Chemistry Reference
In-Depth Information
R
R
N
N
R
R
X
N
R
1
R
1332
X = Cl
R = R
1
= nBu :
HBGCl
R = R
1
=Me :
HMGCl
R = nBu, R
1
= nPr:
PBGSiCl
(silica-supported
PBPGCl
)
General procedure. Chlorination of carboxylic acids (stearic acid) [979]:
(Caution:
Hood! Review phosgene safety precautions before repeating). The carboxylic acid
(0.2 mol) and the PBGSiCl catalyst 1332 (10 g, 2 mmol Cl
) were heated at 100-
120
C. After stabilization of the temperature, gaseous phosgene (for a safe source
and safe phosgenation, see Chapter 7) was bubbled into the suspension and con-
densed in a trapping funnel by a dichloromethane/dry-ice mixture. The reaction was
monitored by GC. After complete consumption of the carboxylic acid (6-8 h), heat-
ing was stopped and the reaction mixture was degassed by a nitrogen stream. The
catalyst was then separated by filtration and the product was analyzed. Spectral data
for the products were consistent with those of commercial acyl chloride samples.
Several phosgene equivalents have been reported to bring about clean and e
-
cient activation of the carboxylic group as an acid chloride.
4.4.2.2
Oxalyl Chloride
Pure 2-cyanoacryloyl chloride, which is useful for the preparation of esters suitable
for contaminant-free adhesives, is manufactured by reacting 2-cyanoacrylic acid
with a chlorinating agent under conditions inhibiting side reactions and polymer-
ization. Oxalyl chloride, thionyl chloride, trifluoroacetyl chloride, and phosgene,
which form only volatile by-products, are the preferred chlorinating agents. The
polymerization is inhibited, for example, by using a catalyst which forms an inter-
mediate complex with the chlorinating agent, thereby preventing the formation of
a mixed anhydride.
Typical procedure. 2-Cyanoacryloyl chloride [1008]:
2-Cyanoacrylic acid (2.0 g) was
dissolved in hot p-xylene (250 mL) containing g-propanesultone (1 mg). Some 50
mL of the xylene was then removed by distillation, and the concentrated solution
was filtered and cooled to 40
C. Me
2
NCHO (5 mg; stock solution in benzene) was
added, and then oxalyl chloride (6 mL) was added dropwise with stirring under a
continuous flow of Ar. The mixture was stirred for 12 h at room temperature, then
ethyl furfurylidenecyanoacetate (5 mg) was added and the volatiles (along with a
part of the solvent) were removed in vacuo to give 100 mL of a clear yellow solution
of 2-cyanoacryloyl chloride in xylene.
