Higher alkanes

Higher alkanes are often defined as alkanes having nine or more carbon atoms. Nonane is the lightest alkane to have a flash point above 25 °C, and so not to be classified as dangerously flammable.

The scientific literature uses the term higher alkanes arbitrarily: sometimes literally as “alkanes with a higher number of carbon atoms”, sometimes according to a definition. For instance, other than based on nonane, one definition distinguishes the higher alkanes as the n-alkanes that are solid under natural conditions.

Uses

Alkanes from nonane to, for instance, hexadecane (an alkane with sixteen carbon atoms) are liquids of higher viscosity, less and less suitable for use in gasoline. They form instead the major part of diesel and aviation fuel. Diesel fuels are characterised by their cetane number, cetane being an old name for hexadecane. However the higher melting points of these alkanes can cause problems at low temperatures and in polar regions, where the fuel becomes too thick to flow correctly.

Alkanes from hexadecane upwards form the most important components of fuel oil and lubricating oil. In latter function they work at the same time as anti-corrosive agents, as their hydrophobic nature means that water cannot reach the metal surface. Many solid alkanes find use as paraffin wax, for example in candles. This should not be confused however with bees wax, which consists primarily of esters.

Alkanes with a chain length of approximately 35 or more carbon atoms are found in bitumen, used for example in road surfacing. However, the higher alkanes have little value and are usually split into lower alkanes by cracking.

Properties

The properties listed here refer to the straight-chain alkanes (or: n-alkanes).

Nonane to hexadecane

This group of n-alkanes is generally liquid under natural conditions.

	Nonane	Decane	Undecane	Dodecane	Tridecane	Tetradecane	Pentadecane	Hexadecane
Formula	C₉H₂₀	C₁₀H₂₂	C₁₁H₂₄	C₁₂H₂₆	C₁₃H₂₈	C₁₄H₃₀	C₁₅H₃₂	C₁₆H₃₄
CAS number	[111-84-2]	[124-18-5]	[1120-21-4]	[112-40-3]	[629-50-5]	[629-59-4]	[629-62-9]	[544-76-3]
Molar mass (g/mol)	128.26	142.29	156.31	170.34	184.37	198.39	212.42	226.45
Melting point (°C)	−53	−30	−26	−9.6	−5	5.5	9.9	18
Boiling point (°C)	151	174	196	216.2	234	253	268–270	287
Density (g/ml)	0.718	0.73	0.74	0.75		0.763	0.769	0.773
Viscosity (cP at 20 °C)	0.711	0.92		1.35		2.18		3.34
Flash point (°C)	31	46	60	71	102	99	132	135
Autoignition temperature (°C)	205	210		205		235		201
Explosive limits	0.9–2.9%	0.8–2.6%					0.45–6.5%

Heptadecane to Tetracosane

From this group on, the n-alkanes are generally solid under natural conditions.

	Heptadecane	Octadecane	Nonadecane	Icosane	Henicosane	Docosane	Tricosane	Tetracosane
Formula	C₁₇H₃₆	C₁₈H₃₈	C₁₉H₄₀	C₂₀H₄₂	C₂₁H₄₄	C₂₂H₄₆	C₂₃H₄₈	C₂₄H₅₀
CAS number	[629-78-7]	[593-45-3]	[629-92-5]	[112-95-8]	[629-94-7]	[629-97-0]	[638-67-5]	[646-31-1]
Molar mass (g/mol)	240.47	254.50	268.53	282.55	296.58	310.61	324.63	338.66
Melting point (°C)	21	28–30	32–34	36.7	40.5	42	48–50	52
Boiling point (°C)	302	317	330	342.7	356.5	224 at 2 kPa	380	391.3
Density (g/ml)	0.777	0.777			0.792		0.797
Flash point (°C)	148	165	168

Pentacosane to Triacontane

	Pentacosane	Hexacosane	Heptacosane	Octacosane	Nonacosane	Triacontane
Formula	C₂₅H₅₂	C₂₆H₅₄	C₂₇H₅₆	C₂₈H₅₈	C₂₉H₆₀	C₃₀H₆₂
CAS number	[629-99-2]	[630-01-3]	[593-49-7]	[630-02-4]	[630-03-5]	[638-68-6]
Molar mass (g/mol)	352.69	366.71	380.74	394.77	408.80	422.82
Melting point (°C)	54	56.4	59.5	64.5	63.7	65.8
Boiling point (°C)	401.9	412.2	422	431.6	440.8	449.7
Density (g/ml)	0.801	0.778	0.780	0.807	0.808	0.810

Hentriacontane to hexatriacontane

	Hentriacontane	Dotriacontane	Tritriacontane	Tetratriacontane	Pentatriacontane	Hexatriacontane
Formula	C₃₁H₆₄	C₃₂H₆₆	C₃₃H₆₈	C₃₄H₇₀	C₃₅H₇₂	C₃₆H₇₄
CAS number	[630-04-6]	[544-85-4]	[630-05-7]	[14167-59-0]	[630-07-9]	[630-06-8]
Molar mass (g/mol)	436.85	450.88	464.90	478.93	492.96	506.98
Melting point (°C)	67.9	69	70–72	72.6	75	74–76
Boiling point (°C)	458	467		285.4 at 0.4 kPa	490	265 at 130 Pa

Heptatriacontane to Dotetracontane

	Heptatriacontane	Octatriacontane	Nonatriacontane	Tetracontane	Hentetracontane	Dotetracontane
Formula	C₃₇H₇₆	C₃₈H₇₈	C₃₉H₈₀	C₄₀H₈₂	C₄₁H₈₄	C₄₂H₈₆
CAS number	[7194-84-5]	[7194-85-6]	[7194-86-7]	[4181-95-7]	[7194-87-8]	[7098-20-6]
Molar mass (g/mol)	520.99	535.03	549.05	563.08	577.11	591.13
Melting point (°C)	77	79	78	84	83	86
Boiling point (°C)

External links

International Chemical Safety Card 1245 (nonane)
NIOSH Pocket Guide to Chemical Hazards (nonane)
International Chemical Safety Card 0428 (decane)

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