Alkynediazonium ions

Alkane-, alkene-, and alkynediazonium ions are structurally and theoretically interesting compounds (Sects. 5.1 and 5.3), but they are of little interest for organic synthesis. 

The dominant property of the alkynediazonium ion 2.291 is the addition of nucleophiles to the triple bond. Addition of water or methanol to the CH2CI2 — SbCls solution leads to alkenediazonium ions 2.292 with OH, CH3O or Cl in the 2-position (2-112). The C—N bond in the alkynediazonium is more stable than the corresponding C — N bond of the alkenediazonium ion. With water, the final product of addition, dediazoniation of the alkenediazonium ion, and addition of HCl is 2-chloro-l-phenylethanone (2.294). Without HCl, 2-hydroxy-l-phenylethanone (2.293) is formed (2-113). 

The higher stability of the alkynediazonium ion towards dediazoniation, relative to that of the alkenediazonium ion, is consistent with structure calculations obtained by Glaser (1987, 1989 see Sect. 5.3). It is unlikely, therfore, that alkyne cations can be obtained by dediazoniation of alkynediazonium ions. An alkynyl cation was formed, however, by spontaneous nuclear decay in l,4-bis(tritioethynyl)benzene, as found by Angelini et al. (1988). 

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