Chemistry Reference
In-Depth Information
carried out in the presence of ethanol, carbamates can be prepared directly [587,
588].
4.3.2.8
Carbamates Prepared with Acryloyl Azide
An improved method that can be easily scaled-up has been developed for the
preparation of benzyl-N-vinyl carbamate 810 (Z-vinylamine), a valuable synthetic
intermediate in the synthesis of b-lactam antibiotics [589]. In this method, vinyl
isocyanate 809, formed by the Curtius rearrangement of acryloyl azide 808, is co-
distilled with a solvent such as toluene into benzyl alcohol containing a catalyst
and an inhibitor. The product thus obtained can be purified by crystallization,
thereby avoiding purification by high-vacuum distillation or chromatography. Po-
tential safety issues associated with the process are important [590, 591].
heat
H
2
O
Toluene
Cl
N
3
NaN
3
NCO
+
-N
2
O
O
806
807
808
809
C
6
H
5
CH
2
OH
N
O
O
810
The thermal stability of acryloyl azide has been studied in some detail. Solutions of
this compound in toluene appear to be stable at sub-ambient temperatures. How-
ever, it can undergo polymerization when stored for long periods, and the crystals
formed can undergo rapid decomposition when dry. Care should be exercised to
avoid this polymerization by storing the solutions below 5
C. It is strongly rec-
ommended that solutions of acryloyl azide be used soon after their preparation.
Typical Procedure. Benzyl N-vinyl carbamate 810 [590].
Note! Some of the chemicals
described below can undergo rapid decomposition and polymerization, with evolution of
gaseous products. Acryloyl azide in neat form may be dangerously explosive, and vinyl
isocyanate is probably very toxic. All experiments should be carried out behind a safety
shield in a well-ventilated hood. Extreme care should be taken to avoid injury.
Acryloyl azide 808: A 1 l reactor was charged with 68.4 g (1.05 mol) of sodium
azide, 200 ml of water, 200 ml of toluene, and 0.09 g of Adogen 464 (methyl-
trialkylammonium chloride). The mixture was cooled with stirring in ice-water
bath, and 90 g (1 mol) of acryloyl chloride was added dropwise over a period of
1.5 h at 0-5
C. After the addition, the mixture was stirred for 45 min. The organic
phase was separated and stored at 0-5
C.
