Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

THE CUETIUS KEACTION 153
(b) THE CUETIUS EEACTION PHENYL CYANATE
Benzhydrazide. 1 —24 g (0 15 mole) of ethyl benzoate (p 141) are
heated for six hours under a small reflux condenser on the water bath
with 9 g of hydrazme hydrate 2 The solid crystalline cake which is
formed on cooling is, after some time, filtered as dry as possible at the
pump and washed with a little ice-cold methyl alcohol If the yield
is too small the filtrate is concentrated and heated agam
The crude product (16-18 g) is sufficiently pure for further
treatment A sample can be recrystalhsed from hot water or from
a little alcohol Melting point 112°
Benzoylazide. 3 —14 g (0 1 mole) of the dry hydrazide are made
into a clear solution with 200 c c of approximately 2V-hydrochlonc
acid in a filter jar (capacity 0 5 1) The solution is cooled in ice and
stirred, while 8 g of sodium nitrite m 50 c c of water are added An
immediate reaction takes place and the azide separates in crystalline
form When a filtered sample of the solution is no longer made
turbid by the addition of a drop of nitrite solution, the precipitate
is filtered dry at the pump, washed well with water, and dried,
first on porous plate and then in a vacuum desiccator over concentrated
sulphuric acid and potassium hydroxide Yield 14 g
Phenyl Cyanate. 4 —The azide used for the preparation of the
cyamc ester must be absolutely dry Test for constant weight on a
good hand balance
Since benzoylazide explodes when rapidly heated or when in contact
with concentrated sulphuric acid, it must be handled carefully Goggles
must be worn until the distillation of the phenyl cyanate has been
completed
The distillation of the end-product is carried out m the flask
which is used for the decomposition, a Claisen flask of capacity
75-100 c c is suitable A capillary tube and a thermometer are got
ready before the decomposition of the azide is carried out All the
apparatus must be thoroughly dry
The Claisen flask is fixed in an inclined position and a small
condenser jacket is slipped over the side tube, which slopes upwards
Atmospheric moisture is excluded by fixing a calcium chloride tube
to the upper end of the side tube Benzoylazide (12 g ) and benzene
1
T Curtius, J pr Chem , 1894, 50, 295
2
This can be obtained cheaply from the firm of Dr F Raschig, Ludwigshafen
am Rhem 3 l
T Curtius, Ber , 1890, 23, 3029 G Schroeter, Ber , 1909, 42, 2339