What is CAS 121-43-7 for Trimethyl borate?

CAS 121-43-7 is the unique numerical identifier assigned to Trimethyl borate by the Chemical Abstracts Service. It is used to cross-reference the substance across regulatory databases, raw material specifications and safety assessment reports.

Annex II Entry 1764 15/01/2026

Trimethyl borate

Q: Is Trimethyl borate banned in EU cosmetics?

Yes. Trimethyl borate is listed in Annex II of EU Cosmetics Regulation 1223/2009 and is prohibited as an intentionally added cosmetic ingredient. Article 17 provides a narrow exception for unintended small quantities that are technically unavoidable under good manufacturing practice, provided the product remains safe under Article 3.

Q: How do I check if my product formula contains Trimethyl borate?

Use the INCI Checker tool on CosIng Checker to paste your full ingredient list and scan it against all Annex II–VI entries. The tool highlights any ingredients that match restricted, prohibited or allergen-flagged records.

Trimethyl borate is listed in Annex II as a prohibited substance for cosmetic products placed on the EU market.

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Prohibited substance— Annex II, EU Regulation 1223/2009

Entry: 1764

Chemical identity and properties

PubChem 2D chemical structure for CAS 121-43-7

CAS 121-43-7PubChem CID 8470

Trimethyl borate

Trimethyl borate is a member of the class of borate esters obtained by the formal condensation of three equivalents of methanol with boric acid. — ChEBI

IUPAC name: trimethyl borate

Molecular formula: C3H9BO3
Molecular weight: 103.92 g/mol
Exact mass: 104.0644743 Da
Topological polar surface area: 27.7 Å²
Hydrogen-bond donors: 0
Hydrogen-bond acceptors: 3
Covalent units: 1
Defined stereocentres: 0

Also known as

TrimethoxyboraneMethyl boratetrimethylborateTrimethoxyboronBoric acid trimethyl esterBorester OBoric acid, trimethyl esterTrimethoxyborine

16 more reported names

Boric acid (H3BO3), trimethyl esterTrimethylester kyseliny boriteNSC-77782U64J6F5NCHEBI:38913RefChem:191751204-468-9934-685-0B(OMe)3B(OCH3)3NSC 777(MeO)3B3349-42-6Trimethyl borate-11BHSDB 5589EINECS 204-468-9

Open full PubChem record PubChem annotations 3D structure image

External database identifiers

ChEBI:CHEBI:38913
EPA DTXSID:DTXSID0037738
PubMed:22002227
PubMed:21953045
PubMed:21582429
PubMed:21581460
PubMed:21472570
PubMed:21426090
PubMed:21239221
PubMed:21201442
PubMed:20189411
PubMed:18363408
PubMed:18351715
PubMed:17429958

Evidence from additional scientific databases

NIH PubChem PUG-View

Exact identifier match8470

Attributed physical-property, hazard, environmental and use annotations.

Boiling Point: 67.5 °C Source: Hazardous Substances Data Bank (HSDB)
Boiling Point: 68 °C Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Boiling Point: 68 °C @760 [mm Hg] Source: PAC Chemical Database, U.S. Department of Energy

Color/Form: Colorless, moisture-sensitive liquid; fumes in air Source: Hazardous Substances Data Bank (HSDB)

Density: 0.915 g/cu cm Source: Hazardous Substances Data Bank (HSDB)
Density: Relative density (water = 1): 0.915 Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Density: 0.92 @ 20°C Source: PAC Chemical Database, U.S. Department of Energy

Flash Point: less than 80 °F (NFPA, 2010) Source: CAMEO Chemicals
Flash Point: < 80 °F (< 27 °C) (closed cup) Source: Hazardous Substances Data Bank (HSDB)
Flash Point: - 7 °C Source: ILO-WHO International Chemical Safety Cards (ICSCs)

LogP: -1.9 Source: ILO-WHO International Chemical Safety Cards (ICSCs)

Melting Point: -29.3 °C Source: Hazardous Substances Data Bank (HSDB)
Melting Point: -29 °C Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Melting Point: -29 °C Source: PAC Chemical Database, U.S. Department of Energy

Physical Description: Trimethyl borate appears as a water-white liquid. Denser than water. Vapors heavier than air. Used as a solvent and fungicide for fruit. Source: CAMEO Chemicals
Physical Description: Liquid Source: EPA Chemical Data Reporting (CDR)
Physical Description: Colorless liquid; [ICSC] Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
Physical Description: COLOURLESS LIQUID. Source: ILO-WHO International Chemical Safety Cards (ICSCs)

Refractive Index: Index of refraction: 1.3568 at 20 °C/D Source: Hazardous Substances Data Bank (HSDB)

Solubility: Miscible with tetrahydrofuran, ether, isoporpylamine, hexane, methanol, nujol, and other organic liquids Source: Hazardous Substances Data Bank (HSDB)
Solubility: Miscible with alcohol, ether; soluble in polar nonhydroxylic solvents Source: Hazardous Substances Data Bank (HSDB)
Solubility: Solubility in water: reaction Source: ILO-WHO International Chemical Safety Cards (ICSCs)

Vapor Pressure: 137.0 [mmHg] Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
Vapor Pressure: 137 mm Hg at 25 °C Source: Hazardous Substances Data Bank (HSDB)
Vapor Pressure: Vapor pressure, kPa at 25 °C: 18 Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Vapor Pressure: 137 [mm Hg] @25 °C Source: PAC Chemical Database, U.S. Department of Energy

Exposure Routes: The substance can be absorbed into the body by inhalation, through the skin and by ingestion. Source: ILO-WHO International Chemical Safety Cards (ICSCs)

First Aid: Excerpt from ERG Guide 129 [Flammable Liquids (Water-Miscible / Noxious)]:; Refer to the "General First Aid" section. Specific First Aid: Wash skin with soap and water. In case of burns, immediately cool affected skin for as long as possible with cold water. Do not remove clothing if adhering to skin. (ERG, 2024) Source: CAMEO Chemicals
ERG2024, Guide 129 (Trimethyl borate): General First Aid:; · Call 911 or emergency medical service.; · Ensure that medical personnel are aware of the material(s) involved, take precautions to protect themselves and avoid contamination.; · Move victim to fresh air if it can be done safely.; · Administer oxygen if breathing is difficult.; · If victim is not breathing:; -- DO NOT perform mouth-to-mouth resuscitation; the victim may have ingested or inhaled the substance.; -- If equipped and pulse detected, wash face and mouth, then give artificial respiration using a proper respiratory medical device (bag-valve mask, pocket mask equipped with a one-way valve or other device).; -- If no pulse detected or no respiratory medical device available, provide continuous compressions. Conduct a pulse check every two minutes or monitor for any signs of spontaneous respirations.; · Remove and isolate contaminated clothing and shoes.; · For minor skin contact, avoid spreading material on unaffected skin.; · In case of contact with substance, remove immediately by flushing skin or eyes with running water for at least 20 minutes.; · For severe burns, immediate medical attention is required.; · Effects of exposure (inhalation, ingestion, Source: Emergency Response Guidebook (ERG)

Signal: Danger Source: Regulation (EC) No 1272/2008 of the European Parliament and of the Council
GHS Hazard Statements: H226: Flammable liquid and vapor [Warning Flammable liquids]; H312: Harmful in contact with skin [Warning Acute toxicity, dermal]; H360FD: May damage fertility; May damage the unborn child [Danger Reproductive toxicity] Source: Regulation (EC) No 1272/2008 of the European Parliament and of the Council
Precautionary Statement Codes: P203, P210, P233, P240, P241, P242, P243, P280, P302+P352, P303+P361+P353, P317, P318, P321, P362+P364, P370+P378, P403+P235, P405, and P501 (click each P-code to see the statement) Source: Regulation (EC) No 1272/2008 of the European Parliament and of the Council
Signal: Danger Source: European Chemicals Agency (ECHA)
GHS Hazard Statements: H225 (40.5%): Highly Flammable liquid and vapor [Danger Flammable liquids]; H226 (59.5%): Flammable liquid and vapor [Warning Flammable liquids]; H301 (14.9%): Toxic if swallowed [Danger Acute toxicity, oral]; H311 (14.6%): Toxic in contact with skin [Danger Acute toxicity, dermal]; H312 (85.4%): Harmful in contact with skin [Warning Acute toxicity, dermal]; H319 (30.3%): Causes serious eye irritation [Warning Serious eye damage/eye irritation]; H331 (14.6%): Toxic if inhaled [Danger Acute toxicity, inhalation]; H360 (11%): May damage fertility or the unborn child [Danger Reproductive toxicity]; H360FD (19.3%): May damage fertility; May damage the unborn child [Danger Reproductive toxicity]; H370 (19.8%): Causes damage to organs [Danger Specific target organ toxicity, single exposure] Source: European Chemicals Agency (ECHA)
Precautionary Statement Codes: P203, P210, P233, P240, P241, P242, P243, P260, P261, P262, P264, P264+P265, P270, P271, P280, P301+P316, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P308+P316, P316, P317, P318, P321, P330, P337+P317, P361+P364, P362+P364, P370+P378, P403+P233, P403+P235, P405, and P501 (click each P-code to see the statement) Source: European Chemicals Agency (ECHA)
ECHA C&L Notifications Summary: Aggregated GHS information provided per 383 reports by companies from 15 notifications to the ECHA C&L Inventory. Each notification may be associated with multiple companies.; Information may vary between notifications depending on impurities, additives, and other factors. The percentage value in parenthesis indicates the notified classification ratio from companies that provide hazard codes. Only hazard codes with percentage values above 10% are shown. For more detailed information, please visit ECHA C&L website. Source: European Chemicals Agency (ECHA)
GHS Hazard Statements: H225 (100%): Highly Flammable liquid and vapor [Danger Flammable liquids]; H312 (97.4%): Harmful in contact with skin [Warning Acute toxicity, dermal]; H319 (100%): Causes serious eye irritation [Warning Serious eye damage/eye irritation] Source: European Chemicals Agency (ECHA)
Precautionary Statement Codes: P210, P233, P240, P241, P242, P243, P264+P265, P280, P302+P352, P303+P361+P353, P305+P351+P338, P317, P321, P337+P317, P362+P364, P370+P378, P403+P235, and P501 (click each P-code to see the statement) Source: European Chemicals Agency (ECHA)
ECHA C&L Notifications Summary: Aggregated GHS information provided per 39 reports by companies from 2 notifications to the ECHA C&L Inventory. Each notification may be associated with multiple companies.; Information may vary between notifications depending on impurities, additives, and other factors. The percentage value in parenthesis indicates the notified classification ratio from companies that provide hazard codes. Only hazard codes with percentage values above 10% are shown. For more detailed information, please visit ECHA C&L website. Source: European Chemicals Agency (ECHA)
GHS Hazard Statements: H225 (100%): Highly Flammable liquid and vapor [Danger Flammable liquids]; H302 (100%): Harmful if swallowed [Warning Acute toxicity, oral]; H319 (100%): Causes serious eye irritation [Warning Serious eye damage/eye irritation]; H360 (100%): May damage fertility or the unborn child [Danger Reproductive toxicity]; H370 (100%): Causes damage to organs [Danger Specific target organ toxicity, single exposure] Source: European Chemicals Agency (ECHA)
Precautionary Statement Codes: P203, P210, P233, P240, P241, P242, P243, P260, P264, P264+P265, P270, P280, P301+P317, P303+P361+P353, P305+P351+P338, P308+P316, P318, P321, P330, P337+P317, P370+P378, P403+P235, P405, and P501 (click each P-code to see the statement) Source: European Chemicals Agency (ECHA)

NFPA Health Rating: 1 - Materials that, under emergency conditions, can cause significant irritation. Source: Hazardous Substances Data Bank (HSDB)
NFPA Fire Rating: 3 - Liquids and solids that can be ignited under almost all ambient temperature conditions. Materials produce hazardous atmospheres with air under almost all ambient temperatures or, though unaffected by ambient temperatures, are readily ignited under almost all conditions. Source: Hazardous Substances Data Bank (HSDB)
NFPA Instability Rating: 1 - Materials that in themselves are normally stable but that can become unstable at elevated temperatures and pressures. Source: Hazardous Substances Data Bank (HSDB)

Environmental Bioconcentration: Trimethyl borate is rapidly hydrolyzed to boric acid and methanol in the presence of water(1,2). Hydrolysis would be expected to be the dominate fate process for trimethyl borate in the environment(SRC). Bioconcentration is not considered an important environmental fate for trimethyl borate(SRC). Source: Hazardous Substances Data Bank (HSDB)

Environmental Fate: TERRESTRIAL FATE: Trimethyl borate is rapidly hydrolyzed to boric acid and methanol in the presence of water(1,2). Hydrolysis would be expected to be the dominate fate process for trimethyl borate in the environment(SRC). Source: Hazardous Substances Data Bank (HSDB)
Environmental Fate: AQUATIC FATE: Trimethyl borate is rapidly hydrolyzed to boric acid and methanol in the presence of water(1,2). Hydrolysis would be expected to be the dominate fate process for trimethyl borate in the environment(SRC). Source: Hazardous Substances Data Bank (HSDB)
Environmental Fate: ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), trimethyl borate, which has a vapor pressure of 136 mm Hg at 25 °C(2), is expected to exist solely as a vapor in the ambient atmosphere. Trimethyl borate is rapidly hydrolyzed to boric acid and methanol in the presence of water(3,4). Hydrolysis would be expected to be the dominate fate process for trimethyl borate in the environment(SRC). Source: Hazardous Substances Data Bank (HSDB)

Industry Uses: Not Known or Reasonably Ascertainable; Reducing agent; Intermediate Source: EPA Chemical Data Reporting (CDR)

Sources/Uses: Used as a flame retardant, welding and brazing flux, chemical intermediate, fungicide, and a solvent for waxes, resins, and oils; [HSDB] Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
Industrial Processes with risk of exposure: Welding [Category: Weld]; Brazing [Category: Heat or Machine]; Farming (Pesticides) [Category: Industry] Source: Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
Uses: As solvent for waxes, resins, oils; catalyst in manufacture of ketones; analysis of paint and varnish ingredients; as neutron detector gas in presence of a scintillation counter; as promoter of diborane reactions Source: Hazardous Substances Data Bank (HSDB)
Uses: Dehydrating agent; fungicide for citrus fruit Source: Hazardous Substances Data Bank (HSDB)
Uses: Intermediate in preparation of metal borohydrides Source: Hazardous Substances Data Bank (HSDB)
Uses: Azeotropic gaseous flux for welding and brazing Source: Hazardous Substances Data Bank (HSDB)
Uses: For more Uses (Complete) data for TRIMETHYL BORATE (6 total), please visit the HSDB record page. Source: Hazardous Substances Data Bank (HSDB)

Mapped by: Existing checksum-valid CAS to unique PubChem CID match. Retrieved: 2026-08-31. Open source record

Scientific classifications and hazard annotations provide context and do not replace the market-specific regulatory decision shown above.

Additional source coverage and match status

Source	Result	Checked
NIH PubChem PUG-View	Exact match	2026-08-31

A recorded no-match is useful evidence that the source was checked; it is not a claim that the substance does not exist elsewhere.

Retrieved from NIH PubChem on 2026-08-31 by checksum-valid CAS matching. Chemical properties do not replace the regulatory decision on this page.

Record details

Chemical name

Trimethyl borate

Regulatory information

Regulation

(EU) 2026/78

See every entry this act set

Key data

CAS

121-43-7

204-468-9

Annex

Entry number

1764

Direct matches are limited for this record, so nearby entries from Annex II are shown as well.

Annex II 1397

Shared CAS number

Perboric acid (H3BO2(O2)), monosodium salt trihydrate [1] Perboric acid, sodium salt, tetrahydrate …

CAS: 13517-20-9 [1], 37244-98-7 [2], 10486-00-7 [3], — [4], 15120-21-5 [5], 7632-04-4/10332-33-9/10486-00-7 [6], 11138-47-9 [7], 12040-72-1 [8], 10332-33-9 [9], 121-43-7 [10]

EC: 239-172-9 [1], 234-390-0 [2], — [3], — [4], 239-172-9 [5], 231-556-4 [6], 234-390-0 [7], 234-390-0 [8], — [9], 204-468-9 [10]

Annex II 1763