Chemistry:Higher alkanes

Short description: Alkanes having nine or more carbon atoms

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

The term higher alkanes is sometimes used literally as "alkanes with a higher number of carbon atoms". One definition distinguishes the higher alkanes as the n-alkanes that are solid under natural conditions.

Uses

Alkanes from nonane to hexadecane (those alkanes with nine to sixteen carbon atoms) are liquids of higher viscosity, which are 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 older 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. Mixtures of the normal alkanes are used as boiling point standards for simulated distillation by gas chromatography.

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, used for lubrication, electrical insulation, and candles. Paraffin wax should not be confused with beeswax, which consists primarily of esters.

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

Names

Some alkanes have non-IUPAC trivial names:

• cetane, for hexadecane
• cerane, for hexacosane

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 standard 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)	−53.5	−29.7	−25.6	−9.6	−5.4	5.9	9.9	18.2
Boiling point (°C)	150.8	174.1	195.9	216.3	235.4	253.5	270.6	286.8
Density (g/ml at 20 °C)	0.71763	0.73005	0.74024	0.74869	0.75622	0.76275	0.76830	0.77344
Viscosity (cP at 20 °C)	0.7139	0.9256	1.185	1.503	1.880	2.335	2.863	3.474
Flash point (°C)	31	46	60	71	79	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 at standard conditions.

	Heptadecane	Octadecane	Nonadecane	Icosane	Heneicosane	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	0.786	0.7886	0.792	0.778	0.797	0.797
Flash point (°C)	148	166	168	176

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	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	474	285.4 at 0.4 kPa	490	265 at 130 Pa
Density (g/ml)	0.781 at 68 °C	0.812	0.811	0.812	0.813	0.814

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)	504.14	510.93	517.51	523.88	530.75	536.07
Density (g/ml)	0.815	0.816	0.817	0.817	0.818	0.819

Tritetracontane to octatetracontane

	Triatetracontane	Tetratetracontane	Pentatetracontane	Hexatetracontane	Heptatetracontane	Octatetracontane
Formula	C43H88	C44H90	C45H92	C46H94	C47H96	C48H98
CAS Number	[7098-21-7]	[7098-22-8]	[7098-23-9]	[7098-24-0]	[7098-25-1]	[7098-26-2]
Molar mass (g/mol)	605.15	619.18	633.21	647.23	661.26	675.29
Boiling point (°C)	541.91	547.57	553.1	558.42	563.6	568.68
Density (g/ml)	0.82	0.82	0.821	0.822	0.822	0.823

Nonatetracontane to tetrapentacontane

	Nonatetracontane	Pentacontane	Henpentacontane	Dopentacontane	Tripentacontane	Tetrapentacontane
Formula	C49H100	C50H102	C51H104	C52H106	C53H108	C54H110
CAS number	[7098-27-3]	[6596-40-3]	[7667-76-7]	[7719-79-1]	[7719-80-4]	[5856-66-6]
Molar mass (g/mol)	689.32	703.34	717.37	731.39	745.42	759.45
Boiling point (°C)	573.6	578.4	583	587.6	592	596.38
Density (g/ml)	0.823	0.824	0.824	0.825	0.825	0.826

See also

• Alkene
• Alkyne
• Cycloalkane
• Hydrocarbon
• Paraffin wax, composed mostly of higher linear alkanes
• Polyethylene, a linear alkane of polymeric length

External links

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