Chemistry Reference
In-Depth Information
carbon disulfide by distillation and addition of crushed ice and hydrochloric acid
yielded 1247 as a pale-yellow powder, which was crystallized from ethanol to give
60 g (72% yield) of colorless needles; mp 130-130.5
C.
In general, phosgene reacts with phenols at oxygen to produce aryl chlorofor-
mates and carbonates [1]. Only a few cases have been reported in which, using
highly hindered phenols, some 4-chlorocarbonylation was observed [937]. On the
basis of these results, phosgene can be considered as the simplest member of the
ortho-C reactive acyl chlorides.
A direct synthesis of salicylic acid chlorides can be achieved through ''metal-
driven'' intra-complex acylation of bromomagnesium and aluminum phenoxides
with phosgene [938]. The products can be reacted further, without purification,
with convenient nucleophilic compounds, thus facilitating a one-pot approach to
a range of phenolic derivatives such as esters, amides, and ketones. Treatment
of bromomagnesium or aluminum phenoxide with an excess of phosgene in
poorly solvating media (toluene or carbon disulfide) results in exclusive ortho-
chlorocarbonylation of the phenol.
MO
O
OM
Toluene or CS
2
15 min, rt
O
Cl
Cl
COCl
2
M
O
R
R
R
Cl
1251
1252
1253
M = Al (III), MgBr
CS
2
NH
4
Cl/H
2
O
38-70 %
1. +1/toluene,15 min,rt
2. NH
4
Cl/H
2
O
50 % for R=2-CH
3
CH
3
OH
CH
3
1. NaOH,H
2
O
2. H
+
CO
OH
OH
OH
CH
3
O
40 %
R
CO
OH
O
1256
1255
1254
The chelation effect of the highly coordinating metal ion is responsible for the
activation and selectivity of the process.
General procedure. Salicylic acids 1254 [938]: Method A: A dry 100 mL three-
necked, round-bottomed flask containing a magnetic stirring bar, equipped with a
reflux condenser and a pressure-equalizing dropping funnel, was fitted with a gas-
inlet tube and thoroughly purged with dry nitrogen. To the flask were added mag-
nesium turnings (0.24 g, 0.01 mol) and dry diethyl ether (20 mL). A solution of
