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Formamide (CAS 75-12-7) is a colourless, hygroscopic, water-miscible liquid with the formula HCONH2 (CH3NO). In molecular biology labs it is used to lower the melting temperature of nucleic acid duplexes (hybridization, RNA loading buffers). It is classified as a reproductive toxicant, so it is handled and stored according to its safety data sheet (SDS). This page is general chemical-safety information, not individual medical or occupational advice.
What is formamide?
Formamide is the simplest amide of formic acid. The International Chemical Safety Card (ICSC 0891) describes it as a colourless, viscous, hygroscopic liquid that is miscible with water, with a relative density of 1.13, a melting point of 2.5 C, a flash point of 120 C (closed cup) and a vapour pressure of 8 Pa at 20 C. Its vapour is heavier than air. Synonyms listed by ICSC and the NIST WebBook include methanamide, carbamaldehyde and (NIST) formimidic acid.
Formamide CAS number, formula and structure
- CAS number: 75-12-7 (ICSC 0891; NIST WebBook)
- EC number: 200-842-0 (ICSC 0891)
- Formula: CH3NO, written structurally as HCONH2: a formyl group (HC=O) bonded to an amino group (NH2)
- Molar mass: 45.04 g/mol (NIST: 45.0406)
- InChIKey: ZHNUHDYFZUAESO-UHFFFAOYSA-N (NIST WebBook)
Formamide boiling point and density
Quoted boiling points differ because formamide begins to decompose near its boiling range, so the number depends on the reference and on whether decomposition is noted. The values below are those listed in the PubChem compound record (CID 713) from named handbooks and agencies.
| Source (as cited in PubChem) | Boiling point reported |
|---|---|
| Merck Index | 210.5 C at 760 mmHg |
| Hawley’s Condensed Chemical Dictionary | 200 to 212 C, with partial decomposition from about 180 C |
| NIOSH / OSHA | 411 F, decomposes |
| US DOE (PAC values) | 220 C |
A practical reading: about 210 C, with decomposition, and the spread is a property of the data, not an error in one source. ICSC 0891 and the NIST WebBook entry do not give a boiling point. For density, ICSC gives a relative density of 1.13 (water = 1).
What is formamide used for in the lab?
In research labs the best-documented use is as a denaturant in nucleic acid work. Thermo Fisher’s product documentation for its deionized formamide notes that formamide lowers the melting temperature of nucleic acid duplexes, which is why it appears in Southern and Northern blot hybridization buffers, and that fresh deionized formamide matters for RNA loading buffer. Cold Spring Harbor Protocols describes a 1.5x RNA loading buffer containing about 95% formamide. For the hybridization context itself, see our guide to in situ hybridization.
Hazards and GHS classification
ICSC 0891 lists the GHS signal word Danger, with hazard statements for damage to fertility or the unborn child, harm if swallowed, in contact with skin or inhaled, and skin and eye irritation. The ACGIH TLV listed in ICSC is 1 ppm as an 8-hour TWA with a skin notation and an A3 designation. On decomposition formamide releases ammonia and hydrogen cyanide, and it attacks aluminium, brass, copper, iron, lead and some plastics (ICSC 0891).
Why two SDSs can show different classifications
PubChem records the primary EU CLP classification as GHS08 (health hazard), Danger, H360D (may damage the unborn child). The ECHA aggregated data, drawn from 26 notifications, shows a wider spread of H351, H360, H360D and H373. Classifications differ by notifier and by the impurities and grade supplied. The practical consequence: read the SDS for the exact product and supplier you hold, not a generic summary. For how SDS sections are organised, see GHS classification of chemicals and OSHA SDS requirements. For how exposure limits such as a TLV relate to OSHA and NIOSH values, see PELs, TLVs and RELs in the laboratory.
Formamide storage
ICSC 0891 says to keep formamide dry and separate from oxidants, acids and bases. Lab protocols add temperature guidance, and the published sources do not all agree, which is itself the useful comparison:
| Source | Material | Stated storage |
|---|---|---|
| ICSC 0891 | Formamide (hazard card) | Dry; separate from oxidants, acids, bases |
| CSH Protocols (deionized formamide recipe) | Deionized formamide | Small aliquots under nitrogen at -70 C |
| CSH Protocols (RNA loading buffer) | 1.5x loading buffer, about 95% formamide | 1 mL aliquots at -20 C for up to 1 year |
| Thermo Fisher AM9342 FAQ | Deionized formamide | Small aliquots at -20 C; an ammonia smell means it is breaking down and it should not be used |
The common thread is small aliquots, cold and dry storage, and discarding formamide that smells of ammonia. For the temperature itself, follow the SDS and the protocol or manufacturer instructions for your specific product.
Formamide vs dimethylformamide
Dimethylformamide (DMF, N,N-dimethylformamide) is a different compound with its own CAS number and its own SDS; its hazards and limits are not interchangeable with formamide’s. Check the regulatory status of either chemical in your jurisdiction from the current SDS and regulator lists rather than from a summary page.
Common misunderstandings
- “The boiling point is one number.” It is a range because of decomposition (see the table above).
- “Formamide and dimethylformamide are the same.” They are different substances with different CAS numbers.
- “All SDSs agree.” Classification differs by notifier; use the SDS for your product.
- “A hygroscopic liquid is fine in a loosely capped tube.” ICSC specifies dry storage, and protocols specify aliquots to limit repeated opening.
FAQ
What is formamide?
A colourless, viscous, hygroscopic, water-miscible liquid (HCONH2, CAS 75-12-7) classified as a reproductive toxicant under EU CLP.
What is formamide used for?
In the lab, mainly to lower nucleic acid duplex melting temperature in hybridization buffers and as the main component of RNA loading buffers.
What is the CAS number for formamide?
75-12-7.
What is another name for dimethylformamide?
N,N-dimethylformamide, abbreviated DMF. It is a separate chemical from formamide, which is also called methanamide or carbamaldehyde.
Is dimethylformamide banned?
This page does not state a regulatory status for DMF, which is a different compound. Consult the current SDS and the regulator’s lists for your jurisdiction.
Where do I find the formamide SDS?
From the supplier of the exact product you hold. Classification and grade vary by supplier, so a generic card such as ICSC 0891 is a reference, not a substitute.
Sources
- ICSC 0891, Formamide, IPCS/ILO, inchem.org (read 2026-11-07)
- NIST Chemistry WebBook, Formamide, webbook.nist.gov (read 2026-11-07)
- PubChem compound 713, Formamide (GHS, boiling point, ECHA aggregate), pubchem.ncbi.nlm.nih.gov (read 2026-11-07)
- Cold Spring Harbor Protocols, formamide loading buffer, cshprotocols.cshlp.org (read 2026-11-07)
- Thermo Fisher Scientific, deionized formamide (AM9342), thermofisher.com (read 2026-11-07)
