Physical properties of alkynes

Physical state

The first three members (ethyne, propyne and butyne) are colourless and odorless gases. Due to the presence of phosphine as an impurity ethyne (acetylene) has garlic smell. The next eight members are liquids, and higher members are solids under normal conditions of temperature and pressure.


Alkynes are insoluble in water, but are fairly soluble in organic solvents such as, alcohol, ether, acetone etc.

Melting and boiling points

The melting and boiling points of alkynes increase with molecular mass. Melting boiling points of some alkynes are,

Ethyne/acetylene (CH º CH), - 83oC or 190 K

Propyne (CH3-CºCH), - 27oC or 246 K

1 - Butane (CH3-CH2-CºCH), 8oC or 281 K

2 - Butane (CH3-CºC-CH3), 29oC or 302 K

1 - Pentyne (CH3-CH2-CH2-CºCH) 48oC or 321 K

2 - Pentyne (CH3-CºC-CH2-CH3) 55oC or 328 K

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