Meta description: A technical comparison of piperazine anhydrous (CAS 110-85-0) vs piperazine hexahydrate (CAS 142-63-6) — melting point, water content, storage and downstream selection.
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Template: D – Technical FAQ / comparison
Primary keyword: piperazine anhydrous vs hexahydrate
Secondary keywords: piperazine hexahydrate, piperazine CAS 110-85-0, piperazine application
Piperazine (hexahydropyrazine) is a six-membered ring diamine. It is traded in two commercial forms: anhydrous piperazine and piperazine hexahydrate. They are the same molecule, but their physical form, water content, handling and downstream use are very different. Buyers often ask which one to specify.
Q1: What is the difference between the two?
Piperazine free base readily forms a hexahydrate — six water molecules of crystallization per piperazine molecule. The two commercial forms are:
| Property | Anhydrous Piperazine | Piperazine Hexahydrate |
|---|---|---|
| CAS | 110-85-0 | 142-63-6 |
| Formula | C₄H₁₀N₂ | C₄H₁₀N₂ · 6H₂O |
| MW | 86.14 g/mol | 194.23 g/mol |
| Appearance | White crystalline flakes / pellets | White crystalline crystals |
| Melting point | ~ 110 °C | ~ 43–45 °C |
| Boiling point | ~ 146 °C | decomposes / loses water |
| Piperazine content | ≥ 99% | ~ 44% (by stoichiometry) |
| Hygroscopic? | Strongly | Stable as hydrate |
Q2: Why do these two forms exist?
Anhydrous piperazine is the concentrated free base. It is produced by distillation and dehydration, then flaked or pelletized. It is the form preferred by plants that want high active content and minimal water.
Piperazine hexahydrate is the natural crystalline form that separates from aqueous solution during manufacturing. It is easier and cheaper to crystallize, dry minimally, and ship as a stable solid. It is the form most commonly used in pharma salt production and corrosion inhibition.
Q3: Which form should you specify for downstream use?
- Pharma intermediates (e.g. piperazine citrate, piperazine phosphate): Most pharmaceutical processes use piperazine hexahydrate, because the reaction is done in aqueous solution and the water is not a problem. Hexahydrate is also easier to handle as a free-flowing crystal.
- Corrosion inhibitors and metal treatment: Both forms are used; anhydrous is preferred when water must be minimized in formulation.
- Polyurethane / epoxy curing: Anhydrous piperazine is preferred because water would interfere with the cure.
- Gas-treating formulations (as MDEA activator): Anhydrous piperazine is the standard — the activator is added at low concentration and water would dilute the amine blend.
- Agrochemicals: Usually hexahydrate, depending on the synthesis route.
Q4: What are the storage and handling differences?
- Anhydrous piperazine is strongly hygroscopic — it picks up moisture from air and slowly converts to the hydrate. It must be stored in sealed drums with desiccant or nitrogen blanketing. It also has a sharp ammoniacal odour and can form dust.
- Piperazine hexahydrate is far more stable, non-hygroscopic, and can be stored in standard woven or paper drums with PE liner. It melts around 43–45 °C, so in hot climates drums must be kept below 40 °C to avoid caking.
Q5: How is it packed for export?
- Anhydrous: 25 kg fibre drums with PE liner, or jumbo bags for bulk.
- Hexahydrate: 25 kg woven bags with PE liner, or 500 kg jumbo bags.
- Both are classified as corrosive / irritant for sea transport and require proper GHS labels.
Q6: Can I substitute one for the other?
Not directly. If a process is formulated for piperazine hexahydrate, switching to anhydrous without adjusting water balance will change the reaction concentration. Conversely, replacing anhydrous with hexahydrate introduces ~ 56% extra water. For most processes, the active piperazine content must be matched by weight:
1 kg of anhydrous piperazine ≈ 2.26 kg of piperazine hexahydrate.
Bottom Line
- Choose anhydrous piperazine when water must be minimized: gas-treating activators, epoxy / polyurethane curing, low-water formulations.
- Choose piperazine hexahydrate for aqueous reactions, pharma salts and corrosion inhibitors where water is acceptable and stable, easy-to-handle crystals are preferred.
- Always match the active piperazine weight, not the gross package weight, when substituting between the two.
*For COA, SDS or sample availability on either piperazine grade, contact the ChinaAmines team.
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