Substance profile
Methyl iodide
Methyl iodide is colorless, transparent liquid (turns brown on exposure to light) with a pungent, ether-like odor.
01 · Identification
What Methyl iodide is
Methyl iodide is colorless, transparent liquid (turns brown on exposure to light) with a pungent, ether-like odor. It boils at 42.5 °C, melts at -66.5 °C, is miscible with water.
Under the GHS it carries the signal word Danger. It is classed as hazardous Air Pollutants (HAPs).
02 · Identifiers
Methyl iodide identifiers and molecular data
Methyl iodide CAS number and EC number
Methyl iodide molecular formula and molecular weight
Other names for Methyl iodide
- iodomethane
03 · GHS classification
Methyl iodide hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Methyl iodide pictograms and signal word
Methyl iodide hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Acute toxicity - oral GHS chapter 3.1 | Category 3 | H301 | GHS06 |
| Acute toxicity - dermal GHS chapter 3.1 | Category 4 | H312 | GHS07 |
| Acute toxicity - inhalation GHS chapter 3.1 | Category 3 | H331 | GHS06 |
| Skin corrosion/irritation GHS chapter 3.2 | Category 2 | H315 | GHS07 |
| Carcinogenicity GHS chapter 3.6 | Category 2 | H351 | GHS08 |
| Specific target organ toxicity - single exposure GHS chapter 3.8 | Category 3 | H335 | GHS07 |
Methyl iodide hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H351 | Suspected of causing cancer <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>. |
| H331 | Toxic if inhaled. |
| H301 | Toxic if swallowed. |
| H312 | Harmful in contact with skin. |
| H335 | May cause respiratory irritation. |
| H315 | Causes skin irritation. |
This page lists only the codes assigned to Methyl iodide. The full reference lives on the hazard statements hub, the precautionary statements hub and the GHS pictograms hub.
Safety Data Sheet
Getting an SDS for Methyl iodide
A Safety Data Sheet is written for a product, not for a substance: the supplier of the grade you actually buy issues it, so two suppliers of Methyl iodide issue two different sheets. That is why there is no single authoritative SDS for a substance to download — what there is, is the job of collecting the sheets for the products you hold and keeping them current as suppliers revise them.
04 · Precautionary statements
Methyl iodide precautionary statements
CLP Annex VI assigns 16 precautionary statements to Methyl iodide. They are grouped the way a label groups them: what to do before handling, what to do when something has already happened, how to store it and how to dispose of it.
Prevention
What to do before and during handling so the hazard never happens.
Response
What to do once exposure, spillage or fire has already happened.
Reading the notation. … is a blank the supplier fills in — not a truncated sentence.· [square brackets] mark a part printed only when it applies.
05 · Names in the regulation
Methyl iodide name in 23 EU languages
CLP Annex VI Part 3 is published in every language edition of the regulation, and the identification column is written out in each of them. Nothing below is translated by us: each line is the name as that edition prints it. Under Art. 18(2) the substance name from Annex VI is a lawful product identifier, so this is the wording to put on a label going to that market — and where the cell lists several designations, any one of them qualifies.
| Language | Name in CLP Annex VI Part 3 |
|---|---|
| Bulgarian български | метилйодид йодометан |
| Spanish español | Yoduro de metilo yodometano |
| Czech čeština | methyljodid jodmethan |
| Danish dansk | methyliodid iodmethan |
| German Deutsch | Methyliodid Iodmethan |
| Estonian eesti | metüüljodiid jodometaan |
| Greek ελληνικά | μεθυλιωδίδιο ιωδομεθάνιο |
| English English | methyl iodide iodomethane |
| French français | iodure de méthyle iodométhane |
| Croatian hrvatski | metil-jodid jodmetan |
| Italian italiano | metil ioduro iodometano |
| Latvian latviešu | metiljodīds jodmetāns |
| Lithuanian lietuvių | metilo jodidas jodmetanas |
| Hungarian magyar | metil-jodid jódmetán |
| Maltese Malti | jodur tal-metil iodometan |
| Dutch Nederlands | methyljodide joodmethaan |
| Polish polski | jodek metylu jodometan |
| Portuguese português | iodeto de metilo iodometano |
| Romanian română | iodură de metil iodometan |
| Slovak slovenčina | metyljodid jódmetán |
| Slovenian slovenščina | metil jodid jodometan |
| Finnish suomi | metyylijodidi jodimetaani |
| Swedish svenska | metyljodid jodmetan |
All 23 language editions of Annex VI carry this entry. Irish is the twenty-fourth official EU language and has no line here for a different reason: no consolidated CLP text has ever been published in Irish, so there is no Irish edition of Annex VI to quote a name from. Source: consolidated CLP, CELEX 02008R1272, language editions. © European Union, https://eur-lex.europa.eu — only the electronic Official Journal of the European Union is authentic.
06 · Label elements
Methyl iodide GHS label elements
Everything CLP Annex VI fixes for Methyl iodide, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Methyl iodide
- Suspected of causing cancer <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>.
- Toxic if inhaled.
- Toxic if swallowed.
- Harmful in contact with skin.
- May cause respiratory irritation.
- Causes skin irritation.
- Obtain special instructions before use.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Wash … thoroughly after handling.
- Do not eat, drink or smoke when using this product.
- Use only outdoors or in a well-ventilated area.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- IF ON SKIN:
- IF INHALED:
- IF exposed or concerned:
- Immediately call a POISON CENTER/doctor/…
- Call a POISON CENTER/doctor/… if you feel unwell.
- Get medical advice/attention.
- Rinse mouth.
- If skin irritation occurs:
- Wash with plenty of water/…
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Methyl iodide in the GHS label constructor →
07 · Health hazards
Methyl iodide health hazards and exposure limits
Methyl iodide hazard summary
Methyl iodide is used as an intermediate in the manufacture of some pharmaceuticals and pesticides, in methylation processes, and in the field of microscopy. In humans, acute (short-term) exposure to methyl iodide by inhalation may depress the central nervous system (CNS), irritate the lungs and skin, and affect the kidneys. Massive acute inhalation exposure to methyl iodide has led to pulmonary edema. Acute inhalation exposure of humans to methyl iodide has resulted in nausea, vomiting, vertigo, ataxia, slurred speech, drowsiness, skin blistering, and eye irritation. Chronic (long-term) exposure of humans to methyl iodide by inhalation may affect the CNS and cause skin burns. EPA has not classified methyl iodide for potential carcinogenicity.
Source: EPA Hazardous Air Pollutants
Methyl iodide carcinogenicity classification
Cancer Classification: Not Likely to be Carcinogenic to Humans at Doses that Do Not Alter Rat Thyroid Hormone Homeostasis
Source: Hazardous Substances Data Bank (HSDB)
Evaluation: No epidemiological data relevant to the carcinogenicity of methyl iodide were available. There is limited evidence in experimental animals for the carcinogenicity of methyl iodide. Overall evaluation: Methyl iodide is not classifiable as to its carcinogenicity to humans (Group 3).
Source: Hazardous Substances Data Bank (HSDB)
An IARC group and a CLP classification answer different questions. IARC judges whether the evidence for cancer in humans is strong enough; CLP Annex VI is the legally binding EU classification. A substance can carry one and not the other.
Methyl iodide occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 5.0 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| PEL | 5 ppm (28 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| PEL | TWA 5 ppm (28 mg/m3) [skin] | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 2 ppm (10 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| REL | Ca TWA 2 ppm (10 mg/m3) [skin] See Appendix A | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 100 ppm ; A potential occupational carcinogen. (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 100.0 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| IDLH | NIOSH considers methyl iodide to be a potential occupational carcinogen. | Hazardous Substances Data Bank (HSDB) |
These are United States values. The European Union sets its own indicative and binding limits, and the figure that applies at a given workplace is the one in the local regulation — not the one shown here.
08 · Physical and chemical properties
Methyl iodide properties
Every value is shown with the conditions it was measured under and the source it came from. Where sources disagree, all values are listed rather than one being picked — the difference is usually a different form of the substance, not an error.
Methyl iodide boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 42.5 °C (108.5 °F) | HSDB | |
| 42.78 °C (109 °F) | NIOSH | ||
| 42.39 °C (108.3 °F) | at 760 mmHg | CAMEO |
Methyl iodide melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -66.5 °C (-87.7 °F) | HSDB | |
| -66.67 °C (-88 °F) | NIOSH | ||
| -66.44 °C (-87.6 °F) | CAMEO |
Methyl iodide density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 2.28 g/cm³ | NIOSH | |
| 2.28 g/cm³ | at 20 °C | HSDB | |
| 2.279 g/cm³ | at 20 °C | CAMEO |
Methyl iodide solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | Miscible with alcohol, ether. | HSDB | |
| Sol in acetone | HSDB | ||
| SOL IN CARBON TETRACHLORIDE | HSDB |
Methyl iodide vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 400 mmHg | NIOSH | |
| 661.76 mmHg | CAMEO | ||
| 405 mmHg | at 25 °C | HSDB |
Methyl iodide autoignition temperature
| Property | Value | Conditions | Source |
|---|---|---|---|
| Autoignition temperature | 355 °C (671 °F) | ICSC |
Methyl iodide lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | 10 % by volume | CAMEO | |
| 8.5 % by volume | ICSC |
Methyl iodide upper explosive limit (UEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Upper explosive limit (UEL) | 15 % by volume | CAMEO | |
| 66 % by volume | ICSC |
Methyl iodide vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 4.9 (air = 1) | HSDB |
Methyl iodide critical temperature and pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Critical temperature and pressure | 254.8 °C (490.6 °F) | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Methyl iodide fire and explosion behaviour
These are descriptions rather than measured values, so they are kept out of the table above and quoted here with the source that reported them.
Methyl iodide fire potential
Iodomethane is not flammable.
Source: Hazardous Substances Data Bank (HSDB)
10 · Handling and storage
Methyl iodide storage and handling
Methyl iodide safe storage
Provision to contain effluent from fire extinguishing. Separated from strong oxidants and food and feedstuffs. Well closed. Ventilation along the floor. Store in an area without drain or sewer access.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Methyl iodide storage conditions
Keep containers closed and store in a dark place.
Source: Hazardous Substances Data Bank (HSDB)
Methyl iodide incompatible materials
Strong oxidizers [Note: Decomposes at 518 degrees F].
Source: Hazardous Substances Data Bank (HSDB)
Methyl iodide reactivity
Halogenated aliphatic compounds, such as METHYL IODIDE, are moderately or very reactive. Halogenated organics generally become less reactive as more of their hydrogen atoms are replaced with halogen atoms. Low molecular weight haloalkanes are highly flammable and can react with some metals to form dangerous products. Materials in this group are incompatible with strong oxidizing and reducing agents. Also, they are incompatible with many amines, alkylphosphines, nitrides, azo/diazo compounds, alkali metals (sodium), and epoxides.
Source: CAMEO Chemicals
Planning storage for a mix of chemicals? Check Methyl iodide in the storage compatibility matrix →
11 · Transport
Methyl iodide UN number and transport classification
Transport classification is a separate system from the GHS classification above. It decides how a package is marked and how a load may be carried; it does not follow from the workplace label, and the workplace label does not follow from it. The entries below are linked by CAS number, never by name.
Methyl iodide under UN 2644 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| METHYL IODIDE | 6.1 | T1 | I | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 6.1 is “Toxic substances” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Methyl iodide | 6.1 | I | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 6.1 is “Poisonous materials” (49 CFR 173.2).
12 · Questions
Methyl iodide — frequently asked questions
What is the CAS number of Methyl iodide?
The CAS number of Methyl iodide is 74-88-4. Its EC number is 200-819-5.
What does a Methyl iodide label have to show?
Under CLP Annex VI the label for Methyl iodide carries the pictograms Skull and crossbones and Health hazard and the signal word is Danger.
Is Methyl iodide flammable?
CLP Annex VI assigns Methyl iodide no flammability hazard class. That is not a statement that it cannot burn: the harmonised list only records the hazards that were assessed for it.
Is Methyl iodide a carcinogen?
CLP Annex VI assigns Methyl iodide H351 — suspected of causing cancer. That is category 2: the evidence points that way but is not conclusive. IARC places it in Group 3: not classifiable as to its carcinogenicity to humans.
What is the exposure limit for Methyl iodide?
The US occupational exposure limit reported for Methyl iodide is 5.0 [ppm] (Haz-Map, Information on Hazardous Chemicals and Occupational Diseases). Limits differ by country: the EU sets its own indicative and binding values, and the figure that applies at a given workplace is the one in the local regulation.
What is the boiling point of Methyl iodide?
The boiling point reported for Methyl iodide is 42.5 °C (108.5 °F) (HSDB).
What is the melting point of Methyl iodide?
The melting point reported for Methyl iodide is -66.5 °C (-87.7 °F) (HSDB).
How should Methyl iodide be stored?
Keep containers closed and store in a dark place. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Methyl iodide
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