the pharmacopoeia asks for, while acetone traps itself in the lattice as an acetone–water heterosolvate that fails the assay at 90.4% · a slurry of the undried wet cake in dichloromethane washes the acetone out and converts it back
Pantoprazole sodium sesquihydrate (Protonix), drawn without its 1.5 waters
water oxidation solvent vs dichloromethane 3 h oxidation time vs 1–2 days 0.02% sulfone impurity vs 0.2% allowed 85% isolated yield vs 78–80%

Against the published routes the authors compare themselves with in Table 1: peroxide with a molybdate catalyst for the reaction time, hypochlorite in dichloromethane for the solvent and the yield. The sulfone figure is measured in the finished API against the European Pharmacopoeia limit of 0.2%.

Awasthi, A. K.; Kumar, L.; Tripathi, P.; Golla, M.; Aga, M. A.; Reddy, C. S.; Kumar, P.
Environmentally Benign and Facile Process for the Synthesis of Pantoprazole Sodium Sesquihydrate: Phase Transformation of Pantoprazole Sodium Heterosolvate to Pantoprazole Sodium Sesquihydrate
ACS Omega 2017, 2, 5460–5469 · Scheme 1, Tables 1–6

Open the paper · DOI 10.1021/acsomega.7b00743 Free to read under an ACS AuthorChoice licence, which allows non-commercial reuse

Background on the chemistry

What the two oxidants are actually doing, measured side by side. Hypochlorite oxidises a thioether around six orders of magnitude faster than hydrogen peroxide does, and the second oxidation, sulfoxide to sulfone, is slower than the first by a wide margin. That gap is the whole reason a hypochlorite process can be controlled by how fast the oxidant is poured in. The work was done on simple aryl thioethers in buffer, not on pantoprazole.

Abdelfattah, A. G.; Bansal, S.; Quaye, J. A.; Kondengadan, S. M.; Gadda, G.; Wang, B.
Thioether Oxidation Chemistry in Reactive Oxygen Species (ROS)-Sensitive Trigger Design: A Kinetic Analysis
Org. Lett. 2025, 27, 3071–3076 · Tables 1 and 2

Open the paper · DOI 10.1021/acs.orglett.5c00747 Read the PDF Open access, CC BY 4.0

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