Org. Synth. 1988, 66, 180
DOI: 10.15227/orgsyn.066.0180
OXIDATIVE CLEAVAGE OF AN AROMATIC RING: cis,cis-MONOMETHYL MUCONATE FROM 1,2-DIHYDROXYBENZENE
[2,4-Hexadienedioic acid, monomethyl ester, (Z,Z)-]
Submitted by Donald Bankston
1
Checked by Won Hun Ham and Leo A. Paquette.
1. Procedure
A.
cis,cis-Monomethyl muconate. A
1000-mL, three-necked, round-bottomed flask is equipped with a
mechanical stirrer and an
addition funnel (
(Note 1),
Fig. 1). The flask is charged with
400 mL of pyridine,
5 mL (0.12 mol) of methanol and
9.9 g (0.10 mol) of cuprous chloride under an atmosphere of
nitrogen (Note 2). The resultant yellow solution is stirred vigorously at room temperature until the
cuprous chloride dissolves
(Note 3). The
nitrogen is removed and
oxygen is bubbled into the flask below the surface of the liquid for approximately 30 min
(Note 4). A solution, composed of
1000 mL of pyridine,
5.5 g (0.05 mol) of 1,2-dihydroxybenzene (catechol), and
5 mL (0.12 mol) of methanol, is degassed and slowly added to the flask over a 2-hr period with efficient stirring
(Note 5). The reaction mixture is stirred for an additional 30 min before the
pyridine is removed at reduced pressure. The dark green residue is dissolved in
300 mL of ethyl ether (Note 6) and
300 mL of 6 N hydrochloric acid; this solution is stirred for 10 min and filtered over Celite, and the organic layer is isolated. The
ether is removed at reduced pressure and the resultant brown residue is boiled sequentially with six
50-mL portions of hexane (Note 7). The hot liquid is carefully decanted, leaving behind most of the dark residue. The yellow-to-colorless solid is crystallized from hot
hexane (or
methanol) to yield
5.6–6.2 g (
71–80%) of colorless needles, mp
80–81°C (Note 8).
Figure 1
2. Notes
1.
The checkers employed an alternate device of the following type and introduced the methanolic
catechol solution subsequently via syringe.
2.
Pyridine (Mallinckrodt Inc., reagent grade) was distilled over
potassium hydroxide, bp
114–116°C.
Cuprous chloride was prepared fresh,
2 washed with anhydrous
methanol (distilled from
magnesium metal), and dried under reduced pressure.
Methanol (Fisher Scientific Company, purified grade) was dried over molecular sieves. The concentration of the
methanol should be within the range of 3–8 mol/mol of catechol3,4 and anhydrous conditions are necessary
4.
3.
Dissolution requires 1.5–2 hr. If the solution is not properly degassed, it will turn green prematurely. The green color indicates that
oxygen absorption by the cuprous chloride–pyridine complex has occurred, but it also means that any undissolved
cuprous chloride has been oxidized. Therefore,
nitrogen should be bubbled into the flask at a brisk rate and stirring should not commence until addition of the
cuprous chloride is complete.
4.
As
oxygen is introduced into the flask the solution becomes dark green and slightly viscous.
5.
Catechol was purchased from Fisher Scientific Company (resublimed). The addition funnel should be charged with a
nitrogen atmosphere throughout addition to obviate oxidation of the
catechol.
6.
Ethyl ether was purchased from Mallinckrodt, Inc. (analytical grade);
methylene chloride may be substituted, but the monomethyl ester is more soluble in
ether. At least two other extractions will be necessary to optimize the yield when
methylene chloride is used.
7.
Hexane was purchased from Fisher Scientific Company (technical grade).
8.
The spectral properties are as follows:
1H NMR (300 MHz, CCl
4) δ: 3.74 (s, 3 H); 5.88–6.09 (m, 2 H); 7.75–8.26 (m, 2 H); 11.29 (s, 1 H).
3. Discussion
Phenol also undergoes oxidative cleavage in the presence of
O2/
CuCl/
pyridine and
methanol to give
cis,cis-monomethyl muconate, but the yield is not high.
4,5 It has also been observed that
catechol, under anaerobic conditions, reacts with
cupric methoxy chloride in
pyridine containing water and
methanol to give
cis,cis-monomethyl muconate in high yield.
6 Catechol and
phenol may also be converted to
cis,cis-muconic acid by a metal-catalyzed
peracetic acid oxidation;
7 subsequently, treatment with
diazomethane gives the monomethyl or dimethyl ester.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
cupric methoxy chloride
CuCl
O2
hydrochloric acid (7647-01-0)
methanol (67-56-1)
ether,
ethyl ether (60-29-7)
magnesium (7439-95-4)
phenol (108-95-2)
oxygen (7782-44-7)
nitrogen (7727-37-9)
pyridine (110-86-1)
potassium hydroxide (1310-58-3)
Catechol,
1,2-DIHYDROXYBENZENE (120-80-9)
cuprous chloride (7758-89-6)
methylene chloride (75-09-2)
Diazomethane (334-88-3)
peracetic acid (79-21-0)
hexane (110-54-3)
cis,cis-Monomethyl muconate,
2,4-Hexadienedioic acid, monomethyl ester, (Z,Z)- (61186-96-7)
cis,cis-muconic acid (505-70-4)
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