CD-4

Developing AgentC11H20N2O5SCAS: 25646-77-9
CD-4
Image: Def2010 — CC0

Physical Properties

  • Molecular Weight: 292.35 g/mol
  • Solubility (20°C): 100 g/L

Also known as: Color Developing Agent 4, 4-(N-Ethyl-N-2-hydroxyethyl)-2-methylphenylenediamine sulfate

CD-4 (4-(N-ethyl-N-2-hydroxyethyl)-2-methylphenylenediamine sulfate; CAS 25646-77-9) is the colour developing agent for C-41 colour negative film — the process used for every standard colour film sold for consumer photography since the 1970s.[1] Structurally closely related to CD-3, CD-4 has a hydroxyethyl substitution that tunes its reactivity for colour-negative couplers specifically. The C-41 process requires CD-4; substituting CD-3 produces incorrect dye densities and wrong colour balance.

Photographic uses

  • C-41 colour developer: CD-4 at 3–5 g/L in a potassium carbonate / sodium sulfite / hydroxylamine sulfate base, with working pH 10–10.4, is the heart of every C-41 developer (Kodak Flexicolor, Fuji Hunt, and all generic equivalents).
  • Some E-6 bleach steps: CD-4 also appears in trace amounts in some E-6 stabilizer or final rinse formulations.
  • DIY colour negative development: Home C-41 workflows (Cinestill Cs41, Unicolor powders, Tetenal C-41) use CD-4 as the active developing agent.

Practical notes

Supplied as white to off-white crystalline powder, usually as the sulfate salt for solubility. Extremely oxidation-sensitive — this is the practical constraint that dominates home C-41 work. Working solutions must be kept tightly sealed and refrigerated between uses; exhausted CD-4 looks dark brown-yellow.

Solution shelf life varies: fresh-mixed without antioxidant preservation, hours to a day; with hydroxylamine sulfate preservative (the commercial kit standard), 2–4 weeks refrigerated.

Regulatory status

Same classifications as CD-3 — skin sensitizer, suspected mutagen, suspected carcinogen.[2]

Related compounds

CD-3 is the E-6/RA-4 sibling. p-Phenylenediamine is the parent compound.

Safety Notes

Same hazard profile as CD-3 — see that page for full acute hazards, chronic hazards, storage/handling, and first aid. Summary:

Acute hazards

  • Toxic by all routes (skin, ingestion, inhalation).
  • Severe skin sensitizer — permanent allergic dermatitis risk on repeated exposure.
  • Severe eye and skin irritant.
  • Suspected mutagen and carcinogen.
  • Very toxic to aquatic life.

Storage & handling

Strict glove compliance + fume-hood ventilation + locked amber storage, identical to CD-3 handling.

First aid

Flush skin 20 min, flush eye 30 min, seek medical attention for any substantial exposure. Consult the Sigma-Aldrich SDS for CD-4 for authoritative instructions.[3]

References

  1. BOOK Haist, Grant. Modern Photographic Processing, Volume 2 1st ed. John Wiley & Sons, 1979. ISBN 0-471-04635-X. ↩
  2. STANDARD European Chemicals Agency (ECHA). REACH Regulation (EC) No 1907/2006, Annex XVII – Restrictions on manufacture, placing on the market and use European Union. https://echa.europa.eu/substances-restricted-under-reach ↩
  3. WEB Sigma-Aldrich (Merck KGaA). Sigma-Aldrich Safety Data Sheets Sigma-Aldrich. https://www.sigmaaldrich.com/US/en/search/safety-data-sheets ↩

Reference databases

Last reviewed 2026-04-22