Butyronitrile
Butyronitrile, also known as butanenitrile or propyl cyanide, is a straight-chain organic nitrile with the chemical formula C₄H₇N and structural formula CH₃CH₂CH₂CN, consisting of a propyl group attached to a cyano functional group.[1][2] This compound appears as a clear, colorless liquid at room temperature, with a molecular weight of 69.11 g/mol, a melting point of −112 °C, a boiling point of 115–117 °C, and a density of 0.794 g/mL at 25 °C.[2] It is slightly soluble in water (approximately 3% at 77 °F) but miscible with most polar organic solvents such as alcohols, ethers, and dimethylformamide, and its vapors are heavier than air.[2][3] Butyronitrile is primarily employed as a chemical intermediate in organic synthesis, serving as a precursor to compounds like n-butylamine, butanamide, and butyric acid, and playing a key role in the production of the poultry coccidiostat drug amprolium.[2] It also finds applications as an industrial solvent due to its high polarity and solvating power, particularly in the manufacture of pharmaceuticals, agrochemicals, and other fine chemicals, as well as in research and development for new materials.[2][4] Industrially, it is produced via the catalytic gas-phase ammoxidation of butanal or butanol with ammonia.[2] Despite its utility, butyronitrile is highly hazardous, classified as a flammable liquid with a flash point of 16.7 °C (62 °F) and capable of forming explosive mixtures with air.[2][3] It is acutely toxic by inhalation, skin contact, and ingestion, with an oral LD50 of 0.14 g/kg in rats, and exposure can cause symptoms such as dizziness, headache, and cyanosis due to cyanide release.[2][3] Butyronitrile reacts vigorously with strong oxidizers, acids, bases, and reducing agents, potentially releasing toxic hydrogen cyanide or nitrogen oxides upon combustion or decomposition, and it is incompatible with metals that may catalyze polymerization.[3] Occupational exposure limits are set at a time-weighted average of 8 ppm (22 mg/m³).[2]Chemical identity
Molecular structure
Butyronitrile has the molecular formula C₄H₇N.[1] Its structural formula is CH₃CH₂CH₂CN, consisting of a linear propyl chain (CH₃CH₂CH₂-) attached to a cyano group (-CN).[5] This arrangement represents the straight-chain isomer of butanenitrile. The molecule features a four-carbon backbone where the terminal carbon is part of the nitrile functional group, characterized by a carbon-nitrogen triple bond (C≡N). The carbon atom in the nitrile group is sp hybridized, forming a linear geometry with a bond angle of 180° at the nitrile carbon.[6] Similarly, the nitrogen atom is sp hybridized, contributing to the triple bond through one σ bond and two π bonds. The C≡N bond length is approximately 1.16 Å, reflecting the strong triple bond character typical of organic nitriles.[7] Butyronitrile (n-butyronitrile) is distinguished from its branched isomer, isobutyronitrile (2-methylpropanenitrile), which has the formula (CH₃)₂CHCN and features a isopropyl group attached to the cyano moiety.[8] These isomers share the same molecular formula but differ in carbon chain arrangement, leading to variations in their physical and chemical behaviors.Nomenclature
Butanenitrile is the preferred IUPAC name for the compound with the formula CH₃CH₂CH₂CN, reflecting the systematic nomenclature for nitriles where the suffix "-nitrile" is added to the name of the parent alkane chain including the carbon of the cyano group.[9] Commonly referred to as n-butyronitrile, propyl cyanide, or 1-cyanopropane, the name "butyronitrile" derives from butyric acid—the four-carbon carboxylic acid from which it is conceptually related—by substituting the "-ic acid" ending with "-nitrile" to denote the -CN functional group. The term "nitrile" itself was coined by German chemist Justus von Liebig in 1832 to describe organic cyanides, building on the 1782 isolation of hydrogen cyanide by Carl Wilhelm Scheele during investigations into the composition of Prussian blue.[2][10][11] This compound is identified by the CAS registry number 109-74-0 and has a molecular weight of 69.11 g/mol.[1]Physical properties
Appearance and thermodynamic data
Butyronitrile is a clear, colorless liquid at room temperature with a sharp, suffocating odor.[12] Key thermodynamic properties include a melting point of −112 °C and a boiling point of 117 °C under standard pressure.[9] The compound exhibits a flash point of 17 °C (closed cup), indicating high flammability.[1] At 20 °C, butyronitrile has a density of 0.794 g/cm³ and a vapor pressure of 2 kPa; its vapors are heavier than air, with a vapor density of approximately 2.4 relative to air.[3][13][14]Solubility and density
Butyronitrile exhibits a density of 0.794 g/cm³ at 20 °C, which is characteristic of many aliphatic nitriles due to their relatively low molecular weight and linear structure.[1] This value decreases with increasing temperature, reflecting typical volumetric expansion in organic liquids. The compound demonstrates limited solubility in water, with approximately 3.3 g/100 mL at 25 °C, indicating poor miscibility that aligns with the hydrophobic nature of longer-chain nitriles compared to shorter analogs like acetonitrile.[15] In contrast, butyronitrile is miscible with polar organic solvents such as ethanol, diethyl ether, and acetone, facilitating its use in organic reactions and extractions. It is also soluble in benzene, a nonpolar aromatic solvent, though to a lesser extent than in polar media.[16] The octanol-water partition coefficient (log P) of butyronitrile is 0.53, signifying moderate lipophilicity that influences its distribution between aqueous and lipid phases in environmental and biological contexts.[1] This value, derived from experimental measurements, underscores the compound's balanced affinity for both hydrophilic and hydrophobic environments.[17]Chemical properties
Reactivity and stability
Butyronitrile exhibits good chemical stability under normal ambient conditions, remaining unreactive at room temperature without exposure to incompatible materials or extreme environments. It maintains integrity during standard storage and transport, with an NFPA instability rating of 0, indicating no inherent tendency toward hazardous reactions under typical handling scenarios.[1][18] The nitrile group (-C≡N) in butyronitrile is prone to hydrolysis under acidic or basic catalysis, yielding butyric acid as the primary product along with ammonia or ammonium species. This reaction proceeds via nucleophilic attack by water, facilitated by H₃O⁺ or OH⁻, to form intermediates such as butanamide before full conversion to CH₃CH₂CH₂CO₂H and NH₄⁺/NH₃; the process is exothermic and requires careful control to manage heat generation. Additionally, the electron-deficient nitrile carbon undergoes nucleophilic addition with organometallic reagents like Grignard compounds (RMgX), forming an imine intermediate that hydrolyzes to a ketone, enabling carbon-carbon bond formation in synthetic applications.[3][4][19] Butyronitrile reacts vigorously with strong oxidizing agents, such as peroxides, potentially leading to exothermic decompositions and the release of toxic nitrogen oxides (NOₓ). Upon heating to decomposition, it breaks down into hazardous fragments, including hydrogen cyanide (HCN) and other cyanide-containing fumes, alongside NOₓ; this thermal instability underscores the need for controlled temperatures to prevent unintended pyrolysis.[1][3]Spectroscopic data
Butyronitrile exhibits characteristic spectroscopic features that aid in its identification, primarily due to the nitrile functional group and the alkyl chain. In infrared (IR) spectroscopy, the most prominent feature is the strong C≡N stretching vibration, appearing as a sharp absorption band at approximately 2250 cm⁻¹. This band is typical for aliphatic nitriles and confirms the presence of the -C≡N moiety.[20][21] Nuclear magnetic resonance (NMR) spectroscopy provides detailed structural information. The ¹H NMR spectrum in CDCl₃ displays three distinct signals corresponding to the propyl chain: the terminal methyl group (CH₃) as a triplet at δ ≈ 1.0 ppm (3H, J ≈ 7 Hz), the middle methylene group (CH₂) as a sextet at δ ≈ 1.7 ppm (2H, J ≈ 7 Hz), and the methylene adjacent to the cyano group (CH₂CN) as a triplet at δ ≈ 2.3 ppm (2H, J ≈ 7 Hz). These multiplicities arise from vicinal coupling in the -CH₂-CH₂-CH₃ segment. In ¹³C NMR, the quaternary carbon of the nitrile group (C≡N) resonates at δ ≈ 120 ppm, while the alpha carbon (CH₂CN) appears at δ ≈ 17 ppm; the other carbons are observed around 13 ppm (CH₃) and 20 ppm (middle CH₂).[22]| Nucleus | Position | Chemical Shift (δ, ppm) | Multiplicity/Notes |
|---|---|---|---|
| ¹H | CH₃ | ≈1.0 | Triplet (3H) |
| ¹H | -CH₂- | ≈1.7 | Sextet (2H) |
| ¹H | -CH₂CN | ≈2.3 | Triplet (2H) |
| ¹³C | C≡N | ≈120 | Quaternary |
| ¹³C | CH₂CN | ≈17 | - |