# Isomers of butylamine
Butylamine is any of several amines with the formula C4H11N; the term most often refers to the four primary-amino structural isomers in which an amino group (NH2) sits on a four-carbon skeleton: n-butylamine, sec-butylamine, isobutylamine, and tert-butylamine.[1](https://www.benchchem.com/product/B146782/docs) The molecular formula also admits four further amine isomers in which nitrogen carries two or three alkyl groups: three secondary amines (methyl-n-propylamine, methyl-isopropylamine, and diethylamine) and one tertiary amine (dimethylethylamine), for eight amine isomers in total.[2](https://www.sarthaks.com/3838531/5-total-number-of-isomers-can-be-shown-by-butylamine-a-3-b-4-c-7-d-8) This article covers the four primary isomers.
| Property | n-Butylamine | sec-Butylamine | Isobutylamine | tert-Butylamine |
|---|---|---|---|---|
| Structure | CH3(CH2)3NH2 | CH3CH2CH(NH2)CH3 | (CH3)2CHCH2NH2 | (CH3)3CNH2 |
| Boiling point | 78 °C[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) | 63 °C[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) | – | 43–47 °C |
| Melting point | −50 °C[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) | −104 °C[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) | – | −67.50 °C |
| Relative density (water = 1) | 0.74[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) | 0.7[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) | – | 0.696 g/mL |
| pKa of conjugate acid | 10.61[1](https://www.benchchem.com/product/B146782/docs) | 10.60[1](https://www.benchchem.com/product/B146782/docs) | 10.77[1](https://www.benchchem.com/product/B146782/docs) | 10.68[1](https://www.benchchem.com/product/B146782/docs) |
| Solubility in water | Miscible[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) | Miscible[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) | – | Miscible (1000 g/L at 25 °C)[1](https://www.benchchem.com/product/B146782/docs) |
| Flash point | −12 °C[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) | −9 °C[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) | – | – |
## Structures and nomenclature
The four isomers differ in two distinct ways. [Chain (skeletal) isomerism](https://www.edgepedia.org/chain-skeletal-isomerism) separates n-butylamine, isobutylamine, and tert-butylamine, whose carbon frameworks are straight-chain butyl, branched isobutyl, and branched tert-butyl groups respectively; n-butylamine and 2-methylpropanamine (isobutylamine) are the classic pair of chain isomers.[5](https://www.embibe.com/exams/isomerism-in-amines/) Amines also exhibit [positional isomerism](https://www.edgepedia.org/positional-isomerism), in which the same carbon skeleton carries the functional group at different positions.[5](https://www.embibe.com/exams/isomerism-in-amines/)
Amines are classified by the number of alkyl groups bonded to nitrogen, and CAS nomenclature attaches the suffix -amine, designating additional nitrogen substituents with the prefix N-.[6](https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(Wade)_Complete_and_Semesters_I_and_II/Map%3A_Organic_Chemistry_(Wade)/03%3A_Functional_Groups_and_Nomenclature/3.12%3A_Amines_-_Classification_and_Nomenclature) All four butylamines are primary amines: one alkyl group on nitrogen.[1](https://www.benchchem.com/product/B146782/docs)
One isomer is chiral. sec-Butylamine (CAS 13952-84-6) exists as two stereoisomers, (R)-butan-2-amine and (S)-butan-2-amine, because the carbon bearing the amino group carries four different substituents.[7](https://webbook.nist.gov/cgi/cbook.cgi?ID=13952-84-6)
## Physical properties
All four isomers are miscible with water at 20–25 °C.[1](https://www.benchchem.com/product/B146782/docs) Branching, however, weakens amine–amine hydrogen bonding in the pure liquid: measured enthalpies of hydrogen bonding fall from 8.4 kJ/mol for n-butylamine to 7.5 for isobutylamine, 6.6 for sec-butylamine, and 4.9 kJ/mol for tert-butylamine.[1](https://www.benchchem.com/product/B146782/docs)
The boiling-point consequence is large. [Chain branching](https://www.edgepedia.org/chain-branching) reduces amine boiling points by 10 to 15 °C per branching step.[8](https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(Wade)_Complete_and_Semesters_I_and_II/Map%3A_Organic_Chemistry_(Wade)/20.01%3A_Structure_and_Physical_Properties_of_Amines) n-Butylamine boils at 351 K (78 °C), 32 K higher than tert-butylamine at 319 K (46 °C), because the straight-chain molecule forms stronger intermolecular hydrogen bonds while the tert-butyl group sterically obstructs them.[9](https://www.benchchem.com/product/b146782) The ICSC values place n-butylamine at 78 °C and sec-butylamine at 63 °C, a 15 °C drop consistent with that rule.[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) • [4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) Melting points do not follow the same trend: sec-butylamine melts far lower (−104 °C) than n-butylamine (−50 °C) or tert-butylamine (−67.50 °C).[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) • [4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2)
## Basicity, steric hindrance and reactivity
In aqueous pKa terms the four isomers are close: the conjugate acids have pKa values of 10.61 (n-), 10.77 (iso-), 10.60 (sec-), and 10.68 (tert-).[1](https://www.benchchem.com/product/B146782/docs) One technical source states an intrinsic basicity order of n-BuNH2 > i-BuNH2 > sec-BuNH2 > t-BuNH2,[9](https://www.benchchem.com/product/b146782) but its own tabulated pKa values put isobutylamine above n-butylamine, so the ordering of the middle isomers is not settled.
Where branching clearly matters is kinetic nucleophilicity (how readily a molecule attacks electron-poor reaction partners), not equilibrium basicity. In acetonitrile, n-butylamine has a Mayr nucleophilicity parameter N of 15.27 against 12.35 for tert-butylamine under identical conditions, roughly 6.9x on the logarithmic scale; in 18-crown-6 picrate extraction, log Kex is 7.9 versus 6.6.[9](https://www.benchchem.com/product/b146782) The bulky tert-butyl group impedes approach of reagents to the nitrogen lone pair and slows solvation of the developing ammonium cation.[1](https://www.benchchem.com/product/B146782/docs)
## Industrial production
Each isomer has a distinct production route. n-Butylamine is usually manufactured by catalytic alkylation of ammonia with butyl alcohol, or from butyraldehyde and ammonia in the presence of [Raney nickel](https://www.edgepedia.org/raney-nickel); US production in 1982 was approximately 1109 metric tons.[10](https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6361286.htm) Catalyst development continues to target selectivity: cobalt on silica at 343 K and 25 bar H2 gives 97% n-butylamine selectivity in [butyronitrile](https://www.edgepedia.org/butyronitrile) hydrogenation, the highest reported among tested catalysts (Ni/SiO2 gives 84%, and platinum systems favor dibutylamine), while acid-treated cobalt catalysts give 90% selectivity in amination of n-butanol with ammonia, holding 87.8% over 120 hours.[9](https://www.benchchem.com/product/b146782)
Isobutylamine has an emerging biotechnological route: engineered E. coli strains produced iso-butylamine at 8.63 g/L in fed-batch fermentation, with a productivity of 0.21 g/L/h and a yield of 0.062 g/g, a 6.50-fold increase over flask culture; conventional short-chain primary amine production dehydrates alcohols with ammonia under harsh catalytic conditions.[11](https://preview-www.nature.com/articles/s41467-020-20423-6)
## Uses and applications
n-Butylamine is used in the manufacture of the fungicide benomyl, the antidiabetic drug tolbutamide, and N,N′-dibutylthiourea, a rubber vulcanization accelerator.[1](https://www.benchchem.com/product/B146782/docs) An estimated 50% of n-butylamine production goes to rubber processing chemicals and 50% to pesticide intermediates (SRI 1982).[10](https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6361286.htm)
It is also a chemical intermediate for tert-butylaminoethyl methacrylate, a lube-oil additive.[10](https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6361286.htm) In modern synthesis chemistry it acts as a cost-effective bifunctional additive (ligand and base) in nickel-catalyzed photoredox C–O and C–N bond-forming reactions.[1](https://www.benchchem.com/product/B146782/docs) sec-Butylamine is used as a fungistat.[10](https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6361286.htm)
## Safety and handling
All the isomers are volatile, flammable liquids with corrosive vapors. n-Butylamine has a flash point of −12 °C, auto-ignition temperature 312 °C, and explosive limits of 1.7–9.8 vol% in air; sec-butylamine has a flash point of −9 °C and auto-ignition temperature 378 °C.[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) • [4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) The vapor is heavier than air and may travel along the ground, allowing distant ignition.[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1)
Occupational limits are similar for the two best-documented isomers: n-butylamine carries a TLV of 5 ppm as STEL with a skin notation and a German MAK of 2 ppm (6.1 mg/m3, pregnancy risk group C), while sec-butylamine has the same MAK value but pregnancy risk group D.[3](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1) • [4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) A ceiling limit of 5 ppm (about 15 mg/m3) applies per ACGIH, MSHA, and OSHA, with an IDLH of 2000 ppm per NIOSH and an odor threshold of 0.17 ppm.[10](https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6361286.htm) sec-Butylamine attacks tin, aluminum, and some steels, a materials-compatibility constraint the other isomers' cards do not record.[4](https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2) [tert-Butylamine](https://www.edgepedia.org/tert-butylamine) has an oral rat LD50 of 464 mg/kg.
## References
1. Butylamine Documentation Hub | BenchChem — https://www.benchchem.com/product/B146782/docs
2. Total number of isomers can be shown by BUTYLAMINE — https://www.sarthaks.com/3838531/5-total-number-of-isomers-can-be-shown-by-butylamine-a-3-b-4-c-7-d-8
3. ICSC 0374 - n-BUTYLAMINE — https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0374&p_lang=en&p_version=1
4. ICSC 0401 - sec-BUTYLAMINE — https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_card_id=0401&p_lang=en&p_version=2
5. Isomerism in Amines - Embibe — https://www.embibe.com/exams/isomerism-in-amines/
6. 3.12: Amines - Classification and Nomenclature - Chemistry LibreTexts — https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(Wade)_Complete_and_Semesters_I_and_II/Map%3A_Organic_Chemistry_(Wade)/03%3A_Functional_Groups_and_Nomenclature/3.12%3A_Amines_-_Classification_and_Nomenclature
7. sec-Butylamine - NIST WebBook — https://webbook.nist.gov/cgi/cbook.cgi?ID=13952-84-6
8. 20.1: Structure and Physical Properties of Amines - Chemistry LibreTexts — https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(Wade)_Complete_and_Semesters_I_and_II/Map%3A_Organic_Chemistry_(Wade)/20.01%3A_Structure_and_Physical_Properties_of_Amines
9. n-Butylamine (CAS 109-73-9) | BenchChem — https://www.benchchem.com/product/b146782
10. Butylamine | 109-73-9 | ChemicalBook — https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6361286.htm
11. Microbial production of multiple short-chain primary amines via retrobiosynthesis | Nature Communications — https://preview-www.nature.com/articles/s41467-020-20423-6
12. Butylamine Market Size to Hit USD 690.02 Million by 2034 | CAGR 5.1% — https://growthmarketreports.com/report/butylamine-market-global-industry-analysis
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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Organic substances › Organic reactions, structure and reference › Stereochemistry and isomerism › Isomerism and structural isomers › Isomer sets of simple homologous series*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026 · Edited: Sep 30, 2026; Oct 11, 2026; Oct 25, 2026 · Last review: Sep 30, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license