Chemistry Reference
In-Depth Information
Diphosgene and triphosgene as phosgene equivalents
L
-Lysine diisocyanate (LDI) 367 was synthesized by refluxing l-lysine monohydro-
chloride with ethanol to form the ester, which was subsequently refluxed with
1,1,1,3,3,3-hexamethyldisilazane to yield a silazane-protected intermediate. N,N
0
-
Bis(trimethylsilyl)-l-lysine ethyl ester 366 reacts with triphosgene to yield ethyl 2,6-
diisocyanatohexanoate 367 [258, 259].
Typical procedure. Ethyl 2,6-diisocyanatohexanoate [258]: A dry 1000 mL three-
necked, round-bottomed flask equipped with a mechanical stirrer was charged with
purified N,N
0
-bis(trimethylsilyl)-l-lysine ethyl ester (50 mL), anhydrous diethyl
ether (400 mL), and triethylamine (39 mL). The mixture was cooled to
20
C,
whereupon a solution of triphosgene (30 g) in anhydrous diethyl ether (200 mL)
was added dropwise over a period of 30 min. The reaction mixture was kept at
20
C for 4 h, and then the flask was removed from the cold bath and reaction
was allowed to proceed at room temperature for an additional 36 h. Triethylamine
hydrochloride was removed by vacuum filtration and the diethyl ether was evapo-
rated in vacuo to yield the crude ethyl 2,6-diisocyanatohexanoate. The product was
purified by vacuum distillation and approximately 15 mL of the fraction that dis-
tilled in the range 120-132
C at 0.1 mmHg was collected.
Octadecylamine was treated with diphosgene in toluene (starting from 60-70
C
and heating up to the bp) to yield 1-isocyanato-octadecane [260].
CCl
3
OCOCl
H
3
C
NH
2
H
3
C
NCO
Toluene, 60-70°C
4
4
368
369
1-Isocyanato-dodecane has been prepared with urea in diethylene glycol mono-
methyl ether at 200
C [261].
Diphosgene has been employed to synthesize several linear and branched alkyl
monoisocyanates 371 [262-264].
CCl
3
OCOCl
R
NH
2
R
NCO
AcOEt, activated charcoal,
heating, 5 h
370
371
R = 1-propyl, 2-propyl, 1-butyl, 2-butyl, (
S
)-
2
-butyl, (
R
)-2-butyl, 1-pentyl, 1-methyl-butyl,
(+/-)-2-methyl butyl, 3-methyl-butyl, (
S
)-2-methyl-1-butyl, 1-hexyl, 3,3-dimethyl-butyl,
3-methyl-pentyl, (
_
)-R-1-methyl-pentyl, 1-heptyl, 1-methyl-hexyl, (
S
)-2-heptyl, 1-octyl,
2-octyl, 1,5-dimethyl-1-hexyl, 2-ethyl-1-hexyl, 3-methylsulfanyl-1-propyl, 3-methoxy-1-
propyl
Hexamethylene diisocyanate 373, benzyl
)-methylbenzyl iso-
cyanate were prepared in yields of 73%, 78%, and 81%, respectively, from their
isocyanate, and (R)-(
þ
