Pentanes

Properties of the pentanes
Surname	n -pentane	Isopentane	Neopentane
other names	Pentane ( IUPAC )	2-methylbutane	2,2-dimethylpropane
Refrigerant	R-601	R-601a	R-601b
Structural formula
CAS number	109-66-0	78-78-4	463-82-1
PubChem	8003	6556	10041
Molecular formula	C 5 H 12
Molar mass	72.15 g mol −1
Brief description	colorless liquids		colorless gas
Melting point	−130 ° C	−160 ° C	−16.6 ° C
boiling point	36 ° C	28 ° C	9.5 ° C
Vapor pressure (20 ° C)	562 mbar	761 mbar	1456 mbar
Vapor pressure (30 ° C)	815 mbar	1080 mbar	2100 mbar
Vapor pressure (50 ° C)	1590 mbar	2042 mbar	3700 mbar
density	0.63 g cm −3	0.62 g cm −3	0.6135 g cm −3
Solubility in H 2 O	39 mg l −1	50 mg l −1	33 mg l −1
Flash point	−49 ° C	−57 ° C	<-7 ° C
lower explosion limit (LEL)	1.1% by volume	1.3% by volume	1.3% by volume
	33 g m −3	38 g m −3	40 g m −3
Upper explosion limit (OEG)	8.7% by volume	7.6% by volume	7.5% by volume
	260 g m −3	230 g m −3	230 g m −3
Ignition temperature	260 ° C	420 ° C	450 ° C

Pentanes are hydrocarbons with the empirical formula C ₅ H ₁₂ and count among the alkanes . There are three constitutional isomers : n- pentane , isopentane and neopentane .

The name is derived from the Greek "penta", five, the molecule has 5 carbon atoms. All larger alkane molecules are also named according to numerals

n- pentane and isopentane are low-boiling liquids that are still liquid at room temperature, but boil on warm skin. They only solidify well below –100 ° C. Neopentane has an even lower boiling point, so it is already gaseous even at room temperature. However, its melting point is much higher compared to the two isomers, the melting temperature of -16.6 ° C means that neopentane would be solid in a freezer.

All three isomers form colorless, clear liquids, the vapor pressure at a certain temperature increases from n-pentane to iso-pentane and - with a little more difference - further to neo-pentane. Pentanes also burn below the freezing point of water and are explosive when mixed with air in areas with a concentration of a few percent by volume.

Handling and storage as a liquid is made difficult by the high vapor pressure. Since the liquids are electrically non-conductive, there is a risk of electrical charging, spark discharge and ignition when pouring out.

Pentane can (out of date) be regarded as an amyl hydride. Amyl alcohol is pentanol.

According to Antoine , the vapor pressure curves can be approximated in the form log ₁₀ (P) = A− (B / (T + C)) (P in bar, T in K ) in the specified temperature ranges with the following parameters:

Vapor pressure functions of the pentanes
	T (K) ranges	A.	B.	C.
n -pentane	268.8-341.37	3,9892	1070.617	−40.454
	341.37-?	?	?	?
Isopentane	190.3-300.9	3.90935	1018,516	−40.081
	300.9-453.5	3.97183	1021.864	−43.231
Neopentane	268.0-313.2	3.86373	0950.318	-36.329
	313.2-3430	?	?	?
	343-433	4,61616	1478.868	41.256

Vapor pressure curves ( logarithmic ) of the pentanes (T = 0… 150 ° C) (green: neo-pentane)

Individual evidence

1. ↑ all data was taken from the GESTIS database, the individual links are in the name line.
2. ↑ Entry for CAS no. 109-66-0 in the GESTIS substance database of the IFA , accessed on January 11, 2017(JavaScript required) .
3. ↑ Entry for CAS no. 78-78-4 in the GESTIS substance database of the IFA , accessed on January 12, 2017(JavaScript required) .
4. ↑ Entry for CAS no. 463-82-1 in the GESTIS substance database of the IFA , accessed on January 12, 2017(JavaScript required) .
5. ↑ ^{a b} Osborn, AG; Douslin, DR: Vapor-Pressure Relations for 15 Hydrocarbons in J. Chem. Eng. Data 19 (1974) 114-117.
6. ^ DR Stull: Vapor Pressure of Pure Substances Organic Compounds , in: Ind. Eng. Chem. 39 (1947), pp. 517-540, doi : 10.1021 / ie50448a022 .
7. ↑ Dawson, PP, Jr .; Silberberg, IH; McKetta, JJ: Volumetric Behavior, Vapor Pressures, and Critical Properties of Neopentane in J. Chem. Eng. Data 18 (1973) 7-15.