Generation of α-acetolactone and the acetoxyl diradical •CH2COO• in the gas phase

The formation of neutral [C-2,H-2,O-2] has been investigated by tandem mass spectrometry in a sector instrument and by energy-resolved collision-induced dissociation in a flowing afterglow-triple quadrupole apparatus. The neutral species are generated by two different methods: (i) neutralization of the distonic anion radical (CH2COO-)-C-. by collisional electron detachment and (ii) collision-induced loss of halides X-concomitant with formation of [C-2,H-2,O-2] from alpha-haloacetate ions XCH2COO-. The tandem mass spectrometry results suggest that neutralization of (CH2COO-)-C-. and high-energy collisional activation of alpha-haloacetate ions lead to a mixture of alpha-acetolactone, c-(CH2C(O)O), and the acetoxyl diradical, (CH2COO.)-C-.. Low-energy collisions with alpha-chloroacetate ions in the triple quadrupole analyzer produce alpha-acetolactone exclusively at the dissociation threshold. From the dissociation threshold measured for the appearance of Cl- from ClCH2COO- the heat of formation of acetolactone is determined to be Delta H-f,H-298 = -47.3 +/- 4.7 kcal/mol. (C) 1997 Elsevier Science B.V.