Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

CHAPTBE III
NITRO-COMPOUNDS AND THEIR REDUCTION PRODUCTS
1. NITROMETHANE 1
CHLOROACETIC acid (94 g.) dissolved in 200 c.c. of water in a wide
beaker is accurately neutralised with 53 g. of anhydrous sodium
carbonate, and 75 g. of sodium nitrite dissolved in 120 c.c. of water
are then added. About 100 c.c. of the mixture thus obtained are
transferred to a round-bottomed flask (capacity 750 c.c.) which is
fitted with a dropping funnel and is connected to a downward
condenser. The flask is now strongly heated in a conical air bath
or on a wire gauze (raise the temperature slowly). A vigorous
reaction sets in with evolution of CO2 even before boiling begins.
By allowing the remainder of the solution to run slowly into the
boiling liquid the reaction is maintained, but is not allowed to become
too vigorous. The nitromethane distils with the steam and forms
the heavier layer in the receiver. As soon as drops of oil no longer
pass over, the receiver is changed and a further 100 c.c. of water containing
dissolved nitromethane are collected separately. The nitromethane
is separated from the first distillate and the aqueous layer
of the latter is combined with the second distillate. The combined
solution is saturated with sodium chloride (35 g. for each 100 c.c.)
and again subjected to distillation; about a quarter of the whole
volume is collected. Then a clear distillate again passes over.
The nitromethane in this second distillate is separated from the
water, combined with the material first obtained, thoroughly dried
over calcium chloride, and then distilled. Boiling point 101°. Yield
20-24 g. (30-36 per cent of theoretical).
Nitromethane is the most easily accessible aliphatic nitro-compound
; Kolbe's method of preparation is much less satisfactory when
applied to higher members of the series. The course of the reaction is
clear, and the reasons for the decomposition which takes place are similar
1 H. Kolbe, J. pr. Chem., 1872, 5, 429; Steinkopf, Ber., 1909, 42, 3438.
156