320
not very large, the most hydrogen bond acidic com- ether, methanol, and hexafluoroisopropanol were completely separ-
ated, and using OV202 on which the two alcohols eluted together,
but well separated from the ether.
pounds being the simple alcohols. The range could not
be extended using carboxylic acids, as these com-
pounds are also reactive irritants (Bronsted acids). In
order to increase the range of hydrogen bond acidity of
the studied irritants, we chose the fluorinated alcohols
Experimental
trifluoroethanol and hexafluoroisopropanol as model
compounds. These have hydrogen bond acidities, as
ꢂ
A 500 cm round bottom three-neck flask was fitted with a ther-
mometer, dropping funnel, still head and condenser. KOH (36 g,
0.64 mol) was added to the flask followed by water (100 cm ). With
&
Ra , of 0.57 and 0.77, respectively, as compared to that
ꢂ
ꢁ
magnetic stirring and ice cooling, hexafluoro-2-propanol (Aldrich
Chemical Co., 100 g, 0.59 mol) was added so that the temperature
did not exceed 20°C. The mixture was then warmed to 70°C and
methyl sulfate (82 g, 0.65 mol) added at such a rate to keep the
temperature in the range 68—70°C. The product distilled (still head
temperature 50—54°C) and was collected in an ice cooled flask to
give a cloudy liquid (82 g). This product was stirred with powdered
KOH (0.5 g) for 0.5 h and then distilled to give a colourless liquid
(77.8 g, b.p. 49—50°C). This liquid was shaken with ice-cold potassi-
of 0.37 for a primary alcohol such as ethanol (Abraham
1993).
In this study, we observed that the sensory irritation
of trifluoroethanol was as estimated from recent QSARs,
but that hexafluoroisopropanol was much more potent
than calculated. Such an increase in potency could be
due to either the presence of the (CF ) group, or to the
ꢂ ꢁ
alcohol now being so strong a hydrogen bond acid that
ꢂ
um hydroxide solution (1 M, 50 cm ), then separated (it is the lower
it can react with the receptor. The former possibility
was investigated by synthesizing and determining the
sensory irritation of methyl hexafluoroisopropyl ether,
(CF ) CH-O-Me. This substance contains the (CF )
layer) and distilled through a 15-cm silvered vacuum jacketed col-
umn, discarding the first 0.6 g (b.p. 47.5—49°C), to give the product
(68.3 g, b.p. 49—51°C).
ꢂ ꢁ
ꢂ ꢁ
group but has little hydrogen bond acidity.
Animals and housing
Ssc:CF-1 male mice, mean weight 25$3 g (number of mice,
n"124) supplied by Statens Seruminstitut, Denmark, were used.
The mice were placed in wire mesh cages placed inside polycarbon-
ate cages with sawdust bedding. Food (Altromin No. 1324) and tap
water were available ad lib. The light:dark cycle was 12:12 h, with
light on from 0700 hour.
For exposure of mice via a tracheal cannula, the animals were
anaesthetizes with 50 mg/kg body wt of sodium pentobarbital
given i.p., supplemented if required. A tracheal cannula was
inserted, secured by a suture, and the skin incision was closed with
cyanoacrylate glue. The mice were allowed to recover prior to
exposure.
Mate rials and me thods
Chemicals
Trifluoroethanol ('99% pure) was obtained from Merck-
Schuchardt, Germany and was used without further purification.
Hexafluoroisopropanol ('99% pure), used in the biological testing,
was also obtained from Merck-Schuchardt, Germany. The high
purity, which was found to be 99.7%, was confirmed by gas
chromatography on a 4-m column with 10% Carbowax 1500 at
87°C. Hexafluoroisopropanol used for some of the experiments was
stored over NaHCO overnight and decanted before use. If acidic
ꢂ
compounds, for example HF, were present they would be neu-
Generation of gas-air mixtures
tralized and their salts possibly also removed from the liquid phase.
If a salt was dissolved in the solvent it would have given rise to
a solid deposit in the aerosol generator used for the generation of the
exposure concentration in the biological experiments. However, this
was not seen.
Dynamic exposure conditions were used with trifluoroethanol and
hexafluoroisopropanol. Briefly, the solvents were evaporated, di-
luted with room air, and led to a 3.3-l exposure chamber. Each
nominal concentration was calculated from the amount of evapor-
ated chemical and the total gas-air flow (set between 18 and
25 l/min). Chamber concentrations were monitored continuously by
infrared (IR) spectroscopy (Nielsen and Alarie 1982; ASTM 1984).
The differences between the nominal and the monitored exposure
concentrations were normally less than 10%. Air concentrations
Synthesis and purity of methyl hexafluoroisopropyl ether
This compound was prepared from hexafluoroisopropanol by
methylation with methyl sulfate and aqueous potassium hydroxide
solution, using a modification of a procedure described in the litera-
ture (Croix 1975). The crude product was purified by distillation
ꢂ
are given in ppm: ml gas per m gas-air mixture (Kristiansen et al.
1989).
Static exposure conditions were used with investigation of methyl
hexafluoroisopropyl ether due to the large quantities of the chemical
required to elicit response. The ether was evaporated in a 34.6-l
stainless steel tank. Tank, exposure chamber, IR analyser and a
pump were connected in a closed loop system (Hansen et al. 1991;
Nielsen and Alarie 1992). The exact exposure concentrations were
obtained from IR spectroscopy.
ꢀ
from potassium hydroxide. The H NMR spectrum (CDCl ,
ꢂ
400 MHz) showed that in addition to the required compound
(d3.74s, 3H and 3.94 sept, 1H), the product contained 3.6% hexa-
fluoroisopropanol (d 4.40m) and 0.2% methanol (d 3.32s). This find-
ꢀꢃ
ing was confirmed by observation of the F NMR spectrum
(CDCl , 376 MHz) which showed a major doublet (J5.7 Hz) with
ꢂ
4.2% of a second doublet at 1.6 ppm to lower field due to hexa-
fluoroisopropanol. Further purification was effected by shaking the
product with aqueous potassium hydroxide solution followed by
distillation to give a product which contained no observable hexa-
fluoroisopropanol (GC) and only a trace of methanol. The GC
analysis was carried out at ambient temperature using the stationary
phases Fomblin Z-Dol and poly(vinyl tetradecanol) on which the
Exposure conditions
Each mouse was placed in a body plethysmograph attached to the
exposure chamber so that the head of the mouse protruded into the