Isoniazid (C6H7N3O): structure, properties and hazards

Names and identifiers

IUPAC name: pyridine-4-carbohydrazide
Synonyms: INH, isonicotinyl hydrazide, tuberculosis
+ 38 more
Isonicotinic acid hydrazide, Isonicotinohydrazide, pyridine-4-carbohydrazide, Isoniazide, Rimifon, Nydrazid, Cotinazin, Dinacrin, Hydrazid, Iscotin, Mybasan, Cedin, Hidrasonil, Isonicotan, Nicotibina, Armazide, Ditubin, Ertuban, Isidrina, Isobicina, Laniazid, Neumandin, Hyzyd, Atcotibine, Isonidrin, Isotebezid, Stanozide, Armazid, Eralon, Isolyn, Isonex, Isonico, Isozide, Neoteben, Niadrin, Nicetal, Nicizina, Niconyl
Molecular formula: C₆H₇N₃O
Empirical formula: C₆H₇N₃O
Molecular weight: 137.14 g/mol
Exact mass: 137.05891
CAS number: 54-85-3
PubChem CID: 3767
Canonical SMILES: C1=CN=CC=C1C(=O)NN
Isomeric SMILES: C1=CN=CC=C1C(=O)NN
InChI: InChI=1S/C6H7N3O/c7-9-6(10)5-1-3-8-4-2-5/h1-4H,7H2,(H,9,10)
InChIKey: QRXWMOHMRWLFEY-UHFFFAOYSA-N
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity

Appearance: Isoniazid appears as odorless colorless or white crystals or white crystalline powder. Taste is slightly sweet at first and then bitter. pH (1% aqueous solution) 5.5-6.5. pH (5% aqueous solution) 6-8. (NTP, 1992)[1]
3 values
From CAMEO Chemicals, the most authoritative source here.
Value As written Source
–shown Isoniazid appears as odorless colorless or white crystals or white crystalline powder. Taste is slightly sweet at first and then bitter. pH (1% aqueous solution) 5.5-6.5. pH (5% aqueous solution) 6-8. (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
– WHITE CRYSTALLINE ODOURLESS POWDER. [2] ILO-WHO International Chemical Safety Cards (ICSCs)
– COLORLESS OR WHITE CRYSTALS, OR A WHITE, CRYSTALLINE POWDER [3] Hazardous Substances Data Bank (HSDB)cites Osol, A. and J.E. Hoover, et al. (eds.). Remington's Pharmaceutical Sciences. 15th ed. Easton, Pennsylvania: Mack Publishing Co., 1975., p. 1151
Melting point: 171.4 °C (340.5 °F, NTP 1992)[1]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source
171.4 °Cshown 340.5 °F (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
170 to 173 °C 170-173 °C [2] ILO-WHO International Chemical Safety Cards (ICSCs)
Solubility in water: Solubility in water, g/100ml at 20 °C: 12.5[2]
3 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source
– greater than or equal to 100 mg/mL at 77 °F (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
– Sol in methyl ethyl ketone, acetone [3] Hazardous Substances Data Bank (HSDB)cites IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work).
–shown Solubility in water, g/100ml at 20 °C: 12.5 [2] ILO-WHO International Chemical Safety Cards (ICSCs)
log P: log Kow = -0.70[3]
pKa: pK1= 1.75[3]
3 values
Only one source reports it.
Value As written Source
–shown pK1= 1.75 [3] Hazardous Substances Data Bank (HSDB)cites Serjeant, E.P., Dempsey B.; Ionisation Constants of Organic Acids in Aqueous Solution. International Union of Pure and Applied Chemistry (IUPAC). IUPAC Chemical Data Series No. 23, 1979. New York, New York: Pergamon Press, Inc.
– pK2= 3.57 [3] Hazardous Substances Data Bank (HSDB)cites Serjeant, E.P., Dempsey B.; Ionisation Constants of Organic Acids in Aqueous Solution. International Union of Pure and Applied Chemistry (IUPAC). IUPAC Chemical Data Series No. 23, 1979. New York, New York: Pergamon Press, Inc.
– pK3= 10.75 [3] Hazardous Substances Data Bank (HSDB)cites Serjeant, E.P., Dempsey B.; Ionisation Constants of Organic Acids in Aqueous Solution. International Union of Pure and Applied Chemistry (IUPAC). IUPAC Chemical Data Series No. 23, 1979. New York, New York: Pergamon Press, Inc.
Vapor pressure: 4.6 × 10⁻⁵ mmHg at 25 °C (estimated)[3]
Flash point: 190 °C (374 °F, NTP 1992)[1]
2 values
Only one source reports it.
Value As written Source
190 °Cshown 374 °F (NTP, 1992) [1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
> 250 °C > 250 °C [2] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
–shown	Isoniazid appears as odorless colorless or white crystals or white crystalline powder. Taste is slightly sweet at first and then bitter. pH (1% aqueous solution) 5.5-6.5. pH (5% aqueous solution) 6-8. (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–	WHITE CRYSTALLINE ODOURLESS POWDER.	[2] ILO-WHO International Chemical Safety Cards (ICSCs)
–	COLORLESS OR WHITE CRYSTALS, OR A WHITE, CRYSTALLINE POWDER	[3] Hazardous Substances Data Bank (HSDB)cites Osol, A. and J.E. Hoover, et al. (eds.). Remington's Pharmaceutical Sciences. 15th ed. Easton, Pennsylvania: Mack Publishing Co., 1975., p. 1151

Value	As written	Source
171.4 °Cshown	340.5 °F (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
170 to 173 °C	170-173 °C	[2] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
–	greater than or equal to 100 mg/mL at 77 °F (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–	Sol in methyl ethyl ketone, acetone	[3] Hazardous Substances Data Bank (HSDB)cites IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work).
–shown	Solubility in water, g/100ml at 20 °C: 12.5	[2] ILO-WHO International Chemical Safety Cards (ICSCs)

Value	As written	Source
–shown	pK1= 1.75	[3] Hazardous Substances Data Bank (HSDB)cites Serjeant, E.P., Dempsey B.; Ionisation Constants of Organic Acids in Aqueous Solution. International Union of Pure and Applied Chemistry (IUPAC). IUPAC Chemical Data Series No. 23, 1979. New York, New York: Pergamon Press, Inc.
–	pK2= 3.57	[3] Hazardous Substances Data Bank (HSDB)cites Serjeant, E.P., Dempsey B.; Ionisation Constants of Organic Acids in Aqueous Solution. International Union of Pure and Applied Chemistry (IUPAC). IUPAC Chemical Data Series No. 23, 1979. New York, New York: Pergamon Press, Inc.
–	pK3= 10.75	[3] Hazardous Substances Data Bank (HSDB)cites Serjeant, E.P., Dempsey B.; Ionisation Constants of Organic Acids in Aqueous Solution. International Union of Pure and Applied Chemistry (IUPAC). IUPAC Chemical Data Series No. 23, 1979. New York, New York: Pergamon Press, Inc.

Value	As written	Source
190 °Cshown	374 °F (NTP, 1992)	[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
> 250 °C	> 250 °C	[2] ILO-WHO International Chemical Safety Cards (ICSCs)

Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.

Calculated

Heavy atoms: 10
Rings: 1
Aromatic rings: 1
Fraction sp³ carbons (Fsp3): 0
H-bond donors: 2
H-bond acceptors: 3
Rotatable bonds: 1
TPSA (Å²): 68
Formal charge: 0
XLogP3: -0.7 PubChem
Complexity: 120 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: C1 of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

C52.55%
H5.15%
N30.64%
O11.67%

Isotope pattern

Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.

Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.

Predicted

log P: -0.31 Crippen (Wildman and Crippen 1999)
log S (water solubility): -0.87 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 1.9 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 137.14
log P ≤ 5 (Crippen): -0.31
H-bond donors ≤ 5: 2
H-bond acceptors ≤ 10: 3

Passes all four rules.

¹³C NMR shifts, predicted

Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.

Safety

Warning

Most widely reported: 400 company reports to ECHA. Source [4].

Harmful or irritant

H302Harmful if swallowed (98.5% of reports)
H315Causes skin irritation (92.5% of reports)

Precautionary statements: P264, P270, P280, P301+P317, P302+P352, P321, P330, P332+P317, P362+P364, P501

First aid

Eyes: First check the victim for contact lenses and remove if present. Flush victim's eyes with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital or poison control center. Do not put any ointments, oils, or medication in the victim's eyes without specific instructions from a physician. Immediately transport the victim after flushing eyes to a hospital even if no symptoms (such as redness or irritation) develop. Skin: Immediately flood affected skin with water while removing and isolating all contaminated clothing.[1]
Fresh air, rest. Refer immediately for medical attention.[2]
Remove contaminated clothes. Rinse and then wash skin with water and soap.[2]
First rinse with plenty of water for several minutes (remove contact lenses if easily possible), then refer for medical attention.[2]

Storage

Cool. Well closed.[2]
Store below 40 °C (104 °C), preferably between 15 and 30 °C (59 and 86 °F), unless otherwise specified by manufacturer. Store in a tight, light-resistant container. Protect from freezing. Note: Crystallization may occur at low temperatures. Upon warming to room temperature, the crystals will redissolve.[3]

Safety data sheets on the supplier’s page: Enamine, Life Chemicals, Smolecule.

Always read the supplier’s safety data sheet before working with it.

Spectra

Experimental spectra held by these sources; each link opens the source's own record.

Literature

Reading PubChem, OpenAlex and GSRS…

Bioactivity

Reading ChEMBL…

References

[1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
[2]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[3]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[4]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[5]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
[6]Human Metabolome Database (HMDB) · Linked only · via PubChem · retrieved 2026-10-14
[7]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
[8]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
[9]MassBank Europe · Linked only · via PubChem · retrieved 2026-10-14
[10]MassBank of North America (MoNA) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
·Literature on PubChem

Data last updated 2026-10-14.