210 ESTERS.
On the other hand, in ethyl sulphonic acid, since this can be formed by
the oxidation of ethyl mercaptan, C 2 H 5. SH, it must be true that the ethyl
is bound directly to the sulphur atom, and that therefore the compound has
the structural formula C 2 H 5. SO 2. OH, while its ester has the corresponding
unsymmetrical structure
, OC 2 HS
o 2 s/
XC
2 HS
As regards the sulphites and free sulphurous acid there are, therefore, two
possible formulas. The fact that solid sulphites react with halogen alkyls to
form unsymmetrical esters suggests that the sulphites have an unsymmetrical
structure. There is no positive proof as to whether the constitution of free
sulphurous acid is represented by the formula
/OH /OH
O : S or by the formula O 2 S
^OH XH
It is perfectly possible that both forms of the acid may exist together in a
state of mobile equilibrium (cf. Cyanic Acid, No. 73). Such a condition is
known as tautomerism or dynamic isomerism (cf. A. Findlay, The Phase
Rule, p. 193.)
Insert a dropping funnel through a cork in the mouth of a 75-c.c.
flask with side-arm condenser (Fig. 7, p. 6), so that the stem of
the funnel reaches just to the bulb of the flask. Place 40 g. of
thionyl chloride (one-third mol) in the bulb and surround it with
a mixture of ice and salt. Then allow 31 g. of alcohol (which has
been dehydrated by standing two hours over a large quantity of
quicklime and then distilled), to drop into the flask. The alcohol
should be added very slowly at first, as the reaction is violent and
considerable heat is evolved. The operation requires thirty to
forty-five minutes. Finally let the liquid become warmed to room
temperature, whereby hydrogen chloride escapes freely (Hood),
exchange the dropping funnel for a thermometer, and distil.
At first, in addition to hydrogen chloride, a little alcohol passesover, then about 38 g. of ethyl sulphite distils between 130° and
160°. Redistil the crude product after cleaning and drying the
apparatus. About 35 grams of the pure ester are obtained, boiling
at 158° to 158.5°.
The ester is a colorless oil of an agreeable odor, and is some-
what more viscous than water. It is not decomposed by watereven on boiling, but when treated with caustic soda, it is saponi-
fied with the formation of ethyl alcohol and sodium sulphite.
Warm a few drops of the ester with 2 c.c. of caustic soda and a