OXALYL CHLORIDE

1

Oxalyl Chloride

O

Cl

O

Cl

[79-37-8]

C

2

Cl

2

O

2

(MW 126.92)

InChI = 1/C2Cl2O2/c3-1(5)2(4)6
InChIKey = CTSLXHKWHWQRSH-UHFFFAOYAG

(versatile agent for preparation of carboxylic acid chlorides;

1

phosphonic acid dichlorides;

2

alkyl chlorides;

3

β

-chloro enones;

4

acyl isocyanates

5

)

Physical

Data:

mp

−12

◦

C;

bp 63–64

◦

C/763 mmHg;

d

1.48 g cm

−3

; n

20
D

1.4305.

Solubility:

sol hexane, benzene, diethyl ether, halogenated

solvents, e.g. dichloromethane and chloroform, acetonitrile.

Form Supplied in:

colorless, fuming liquid; widely available;

2 M soln in dichloromethane.

Handling, Storage, and Precautions:

liquid and solution are

toxic, corrosive, and severely irritating to the eyes, skin, and res-
piratory tract. Use in a fume hood and wear protective gloves,
goggles, and clothing. Bottles should be stored in a cool, dry
place and kept tightly sealed to preclude contact with moisture.
Decomposes violently with water, giving toxic fumes of CO,
CO

2

, HCl.

Original Commentary

Roger Salmon
Zeneca Agrochemicals, Bracknell, UK

Preparation of Carboxylic Acid Chlorides (and Anhy-

drides). Oxalyl chloride has found general application for the
preparation of carboxylic acid chlorides since the reagent was in-
troduced by Adams and Ulich.

1

Acid chlorides produced by this

means have subsequently featured in the synthesis of acyl azides,

6

bromoalkenes,

7

carboxamides,

8

cinnolines,

9

diazo ketones,

10

(thio)esters,

11

lactones,

12

ketenes for cycloaddition reactions,

13

intramolecular Friedel–Crafts acylation reactions,

14

and the

synthesis of pyridyl thioethers.

11

Like Thionyl Chloride, oxalyl chloride gives gaseous byprod-

ucts with acids and the chlorides can be readily isolated in a pure
form by evaporation of the solvent and any excess reagent, or used
in situ for further elaboration (eq 1).

O

Cl

O

Cl

(1)

O

R

OH

O

O

R

O

O

Cl

O

Cl

R

+

+

CO

2

+

CO

+

HCl

Prior formation of an amine or alkali metal salt, with or with-

out pyridine,

1

has been used to advantage with substrates that are

sensitive to strong acids or are bases (see also Oxalyl Chloride–
Dimethylformamide for a procedure conducted under neutral
conditions using silyl esters). By adjusting the molar proportions
of oxalyl chloride to substrate, anhydrides can also be prepared
using these methods (eq 2).

15

N

-Carboxy-α-amino acid anhy-

drides can also be made this way.

16

(2)

COCl

N

N

CO)

2

O

CO

2

–

K

+

N

(COCl)

2

0.5 equiv (COCl)

2

benzene, reflux

85%

benzene, reflux

85%

The use of nonpolar solvents such as hexane or toluene allows

for the removal of inorganic or amine salts which may otherwise
interfere with subsequent reactions.

Under the mild conditions employed (eqs 3 and 4),

17

racemi-

zation of stereogenic centers, skeletal rearrangement, or byprod-
uct formation, seen with other reagents such as thionyl chloride/
pyridine,

18

are seldom observed.

(3)

(COCl)

2

CH

2

Cl

2

reflux

H

O

O

O

OH

Cl

O

O

O

H

HO

2

C

NHCOCF

3

NHCOCF

3

Cl

O

(4)

(COCl)

2

pyridine

0 °C to rt

Conversion of β-bromoacrylic acid to the acid chloride

using thionyl chloride/DMF, Phosphorus(III) Chloride, or ben-
zotrichloride/zinc chloride also resulted in bromine for chlorine
exchange. Use of oxalyl chloride with the preformed ammonium
salt provided a mild, general method to β-bromoacryloyl chlo-
rides (eq 5)

19

without halogen exchange or (E/Z) equilibration.

β

-Fluoro- and iodoacrylic acids have been cleanly converted to

the acid chlorides without prior salt formation.

Br

O

–

NH

4

+

O

Br

Cl

O

(5)

(COCl)

2

hexane, reflux

80%

As well as forming acid chlorides, α-tertiary amino acids can

react with oxalyl chloride and undergo an oxidative decarboxy-
lation to give iminium salts, or ring expansion, depending on the
substituents and their stereochemistry (eq 6).

20

R

1

R

2

H

N

O

N

+

R

3

OH

R

3

N

R

2

R

1

O

R

1

R

2

R

3

Cl

+

(6)

R

3

t

-Bu

c

-Hex

Me

(A)

0
0

30

(B)

69
59

0

% Yield

(COCl)

2

(B)

(A)

R

1

Me
H
H

R

2

H
CO

2

Me

Me

Avoid Skin Contact with All Reagents

2

OXALYL CHLORIDE

Preparation of Phosphonic Acid Chlorides.

Phosphonic

acid dichlorides have been obtained in high yield (determined
by

31

P NMR) at low temperature from the corresponding acids

using oxalyl chloride and Pyridine (eq 7).

2

P

O

R

OH

OH

P

O

R

Cl

Cl

1. THF, py, 25 °C
2. –78 °C, (COCl)

2

(7)

R = Et, PhCH

2

, CF

2

H, arabinomethyl, phthalidyl

3. rt

Similarly, monoalkyl methylphosphonochloridates (eq 8)

21

can be made from dialkyl esters; thionate acid chlorides could
not be made by this method. Thionyl chloride and PCl

5

were also

used to make this type of compound (see also Oxalyl Chloride–
Dimethylformamide).

P

O

Me

OR

OR

P

O

Me

Cl

OR

1. (COCl)

2

, Et

2

O

2. rt, 24 h

(8)

+

RCl

R = Me, Et, Pr, i-Pr, Bu

Numerous other reagents such as PCl

3

, PCl

5

, POCl

3

, and Ph

3

P/

CCl

4

are available for the preparation of acid chlorides and anhy-

drides but may not be as convenient as the byproducts are not so
easily removed, or the reactions require more vigorous conditions.

Direct Introduction of the Chlorocarbonyl Group (Halo-

carbonylation). Alkanes or cycloalkanes react with oxalyl chlo-
ride under radical conditions; typically, mixtures are produced.

22

However, bicyclo[2.2.1]heptane undergoes regio- and stereo-
specific chlorocarbonylation, giving the ester on subsequent
methanolysis (eq 9).

23

1. (COCl)

2

, (PhCO

2

)

2

PhCl, 85 °C

H

CO

2

Me

(9)

2. MeOH

Certain alkenes such as 1-methylcyclohexene and styrene react

with oxalyl chloride, under ionic conditions without added cat-
alyst, to give alkenoic acid chlorides in variable yields. Alkenes
such as octene and stilbene did not react under these conditions.

24

Reactions of aromatic compounds with oxalyl chloride/Lewis

acid catalysts have been reviewed.

25

Anthracene is unusual as it

undergoes substitution without added catalyst (eq 10).

26

(COCl)

2

, PhNO

2

120–240 °C

(10)

COCl

Preparation of Chloroalkanes. Alcohols react with oxalyl

chloride to give oxalyl monoalkyl esters, which if heated in the
presence of pyridine give the alkyl chloride (eq 11).

3

RO

O

Cl

O

(11)

ROH

(COCl)

2

benzene, rt

pyridine

120–125 °C

RCl

+

CO

+

CO

2

Tertiary alcohols have been converted to tertiary chlorides in

a Barton–Hunsdiecker type radical process using hydroxamate
esters (eq 12).

27

RO

O

Cl

O

(12)

ROH

(COCl)

2

benzene, rt

CCl

4

, reflux

RCl

+

2 CO

2

+

N
O

–

Na

+

S

N

SCCl

3

e.g. R = Me(CH

2

)

16

CMe

2

–

Chlorination of Alkenes. A novel stereospecific dichlorina-

tion of electron rich alkenes has been reported using a manganese
reagent generated from Benzyltriethylammonium Chloride and
oxalyl chloride (eqs 13–17).

28

No oxygenation byproducts are

observed.

(13)

R

1

R

2

R

1

R

2

Cl

Cl

–45 °C

PhCH

2

NEt

3

+

MnO

4

–

+ (COCl)

2

[Mn]

Ph

98%

[Mn]

(14)

Ph

Cl

Cl

C

5

H

11

(15)

69%

C

5

H

11

Cl

Cl

[Mn]

80%

[Mn]

(16)

Cl

Cl

96%

[Mn]

(17)

O

O

O

O

Cl

Cl

Reactions with Carbonyl Groups.

Unsaturated 3-keto

steroids give the corresponding 3-chloro derivatives with oxalyl
chloride (eq 18).

4

Prolonged heating can give rise to aromati-

zation.

4

Tropone gives the chlorotropylium chloride in high

yield.

4

In a related reaction, 1,2-dithiol-3-ones and -3-thiones give

dithiolium salts when heated in toluene or chloroform with the
reagent.

4

A range of β-chloro enones has been prepared from dike-

tones. Dimedone gives the β-chloro enone in high yield (eq 19).

29

Keto esters did not react to give β-chloro esters.

(18)

O

O

Cl

O

(COCl)

2

rt, benzene

A list of General Abbreviations appears on the front Endpapers

OXALYL CHLORIDE

3

(19)

(COCl)

2

, CHCl

3

rt, reflux

92%

O

Cl

O

O

β

-Keto aldehydes give a single regio- and stereospecific isomer,

the chlorine being cis to the carbonyl group (eq 20).

(20)

(COCl)

2

CHCl

3

83%

O

O

CHO

H

Cl

Certain triketones give 3-chlorides with excess oxalyl chloride,

in good yield (eq 21).

30

(21)

(COCl)

2

O

OH

O

MeO

MeO

O

Cl

O

Preparation of Acyl Isocyanates and Aryl Isocyanates. Cer-

tain primary carboxamides can be converted to acyl isocyanates
in yields from 36–97% with the reagent (eq 22);

5

Phosgene

gives nitriles under similar conditions. Oxalyl chloride has found
limited application for the preparation of triazine and quinone
isocyanates.

5

(22)

(COCl)

2

, reflux

ClCH

2

CH

2

Cl

R

O

NH

2

O

NCO

R

R = ClCH

2

, CCl

3

, PhCH

2

, 3,4-Cl

2

C

6

H

3

, Ph

2

CH

Miscellaneous Applications. Oxalyl chloride has been used

in the preparation of 2,3-furandiones from alkenyloxysilanes,

31

o

-aminophenols from N-aryl nitrones,

32

dihydroquinolines

via a modified Bischler–Napieralski ring closure,

33

2,3-β-

furoquinoxalines from quinoxazolones,

34

sterically hindered

salicylaldehydes from phenoxyoxalyl chlorides,

35

and in mild

cleavage of 7-carboxamido groups in cephalosporin natural prod-
ucts, without cleavage of the lactam ring or disruption of optical
centers.

36

First Update

Ivan V. Efremov
Pfizer Inc., Groton, CT, USA

Preparation of Carboxylic Acid Chlorides. As described in

the original article, oxalyl chloride is widely need for the synthesis
of carboxylic acid chlorides. This general approach has found use
in new chemistry fields such as combinatorial chemistry

37

and

dendrimer synthesis.

38

–

40

An interesting downstream application

was formation of macrocyclic diamides without resorting to high
dilution.

41

Source of Other Oxalyl Derivatives. A variety of other oxa-

lyl derivatives is known—oxalyl diimidazole can serve as an

example (see also Oxalyl Bromide and Diethyl Oxalate). Re-
cently, the preparation of new reagents starting from oxalyl chlo-
ride has been reported. Thus, reaction of 1H-benzotriazole with
oxalyl chloride led to formation of the corresponding dibenzotri-
azole derivative which, in turn, was shown to be an excellent tool
for the preparation of unsymmetrical tetrasubstituted oxamides.

42

Drawing upon the utility of Weinreb amides, N, N

′

-dimethoxy-N,

N

′

-dimethylethanediamide was prepared from oxalyl chloride and

demonstrated to have utility for the synthesis of α-keto amides and
1,2-diketones.

43

Formation of Chloroiminium Salts. Oxalyl chloride reacts

readily with amides or lactams to afford chloroiminium salts
that have many synthetic applications (eq 23) (see also Oxalyl
Chloride-Dimethylformamide).

R

1

N

O

R

2

R

3

N

R

1

Cl

R

2

R

3

(COCl)

2

Cl

(23)

+

–

For example, efficient syntheses of thioamides and thio-

lactams are based on this methodology.

44,45

Certain types of

chloroiminium salts can serve as precursors for high-energy syn-
thetic intermediates. Thus, azomethine ylides were obtained by
treatment of β-acylamino carboxylic esters with oxalyl chloride
(eq 24).

46

(COCl)

2

R

1

N

O

Me

COOR

2

R

1

N

Cl

Me

COOR

2

R

1

N

Cl

Me

COOR

2

(24)

Chloroiminium salts prepared from formaldehyde led to amino-

chlorocarbenes when treated with base (eq 25).

47,48

R

1

N

Me

H

O

R

1

N

Me

Cl

1. (COCl)

2

2. base

(25)

Oxalyl Chloride as a C2 Synthon. Oxalyl chloride has found

widespread use as a C2 building block in organic synthesis. Ap-
plications of this reagent in such a fashion for the synthesis of
heterocycles have been reviewed.

49

A particular area of interest

involves the synthesis and utility of oxazolidine-4,5-diones.

50

A general synthesis of butenolides taking advantage of one-pot

cyclization of silyl enol ethers with oxalyl chloride was developed
by Langer and applied to a number of synthetic problems. This
useful methodology has recently been reviewed.

51

Additional examples of the utilization of oxalyl chloride as a

C2 synthon include preparation of maleic anhydrides,

52,53

1,4-

dioxane-2,3-diones

54,55

and 1,2-diketones.

56

–

58

A useful in situ

reduction of the latter was developed to allow for a streamlined
synthesis of vicinal diamines (eq 26).

59

Avoid Skin Contact with All Reagents

4

OXALYL CHLORIDE

N

H

N

N

(26)

(COCl)

2

NaBH

4

TFA

62%

Oxalyl Chloride as a C1 Synthon. Although oxalyl chlo-

ride is mainly employed as a C2 equivalent in organic synthesis,
there are successful examples of using this reagent for the intro-
duction of a single carbon functionality. Thus, in addition to the
expected formation of 1,4-dioxane-2,3-diones when reacted with
1,2-diols, the reaction can also lead to the preparation of cyclic
carbonates.

55,60

Also, oxalyl chloride can react with ambident

dianions as a C1 synthon (eq 27).

61

N

N

CH

2

N

N

O

O

Ph

Ph

2 Li

Ph

2

CO

(COCl)

2

(27)

46%

Miscellaneous Applications. Oxalyl chloride has been used

as a reagent for stereospecific synthesis of 2-azetidinones from
aziridine-2-carboxylates (eq 28).

62

N

R

2

R

1

COONa

N

Cl

R

1

O

R

2

(28)

(COCl)

2

, NEt

3

25

°C

Another interesting stereospecific transformation is the con-

version of enantiomerically pure α-Li alkyl sulfoxides to vicinal
chloroamines (eq 29).

63

The “nonoxidative” chloro-Pummerer re-

arrangement was proposed as the mechanism. The final products
can be converted to the corresponding aziridines by treatment with
sodium borohydride followed by sodium hydride.

Ar

S

NHCOOR

5

R

1

R

3

O

R

2

R

4

Cl

N

S

COOR

5

R

1

R

3

R

2

R

4

Ar

(29)

(COCl)

2

symm-

collidine

Treatment of serine-containing peptides with oxalyl chloride

resulted in mild dehydration to afford the corresponding α-Ala
derivatives (eq 30).

64

Z

N

N

COOMe

O

H

H

R

H

OH

Z

N

N

COOMe

O

H

H

R

(30)

0

°C

(COCl)

2

NEt

3

CH

2

Cl

2

N

-Formylimidazole was shown to be a convenient formylat-

ing agent for a variety of amines and could be prepared in situ
from oxalyl chloride, formic acid, and imidazole. The reaction

occurs through initial formation of formyl chloride.

65

Symmet-

rical tetrasubstituted oxamides could be prepared from N-alkyl
cyclic amines. The postulated first step is the formation of an N-
acyltrialkylammonium salt followed by selective loss of the alkyl
substituent most capable of forming a stable carbocation. The
observed substituent effects were consistent with the proposed
mechanism.

66

Aryl isocyanates could be obtained directly from

aniline hydrochlorides by treatment with oxalyl chloride. The
final products result from thermal decomposition of initially
formed oxamic chlorides.

67

Related Reagents.

Dimethyl Sulfoxide–Oxalyl Chloride;

Oxalyl Chloride–Aluminum Chloride.

1.

Adams, R.; Ulich, L. H., J. Am. Chem. Soc. 1920, 42, 599.

2.

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4.

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Lett. 1968

, 5149.

A list of General Abbreviations appears on the front Endpapers

OXALYL CHLORIDE

5

19.

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14

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39

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