c005 — Cinoxate
Section 1: Identity
| Field | Value | Conf. |
|---|---|---|
| INCI | Cinoxate | C1 |
| IUPAC | 2-Ethoxyethyl (2E)-3-(4-methoxyphenyl)prop-2-enoate | C1 |
| Other names | 2-ethoxyethyl p-methoxycinnamate; Sunarome WMO; Giv-Tan F | C1 |
| CAS | 104-28-9 | C1 |
| Molecular formula | C₁₄H₁₈O₄ | C1 |
| Molecular weight | 250.29 g·mol⁻¹ | C1 |
| EC number | 203-191-9 | C1 |
Regulatory Status
| Jurisdiction | Status | Max conc. | Source / entry | Conf. |
|---|---|---|---|---|
| USA (FDA) | Permitted Cat. III | 3 % | 21 CFR 352.10(d) | C1 |
| EU (Annex VI) | Not listed / not permitted | n/a (delisted) | Not in current Reg. 1223/2009 Annex VI | C1 |
| Australia (TGA) | Permitted | 6 % | TGA ARTG | C2 |
| Japan | Permitted at 5 % historically; rare in current formulations | 5 % | MHLW Standard | C2 |
| Korea (MFDS) | Not listed | n/a | KFDA | C3 |
| ASEAN | Not listed | n/a | ASEAN ACD | C3 |
Approved by FDA in 1961 but rarely used in current formulations (replaced by octinoxate, which has higher ε at the same wavelength).
Section 2: UV Absorption Spectrum
UVB filter (270–328 nm).
| Solvent | λmax (nm) | ε (M⁻¹ cm⁻¹) | E(1%, 1cm) | Conf. | Source |
|---|---|---|---|---|---|
| Ethanol | 289 (some sources 308) | ~20,650 | ~825 | C1 | Sayre RM, J Soc Cosmet Chem 31 (1980) 133 — also reproduced in Shaath 2005 textbook Table |
| Methanol | 308 | ~22,000 | ~879 | C2 | Cinoxate Wikipedia + ChemicalBook citing experimental UV |
| Cyclohexane (apolar) | ~289 | ~20,000 | ~800 | C2 | Sayre 1980 (digitized) |
There is some confusion in secondary sources between two reported peak values for cinoxate: 289 nm (in apolar/some early references) and 308 nm (in alcohols). This mirrors the cinnamate solvatochromism of OMC (291 → 310 between cyclohexane and ethanol). The accepted "headline" value is λmax ≈ 308 nm in alcohol with ε ≈ 20,650 M⁻¹ cm⁻¹ [C1].
E(1%, 1cm) ≈ 825 — relatively high among UVB filters (similar to OMC).
Two independent peer-reviewed sources for λmax: Sayre 1980 (ethanol/cyclohexane); Shaath 2005 textbook table reproduces 308 nm in EtOH with ε 20,650.
Section 3: Photodegradation Kinetics
Cinoxate is structurally a methoxycinnamate, so it shares the photoisomerization chemistry of octinoxate but with a 2-ethoxyethyl ester instead of 2-ethylhexyl ester.
- trans → cis photoisomerization is the dominant primary photochemistry (analogous to OMC; cis isomer has lower ε) — C2 (extrapolated from Stange 2015 OMC paper which discusses cinnamate family).
- Photostationary state retains ~70 % of initial absorbance in alcohol (analogous to OMC) — C3 (estimated from cinnamate family behaviour).
- No published photodegradation rate constants in modern peer-reviewed photochemistry literature for cinoxate specifically (the molecule has fallen out of fashion). Tarras-Wahlberg et al. 1999 grouped cinnamates collectively; cinoxate not specifically discussed [C5].
- Photoproducts (by analogy to OMC): cis-cinoxate, [2+2] photodimers (truxillic/truxinic diesters), and 4-methoxybenzaldehyde + 2-ethoxyethanol via Norrish [C3].
Photodegradation half-life
- C5 — couldn't find a direct measurement of half-life or k under standardized solar exposure in the open literature.
- By analogy with OMC: half-life on skin film likely 1–2 hours under 1 MED/h solar simulator [C3].
Quantum yields
- C5 — no published Φ values for cinoxate specifically. By analogy with OMC, Φ(trans→cis) ≈ 0.3–0.4 in alcohol expected [C3].
Section 4: Notable Issues
- Photoallergy: Reported skin-sensitizer in older clinical studies; a known cause of photo-contact dermatitis (e.g. de Groot AC, Frosch PJ, "Adverse reactions to sunscreens" Adv Dermatol 7 (1992) 75).
- Skin penetration: No modern biomonitoring data; the 2-ethoxyethyl moiety is more polar than the 2-ethylhexyl of octinoxate so skin permeation is plausible but unmeasured for current formulations [C5 on quantitative penetration data].
- Endocrine concerns: Cinnamates as a class have shown estrogenic activity in vitro (Schlumpf 2001); cinoxate not separately tested in modern panels [C2].
- ROS: No specific measurements; expected behavior similar to OMC (low quantum yield singlet oxygen production from monomer; aggregate-form ROS possible) [C3].
- Aquatic toxicity: Limited modern data. Not on Hawaii/Palau ban lists. [C5 on quantitative ecotoxicity]
- Synergy/antagonism: None reported; obsolete in modern formulations.
Note on data scarcity: Cinoxate has fallen out of commercial use, leading to a paucity of modern photodegradation/biomonitoring research. Most photochemical understanding is by analogy to its better-studied close cousin octinoxate (OMC, c001) — both share the p-methoxycinnamate chromophore.
Sources
- 21 CFR 352.10(d) — FDA OTC sunscreen monograph.
- Sayre RM, Agin PP, LeVee GJ, Marlowe E. "A comparison of in vivo and in vitro testing of sunscreening formulas". Photochem Photobiol 29 (1979) 559-566.
- Sayre RM. J Soc Cosmet Chem 31 (1980) 133.
- Shaath NA. Sunscreens: Regulations and Commercial Development, 3rd ed., Marcel Dekker 2005, Chapter 12 — table of UV filter spectroscopic data.
- de Groot AC, Frosch PJ. "Adverse reactions to sunscreens". Adv Dermatol 7 (1992) 75-90.
- Stange et al., Photochem Photobiol Sci 14 (2015) 1701-1709 — analogous OMC photochemistry framework.
- Cinoxate PubChem CID 5373773; ChemicalBook record 104-28-9.
C5 items for c005: * No modern peer-reviewed photodegradation kinetics (k, t½) measurement in cosmetic vehicle for cinoxate specifically. * No quantum yield Φd or Φisomerization measured directly for cinoxate. * No biomonitoring (skin penetration % per typical application) data for cinoxate. * No quantitative aquatic toxicity LC50 in modern studies.