Propyne, boiling point

Propargyl alcohol (2-propyn-l-ol, boiling point 114°C) is a colorless volatile liquid with an unpleasant odor that is the only commercially available acetylenic primary alcohol. It is miscible with water and with many organic solvents. The commercial material is specified as 97% minimum purity, determined by gas chromatography or acetylation. Moisture is specified at 0.05% maximum (Karl-Fischer titration). Formaldehyde content is determined by bisulfite titration. 

It will be immediately clear from the boiling point of trimethylsilylpropyne (96 C at atmospheric pressure) that the use of a hexane solution of BuLi for the lithiation of propyne is not advisable. The best way is to metallate propyne with a solution of ethyllithium in Et20, prepared from C2HjBr and lithium. iJwy/lithium in Et70 would be less suitable, because of the formation of small amounts of octane (b.p. 128 C) during its preparation (Wiirtz-coupling). 

At room temperature, the first three members of the series (ethyne, propyne and butyne) are gases, the others are liquids. Branching, as in the other hydrocarbons, decreases the boiling point. 

The physical properties of alkynes (Table 9-1) are similar to those of alkanes and alkenes of similar molecular weights. Alkynes are relatively nonpolar and nearly insoluble in water. They are quite soluble in most organic solvents, including acetone, ether, methylene chloride, chloroform, and alcohols. Many alkynes have characteristic, mildly offensive odors. Acetylene, propyne, and the butynes are gases at room temperature, just like the coitesponding alkanes and alkenes. In fact, the boiling points of alkynes are nearly the same as those of alkanes and alkenes with similar carbon skeletons. 

Alkynes have boiling points very similar to those of the corresponding alkenes and alkanes. Ethyne is nnnsnal in that it has no boiling point at atmospheric pressnre rather, it sublimes at 84°C. Propyne (b.p. -23.2°C) and 1-butyne (b.p. 8.1°C) are gases, whereas 2-butyne is barely a Uquid (b.p. 27°C) at room temperature. The medium-sized alkynes are distillable liquids. 

The boiling points of acetonitrile and 1 -propyne are 81.5 and -23 °C, respectively. Account for this difference in boilmg point between two compounds with similar molecular weights. 

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