48
P.S. Bhadury et al. / Journal of Fluorine Chemistry 113 02002) 47±50
Scheme 1. Synthesis of O-ꢀchlorodifluoroacylated) alcohols.
Table 1
NMR and mass spectral data of esters I±VI
Compound no.
1H NMR d ꢀppm)
19F NMR d ꢀppm)
EI±MS ꢀm/z)
CI±MS
I
CH2 4.80 ꢀq)
CH2 4.85 ꢀt)
CF3 À76.5 ꢀt) CF2Cl À62.5 ꢀs)
CF3 À124.3 ꢀt) CF2 À84.7 ꢀm)
CF2Cl À64.8 ꢀs)
213/215, 193/195, 173, 127, 99, 85/87, 83, 69, 50
263/265, 243/245, 227, 215, 177, 143/145, 133,
113, 85/87, 69, 51
213/215
263/265
II
III
CH 5.75 ꢀm)
CF3 À73.4 ꢀd) CF2Cl À64.7 ꢀs)
281/283, 261/263, 245, 241/243, 225, 195, 157, 151,
129, 113, 99, 85/87, 69, 51
281/283
IV
V
±
±
±
CF2Cl À63.1 ꢀs)
CF2Cl À63.4 ꢀs)
CF2Cl À64.0 ꢀs)
145/147, 131/133, 109, 85/87, 59
145/147
159/161
243/245
159/161, 131/133, 123, 115, 95, 85/87, 78, 59, 50
243/245, 224, 187, 173, 157, 143, 115/117, 99,
85/87, 69, 56.
VI
of the solvent DMF into a proton donor source under similar
conditions has been observed earlier [1]. As with any other
SN2 displacement, the reactions are more facile with elec-
tron de®cient poly¯uorinated alcohols where the creation of
a positive centre is possible at the carbon atom attached to an
alcoholic OH group. With normal hydrocarbon alcohols, the
reactions are sluggish and do not occur at all even with a
secondary alcohol like isopropanol. As with most other SN2
displacements, the reaction fails to take place with poly-
¯uorinated tertiary alcohols, such as 2-ꢀ4-¯uorophenyl)-
1,1,1,3,3,3-hexa¯uoro-2-propanol probably due to steric
factors. It should also be noted that the esteri®cation reaction
does not occur in other media, such as diglyme, triglyme,
acetonitrile and dimethylsulphoxide and only alcohols but
not organohalides can undergo this reaction. The esters
The mass spectra of all the esters showed ꢀM H) ions
rather than M ions as the highest mass peaks. In order to
con®rm this observation and the molecular weight of the
compounds, chemical ionisation MS was also performed
using methane as the reagent gas. All the compounds gave
the expected pseudomolecular ions in CI. The EI mass
spectra of all the O-ꢀchlorodi¯uoroacylated) alcohols showed
some interesting fragmentation due to the loss of F, Cl,
CF2Cl, and CO2CF2Cl from their respective molecular ions.
All the esters showed a prominent ionÐbase peak at m/z 85/
87 in most of the cases due to the formation of a highly
stabilised CF2Cl ion. The esters formed from poly¯uori-
nated alcohols also showed a prominent ion at m/z 69
corresponding to the CF3 ion ꢀTable 2). In certain esters,
speci®c ions were also observed due to the loss of HF from
different fragment ions and ions corresponding to ¯uori-
nated hydrocarbon/hydrocarbon moieties. The genesis of the
formation of various ions is shown in Scheme 2. In order to
con®rm the mechanism of fragmentation, tandem mass
spectrometric experiments in daughter ion and parent ion
modes were also performed. The daughter ions obtained
from various parent ions in MS/MS experiments are shown
in Table 3.
1
obtained have been characterised on the basis of H and
19F NMR spectra and mass spectral data in both electron
impact ꢀEI) and CI modes ꢀTable 1). The NMR data corre-
spond to the assigned structures. The mass spectral data were
obtained for total identi®cation of the compounds. The
interesting features observed in the EI±MS data obtained
led us to investigate the fragmentation mechanism by using
tandem mass spectrometry.
Table 2
Fragment ions observed in I and corresponding ions in esters II±VI
Compound
no.
Molecular
weight
ꢀM H) ꢀi) ꢀM À F) ꢀii) ꢀM À Cl) ꢀiii)
ꢀiii À CF2) ꢀiv) ꢀM À CO2CF2Cl) ꢀv) ꢀCF2Cl) ꢀvi) ꢀCF3) ꢀvii)
I
212/214
262/264
280/282
144/146
158/160
242/244
213/215
263/265
281/283
145/147
159/161
243/245
193/195
177
227
245
109
123
±
127
177
195
59
83
133
151
±
85/87
85/87
85/87
85/87
85/87
85/87
69
69
69
±
II
243/245
III
IV
V
261/263
±
±
±
73
±
±
VI
157
113
±