COPPER(II) CHLORIDE 1
Copper(II) Chloride allowing facile transformation to 4-hydroxyindoles (eq 3).4 The
ability of the reaction to form Ä…-chloro ketones selectively has
been further improved by the use of trimethylsilyl enol ethers
CuCl2
as substrates.5 Recently, phase-transfer conditions have been
employed in a particularly difficult synthesis of RCH(Cl)C(O)Me
[7447-39-4] CuCl2 (MW 134.45) selectively from the parent ketones (eq 4).6
InChI = 1/2ClH.Cu/h2*1H;/q;;+2/p-2/f2Cl.Cu/h2*1h;/q2*-1;m/
rCl2Cu/c1-3-2
O O
InChIKey = ORTQZVOHEJQUHG-NFHYJNRTCJ
Cl
CuCl2
(·2H2O)
(3)
aq AcOH, "
N N
[10125-13-0] Cl2CuH4O2 (MW 170.48)
R = Ts, 86%
RR
InChI = 1/2ClH.Cu.2H2O/h2*1H;;2*1H2/q;;+2;;/p-2/f2Cl.Cu.2H
R = Bn, 81%
2O/h2*1h;;;/q2*-1;m;;/rCl2Cu.2H2O/c1-3-2;;/h;2*1H2
InChIKey = MPTQRFCYZCXJFQ-FBUIOTBGCV
CuCl2, H2O
O
O
EtNH3NO3
R
R (4)
(chlorinating agent; oxidizing agent; Lewis acid)
C5H5N(CH2)15MeCl
n = 4, 70% Cl
ć%
Physical Data: anhydrous: d 3.386 g cm-3; mp 620 C (reported
ć%
R = Me(CH2)n, n = 2 5, 8
mp of 498 C actually describes a mixture of CuCl2 and CuCl);
ć%
partially decomposes above 300 C to CuCl and Cl2; dihydrate
ć%
d 2.51 g cm-3; mp100 C.
Solubility: anhydrous: sol water, alcohol, and acetone; dihydrate:
Chlorination of Aromatics. Aromatic systems may be chlori-
sol water, methanol, ethanol; mod sol acetone, ethyl acetate; sl
nated by the reagent. For example, 9-chloroanthracene is prepared
sol Et2O.
in high yield by heating anthracene and CuCl2 in carbon tetrachlo-
Form Supplied in: anhydrous: hygroscopic yellow to brown
ride (eq 5).7 When the 9-position is blocked by a halogen, alkyl,
microcrystalline powder; dihydrate: green to blue powder or
or aryl group, the corresponding 10-chloroanthracenes are formed
crystals; also supplied as reagent adsorbed on alumina (approx.
by heating the reactants in chlorobenzene.8,9 Under similar condi-
30 wt % CuCl2 on alumina).
tions, 9-acylanthracenes give 9-acyl-10-chloroanthracenes as the
Analysis of Reagent Purity: by iodometric titration.70
predominant products.10 Polymethylbenzenes are efficiently and
Purification: cryst from hot dil aq HCl (0.6 mL g-1) by cooling
selectively converted to the nuclear chlorinated derivatives by
in a CaCl2 ice bath.71
CuCl2/Alumina (eq 6).11
Handling, Storage, and Precautions: the anhydrous solid should
be stored in the absence of moisture, since the dihydrate is
H
formed in moist air. Irritating to skin and mucous membranes. Cl
CuCl2
(5)
"
Original Commentary
R
R
R = H, Me, Ph, Ac
Nicholas D. P. Cosford
SIBIA, La Jolla, CA, USA
Chlorination of Carbonyls. Copper(II) chloride effects
CuCl2, Al2O3
the Ä…-chlorination of various carbonyl functional groups.1 The (6)
PhCl, "
reaction is usually performed in hot, polar solvents containing
82%
Lithium Chloride, which enhances the reaction rate. For example, Cl
butyraldehyde is Ä…-chlorinated in DMF (97% conversion, eq 1)
while the same reaction in methanol leads to an 80% yield of the
corresponding Ä…-chloro dimethyl acetal (eq 2).2
Reactions with Alkoxy and Hydroxy Aromatics. Hydroxy
O O
aromatics such as phenols and flavanones undergo aromatic
CuCl2
(1)
nuclear chlorination with copper(II) chloride.12 Thus heating 3,
H DMF, " H
ć%
5-xylenol with a slight excess of the reagent in toluene at 90 C
97%
Cl
gave a 93% yield of 4-chloro-3,5-xylenol (eq 7).13 2-Alkoxynaph-
O OMe
thalenes are similarly halogenated at the 1-position.14 Attempted
CuCl2
ć%
(2)
reaction of CuCl2 with anisole at 100 Cfor 5 h gave no prod-
H MeOH, " OMe
ucts; in contrast, it was found that alkoxybenzenes were almost
80%
Cl
exclusively para-chlorinated (92 95% para:0.5 3% ortho) using
The process has been extended to carboxylic acids, anhydrides, CuCl2/Al2O3 (eq 8).15 Anisole reacts with benzyl sulfides in
and acid chlorides by using an inert solvent such as sulfolane.3 the presence of equimolar CuCl2 and Zinc Chloride to give
4-Oxo-4,5,6,7-tetrahydroindoles are selectively Ä…-chlorinated, anisyl(phenyl)methanes (para:ortho =2 : 1, eq9).16,17
Avoid Skin Contact with All Reagents
2 COPPER(II) CHLORIDE
OH
OH
The intramolecular variant of this reaction producing carbo-
cyclic derivatives has been reported.23 Copper(II) chloride
CuCl2
(7)
catalyzes the Knoevenagel condensation of 2,4-pentanedione
PhMe, "
93% with aldehydes and tosylhydrazones (eq 13).24 The reagent also
Cl
catalyzes the reaction of various 1,3-dicarbonyls with dithianes
such as benzaldehyde diethyl dithioacetal to give the correspond-
OEt
OEt OEt
ing condensation products (eq 14).25
Cl
CuCl2, Al2O3
+ (8)
PhCl, "
O O
CuCl2
O
O O NNHTs
THF, 25 °C
Cl
+ or
(13)
R
94% R 48 95%
<0.5%
R
OMe OMe OMe R = alkyl, aryl
Bn
CuCl2, ZnCl2
+ (9)
BnSMe, "
53%
Bn
CuCl2 O O
O O
SEt
2:1
THF, 25 °C
+ Ph (14)
R
R
R = Me, 65%
SEt
R = OEt, 46%
Ph
Reactions with Active Methylene-containing Compounds.
9-Alkoxy(or acyloxy)-10-methylanthracenes react with CuCl2 to
give coupled products (eq 10), while the analogous 9-alkoxy(or
Catalyst for Conjugate Additions. The catalytic effect of
acyloxy)-10-benzyl(or ethyl)anthracenes react at the alkoxy or
copper(II) chloride on the 1,4-addition of ²-dicarbonyl
acyloxy group to afford 10-benzylidene(or ethylidene)anthrones
compounds to (arylazo)alkenes26,27 and aminocarbonylazo-
(eq 11).18 The reactions are believed to proceed via a radical
alkenes28,29 has been studied in some detail. The reactions pro-
mechanism.
ceed at ambient temperature in THF and afford the corres-
O
ponding pyrrole derivatives (eq 15). This mild method requires
no other catalyst and succeeds with ²-diketones, ²-ketoesters, and
OR ²-ketoamides. Copper(II) chloride also catalyzes the addition of
water, alcohols, phenol, and aromatic amines to arylazoalkenes
CH2
CuCl2
(10) (eq 16).30
CH2
O
X R3
O O
CuCl2
R = Me, Ac
R1 N
R3
+ N (15)
X
OR
R2 THF, 25 °C N R2
X = alkyl, aryl, OR, NHR
NHR1
R1 = Ar, ArNHCO
R2, R3 = alkyl, aryl, CO2R
OCH2R
O
CuCl2
(11)
R3
CH2R
CHR
CuCl2
R1 N
R1 N
R = Me, Ph
R3
ArNH2 + N (16)
NHAr
N
H
R2 THF, 25 °C
R2
Under similar conditions, 9-alkyl(and aryl)-10-halogeno-
R1, R2, R3 = Ar
anthracenes give products resulting from replacement of the
halogen, alkyl, or aryl groups with halogen from the CuCl2.19
Boiling toluene reacts with CuCl2 to yield a mixture of phenyl-
Oxidation and Coupling of Phenolic Derivatives. In the
tolylmethanes.20
presence of oxygen, copper(II) chloride converts phenol deriva-
Lithium enolates of ketones21 and esters22 undergo a coupling
tives to various oxidation products. Depending on the reaction
reaction with copper(II) halides to afford the corresponding 1,4-
conditions, quinones and/or coupled compounds are formed.31
dicarbonyl compounds. Thus treating a 3:1 mixture of t-butyl
Several groups have examined different sets of conditions
methyl ketone and acetophenone with Lithium Diisopropylamide
employing CuCl2 to favor either of these products. Thus
and CuCl2 gives a 60% yield of the cross-coupled product (eq 12).
2,3,6-trimethylphenol was selectively oxidized to trimethyl-p-
O OO O
1. LDA
benzoquinone with CuCl2/amine/O2 as the catalyst (eq 17),32
+ (12)
while 2,4,6-trimethylphenol was converted to 3,5-dimethyl-4-
Ph Ph
2. CuCl2
hydroxybenzaldehyde using a catalytic system employing either
60%
3:1
acetone oxime or amine (eq 18).33,34
A list of General Abbreviations appears on the front Endpapers
COPPER(II) CHLORIDE 3
O
OH
Dioxygenation of 1,2-Diones. 1,2-Cyclohexanedione deriva-
CuCl2, O2
tives have been converted to the corresponding 1,5-dicarbonyl
Et2NH
(17)
compounds by oxidation with O2 employing copper(II) chloride
ROH, 25 °C
as the catalyst.43 More recently, CuCl2 Hydrogen Peroxide has
O
been used to prepare terminal dicarboxylic acids in high yield.44
76.7% + 0.9% coupled product
While 1,2-cyclohexanedione afforded Ä…-chloroadipic acid in 85%
yield, 1,2-cyclododecanedione was converted to 1,12-dodecane-
O
OH OH
dioic acid in 47% yield under identical conditions (eq 22).
CuCl2, O2
Me2CNOH
+ (18)
O
ROH, 25 °C
O
1. CuCl2, H2O2
O
CHO
MeOH, H2O, 20 °C
HO2C CO2H
( )10 (22)
85.6% 6.1%
2. H2SO4
47%
The oxidation of alkoxyphenols to the corresponding quinones
has been studied,35 and even benzoxazole derivatives are oxi-
dized by a mixture of copper(II) chloride and Iron(III) Chloride
Addition of Sulfonyl Chlorides to Unsaturated Bonds. The
(eq 19).36 A CuCl2/O2/alcohol catalytic system has been used for
addition of alkyl and aryl sulfonyl chlorides across double and
the oxidative coupling of monophenols.37
triple bonds is catalyzed by copper(II) chloride.45 51 The reac-
tion appears to be quite general and proceeds via a radical chain
Et
O O mechanism. The 2-chloroethyl sulfones produced in the reac-
CuCl2, FeCl3
N
HO tion with alkenes undergo base-induced elimination to give vinyl
HCl, H2O, EtOH
(19)
sulfones (eq 23).45 48 1,3-Dienes similarly react, yielding 1,4-
"
OH addition products (eq 24) which may be dehydrohalogenated to
N
94%
O
O 1,3-unsaturated sulfones.45,49
Et
1. CuCl2, MeCN, "
SO2Ph
+ PhSO2Cl (23)
Ph
Ph
Copper(II) amine complexes are very effective catalysts 2. NEt3
for the oxidative coupling of 2-naphthols to give symmetri- 87%
cal 1,1 -binaphthalene-2,2 -diols.38 Recent work has extended
this methodology to the cross-coupling of various substituted Cl
2-naphthols.39,40 For example, 2-naphthol and 3-methoxy-
CuCl2
carbonyl-2-naphthol are coupled under strictly anaerobic condi- (24)
PhSO2Cl
+
100 °C
tions using CuCl2/tert-Butylamine in methanol to give the un-
62%
symmetrical binaphthol in 86% yield (eq 20).
SO2Ph
The stereoselectivity of the addition to alkynes can be con-
CuCl2, t-BuNH2
OH trolled by varying the solvent or additive, and thus favoring either
MeOH, "
OH
+ (20)
the cis or trans ²-chlorovinyl sulfone.50,51 For example (eq 25),
OH
86%
OH when benzenesulfonyl chloride is reacted with phenylacetylene in
acetonitrile with added triethylamine hydrochloride, the trans:cis
CO2Me
CO2Me ratio is 92:8, while the same reaction performed in CS2 without
additive favors the cis isomer (16:84).
Other ligands such as methoxide are also effective; a mecha-
Cl Ph
(a) or (b)
nistic study indicates that the selectivity for cross- rather than
+ PhSO2Cl + (25)
Ph
homo-coupling is dependent upon the copper:ligand ratio.41 A 1:1 100 °C
Ph SO2Ph Cl SO2Ph
mixture of 2-naphthol and 2-naphthylamine is cross-coupled with
trans cis
CuCl2/benzylamine to give 2-amino-2 -hydroxy-1,1 -binaphthyl
(a) = CuCl2, NEt3HCl, MeCN trans:cis = 92:8
(68% yield, eq 21).42 The cross-coupled products from these
(b) = CuCl2, CS2 trans:cis = 16:84
reactions are important in view of their use as chiral ligands for
asymmetric synthesis.
Acylation Catalyst. N-Trimethylsilyl derivatives of (+)-bor-
nane-2,10-sultam (Oppolzer s chiral sultam) and chiral 2-oxazoli-
CuCl2, t-BuNH2
dinones (the Evans chiral auxiliaries) are N-acylated with a
OH
OH
MeOH, "
(21) number of acyl chlorides including acryloyl chloride in reflux-
+ NH2
68%
ing benzene in the presence of CuCl2.52 The N-acylated products
NH2
were prepared in high yields; the method does not require an aque-
ous workup, making it advantageous for large-scale preparations.
Avoid Skin Contact with All Reagents
4 COPPER(II) CHLORIDE
Racemization Suppression in Peptide Couplings. A mixture a 53% yield of the isomeric cyclopropanes. The reaction also pro-
of copper(II) chloride and Triethylamine catalyzes the forma- ceeds with styrene, 1-decene, and isobutene. Byproducts formed
tion of peptide bonds.53 Furthermore, when used as an addi- from the addition to the alkene are removed with Potassium Per-
tive, CuCl2 suppresses racemization in both the carbodiimide54 manganate.
and mixed anhydride55 peptide coupling methods. Recently it
was shown that a combination of 1-Hydroxybenzotriazole and
CuCl2 gives improved yields of peptides while eliminating
racemization.56,57
First Update
Reaction with Palladium Complexes. Ä„-Allylpalladium
complexes undergo oxidative cleavage with copper(II) chloride
Pauline Pei Li
to form allyl chlorides with the concomitant release of PdCl2 Hong Kong Polytechnic University, Kowloon Hong Kong,
(eq 26).58
P. R. China
Copper(II) Chloride-catalyzed Oxidation of Hydrocarbons
Cl CuCl2
(26)
with Molecular Oxygen.
Pd EtOH
85%
2
Cl
Oxidation of Hydrocarbons to Alcohols and Ketones. A com-
bination of CuCl2 and a crown ether is an efficient catalytic
This methodology has been used in the dimerization of allenes
system for the aerobic oxidation of alkanes in the presence of
to 2,3-bis(chloromethyl)butadienes.59 1,5-Bismethylenecyclo-
acetaldehyde.73,74 For example, oxidation of cyclohexane in the
octane was transformed into the bridgehead-substituted bicyclo
presence of CuCl2 (2.5 × 10-4 mol %), 18-crown-6 (2.5 ×
[3.3.1]nonane system using CuCl2/HOAc/NaOAc, while the same
ć%
10-4 mol %), and acetaldehyde (10 mol %) at 70 C under O2
substrate produced bicyclo[4.3.1]decane derivatives (eq 27) with
at 1 atmosphere gave cyclohexanone (61% yield based on ac-
a Palladium(II) Chloride/CuCl2 catalytic system.60
etaldehyde) and cyclohexanol (10%). This catalytic system has
high turnover number of 1.62 × 104 for the aerobic oxidation of
CuCl2
X
cyclohexane (eq 29). The presence of crown ether forms a com-
HOAc
plex with copper ions which enhances the catalytic activity of the
NaOAc
(27)
copper chloride. Thus, the CuCl2-18-crown-6 complexes catalyze
oxidation of acetaldehyde with molecular oxygen to give peracid.
PdCl2, CuCl2
XX
The reaction of copper complexes with peracid then gives the
LiCl, O2, HOAc
oxo-copper intermediate. Hydrogen abstraction of alkane by the
oxo-copper complex, followed by oxygen transfer yields the cor-
X = Cl, OAc
responding alcohol. The alcohol suffers further oxidation to the
corresponding ketone under the reaction conditions.
While reaction of a steroidal Ä„-allylpalladium complex with
AcOK yields the allyl acetate arising from trans attack, treatment
OH
O
of a steroidal alkene with PdCl2/CuCl2/AcOK/AcOH gave the
allyl acetate arising from cis attack.61
CH3CHO, O2 (1 atm)
+ (29)
CuCl2, CH2Cl2, 70 °C
Reoxidant in Catalytic Palladium Reactions. Copper(II)
18-crown-6
10%
61%
chloride has been used extensively in catalytic palladium chem-
istry for the regeneration of PdII in the catalytic cycle. In particu-
lar, the reagent has found widespread use in the carbonylation of
A highly catalytic bimetallic system for the low temperature
alkenes,62 64 alkynes,65 and allenes66,67 to give carboxylic acids
selective oxidation of methane, ethane, and butane with oxygen
and esters using PdCl2/CuCl2/CO/HCl/ROH, and in the oxida- as the oxidant has been reported.75 The catalytic system con-
tion of alkenes to ketones with a catalytic PdCl2/CuCl2/O2 system
sists of a mixture of copper chloride and metallic palladium in
(the Wacker reaction).68 The PdCl2/CuCl2/CO/NaOAc catalytic
a 3:1 mixture (v/v) of trifluoroacetic acid-water in the presence
system has been used in a mild method for the carbonylation of
of oxygen and carbon monoxide. For example, methane can be
ć%
²-aminoethanols, diols, and diol amines (eq 28).69
selectively converted to methanol at 80 85 C for 20 h in a bomb
(eq 30), pressurized to 200 psi with carbon monoxide, 1200 psi
O
with methane, then 1300 psi with oxygen. An increase in reac-
R1HN OH
PdCl2, CuCl2
O (28)
R1N tion temperature significantly increases the rate of methane to
CO, NaOAc
R2
methanol conversion. The rate of formation of methanol is ca.
R2
ć%
65 × 10-4 M min-1 at 145 150 C.
CuCl2 (0.1 mmol)
CH4
CH3OH (30)
Cyclopropanation with CuCl2 Cu(OAc)2 Catalyst. Ethyl
2 2
2 2
5% Pd on carbon
Cyanoacetate reacts with alkenes under CuCl2 Copper(II)
H2O/CF3CO2H
CO/O2
Acetate catalysis to give cyclopropanes.72 Thus heating cyclo-
ć% 80 85 °C, 20 h
hexene in DMF (110 C, 5 h) with this reagent combination gives
A list of General Abbreviations appears on the front Endpapers
COPPER(II) CHLORIDE 5
Ä… ²-Acetylenic Ketones. Various
For oxidation of ethane and n-butane under similar oxidation Oxidation of Alkynes to Ä… ²
Ä…,²
conditions, products derived from C C bond cleavage compete alkynes have been converted to the corresponding Ä…,²-acetylenic
with or dominate those derived from C H bond cleavage on a ketones by oxidation with oxygen and t-BuOOH using copper(II)
per bond basis. The overall transformation encompasses three chloride as the catalyst (eq 33).78 The catalytic system gives
catalytic steps: (1) Pd-catalyzed reaction between CO and H2Oto both high conversion and selectivity in the formation of the Ä…,²-
form CO2 and H2; (2) Combination of H2 and O2 to yield hydrogen acetylenic ketones. This selectivity results from rapid oxidation of
peroxide; and (3) Cu-catalyzed oxidation of the alkane by hydro- the intermediate acetylenic alcohol, RC=CCH(OH)R , to ketone
gen peroxide. This catalytic system shows interesting synergism, under the reaction conditions. The resulting acetylenic ketone is
in that the principle role of metallic Pd is to generate hydrogen deactivated from further oxidation.
peroxide in situ, and the CuCl2 activates hydrogen peroxide for
oxidation of the substrates.
This catalytic system has been extended to the hydroxylation
H
O
CuCl2·2H2O
of remote primary C H bonds of various acids, alcohols, and
R1 C C C R2
R1 C C C R2 (33)
t BuOOH/t BuOH
aliphatic halides.76 For example, propionic acid can be converted
H
70 °C, O2
to 3-hydroxypropionic acid in 22% yield (eq 31). This catalytic
system exhibits two important features: (1) Reactions are very
R1=H, aliphatic, or aromatic group
specific, and only hydroxylation is observed; further oxidation
R2=aliphatic group
to aldehyde and carboxylic acid does not occur; (2) C C bond
cleavage and overoxidation can be minimized under suitable
conditions.
Copper(II) chloride not only catalyzes the decomposition of
t-BuOOH, but also plays a key role in converting the acetylenic
alcohol intermediates to Ä…,²-acetylenic ketones. To obtain both
CuCl2/Pd on carbon
high conversion and selectivity towards Ä…,²-acetylenic ketones,
CO/N2/O2
O
(200 psi/800 psi/100 psi) optimal reaction conditions are determined to be CuCl2·2H2O:
CH3 CH2 C OH
ć%
alkyne:t-BuOOH in a 1:25:50 ratio in t-BuOH at 70 C under an
CF3COOH/H2O
oxgen atmosphere. The reaction has broad substrate applicability,
75 °C, 18 h
where R and R can be a variety of aliphatic or aromatic groups
(Table 1).
O
(31) The oxidation to the Ä…,²-acetylenic ketone proceeds with both
HO CH2 CH2 C OH
high conversion and selectivity. The only major side-product
after 24 h is the acetylenic alcohol. If a longer reaction time is
employed, this side-product is completely converted to the Ä…,²-
acetylenic ketone. Alkyne reactivities correlate with the ease of
Copper(II) Chloride-catalyzed Oxidation of Hydrocarbons C H atom abstraction. Symmetric internal aliphatic alkynes, such
with tert-Butyl Hydroperoxide. as 3-hexyne, 4-octyne, and 5-decyne, give excellent conversion
and selectivity for ketone formation. The aliphatic chain length
Oxidation of Allylic Compounds. Allylic oxidation reaction of
has little effect on the reactivity and selectivity. Unsymmetrical
various types steroids have been preformed in the presence
internal aliphatic alkynes, such as 3-heptyne and 4-nonyne,
of t-butyl hydroperoxide (t-BuOOH) catalyzed by copper(I),(II)
afford a pair of acetylenic ketones with approximately equal
or copper metal.77 For example, allylic oxidation of the 5-3²-
distribution, indicating that the system cannot distinguish between
acetoxy steroid (1) was catalyzed with CuCl2 in the presence of
the two chemically similar Ä…-CH2 groups of the substrate.
ć%
t-BuOOH at 50 55 C for 20 h to give 81% yield of 2 (eq 32). No
However, the oxidation of 2-decyne is regiospecific, yield-
oxidation is detected in the absence of copper catalyst.
ing 2-decyn-3-one in 70% yield with no C H abstrac-
tion from the C-1 methyl group. Terminal acetylenes also
yield acetylenic ketones although the substrate reactivity is
O diminished. Besides the aliphatic alkynes, aromatic alkynes
such as 1-phenyl-1-pentyne can be oxidized to the corres-
t-BuOOH/CuCl2
ponding conjugated acetylenic ketone in good yield. The reac-
CH3CN/N2
tion conditions can also be employed for oxidation of other related
50 55 °C
substrates, such as cis-cyclooctene, which yields 3-cyclooctenone
with lower selectivity. Adjacent carboxylate groups severely
AcO
inhibit the alkyne reactivity. No apparent substrate oxidation
O
1
is observed for methyl-2-octynoate or 2-octynoic acid after
24 h. By contrast, 3-hexyn-2,5-diol is rapidly converted to
3-hexyn-2-ol-5-one in high yield with some further oxida-
(32)
tion to 3-hexyn-2,5-dione. Acetylenic alcohols, while not
typically as reactive as 3-hexyn-2,5-diol, are still activated
O
AcO
for further reaction to acetylenic ketones. However, like acetylenic
2
esters or acids, the acetylenic ketones are strongly deactivated.
Avoid Skin Contact with All Reagents
6 COPPER(II) CHLORIDE
Table 1 Oxidation of alkynes catalyzed by CuCl2·2H2O/t-BuOOH under oxygena
c
Substrate Conv.b (%) Product Yield (%)
a" a"
CH3CH2C CCH2CH3 91 CH3C(O)C CCH2CH3 59
3-hexyne
a" a"
CH3(CH2)2C C(CH2)2CH3 99 CH3CH2C(O)C C(CH2)2CH3 74
4-octyne
a" a"
CH3(CH2)3C C(CH2)3CH3 95 CH3(CH2)2C(O)C C(CH2)3CH3 66
5-decyne
a" a"
CH3CH2C CCH2CH2CH3 100 CH3C(O)C CCH2CH2CH3 37
3-heptyne
a"
CH3CH2C CC(O)CH2CH3 31
a" a"
CH3(CH2)2C C(CH2)3CH3 99 CH3CH2C(O)C C(CH2)3CH3 39
4-nonyne
a"
(CH2)2C C(O)(CH2)2CH3 37
a" a"
CH3C C(CH2)6CH3 84 CH3C CC(O)(CH2)5CH3 70
2-decyne
a" a"
HC C(CH2)5CH3 61 HC CC(O)(CH2)4CH3 51
1-octyne
a" a"
C6H5C C(CH2)2CH3 85 C6H5C C(O)CH2CH3 78
1-phenyl-1-pentyne
a"
C5H11C CCOOCH3 No reaction
Methyl-2-octynoate
a"
C5H11C C-COOH No reaction
2-Octynoic acid
O
97 42
cis-Cyclooctene
a" a"
CH3CH(OH)C CCH(OH)CH3d 100 CH3C(O)C CCH(OH)CH3 65
3-hexyn-2,5-diol
a"
CH3C(O)C C(O)CH3 15
a ć%
Reaction conditions: CuCl2·2H2O:substrate:t-BuOOH = 1:25:50 (molar ratio). Reaction was carried out at 70 C under O2.
b
Conversion was determined by GC analysis using an internal standard, t-butylbenzene. By-products were mainly acetylenic alcohol.
c
Isolated yield.
d
10 h reaction.
Oxidation of Poly(Methyl styrene). Anionic or cationic
CH3
poly(methyl styrene) (PMS) latex particles can be functionalized
via oxidation of the benzylic methyl group to the corresponding
emulsion polymerization
aldehyde and carboxylic acid in water. The oxidation of PMS
C12H25SO3-Na+ AIBN/CTAB
latex dispersion has been achieved using t-butyl hydroperoxide
V 50, 70 °C
K2S2O8, 80 °C
60 °C
as an oxidant catalyzed by a small amount of copper(II) chloride
CH3
H3C
CH3
H2C
under air (Scheme 1).79 83 The oxidation mechanism involves
initial copper(II) chloride-catalyzed decomposition of t-BuOOH
to both t-BuO· and t-BuOO. radicals. These reactive radicals H3C
CH3 H3C
CH3
abstract benzylic hydrogens to generate benzylic radicals, which
CuCl2/t BuOOH CuCl2/t BuOOH
are oxidized to the corresponding aldehyde groups under air. Since
H2O/t BuOH H2O, 60 °C, air
the aldehyde groups are easily oxidized to the carboxylic acid
60 °C, air
under the oxidative conditions, a mixture of aldehyde and car-
CHO
H3C
CHO
H3C
boxylic acid functionalities result. The distribution of these two
functional groups can be controlled by varying reaction con-
H3C
ditions such as concentration of t-BuOOH, type of surfactant,
H3C COOH
COOH
reaction temperature, and time. Since the CuCl2/t-BuOOH/O2
Scheme 1
is an effective system for benzylic C H oxidation in aqueous
A list of General Abbreviations appears on the front Endpapers
COPPER(II) CHLORIDE 7
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Avoid Skin Contact with All Reagents
8 COPPER(II) CHLORIDE
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A list of General Abbreviations appears on the front Endpapers